PEL PLASTICS UPDATE highlights recent progress in key areas of polymer/plastics technology including: catalysis, biopolymers, smart/functional polymers, alloys & blends and polymer modification. A recent issue of PEL Plastics Update follows.

Complimentary Copy
Vol. 7, No. 2
PEL PLASTICS UPDATE
Sept.-Oct., 1999
By Mort Wallach
ISSN 1094-656X
 

Nanocomposites-At the Nanocomposite Materials Conference near Anchorage Alaska General Electric reported new PPE/PA carbon nanotube composites with conductive features suitable for spray painting auto exterior panels, and PBT clay nanocomposites with enhanced performance including flame retardant properties aimed at the electrical connector market. Carbon nanotubes are candidate reinforcements for a new generation of nanocomposite materials.

• T. Feist and coworkers at General Electric have addressed the problem of adapting polymer composites to electrostatic spray painting automotive exteriors by developing a conductive nanotube-filled, impact toughened PPE/PA formulation. Industrial interest in these materials is high, and companies are collaborating with academic labs to explore their potential. GE is also working with poly(butylene terephthalate) nanoclay dispersions which have yielded improved performance over traditional fillers and encouraging flame retardant properties required in PBT electrical connector applications. Nanotubes confer high conductivity at lower loadings (<10%) than carbon black or other conductive micrometer-sized fillers and have been successful in various engineering resins including polycarbonate, nylon, and polyesters, as well as PPE/PA. Many scientists believe that carbon nanotubes should be an ideal reinforcing fiber for composites. One reason is that these graphitic tubes have a very high aspect ratio of 1000 or more and their strength is expected to be two orders of magnitude greater than any other known material. Moreover, nanotubes are much stiffer and less brittle than carbon fibers. Carbon fibers which are used to strengthen materials in sports equipment and in aerospace and marine applications, break at very low strain of < 1% deformation while muliwalled nanotubes embedded in a polymer matrix can withstand deformations up to 15% before failure. Another advantage of nanotube composites is in the ease of processing especially the lack of breakdown during processing which is a big problem with carbon fibers. The low density of nanotubes is another advantage. These and other considerations suggest that nanotubes have the potential to usher in a new generation of tough, lightweight, high strength nanocomposites. But there are some important challenges including dispersion, interfacial adhesion, and tailoring orientation, as well as cost, availability, and manufacturability. (R. Dagani, C&EN, June 7, 1999, p. 25)

Macro Composites-Improvement of fiber/matrix adhesion in aramid fiber reinforced SEBS composites was achieved via reactivity enhancement and resultant fiber/matrix coupling.

• T. Amornsakchai and coworkers at Mahidol U. in Bangkok have employed aramid fiber (poly-m-phenylene isophthalamide) to reinforce SEBS thermoplastic elastomer [styrene(ethylene butylene)styrene]. Improvement of tensile properties and interfacial adhesion was achieved by slightly hydrolyzing the fiber to increase the number of reactive amino end groups, followed by mixing with the SEBS matrix polymer and reactive coupler (maleic anhydride grafted SEBS) (SEBS-g-MA). Extracted fiber evaluation revealed that rubber was chemically bonded to the fiber surface. However, the fractured surface of the treated composite showed more fiber breakage than the untreated material, possibly resulting from the hydrolysis. The overall results suggest good coupling performance of SEBS-g-MA via fiber amino functionality. Fiber/matrix adhesion is an important and active area of composite R&D to remove defects and enhance composite strength. (Polymer, 40(11), 2993, 1999)

Smart/Functional Polymers-New two-photon absorption polymer systems show promise in data storage and microlithography.

• J. Perry of Cal. Tech. and S. Marder of U. of Arizona have developed a new class of molecules with high two-photon absorption cross sections. These materials have promise in the development of futuristic devices including 3D optical memory and microlithography. Recently they demonstrated that molecules based on stilbene and bis(styrl) benzene derivatives can facilitate two-photon absorption chemistry. When incorporated into an acrylate resin, the molecules once excited (usually via high in- tensity lasers) transfer charge to the acrylate causing the material to further polymerize in tiny spots. As in standard lithography, the polymerized spots (which are likely crosslinked) are less soluble while the rest of the material can be washed away leaving a pattern. This new research combines high lateral and depth resolution (of ~1mm). Because the effect occurs only at the beam focus the polymerization can be induced at single spots deep inside material up to 200 mm thick. This compares with only a few micrometers for traditional photoresists. In this manner Perry and Marder demonstrated that they can make a variety of 3D microstructures. There is also real potential for this technology in optical storage materials since some of the molecules are fluorescent but lose this feature when embedded in an acrylate resin. However, once polymerized via the two-photon process the molecules in the tiny spots regain their fluorescing ability. The spots can then read out as information bits by using the exciting laser. Since the polymerization also alters the bit index of refraction this provides another way of retrieving data. (M. Wheeler, Photonics, May 1999, p.32)

Polymer Modification/Lithography-At the recent ACS Meeting (Aug. 22-26) in New Orleans advances in imaging materials were presented which promote semiconductor manufacturing processes that allow for new devices with ever-smaller features.

• C. Grant Wilson of U. of Texas reviewed the chronology of recent progress. As the wavelength of exposure radiation is reduced to provide higher resolution the number of materials that can be considered in resist design decreases. Diazo- naphthoquinone positive-tone resists carried the industry through exposure at 365 nm. Unfortunately, these materials are opaque below 300 nm hence a new class of materials had to be developed for deep ultraviolet (DUV) lithography. The chemically amplified materials for today's DUV lithography are all based on poly(p-hydroxystyrene). They have served well but poly(p-hydroxystyrene) is opaque at 193nm. So again, new chemistry had to be found. Alicyclic polymer systems under development show great promise for this application. The next challenge is 157 nm where even carbonyl groups cannot be included because of high extinction coefficients. New imaging chemistry for vacuum UV exposure must now be found. (PMSE, 81, 32, 1999)

Alloy & Blend Patents-Among 1000 patents reviewed during this period, there are several noteworthy inventions involving: paintable ethylene-acrylic interpolymers, fluorinated polymers with low surface energy, thermoplastic elastomer/polyolefin blends, and blended syndiotactic polystyrene foam with improved properties.

• "Paintable Tough Moldings Of Olefinic Interpolymer Compositions And Blends". Y-C Hwang et. al. (Dow Chemical Co.; Dow Europe S.A.) US 5,883,188, March 16, 1999. The title compositions for automotive applications, comprise (i) ~30-70% of >1 graft-modified polypropylene, (ii) ~10-40% of >1 nongrafted or graft-modified homogeneously branched linear ethylene polymer (no long chain branching; e.g., Exact), ethylene-propylene rubber, ethylene-propylene-diene rubber, heterogeneously branched linear ethylene polymer, styrene block copolymer, or their combination and (iii) ~5-50% of an interpolymer of ethylene and an a,b -unsaturated carbonyl copolymer, e.g., a copolymer of ethylene and acrylic acid. The compositions exhibit excellent paintability with conventional paints without prior application of a primer or surface treatment, good heat resistance, good low temperature impact resistance, and they can be recycled by melt blending the compositions with thermoplastic materials, e.g., in an extruder. Thus, moldings prepared from a blend of Admer QF 500 50, Tafmer P0180 20, and Primacor 3460 30 parts, had good paint adhesion and Izod impact strength 8.7 ft-lb/in., vs. paint adhesion failure and 0.47, respectively, for a molding of Admer QF 500 (100%). (Chem. Abs. 130: 253103g)

• "Semifluorinated Side Chain-Containing Polymers With Low Surface Energy". C. Ober et. al. (Cornell Research Foundation, Inc.) US 5,907,017, May 25, 1999. Fluorinated polymers (or a blend with compatible homopolymer or copolymer which is not fluorinated) have a low surface energy (anti-stick, nonwetting, low friction) surface which is stable on immersion in H₂O, has a weight average molecular weight (M_w) of 10³-10⁶ and comprises a backbone containing (a) methylene groups and (b) side chain bearing groups Q(CF₂)_qF (Q = alkylene; fluoroalkyl group spaced by r atoms from the atom in the backbone to which Q is attached, q = 6-15, r = 6-18, and the q/r ratio is 0.6-1.8:1. Fluorinated polymers include semifluorinated block copolymers of modified isoprene and styrene and semifluorinated ionenes. Thus isoprene-styrene block copolymer was treated under hydroboration conditions to produce surface OH groups and this polymer reaction product with F(CF₂)₈(CH₂)₃COOH and/or F(CF₂)₈(CH₂)₃COCl in THF/pyridine had semifluorinated side chains, advancing water contact angle (dry film) 120°, receding water contact angle 109°, and critical surface tension 8.5 dynes/cm. (Chem. Abs. 130: 352812u)

• "Compatibilized Blends Of A Thermoplastic Elastomer And A Polyolefin". J. Farkas et. al. (B.F. Goodrich) PCT Int. Appl. WO 99 19,406, April 22, 1999. The title compatibilized blends of a thermoplastic elastomer and a polyolefin are prepared by heating the elastomer. The compatibilizer is a thermoplastic polyurethane formed by the reaction of a substantially hydrocarbon intermediate such as a polybutadiene polyol, a diisocyanate such as MDI, and an amine or diol chain extender such as neopentyl glycol. The compatibilizer has high amounts of soft segments therein and imparts improved properties to blends of a thermoplastic elastomer and polyolefin such as good impact resistance, good tensile strength, good tear resistance, and good delamination resistance. (Chem. Abs. 130: 297440u)

• "Syndiotactic Styrene Polymer Foam Having Improved Heat Resistance And Mechanical Properties". K. Suh et. al. (Dow Chemical Co.) PCT Int. Appl. WO 99 03,919, Jan. 28, 1999. Title foam is obtained from a polymer blend comprising a syndiotactic styrene polymer and an amount of an amorphous polymeric material which will impart a heat distortion temperature > 130° C. Thus, a composition comprising 60% syndiotactic polystyrene and 40% maleic anhydride-modified polyphenylene oxide gave a foam having density 3.60 pcf, cell size 0.75 mm, and heat distortion temperature >200°C, compared with 4.25, 1.62, and 80, respectively, for 100% syndiotactic polystyrene foam. (Chem. Abs. 130: 126081y)

New Polymer Ventures-In a difficult polyester market, DuPont has implemented a strategy of global 50:50 joint ventures. Four JVs have been formed so far, accounting for 80% of DuPont's polyester business.

• Having been hurt by polyester overcapacity, low prices, and the Asian market downturn, DuPont is radically revamping its polyester business through the formation of various 50:50 joint ventures. This is unlike the broader industry consolidation where Hoechst, Rhodia, and ICI have sold their polyester operations. Reportedly, according to DuPont senior VP Eduard J. C. M. van Wely the intent is to end up with a strong, competitive, low-cost, and high technology set of businesses with a network of alliances having combined annual revenue in excess of $5 billion. Recent earnings from their polyester business were not up to DuPont standards with an after-tax operating loss of $228 million in 1998 on sales of $2.8 billion. Even after excluding write-offs for the late-1997 acquisition of ICI's polyester business and productivity improvements there was a loss of $7 million. Film and fibers (the largest worldwide market) have been most difficult with better activity in the growing bottle resin market. What DuPont appears to gain through the joint ventures is global reach, dividing its business both by product and geographical area with low cost producers in regions such as Mexico and Turkey. So far DuPont has put 80% of its polyester business into joint ventures. Partners include Alpek, Teijin, Sabanci, and Akra/Teijin JV in staple, film, filament/staple/ resins and filament, respectively. What DuPont has kept at least for now are its specialty products, R&D, technology development, and resins and intermediates largely in North America. Van Wely reportedly says they plan to keep a small organization within the company to provide marketing, merchandising, and technology leadership, making them accessible to the joint ventures. Planning is underway for its longer term presence in resins and intermediates (such as purified terephthalic acid) where the same strategy is likely. New technology under development could be a key reason DuPont is holding on to a piece of the business. A new low-investment high-speed spinning process is expected within two years. DuPont R&D has developed new polyester polymerization process technology which would however require new plant investment. They do have another cost-effective process that can be retrofitted and production of the key intermediate terephthalic acid is being improved. Also, through its life sciences thrust, DuPont has developed a biological route to make propanediol-a future key intermediate for its new polyester propylene terephthalate. Overall, this looks like a conservative approach to remain a successful global polyester player via shared risk, lower cost overseas operations with the potential to inject potentially profitable technology in a future healthier environment for the polyester business. (A. Thayer, C&EN, May 10, 1999, p.14)