The Canadian Aboriginal History Article/Book Chapter Prize sponsored by the Aboriginal History Group of the Canadian Historical Association, for the best article ,or chapter in an edited collection, written in English or in French dealing with the history of Aboriginal Peoples in Canada.
Rationale – Historical studies dealing with Aboriginal peoples now constitute a well-established and diverse body of scholarship in Canada. This prize will help draw attention to Aboriginal history while promoting its further growth and maturity.
Eligibility -- Scholarly articles and book chapters concerning the history of Aboriginal peoples whose territory overlaps with that of the current Canadian state, and/or books concerning Aboriginal people whose history involves significant interaction with institutions (state, ecclesiastic, corporate, or other) that are closely associated with what would become Canada.
Adjudication Criteria -- The award is presented to the author(s) of the best scholarly article or book chapter in Canadian Aboriginal history as ascertained by a committee of judges appointed by the Aboriginal History Study Group Eligible submissions will build on theoretical, interpretive, and descriptive work within a community of scholars and contribute to the creation and transmission of knowledge. They must have been subjected to peer review. The publisher of a submitted work need not be Canadian, and all of the submissions should show potential readability by a wider audience.
Submission process – Articles and book chapters bearing an imprint of 2012 (or appearing for the first time in 2012) are eligible for the 2013 prize. One copy of each entry should be sent to each of the following jury members by February 29, 2013.
Prize – The Canadian Aboriginal History Article/Book Chapter Prize consists of a certificate (signed by president of the Aboriginal History Study Group (AHSG) and by the president of the Canadian Historical Association (CHA), and (when resources allow) a financial or some equivalent prize such as subscriptions to relevant journals or a work of Aboriginal art.
Presentation of the prize The prize will be presented at the annual meeting of the CHA during their awards ceremony.
Referees -- The adjudication committee will be appointed by the president of the Aboriginal History Study Group from people who are members of the Canadian Historical Association and members of the Aboriginal History Group. The president's selection of referees will be guided by the following considerations: committee members must have published a peer reviewed article or book chapter of their own; they must be respected within the discipline of history.
1) Chair: Dr. Kathryn Labelle
9 Campus Drive
S7N 5A5
kmageelabelle@gmail.com
2) Dr. Keith Carlson
keith.carlson@usask.ca
3) Dr. Carolyn Podruchny
2140 Vari Hall
carolynp@yorku.ca


Iwo Jima Marines, gay pride and a photo adaptation that spawns fury
At left, the iconic photograph of the 1945 flag-raising by Marines on Iwo Jima. At right, a gay pride adaptation of the original image that has gone viral in recent days, years after it was published. (Original image by Joe Rosenthal/The Associated Press. Second image by Ed Freeman/ Getty Images.)
By Dan Lamothe
Dan Lamothe
Reporter covering the Pentagon and the U.S. military
More than a decade ago, photographer Ed Freeman set out to capture the gay rights struggle in a photograph for the cover of Frontiers, a gay magazine. To do so, he relied on an image — the flag-raising at Iwo Jima — that has been imitated and adapted countless times since it was captured in the midst of one of America's bloodiest battles.
The photograph was taken Feb. 23, 1945, four days into an operation that would rage for more than a month. Associated Press photographer Joe Rosenthal snapped the image as five Marines and a Navy corpsman raised an American flag on Mount Suribachi, the highest summit on the Pacific island. Within weeks, three of those Marines were killed in combat, putting them among the 6,821 American fatalities on Iwo Jima. An additional 19,000-plus U.S. troops were wounded, and more than 18,800 Japanese troops died.
[A stirring visual presentation of World War II and the deaths it caused]
Rosenthal's photograph received a Pulitzer Prize, and became the centerpiece of a multi-billion dollar war bond effort. It also inspired the Marine Corps War Memorial, the equally iconic bronze monument at the entrance to Arlington National Cemetery that was erected in honor of all Marines killed in combat. In short, Rosenthal's image became — and remains — a spiritual force.
The U.S. Marine Corps War Memorial is shown here in December 2014, with the Washington Monument in the distance across the Potomac River. BRENDAN SMIALOWSKI/AFP/Getty Images
Freeman found that out the hard way last week. More than a decade after his adaptation of the photograph was published, it circulated on social media following the Supreme Court's decision Friday to allow same-sex marriage in all 50 states.
That prompted a backlash against Freeman — including a death threat he says he reported to the FBI.
"He said if he ever saw me, he'd kill me," Freeman said in a phone interview. "I got swamped with vitriolic hate mail."
Reaction on Twitter also included a lot of criticism:
Altering the American flag colors && trying to remake the "Raising the Flag on Iwo Jima" photograph with the gay pride flag is degrading
— Taylor Paulk (@taypaulk) July 1, 2015
Alright, I'm glad for gay marriage but I've been seeing the flag changed to rainbow. And in specific The Iwo Jima depiction, that's not cool
— WrongThink™ (@ryan1357nayr) June 26, 2015
Freeman, who is gay, also was blasted on Facebook after posting his gay pride Iwo Jima image along with a message saying it never occurred to him that it would "someday come to symbolize the victory we are celebrating today."
When I took this picture almost ten years ago, it never, never occurred to me that it would someday come to symbolize the victory we are celebrating today. Congratulations to all of us! Love to you all.
Posted by Ed Freeman Photography on Friday, June 26, 2015
Many of the responses were heated.
"Im all for gay rights and equal for all but DO NOT DISRESPECT THOSE WHO SERVED, SACRIFICED, AND DIED FOR YOUR COUNTRY AND YOUR RIGHTS AND FREEDOM," wrote one commentor in response. "Its this [expletive] that will drive ppl to hate on you. You WANT RESPECT THEN GIVE IT TO THOSE WHO DESERVE AND EARNED IT."
A closer look at the reinterpretation of the Joe Rosenthal photograph of the flag-raising on Iwo Jima during World War II. (Photo by Ed Freeman/ Getty Images)
Freeman, whose studio is in Los Angeles, said he never expected the backlash. The image, taken before social media was ubiquitous, was partially staged using models, and completed with Photoshop, he said.
"The principle complaint that people have is that I am equating the gay struggle with the contribution and sacrifice of American servicemen," he said. "But there is no equal sign here. This is not meant as a sign of disrespect. For God sake, no. I totally support people in uniform. There is no comparison going on here. The comparison is going on in people's heads, and they're spoiling for a fight. They're already on edge because of the gay marriage decision."
[Under Armour apologizes for 'Band of Ballers' shirt after being accused of disrespecting the military]
Freeman said that before social media, his version of the image would only have been seen by people who wanted to view it, not "straight people from small towns in Idaho." The Iwo Jima photo "is one of the greatest pictures ever," and has been duplicated to do everything from sell Ol' Glory beer to promote the Hard Rock Cafe, he noted.
Outrage about the adaptation of Rosenthal's image is nothing new, however. In 2008, for example, Time magazine came under heavy criticism for publishing a cover in which the American flag in it was swapped for a tree for a global warming-themed issue.
The original image: U.S. Marines raise the flag atop Mount Suribachi on the Pacific island of Iwo Jima during World War II. (AP Photo/Joe Rosenthal/FILE)
More recently, the British Airlines Stewards and Stewardesses Association (BASSA) union came under fire in 2010 for adapting the Iwo Jima image to show stewardesses raising a union flag, and Under Armour apologized this year for adapting it for a T-shirt in which athletes are shown raising a basketball hoop. The shirt was removed from stores, and company officials said in a tweet that "we deeply regret and apologize the release of a shirt that is not reflective of our commitment to support & honor our country's heroes."
Astronaut Edwin E. 'Buzz' Aldrin poses for a photograph beside the U.S. flag on the Moon during the Apollo 11 mission in this July 20, 1969, file photo. (AP Photo/FILE/Neil Armstrong, NASA)
Freeman said there is "no way in hell" that he meant his adaptation of the Iwo Jima image to be provocative.
"This picture was just a flashpoint for a lot people who are looking for a reason to lash out, so I guess I get to be the whipping boy," he said. "I'm fine with that if that's what it takes."
Tongue in cheek, Freeman said one critic already has given him another idea.
"One of them said, 'Well, why don't you have an astronaut planting a gay flag on the moon?'" he laughed. "And I said, 'Well, why not?'"


University of NottinghamNewsPress releases2017April
Press releases archive
A world-first in how to end slavery for The University of Nottingham
Artificial intelligence can accurately predict future heart disease and strokes, study finds
Big wins for Nottingham at Student Nursing Times Awards 2017
Bringing Vikings back to the East Midlands
Eat wild venison to support native woodland birds, says ecologist
Entrepreneurs scoop top prizes at Ingenuity17
Helping young people into university for 5 years
I now pronounce you husband and wife
New MyAsthma app can help relieve the stress of asthma management
Nottingham doctoral student wins Best Clean Sky Award for his thesis on more electric aircraft
Nottingham vet students assist army in declaring military equine population as Strangles-free
Our quackers April Fool
Partnership with India to train tomorrow's teachers
Science-photography-prize-for-polymer-particles-resembling-golf-balls
Silk clothing offers no benefit for children with eczema, study finds
The University of Nottingham in top 20 universities in the UK
Threads of Empire: Rule and resistance in colonial India c1740-1840
Trump: the first 100 days
University workshop increases the understanding of music in dementia care
Why do bunnies deliver chocolate eggs at Easter?
Expertise for the media
BSA Media Fellowship Scheme
A partnership that helps break down the barriers to higher education is celebrating its 5th anniversary.
Student nurses and staff at The University of Nottingham are celebrating after scooping four awards at the prestigious Student Nursing Times Awards 2017 – almost a quarter of the total awards presented nationally.
A panel of experts at The University of Nottingham will discuss what US President Donald Trump has achieved in his first 100 days in office. Te event takes place on Monday 8 May and is hosted by the Department of American and Canadian Studies in the Clive Granger Building on University Park campus
TV Presenter lends support to world exclusive dinosaur exhibition
The ground-breaking Dinosaurs of China exhibition, which is bringing some of the best-preserved dinosaur fossils in the world to the UK this summer, has a new high profile supporter in the form of respected TV presenter and naturalist Chris Packham.
The University of Nottingham is in the top 20 universities nationally according to TheCompleteUniversityGuide.co.uk's 2018 rankings, published today (Wednesday 26 April).Following its jump of four places last year, Nottingham has risen by three to rank 18th, second place in the East Midlands region.
Forty interns make a contribution to Nottinghamshire organisations
An internship programme launched by The University of Nottingham has trebled in size to support more small businesses and charities across the county.
Self teaching computer systems are better than current standard human-programmed tools for predicting risk of heart disease and strokes, according to a new study by epidemiologists and computer scientists.
I now pronounce you husband and wife…. And husband and wife... And husband and wife
Ten couples have shared their special day in the first mass wedding ceremony to take place at The University of Nottingham Ningbo (UNNC).The couples, who met and fell in love while studying at the university, were invited to come back as part of celebrations to mark a decade of the organisation's alumni association. The wedding ceremony took place at 10am on Saturday 15 April outside the Trent Building at UNNC, in coastal province of Zhejiang, near Shanghai, China.
A major new Viking exhibition is opening at The University of Nottingham Museum at Nottingham Lakeside Arts in November 2017.
The creators of an automated defibrillator and an online food delivery service have claimed top prizes at the UK's largest competition for entrepreneurs.
A workshop recently took place at the University which examined how the therapeutic qualities of sound and music can be used in the care of dementia patients.
A new and unique smartphone app to help people with asthma manage their condition has been developed by lung experts at the Nottingham Respiratory Research Unit and the pharmaceutical company GlaxoSmithKline (GSK).
Wearing silk clothing offers no additional benefit for children who suffer from moderate to severe eczema, a study led by researchers at The University of Nottingham has found.
Dr Fei Gao, who just completed his doctorate at The University of Nottingham has won the Best Clean Sky PhD Award for his thesis in applied sciences and engineering for aeronautics.
Wild deer in Britain should be hunted for venison to drastically reduce their populations and support the re-emergence of our native woodland birds, according to an academic at The University of Nottingham.
The University of Nottingham is offering a Masters course in Slavery and Liberation – the first of its kind in the world.
Vet students from The University of Nottingham have helped in a major project to screen The Queen's most iconic military ceremonial horses for a potentially life-threatening disease called Strangles. The Household Cavalry Mounted Regiment and Kings Troop Royal Horse Artillery have now been declared Strangles-free.
Historians at The University of Nottingham take a look at the resistance that shaped the British Empire in India as part of a new exhibition at Nottingham Lakeside Arts.
A free event at The University of Nottingham will give members of the public the chance to learn everything they ever wanted to know about the most important and oldest festival of the Christian Church.
The University of Nottingham has agreed a partnership with The International School Bangalore (TISB) Training Academy in India to run a postgraduate teacher education course.
Science photography prize for polymer particles resembling golf balls
Science photography prize for picture of tiny 'golf ball' shaped microparticles that could one day be used to repair damaged human tissue.
Were you caught out by our April Fool story?Earlier today we shared news of an exciting new development on University Park campus #goosetunnel.We can now reveal that the news that our resident Canada Geese were getting their own walkway under East Drive was an April Fool.
Media Relations - External Relations
C Floor, Pope Building (Room C4)
Nottingham, NG7 2RD
email: pressoffice@nottingham.ac.uk


Inside Training: The hard work continues
@BarnetFC
Take a look at the best of the action as the Bees Vanarama National League play-off preparation's stepped up an extra gear this week.
The squad, which was announced on Monday, were in high spirits as they continued their training at The Hive London.
The return to training has come as a boost for formerly injured players Shaquile Coulthirist and Alfie Pavey who looked sharp as they were put through their paces by boss Darren Currie.
You can see the best of the snaps from training so far this week above and there'll be plenty more content to come across our social media channels.
Take a look at the best of the goalmouth action via the video below!
Match Pack: Notts County 2-0 Barnet FC
The Bees fell to semi final defeat as goals either side of half time ensured the host's qualified for the Vanarama National League play-off final.
Play Off Preview: Notts County
The Bees sit on the verge of a trip to Wembley Stadium but face a difficult task as they take on Notts County in the Vanarama National League play-off semi finals. Preview in association with LV Bet
Darren Currie previews semi-final clash
Head Coach Darren Currie was quick to highlight the pride he would feel if he managed to guide the Bees to their first outing at Wembley Stadium since it was rebuilt.
Only a handful of tickets remain for Semi-Final screening
Only a handful of tickets remain available for the live screening of our play-off semi-final clash with Notts County.
Trip to Aldershot Town rearranged
The Bees previously postponed trip to Aldershot Town has now been rearranged.
Bees trip to Sutton United to be rescheduled
The Bees Vanarama National League trip to Sutton United will have to be rescheduled, after the U's progressed in the Buildbase FA Trophy.
New date confirmed for Yeovil clash
Our Vanarama National League fixture with Yeovil Town has now been rescheduled.
Trip to Boreham Wood postponed
Our scheduled Vanarama National League fixture with Boreham Wood has been postponed, after the Wood's FA Trophy clash with Torquay was rearranged.


Nats fire Acta
← return to Chatter
By Mark Zuckerman The Washington Times - July 13, 2009, 01:51AM
The Nationals have fired manager Manny Acta.
Acta confirmed by email he was informed of his fate Sunday night, after his team lost 5-0 to the Astros in Houston to close out the first half of the season with a 26-61 record.
There was no immediate word who would succeed the 40-year-old as manager. Bench coach Jim Riggleman, widely considered the most likely replacement on a temporary basis, has experience managing the Padres (1992-94) and Cubs (1995-99) and last year served as the Mariners' interim manager after John McLaren was fired in mid-season.
"I thank the Nationals for giving me this opportunity and I'm sorry that things didn't work out as expected," Acta told ESPNDeportes.com, which first reported the news. "It's normal for the manager to pay the price when the team is not doing well."
Acta's tenure comes to an end after 2 1/2 seasons with a 158-252 overall record. He originally signed a two-year contract in 2007 with two separate club options. The Nationals picked up his first option at the end of the 2007 season but had not done the same with the second option, essentially making him a lame duck this year.


EPA & MassDEP Requirements
The National Pollution Discharge Elimination System (NPDES) Phase II Stormwater Program became effective in Massachusetts in May 2003, and regulates Municipal Separate Storm Sewer Systems (MS4) located within urbanized areas. An urbanized area (UA), as defined by the U.S. Census Bureau, is an area with a population of at least 50,000 and a minimum average population density of more than 1,000 people per square mile. UAs are geographical areas and not limited to jurisdictional boundaries like city, town or state lines.
If we do not properly manage our stormwater runoff, our waterways and natural resources will deteriorate over time and become polluted. The Clean Water Act and the National Pollution Discharge Elimination System were enacted by Congress to protect the waters of the U.S. Failure to comply with the Clean Water Act will expose the town to fines and penalties.
Objectives of the Phase II Stormwater Program are to reduce the discharge of stormwater pollutants to the maximum extent practicable, to protect water quality, and to satisfy the appropriate water quality requirements of the Clean Water Act. In order for a municipality to meet these objectives, EPA has defined the following "6 Minimum Control Measures" that are to be addressed:
Public Participation and Involvement
Illicit Discharge Detection and Elimination
Construction Site Runoff Control
Post-Construction Runoff Control
Pollution Prevention/Good Housekeeping for Municipal Operations
The intent is for municipalities to address these six minimum control measures by identifying and implementing the appropriate Best Management Practices (BMPs) that apply to their community.
Northern Middlesex Stormwater Collaborative
Massachusetts Department of Environmental Protection Stormwater
United States Environmental Protection Agency MS4 Permit for Massachusetts
Why Stormwater Matters
Pepperell Stormwater Fee
Hazards of Dog Waste
Hazards of Residential Runoff
The Town of Pepperell
Pepperell, MA 01463
Town Hall Hours:
Mon. 8:00 a.m. - 6:00 p.m.
Tues-Thurs. 8:00 a.m. - 4:30 p.m.
Fri. 8:00 a.m. - 12:30 p.m.
Pepperell Outlook Web App
Police Department Facebook
Fire Department Facebook
Lawrence Library Facebook


Haiti News | 7/7 on Haitilibre.com
Haiti - Senegal : No special treatment for Haitians
For social integration, the Haitian students will have exactly the same grants that the Senegalese said the minister, adding that for the academic integration there will be no favor...
Haiti - Social : Sarodj Bertin, Woman of the Year
Sarodj Bertin (Miss Haiti 2010, losing candidate in the contest of Miss Universe 2010), received the prize Woman of the Year during the 8th Latins Awards 2010 which were held last Friday at the Symphony Space Theatre located on Broadway in...
Haiti - Tomas : Recognition and damage assessment
The amphibious assault ship USS Iwo Jima (LHD 7) arrived off the coast of Haiti on Friday. Saturday at the request of the Haitian Government...
Haiti - Quebec : Reinforcement of Haitian education
Joined together in Montreal this week, several representatives of education organizations in Quebec have had a historic meeting with Mr. Joel Desrosiers Jean-Pierre, Minister of Education and Training of Haiti...
Haiti - France : Arrival Saturday of a military aircraft with humanitarian aid
As of the reopening of the Toussaint Louverture International Airport on Saturday morning, a French military aircraft, delivered humanitarian supplies to Port-au-Prince...
Haiti - i-Vote : Results tenth week
The campaign goes hard on the ground through floodwaters, following Hurricane Tomas and the fear of cholera spread throughout the country in the coming days.
Haiti - Social : 4.540 Haitian "repatriated" in Haiti
According to César Nicolás Castaing Jimenez, the Chief of CESFRONT (the special unit of border surveillance), which made a assessment of this special unit, announced that 4.540 Haitians were repatriated to Haiti between August 16th and...
Haiti - Leogane : At least 35,000 people affected by floods
The provisional and fast evaluation of the situation by Save the Children teams, estimates at 35.000 the number of people affected by the floods, caused by the passage of the Tomas hurricane. The assessment of material damage in the camps is...
Haiti - Unesco : Michaëlle Jean taking up her duties Monday
Irina Bokova, the Director General of the United Nations Educational, Scientific and Cultural Organization (UNESCO) will formally appoint Michaëlle Jean as UNESCO Special Envoy for Haiti at a ceremony that will take place at UNESCO's Paris Headquarters...
Haiti - Tomas : Special bulletin
The red level of vigilance is maintained over the country because of the risk of heavy rain. Hurricane Tomas moves this morning on the Atlantic Ocean near the Turks Caicos Islands. The center Tomas was located at 8:00 this morning at 22.5 degrees...
« Previous12...3090309130923093309430953096...31393140Next »


Pronouns:
University of California San Diego School of Medicine
Christine Prochnow, MD
Hiking, climbing, spending time with my significant other and co-residents, watching movies, as well as exploring museums, Nashville foodie spots and coffee shops.
Why did you choose VUMC Emergency Medicine?
I was attracted to the southern hospitality! It's a real thing! I loved the warmth and sincerity of the faculty and residents, witnessed the readily apparent camaraderie between residents throughout the interview day as well as the interview dinner, and the legacy of dedication to excellence in teaching.
What are your interests within Emergency Medicine?
Ultrasound, Wilderness Medicine, Medical Student Teaching
What would you be doing if you weren't doing Emergency Medicine?
I honestly have no idea.
What's your 5-year plan?
Complete residency in 2023 and either complete a fellowship vs. chief year. I ultimately see myself in academics or working in combination at an academic site and community site.
What's a random fact about you?
I played NCAA Division I softball in college.


EPPC Online
By James Bowman
Flubber, directed by Les Mayfield, is a Disney remake of an original Disney movie of 1961 about a wonderful kind of "flying rubber" and called The Absent Minded Professor, directed by Robert Stevenson. It wasn't a very good movie the first time around and it is, naturally enough, a much worse movie in the remake. Its essential mistake is not to realize that the title role, that of the other-worldly Professor Brainerd who invents the stuff and teaches chemistry at little Medfield College somewhere in the heartland, is a straight-man role, more suited to its first actor (Fred MacMurray) than to a manic comic like Robin Williams. Williams is too hip—which is to say, too knowing in the ways of the world—to be even remotely convincing as the nerd who suddenly breaks out of his shell, is taken seriously and admired. In this film he is a comic whose mobile face is unemployed, when what is wanted is MacMurray's skill with the deadpan.
There are other interesting changes. The professor is called Ned in the original version, Philip in the remake, while his girlfriend was Betsy (Nancy Olson) instead of Sarah (Marcia Gay Harden). At one point MacMurray sings an adapted version of "Sweet Betsy from Pike" which is, I suppose, just too uncool for words, though it is perfect for the putative professor. But neither the name nor the song survives in the updated (and up-cleaned) version. Instead of being secretary to the president of Medfield, like Betsy, Sarah is (of course) president herself. Betsy is endearingly dumb in the old version and mistakes the Jefferson Memorial for Grant's Tomb. When Brainerd sets her straight, she says, "Oh, you mean Monticello." Of course no 1990s woman would make such a mistake! Nor would she say, as her boyfriend is about to land his flying jalopy on the White House lawn, "Oh, Ned! Not there!"
"Because my hair's a mess and I haven't got a thing to wear."
It is interesting to speculate, by the way, whether the Monticello joke was cut as being sexist or just incomprehensibly intellectual to kids who will never have heard of Jefferson, Grant or Monticello.
Another change is that the dog, Charlie, to whom MacMurray talks incessantly, and his housekeeper, who urges him to go out and fight for the hand of the fair Betsy, have both become absorbed into the character of the flying computer called Weebo—conceived of as feminine and, Galatea-like, with a huge crush on her creator. At times this conceit begins to get worryingly twisted, as when Weebo is bashed by the comic bad guys that are the trademark of John Hughes (who co-wrote the screenplay). The professor and Sarah are united in mourning for the machine, and then discover that she has left behind a sexy daughter called Weebette. As they leave on their honeymoon in the flying car (a classic T-bird instead of a model T), Weebette sits in the back bickering with the protean flubber-man—who is green jello in the form, alternately, of a baby otter and the Pillsbury doughboy.
The 1961 version may be pretty brainless, but at least it is not terminally cute. In fact, Professor MacMurray's treatment of his rival in love and the greedy businessman who wants to steal his formula would doubtless have come across to contemporary audiences as "mean," and so is here softened considerably. Most interestingly, the new version cuts out the admittedly rather feeble but generous-spirited satire of the federal government bureaucracy, which is also hot on the trail of the miraculous flubber. And in the end, MacMurray's Brainerd escapes with his invention so as to be able to present it to the government for the sake of the national defense effort, whereas Williams's version sells it to the Ford Motor Company only to enrich himself. There's another 1990s lesson to teach the children. Haven't we come a long way in 36 years?
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Justia Patents Resin, Rubber, Or Derivative Thereof ContainingUS Patent Application for SEMICONDUCTIVE POLYOLEFIN COMPOSITION COMPRISING CONDUCTIVE FILLER Patent Application (Application #20130037759)
SEMICONDUCTIVE POLYOLEFIN COMPOSITION COMPRISING CONDUCTIVE FILLER
Apr 5, 2011 - BOREALIS AG
The present invention relates to a semiconductive polyolefin composition comprising graphene nanoplatelets. It also relates to a semiconductive polyolefin composition comprising the combination of graphene nanoplatelets and carbon black. Moreover, the present invention is related to a process for producing the semiconductive polyolefin composition as well to the use of the semiconductive polyolefin composition in a power cable. Further, the invention is also related to an article, preferably a power cable comprising at least one semiconductive layer comprising said polyolefin composition.
Latest BOREALIS AG Patents:
Multimodal copolymer of ethylene and at least two alpha-olefin comonomers and final articles made thereof
Aluminoxane-activated metallocene catalysts
Method for improving the cooling capacity of a gas solids olefin polymerization reactor
POLYMER COMPOSITION AND ARTICLE
Cable made from crosslinkable composition without antioxidant and with beneficial methane formation
The present invention relates to a semiconductive polyolefin composition comprising graphene nanoplatelets. It also relates to a semiconductive polyolefin composition comprising the combination of graphene nanoplatelets and carbon black. Moreover, the present invention is related to a process for producing the semiconductive polyolefin composition as well as to the use of the semiconductive polyolefin composition in a power cable. Further, the invention is also related to an article, preferably a power cable comprising at least one semiconductive layer comprising said polyolefin composition.
A semiconductive material is defined as a material having an electrical conductivity intermediate between insulators and conductors. A typical range of electrical conductivity for semiconductors is in the range from 10−9 to 103 S/cm corresponding to electrical resistivity between 109 to 10−3 ohm·cm (see for example McGraw-Hill Dictionary of Scientific and Technical Terms, 4th Ed., pp. 1698, 1989).
A common means to achieve a semiconductive polymer composite is to incorporate carbon black in the polymer with typically 30 to 50 wt % such as for example disclosed in U.S. Pat. No. 5,556,697. However, high loadings of carbon black result in high viscosity of the compounds. Lower carbon black loadings are desirable to improve the processability of the compounds in cable extrusions yet maintaining high conductivity. One option is high structure carbon black such as Ketjen Black. This can reduce the required amount of conductive filler but, due to the high structure the viscosity is drastically increased even at these low loadings.
A further drawback of carbon black fillers is that upon heating volume resistivity (VR) is drastically increased when the polymer composition is heated to standard operating temperature of about 90° C. Additional carbon black may be included to mitigate the temperature dependence of VR but this will result in worsening of the processing properties.
Carbon black may be replaced by expanded graphite to increase the conductivity, as described in WO2008/079585. WO2008/079585 discloses a semiconductive composition comprising a polyolefin polymer and an expanded graphite which is contained in the composition in an amount of 0.1 to 35 wt. % of the total formulation. Processes for preparing the expanded graphite are also disclosed. However, the loading required for expanded graphite to achieve a substantial increase in conductivity is 10 to 15 wt % giving a significant contribution to the viscosity. Even more important is that the large particles of expanded graphite give a very rough surface, which is undesired in cable applications. Hence, there is a need for semiconductive polymeric compositions that combine high conductivity, low viscosity and high surface smoothness.
Other options for increasing the conductivity in semiconductive materials are the incorporation of carbon nanotubes (CNTs) and graphene nanoplatelets (GNPs). US patent application US 2005/0064177 A1 discloses semiconductive compositions with a combination of carbon black (CB) and carbon nanotubes (CNTs). However, the combined loadings of CNT and CB required to achieve a low resistivity is typically in excess of 15 wt %, which results in a reduced ability to flow. It is therefore desirable to have a semiconductive composition with reduced overall filler concentration, enabling smooth surface and good flowability. Moreover, CNTs are presently disfavored due to their extremely high price.
On the other hand, GNPs have recently found applications in electroconductive materials.
Possible production procedures of graphene nanoplatelets and single graphene sheets have been disclosed in e.g. US 2002/054995 A1, US 2004/127621 A1, US 2006/241237 A1 and US 2006/231792 A1. Such processes are for example further discussed by Stankovich et al, Nature 442, (2006) pp. 282, and by Schniepp, Journal of Physical Chemistry B, 110 (2006) pp. 853. Non-limiting examples of materials are Vor-X™ provided by Vorbecks Materials and xGNP™ provided by XG Science.
US2002/054995 A1 discloses how nanoplatelets can be created by high pressure mill giving an aspect ratio between the lateral size and the thickness of 1500:1 and a thickness 1-100 nm.
U.S. Pat. No. 7,071,258 discloses a process for production of nano-scaled graphene plate material comprising a) partially or fully carbonizing a precursor polymer or heat-treating petroleum or coal tar pitch to produce polymeric carbon containing micron- and/or nanometer-scaled graphite crystallites with each crystallites comprising one sheet or a multiplicity of sheets of graphite plane; b) exfoliating the graphite crystallites; and c) mechanical attrition treatment. One dimension is less than 100 nm.
WO2008/045778 A1 discloses a process for functionalisation of graphene sheets. The method is based on adding solvent to obtain graphite oxide with spatially expanded graphene interlayers and subsequently superheating the graphite oxide to decompose the graphite oxide. The obtained surface area is in the range of 300 to 2600 m2/g.
However, from literature reference it can be inferred that an average platelet thickness less than 50 nm cannot be achieved by sonication of expanded graphite materials, see for example Chen et al, Polymer 44 (2003) pp. 1781 and references cited therein.
Electrically conductive polymer nanocomposites have been disclosed using single or multi-layers graphene nanoplatelets as in WO2008/045778A1 and WO2008/143692A1. However, composites with a combination of surface smoothness, low viscosity and low electrical resistivity, have not been disclosed and cable applications are not targeted. This unique combination of properties is central for cable applications, especially semiconductive shields in power cables.
In another aspect, mixtures of GNPs and carbon black as conductive filler are disclosed, e.g. in U.S. Pat. No. 4,971,726 discloses semiconductive composites with carbon black and expanded graphite having an average particle size of 40 μm or more, but it does not consider graphene nanoplatelets with small thickness and large aspects ratio between the thickness and the diameter. Large particle size of the expanded graphite leads to rough surface and hence is not suitable for power cable applications. Moreover, to obtain suitable electrical properties substantial amounts of expanded graphite and carbon black are required which gives an undesired increase in the viscosity of the compound.
The present invention is based on the finding that a semiconductive polyolefin composition comprising an olefin polymer base resin and graphene nanoplatelets can achieve the above objects. Especially such a polyolefin composition provides a unique property profile with combination of low viscosity, smooth surface, low resistivity and low temperature dependence of volume resistivity which is advantageous for cable applications.
In a preferred embodiment of the present invention the above objects are achieved by admixing a solid conductive filler different from graphene nanoplatelets to the polyolefin composition described above.
The present invention is also directed to an article comprising the inventive semiconductive polyolefin composition. Preferably, the article is a power cable, more preferably a power cable comprising a semiconductive layer which comprises the semiconductive polyolefin composition according to the present invention.
Even further, the present invention is also directed to the use of the semiconductive polyolefin composition of the invention in a semiconductive layer of a power cable.
In the following, the figures illustrating the present invention are briefly described. In the figures:
FIG. 1 shows optical microscopy photos of the MFR-strings used to determine the surface smoothness of Example #1;
FIG. 3 shows optical microscopy photos of the MFR-strings used to determine the surface smoothness of Comparative Example #1; and
FIG. 4 shows optical microscopy photos of the MFR-strings used to determine the surface smoothness of Comparative Example #2.
FIG. 5 shows a heating scan in the determination of the temperature dependence of the volume resistivity of Example 3, Comparative Example 4 and Comparative Example 5.
FIG. 6 shows a cooling scan in the determination of the temperature dependence of the volume resistivity of Example 3, Comparative Example 4 and Comparative Example 5.
FIG. 7 shows the annealing dependence of volume resistivity of Example 3 and Comparative Example 4.
The present invention discloses a semiconductive polyolefin composition with low loading filler concentration that has surprisingly low viscosity, high conductivity, excellent surface smoothness and low temperature dependence of volume resistivity. The invention is based on a semiconductive polyolefin composition in which graphene nanoplatelets (GNP) are used in combination with an olefin polymer base resin. In a preferred embodiment optionally a solid conductive filler, different from GNP may be used in the semiconductive polyolefin composition of the present invention.
In the whole disclosure of the present invention the term "expanded graphite" encompasses graphite having no significant order as determined by X-ray diffraction pattern. Expanded graphite has been treated to increase the inter-planar distance between the individual layers that form the graphite structure. It is intended that the term "expanded graphite" throughout the present description relates to a graphite material where the distances between the graphene layers have been substantially increased compared to pure graphite. It should be noted in the context of the present invention that general "expanded graphite" structures do not necessarily form graphene nanoplatelets (GNP's) as defined by this invention.
Graphene nanoplatelets (GNPs) are characterised in that the material is composed of one or several layers of two-dimensional hexagonal lattice of carbon atoms. The platelets have a length parallel to the graphite plane, hereafter labeled diameter, and a thickness orthogonal to the graphite plane, hereafter labeled thickness. Another characteristic feature of GNPs is that the platelets are very thin yet have large diameter, hence GNPs have a very large aspect ratio. The typical thickness of graphene nanoplatelets is 100 nm or less, preferably 40 nm or less, more preferably 20 nm or less or 10 nm or less. The included lower limit of graphene nanoplatelets are single graphene sheets. The thickness of a single graphene sheets is around 1 nm, as for example measured with atomic force microscopy (AFM) described in detail e.g. by Stankovich et al, Nature 442, (2006), pp. 282. The lateral diameter on the other hand, which can also be measured with AFM, is typically 200 micrometers or less, preferably 50 micrometers or less or even more preferably 10 micrometers or less. The lateral extension can be controlled by for example milling to the desired size.
It is preferable that the aspect ratio between the diameter and the thickness is 50 or more, more preferable above 500 and most preferable above 1000.
The BET-value of graphene nanoplatelets are typically above 80 m2/g, and can even be up to 2500 m2/g for materials with a large fraction of single graphene sheets (ASTM D3037).
In another aspect graphene nanoplatelets also include graphene platelets that are somewhat wrinkled such as for example described in Stankovich et al, Nature 442, (2006), pp. 282. Additionally graphene materials with wrinkles to another essentially flat geometry are included. Also more complex secondary structures such as cones are also included, see for example Schniepp, Journal of Physical Chemistry B, 110 (2006) pp. 8535. The definition of GNP does not include carbon nanotubes.
In another aspect the GNPs can be functionalised to improve interaction with the base resins. Non-limiting examples of surface modifications includes treatment with nitric acid treatment; O2 plasma; UV/Ozone; amine; acrylamine such as disclosed in US2004/127621A1.
A specifically preferred embodiment of the graphene nanoplatelets used in the present invention is the commercial product xGNP from XG Science.
In one aspect, the present invention relates to a semiconductive polyolefin composition comprising an olefin polymer base resin, optionally being a polymeric blend comprising one or more olefin polymers, and graphene nanoplatelets, wherein the graphene nanoplatelets are contained in the total composition with a weight percentage of including, but not limited to 2 wt % to 20 wt %, preferably of from 2 to 15 wt %. Further preferred weight ranges may be from 4 to 15 wt %, more preferably 4 to 14 wt %, and most preferably 6 to 12 wt %. The lower limit is due to electrical requirements and the upper limit is due to limitation in the viscosity and surface roughness of the composition.
In another aspect, the graphene nanoplatelets have an average platelet thickness of 50 nm or less, preferably of 40 nm or less, preferably 20 nm or less.
In yet another aspect the present invention relates to graphene nanoplatelets having an aspect ratio of the length divided by the thickness of 50 or more which may be measured by atomic force microscopy (AFM).
The semiconductive polyolefin composition as defined in claim 1 surprisingly provides a combination of advantages. It improves not only processability due to comparatively low viscosity (higher MFR2 values) than conventional semiconductive polyolefin compositions containing carbon black as the conductive filler. Unexpectedly, the present GNP as conductive filler provides at lower loadings the same or even improved level of conductivity compared to conventional carbon blacks. Thus a conveniently low volume resistivity is obtained. Furthermore, the incorporation of GNP into the semiconductive polyolefin compositions gives excellent surface smoothness as expressed by surface roughness calculated as the R_RMS. The method is detailed below. This excellent surface smoothness cannot be achieved by the use of general purpose expanded graphite which usually has rather high particle dimensions, giving increased surface roughness.
Preferably, the semiconductive polyolefin composition according to the present invention has surface roughness characterized by R_RMS, measured on extruded samples, of 100 micrometer or less.
It has further been surprisingly found that the semiconductive polyolefin composition according to the present invention has superior temperature dependence of volume resisitivity compared to respective carbon black based semiconductive polyolefin compositions. It was also found that the electrical performance such as VR of the semiconductive polyolefin composition according to the present invention improves upon annealing at temperatures below the melting temperature of the polymer, which is not observed in carbon black based semiconductive polyolefin compositions.
According to a preferred embodiment of the invention, the semiconductive polyolefin composition comprises an olefin polymer base resin which may be a polymeric blend comprising one or more olefin polymers, and a combination of graphene nanoplatelets and a solid conductive filler. In an even more preferred embodiment, the solid conductive filler is carbon black.
Preferably, said carbon black fulfills at least one of the following requirements:
a iodine number of at least 30 mg/g, measured in accordance with ASTM D 1510,
a DBP oil adsorption number of at least 30 ml/100 g, measured in accordance with ASTM D 2414,
a BET nitrogen surface area of at least 30 m2/g, measured in accordance with ASTM D 3037,
a statistical surface area (STSA) of at least 30 m2/g measured in accordance with ASTM D5816.
Preferably, said carbon black fulfills any combination of said requirements, more preferably all of said requirements.
The solid conductive filler may be contained in the composition with a fraction of 5 to 95 wt %, preferably 10 to 80 wt %, more preferably 20 to 60 wt % and even more preferably 25 to 50 wt %, in relation to the weight of the graphene nanoplatelets.
It is intended throughout the present description that the expression "solid conductive filler" embraces any type of filler which is electrically conductive and can be dispersed in a polymer. Non limiting examples are electrically conductive carbon black and intrinsically conductive polymers. Any carbon black which is electrically conductive can be used. Preferably the carbon black has one or more of the following properties: i) iodine number of at least 30 mg/g according to ASTM D1510, ii) oil absorption number of at least 30 ml/100 g which is measured according to ASTM D2414, iii) nitrogen surface area (BET measurements) of at least 30 m2/g according to ASTM D3037, and iv) statistical surface area (STSA) of at least 30 m2/g according to ASTM D5816. Non-limiting examples of preferable carbon blacks include furnace carbon blacks and acetylene blacks. Non-limiting examples of intrinsic conductive polymers includes poly(p-phenylenevinylene), polyfluorene, polyaniline and polythiophene.
It was unexpectedly found out that with the combination of GNPs and carbon black in the olefin polymer base resin all the above described advantages are retained with the unexpected further reduction of resistivity and viscosity, while a further improvement of surface smoothness and lower temperature dependence of resistivity is achieved. Additionally, a "self-healing" effect was observed, i.e. during operation of the cable the electrical performance will improve with time upon annealing.
Throughout this invention the term "polyolefin" or "olefin polymer" encompasses both an olefin homopolymer and a copolymer of an olefin with one or more comonomer(s). As well known "comonomer" refers to copolymerisable comonomer units.
The polyolefin can be any polyolefin suitable for a semiconductive layer. Preferably, the polyolefin is an olefin homopolymer or copolymer which contains one or more comonomer(s), more preferable an ethylene homo- or copolymer or a propylene homo- or copolymer, and most preferably a polyethylene, which can be made in a low pressure process or a high pressure process. The polyolefin can be e.g. a commercially available polymer or can be prepared according to or analogously to known polymerization process described in the chemical literature.
When the polyolefin, preferably polyethylene, is produced in a low pressure process, then it is typically produced by a coordination catalyst, preferably selected from a Ziegler Natta catalyst, a single site catalyst, which comprises a metallocene and/or non-metallocene catalyst, and/or a Cr catalyst, or any mixture thereof. The polyethylene produced in a low pressure process can have any density, e.g be a very low density linear polyethylene (VLDPE), a linear low density polyethylene (LLDPE) copolymer of ethylene with one or more comonomer(s), medium density polyethylene (MDPE) or high density polyethylene (HOPE). The polyolefin can be unimodal or multimodal with respect to one or more of molecular weight distribution, comonomer distribution or density distribution. As one embodiment low pressure polyethylene may be multimodal with respect to molecular weight distribution. Such a multimodal polyolefin may have at least two polymer components which have different weight average molecular weight, preferably a lower weight average molecular weight (LMW) and a higher weight average molecular weight (HMW). A unimodal polyolefin, preferably low pressure polyethylene is typically prepared using a single stage polymerisation, e.g. solution, slurry or gas phase polymerisation, in a manner well known in the art. A multimodal (e.g. bimodal) polyolefin, for example a low pressure polyethylene can be produced by mechanically blending two or more, separately prepared polymer components or by in-situ blending in a multistage polymerisation process during the preparation process of the polymer components. Both mechanical and in-situ blending is well known in the field. A multistage polymerization process may be preferably carried out in a series of reactors, such as a loop reactor which may be a slurry reactor and/or one or more gas phase reactor(s). Preferably a loop reactor and at least one gas phase reactor is used. The polymerization may also preceded by a prepolymerisation step.
When the polyolefin, preferably polyethylene, is produced in a high pressure process, a LDPE homopolymer or an LDPE copolymer of ethylene with one or more comonomers may be produced. In some embodiments the LDPE homopolymer or copopolymer may be unsaturated. For the production of ethylene (co)polymers by high pressure radical polymerization, reference can be made to the Encyclopedia of Polymer Science and Engineering, Vol. 6 (1986), pp 383-410 and Encyclopedia of Materials: Science and Technology, 2001 Elsevier Science Ltd.: "Polyethylene: High-pressure, R. Klimesch, D. Littmann and F.-O. Mähling pp. 7181-7184.
In another aspect polyolefin polymers include, but are not limited to, copolymers of ethylene and unsaturated ester with an ester content of at least about 50 wt %, based on the weight of the copolymer. Non-limiting examples of unsaturated esters are vinyl esters, acrylic acid and methacrylic acid esters, typically produced by conventional high pressure processes. The ester can have 4 to about 20 carbon atoms, preferably 4 to 10 atoms. Non-limiting examples of examples of vinyl esters are: vinyl acetate, vinyl butyrate, and vinyl pivalate. Non-limiting examples of acrylic and methacrylic acid esters are: methyl acrylate, ethyl acrylate, t-butyl acrylate, n-butyl acrylate, isopropyl acrylate, hexyl acrylate, decyl acrylate and lauryl acrylate. An exemplary polyolefin which may be used in the present invention is Escorene™ 783 commercially available from ExxonMobile.
In another aspect of this invention the polyolefin is elastomeric ethylene/α-olefin copolymers having an α-olefin content of from 15 wt %, preferably 25 wt % or more, based on the weight of the copolymer, These copolymers typically have an α-olefin content of 50 wt % or less, preferably 40 wt % or less and most preferably 35 wt % or less, based on the weight of the copolymer. The α-olefin content is measured by 13C nuclear magnetic resonance (NMR) spectroscopy as described by Randall (Re. Macromolecular Chem. Phys. C29 (2&3)). The α-olefin is preferably a C3-20 linear, branched or cyclic α-olefin. The term "copolymer" refers to a polymer made from at least two monomers. It includes, for example, copolymers, terpolymers and tetrapolymers, Examples of C3-20 α-olefins include propene, 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene, 1-decene. 1-dodecene, 1-tetradecene, 1-hexadecene and 1-octadecene. The α-olefins also can contain a cyclic structure cyclohexane or cyclopentane, resulting in an α-olefin such as 3-cyclohexyl-1-propene and vinyl cyclohexane. Although not α-olefins in the classical sense of the term, for the purpose of this invention certain cyclic olefins such as norbornene and related olefins, particular 5-ethylidene-2-norborene, are encompassed by the term "α-olefins" and can be used as described above. Similarly, styrene and its related olefins, e.g. α-methylstyrene, etc are α-olefins for the purpose of this invention, Illustrative examples of copolymers include ethylene/propylene, ethylene/butane, ethylene/1-hexene, ethylene/1-octene, ethylene/styrene and similar. Illustrative examples of terpolymers include ethylene/propylene/1-octene, ethylene/butane/1-octene, ethylene/propylene/diene monomer (EPDM) and ethylene/butane/styrene, The copolymer can be random or blocky.
In another aspect of this invention the polyolefin may comprise an olefin polymer with hydrolysable silane groups and optionally a silanol condensation catalyst. The polymer composition according to this aspect is preferably an ethylene homopolymer or ethylene copolymer containing crosslinkable silane groups, which have been introduced by either copolymerization or graft polymerization. Non-limiting examples of preferred silane compounds are vinyltrimethoxy silane, vinylbismethoxyethoxy silane, vinyltriethoxy silane, gamma-(meth)acryloxypropyltrimethoxy silane, gamma-(meth)-acryloxy-propyltriethoxy silane and vinyltriacetoxy silane. Preferably, the silane-containing olefin copolymer or graft polymer is crosslinked under the action of water and a silanol condensation catalyst.
Copolymerisation can be carried out in the presence of one or more further comonomers which are copolymerisable with the two monomers and which, for example, may comprise one or more selected from vinylcarboxylate esters such as vinyl acetate and vinyl pivalate; (meth)acrylates such as methyl(meth)-acrylate, ethyl(meth)acrylate and butyl(meth)acrylate; (meth)acrylic acid derivatives such as (meth)acrylonitrile and (meth)acrylamide; vinyl ethers, such as vinylmethyl ether and vinylphenyl ether; alpha olefins such as propylene, 1-butene, 1-hexene, 1-octene and 4-methyl-1-pentene; olefinically unsaturated carboxyl acids, such as (meth)acrylic acid, maleic acid and fumaric acid; and aromatic vinyl compounds, such as styrene and alpha-methyl styrene.
Preferred comonomers are vinyl ethers of monocarboxylic acids having 1-4 carbon atoms, such as vinyl acetate and (meth)acrylate of alcohols having 1-8 carbon atoms, such as methyl(meth)acrylate. The expression"(meth)acrylic acid" used herein is intended to include both acrylic acid and methacrylic acid. The comonomer content in the polymer may amount to 40 wt % or less, preferably 0.5-35 wt %, more preferably 1-25 wt %.
According to the invention, the silane-containing polymer contains 0.001-15 wt % of the silane compound, preferably 0.01-5 wt % and especially preferred 0.1-3 wt %. In order to facilitate the incorporation of the solid conductive filler in the present invention it is preferred that the polymer comprises, apart from ethylene and the silane compound, at least one additional monomer chosen from the vinylcarboxylate esters, (meth)acrylates, (meth)acrylic acid derivatives and vinyl ethers mentioned above. This facilitates the mixing of the conductive filler. It is especially preferred that the olefin polymer comprises a terpolymer of ethylene, silane monomer and a third comonomer, which may be selected from one or more of C3-C8 alpha-olefins; vinyl esters of monocarboxylic acids having 1-4 carbon atoms, preferably vinyl acetate; and (meth)acrylates of alcohols having 1-8 carbon atoms, such as methyl(meth)acrylate, ethyl(meth)acrylate, propyl(meth)acrylate, and butyl(meth)acrylate. Copolymers of ethylene, silane monomer and methyl-, ethyl- or butyl acrylate are especially preferred.
The copolymerization of ethylene, the unsaturated silane compound and, optionally, additional comonomers may be carried out under any suitable conditions resulting in the formation of the desirable polymer. The crosslinking of the silane polymer is carried out with the aid of a catalysts, preferably a silanol condensation catalyst. In general any silanol condensation catalyst may be used in the present invention and a silanol condensation catalyst may be selected from the group consisting of carboxylates of metals, such as tin, zinc, iron, lead and cobalt; organic bases, as well as inorganics acids and organics acids. Special examples of silanol condensation catalysts are dibutyltin dilaurate, dibutyltin diacetate, dioctyltin dilaurate, stannous acetate, stannous caprylate, lead naphthenate, zinc caprylate, cobalt naphthenate, ethyl amines, dibutyl amine, hexyl amines, pyridine, inorganic acids, such as sulphuric acid and hydrochloric acid and organics acids, such as toluenesulphonic acid, acetic acid, stearic acid and maleic acid, Tin carboxylates are especially preferred catalyst compounds.
The amount of silanol condensation catalyst employed is generally in the order of 0.001-2 wt %, preferably 0.01-0.5 wt %, of the amount of silane-containing polymer in the composition.
Other examples of olefin polymers are: polypropylene, propylene copolymer; polybutene, butene copolymers; highly short chain branched α-olefins copolymers with an ethylene co-monomer content of 50 mole percent or less; polyisoprene; EPR (ethylene copolymerized with propylene); EPDM (ethylene copolymerized with propylene and a diene such as hexadiene, dicyclopentadiene, or ethylidene norbornene); copolymers of ethylene and an α-olefin having 3 to 20 carbon atoms such as ethylene/octene copolymers; terpolymers of ethylene, α-olefin and a diene; terpolymers of ethylene, α-olefin, and an unsaturated ester; copolymers of ethylene and vinyl-tri-alkyloxy silane; terpolymers of ethylene, vinyl-tri-alkoloxy silane and an unsaturated ester; or copolymers of ethylene and one or more acrylonitrile and maleic acid esters. In a further embodiment of the present invention, the olefin polymer may comprise ethylene ethyl acrylate. The comonomers can be incorporated randomly or in block and/or graft structures.
In another embodiment of the present invention the olefin polymer may comprise or may be a heterophasic olefin copolymer, e.g. a heterophasic propylene copolymer. The heterophasic propylene copolymer may be preferably a heterophasic copolymer comprising a propylene random copolymer as matrix phase (RAHECO) or a heterophasic copolymer having a propylene homopolymer as matrix phase (HECO). A random copolymer is a copolymer where the comonomer part is randomly distributed in the polymer chains and it also consists of alternating sequences of two monomeric units of random length (including single molecules). It is preferred that the random propylene copolymer comprises at least one comonomer selected from the group consisting of ethylene and C4-C8 alpha-olefins. Preferred C4-C8 alpha-olefins are 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene or 1-octene, more preferred 1-butene. A particularly preferred random propylene copolymer may comprise or consist of propylene and ethylene. Furthermore, the comonomer content of the polypropylene matrix preferably is 0.5 to 10 wt %, more preferably 1 to 8 wt % and even more preferably 2 to 7 wt %. For combining optimum processability with the required mechanical properties, the incorporation of the comonomer can be controlled in such a way that one component of the polypropylene contains more comonomer than the other. Suitable polypropylenes are described e.g. in WO 03/002652.
According to a further embodiment of the present invention the ratio between the MFR2 of the semiconductive polyolefin composition to the MFR2 of the olefin polymer base resin is preferably as high as possible. The increase in melt flow rate caused by adding the solid conductive filler or the GNP is as low as possible. A high ratio of MFR2 of the semiconductive polyolefin composition to the MFR2 of the olefin polymer base resin is beneficial for processing properties, e.g scorch performance, and mechanical properties. The typical MFR2 of the olefin polymers is in the range of from 0.1 to 100 g/10 min as measured at 190° C. for polyethylene, at 230° C. for polypropylene and a load of 2.16 kg according to ISO 1133.
Preferably, the semiconductive polyolefin composition according to the present invention has a ratio of MFR2 of the polyolefin composition to the MFR2 of the olefin polymer base resin of 0.30 or more, wherein the MFR2 is measured at a load of 2.16 kg in accordance to ISO 1133, at a temperature of 190° C. for polyethylene and at a temperature of 230° C. for polypropylene.
In one embodiment the semiconductive polyolefin compositions are crosslinkable. "Crosslinkable" means that the cable layer can be crosslinked before the use in the end application thereof. In crosslinking reaction of a polymer, interpolymer crosslinks (bridges) are primarily formed. Crosslinking can be initiated by free radical reaction using irradiation or preferably using a crosslinking agent, which is typically a free radical generating agent, or by the incorporation of crosslinkable groups into polymer component(s), as known in the art. Moreover, in cable applications the crosslinking step of the semiconductive composition is typically carried out after the formation of the cable.
The free radical generating crosslinking agent can be a radical forming crosslinking agent which contains at least one —O—O— bond or at least one —N═N— bond. More preferably, the crosslinking agent is a peroxide, whereby the crosslinking is preferably initiated using a well known peroxide crosslinking technology that is based on free radical crosslinking and is well described in the field. The peroxide can be any suitable peroxide, e.g. such conventionally used in the field.
As mentioned above crosslinking may also be achieved by incorporation of crosslinkable groups, preferably hydrolysable silane groups, into the polymer component(s) of the semiconductive composition. The hydrolysable silane groups may be introduced into the polymer by copolymerisation of e.g. ethylene monomers with silane group containing comonomers or by grafting with silane groups containing compounds, i.e. by chemical modification of the polymer by addition of silane groups mostly in a free radical grafting process. Such silane groups containing comonomers and compounds are well known in the field and e.g. commercially available. The hydrolysable silane groups are typically then crosslinked by hydrolysis and subsequent condensation in the presence of a silanol-condensation catalyst and water trace in a manner known in the art. Also silane crosslinking technique is well known in the art.
Preferably, the crosslinkable semiconductive composition layer comprises crosslinking agent(s), preferably free radical generating agent(s), more preferably peroxide. Accordingly, the crosslinking of at least the insulation layer, and optionally, and preferably, of the at least one semiconductive layer, is preferably carried out by free radical reaction using one or more free radical generating agents, preferably peroxide(s).
When peroxide is used as a cross-linking agent, then the cross-linking agent is preferably used in an amount of less than 10 wt %, more preferably in an amount of between 0.1 to 8 wt %, still more preferably in an amount of 0.2 to 3 wt % and even more preferably in an amount of 0.3 to 2.5 wt % with respect to the total weight of the composition to be cross-linked.
Non-limiting examples of peroxidic crosslinking agents are organic peroxides, such as di-tert-amylperoxide, 2,5-di(tert-butylperoxy)-2,5-dimethyl-3-hexyne, 2,5-di(tert-butylperoxy)-2,5-dimethylhexane, tert-butylcumylperoxide, di(tert-butyl)peroxide, dicumylperoxide, butyl-4,4-bis(tert-butylperoxy)-valerate, 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane, tert-butylperoxybenzoate, dibenzoylperoxide, bis(tert butylperoxyisopropyl)benzene, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, 1,1-di(tert-butylperoxy)cyclohexane, 1,1-di(tert amylperoxy)cyclohexane, or any mixtures thereof. Preferably, the peroxide is selected from 2,5-di(tert-butylperoxy)-2,5-dimethylhexane, di(tert-butylperoxyisopropyl)benzene, dicumylperoxide, tert-butylcumylperoxide, di(tert-butyl)peroxide, or mixtures thereof.
In another embodiment of the present invention the semiconductive polyolefin composition can also contain further additive(s), such as antioxidant(s), stabiliser(s), water tree retardant additive(s), processing aid(s), scorch retarder(s), filler(s), metal deactivator(s), crosslinking booster(s), flame retardant additive(s), acid or ion scavenger(s), additional inorganic filler(s), voltage stabilizer(s) or any mixtures thereof. Additives are typical use in concentrations from 0.01 wt % to 10 wt %.
As non-limiting examples of antioxidants e.g. sterically hindered or semi-hindered phenols, aromatic amines, aliphatic sterically hindered amines, organic phosphites or phosphonites, thio compounds, and mixtures thereof, can be mentioned.
Preferably, the antioxidant is selected from the group of diphenyl amines and diphenyl sulfides. The phenyl substituents of these compounds may be substituted with further groups such as alkyl, alkylaryl, arylalkyl or hydroxy groups.
Preferably, the phenyl groups of diphenyl amines and diphenyl sulfides are substituted with tert.-butyl groups, preferably in meta or para position, which may bear further substituents such as phenyl groups.
More preferred, the antioxidant is selected from the group of 4,4′-bis(1,1-dimethylbenzyl)diphenylamine, para-oriented styrenated diphenyl-amines, 6,6′-di-tert.-butyl-2,2′-thiodi-p-cresol, tris(2-tert.-butyl-4-thio-(2′-methyl-4′ hydroxy-5′-tert.-butyl)phenyl-5-methyl)phenylphosphite, polymerized 2,2,4-trimethyl-1,2-dihydroquinoline, or derivatives thereof. Of course, not only one of the above-described antioxidants may be used but also any mixture thereof.
The amount of an antioxidant is preferably from 0.005 to 2.5 wt %, based on the weight of the semiconductive composition. The antioxidant(s) are preferably added in an amount of 0.005 to 2 wt %, more preferably 0.01 to 1.5 wt %, even more preferably 0.04 to 1.2 wt %, based on the weight of the semiconductive composition. In a further preferable embodiment, the semiconductive composition may comprise free radical generating agent(s), one or more antioxidant(s) and one or more scorch retarder(s).
The scorch retarder (SR) is a well known additive type in the field and can i.e. prevent premature crosslinking. As also known the SR may also contribute to the unsaturation level of the polymer composition. As examples of scorch retarders allyl compounds, such as dimers of aromatic alpha-methyl alkenyl monomers, preferably 2,4-di-phenyl-4-methyl-1-pentene, substituted or unsubstituted diphenylethylenes, quinone derivatives, hydroquinone derivatives, monofunctional vinyl containing esters and ethers, monocyclic hydrocarbons having at least two or more double bonds, or mixtures thereof, can be mentioned. Preferably, the amount of a scorch retarder is within the range of 0.005 to 2.0 wt. %, more preferably within the range of 0.005 to 1.5 wt. %, based on the weight of the semiconductive composition. Further preferred ranges are e.g. from 0.01 to 0.8 wt %, 0.03 to 0.75 wt %, 0.03 to 0.70 wt %, or 0.04 to 0.60 wt %, based on the weight of the semiconductive composition. One preferred SR added to the semiconductive composition is 2,4-diphenyl-4-methyl-1-pentene.
Examples of processing aids include but are not limited to metal salts of carboxylic acids such as zinc stearate or calcium stearate; fatty acids; fatty amids; polyethylene wax; copolymers of ethylene oxide and propylene oxide; petroleum waxes; non ionic surfactants and polysiloxanes.
Non-limiting examples of additional fillers are clays precipitated silica and silicates; fumed silica calcium carbonate.
It is intended throughout the present description that the expression "compounding" embraces mixing of the material according to standard methods to those skilled in the art. Non-limiting examples of compounding equipments are continuous single or twin screw mixers such as Farell™, Werner and Pfleiderer™, Kobelco Bollling™ and Buss™, or internal batch mixers, such as Brabender™ or Banbury™.
Any suitable process known in the art may be used for the preparation of the semiconductive polyolefin compositions of the present invention such as dry-mixing, solution mixing, solution shear mixing, melt mixing, extrusion, etc.
The present invention is also directed to a process for producing the preferred inventive semiconductive polyolefin composition, comprising pre-mixing the graphene nanoplatelets and the solid conductive filler.
Pre-mixing as used herein shall indicate that the mixing occurs before the resulting mixture is contacted and mixed with the olefin polymer base resin.
As mentioned above, the semiconductive polyolefin composition of the present invention is highly useful in a wide variety of wire and cable applications. Especially it may be incorporated into an electric power cable, particularly in a semiconductive layer of the cable. A power cable is defined to be a cable transferring energy operating at any voltage, typically operating at voltages higher than 1 kV. The voltage applied to the power cable can be alternating (AC), direct (DC), or transient (impulse). Electric power cables, especially medium voltage, high voltage and extra high voltage cables, typically comprise two semiconductive layers and one insulation layer. The term "semiconductive" refers to electrical conductivity intermediate between that of insulating materials and conducting materials. A typical range of electrical conductivity for semiconductors is in the range from 10−9 to 10+3 S/cm (see for example McGraw-Hill Dictionary of scientific and technical terms), corresponding to electrical resistivity between 109 to 10−3 ohm cm. Hence the term "semiconductive" excludes insulation materials. Likewise the present semiconductive polyolefin composition and the ingredients therefor exclude any applications for insulating compositions or insulating layers in a power cable.
The cable comprises preferably one or more conductors surrounded by at least a semiconductive layer and an insulation layer, in that order. More preferably, the cable comprises a conductor surrounded by an inner semiconductive layer, an insulation layer and optionally, and preferably, an outer semiconductive layer, in that order, as defined above. More preferably, at least the inner semiconductive layer comprises the semiconductive composition. Preferably also the outer semiconductive layer comprises the semiconductive composition.
In a preferred embodiment at least the inner semiconductive layer of the cable is crosslinkable. The outer semiconductive layer of the cable may be crosslinkable or non-crosslinkable, depending on the end application. Moreover, the outer semiconductive layer of the cable, if present, may be bonded or strippable, which terms have a well known meaning in the field. The semiconductive composition of the cable may comprise further component(s), such as further polymer component(s) and/or one or more additive(s).
It is evident to a skilled person that the cable can optionally comprise one or more other layer(s) comprising one or more screen(s), a jacketing layer or other protective layer(s), which layer(s) are conventionally used in of field of wire and cable.
The preferred cable is preferably an alternating current (AC) or direct current (DC) power cable, more preferably a medium voltage (MV), a high voltage (HV) or an extra high voltage (EHV) power cable. It is evident that the following further preferable embodiments, subgroups and further properties of the polymer compositions, and components thereof, and of the layers of the cable are generalisable and independent definitions which can be used in any combination for further defining the cable.
The polyolefin composition of the present invention is highly suitable for power cables, especially for power cables operating at voltages higher than 6 kV to 36 kV (medium voltage (MV) cables) and at voltages higher than 36 kV, known as high voltage (HV) cables and extra high voltage (EHV) cables, which EHV cables operate, as well known, at very high voltages. The terms have well known meanings and indicate the operating level of such cables. Combined with good electrical conductivity, the semiconductive composition has also superior surface smoothness and high processability.
The invention also provides a process for producing a cable, preferably a crosslinkable power cable, as defined above or in claims, comprising steps of applying on a conductor, preferably by (co)extrusion, at least a semiconductive layer comprising the semiconductive polyolefin composition of the present invention. Further layers may be applied in the same or additional coextrusion step(s).
EXAMPLES 1. Measurement Methods (a) Melt Flow Rate
The MFR2 was measured with 2.16 kg load at 190° C. for polyethylene and at 230° C. for polypropylene according to ISO 1133.
(b) Volume Resistivity
For the measurement of volume resistivity 2 mm thick plaques were pressed at 150° C. for two minutes. The plaques were cooled down to room temperature. The plaques were placed in between two metallic electrodes and the plaques heated to 120° C. for 30 min to anneal the sample and ensure a good contact between the compound and the electrodes. The compounds were slowly cooled down to room temperature, roughly 22° C. The resistance R in ohm is measured using an ohm-meter. The area A is calculated as A=π (d/2)2 where d is the diameter of the circular electrodes in cm. L is the thickness in cm of the plagues after annealing. All the distances are measured by callipers or micrometer screw. The volume resistance VR is calculated as VR. R×A/L.
(c) Temperature Dependence of Volume Resistivity
The volume resistivity was measured on plaques with a thickness between 1 to 3 mm and a diameter of 20 to 50 mm. The plaques were produced by applying pressure to the sample at temperatures in the range of 150 to 180° C. The volume resistance was measured with a broadband dielectric spectrometer (Novocontrol, Alpha) at a frequency of 50 Hz using stainless steel electrodes. The heating and cooling rate was 5K/min (GNP composition) or 10K/min (CB compositions). Before the thermal cycle the materials were annealed at or above 120° C. for 10 minutes to remove the influence of thermal history. In the heating scan additional annealing stages have been performed for 10 or 5 min for the sample of Example 3 and the sample of Comparative Example 4. Annealing is done by heating a sample and keeping it at that increased temperature for a prolonged period of time. The temperature is chosen so that it is above the melting temperature of the resin. The time is selected to remove any thermal history. The treatment removes internal stress and all parameters which were affected due to manufacturing.
The volume resistance VR is obtained directly from the instrument and calculated as VR=R×A/L, where L is the thickness of the plaques and the area A is calculated as A=π (d/2)2, where d is the diameter of the circular electrodes. All the distances used in the calculations are measured by calipers or micrometer screw.
(d) Surface Roughness
The surface roughness of the material was determined by investigations with optical microscopy of the surface of strings extruded under conditions applied in MFR (ISO 1133, with 2.16 kg load at 190° C.) experiments. The surface of the strings was recorded with an optical camera focused on the profile of the string. The typical profile length investigated was 2.5 mm and the optical enlargement 50 times. The distances were calibrated with special objective glass with millimetres marks. The recorded profiles was analysed and position of the edge extracted. This can for example be performed with edge detection routines e.g. available in MatLab™. The long range bend or curvature of the strings was corrected for by a least-square curve fit with a polynomial of the order 2. The surface roughness was then calculated as the R_RMS calculated as Equation 1
R_RMS = ( 1 n  ∑ i = 1 n   ( Δ   y i ) 2 ) 1  /  2 . Equation   1
Here Δyi is the deviation in micrometers between the recorded edge and the polynomial, i is the index of different pixels along the profile. For each material at least 8 different photos were recorded and analysed. The standard deviation of the obtained surface roughness index, R_RMS, was calculated.
2. Materials
Graphene Nanoplatelets. GNP
xGNP™, commercially available from XG Science. The density of the xGNP is around 2.0 g/cm3 and the platelet thickness is in the range from 8 to 13 nanometers. The average lateral size (diameter) is around 5 micrometer. The BET data showed the surface area of the xGnP reached more than 100 m2/g.
Elftex™ 254, commercially available from Cabot Corporation, Leuwen, Belgium with the following properties:
Iodine number measured by ASTM D1510 <180 m/g Particle size measured by ASTM D3849, procedure D <25 nm Ash content measured by ASTM D1506 <0.1% Toluene extract measured by ASTM D4527 <0.03%
Expanded Graphite
TIMREX® BNB90™, commercially available from Timcal Graphite and Carbon. This material has a particle size distribution with a D90 less than 100 μm. The surface areas are characterized with BET=28 m2/g and Oil adsorption number of 150 ml/100 g.
Escorene™ 783, commercially available from ExxonMobile
The vinyl acetate-content of the material was 33% and the MFR2=43 g/10 min at 190° C. and 2.16 kg.
The materials were produced by mixing the polymer with the conductive filler using a Brabender mixer. For all compounds the conductive filler constitutes 10 percent based on weight shown in the table below. The base resin for the materials in Table 1 is an ethylene vinyl-acetate (ESCORENE™ 783) with a vinyl-acetate content of 33 wt % and MFR2 of 43 g/10 min (EVA1). For Comparative Example 4, an ethylene vinyl-acetate (ESCORENE™ 783) with a vinyl-acetate content of 20 wt % and MFR2 of 20 g/10 min (EVA2) and for Comparative Example 5, an ethylene vinyl-acetate (ESCORENE™ 783) with a vinyl-acetate content of 9 wt % and MFR2 of 9 g/10 min (EVA3) was used. The GNP used was obtained from XG Science (xGNP™) with a typical thickness in the range from 8 to 13 nanometers and a diameter around 5 micrometers. The expanded graphite was TIMREX BNB90™. The carbon black was Elftex 254 from CABOT.
The compounds were produced in general accordance with the description of Kalaitzidou et al. Composites Science and Technology 67 (2007) 2045. The following processing scheme was adopted.
The base resin was cooled with liquid nitrogen and ground to a powder. The proper amount of the GNP or carbon black was dispersed in isopropanol in a glass bottle, with roughly 10 times more isopropanol by weight. For composition with a combination of carbon black and GNP the carbon black was dispersed in the isopropanol solution after the GNP. The isopropanol solution with the GNP and/or carbon black was placed in an ultrasound bath for 30 minutes at room temperature. The base resin was dispersed in the isopropanol solution with the GNP and/or carbon black to make a slurry. The slurry was placed in an ultrasound bath for another 30 minutes. Excessive isopropanol was evaporated by storage at room temperature for some days. The slurry was compounded into Brabender batch mixer preheated to 190° C. and mixed at 50 revolutions per minute (RPM) for 10 min.
TABLE 1 Comp. Comp. Comp. Example #1 Example #2 Example #1 Example #2 Example #3
EVA1 wt % 90 90 90 90 100 xGNP wt % 10 8 Expanded graphite wt % 10 Carbon black wt % 2 10 MFR2 g/10 min 15.12 21.68 12.05 34.83 43 (190° C./2.16 kg) VR ohm cm 9.5 × 106 2.5 × 104 1.7 × 105 8.3 × 109 >1 × 1013 R_RMS μm 79.7 ± 6.2 57.1 ± 13.4 123.6 ± 14.7 66.5 ± 22.8 NA MFR2(composition)/ 0.35 0.50 0.28 0.81 1.00 MFR2(base resin)
The measurements show that with expanded graphite the surface is very rough, R_RMS above 100 micrometer, and unsuitable for cable applications. Example 1 containing 10 wt % of GNP has excellent surface smoothness, while the viscosity and volume resistivity is in a suitable range for semiconductive applications. In contrast, Comparative Example 2 shows that with 10 wt % carbon black the resistivity is too high, i.e. the material is not semiconductive. For all other compositions the volume resistivity is in the semiconductive range. The lowest volume resistivity is observed for the mixture of GNP and carbon black. The measurements also show that the lowest MFR values are obtained with expanded graphite, thus leading to unacceptable flowability and also the surface smoothness was unacceptable for cable applications With GNP or carbon black the ability to flow is sufficiently high. The MFR2 of the pure EVA is 43 g/10 min. To summarize the measurements show that the GNP-based semiconductive compositions gives superior surface smoothness and higher MFR (lower viscosity) as well as low volume resistivity. Especially beneficial is the combination of GNP and carbon black.
In another series of experiments the temperature depencence of the volume resistivity and the self-healing effect upon annealing were examined. The compositions according to the following Table 2 were prepared and tested. The compositions according to Example 3, Comparative Example 4 and Comparative Example 5 were prepared in accordance with the procedures described for the compositions shown in Table 1 above.
TABLE 2 Comp Comp Ex. 3 Ex. 4 Ex. 5
EVA1 ESCORENE 783 90 (MFR2 = 43, 33% VA) EVA2 MFR2 = 20, VA = 20% 84.2 EVA3 MFR2 = 9, VA = 9% 63.2 GNP xGNP (XG Science) 10 CB Conductex 7051 15 36 AO TMQ 0.8 0.8 VRpeak/VRRT 14 43.300 230 (heating) VRpeak/VR50° C. 1.2 75 20 (cooling)
FIG. 5 and FIG. 6 show the volume resistivity as a function of temperature for the three compositions upon heating and cooling, respectively. FIG. 5 shows that the temperature dependence of VR for the inventive Example 3 comprising GNP is much less pronounced than for the comparative examples comprising carbon black. In the Comparative Examples 4 and 5 two different CB contents (36 wt % and 15 wt %) were used. It can be seen that the ratio of the maximum VR over VR at room temperature (23° C.) is roughly 230 and 43300 at 36 wt % and 15 wt % CB loadings, respectively, while the corresponding value for the GNP-composite is 14. This shows that VR of the GNP-composition has much less pronounced temperature dependence than the CB compositions. This is a distinct advantage for semiconductive polymer compositions in power cable applications since the semiconductive composition and layer will have smaller temperature variation when operated at different power loadings, which in turn result in the development of varying rise of temperature. The lower temperature dependence infers that a higher VR can be accepted at room temperature and the overall filler loading can thus be reduced.
The difference between GNP and CB compositions is even more pronounced when the cooling cycle is considered, as displayed in FIG. 6. The GNP composition (Example 3) reveals an almost perfect flat line whereas the CB compositions (Comparative Examples 4 and 5) have a similar performance as upon heating with a pronounced peak, although the peak position is slightly shifted to lower temperatures. The observed values for VRpeak VR50° C. upon cooling are 1.2 for Example 3, 75 for Comparative Example 4 and 20 for Comparative Example 5, respectively.
The absence of a peak for the GNP composition hence infers that the percolation pathways in this system is not perturbed by the crystallisation of the polymer, or in other words, the polymer crystallises in domains around the GNP.
An additional new finding with the inventive semiconductive polymer compositions is the reduction of VR upon annealing at temperatures below the melting temperatures. For the compositions according to the Comparative Examples 4 and 5, the VR remains almost unchanged when the temperature is kept constant as is shown in FIG. 7. This is in contrast to the inventive Example 3 where a reduction of VR of more than 25% is observed when annealed for 5 min. Further extending the annealing appears to even further reduce VR. This is a key beneficial feature for semiconductive compositions for power cables since one of the restricting factors is that thermal cycling and prolonged annealing have resulted in deterioration of VR-performance for semiconductive polymer compositions including carbon black so that the GNP compositions of the invention achieve substantial advance in long-term VR performance, if the compositions are used in semiconductive layers for power cables.
Thus the semiconductive polyolefin composition of the present invention does not only provide substantial decrease in surface roughness and volume resistivity, but also provides substantial increase in processability and flowability which is highly desirable for the manufacture of semiconductive layers in power cables. Moreover by the inventive combination of graphene nanoplatelets and carbon black in a semiconductive composition not only could the above effects be achieved but the process costs could be sharply decreased. The partial replacement of graphene nanoplatelets which are rather costly by carbon black leads to cost savings while the partial replacement of carbon black by graphene nanoplatelets gives synergistic effects regarding surface roughness decrease, conductivity increase and simultaneous flowability of the inventive composition. Furthermore, the temperature dependence of the volume resistivity could be reduced and a self-healing effect could be observed in long-term VR performance over conventional carbon black filled semiconductive compositions.
1-15. (canceled)
16. A semiconductive polyolefin composition comprising
(a) an olefin polymer base resin, and
(b) graphene nanoplatelets.
17. The semiconductive polyolefin composition according to claim 16, further comprising
(c) a solid conductive filler different from (b).
18. The semiconductive polyolefin composition according to claim 16, wherein the average thickness of the graphene nanoplatelets (b) is in the range of from 1 nm to 50 nm, preferably of from 1 nm to 40 nm, more preferably of from 1 nm to 20 nm.
19. The semiconductive polyolefin composition according to claim 16, wherein the graphene nanoplatelets (b) have an aspect ratio of diameter to thickness that is 50 or more, measured by atomic force microscopy.
20. The semiconductive polyolefin composition according to claim 16, wherein the graphene nanoplatelets (b) are contained in the range of from 2 to 20 wt %, preferably in the range of from 4 to 15 wt %, more preferably in the range of from 4 to 14 wt %, and even more preferably in the range of from 6 to 12 wt %, based on the total weight of the polyolefin composition.
21. The semiconductive polyolefin composition according to claim 17, wherein the solid conductive filler (c) is carbon black.
22. The semiconductive polyolefin composition according to claim 21, wherein said carbon black fulfills at least one of the following requirements, preferable a combination thereof, more preferably all of them:
(a) an iodine number of at least 30 mg/g, measured in accordance with ASTM D 1510,
(b) a DBP oil adsorption number of at least 30 ml/100 g, measured in accordance with ASTM D 2414,
(c) a BET nitrogen surface area of at least 30 m2/g, measured in accordance with ASTM D 3037,
(d) a statistical surface area (STSA) of at least 30 m2/g measured in accordance with ASTM D5816.
23. The semiconductive polyolefin composition according to claim 17, wherein the solid conductive filler (c) is contained in the composition with a fraction of 5 to 95 wt %, in relation to the weight of the graphene nanoplatelets (b).
24. The semiconductive polyolefin composition according to claim 16, wherein the olefin polymer base resin (a) comprises an ethylene homo- or copolymer or a propylene homo- or copolymer.
25. The semiconductive polyolefin composition according to claim 16, wherein the olefin polymer base resin (a) comprises a copolymer of ethylene with at least one comonomer selected from unsaturated esters, preferably from vinyl esters, acrylic acid or methacrylic acid esters, more preferably the at least one comonomer is selected from methyl acrylate, ethyl acrylate or butyl acrylate, more preferably with the amount of acrylate comonomer units from 1 to 15 mol % with regard to the total amount of monomers in the polymeric part of the composition.
26. The semiconductive polyolefin composition according to claim 16, having a ratio of MFR2 of the polyolefin composition to the MFR2 of the olefin polymer base resin of 0.30 or more, wherein the MFR2 is measured at a load of 2.16 kg in accordance to ISO 1133, at a temperature of 190° C. for polyethylene and at a temperature of 230° C. for polypropylene.
27. The semiconductive polyolefin composition according to claim 16, wherein the surface roughness characterized by R_RMS, measured on extruded samples, is 100 micrometer or less.
28. A process for producing the semiconductive polyolefin composition according to claim 16, comprising pre-mixing the graphene nanoplatelets (b) and the solid conductive filler (c).
29. Article comprising the semiconductive polyolefin composition according to claim 16, preferably the article being a power cable, more preferably a power cable comprising a semiconductive layer which comprises the semiconductive polyolefin composition according to claim 16.
30. A process for the production of a semiconductive layer of a power cable employing the semiconductive polyolefin composition according to claim 16.
Filed: Apr 5, 2011
Publication Date: Feb 14, 2013
Patent Grant number: 9543056
Applicant: BOREALIS AG (Vienna)
Inventors: Christer Svanberg (Kallered), Tung Pham (Linz), Muhammad Ali Malik (Stenungsund), Francis Costa (Linz), Yi Liu (Linz), Takashi Uematsu (Stenungsund), Thomas Gkourmpis (Gothenburg)
Current U.S. Class: Resin, Rubber, Or Derivative Thereof Containing (252/511); Fullerenes (i.e., Graphene-based Structures, Such As Nanohorns, Nanococoons, Nanoscrolls, Etc.) Or Fullerene-like Structures (e.g., Ws2 Or Mos2 Chalcogenide Nanotubes, Planar C3n4, Etc.) (977/734)
International Classification: H01B 1/04 (20060101); B82Y 30/00 (20110101);