Partly Cured Thermoplastic Elastomer Blends

DYNAMICALLY PARTLY CURED THERMOPLASTIC ELASTOMER BLENDS 

In a recent set of patents Fischer disclosed a novel method of preparing thermoplastic elastomers from EPDM and isotactic polypropylene, as well as other, chemically related species (EPM plus polyethylene, etc.) Fischer s work has led to the thermoplastic rubber known as Tpr (31) portion of this work, describing the blending operation, is described elsewhere. 

The basic feature involves blending polypropylene (10%-50%) with EPDM (50%-90%), plus less than the usual amounts of peroxide. The effect the dynamic semicure, the rubber, plastic, and curing agent are worked on an open roll mill, a Banbury mixer, or an extruder mixer.During this time, between 60% and 93% of the material becomes insoluble in cyclohexane at 73 F. (Note the plastic portion probably was already insoluble under these conditions the reaction is partly gelling the elastomer.) 

In the case of the peroxide crosslinked blends, the dynamic aspects probably prevent the crosslinking phase from becoming truly continuous since the material will flow. The final blend is thus thermoplastic and can be 

Typical data are shown in Table 8.6 showing the effect of varying the peroxide level. An 80/20 EPDM/polypropylene mix was processed for seven minutes at 360 F in each experiment. The peroxide employed was 2,5-bis( er -butyl(peroxy))-2,5-dimethylhexane. 

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DYNAMICALLY PARTLY CURED THERMOPLASTIC ELASTOMER BLENDS... 

Table 8.6. Dynamically Partly Cured Thermoplastic Elastomer Blends ...

Plastic types are variable, ranging from flexible to rigid and from thermoplastic to thermoset. Because of these variations, the type of coating applied to them also varies, depending on cure response, solvent sensitivity, and modulus. The type of coating also depends upon the end use of the coated plastic. For example, topcoats can be applied directly to the plastic without the use of a conductive primer if two-toning or blackout areas are not part of the styling latitude. Adhesion promoters also are often utilized if a particularly difficult-to-adhere-to plastic is encountered (i.e., polypropylenes or thermoplastic polyolefins (TPOs), a blend of elastomer and olefin). 

TPEs are blends of various amorphous rubbers such as ethylene-propylene and of polyolefin semicrystalline plastics such as PP. They are part of the family of TP olefins (TPOs). TPOs are mechanical blends consisting of a hard plastic and softer rubber. They are considered different from blends that are dynamically thermoplastic vulcanized (TPV) a process in which the elastomer phase is cured during mixing of the polymers.84 94... 

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