Preparation and Properties of PVC-Silica Composites using Different Catalysts Via Sol-Gel Process
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*Chemistry Department, Kansas State University, Manhattan, KS 66506, [email protected] "**ChemistryDepartment, Quaid-i-Azam University, Islamabad, PAKISTAN
Novel micro-composites from Polyvinyl chloride (PVC) and silica were prepared using solgel technique. Different catalysts were used for the in-situ generation of silica network from tetraethylorthosilicate (TEOS) in the PVC matrix. Thin transparent films containing various proportions of silica in PVC were cast by the solvent elution technique. Mechanical properties of these films were studied. The results showed an increase in the value of Young's modulus and strain at rupture by the addition of small amount of silica in PVC. However, the stress at yields point and stress at rupture decreased with the addition of silica contents. Scanning electron microscopy (SEM-EDAX) studies were also performed on these samples. INTRODUCTION High polymers and metal oxides possess diverse characteristics. High polymers are flexible and thermally less stable while metal oxides are rigid and brittle although they have superior thermal stability over natural and synthetic polymers. A suitable combination of the two can generate desirable properties in the hybrid material. There are number of ways in handling of the treatment of inorganic oxide particles with organic polymeric materials in which the size of the particles treated can be of the order of micrometer or more. These are normally prepared by grinding and mixing the ingredients. However to get a homogenous composite finer metal oxide particles are required which must be dispersed uniformly in the organic matrix. In generating fine inorganic particles throughout the organic matrix, sol-gel process has played an important role. This is a mild method to generate inorganic network. In this process, depending on the requirement of the size/network of inorganic particles in the composite, a measured quantity of water and a catalyst is added to start the in-situ hydrolysis/condensation of metal alkoxides [ 1-7]. An important example of a polymer metal-oxide composite material prepared using the 'sol-gel' process is the hard contact-lens material reported by Schmidt in 1984 [8]. Mechanical properties of composite materials can be enhanced if the bonding between the inorganic and organic phase becomes stronger. Ahmad and co-worker have reported extensive work of these attributes [9-19]. Different organic precursors have been used to generate inorganic particles e.g., boehmite, titania, ziconia [20-26] but the attention recognized by tetraethylorthosilicate (TEOS) for the generation of SiO 2 is above all and a great deal of work has been done on it with different polymeric matrices [27-32]. In the present study, sol-gel method is used to develop a silica network in the PVC matrix. Three different experimental systems were designed using hydrochloric acid (HCI), ethylamine (EA) and formic acid (FA) as catalyst for the in-situ polymerization of TEOS. The mechanical and optical measurements performed on these thin films are reported. EXPE
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