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. 1
PEL PLASTICS UPDATE
May-June, 1999
By Mort Wallach
ISSN 1094-656X
 

Nanocomposites-New monomeric routes to polystyrene and PMMA nanocomposites employ functional clay surfactants to render the silicate more wettable by the hydrophobic polymer. Polymerization proceeds within the galleries separating the silicate layers to form a uniform dispersion. In another approach to nanocomposites, block copolymer/clay surface layer interaction via ionic or H-bonding was demonstrated to effect clay sheet separation. Also, a new and versatile core-shell route to nanocomposites offers a variety of potential applications including, porous films, 3D memory storage, and permanent recording. Clearly, there is significant progress in various nanocomposite technologies and applications.

• Prof. Giannelis and coworkers at Cornell have developed new PS and PMMA nanocomposites. With PS they employed ionic bonding of an organic surfactant to the silicate interlayer surface which enhances it's wettability by the styrenic polymer. The surfactant initiates styrene living free-radical polymerization via nitroxyl functionality. On heating, the styrene molecules diffuse into the galleries and polystyrene chains begin growing from the bound surfactant molecules. As the polymerization proceeds, the galleries become increasingly congested with polymer chains and the silicate layers are gradually forced apart until they are well separated leading to a well dispersed nanocomposite. X-ray diffraction and other data confirm the presence of a uniform dispersion wherein only intercalated structures had been obtained previously (J. Am. Chem. Soc., 121, 1615, 1999). Since this is a living polymerization it offers control of molecular weight and its distribution, and potential formation of block copolymer. Another method devised by Giannelis for PMMA involves polymerizing methyl methacrylate in an aqueous emulsion containing the powdered silicate. The water in the reaction mixture separates the silicate stacks into single layers. Since PMMA is produced commercially using a similar emulsion process this method is attractive to industry. In addition these nanocomposites are transparent and colorless which are requirements for their use in paints and coatings, and montmorillonite clay imparts improved stability of the transparent nanocomposite to heat and UV light. (R. Dagani, C&EN, June 7, 1999, p. 25

   

• H. Fischer and coworkers at the Institute of Applied Physics in Eindhoven, Netherlands prepared nanocomposites consisting of polymer matrix materials and natural layered minerals, by using special compatibilizing agents between these two intrinsically non-miscible components. Block or graft copolymer couples one part of it's polymer chain that is identical and/or completely miscible with the matrix polymer, and another part that is compatible with the natural mineral. The interaction between the compatibilizer and mineral is preferentially an ionic interaction or an interaction via H bonds which leads to a separation of the mineral into single sheets and/or small clusters containing ~2-10 sheets and a subsequent homogeneous incorporation of these clusters into the polymer matrix material. (Acta Polym., 50(4), 122, 1999)

• E. Kumacheva and O. Kalinina at U. of Toronto have developed a core-shell approach to producing 3D polymer nanocomposites with a variety of potential applications. First they synthesize a core-shell latex dispersion with hard functionalized cores and soft inert shells. Then they assemble the latex particles in a 3D close-packed structure via sedimentation. Heat treatment of the 3D compact assembly leads to flow of the soft shells and formation of a nanocomposite. Using this generalized approach, polymer nanocomposites with various properties and applications can be tailored by using different core and shell forming polymers and introducing various functional groups. Introduction of inorganic cores with tailored variation in refractive index leads to composites with potential in photonic applications. Porous films can be obtained by dissolving the core from a rigid shell/soft core system. Polymer materials for 3D memory storage can be obtained by attaching chromophores to core particles with every core particle representing a single bit. In general, electroconductive or magnetic properties can be introduced into the core or matrix polymer using the appropriate species attachment. In a recent application permanent recording was demonstrated via local photobleaching of fluorescent core particles. Clearly, this technique has real potential. (Macromolecules, 32, 4122, 1999)

Macro Composites/Pultrusion-Dow Plastics recently introduced a new pultrusion material and process based on its Isoplast engineering thermoplastic urethane. Applications include parts for sports equipment, furniture, building profiles, and inserts for overmolding into a variety of engineered parts.

• These Isoplast resins are particularly adaptable to thermoplastic composites because of their ability to depolymerize in the melt followed by rapid molecular weight increase on cooling. This results in a melt viscosity at least an order of magnitude lower than other thermoplastics facilitating good glass wet-out. Also, Isoplast has a good affinity for glass. Unidirectional composites were pultruded containing up to 70% by volume of glass at speeds of 10 meters/min with void contents below 2%. Glass volume fractions of 45-70% result in longitudinal tensile strength of 150-201 kpsi, flex modulus of 4.6-7.3 Mpsi, and density of 1.74-2.02 g/cc. These composites trade-named Fulcrum can then be formed with heat and pressure to produce curved or angled parts for sports equipment, furniture, building profiles, or inserts for overmolding into a variety of engineered parts. Forming requires preheating pultruded strips for 3 min at 435F and then compressing them between matched molds. Fibers should be lightly tensioned by clamping the ends of the profile at around 150 psi, which allows the fibers to slip into the mold on pressing. Composite scrap can be granulated and reused by injection molding in a blend with unfilled Isoplast. One of the first licensees for the Fulcrum process (Bemis Manufacturing, Sheboygan Falls, WI) is setting up a line to pultrude 1/4 in wide strips for use in office furniture and lawn and garden equipment. (M. Naitove, Plastics Technology, June, 1999, p. 51)

Catalysis-The annual Polyolefins XI Conference was held in Houston on Feb 21-24. Key technical issues presented include catalytic process improvements and product enhancement.

• Comparing the four primary commercial processes Ken Sinclair reviewed high pressure, solution phase, slurry phase, and gas phase processes. Among these only solution phase and gas phase (super-condensing) are expected to be scaleable to single line capacities of 400-500kt/yr. Such large plants should be commonplace early in the next century. New catalyst/process combinations are expected to produce polyethylene and polypropylene to serve markets requiring higher performance and lower cost. Metallocene single-site catalyst development is clearly the dominant technology and is now used in several families of new and improved polymers. However many companies including Nova, Equistar, and DuPont are reporting new nonmetallocene catalyst technologies. Townsend Tarnell estimate worldwide production of polyolefins at 500 kt in 1998. For commercialization a new catalyst must meet a complex set of kinetic performance requirements. Using a gas phase fluid bed reactor (e.g., as described by M. Muhle of Innovation Technologies) such needed information can be obtained and the required polymerization and product performance can then be defined in detail. A wide range of ligand types and combinations available with metallocenes provides an increasing portfolio of new products and improved manufacturing economics. (A. Blanco, Plastics Engineering, April, 1999, p.21)

Alloys & Blends-Syndiotactic polystyrene (sPS)/thermoplastic polyurethane (TPU) blends were compatibilized in the melt by the block copolymer poly(styrene-b-4-vinyl-pyridine). The TPU adds toughness and abrasion resistance, while the PS contributes tensile properties and processibility to the system.

• S. Xu and coworkers at the Chinese Academy of Sciences in Changchun investigated the effect of adding diblock copolymer poly(styrene-b-4-vinylpyridine) [P(S-b-4VPy)] to immiscible blends of (sPS)/(TPU). The morphology, thermal transition, crystal structure, rheological and mechanical properties of the blends were then characterized. The diblock copolymer was synthesized by sequential anionic copolymerization and was melt-blended with the sPS and TPU. SEM showed that the added block copolymer reduced the domain size of the dispersed phase in the blends. Differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD) revealed that the extent of compatibility between sPS and TPU affected the crystallization of sPS in the blends. Tensile strength and elongation at break increased, while the dynamic modulus and complex viscosity decreased with the amount of P(S-b-4VPy) in the blend. The compatibilizing effect of the diblock copolymer is the result of its location at the interface between the sPS and the TPU phases, i.e., the polystyrene block enters the noncrystalline interfacial regions of the sPS, and the poly(4-vinylpyridine) block interacts with TPU through intermolecular hydrogen bonding. (Polymer, 40(12), 3399, 1999)

Alloy & Blend Patents-Among 1500 patents reviewed during this period, there are several noteworthy inventions involving: grafted thermoplastic elastomers, rubbery compositions from waste tires, and toughened polyacetals.

• "Grafted Thermoplastic Elastomeric Compositions Formed By Sequential Melt Blending Of A Thermoplastic Material, Glycidyl-Containing Ethylene Copolymers And Acid-Containing Ethylene Copolymers With Improved Properties". R. Statz (E.I. DuPont de Nemours and Co.) US 5,889,114, March 30, 1999. Grafted multiphase thermoplastic elastomer compositions formed by melt blending 10-30 parts thermoplastic material, especially a polyester and/or polyether-polyester having a high softening point and M_n > 5,000, with 1-22 parts of a glycidyl-containing ethylene copolymer followed by melt blending with 50-89 parts of an acid-containing ethylene copolymer have a unique combination of unexpectedly good high temperature properties, compression set resistance and/or rebound. The hardness of the composition is influenced by the hardness and ratio of the acid-containing ethylene copolymers. The compositions have potential use in molded or extruded items such as hose covers, gaskets, wire jacketing, golf balls, toys, and automotive body moldings. Thus, a composition prepared by blending 27.3% block polyester containing 15% terephthaloyl units, 6% isophthaloyl units, 67.7% polytetramethylene ether glycol (average molecular weight ~2,000), and 11.6% 1,4-butanediol units with 9.1% 27.6:64.2:8.2 butyl acrylate-ethylene-glycidyl methacrylate copolymer on a roll mill at ~220-230° C for 2-3 minutes, adding 63.6% 24.5:66.9:8.6 n-butyl acrylate-ethylene-methacrylic acid copolymer sodium salt (50% neutralized), and blend for a total of 5-10 minutes until homogeneous, gave compression-molded test pieces showing compression set (22 hrs. at 100° C) 31, Shore A hardness 78, tensile strength at break (100° C) 1.9 MPa, elongation at break 140%, oil swell (70 hr at 100° C, ASTM No. 1) 37%, and Clash Berg Temp. (ASTM D-1043) -30° C. (Chem. Abs. 130: 268418n)

• "Thermoplastic Rubbery Compositions Manufactured From Waste Tire Rubber". A. Coran et. al. (U. of Akron) US 5,889,119, March 30, 1999. A method of recycling vulcanized rubber comprises the steps of grinding vulcanized rubber into particles having an average diameter in the range from about 50 m m to about 1.2 mm, and adding the ground tire rubber to a low-modulus binder to form a thermoplastic rubbery composition comprising from about 10 to about 80 parts by weight of the low-modulus binder including from about 25 to about 75 parts by weight of a crystalline polyolefin resin, and from about 25 to about 75 parts by weight of a binder rubber, wherein the rubber is vulcanized by dynamic vulcanization to form fine particles in the binder resin, and from about 20 to about 90 parts by weight of ground vulcanized rubber wherein said step of adding the ground rubber occurs at a temperature above the melting point of the crystalline polyolefin resin. Use of the binder containing rubber and crystalline polyolefins provides products that withstand more stretching before breaking, increased ultimate tensile strength, lower hardness, and lower 5% modulus than similar products not containing the rubber in the binder. (Chem. Abs. 130: 268417m)

• "Polyacetal Composition With Improved Toughness". K. Shinohara et. al. (E.I. DuPont De Nemours and Co.) PCT Int. Appl. WO 99 19,401, April 22, 1999. A polyacetal composition with improved toughness, wear resistance, and flowability contains a mixture of 95-99.5 wt.% polyacetal and 0.5-5 wt.% of a triblock copolymer having an amorphous polymer center segment that forms an elastic domain at room temperature and polyethylene glycol chains with molecular weight > 2,000 as terminal segments. Thus, a blend of 99% Delrin 1700PNC10 and 1% Newpol PE 108 showed tensile strength 65.5 MPa, elongation at break 35.4%, and Izod impact strength 54.9 J/m. (Chem. Abs. 130: 297437y).

New Environmentally Friendly Ventures-Supercritical CO₂ polymerization solvent was employed successfully in Teflon fluoromonomer polymerization replacing the unfriendly chloro-fluorocarbons and the alternative aqueous solvent. As a result, DuPont will build a new $40 million development facility to evaluate the technology for producing its fluorinated ethylene-propylene and perfluoroalkoxy resins. Other products such as polytetrafluoroethylene can also be made with the new technology.

• DuPont and Prof. J. DeSimone of U. of North Carolina have teamed to develop this process for fluoropolymers. DuPont was reportedly attracted to this technology because the company was moving away from the environmentally unfriendly chlorofluorocarbons as reaction solvents but finding drawbacks with alternatives such as water. Fluoromonomers are much more soluble in CO₂ than in water improving the efficiency and flexibility of the polymerization process. Using supercritical CO₂ as solvent avoids the polymer isolation and drying required with water, as well as waste disposal steps. DeSimone says that many polymers now made in water including PVC, acrylics, and styrenics, could be switched to CO₂ with substantial cost and environmental savings. Meanwhile DuPont will build a $40 million development facility in Fayettville, NC to evaluate the technology for its Teflon fluoropolymers. If this is successful the company plans a $235 million worldscale fluoropolymer and monomer plant. (M. McCoy, C&EN, April 26, 1999, p. 10)