|M.Sc Student||Goldis Leonid|
|Subject||Characterization of Structure-Property Relationships of|
|Department||Department of Chemical Engineering||Supervisor||Professor Emeritus Moshe Narkis|
|Full Thesis text|
Polymer blending has been recognized as the most versatile and economic method to produce new materials able to satisfy various demands. The annual growth rate of the polymer blending industry is ~10% and it is estimated that 60-80% of all polymers are sold as polymer blends.
Polymer melt mixing, using twin screw extruders, is one of several techniques by which polymer blends can be prepared. Three major types of polymer blends can be distinguished: miscible, partially miscible, and immiscible blends.
The objectives of the present work were to study, characterize and analyze thermal, mechanical and morphological behavior of semi-crystalline Polyamide 6 blended with amorphous copolyamide (51% Polyamide 6 and 49% Polyamide 6.9) using a twin screw extruder. For this, differential scanning calorimetry (DSC), scanning electron microscopy (SEM), accelerated aging tests and tensile mechanical tests were carried out.
A “cold crystallization“ phenomenon of copolyamide 6-6.9 was investigated and found to be related to process conditions. In Polyamide 6-6.9 rich blends, partial miscibility of Polyamide 6 in Polyamide 6-6.9 matrix was observed. Negative interaction parameters, calculated from the Flory-Huggins theory of mixing, can be attributed to chemical interaction between the blend components, which lead to miscibility. Still, in Polyamide 6 rich blends, the interaction parameters indicated preferred miscibility. This was supported both by crystallization dynamics, thermal and mechanical analyses and by SEM observations. Using Avrami crystallization theory a higher crystallization rates in Polyamide 6 rich blends were obtained. Polyamide 6-6.9 rich blends are characterized both by a slight melting point depression and two distinguished glass transition temperatures. Mechanical analysis pointed to possible phase inversion due to discontinuity in the stress and elongation at break and in the specific volume where the composition of the blend contains equal weight fractions of the two components. The effect of UV irradiation on morphology of cryogenically fractured and external surfaces of injection-molded specimens was studied using SEM. After 310 hr of UV irradiation, the morphologies of the neat polymers and their blends have changed presumably due to erosion of the amorphous copolyamide 6-6.9.