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. 6, No. 1
PEL PLASTICS UPDATE
Jan-Feb., 1998
By Mort Wallach
ISSN 1094-656X
 

Nanotechnology-Work is progressing worldwide on mineral filled nanocomposites which is one of the hottest fields in polymer technology with applications in tougher and lighter automotive parts, improved gas-barrier films, and enhanced flame retardance. In other recent developments novel nanometer-scale conductive wires of silver coated DNA molecules have potential applications in microelectronic devices.

• Development projects on mineral filled nanocomposites in Japan, Taiwan, UK, USA, and elsewhere include matrix materials such as polyamides, polyesters, polypropylene, polystyrene, fluoropolymers, epoxies, and other plastics. The filler is typically montmorillonite clay platelets, a multiple layered material with each layer about a nanometer thick and surface dimensions of 1000 nm (1 micron), and surface area of about 750 m2/g. Surface chemistry and layer spacing can be modified to enhance particle-matrix bonding and clay distribution. The particles, due also to their very high aspect ratios, yield improved mechanical, flame retardant, thermal, and barrier properties without significant trade-offs. Initial research on nylon 6 began in Japan in the 1980s at Toyota's Research Laboratories. Some of the key projects underway today include: Ube Industries, Ube City, Japan-Toyota licensee involved with nylon 6, 66, and 12 compounds; Nanocor, Arlington Heights, IL-focusing on nylon, polyester, and PP, using parent Amcol Intl. patents and non-exclusive Toyota license; Dow Chemical, Midland, MI-received recent NIST contract to study nanocomposites in vehicle manufacture with Magna Intl; ICI Polyester, Middlesborough, England-commercializing clear polyester barrier film; Ford Motor, Dearborn, MI-focusing on polypropylene for interior and exterior automotive applications; AlliedSignal, Morristown, NJ-focusing on nylon 6 on which it holds nanocomposite patents; Solutia, St. Louis, MO-focusing on nylon 6, 66 and copolymers for which it has developed technology aimed at automotive applications; DuPont, Wilmington, DE, focusing on fluoropolymers for coatings; Claytec, Lansing, MI-startup commercializing epoxy end uses; Industrial Technology Research Inst., Taipei, Taiwan-focusing on improved antistat, gas barrier, and mechanical properties of conducting polymers, polystyrene, and polyester. Clearly, there are many programs underway in mineral filled nanocomposites, with key applications in automotive and packaging. (Doug Smock, Modern Plastics, Feb., 1998, p. 26).

   

• Y. Eichen and coworkers at the Technion-Israel Institute of Technology have developed nanometer-scale wires with diameters well below dimensions attained by standard microelectronics technology. Expectations are that the technique will yield electrical wires just a few nanometers thick. Basically, the team forms a DNA bridge by attaching two different oligonucleotides to two gold electrodes via disulfide-metal bonds. The electrodes are linked by a DNA molecule bearing 'sticky' ends complimentary to the oligonucleotides. Silver ions are localized along the DNA by exchanging them for sodium ions. Silver ion reduction yields nanometer-sized silver clumps bound to the DNA skeleton. As in photo film processing, the silver aggregates are developed further with an acidic solution of hydroquinone and silver ions under low light conditions. The structure, size, and conduction properties of the metal wire can be tailored by the silver development conditions. This approach could lead to nanometer scale electronic devices. (Nature, 391, 775, 1998).

Smart/Functional Polymers-Using molecular engineering, a highly photorefractive polymer with a unique chromophore and near-IR sensitivity was fabricated with potential applications in medical and biorelated imaging.

• B. Kippelen and coworkers at U. of Arizona and S. Marder and coworkers at Cal. Tech. and the Jet Propulsion Lab have developed a near-IR (830 nm) active material which could be useful in photonic applications such as imaging through scattering media. The key to this development is a new IR sensitive chromophore for photorefractive composites. The chromophore is based on a linear conjugated molecule, or polyene, with dihexylamino and dicyanomethylidene moieties. This polyene was designed to have just the right combination of properties, including a large dipole moment and a very strong preference to polarize along the axis of the molecule. The polyene was incorporated into a poly(N-vinyl- carbazole) matrix containing N-ethylcarbazole as plasticizer and 2,4,7-trinitro-9-fluorenone (TNF) as the sensitizer. Optical tests revealed that the refractive index changes were five times greater than previous materials and aging tests predicted a lifetime of several years at room temperature. Near-IR sensitivity was obtained by replacing TNF with a commercially available sensitizer 2,4,7-trinitro-9-(fluorenylidene)malonitrile. Example applications-using lower cost IR lasers-include imaging of biological tissues such as tumors, and increased efficiencies of optical correlation systems used to authenticate credit cards, passports or other documents. This work is an excellent example of the use of molecular engineering to develop useful products in medical and biorelated imaging. (Science, 279, 54, 1998)

Catalysis-Double-headed initiators employed in dual living free radical and ring opening polymerizations, yield novel functional and block polymers with narrow molecular weight distributions and controllable block size. These polymers could be tailored to new applications and can serve as compatibilizers of novel alloys and blends.

• C. Hawker and coworkers at IBM Almaden in San Jose and U. of Liege, Belgium have prepared both novel block copolymers and functional polymers using double-headed initiators in dual living free radical and ring opening polymerizations. Hydroxy and alkoxyamine, or tribromo initiating groups were fully compatible with both mechanisms. In this manner it was demonstrated that a variety of vinyl monomers can be polymerized with ?-caprolactone. Since the latter is miscible with many polymers a variety of blends with vinyl based polymers can be prepared. Other living polymerization systems and monomer combinations are being investigated. (Macromolecules, 31, 213, 1998).

Alloys & Blends-Compatibilization of the polypropylene/polycarbonate system with function- alized polypropylene (PP-g-GMA) was confirmed by characterization data and formation of an in-situ copolymer PP-g-PC during the blending process.

• Z. Yin and coworkers of the Chinese Academy of Sciences in Changchun have studied the effects of the compatibilizer polypropylene grafted with glycidyl methacrylate (PP-g-GMA) on the morphology, thermal, rheological, and mechanical properties of polypropylene/polycarbonate blends. It was found that the addition of PP-g-GMA significantly changed the blend morphology. The mean size of domains was reduced from 20 ?m to less than 5?m. The dispersed domain size is also strongly dependent upon the content of PP-g- GMA. The interfacial tension of PP/PC/PP-g-GMA (50/30/20) is only about one-tenth of PP/PC (70/30). The crystallization temperature of PP in PP/PC/PP-g-GMA is 5-8?C higher than that of PP in PP/PC blends. Characterization studies based on mechanical properties, differential scanning calorimetry, rheological, and morphological evidence obtained by using SEM, support the hypothesis that the copolymer PP-g-PC was formed in-situ during the blending process. (Polymer, 39, 547, 1998).

Alloy & Blend Patents-Among 1000 patents reviewed during this period, there are several noteworthy inventions involving: condensation monomer recovery by depolymerization, polyester fibers containing naphthalate, olefin auto components with improved adhesion and chemical resistance, and linear constrained-geometry ethylene graft copolymer blends.

• "Recovery Of Monomers And Other Depolymerization Products From Contaminated Polymers". F. Gallagher (DuPont Co.) WO 97 49,652, Dec. 31, 1997. An improved process for recovering depolymerization products from polymers such as polyesters, polyamides, and polyesteramides, especially when the starting polymer content is less than about 98%, comprises (1) depolymerizing the polymer by means of a depolymerizing agent to yield volatile reaction products, (2) vapor-phase stripping of the volatile reaction products to yield a stripping agent/product distillate, and (3) recovering the reaction products from the distillate while leaving non-volatile residue material with the support material. The depolymerization and vapor phase recovery of monomers and other reaction products are conducted in the presence of a solid support. (Chem. Abs. 128: 89270v)

   

• "Polyester Fibers Containing Naphthalate Units". S. Sakellarides (Amoco Corp.) WO 98 00,591, Jan. 8, 1998. Heat-shrinkable polyester fiber contains aromatic ester units of at least terephthalate and 2,6 naphthalate where the 2,6 naphthalate units comprise about 10 mol percent of the total aromatic ester units in the polyester. The fibers may be manufactured from blends to achieve the required naphthalate unit content. (Chem. Abs. 128: 89978g)

   

• "Method Of Making Painted Automobile Components Having Improved Adhesion For Paints And Resistance To Gasoline Which Comprise Polyolefins And High And Low Molecular Weight Ethylene-Propylene-Diene Rubbers". S. Srinivasan et. al. (Honda; D & S Plastics Intl.) US 5,693,710, Dec. 2, 1997. A method of making articles, such as automobile bumpers, from thermoplastic polyolefin compositions having improved resistance to gasoline and other fluids when painted with flexible coatings such as two- component polyurethane paints is disclosed. The compositions used to form these articles include a thermoplastic polyolefin such as crystalline polypropylene, crystalline polyethylene or mixtures thereof with a first rubber component of an ethylene-propylene-diene rubber having a high molecular weight and a second rubber component of an ethylene-propylene- diene rubber having a low molecular weight, wherein the first rubber component has a molecular weight of 4 to 200 times that of the second rubber component. Thus, a composition comprising polypropylene (Mw > 100,000) 70, ethylene-propylene-diene rubber 20, and dicyclopentadiene-ethylene-propylene rubber (Mn 5200) 10 wt. % was molded into a shaped article followed by coating with an adhesion promoter, R784 (two-component urethane metallic base coat), and R789 (two-component urethane clear coat) giving gasoline resistance > 30 min and 0 % peel at 30 min compared with gasoline resistance 5 min and > 90 % peel at 30 min using ethylene-propylene copolymer (Mw 50,000) instead of the rubbers. (Chem. Abs. 128: 35694t)

   

• "Blends Of Graft-Modified Substantially Linear Ethylene Polymers". M. Hughes et. al. (Dow Chemical Co.) US 5,705,565, Jan. 6, 1998. The title blend contains thermoplastic polymers and substantially linear ethylene polymers, e.g., polyethylenes, prepared by constrained geometry catalysis, which are grafted with > 1 unsaturated organic compounds containing both ethylenic unsaturation and a carbonyl group, the ethylene polymer characterized as having (i) a melt flow ratio, I10/I2 > 5.63; (ii) a molecular weight distribution, Mw/Mn, Mw/Mn < (I10/I2)-4.63; (iii) a density > 0.850 g/cm3 ; and (iv) a critical shear rate at the onset of surface melt fracture > 50 % greater than the critical shear rate at the onset of surface melt fracture of a linear olefin polymer having about the same I2 and polydispersity. These graft-modified substantially linear ethylene polymers impart desirable compatibility and impact properties to various thermoplastic polymer blends. Thus, an 80/20 blend of poly(butylene terephthalate) (I) and maleated substantially linear ethylene polymer was molded into test parts having notched Izod impact strength 6.46 J/cm and -30? Dynatup impact strength 84.3 J; vs. 0.64 and 39.5 respectively, for I only. (Chem. Abs. 128: 89591a)

New Polymer Ventures-Dow Chemical Co. and Cargill are forming a 50/50 limited liability company (Cargill Dow Polymers LLC) to develop and market polylactic acid (PLA) polymers. These fully compostable and recyclable aliphatic polyester materials are derived from renewable agricultural resources such as corn, sugar beets or starch. In this process starch is converted to sugar and fermented by bacteria to yield lactic acid. Water is then removed to form a lactide which is converted to PLA via a solvent free polymerization. Over the last ten years Cargill has invested significantly in PLA polymers and has acquired an extensive patent portfolio. Dow with its world class polymer science, applications technology, and global customer base should help accelerate the commercialization of these materials. This development follows a 1 1/4 year joint program to evaluate the polymer family's potential and the benefits of pursuing a joint venture. Target application areas include cast and oriented films, fibers and nonwovens, blown films, rigid containers, foamed sheet, and paperboard coatings. Other companies involved in PLA development include Mitsui Toatsu, Shimadzu, Neste, and Chronopol. Although the Cargill Dow venture has the largest production capacity (8 million lb/yr which will double by the end of 1998 and a world-scale facility projected for 2001) it will take large volume economies of scale to bring the price down from $1.30-3.00/lb to within the 40-60?/lb range of most commodity polymers. The strategy is to compete not only in the biodegradable market (which has been less than a major success story to date) but also hydrocarbon based thermo- plastics such as polyethylene, polystyrene, polypropylene and PET. PLA resins can be flexible or rigid and can be copolymerized with other polymers. A special attribute is that lactic acid exists as stereo isomers and therefore changes in stereochemistry can produce amorphous, semicrystalline or crystalline polymers with varied property profiles. In addition, additives, blends, and copolymers, are being considered in a strategy to formulate based on consumer needs. Clearly, these possibilities present some interesting opportunities. The company will be managed by a joint Cargill/Dow team. Overall, the business rationale appears to be based on captive low cost renewable resources, product versatility with various profiles, combined partner global strength, and environmental good will. (Plastics Engineering, Feb., 1998, p.12).