Expansion Characteristics of Expandable Styrene/Methyl Methacrylate Copolymer Beads: The Effects of Monomers Composition and Cell Modifying Aid

Part casts of metal such as iron, using expandable polystyrene (EPS) foams, may have an unacceptable amount of surface defects, such as lustrous carbon. The use of foams made of styrenic/acrylic copolymers can improve the quality of foam molds and metal parts made using such molds. Lost foam copolymer was synthesized by suspension copolymerization of styrene and methyl methacrylate in the presence of blowing agents (pentane isomers). When the surrounding temperature was high enough to vaporize the blowing agent and soften the polymer shell, the microspheres were expanded. The effects of monomers compositions and cell structure modifying aid (Polyethylene Wax) concentration on the average molecular weight and molecular weight distribution of the produced particles, pentane content and expansion properties (density, residual pentane of pre-expanded particles and cell structure) of the pre-expanded particles were investigated. The findings suggested that, monomer composition had a significance effect on copolymerization kinetic and the copolymermolecular weight. The rate of copolymerization and copolymer molecular weight increaseddramatically with increasing MMA concentration in monomers feed. So the expansion properties of these beads (especially pentane content and density) were different completely. In addition, the most significant result which must be taken into consideration is that cell structure modifying aid (PW) had an important effect on pre-expanded particles morphology such as cell structure, cell density, and cell size and cell size distribution. The cells size became smaller and cells size distribution became narrower with increasing polyethylene wax concentration

کلیدواژه ها:

Suspension Polymerization ، Expandable Particles ، Expansion properties ، Monomer Composition ، Cell Structure