(280c) Studies on Mechanical Properties and Enzymatic Degradation of Partially Biodegradable Laminated Ldpe - Starch Blend Film

Plastic is one of the largest groups of polymeric materials of petrochemical-based organic origin formed into useful shapes by application of heat and pressure. It has very important position as engineering and packaging materials. But the use of plastics is not environment friendly as these are not biodegradable and can take years to decompose. With the increasing volume of the industrial and municipal wastes, and depleting petroleum resources, there has been an urgent need for the development of modified plastics or substitutes, to enhance the biodegradability and to lessen the dependency on the petroleum resources. One of the viable alternatives to accelerate the degradation and to guarantee at least partial biodegradation is the addition of natural polymers. Modified plastics derived with biodegradable agricultural feed stocks, like LDPE-starch blend films offers an elegant approach to meet the requirements of responsible and ecologically sound utilization of resources and ultimate disposability. Since the starch is biodegradable, it would be metabolized by a wide array of microorganisms resulting in the creation of pores. This causes deterioration of the matrix, which accelerate the disintegration of the plastic materials. It may also enhance the polymer chain oxidations, due to oxygen based reactions making the polymer susceptible to further biological degradation process. However, the blending of the hydrophilic starch and hydrophobic LDPE are not compatible in nature and have poor surface adhesion leading to phase separation during the processing of the blend film. The previous studies reported in the literature have shown that the mechanical properties of the films deteriorate rapidly with the increase in starch concentrations. Improvement of the quality of the blend films have been tried through various modifications of the starches. Along with the production of modified plastics, speeding up of the biodegradation is also an important parameter. The biodegradability of blend film decreases with the addition of the non-degradable synthetic polymers and starch modifications. Biodegradation occurs by hydrolysis of the polymers by enzymes and / or the bio-assimilation of the smaller fragments by the microrganisms. The enzymes are produced by the microorganisms present in soil / compost. For the purpose of the enzymatic degradations in waste treatment applications the use of crude enzyme are preferred. In the present work, with the objectives to enhance the mechanical properties at higher starch content i.e. improved biodegradation properties, laminated films of the LDPE-starch blend film laminated on both sides of the LDPE films have been prepared. The mechanical properties and enzymatic biodegradations of the films have been studied. In the enzyme biodegradation of the films, thermostable á-amylase has been produced using the Bacillus licheniformis and the extracellurly produced enzyme in the fermentation broth was directly applied for the degradation studies. Films have been characterised before and after the degradations. LDPE film, LDPE - native starch and LDPE-plasticized (glycerol) starch blend films were prepared by twin screw extruder and blow film plant. The concentration of the starch in the blend films were varied upto 15 %. Laminated films were prepared with blend films on the both sides of the pure LDPE film by drawing the films through and simultaneously hot pressing between the rolls. Mechanical properties of all the films were measured to see the effect of starch on tensile strength, % elongation, melt flow index and burst strength with respect to LDPE films. Results showed that addition of starch decreased the tensile strength and % elongation of the blend films and laminated films. It was observed that the tensile strengths were higher for laminated films than the individual blend films at the corresponding level of starch concentrations. The rate of decrease in values of tensile strengths with the increase in the starch concentrations were less as compared to the ordinary blend films. In case of % elongation the reverse was observed. The % elongation was lower for the laminated film and decreased rapidly with starch concentrations. Addition of starch increased the burst strength of all the films and the rate of increase was higher for the laminated films. The melt flow index decreased with the addition of starch in the blend film but for the laminated film melt flow index increased. In overall, laminated films showed better tensile strength property compared to the simple blend films. All the results have been explained in light of the compatibility of the blend, effect of the plasticizer glycerol, characteristics of the single and laminated films. In the enzymatic degradations of the films by the enzyme alpha-amylase produced from Bacillus licheniformis, results showed that starches in the blend films were degraded by the enzyme but rates varied with accessibility of starch to the enzyme. Characteristics of the films before and after degradation were evaluated by mechanical properties and scanning electron microscopy. Reduction in tensile strength and % elongation depending upon starch content of films were observed after degradations. The change in the surface morphologies of the films were observed by scanning electron micrographs of films.