CompositesWorld

FEB 2016

CompositesWorld

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FEBRUARY 2016 34 CompositesWorld WORK IN PROGRESS Read this article online | short.compositesworld.com/WIPLignin Read more online about how PAN-based carbon fiber is made in "The making of carbon fiber" | short.compositesworld.com/MakingofCF CW's editor-in-chief Jeff Sloan comments online on the subject of alternatives to PAN precursor in "Why CFRP?" | short.compositesworld.com/Uu6ivbCH Domtar's commercial lignin plant is described in this online CW News story, titled, "Domtar inaugurates commercial lignin production" | short.compositesworld.com/BioChoice See how lignin is processed into powder form and filament form in this YouTube video produced by ORNL | short.compositesworld.com/ORNLlignin the panel will join another demonstrator — a radio-frequency toy car (including the toy's batteries) made with lignin-based carbon fber — to generate interest in a full-scale lignin-fed carbon fber line in Sweden. Says Tomani, "We hope that both industry and society will be bold enough to invest in this scale-up, for more sustainable products." Stora Enso (Helsinki, Finland), another pulp-and-paper giant, has investigated carbon fber manufacture using its lignin sources. Niklas Garof, senior development engineer at the company, reports that, unlike with PAN, desirable linearly oriented graphite domains are not formed during lignin stretching and carboniza- tion. To rectify that, the company is researching a hybrid chem- istry that combines cellulose, also derived from its pulp-and-paper activities, with lignin, in an air-gap spinning process, using an N-methylmorpholine N-oxide solution. A demonstration project has been carried out with polymer specialist Fraunhofer IAP (Pottsdam, Germany). Stora Enso believes the successful demon- stration of the novel technology has high-value potential for carbon fbers. In North America, signifcant research is being carried out in Canada, under the Biomaterials and Chemicals Research Network. Dubbed Lignoworks, it is one of four research networks created in 2010 as part of the Natural Sciences and Engineering Research Council of Canada's (NSERC) Forest Sector R&D; Initia- tive. Lignoworks participants include all of Canada's major universities, together with industrial partners Weyerhaeuser, FPInnovations (Pointe-Claire, QC, Canada) and Alberta Pacifc Forest Industries Inc. (Boyle, AB, Canada). Canada's frst commer- cial lignin plant, in Hinton, AB, was developed to use the Ligno- Force technology developed by FPInnovations to produce high- quality lignin from black liquor generated by West Fraser Timber Co.'s adjacent paper mill. Professor Frank Ko of the University of British Columbia is heading the polymeric products research eforts to convert the lignin source into carbon fber for automo- tive and bio-composite applications. Space precludes describing the many other current lignin research eforts, which range from Volkswagen's (Wolfsburg, Germany) work on lignin-based carbon fber for automotive Carbon fbers produced from high-quality polyac- rylonitrile (PAN) precursor are typically the highest in quality, fnd use in structural composite parts (for example, commercial aircraft airframes) and thus have earned the descriptor aerospace-grade, and make up 95% of the current carbon fber market. But carbon fbers made from other precursors are in use, commercially, and many more precursor alternatives have been investigated. The best-known commercial alternatives are pitch and rayon. Pitch-based carbon fbers, frst produced in the early 1960s by Union Carbide, now GrafTech (Independence, OH, US), are derived from the remnants of crude oil or coal distillation that are rich in aromatic hydrocarbons. The fbers can be formed without mechanical stretching, making them easier to process than PAN, but the result is fnished carbon fbers with high modulus and excellent thermal conductivity, depending on the degree of processing and graphitiza- tion, but tensile strength lower than that found in PAN-based carbon fber. Pitch fbers are used in applications that range from aircraft brakes to space satellite structures, where heat management is critical. Rayon precursor, based on cellulose, dates to Thomas Edison's frst electric light bulbs, where fbers were used as the bulb flaments. Rayon-based carbon fbers, in a phenolic matrix, are still used to make ablative insulating material in solid rocket motors (SRMs), where they perform better than any other carbon fber. The fbers' crenulated ("dog bone") cross section translates to good interlaminar shear performance and bonding with the phenolic resin, as well as low thermal conductivity. Virtually all rayon manufacturing has moved ofshore of the US, but there is active research aimed at reshoring rayon fber production: the University of Tennessee, together with the Air Force Research Laboratory (AFRL) and Advanced Cerametrics (Lambertville, NJ, US), has recently reported progress on an experimental rayon fber-based carbon fber. Currently in the spotlight, lignin was frst considered a viable candidate for carbon fbers decades ago. One example is Kayacarbon carbon fbers, produced by Nippon Kayaku Co. in the early 1970s. But, the patent literature reveals many more potential precursors, among them polyethylene (high density and low density), polyolefn, Saran (poly[vinylidene chloride]-polyvinyl chloride copolymer), polystyrene, polybutadiene, polyimide, phenol/hexamine and phenol/formaldehyde/ammonia, phenolic, aromatic polyamide 6/6, varieties of polyphenylene-benzothiazoles (PBZTs), and poly(p-phenylenebenzobisoxazole (PBO). All of these have been investigated at lab or pilot scale, with varying degrees of success and at projected lower costs than aerospace-grade PAN. An excellent historical review of the investigations cited here is contained in the scientifc journal Angewandte Chemie [Applied Chemistry] International Edition, 2014, by M.R. Buchmeiser, et al., published by Wiley-VCH Verlag GmbH & Co. (Weinheim, Germany). Alternative precursor R&D;: What are the alternatives to PAN? o d u c e d f r o m h i g h - q u a l i t y p o l y a c - p r e c u r s o r a r e t y p i c a l l y u a l i t y , f n d u s e i n o s i t e p a r t s ( f o r e r c i a l a i r c r a f t h u s h a v e e a r n e d e r o s p a c e - g r a d e , % o f t h e c u r r e n t r k e t . B u t c a r b o n m o t h e r p r e c u r s o r s m e r c i a l l y , a n d m a n y a l t e r n a t i v e s h a v e b e e n w n c o m m e r c i a l a l t e r n a t i v e s a r e p i t c h a n d r a y o n . b o n f b e r s , f r s t p r o d u c e d i n t h e e a r l y 1 9 6 0 s b y SIDE STORY

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