| "Green Polymers", have been paid much attention, because serious pollution caused by plastics makes a threat to the sustainable environment for human being. Starch, as the abundant and renewable resources in nature, are non-toxic and biodegradable, and thus its utilization have 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: many properties of starch film, such as strength, flexibility, water-resistance, can be improved greatly when starch is modified by nano-silica and is cross-linked, plasticized, strengthened at the same time. 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 as main material, full-biodegradable films were prepared by casting method, via stepwise modification and solution blending. The creative achievement of this work is as follow: the nano-SiO2 was dispersed in aqueous solution and then was used to modify starch films.The main contents and conclusions are as follows:1. Polyvinyl Alcohol ( PVA) was the best intensifier of starch films. The optimal mass proportion of PVA to starch was 2:3. And the optimum mass ratio of solid to liquid was 1:9.2. Glutaraldehyde was the best cross-linker of starch and PVA. The orthogonal experiment showed that: the optimum cross-linking condition was glutaraldehyde 3.5% (of starch and PVA), pH10, reaction temperature 85C and reaction time 30 minutes.3. Mechanical properties and water-resistance of the blend films were improved by adding 35% melamine of cross-linker and 1.5% borax of starch and PVA.4. Plasticizing mechanism of large molecular plasticizers were different from those of small. Large plasticizers presented much effect on film's mechanical properties, decreasing the tensile strength, but increasing the breaking elongation. While, smallplasticizers showed only a little effect. Mechanical properties of blend films were enhanced by adding large and small plasticizers simultaneously. The orthogonal test affirmed that the optimum content of three plasticizers was ethylene glycol 3%, glycerol 3%, polypropylene glycol 6% (of starch and PVA).5. kind and amount of foam-killing agent, release agent and stabilizing agent were studied, and were sorbitantristeareate 1.0%, paraffin liquid 1.5%, ammonium chloride 1.5%, respectively.6. The optimal operating conditions were also discussed. The mixing speed was 110 r/min and the casting films were dried at 110C for 30 minutes.7. Nano-silica is easily agminate, so the dispersion is very important. The dispersion liquor, with nano-silica 2% (of starch and PVA), PA dispersant 1.5% (of nano-silica) and pHIO, was obtained by mechanical grinding dispersion for lh. Then the blend solution of ST-PVA with the dispersion liquor put in, was mixed for 15 min at high mixing speed. The mechanical properties, light transmittance, water-resistance and humidity adaptability of starch films were improved remarkably by adding a little amount of nano-silica. The tensile strength of the film was 34.82 MPa, and the breaking elongation rate was 331%, which reach for the national standard GB4456-84.8. The structural characteristics of the films were investigated by infrared spectroscopy(IR), X-ray diffraction and scanning electron micrography(SEM). The results demonstrated that: Starch and PVA were cross-linked by glutaraldehyde and were farther articulated by nano-silica, then dense and homogeneous network was generated.9. By means of degradable trials of soil and microbe and field characteristic test, the biodegradability and field ch...
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