Iranian Journal of Polymer Science and Technology
Year:2001 | Volume:14 | Issue:1 (ISSUE NO.51)|Papers Count:6

One of the most important parameters affecting the cost of a moulding process is reducing the moulding cycle of a manufacturing process. Resin transfer moulding (RTM) is a flexible manufacturing process used for fabrication of a wide range of composite products. In this context, mould filling time is an important issue affecting the moulding cycle in RTM. In this paper, different parameters that can affect mould filling time in RTM process have been reported experimentally and theoretically. The effects of resin injection pressure, fiber volume fraction and resin viscosity on mould filling time have been studied for glass fiber polyester composite systems. Moreover, the effects of these parameters have been studied by simulation of the mould filling by using LCMFlot software. Results show that there is a good agreement between experimental and simulation results. They also emphasize that it is cost effective to conduct numerical simulation in order to study the effect of these variables and also injection port and vent locations before manufacturing of a mould.

Denture base is part of a full denture prosthesis on which the plastic teeth are mounted. Apart from good physical and mechanical properties, denture base polymer should have appearance similar to the oral tissues. Nowadays most of denture bases are made of poly (methyl methacrylate) and its copolymers. In this study a reference denture base material was characterized completely using FTIR, GC, GPC, DMTA, DSC, NMR analysis and particle size determination methods. According to the results of characterization, some denture base polymers were synthesized via suspension polymerization of methyl methacrylate. The characteristics of prepared denture base polymer were very similar to the reference samples.

The effect of monomer concentration on the kinetics of the emulsifier-free emulsion polymerization of vinyl acetate and methyl acrylate were studied. The polymerizations were carried out using potassium persulfate (KPS) as the initiator. From the electron micrographs of the resulting latices, monodisperse PVAc and PMA lattices with particle diameters varying between 149-443 nm and 112-497 om, respectively were processed. Uniformity of particle size indicated that nucleation of stable particle occurs early in the polymerization process. The polymerization rate was found to be proportional to the 0.88 and 1.5 power of the initial monomer concentration of vinyl acetate and methyl acrylate, respectively. Higher monomer concentration results in fewer particles and larger final particle diameter. With increasing monomer solubility in water the size of particle decreases and its distribution broadens.

Polyurethane elastomer was synthesized with propylene glycol (PPG) and toluene diisocyanate (TDI) with ferric acetylacetonate (FeAA) catalyst. This polymerization was modeled using the kinetic equations. The number and weight average degrees of polymerization (D`Pw & D`Pn), the number and weight average molecular weights (`Mw &`Mn) and the polydispersity index (PDI) parameters. were found and tested as function of time and conversion and they were finally compared with GPC laboratory and experimental results. The effect of concentration of the catalyst and the addition sequence of starting materials and catalyst on `Mn, `Mw, DPI and `Mz/`Mn are reported and discussed.

Melamine-formaldehyde molding compounds have found different industrial applications. This is due to their good mechanical properties such as hardness, gloss and high modulus and strength. One of the major components of these compounds is a- cellulose fiber and has a major effect on the mechanical properties. Although this fiber is being used in these compounds for a long time, there is not much data available of a- cellulose fiberson the physical and mechanical properties of melamine-formaldehyde molding compounds being investigated. Results show that although the microstructures of these two fibers are quite different from each other, but they do not have any effect on the mechanical properties of the molding. whereas, it has a significant effect on the wettability (processing condition) and glossiness of the moldings. Since this latter property is very important in houswares applications, the darker moldings can not be used in domestic applications.

Since 1978, acrylic fibers have been prepared by slurry polymerization comprizing of about 94% acrylonitrile (AN) and 6% methyl methacrylate (MA) as a comonomer to a make bulky polymer and improve the dyeability of acrylic fibers in a continuous process by redox initiatior (potassium persulfate and ammonium, ferrous sulfate). The slurry polymer obtained after neutralization, washing and drying are converted to polymer powder. The polymer is dissolved in dimethyl formamide (DMF) and converted to acrylic fibers. Since 1998, it has been suggested that MA may be replaced by vinyl acetate (VAc), because VAc has properties like MA and is a monomer produced by Arak Petrochemical CO. Therefore, in this project AN and VAc were polymerized under the same conditions of AN and MA copolymerization process. Many tests have been carried out on the resulted polymer such as IR, viscosity, particle size, whiteness of polymer powder and similar results were obtained as in the for former copolymer. In this work some important factors such as concentration of VAc, time and temperature of polymerization reaction and also speed of agitator have been optimized.