Studies On Full-biodegradable Films Modified By Blowing

"Green Polymers", have been paid much attention, finding the substitute of normal plastics has already been the important field of the world because world energy sources crisis and serious white pollution destroy the sustainable environment for human being. Starch, non-toxic and biodegradable, is the abundant and renewable resource in nature, and thus its utilization has become the focus of research in the field of truly biodegradable material science. But its application is restricted by poor mechanical properties and water-resistance. It has been proved in our lab: Water-resistance of starch has been improved by esterification and microwave. Many properties of starch film, such as strength, flexibility, water-resistance, can be improved greatly when starch is crossed-linked, plasticized, strengthened at the same time. With degradable Polyvinyl Alcohol (PVA) as the basic material in this experimentation, full-biodegradable film were prepared by appending modified starch and blowing-model. Therefore, starch plastics provide reliable path, which solve worldly pollution of plastics, and have a boundless prospective and bright future.In this thesis, it has been reviewed that the research situation at home and abroad and developing trend of biodegradable plastics. To the existing problems in biodegradable plastics, an ideal to develop starch-based full-biodegradable films with good mechanical properties and water-resistance has been provided. With corn starch (ST) and Polyvinyl Alcohol (PVA) as the main material, full-biodegradable films were prepared by casting method, via chemical modification and solution blending. The creative achievement of this work is as follow: starch's hydrophile has been changed completely and improved the intensity and toughness by chosen plasticizer of PVA in lab, PVA melt and medical modification following polymerization with polymers. Through blown method full-biodegradable films were produced by designing the polymer.The main contents and conclusions are as follow:1. PVA melt temperature declined far away from its disassemble temperature was observed on the DSC atlas by Chosen non-water intensifier of PVA appending. That made it very easy to prepare films. Starch and PVA will blend by 1:1 because the cost and technics reason.2. The intensifier of ST and PVA is co-intensifier. The orthogonal experiment showed that: the best composing is formamide 8%, glycol 8%, mixture of glycerol and water 4%. The weight of total intensifier is 20% of drought weight of ST and PVA.3. Plasticizing mechanism of poly-hydroxys molecular plasticizers were different from those of less-hydroxys molecular. Less-hydroxys molecular plasticizers presented much effect on film's mechanical properties, decreasing the tensile strength, but increasing the breaking elongation. However, poly-hydroxys molecular plasticizers showed only a little effect. Mechanical properties of blend films were enhanced by adding mixture of these two plasticizers.4. Water-resistance of the blend films was improved by adding 3.5% cross-linker, which was the foundation of industry.5. The optimal operating conditions were also discussed. The screw speed was 18r/min,the thermoplastic temperature was 120"C.6. The structural characteristics of the films were investigated by infrared spectroscopy (IR), X-ray diffraction and DSC. The results demonstrated that: Starch and PVA were cross-linked then dense and homogeneous network was generated. PVA melt temperature declined by intensifier.7. By means of degradable trials of soil and microbe and field characteristic test, the biodegradability and field character of starch films were determined. The results showed that starch films had good biodegradability. So, the degradation time of the films could be regulated by controlling amounts of them.The results of the foundational research mentions will provide theoretical base and practical references for using starch as polymers material, for making starch-based full-biodegradable films by blowing method, eliminating "white pollution" and raising crop production.