Study On Biodegradable Composites From Wheat Straw And Starch

Energy saving and environmental protection are the world’s urgent requirements. Development and utilization of agricultural waste and other renewable and degradable composites materials have become a research focus, which is environmental-friendly materials’ research direction for future development, and also an effective way of using crop waste and reducing environmental pollution. Composites made from straw and starch are light weight and low cost, renewable nature, and acceptable biodegradability, which other composites can not match. Research and applications of straw/starch composites have important significance for sustainable development.In this topic, glycerin as a plasticizer and potato starch as a substrate were prepared for the thermoplastic starch by the method of mixing compression. Then, use wheat straw powder as filler material modified by5%silicone hydride coupling agent KH550, and the thermoplastic starch as a substrate to prepare wheat straw/starch composites by the method of compression molding with different content of glycerin:0%,10%,20%,30%,40%,50%,60%and with different content of wheat straw powder:20%,40%,60%,80%, and with different fiber size of wheat straw:5mm,10mm,15mm, and three different substrates wheat straw fiber-reinforced fully biodegradable composite materials. The effect on these composites’ mechanical properties, hardness, thermal conductivity, and surface water moisture and absorption and microstructure surface with different glycerol content, different wheat straw filler content, different fiber size of wheat straw, different substrates were compared. The main conclusions can be drawn as follows:(1) Wheat straw/starch biodegradable composites were made by compression molding process, with its tensile strength, flexural strength as the optimization objective, the best molding process parameters for Wheat straw/starch biodegradable composites were determined by orthogonal experiment, The best molding temperature was150℃, molding pressure was12MPa, molding time was10min.(2) Wheat straw/starch composites were prepared by60%wheat straw powder and40%thermoplastic starch, with different content of glycerin:0%,10%,20%,30%,40%, 50%,60%, Studies of the properties of wheat straw/starch composites with different glycerin contents have shown that when the glycerin content is less than10%, the composites were yellow and brittle, and degradated obviously; when the glycerin content is more than50%, the wheat straw/starch composites were oily, and showed poor mechanical properties and bad effect of plasticizing. when the glycerin content (representing the percentage of starch quality) was40%, the wheat straw/starch biodegradable composite had better overall properties:Cmmpared with sample without any glycerin, the tensile strength increased by100.72%, the ratio of elongation at break increased by25.50%, the bending strength increased by116.69%, the bending modulus increased by43.51%, the impact strength increased by101.79%, while the thermal conductivity reduced by2.73%.(3) Wheat straw/starch composites were prepared by thermoplastic starch wich containing40%glycerin, respectively with20%,40%,60%,80%wheat straw powder. Studies of the properties of wheat straw/starch composites with different filler contents of wheat straw powder have shown that when the filler content of the wheat straw powder was80%, the wheat straw/starch biodegradable composite had better overall properties: Cmmpared with sample containing20%wheat straw powder, the tensile strength increased by317.82%, the bending strength increased by444.54%, the bending modulus increased by1559.73%, the impact strength increased by9.84%, the hardness increased by181.38%, while the thermal conductivity reduced by28.08%.(4) Wheat straw/starch composites were prepared by thermoplastic starch wich containing40%glycerin, with wheat straw fiber with different fiber size:5mm,10mm,15mm. Wheat straw fiber was attached unevenly to the surface of the prepared material, which is naturally beautiful with beautiful surface appearance. Studies of the properties of wheat straw/starch composites with different fiber size of straw have shown that when the fiber size of the wheat straw was10mm, the wheat straw/starch biodegradable composite had better overall properties:Cmmpared with sample with5mm and15mm wheat straw fiber, the tensile strength increased respectively by267.38%and65.50%, the ratio of elongation at break increased respectively by63.65%and10.46%, the impact strength increased respectively by9.18%and21.82%,while the transient water absorption reduced respectively by0.43%and0.85%.(5) We choose three kind biodegradable material as substrate:thermoplastic starch wich containing40%glycerin, starch adhesive, peach gum powder, respectively to mix and compression molding with wheat straw powder prepared for biodegradable composites, wherein, the content of wheat straw powder all was60%. Test results showed that wheat straw/peach gum powder biodegradable composites had better overall properties:Cmmpared with sample with thermoplastic starch and starch adhesive, the tensile strength increased respectively by27.20%and799.23%, the ratio of elongation at break increased respectively by34.26%and258.51%, the bending strength increased respectively by50.41%and582.47%, the bending modulus increased respectively by109.21%and8023.00%.