Impact modifiers polyolefin elastomers

Obviously, there exists severe interplastics competition, e.g. PP vs. ABS, clarified PP vs. PS, PA, PVC, HDPE and PS (Table 10.7). A wide range of cross-linked and thermoplastic elastomer applications, from footware to automotive parts and toothbrushes, are adopting new metallocene-catalysed polyolefin elastomers (POEs). These low-density copolymers of ethylene and octene were first accepted as impact modifiers for TPOs, but now displace EPDM, (foamed) EVA, flexible PVC, and olefinic thermoplastic vulcanisates (TPVs). Interpolymer competition may also result from... 

To lower PA s sensitivity to crack propagation under impact conditions, the resins are blended with 10-25% of an elastomer or a polyolefin. The impact-modified PA s exhibit good processability. They are mostly formed by injection molding. Special compositions have been formulated for extrasion of tubings. 

Acrylic copolymers (i.e., core-shell impact modifiers with a shell of PMMA and a core of butyl acrylate elastomer) have been developed mainly for impact modification of PVC for outdoor applications. Butadiene-styrene copolymers are used exclusively for PVC, PC or styrene-acrylonitrile (SAN). Thermoplastic elastomers in the form of styrenic copolymers, e.g., SBS, are used preferably for styrenics and PA. Polyolefins, like EVA, are used for impact modification of technical polymers. 

Uses of Ethylene-Propylene Rubbers. EPDM and EPR vulcanizates are used in extruded profiles, cable insulation and jacketing, and roofing membranes. There are many automotive uses radiator hose, door and trunk seals, insulation, jacketing, and others. These elastomers are also used in applications such as window and architectural profiles, dock fenders, and washing-machine hoses. In short, their applications are extensive and diverse. Ethylene-propylene rubbers may be the most versatile of general-purpose rubbers. In addition, EP rubbers are added to polyolefin plastics as impact modifiers and as components of certain thermoplastic elastomer compositions (e.g., thermoplastic vulcanizates, which are discussed later in this chapter). 

Polycarbonate has been blended with commercial polyamides (PA-66 and PA-6), in order to improve its poor solvent resistance while maintaining a reasonable level of heat resistance and toughness. However, simple blends of polycarbonate and polyamides were highly incompatible and hence not useful. Several different additives such as phenoxy resins, polyester amide elastomers in combination with maleated polyolefins, polyetheramide block copolymers, and polyamide-polyacrylate block copolymers have been used as potential compatibilizers and impact modifiers. 

Thermoplastic olefin (TPO) compositions typically consist of an immiscible blend of an isotactic polypropylene mixed with a polyolefin elastomer that acts as an impact modifier. It is possible to toughen these compositions further by using ethylene-propylene, ethylene-octene or ethylene-hexene impact modifiers. 

These trends are illustrated by DuPont Dow Elastomers range of Engage polyolefin elastomers, intended as impact modifiers for polypropylene in automotive bumpers and fascias. They combine stiffness with ductility, and are claimed to give very good low temperature impact strength. Engage 8842 is said to have a particularly wide range of applications. 

Impact-resistant properties, especially at low temperatures, low-temperature toughness, melt-processing properties, and dimensional stability of thermoplastic polyurethane elastomers are improved by the addition of a carbonyl-modified polyolefin [54,55]. These improvements are particularly useful for reinforced polyurethanes. Small amounts of polyolefin homopolymer or copolymer with TPU blends are useful for molding plastic articles by injection molding, extrusion, calendering, or similar process for molding thermoplastic articles [56]. 

Only two classes of polypropylene (PP) blends have achieved commercial success blends wiA polyolefins and with polyamides (PA). With PP/polyolefin blends, the goal is either to improve the impact resistance of the base resin (impact-modified PPs) or to produce thermoplastic elastomers (d)mamically vulcanized blends). PA/PP blends aim at bridging the property gap between the two pol5oners. Therefore, sigitificant information on processing is available only for these two families of blends. 

Solid-state NMR has been widely employed for problems related to flame retardants, impact modifiers, plasticisers (and plasticiser motion), fillers (including polymer-filler interactions), co-polymers, grafting, elastomers and filled vulcan-isates, molecular symmetry and heterogeneity, etc. Use of NMR is recommended particularly for insoluble components (such as high-MW species) at high levels (typically >1%). Obviously, direct NMR of polymers suffers from matrix interference of the polymer carbon backbone yielding complex spectra. Therefore, studies on polyolefins and PVC are relatively favoured, whereas polyacrylates are unfavoured. (SPE and CP/MAS) NMR and in situ NMR were used in a study of PU/melamine [676],... 

PE/Elastomer Blends Polyolefins have been modified by the incorporation of elastomers to improve low temperature impact strength and elongation. Table 1.39 provides examples of these systems. 

Processes of ethene/a-olefin copolymerization are of great practical importance. Copolymerization of ethene with small amounts of highest a-olefins (1-butene, 1 -hexene, 1 -octene) allows one to produce linear low density polyethylene (LLDPE), which is one of the most widely used large-scale polyolefin products. Polypropylene, modified with small amounts of ethene, exhibits higher impact strength compared to isotactic homopolypropylene. Copolymerization of propene with large amounts of ethene and terpolymerization of ethene/propene/diene result in amorphous elastomer materials (rubbers) [103]. 

Uses Polymer additive for PVC and rubber, polyolefin and ABS processing, engineering plastics, PU rigid foams and elastomers, polyamides and polyesters, polyurethanes and epoxies modifier (increases flexibility, impact resist., toughness, hydrolytic stability) for industrial coatings (automotive, coil, textile, leather, wood lacquers)... 

As much as 30% of all polyolefin products involve blends (Robeson 2007). It has been found, for example, that blending metallocene-catalyzed linear low-density polyethylenes (mLDPEs) with HDPE improves the Izod impact strength and some tensile properties of HDPE. Adding mLLDPE to LDPE increases the ductility of LDPE (Cran and Bigger 2009). In general, PE blends can be divided into three categories (1) PE lots blended to meet standard specifications for density and melt flow, (2) PE modified with <15 wt% of other polymer(s), and (3) PE bends with other thermoplastics or thermoplastic elastomers. 

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