Silane‐grafted polyethylene materials are processed in conventional thermoplastic fabrication machines. The shaped articles are then crosslinked in water by the formation of Si‐O‐Si crosslinks. This paper represents studies on the crosslinking progress in different environments at various temperatures. Molecular orientation is shown to become permanent and mostly irrecoverable even at 150°C, in the silane‐grafted solid state crosslinked specimens (the crosslinking temperature in water is well below the polymer melting temperature). These frozen molecular orientations have a significant effect on the tensile properties of the crosslinked materials causing higher yield stresses and lower elongations at break. The thermal and tensile properties of some silane‐grafted crosslinked polyethylene samples and peroxide‐crosslinked materials are compared and analyzed.
This article describes an ultrasonically assisted in situ interfacial dynamic inverse emulsion polymerization process of aniline in the presence of multiwalled carbon nanotubes (MWNT) in chloroform. During polymerization, MWNT are coated with polyaniline (PANI) forming a core-shell structure of nanowires, as evidenced by cryogenic transmission electron microscopy. Thermogravimetric analysis curves and conversion measurements provided important knowledge regarding the unique polymerization method. Scanning electron microscopy images and surface resistivity imply that PANI/ MWNTs are characterized by a structural synergistic effect. The PANI coating of MWNT leads to a remarkable improvement in separation and dispersion of MWNT in chloroform, which otherwise would rapidly coagulate and settle. The presented interfacial dynamic polymerization process is very fast, reaching 82% conversion within 5 min of sonication and produces stable clear dispersions of doped PANI in chloroform. V C 2010 Wiley Periodicals, Inc. J Appl Polym Sci 120: [676][677][678][679][680][681][682] 2011
Ethylene vinyl alcohol (EVOH) copolymer is studied as a host for low concentrations, up to 1 wt%, of organically treated clay. The clay develops a high interaction level with EVOH and thus high torque levels accompany the structuring process leading to the formation of nanocomposites. Extrusion residence time, successive extrusion passes, screw rotational speed, and processing temperature were all found to affect the morphology and the thermal and mechanical properties of the resulting composites. The extrusion compounded composites were subsequently injection molded. A subtle balance of processing parameters is required to achieve improved properties. Long extrusion residence times were found important for good clay dispersion in some cases, whereas in other cases an exfoliated structure was obtained already after the first extrusion pass. Two organically treated clay types processed at the same conditions were examined, and found to result in different morphology and mechanical behavior. Compression molding of extrusion compounded materials, under several extrusion conditions, was studied to illustrate the effect of shear level on the resulting morphology. The delamination level was higher after compression molding compared to that after injection molding. EVOH thermal properties and thermal stability of the related composites were also examined using differential scanning calorimetry and thermal gravimetric analysis. Higher extrusion processing temperature (220 compared to 200°C) was found to change the crystallization process of EVOH in the presence of clay, leading to significant decrease in Tm and Tc compared to that of the neat EVOH. POLYM. COMPOS., 26:343–351, 2005. © 2005 Society of Plastics Engineers
This article describes an in situ bulk polymerization process of styrene in the presence of silica nanoparticles. In this peroxide bulk polymerization process, two polystyrene fractions are formed: A polystyrene (PS) fraction attached to the particle's surface, which cannot be detached by hot xylene extraction, and an unattached PS fraction which dissolves in xylene. Solvent extraction and TGA measurements have confirmed the existence of grafted PS chains to the silica surfaces. FTIR measurements have indicated the existence of SiOC bonds connecting the PS grafts to the silica surface. Polypropylene (PP) was blended with the extracted PS‐g‐silica particles to produce concentrations of 1–3% nanoparticles in the PP composites. A remarkably improved dispersability of the nanoparticles was achieved, thus grafting reduces re‐agglomeration and increases the affinity of the grafted surface to the polymer matrix. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers
Polyamides are semicrystalline polymers that are useful in a wide range of applications in the plastics industry. Some applications require higher flexibility and improved workability of polyamides; thus, a plasticization approach that eases compounding and processing procedures and produces better desired product properties can be utilized. Common plasticizers are high‐boiling liquid esters, but solid plasticizers also have been considered. The present research has focused on plasticization of nylon 66/6 (80/20) copolymer by using selected low molecular weight organic materials. Plasticization of the copolyamide was studied with glycerin mono stearate, benzene sulfonamide, and methyl 4‐hydroxybenzoate as the solid plasticizers and diethylhexyl phthalate as the liquid plasticizer. The materials were prepared and characterized by thermal, mechanical, dynamic, rheological, and morphological properties. The experimental results were supported by simulated polymer and plasticizer interactions using molecular dynamic simulations. Plasticization and antiplasticization phenomena were observed and discussed. The plasticizers were classified by their efficiency in reducing Tg and by modification of the other polyamide properties. Copyright © 2011 John Wiley & Sons, Ltd.
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