ENVIRONMENTALLY DEGRADABLE STARCH FILLED LOW-DENSITY POLYETHYLENE

Legislative threats restricting the use of disposable nondegradable pl astic because of its environmental problems have generated interest in the use of degradable plastics. An extensive search for potential bio degradable fillers for thermoplastics led to the conclusion that, even today, starch is a cost effective additive with the best commercial p romise. Demand for biodegradable plastics is increasing, so starch fil led thermoplastics are commercially very attractive, but unmodified st arch, which is the most widely available form, is not best suited for this application. The aim of this study was to characterize the initia l 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 syste m was mixed with LDPE on a two roll mill at 125-130 degrees C. A singl e screw Brabender extruder was used to obtain starch filled LDPE strip s. Accelerated degradation of the starch filled LDPE strips was carrie d out using various laboratory tests (starch hydrolysis by a-amylase a t 95 degrees C, thermal oxidation in an air oven at 80 degrees C and e xposure to 254 nm UV radiation). Changes in the various properties of the strips during the course of degradation were evaluated using the f ollowing: Universal Testing Machine (UTM) for mechanical properties, E xtrusion Plastometer for melt flow index, Scanning Electron Microscope (SEM) for surface morphology and infrared (IR) spectrometry. SEM micr ographs after starch hydrolysis show that alpha-amylase acts on the su rface starch to cause cracks, holes, pitting and erosion which increas e the surface area. The starch filled LDPE becomes brittle when it und ergoes thermal oxidation. The pro-oxidant system (oleate and Fe) enhan ces the rate of thermal oxidation of the samples by 15-20%. An increas e in the carbonyl and vinyl concentrations shows that chain scission r eactions in the polymer chain were initiated by UV radiation. Thus var ious environmental factors have synergistic effects on the degradation mechanism of starch-LDPE.