ENVIRONMENTALLY DEGRADABLE STARCH FILLED LOW-DENSITY POLYETHYLENE

Legislative threats restricting the use of disposable nondegradable plastic because of its environmental problems have generated interest in the use of degradable plastics. An extensive search for potential biodegradable fillers for thermoplastics led to the conclusion that, even today, starch is a cost effective additive with the best commercial promise. Demand for biodegradable plastics is increasing, so starch filled thermoplastics are commercially very attractive, but unmodified starch, which is the most widely available form, is not best suited for this application. The aim of this study was to characterize the initial degradation mechanism of starch filled LDPE. Swelling of the starch in the starch-LDPE strips was observed when native starch was used. So, LDPE was compounded with well dried, modified, granular starch (CATO-32) according to the Griffin technique. The starch and additive system was mixed with LDPE on a two roll mill at 125-130 degrees C. A single screw Brabender extruder was used to obtain starch filled LDPE strips. Accelerated degradation of the starch filled LDPE strips was carried out using various laboratory tests (starch hydrolysis by a-amylase at 95 degrees C, thermal oxidation in an air oven at 80 degrees C and exposure to 254 nm UV radiation). Changes in the various properties of the strips during the course of degradation were evaluated using the following: Universal Testing Machine (UTM) for mechanical properties, Extrusion Plastometer for melt flow index, Scanning Electron Microscope (SEM) for surface morphology and infrared (IR) spectrometry. SEM micrographs after starch hydrolysis show that alpha-amylase acts on the surface starch to cause cracks, holes, pitting and erosion which increase the surface area. The starch filled LDPE becomes brittle when it undergoes thermal oxidation. The pro-oxidant system (oleate and Fe) enhances the rate of thermal oxidation of the samples by 15-20%. An increase in the carbonyl and vinyl concentrations shows that chain scission reactions in the polymer chain were initiated by UV radiation. Thus various environmental factors have synergistic effects on the degradation mechanism of starch-LDPE