Polyethylene/clay grafting

Polymer-Filler Composites thru In Situ Graft Copolymerization Polyethylene-Clay Composites... 

NG. Gaylord, H. Ender, L. Davis, A. Takahashi, Polymer-flUer composites thru in situ graft copolymerization polyethylene-clay composites , in Modification of Polymers , CE.Carraher, M. Tsuda, Eds, ACS Symp Ser 121, Washinbton D C, 1980... 

MASTERBATCHED POLYETHYLENE-CLAY COMPOSITES PREPARED THROUGH IN SITU GRAFT COPOLYMERIZATION OF MALEIC ANHYDRIDE... 

H. Lu, Y. Hu, M. Li, Z. Chen, and W. Fan, Structure characteristics and thermal properties of silane-grafted-polyethylene/clay nanocomposite prepared by reactive extrusion. Compos. Sci. Technol. 66(15), 3035-3039 (December, 2006). 

Here, again, we start from compressible SCFT formalism described in Section 2.2 and consider a model system in which bulk polymer consists of "free" matrix chains (Ny= 300) and "active" one-sticker chains (Na= 100). Flory-Huggins interaction parameters between various species are summarized in Table 1. This corresponds to the scenario in which surfactants, matrix chains, and functionalized chains are all hydrocarbon molecules (e.g., surfactant is a C12 linear chain, matrix is a 100,000 Da molecular weight polyethylene, and functionalized chain is a shorter polyethylene molecule with one grafted maleic group). The nonzero interaction parameter between voids and hydrocarbon monomers reflects the nonzero surface tension of polyethylene. The interaction parameter between the clay surface and the hydrocarbon monomers, Xac= 10 (a = G, F, A), reflects a very strong incompatibility between the nonpolar polymers and... 

Gaylord evaluated various clays in polyethylene using peroxide/maleic anhydride treatments [18]. He found very variable results, largely influenced by the nature of the clay surface, and concluded that some filler surfaces could actually inhibit the free radical grafting processes. 

A butadiene-modified clay was prepared to produce PS, HIPS, ABS terpolymer, PMMA, polypropylene, and polyethylene nanocomposites by melt- or solution blending [73, 74]. The butadiene surfactant was obtained from the reaction of vinylbenzyl chloride-grafted polybutadiene with a tertiary amine (Table 3.6). All the composites were immiscible microcomposites. 

Gaylord and coworkers recently presented evidence to show that the compatibilization of the low- and high-density polyethylene and kaolin or bentonite clays in the presence of MA involves both grafting and anhydride-hydroxyl reactions. The peroxide-catalyzed reactions were studied in a Brabender Plasticorder at 130-165°C. Presumably the in situ grafting and condensation reactions occurred as follows ... 

With up to 40% clay, the compatibilized polymer/clay composites exhibit lower water vapor permeability than typical unfilled polyethylene. The compatibilized composites containing the clay particles were crosslinked, with the anhydride-grafted polyethylene bonded to the clay particles and uncrosslinked polyethylene. The composites exhibited improved flexural modulus, break strength, and notched Izod impact properties. 

Poly(ethylene-co-MA), 288 grafted to polyethylene, 677 Poly[(ethylene)-g-MA], 459-462 applications, 461, 462 bentonite blends, 461 clay composites, 462 kaolin blends, 461 polypropylene blends, 461 properties, 461... 

Nevertheless, in other cases, a plastidzing effect of the nanopartides has been reported, which leads to a decrease in both the values of Tg and the storage modulus. Artzi et al. [127] reported in EVOH-montmorillonite nanocomposites a decrease of Tg values from 5 wt% of day. The same authors predict two opposing effects on the transition the confined chain mobility owing to interaction buildup, and an increased mobility due to reduction in the crystallinity degree as a consequence of polymer-clay interaction [128]. The addition of a compatibilizer, either maleic anhydride-grafted ethylene-vinyl acetate (EVA-g-MA) or maleic anhydride-grafted linear low-density polyethylene (LLDPE-g-MA), led to a decrease in the Tg values [129]. This 5wt% day content maximum is also described by McAdam et cd. in PA6-day nanocomposites [130]. 

Fang ZP, Xu YZ, Tong LF. Effect of clay on the morphology of binary blends of polyamide 6 with high density polyethylene and HDPE-graft-acrylic acid. Polym Eng Sci 2007 47(5) 551-559. 

The influence of the inclusion size, shape, and surface treatment on the gas permeability of polyethylene in its micro- and nanocomposites has been investigated in various papers.Kato et al. report the N2 permeability of nanocomposites based on polyethylene (PE) melt compounded with maleic anhydride grafted polyethylene (MA-g-PE) and octadecylamine (C18-MMT) modified montmorillonite. The gas permeability coefficient for all the prepared samples are reported in Fig. 11.8. Interestingly, polyethylene, maleic anhydride grafted polyethylene, a 70/30 blend of PE/MA-g-PE and a blend of PE/MA-g-PE/MMT have almost the same permeability coefficient. Only the composites obtained by mixing the polymeric matrices with the modified montmorillonite show for PE/MA-g-PE/C18-MMT (PECHl) a decrement of 30% in permeability and for MA-g-PE/C18-MMT (PECH3) a decrement of 35%. The differences in the gas barrier property were attributed to the different dispersion of the clay silicate layers in the matrix. 

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