Impact modifiers plastomers, metallocene

POEs or metallocene plastomers in pellet form are easier to handle and process than standard rubbers. They have displaced about 70% of the traditional EPDM modifiers used in TPOs, though EPDM-modified materials still have advantages for low-temperature impact applications. Still, metallocene/POE technology is probably the most important impact-enhancing technology developed over the last 20 years. 

Impact-modifying additives designed to inaease the drop impaa resistance of rigid PP containers, for example, may also be chosen for how they affea darity. PO bottles require low-temperature drop-impact properties in particular, which can be enhanced with additions of metallocene plastomer modifiers. However, these modifiers can create haze if they have shown large enough differences in refractive index with the base resin. Specifically, in tests of HDPE bottles, plastomers with lower densities ( 0.900) were found to affea darity very little (20%-24% haze), whereas a 0.910-density plastomer produced "noticeable" haze (37%) [10-22]. 

One of the most important applications for impact-modified PP is automotive TPO, commonly used for automotive bumper fascia, external body cladding, and interior trim. Compounds are typically three-component blends of ICP with talc and an impact modifier such as a metallocene plastomer or EPR. The impact modifier provides low temperature toughness but softens the matrix. The talc particles restore the stiffness of the compound but detract from impact strength. The objective of TPO compounding is to select the combination of the three components that provides an optimum balance of stiffness and impact strength. 

The experiment described below was carried out to illustrate the effects of metallocene plastomer and talc on the properties of a TPO composition. Experiments were designed around a typical automotive bumper composition of 60 wt% ICP, 30 wt% impact modifier, and 10 wt% talc (29). 

The response contour surfaces for several key properties were generated using the mixture polynomial to highlight the performance differences of plastomer versus conventional EPR. The metallocene plastomer and EPR provided very similar impact enhancement in both notched Izod and instrumented Impact tests (Figs. 7.25 and 7.26). In all four cases, impact strength depended primarily on the impact modifier and less on the talc content. Flexural moduli were similar for plastomer and EPR compounds (Fig. 7.27). The plastomer formulations showed... 

Metallocene plastomers are already widely used as PP impact modifiers and are positioned to become the leading modifier type in the near future, displacing EPR and EPDM. Plastomers provide equivalent impact enhancement (including at low temperatures) with additional performance advantages including easier dispersion, superior impact in high flow PP resins, and low haze in clarified RCP resins. 

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