| There are rich bagasse resources in China. However, the utilization of bagasse currently has lots of disadvantage, such as lower utilization, easy to cause secondary pollution, and so on. The addition of bagasse to PLA/starch for preparing absolutely biodegradable composites can solve “White Pollution”, promote comprehensive utilization of agriculture wastes and provide great strides for industrialization of biomass materials, which has important economic function and social meaning.Firstly, we modified starch/bagasse with plasticizers, then prepared PLA/starch/bagasse composites by extrusion and injection, and studied the effects of the type and content of plasticizers and constituent material proportion on the mechanical properties, processing properties, water absorption, thermal properties of the prepared composites, etc. The changes of ingredient and crystallinity for bagasse after alkali treatment and their effects on the mechanical properties of composites were also investigated. At last, we studied natural degradation behavior of composites in soil systematically.The results showed that glycerinum, formamide and ethanediol have obvious plasticization for starch/bagasse system, and formamide has the best plasticizing effect. When the content of plasticizer was 30 percent, the composites prepared possessed better mechanical property and processability. The tensile strength of PLA/starch/bagasse(60/20/20) modified with formamide was about 43.9MPa, the one modified with glycerinum was about 36.4MPa, while all of them have a low elongation at break.It was found that increasing the content of starch/bagasse in composites increased the melt viscosity and water absorbing and weakened the mechanical properties. For instance, the balanced water absorption, tensile strength and elongation at break of PLA/starch/bagass(20/40/40) were 38%, 37 MPa and 3.0%, respectively, which were increased by 489.1%, decreased by 28.57% and 50%, respectively, compared with those of PLA/starch/bagasse(80/10/10).The mechanical performance of PLA/starch composites were enhanced by adding bagasse, for example, the tensile strength and bending strength of PLA/St/BF(60/20/20) were increased by 17.42% and 12.32%, respectively, compared with PLA/St(60/40).After the treatment of bagasse with a certain concentration of alkali, pectin and lignin in bagasse were effectively removed, which increased the crystallinity of the bagasse. But high alkali concentration and excessively long processing time destroyed the crystal structure, reduced the strength of bagasse fibre. The tensile strength and bending strength of composite with bagasse treated by 1% NaOH solution in one hour were increased by 17.49% and 20.67% compared with those of the composite with bagasse untreated.The biodegradability of PLA/strach/bagasse composites was improved by increasing the content of starch/bagasse. The degradation percentage of PLA/St/BF(20/40/40) in soil after two month was about 57.35%. In addition, degradation test in soil also proved that starch exhibited better biodegradability than bagasse. SEM analysis showed a large number of holes were left in the matrix of composites and layer stripping was also found on the surface of composites after biodegradation. Besides, with the extension of degradation time, the retention of mechanical properties for the composites was falling roughly. However, in a certain biodegradation time, the crystallinity and thermal stability of the composite were increasing and getting better, which indicated that biodegradation began from amorphous regions, and then extended to crystalline regions. |
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