Maleic clay composite, preparations

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

The influence of the various components of a HDPE/clay composite on the properties is shown in Table II. A 30/70 PE/clay concentrate was prepared from 15 parts HDPE Fortiflex A60-70R (Allied Chemical Corp.) and 35 parts of Hydrite 10 by mixing at 150 C in the presence of 3 parts of maleic acid (MA) and 0.75 parts of tBPB. The concentrate was then blended at 150 C with additional HDPE to yield a 50/50 HDPE/clay composite. 

The compatibilization of clay with LDPE and HDFE is accomplished by the in situ polymerization of MAH or its precursor maleic acid, in the presence of a radical catalyst. The latter must be capable of initiating the homopolymerization of MAH, i.e. it must be present in high concentration and/or have a half-life of less than 30 min at the reaction temperature, e.g. t-butyl per-benzoate (tBFB) at 150°C. In a one-step process, the clay and PE are mixed with MAH-tBPB in the desired PE/clay ratio. In the preferred two-step process, a 70/30-90/10 clay/PE concentrate is prepared initially in the presence of MAH-tBPB and then blended with additional PE to the desired clay loading. The compatibil-ized or coupled PE-MAH-clay composites have better physical properties, including higher impact strengths, than unfilled PE or PE-clay mixtures prepared in the absence of MAH-tBPB. 

An alternative route to the compatibilization of a filler such as clay with LDPE and HDPE, through the radical catalyzed polymerization of maleic anhydride (MAH) in the presence of the polymer and clay, has been shown to yield PE-g-MAH-clay composites having better mechanical properties than unfilled PE or PE-clay mixtures prepared in the absence of MAH and a radical catalyst, In the present paper, further improvements in the preparation and properties of HDPE-clay composites are described. These result from the use of high melt index HDPE as "coating PE" in the preparation of the PE/clay masterbatch and low melt index HDPE as "matrix PE" in the final HDPE-clay composite. The crosslinking which accompanies the graft polymerization of MAH onto PE also plays a significant role in the enhancement of the mechanical properties of the composite, ... 

Kurokawa et al. [258-260] developed a novel but somewhat complex procedure for the preparation of PP/clay nanocomposites and studied some factors controlling mechanical properties of PP/clay mineral nanocomposites. This method consisted of the following three steps (1) a small amount of polymerizing polar monomer, diacetone acrylamide, was intercalated between clay mineral [hydrophobic hectorite (HC) and hydrophobic MMT clay] layers, surface of which was ion exchanged with quaternary ammonium cations, and then polymerized to expand the interlayer distance (2) polar maleic acid-grafted PP (m-PP), in addition was intercalated into the interlayer space to make a composite (master batch, MB) (3) the prepared MB was finally mixed with a conventional PP by melt twin-screw extrusion at 180°C and at a mixing rate of 160 rpm to prepare nanocomposite. Authors observed that the properties of the nanocomposite strongly dependent on the stiffness of clay mineral layer. Similar improvement of mechanical properties of the PP/clay/m-PP nanocomposites was observed by other researchers [50,261]. 

PP has great potential for composites and nanocomposites because it can be processed by conventional technologies, such as extrusion and injection molding, to make parts for automotive apphcations. Reinforcement of PP by micro- and nanofillers yields composites with high rigidity and toughness. PP-clay nanocomposites have been prepared at Toyota Central R D via melt intercalation (see Polymer Nanocomposites in Chapter 2) of montmorillonite organo-clays with PP modified with either maleic... 

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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