Thermoplastic polyesters: a wider spectrum.

New abilities to tailor crystallization rates and improve process-ability, a plethora of chemical varieties, an expanded range of high-end performance in thermal and mechanical properties, and an accommodating nature with regard to alloying and copolymerization, all mark thermoplastic polyesters as a dynamic engineering resin technology for the 1990s.

TP polyesters already comprise an extensive array of material technology options: crystalline and amorphous versions, high-clarity grades, elastomers and high-strength structural compounds, packaging and molding grades, and highly competitive thermal and mechanical properties. But as with many engineering resin groups, current development efforts for TP polyesters are being driven by the need for processing improvements, as well as by the demands of specific market applications.

Interviews with virtually all U.S. producers of TP polyesters reveal clear development trends for the 1990s. One major area being explored by several producers is in reformulating resin chemistry in order to control and custom-tailor crystallization rates. Processors soon will have the capability to extrusion blow mold large PET containers with jug handles--widely viewed as a major improvement over current stretch-blow molding techniques.

Materials suppliers point out that more control over crystallization rates also will translate into faster cycle times, as well as improvements in dimensional stability, barrier properties, resin clarity, surface quality and mechanical properties.

Resin producers also say they are investing much research into formulating new amorphous and elastomeric grades of TP polyesters. These novel polyester versions offer greater toughness, a different processing profile, and a new range of mechanical properties. Developments in flame retardancy and color stability also are seen.

New compounding methods are being explored for glass and mineral fillers. The trend is to incorporate higher loadings of reinforcements while maintaining processability and surface properties by means of lubricants and a secondary polymer adjuvant, as well as to tinker with the polymer structure itself.

TP polyesters continue to find their way into the recipes of new high-performance alloys. Research into alloys is widely identified as the leading edge of polymer development for the 1990s. New compatibilized blends of engineering and elastomeric alloys continue to exploit TP polyesters as a cost-effective means to upgrade thermal and mechanical properties.

There is extensive research work under way to boost the thermal performance range of TP polyesters. In particular, new generations of TP polyesters, offering alternative chemistries to the traditional PET and PBT families, seek to boost the high-end heat-resistance range by 25 [degrees] to 50 [degrees] F. Such a boost would open significant new applications for these materials.

Liquid-crystal polymers (LCPs) and polyarylates, representing separate, specialized segments of engineering TP polyesters, will not be reviewed in this article. A full report on LCPs appeared in PT, April '90, p. 92.

FINE-TUNING CRYSTALLINITY

Much of the current development work centers around fine-tuning crystallization rates in order to attain certain target properties as well as facilitate processing and speed cycle times. Material properties that rely on precise crystallization range from clarity to mechanical properties to dimensional stability.

The "magic ingredient" that allows the Performance Plastics unit of Eastman Chemical Co. to tailor the crystallization rates of its engineering polyesters is its cyclohexanedimethanol (CHDM) glycol monomer, according to Leonard P. Davis, manager of development and technical service. CHDM glycol also is a key to permitting miscibility with other engineering resins such as polycarbonates for alloying possibilities. Davis points out Eastman is the only firm making use of the proprietary CHDM monomer.

Robert Seymour, research associate at Eastman, says processability is now the determining factor in steering the development of new injection molding grades of glass-filled crystalline PCT polyester for electrical/electronic surface-mount components. Eastman is the only producer of PCT resin, though GE Plastics modifies Eastman's PCT to produce a proprietary blend in its Valox line. Eastman's major new entry for surface-mount electronics is Ektar PCT CG907.

Seymour says compared with polyphenylene sulfide (PPS), now used in this application, PCT is tougher, offers more resistance to cracking, provides up to 50% faster cycles, costs 15% less, and virtually eliminates flashing around holes and edges. The need to deflash parts is a complaint widely attributed to PPS, according to Eastman.

The presence of CHDM in the polymer structure imparts toughness to PCT and raises its melting point to about 554 F. As an added advantage, PCT is compatible with existing tooling for PBT and PET, according to Eastman executives.

Accurately controlling the rate of crystallization under molding conditions will also be a major focus of R&D at Du Pont Co. in this decade. William E. Garrison Jr., senior research fellow for the Engineering Polymers Div., and Peter J. Rigby, senior marketing programs manager for Rynite, say the complete and rapid crystallization characteristics engineered into Rynite and Bexloy remain the foundation of Du Pont's technology in this area.

Right now, development work at Du Pont is seeking to push the HDT of glass-filled Rynite beyond the 470 F mark. "The cost/performance usefulness of PET is built around its heat resistance," Garrison says. "The challenge will be to balance the tradeoffs. We want to keep Rynite in a comfortable processing range for the molder while pushing the envelope of usefulness to deliver new performance levels for end users. Moving the HDT of glass-filled PET beyond 470 F means we'll be flirting with newer application areas."

Using a proprietary additive package, Novacor Chemicals (formerly Polysar) has apparently enabled its Petsar PD-8201 PET with 30% glass to achieve optimum crystallinity at relatively low mold temperatures--around 140 F, similar to PBT--while other PETs commonly use mold temperatures of 180 F and up (see PT, June '90, p. 38). In addition, Novacor claims to have achieved higher flow, faster cycles and--particularly unusual--lower moisture sensitivity than other PETs. The latter produces a more "forgiving" compound, in contrast to PET's notorious sensitivity to inadequate drying.

DEVELOPMENTS FOR PACKAGING

Greater control over crystallization technology dovetails with development of new higher-melt-strength packaging materials being engineered for extrusion blow molding applications. As reported earlier this year, several firms are developing extrusion blow molding grades of PET (see PT, Feb. '91, p. 23). Extrusion blow molding of PET offers significant economic and processing advantages compared with current injection stretch-blow molding techniques now required for bottles and containers.

Improving melt strength of PET in order to process it by extrusion blow molding is the thrust of several development efforts. Eastman Chemical is preparing to unveil its new Kodapak EBM Copolyester 13339 for this application.

Eastman researchers say higher PET molecular weight and intrinsic viscosity (I.V.) is responsible for improved melt strength of the material, making it possible to support a parison for extrusion blow molding of larger containers with jug handles. Incorporation of 1,4-CHDM glycol acts to slow the crystallization rate of the PET, preventing the resin from becoming hazy and losing clarity. The CHDM also helps to impart good impact properties.

Kodapak EBM 13339, a clear, high-molecular-weight copolyester, has a glass-transition temperature (Tg) of 176 F, I.V. of 1.05, haze reading of 1.4%, crystalline melting point of 473 F, and axial tensile modulus of 328,000 psi. As a guide to blow molding conditions for a 38-oz container, Eastman lists a melt temperature of 535 F, mold temperature of 50 F, screw speed of 29 rpm, bottle thickness of 25 mils, and an overall cycle time of 13 sec. The material is expected to be priced at about 85 cents/lb tl.

Another new developmental packaging grade from Eastman is Thermx Copolyester 13319, now being test marketed and said to have better temperature and hydrolytic stability than PET. Thermx Copolyester 13319 is a PCTA copolyester (another variety unique to Eastman) with terephthalic acid (TPA) as its primary acid group and CHDM as its primary glycol.

Eastman executives cite oriented and extruded film, monofilament, and sheet for thermoforming as projected applications for the new grade. Through orientation and crystallization processes, thermal properties for the material could be tailored to reach above 500 F.

Development work on another extrusion blow molding PET is now under way at the Polyester Div. of Goodyear Tire & Rubber Co. Known as VFR 10313, it too is a PET copolymer, using isophthalic acid to modify the material's crystallinity level and improve melt strength. Its I.V. is 1.04.

Terry L. Persinger, v.p. and general manager, and Richard J. Steichen, director of R&D, say the highest melt strength is achieved with this material by proper drying (up to 5 hr at 350 F) as well as by employing minimum temperatures during extrusion--nominally about 530 F. A mold temperature of about 50 F is recommended to shorten cycle times and prevent crystallization. Low-shear screws also are recommended.

Goodyear also continues development of its new family of Cleartuf HP polyesters, which are based on dimethyl 2,6-naphthalene dicarboxylate (see PT, May '88, p. 15). Company executives point out the Cleartuf HP line is related to a polyester material technology known as polyethylene naphthalate (PEN), which is said to provide significantly better thermal and gas-barrier properties than PET. Eastman, ICI Americas, Inc., Wilmington, Del., and Hoechst Celanese are also working on PEN (see PT, Dec. '89, p. 25 and Sept. '89, p. 33).

Goodyear is focusing its development efforts on a clear, crystalline, homopolymer version of Cleartuf HP, offering hot-fill and pasteurization capability at 212 F, with greater than 50% improvement in moisture barrier and a three-fold advantage in oxygen/carbon dioxide barrier compared with PET. Cleartuf HP has a melt temperature of 518 F, Tg of 248 F, axial tensile yield strength of 19,000 psi and axial elongation at break of 19.4%. Full commercial production of the resin isn't slated for at least another 12-18 months.

Commercial production of B-010 copolyester, developed several years ago by Owens-Illinois Plastic Products Inc., Toledo, Ohio, is slated to begin later this year in Japan through an exclusive licensing agreement with Mitsui Petro-chemical Industries Ltd, Tokyo. The material was developed to provide enhanced barrier properties for packaging applications, compared with PET (see PT, Dec. '85, p. 57).

Bhupendra Khetani, v.p. of O-I's International Plastics Enclosures operations, says the addition of diethylene resorcinol (DER) comonomer to PET improves gas-barrier properties between 25% and 50%, though still falling short of the barrier performance of EVOH or PVDC.

B-010 will be priced about 10% above existing PET grades, and requires more care from processors in preliminary resin drying steps, according to Khetani. He expects B-010 to find use in medical and packaging markets as an intermediate-barrier material priced well below EVOH.

DEVELOPMENTAL AMORPHOUS

GRADES

Development work at Eastman continues toward boosting the glass-transition temperatures of the company's amorphous, glycol-modified PETG and PCTG resin lines (see PT, June '90, p. 80). Neither of these unique Eastman families currently can match the high-end thermal properties of polycarbonate; PCTG can equal the toughness and clarity of PC, while PETG can match PC's clarity. Seymour says the aim is to push the glass-transition temperatures of PETG and PCTG beyond 212 F from their current range of 176-194 F. Eastman research mainly focuses on unfilled grades of these two polyesters.

A new Eastman PETG grade known as GN001 is designed with a higher melt strength for blow molding and extrusion applications. A new PCTG grade, DN001, is designed primarily for injection molding, with some extrusion applications.

Other research on PETG is concentrating on improvement of flow, clarity and mold release. A new grade of PCTG, now under development, is being engineered for higher flow rates for filling thinner parts, while giving up some toughness. The flow would be improved by tailoring the resin's molecular weight during polymerization, rather than through additives or blends.

Another ongoing research thrust for PETG and PCTG is development of compatibilizaton technology with polyolefins to improve resistance to aromatic hydrocarbons and fuels--an area generally considered to be a weakness for noncrystalline polyesters. This compatibilization work, much like the research to raise the thermal limits of these two polyester types, has yet to achieve fruition. Eastman, a producer of polypropylene and LDPE, expects to have closer ties between its polyester and its polyolefin research operations following the completion of Eastman's internal corporate reorganization.

Seymour indicates research will focus on compatibilization of various polyesters and co-polyesters with PP and TPOs, including glass-reinforced alloys. He did not provide a time frame for potential commercial introduction of such an alloy.

The Engineering Plastics Div. of Hoechst Celanese Corp., Chatham, N.J., is poised to introduce new amorphous and semicrystalline polyester grades. Donal McNally, business manager of polyester, says the major strength of the company in developing new polyesters is being able to make changes on the polymer backbone.

The developmental grade of amorphous copolyester PET now being test sampled by customers is called Transpet EKX-105. It's designed for injection molding, although it also can be extruded into film and sheet. Thermoforming applications also are being developed. McNally says it offers higher mechanical strength and stiffness than other available amorphous copolyesters, while also providing enhanced barrier properties and resistance to various lubricants, solvents and alcohol-based fluids. The resin is glass-clear and water-white, remaining clear and amorphous below 275 F. However, it can be crystallized in a post-processing operation.

Recommended melt temperature of the material is between 490 and 520 F, with a mold-temperature range of 65-115 F. Transpet EKX-105 has a specific gravity of 1.30, tensile strength at yield of 8600 psi, elongation at break of 65%, flexural strength of 12,000 psi, flexural modulus of 374,000 psi, notched Izod of 0.5 ft-lb/in., and a HDT of 167 F at 66 psi.

Another new developmental grade from Hoechst Celanese is Celanex JLX-003, an ultra-high molecular weight, unfilled, semi-crystalline PBT designed for extrusion, with elevated resistance to hydrolysis and hot-water aging. It has a specific gravity of 1.31, tensile strength at break of 8000 psi, elongation at break greater than 200%, flexural strength of 12,000 psi, flexural modulus of 330,000 psi, notched Izod impact of 1.0 ft-lb/in., and HDT (at 66 psi) of 310 F. Recommended melt temperature is 480-500 F, and mold temperature 150-200 F.

POLYESTER TP ELASTOMERS

Significantly better flexural fatigue, wider performance-temperature range, and improved abrasion resistance are targets of new Super-Flex blow molding resins in Du Pont's Hytrel line. Company executives say Hytrel has been expanded into blow molding applications through development of a new chemical additive chain extender that enhances the melt strength of the block copolymer material. The proprietary additive provides a means to build molecular weight and increase the viscosity.

Officials at Du Pont say the new generations of Super-Flex copolyester, like all grades of Hytrel, feature in-reactor copolymerization of crystalline PBT and polyether soft segment, which offers a service-temperature performance window between -40 F and +212 F. (Part design also is an important factor in the material's end-use temperature performance.) Super-Flex also offers five times greater flexural fatigue than previous Hytrel grades. Du Pont executives point out blow molded automotive applications as the driving force behind thermal- and mechanical-property improvements in Super-Flex.

As goals for later in this decade, Du Pont officials say the next generation of Super-Flex Hytrel will focus on improved abrasion resistance, more sophisticated barrier properties, and even greater flex-fatigue performance. Increasing the upper temperature capability of Super-Flex is another goal for the next 10 years, as automotive customers demand service-temperature ranges exceeding 300 F.

Current grades in the Super-Flex line include HTR-8136BK and HTR-8105BK, both designed for extrusion blow molding, and HTR-8139LV, which is suitable for injection blow molding. These three grades span a hardness range of Shore 46D to Shore 50D.

Extending the hardness/softness range and mechanical property limits of the Hytrel line is also under way at Du Pont, as is enhancing barrier properties for blocking liquid transmission but permitting breathability of moisture vapor. The Hytrel hardness range now runs from Shore 30D (with a flex modulus of 4000 psi) to Shore 82D (175,000 psi).

Du Pont officials say the company also is developing a new range of stiffness for blow molded grades of Hytrel through low-level addition of an unnamed "non-polyester" polymer, which provides a post-reactor polymeric chain extension, increasing the melt viscosity and stiffness.

New in-reactor stabilizer chemistry in Hytrel W grades offers a means for better retention of whiteness and bright colors, with some sacrifice in long-term heat agin. Two grades in the new W series (G-3548W and G-4078W) are available. They have a hardness rating of Shore D35 and Shore D40 respectively. Future development work will target color retention and improved long-term heat aging.

Du Pont, in cooperation with Astro Valcour Inc., Glen Falls, N.Y., also is making strides in the process technology side of polyester elastomers. Spurred by the needs of footware manufacturers, the two firms recently patented a new high resilience structural foam processing system.

Seven new grades of Riteflex modified-PBT elastomer will be unveiled later this year by Hoechst Celanese. The new grades range in durometer from 35D to 72D and in flex modulus from 8800 to 28,800 psi. Designed for various processing techniques, they reportedly feature superior fatigue resistance, good low-temperature impact properties, and use-temperature range from -40 F to +250 F. Six of the new grades (Riteflex 635, 640, 647, 655, 663 and 672) comply with FDA regulations for food contact. The seventh new grade, 655HS, contains a high-temperature stabilizer package that does not conform to FDA food-contact regulations.

Hoechst's McNally says the company has extended its Riteflex line with new grades that possess the high molecular weight necessary for advanced levels of elongation (over 300%), while retaining high melt flow. This balancing of properties and processability is attained by proprietary copolymerization techniques to modify the PBT molecular structure and introducing soft segments to the polymer backbone, McNally points out.

He declines to identify the elastomeric "soft" phase in the copolyester, but did note that the new grades make us of at least four different soft segments linked to the polymer backbone. One minor tradeoff in this balance of high flow and high molecular weight is some sacrifice in modulus, McNally says.

Two developmental grades in the Riteflex line are identified as RKX-130 and 131. Both are said to be creamy white in color and target extrusion applications such as wire coating and monofilament. Melt temperature for these grades is 480 F. They're very close in mechanical properties, with Shore hardnesses of 76-77D, tensile yield strengths of 5260-6200 psi, ultimate elongations of 310-350%, flex moduli of 100,000-185,000 psi, and notched Izod impact values of 0.6-0.8 ft-lb/in.

GE Plastics recently announced an extension of its Lomod copolyester elastomer line aimed at automotive fascias. Lomod AE series utilizes a new, unidentified soft-block phase, which enhances surface finish and allows the material to readily accept primerless one- and two-component paint systems, as well as some water-borne systems. GE says the Lomod AE series, priced at $1.58/lb tl, encompasses four grades with a flex-modulus range of 30,000 to 90,000 psi.

Conductive elastomeric copolyesters represent the leading edge of polyester development for Akzo Engineering Plastics. Steve Gerteisen, manager of new product development, says two new grades in the Electrafil line will be introduced before year's end. The base polymers for the two grades will be produced by Akzo in the Netherlands and then custom compounded in the U.S. They will be based on Arnitel UL-550 and EM-400 PBT. Both grades, designed for injection molding, ar filled with conductive carbon black, which provides static-discharge protection. Both grades also can incorporate glass-fiber loadings between 5% and 40% to tailor mechanical properties.

The Electrafil grade using Arnitel UL-550 base resin will have a service-temperature range up to 302 F, Shore hardness of 55D, tensile strength of 5075 psi, elongation of 450%, and flexural modulus of 26,100 psi. The grade using Arnitel EM-400, a general-purpose grade, will have Shore hardness of 38D, tensile strength of 2465 psi, elongation of 650% and flexural modulus of 7250 psi. Gerteisen says that depending on the selection of conductive fillers, the new Arnitel grades will be priced between $4 and $8/lb tl.

FLAME-RETARDANT

POLYESTERS

In the area of flame-retardant polyester alloys, Hoechst Celanese is now developing Vandar VKX-083. McNally did not reveal the alloy components of the developmental grade, but says the material is designed for injection molding and extrusion applications that require superior toughness and ductility while meeting UL94V-0 specs at 1/32-in. thickness.

Melt-temperature range for Vandar VKX-083 is 475-500 F, with a mold temperature between 75 and 150 F. It has a tensile strength of 4500 psi, elongation at break of 150%, flexural strength of 5200 psi, flex modulus of 150,000 psi, "No Break" rating for notched Izod, an melt flow rate of 12 g/10 min.

In addition to this developmental Vandar grade, the company is expected to introduce two new high-impact Vandar alloys with UL94V-0 ratings. McNally did not elaborate on the two new alloys (Vandar 8000 and 8001), other than to say they would be unreinforced, toughened PBT grades designed for high flow and processability.

Hoechst Celanese soon will announce four new halogenated flame-retardant grades in its Celanex PBT line (Celanex 2016, 3116, 3216 and 3316). Improved processability and nonblooming flame retardants are key advantages claimed for these grades. Celanex 2016 and 3316 (developmentally known as JKX-905 and JKX-907, respectively) have undergone extensive field testing and meet UL 94V-0 at 1/32-in. Both have a melt-temperature range of 480-500 F and mold-temperature range of 150-200 F. Both are designed for injection molding, with 2016 offering more toughness and ductility, while 3316 provides higher stiffness and HDT.

Celanex 2016 is an unreinforced PBT with specific gravity of 1.44, tensile strength at yield of 8600 psi, elongation at break of 27%, flexural strength of 15,400 psi, flexural modulus of 47,700 psi, notched Izod of 0.6 ft-lb/in., and HDT (at 264 psi) of 328 F.

Celanex 3316 is a 30% glass-reinforced PBT, with specific gravity of 1.66, tensile strength at yield of 19,500 psi, elongation at break of 2.3%, flexural strength of 29,500 psi, flexural modulus of 140,000 psi, notched Izod of 1.4 ft-lb/in., HDT (at 262 psi) of 403 F, and a Comparative Tracking Index of 250 v.

Celanex 3116 is 4.5% glass-filled, and 3216 is filled at a 15% level. Still emerging from the lab, these two grades have not yet received extensive field testing exposure and are considered more developmental.

Du Pont is developing Rynite RE9057, a new low-outgassing, high-stiffness, flame-retardant PET with 30% glass fiber. It has a UL 94V-0 rating at 1/32 in. This grade has a specific gravity of 1.74, tensile strength of 20,000 psi, elongation of 1.9%, flex modulus of 1.4 million psi, flex strength of 31,000 psi, notched Izod of 1.5 ft-lb/in., and HDT (264 psi) of 440 F.

Rynite RE9057 boasts enhanced electrical properties, as well as low outgassing of volatiles when parts are exposed to use-temperature peaks exceeding 390 F. The material was developed for molded components in automotive relays.

ADDING COLOR STABILITY

Long-term color stability at elevated temperatures is another major development thrust for Du Pont. Two new developmental color-stable grades of Rynite (RE5210 and RE5211, both with 30% glass) to be unveiled at NPE, are designed for injection molding. The two grades are now being evaluated by processors.

Rynite RE5210 has a specific gravity of 1.60, tensile strength of 22,000 psi, elongation of 2.5%, notched Izod of 1.8 ft-lb/in., flexural modulus of 1/.4 million psi, and HDT (at 264 psi) of 448 F.

Rynite RE5211 has tensile strength of 25,000 psi, elongation at break of 2%, flexural modulus of 1.56 million psi, notched Izod of 1.94 ft-lb/in., and HDT of 457 F.

Du Pont suggests a melt temperature of 545 F and a mold temperature above 248 F and a mold temperature above 248 F to attain full crystallization during molding, with a slightly lower mold temperature (200-200 F) suggested for RE5210.

'HEAVY' PBTs 'BRANCH' OUT

New developmental branched versions of highly filled "Heavy" Valox PBT represent the leading edge of TP polyester research at GE Plastics. Mark Bulriss, general manager of crystalline resin business, says the Heavy Valox is branched in a secondary process through the presence of an unidentified polymer--possibly a thermoset system--that links integrally with the polymer backbone, forming a "tri-functional species."

While the Heavy Valox remains crystalline, the branching creastes a tougher material with increased melt strength for blow molding, extrusion and thermoforming applications. Prior to this branched version of Heavy Valox, the material was primarily limited to injection molding. Extruded rod stock will be another extension of the higher melt-strength material. Another future development area for Heavy Valox will be flame-retardant versions, he says.

GE formally launched Heavy Valox last year with two injection molding grades: HV7065 and HV7070 (see PT, Sept. '90, p. 109 and Dec. '89, p. 23). Using proprietary lubricants and compounding technology, the material is loaded with an unnamed mineral filler at a 65% level, yet attains a melt-flow rate in excess of 80 g/10 min.

Along with the branched/high-melt-strength and flame-retardant versions of Heavy Valox, GE also continues development on a "heavy" version of Lomod copolyester elastomer. As for the traditional Valox line, GE recently introduced Valox 9731, a new higher heat resin for surface-mount applications. The Valox 9700 series is based on PCT from Eastman Chemical, which is compound and modified for processability.

OTHER REINFORCED ENTRIES

A new high-temperature, glass-filled grade of PET will be introduced shortly by the Plastics Div. of Phillips 66 Co. Phillips added Aspect PET compounds to its lineup of engineering resins just three years ago (PT, June '88, p. 112). Aspect AO55 BA01 will contain 55% glass, giving it an HDT of 446 F at 264 psi. The injection molding grade has a specific gravity of 1.8, tensile strength of 22,000 psi, flexural strength of 37,000 psi, flexural modulus of 2.5 million psi, and notched Izod of 1.5 ft-lb/in.

A Phillips spokesman says an important feature of this new grade will be the compounding technology used to incorporate a high loading of glass fibers while not sacrificing a superior surface finish.

One new engineering grade of PBT slated for commercialization before year end by ICI Advanced Materials/LNP Engineering Plastics is an impact-modified, glass-filled line, currently designated as WF1006HI. The initial offering will have 30% glass, although ICI will offer a range of 10-40%. The impact modifier for this grade will be a proprietary chemical additive system, not a resin alloy. The WF1006HI grade, designed for injection molding, will have a notched Izod of 3.7 ft-lb/in., tensile strenght of 13,000 psi, flexural modulus of 700,000 psi, and HDT of 385 F at 264 psi.

ICI also will introduce a lubricated, unfilled extrusion grade designed for the linings of push/pull cables and automotive brake cables. An ICI spokesman says the as-yet-unnamed material offers wear characteristics similar to nylon and acetal, with an upper use-temperature limit of 300 F, while offering a lower price. This grade will complement an existing lubricated injection molding grade of PBT.

As an example of its wear resistance, ICI says the new lubricated extrusion grade offers a static-mode (40 psi) coefficient of friction of 0.08, compared with 0.19 for standard PBT. The dynamic-mode (50 ft/min) coefficient of friction is 0.13, vs. 0.25 for standard PBT.

The lubricated grade offers a HDT of 180 F, tensile strength of 6800 psi, flexural modulus of 250,000 psi, and a notched Izod of 1.0 ft-lb/in.

AUTO BODY PANELS BECKON 

A major research thrust for Du Pont's Bexloy glass-filled PET is investigating production of horizontal automotive body panels through compression molding. Martin D. Drigotas, senior development programs manager, says the effort is in a preliminary stage of development. He did not reveal the particular material formulation being used in this program, other than to say it was a glass-filled system based on the PET in the current Bexloy K-550 line. The material can survive E-coat temperatures approaching 390 F, allowing them to be painted on-line with steel, he says.

As previously reported, injection molding of thermoplastic, horizontal body panels remains unsuccessful, due to unresolved drawbacks in surface quality, inadequate stiffness and dimensional stability (see Pt, Sept. '89, p. 84). Drigotas indicates the Du Pont TP polyester/compression molded candidate material appears to overcome these difficulties.

One key element in meeting the challenge of competitive cycle times, surface quality and mechanical stiffness in the new Bexloy development is a cross-fertilization with Rynite's rapid crystallization technology for injection molding. "The real trick will be to attain Class-A surface properties," Drigotas says, pointing out micro-wrinkling as a major problem in the processing system. "The key is getting rapid crystallization rates, so the part is fully crystallized out of the mold."

By modifying standard SMC compression molding equipment, Du Pont recently was able to achieve 90-sec clamp-to-clamp cycle times in a test production run at an unnamed domestic automotive plant.

Du Pont officials acknowledge that Bexloy K-550 will be utilized on an injection molded fender program for a 1992 auto platform, an application that has been anticipated for two years. Du Pont has yet to name the car model or automotive OEM utilizing the material. However, much of Du Pont's development work in this area during recent years has been done with Chrysler Corp.

A 'FRIENDLY' ALLOY PARTNER

TP polyesters are key ingredients in many new alloys and elastomers. Industry executives say the reason is that polyesters offer many cost-effective engineering characteristics: a boost in heat resistance, good dimensional stability and low moisture absorption, good mechanical properties stemming from flexible crystallization rates, and a relatively friendly polymer chemistry with regard to compatibilization and miscibility.

An example of this alloying thrust comes from Dow Chemical U.S.A., Midland, Mich., which recently introduced its new Sabre family of PC/PET and PC/PBT alloys for automotive body panels (see PT, April '91, p. 27). The alloys contain a proprietary thermoplastic compatibilizing agent as well as a specially designed impact modifier.

Another firm that recently began exploring PC/PET alloys is Novacor Chemicals (formerly Polysar), which has been gradually expanding a line introduced in early 1989 (PT, April '89, p. 13; May '89, p. 92; June '90, p. 109). Eastman Chemical recently has commercialized Ektar MB DA003, an alloy that pairs its copolyester PCTG with PC.

Two new developments from Monsanto Chemicals also provide an indication of this interest in TP polyesters as an alloy partner. A research official at Advanced Elastomer Systems, the newly formed joint venture between Monsanto and Exxon Chemical, says a developmental elastomer, known as TPE 4000, is likely to use polyester as a continuous-phase matrix material, alloyed with a dispersed phase of acrylate rubber (see PT, April '91, p. 73). An executive at Monsanto's development lab in Springfield, Mass., recently disclosed that the firm's emerging line of alloys known as Triax 4000 includes various combinations of both amorphous and crystalline polyester alloyed with polycarbonate (see PT, March '91, p. 96).

Last year a developmental alloy series that featured the rare combination of two crystalline thermoplastics--PBT and nylon 6--was unveiled by Daicel Chemical Industries, Fort Lee, N.J. (PT, May '90, p. 25). SMA served as the compatibilizing agent for this alloy line, which featured six grades, three of which were glass-filled.

A flurry of alloy introductions two years ago reflected new efforts at combining TP polyester with styrenic resins. Among the first in this series was a glass-reinforced PBT/ASA from BASF, developed in Germany and introduced at the 1989 SAE show in Detroit (PT, April '89, p. 127). Following on the heels of the BASF announcement was an introduction by Arco Chemical Co. of a PBT/SMA known as the Dylark DPN-500 series (PT, May '89, p. 45). Later that year GE Plastics launched a foray into the same territory by commercializing four grades of its Cycolac G-Series, an alloy of PBT and ABS (PT, Oct. '89, p. 14). GE, which first introduced PC/polyester blends (trade-named Xenoy), has also blended polyester with PPO (Gemax).

Allied-Signal Engineering Plastics offered a glimpse of an ongoing alloy development effort involving an "amorphous" PET (PT, June '90, p. 80 and Feb. '90, p. 80). Reportedly designed for both injection molding and extrusion, the alloy was said to fall under Allied-Signal's Synergy series. Company officials recently declined further comment on this material, saying only that research work was continuing.