Structure and Properties of Polymer Blends

Abstract

The mechanical properties, morphology, light and thermal stability of pure polymers (eg LDPE, PP etc) and blends of PE/PVC, PE/PP and PE/PS with and without additives have been studied using a variety of physical and chemical techniques. The change in mechanical properties occurring during the ultra-violet light accelerated weathering of these polymers and polyblends was followed by a viscoelastometric technique (Rheovibron), stress-strain and impact measurements in the solid phase at room temperature (20 +- 1°C). The results showed that tensile strength, elongation at break, impact strength and tan§ (20°C) decreased with increasing PVC, PP and PS content. It was concluded that hydroperoxides are the most important initiators in normally processed polymers during the early stages of photo-oxidation. On exposure to uv light, the blends (PE/PVC, PE/PP and PE/PS) showed lower stability than pure LDPE. A study of the mechanical properties during uv irradiation indicated that the tensile strength of the blends decreased initially but at a later stage increased with irradiation time. The elongation at break and impact strength decreased continuously with exposure time. In the thermal degradation of PE/PVC blends, PVC behaved as a stabiliser and this effect was significant at high concentrations of PVC (eg 20%). Blends of PE/PVC, PE/PP and PE/PS which are found in domestic waste exhibit poor mechanical properties due to incompatibility. Therefore, reprocessing of such unseparated mixtures results in products of little technological value. The inclusion of some commercial block and graft copolymers which behave as solid phase dispersants (SPD's) increase the toughness of the blends. Optical and electron microscopy were used to study the morphology of the blends in order to assist in the understanding of structure/property relationships of the blends.