New polymer blends provide toughness, elasticity.

Using resin modifiers in new ways to create unusual polymer blends was the subject of three reports at the recent Additives '96 conference in Houston, sponsored by Executive Conference Management Inc., Plymouth, Mich. The reports told how to formulate new thermoplastic elastomers and high-impact engineering-resin alloys.

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CPE/STYRENIC-BASED TPEs

A patent-pending TP elastomer technology developed by GE Specialty Chemicals, Parkersburg, W. Va., expands potential applications for the company's Blendex ABS and ASA impact modifiers beyond PVC. GE says these modifiers can be alloyed with chlorinated PE (CPE) to create new types of TPEs without need of a compatibilizer. Such TPEs can compete with PP/EPDM thermoplastic vulcanizates (TPVs) such as Santoprene from Applied Elastomer Systems, Akron. Potential uses include weather gasketing for automobiles and building construction.

Optimized alloys require modifiers with high rubber content - i.e., ABS modifiers having 65% or more of polybutadiene or styrene-butadiene rubber, and ASA modifiers with at least 60% acrylate rubber. Such blends reportedly exhibit good strain recovery and better tensile and tear strengths, abrasion resistance, and paintability than CPE alone. ASA blends provide outdoor weatherability.

The accompanying table shows examples of such blends. CPE/ABS blends were prepared using Tyrin 3615, a high-molecular-weight, 36%-chlorine CPE formerly available from Dow Chemical Co. and now sold by the new DuPont Dow Elastomers joint venture in Wilmington, Del.

TOUGH, FLEXIBLE NYLON/PBT

A reactively modified olefinic impact modifier for PBT has new potential as a compatibilizer for blends of nylon 6 with 66 and nylon with PBT. Lotader AX 8900 GMA is a reactive ethylene-acrylic ester-glycidyl methacrylate terpolymer from Elf Atochem North America, Inc., Philadelphia. It chemically bonds with these otherwise incompatible engineering resins, according to a paper at the conference. The result is said to be alloys with good balances of impact strength and flexural modulus, as well as improved heat and chemical resistance.

This alloying technology is based on predispersing one of the components in the Lotader reactive elastomer. According to technical marketing manager Igor Leclere, the alloy component with the highest melting point must be preblended above its melting temperature with Lotader in a ratio of 40/60 in order to "encapsulate" the engineering resin with the compatibilizer matrix. The preblend is then diluted to 10-40% in the other engineering plastic at a process temperature between the melting points of the two engineering resins. The resulting alloy has a matrix of the lower-melting engineering plastic and a dispersed phase with a core/shell structure. The hard core is the higher-melting engineering resin, encapsulated by a soft shell of functionalized elastomer.

One example featured in Leclere's paper is composed of a PBT matrix, a Lotader AX 8900 GMA terpolymer shell, and a nylon 66 core. Impact strength at both room temperature and -40 F is higher than for PBT containing the same amount of Lotader impact modifier alone.

According to Leclere, this concept can produce new types of supertough formulations with extremely stable morphology using low levels of reactive elastomer. The reduced Lotader content can yield higher HDTs and better solvent resistance. This technology also has potential for making blends of nylon 6 and 66, nylon and PET, and either nylon or PBT with PPS.

METALLOCENE POEs TOUGHEN NYLON, PBT

Metallocene-catalyzed polyolefin elastomers (POEs) have already proven successful as impact modifiers for PP. Now, researchers at Dow Chemical Co., Midland, Mich., report that POEs functionalized with maleic anhydride can be used to toughen polar engineering thermoplastics that possess reactive end groups, such as nylon 66 and PBT.

In Dow's research, Engage POEs (now marketed by DuPont Dow Elastomers) were functionalized by grafting with 0.5-1.0% of maleic anhydride by reactive extrusion. The grafted POEs are said to show better dispersability, resulting in better impact properties than are obtained with MA-grafted EPDM or ungrafted POE. Dow also says the functionalized POEs cost less than commercial acrylic core/shell impact modifiers for engineering resins.