|M.Sc Student||Hammer Shir|
|Subject||Development and Characterization of Modified Rigid PVC|
|Department||Department of Chemical Engineering||Supervisors||Professor Emeritus Moshe Narkis|
|Professor Yachin Cohen|
|Full Thesis text|
The present study aims on the investigation of semi-interpenetrating polymer networks (semi-IPNs) based on rigid polyvinyl chloride (PVC). The semi-IPNs are achieved by an in-situ surfactant-free polymerization/crosslinking of monomers (25%wt) within seed porous PVC particles. The modifying polymers are polystyrene (PS) or poly(styrene-co-methyl methacrylate) (P(St-co-MMA)) crosslinked with divinyl benzene (DVB), and polybutyl acrylate (PBA) or polyethylhexyl acrylate (PEHA) crosslinked with ethylene glycol dimethacrylate (EGDMA). The formation of semi-IPNs is generally known to enable control of phase separation, promote compatibility between immiscible polymers pairs, and thus provide a method for generation of desired properties, e.g., fracture toughness and impact resistance. The in-situ polymerization method, thermal, physical and mechanical properties of these blends, along with the study of their morphology have been carried out.
Differences between the modifying polymers result in significant difference in structure and properties of the multiphase PVC-based polymeric materials. The mechanical properties of the blends at room temperature depend primarily on the glass transition temperatures of the neat components. PVC/PS blends and PVC/P(St-co-MMA) blends are stiff and glassy in character. Tensile properties of the PVC/P(St-co-MMA) blend reveal a substantial increase in elongation at break and a necking rupture behavior. Fine morphology, thin threads like, observed by SEM could attribute to the improved fracture resistance. On the other hand, PVC/PS blends exhibit a brittle failure, i.e., failing without yielding.
The rigidity of PVC/PEHA blends and PVC/PBA blends is significantly reduced owing to the incorporation of the polyacrylates having a rubbery character. Yield stresses and elastic moduli of PVC/PEHA blends are decreased. Notched Izod impact tests of these blends reveal a prominent increase in impact strengths, particularly when the blend is crosslinked (2%wt). The rubber is well dispersed in the matrix and under stress forms a three-dimensional network structure with the PVC. The energy is dissipated down the branches of the network structure in a crack propagation and shear banding mechanism. A shift from brittle failure to ductility has been observed in PVC through the introduction of PEHA. SEM studies have been carried out to support these observations.