Surface Modification of Silica with Ultrahighmolecular Weight Polyethylene (UHMWPE)
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Surface Modification of Silica with Ultrahighmolecular Weight Polyethylene (UHMWPE) Subir Debnath, Jiang Ding, Stephanie L. Wunder and George R. Baran1 Department of Chemistry, 13th and Norris Street, Temple University, Philadelphia, PA 19122, U.S.A. 1 College of Engineering, 1947 N. 12th Street, Temple University, Philadelphia, PA 19122, U.S.A. ABSTRACT UHMWPE (Ultrahighmolecular Weight Polyethylene) was attached to silica using a two step process, in which the first step involves silanating the silica surface with a 0.5-1.2 mole % vinyltrimethoxysilane-ethylene copolymer (PE-silane), and in which the UHMWPE (Mw = 3-6 x 106) is solution coated onto the silanated silica in the second step. Glass beads (3.6 µm diameter) were cleaned using distilled water or refluxed with 5% aqueous Na2S2O8, to remove metallic surface contaminants, were used for UHMWPE attachments. SEM and optical microscopy showed individual particles. TGA (thermogravimetric analysis) studies confirmed the attachments as well as their stability after attachment. The integrity of the coatings was examined by SEM following treatment with HF, which left thin “skins” of polymer remaining. Both washing methodologies for the glass beads provided similar UHMWPE coatings. Bend bars (10) prepared using UHMWPE coated beads show no adverse drop in moduli and strength. INTRODUCTION Improvement in mechanical properties of composites using glass-reinforced resins may be limited by the properties of the interface region [1]. The yield strength and ductility of the interphase, in addition to adhesion between the organic matrix and inorganic filler, is believed to be a critical parameter for determining failure in composites. UHMWPE has high yield strength and ductility, but is chemically inert, and therefore difficult to attach to silica particles, as well as to the resin. Decreases in stiffness and hardness are expected for resin matrices modified only with UHMWPE additions [2]. The glass beads coated with UHMWPE system is proposed as a method to achieve improved matrix toughness. In the present study, a two step method to attach UHMWPE onto glass beads was carried out, and the stability of attached species was investigated by SEM and TGA. An alternate two step route for UHMWPE attachment, in which the first step involved attaching octadecyltrichlorosilane (OTS) onto silica, as well as a control coating (one step UHMWPE onto glass attachment) experiment, was also carried out.
EXPERIMENTAL DETAILS Glass beads (3.6 µm average diameter) were obtained from Mo-Sci (Rolla, MO); bis-phenolA bis- (2-hydroxypropyl) methacrylate (BisGMA), tri (ethylene glycol) dimethacrylate (TEGDMA), hydroquinone monomethylether (HMME), tertiary amine dimethylaminoethyl methacrylate (DMAEMA), polymethylmethacrylate (PMMA) and camphorquinone (CQ) were obtained from ESSTECH, stored under refrigeration and used as received. Hydrofluoric acid (48%), UHMWPE powder, p-xylene, phenyl ether, decalin, acetone, methanol,
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octadecyltrichlorosilane (OTS) were procured from Aldrich a
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