Iranian Journal of Polymer Science and Technology
Year:2003 | Volume:16 | Issue:1 (ISSUE NO. 63)|Papers Count:6

In this work, some well defined diblock and triblock copolymers were prepared by living free radical polymerization using PEMA-TEMPO and TEMPO-PEG-TEMPO macroinitiators where PEMA is polyethylmethacrylate, PEG is polyethyleneglycol and TEMPO is 2,2,6,6- tetramethyl piperidinyl-1-oxy. Triblock copolymers were crosslinked by 1,3,5-tris (bromomethyl) benzene (C9H9Br3)center. Diblock copolymers content polystyrene was brominated using N-Bromosuccinirnide (NBS) and crosslinked using PEG anion. Also the effect of degree of bromination and thus branching of diblock copolymers on the properties of network copolymers were investigated.

The effects of acetic acid and polyethylene glycol (PEG) on morphology and characteristics of polyvinyl alcohol (PVA) membrane were investigated. The membranes were prepared using phase inversion technique. For membrane manufacturing, a dope containing PVA, water and either acetic acid or PEG was prepared. The dope was moulded by casting and floated in a precipitation bath containing Na2So4/ NaOH/ H2O. The results show that addition of acetic acid or PEG to PVA, would change the mechanism of membrane preparation leading to the changes in membrane's morphology and characteristics. Increasing the acetic acid concentration results in reduction in skin layer thickness and increase of its sub layer thickness, porosity and pore size. A reduction in skin layer thickness and porosity results in higher permeability and better membrane performance. This may be explained due to the higher concentration of H3O+ in polymer dope resulting from an increase in acetic acid concentration. Higher concentrations of positive ions facilitate the non-solvent entrance from precipitation bath to polymer dope resulting higher rate for acid-base equilibrium. PEG is a polar and hydrophilic polymer, which performs as an electrolyte in polymer solution. Higher concentration of PEG results in higher rate of non-solvent entrance from precipitation bath to polymer dope. In comparison with acetic acid, PEG shows lower effect on membrane performance (permeability), reduction of skin layer thickness and increase in sublayer thickness.

Scrap rubbers can be reclaimed, processed and crosslinked. But, because of the wide use of synthetic rubbers in making many products and the absence of scrap rubbers, reclaim rubbers do not play an important role in rubber industry. They are however used in specific applications. Therefore, it should be mentioned that the main motivation behind this study has been to make a survey on its economic feasibility, application fields and finally, to tackle the problem of environmental pollution. In this paper, reclaimed rubber substitution for NR, SBR and BR with carbon black in cars' light weight tire manufacturing has been studied, and the optimum and favoured properties for static use items have been reached.

The use of continuous filament with special characteristics in the formation processes of the composites, including filament-winding, pultrusion is increasing rapidly. In this study, fiber-glass and saturated polyester yarn (with different structures) are applied as the central core and the cover, respectively. The former, due to its high modul us and tensile strength and the latter, due to its high extensibility are used in a matrix of unsaturated polyester resin in the form of three layered, unidirectional fabric. The present article studies the influence of covering percentage and polyester cover structure on physical and mechanical properties of the compounds. Physical and mechanical tests have been carried out in both vertical and horizontal directions to the fiber orientation. Results showed that the tensile and impact energy absorption as well as the other mechanical characteristics of the compound are being reinforced with glass yarn, which is in turn covered with spun polyester, show a much better performance than the others. Furthermore, a twist of 400 TPM covering yarn can improve the mechanical properties of the compounds significantly. Twist, structure and the type of covering yarn could have an influence on the surface fracture of the composites. Thereby, it would become possible to alter the surface fracture from a destructive state into a controlled condition.

One of the biocompatible polymers is polydimethyl siloxane. This polymer has various applications due to its high performance. In this research work, the o-rings used in blood dialyzer filter have been produced using a blend of silicone rubber of 40 and 70 shore A hardness, at 35 and 65 phr with different parts of dicumyl peroxide at 0.4,0.6, 0.8,1.0 and 1.2 phr, as curing agent. The effect of curing agent, hence the amount of crosslink density on thermal behaviour, physical and mechanical properties, such as DSC, DMTA, hardness, compression set, tensile strength and elongation at break, were measured before and after postcuring. The results showed the optimum properties at 0.8 phr curing agent with an improvement in all properties after postcuring of the vulcanizates. The adhesion of platelet on o-ring were also investigated and the quantity of adhesive platelet were measured using dehydrogenated lactate. The rate of platelet adhesion on o-ring was increased when curing agent was used above 0.8 phr.

Epoxy resins are the most commercially important polymers, which have found a broad range of applications because of their excellent adhesion, toughness, insulation and good physical and chemical properties. In this project, liquid epoxy resin with narrow molecular weight distribution was synthesized by polymerization reaction of epichlorohydrin and bisphenol A in molar ratio of 12 to 1 in presence of sodium hydroxide. This product was characterized by FTIR and 1H NMR spectroscopy and its thermal degradation was studied by using DSC and TGA thermograms. Epoxy equivalent and chlorine content were determined by chemical analysis. Some effective parameters such as the method employed and the adding amount of sodium hydroxide in the reaction system were changed in order to gain qualified epoxy resin. Epoxy equivalent of this resin was 0.53 per 100 g of resin and its chlorine content was 0.25 percent. Epoxy equivalent weight of this resin was 169 g per one equivalent of resin. Viscosity of the product was studied at different temperatures and the constituting liquid epoxy resin was determined by TLC.