Preparation of polyethylene blends with various biopolymers and investigation of biodegradability of these blends

Application of polymers had been increased industrially because of the unique properties of these materials such as lightness, low cost and easy production. Ascending production of synthetic thermoplastics directly effected the raito of these polymers as a solid waste in ecosystem. Polyolefins like polyethylene, polypropylene, were petroleum based synthetic thermoplastics which could not be degraded over hundred years in nature because of the stability of their chemical structure. Recent studies had been focussed on enhancing the biodegradation behavior of these polymers to prevent harmfull effects of polyolefins on environment. Biodegradation of polyolefins had been provided by two methods. First method was aimed to degrade these materials by photo or chemical degradation in the presence of additives called pro-oxidants. Secondly, polyolefins were blended with biodegradable polymers for preparing biocomposites. In both of these methods, as the degradation behaviour of synthetic matrice had been improved, matrice became more susceptible to degrade biologically and decayed into low molecular weight compounds more quickly. In this thesis, in order to investigate the effect of synthetic and renewable matrix on biodegradation behaviour, two series of studies were performed. At first, effect of starch source on the biodegradation behaviour of low density polyethylene (LDPE) had been examined by extrusion process. In this step, for observing the effect of starch source on LDPE matrix, potato starch, corn starch and rice starch having different amylose/amylopectin ratios had been used. In second series, poly(lactic acid), which was a renewable polymer having similar properties with LDPE, had been blended with potato starch with same procedure in LDPE/Potato starch blends. With the aim of increasing the interface adhesion between hydrophilic natural polymer starch and hydrophobic LDPE and PLA matrice, LDPE and PLA matrice blended with starch by an co-rotating twin screw extruder having a L/D ratio 24 and 16 mm screw diameter. Thermal, machanical and morphological properties of LDPE/Thermoplastic starch and PLA/Thermoplastic starch were investigated by differential scanning calorimetry (DSC), thermal gravimetric analyse (TGA), stress-strain and scanning electron microscobe (SEM) analysis, respectively. Biodegradation behaviour of LDPE/thermoplastic starch and PLA/ thermoplastic starch blends were investigated by water absorption, bacterial strength and soil burial tests. As a result of studies performed in this thesis, rice starch had determined as the most effective starch type in developing the biodegradation behaviour of LDPE matrice. Especially in blends having 30 % rice starch, 50 % weight loss had been observed at the end of three months soil burial period. However, in the presence of rice starch, mechanical properties of blends were significantly deteriorated compared to LDPE matrice. Besides, biodegradation behaviour of LDPE/corn starch20 blends, prepared by blending 20 % (w/w) corn starch with LDPE matrice, had been developed while maintaing thermal, mechanical and morphological properties of these blends. PLA/thermoplastic starch blends which were prepared by blending aliphatic polyester PLA with biopolymer potato starch had been observed to degrade in three months soil burial period over hydrolysis mechanism. However, descending mechanical and physical properties of PLA/thermoplastic starch blends could be limited the application of these blend films as a packaging material.