| Thermoplastic starch(TPS) is a source of biodegradable plastics material with advantages such as availability, low cost and machinability which is believed to replace conventional plastics in the areas of packaging, food, agriculture films and others. The widely use of TPS will relieve the pressures in resource and environment. It will also have a major significance in sustainable human development. But the poor water resistance and the low mechanical properties of starch limit its widespread application.In this paper, we blended native corn starch with STMP cross-linked starch as the matrix material first. Prepare the composite matrix in the effect of the compound plasticizers which including glycerol, sorbitol, and urea through single-crew extrusion. Investigate the influence of the mass fraction of the cross-linked starch and the processing temperature on the properties of the composite matrix. Afterwards, ramie noil fiber was used as the composite reinforcement. In order to enhance the interface properties between the noil fiber and starch matrix, plasma and aminopropyltriethoxysilane(APS) were selected to modify the surface of noil fiber. Discuss the influence of the different methods of the fiber modification on the properties of the composites. What can be obtained through the performance testing and characterization was listed as follow:1. After mixing cross-linked starch, in the role of the plasticizing effect of the compound plasticizers and the shearing force of single screw, tensile strength of the mixed-starch matrix increased 44.76%, moisture absorption decreased 38.64%. This proves that cross-linked starch has significantly enhanced effect on matrix. When the content of cross-linked starch increased over 15wt%, the increase in the tensile properties of matrix material trended to flat. Considering, the 15wt% content of cross-linked starch is most reasonable.2. There were new-OH appeared on the ramie fibers treated by cold plasma. Pectin and other impurities have been completely removed. Besides, moderate fiber surface etching effect appeared at a handling power of 200W. C-Si and C-O-Si bonds appeared on the surface of the fibers after coupling by the APS, and there were a kind of complete and smooth layer by condensation of APS at the concentration of 5%. The combined treatment has the effect of both treatment methods, and the coupling layer on the fiber surface formed compact and uniform. Although, the tensile tests of single fibers showed that there are no dramatic effects on the fibers by the three treatment methods. Besides, the results of pull-out experiment suggested that adhesion properties are improved by the surface modifying treatments. The most obviously increase appeared on the fibers, which are combined treated, that the IFFS increase to 8.25MPa.3. The TPS composites reinforced by cross-linked starch and noil fibers which are treated by both plasma and APS, had better performance on mechanical properties and water resistance. The tensile strength and flexural strength had been improved to 28.95MPa and 49.71MPa respectively. Moreover water absorption rate fell 7.55 percent points in 7 days and dimensional change rate was only 0.89% in 120 days, which suggesting that application performance of composites have been improved by treated fibers.Through the study of thermoplastic starch composites reinforced by surface modified noil fibers, we found that the cross-linked starch can be used as reinforcement of TPS, with which we can gain better composite matrix; the ramie noil fibers treated by plasma and APS have better adhesion properties which can gain composite better mechanical properties and water resistance. |
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