Manufacture and Properties of Thermoplastic Starch Biocomposites

Bio-composites have attracted considerable attention from the industry as potential substitutes for petroleum-derived composites. Starch is a potential candidate because it is biodegradable and is readily available sustainable polymer from agriculture resources. However, it is not easy to process like petroleum-derived polymers because of the lack of defined melting point and is sensitive to high humidity with poor mechanical properties. This study evaluated the processability of starch, lignin and pulp fibers using a BrabenderRTM Torque Rheometer. Type of starch exerted great influence on processability. Gelation characteristics of the four composite mixtures correlated with starch type. Amylose containing composite mixtures (#1 and #2) was associated with higher gelation characteristics. The lowest gelation torques and energies were exhibited by composites #3 and #4 (amylopectin starch). This can be attributed to the crystallinity melting temperature of the two starch composites. Amylopectin is the more crystalline structure of the two starches, so therefore would have the greater influence on such things as hardness, modulus, tensile and even stiffness, respectfully. Higher mechanical properties were associated with starch bio-composites containing amylopectin. Composites #1 and #4 exhibited the highest water absorption and Composites #2 and #3 exhibited the lowest water absorption; the type of lignin used as filler made a greater contribution of the hydrophobicity of the starch composites. Moisture content of all starch composites was similar between all starch-lignin composites (16% - 17%). Fourier Transform Infrared spectra analysis of composites showed the absence of any discernible chemical bonds. Bio-composites containing amylopectin exhibited the highest glass transition. Thermal degradation patterns for all starch composites were different. Mass loss below 100°C was associated with loss of water. Loss of glycerol commenced around 200°C and its thermal degradation was completed around 300°C. Thermal degradation of pulp fiber occurred in two stages: 230°C and 230-390°C where the largest mass loss occurred. Scanning electron microscope showed that pulp fibers were not well dispersed and aligned within the composites. Biodegradation of the samples were examined from a 6-hr period to a 48-hr period. Biodegradation of the four composite mixtures correlated with starch type. Amylose containing composite mixtures (#1 and #2) was associated with similar digestion rates; Composite #1 biodegrades at 12.13%/hr. and Composite #2 biodegrades at 12.95%/hr. The best digestion rate was exhibited by amylopectin containing mixture Composite #3 biodegrades at 14.00%/hr. and Composite #4 biodegrades at 7.26%/hr., making it the composite that takes the longest to biodegrade. Therefore, meaning that the interaction between the composites fillers has an effect on the digestion rates of the starch-lignin composites