HDPE, additives Fillers

As rubber has a much better coefficient of friction compared with polyoleflns, it might be helpful to add rubber powder or small particles into, say, HDPE-based composite matrix. Coarse grades of calcium carbonate could serve the same purpose (this would be again a certain trade-off in properties of the flnal composite material). Additional benefits can be obtained if the same additive/ filler enhances both friction and impact resistance (a rubber might be a good candidate in this case). 

Heat-resistant [218] soft foams were prepared from the blends of hdPE with E-P random copolymers. The azodicarbanamide acts as a thermal antioxidant and the crosslinking of the blend was increased by electron beam radiations and foamed at 225 °C with 2320% expansion. A blend of 35 wt.% PE-PP (8 92), 15 wt.% E-P block copolymers, and 50 wt.% EPDM showed accelerated weathering resitance [219] 1000 h probably due to crosslinking between constituents of the block copolymer, polyblend and EPDM. The effect of filler and thermodynamic compatibility on kaolin-filled PE-PP blend was studied by Lipatov and coworkers [220]. The thermodynamic interaction parameter (%) decreased and thermodynamic stability increased by filler addition, the degree of crystallinity decreased with increasing thermodynamic compatibility of the components due to sharp decrease in the phase separation rate during cooling. 

U.S. Pat. No. 6,632,863 [115] (by Crane Plastics Company, Timber-Tech) discloses a wood-plastic composition manufactured as feedstock pellets comprising 55-90% cellulosic material such as wood flour and wood fiber, 10-40% of polyolefin such as HDPE, LDPE, and polypropylene, and 0-35% total of additive(s), such as lubricants and inorganic fillers, such as talc and mica. 

Mineral fillers generally do not absorb water (or absorb very little of it), so, naturally, they decrease the water absorption. For example, a composite deck board consisting of 65% rice hulls and 35% HDPE (minis minor additives) absorbed... 

TABLE 17.6 Effect of filler and additives in HDPE (MEI 0.48 g/10 min) on the consistency index (j/o) [zero viscosity] and power-law index (n) determined in the parallel plate (dynamic shear) rheometer... 

The process can combine conventional glass fiber roving, aramid, or carbon fiber tows with TPs, most commonly polyethylene terephthalate (PET) and nylon (polyamide/PA). Other plastics used include polyphenylene sulphide (PPS), styrene-maleic anhydride (SMA), high-density polyethylene (HDPE), and polypropylene (PP). The TPs can take the form of pellets, chips, chunks, or shreds, and as the process uses hot-melt injection, no solvents or two-part systems are involved. Additives such as colorants and fillers can be used as required. 

GiU, T.S. and Xanthos, M. (1996) Effects of fillers on permeability and mechanical properties of HDPE blown films. J. Vinyl Addit. Technol., 2 (3), 248. 

HDPE immiscibly blends with hutyl ruhher [14] to provide improved chemical resistance, compression set and high-temperatnre mechanical properties versus nnvnlcanised hlends. LDPE and HDPE blend immiscibly with ethylene copolymers to improve environmental stress crack resistance, tonghness, filler acceptance, film tear resistance, improved flexibility and so on. In polyolefin, polybntene-1 forms miscible blends with PP [15,16]. The addition of PP to polybutene-1 increases the crystallisation rate of polyhntene-1 and would have utility as a nucleation additive. 

Machalkova [643] has described analysis of polymer composites and rubber blends with emphasis on separation of low-MW additives by instrumental methods. Examples refer to analysis of inorganic filler- or synthetic fibre-reinforced plastics and laminated plastic Aims using PyGC and IR. The versatility of PyGC has further been exemplified by Jones [633] as a thermovolatilisation technique for direct determination of occluded volatiles and low-MW additives in lube oil, novolac resins and HDPE, of plasticisers and vinylchloride in PVC, and of solvent residues in paints and bitumens, etc. Dicumylperoxide (DCP) in LDPE was identified through detection of three main by-products of reaction, acetophenone, a-methylstyrene and 2-phenylpropan-2-ol [633]. 

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