尿素和甲酰胺塑化热塑性淀粉

THERMOPLASTIC STARCH PLASTICIZED BY THE MIXTURE OF UREA AND FORMAMIDE

用甲酰胺和尿素作为塑化剂制备了热塑性淀粉 (TPS) .扫描电镜显示甲酰胺和尿素混合物可以使淀粉塑化 ,形成均一的连续相 ;根据FT IR谱图可以确定 ,与甘油相比 ,甲酰胺可以使热塑性淀粉体系在保存时更稳定 ,各基团的化学环境变化更小 ,这是由于甲酰胺可以和淀粉羟基形成更稳定的氢键 .X ray衍射说明甲酰胺和尿素 (重量比为 10 % 2 0 % )作为混合塑化剂可以有效抑制淀粉的回生 ,同时防止尿素结晶析出 .在RH=33%的湿度环境保存 1周 ,这种热塑性淀粉有良好的拉伸强度、伸长率和断裂能 ,分别达到 4 83MPa ,10 4 6 %和 2 17N·m .水含量对热塑性淀粉的力学性能的影响也被研究 .另外 。

The main disadvantages of the conventional thermoplastic starch (TPS) are the retrogradation,poor water resistance and unsatisfactory mechanical properties particularly under wet or dry environments. In this paper, formamide and urea were used as a mixed plasticizer to prepare urea/formamide-plasticized TPS (UFPTPS) with both the good mechanical properties and the good retrogradation resistance. FTIR analysis indicated that the micro-environments of the chemical groups in formamide-plasticized TPS(FPTPS) changed less than in glycerolplasticized TPS(GPTPS) during a period of 70 days. This was related to the fomation of more stable hydrogen bonds between formamide and starch. By Scanning Electron Microscope (SEM) the native cornstarch granules were proved to transfer to a continuous phase with the destruction of all crystallinity. The effect of water contents on the mechanical properties of UFPTPS was also studied, and UFPTPS had good ductility at water contents of 9 % similar to 34 %. After being stored for one week at RH = 33 %, the tensile strength, elongation and energy at break of this TPS reached 4.83 MPa, 104.6 % and 2.17 N (.) m, respectively. The influence of formamide and urea on the retrogradation of TPS was studied using X-ray diffractometry. It was found that the mixture of formamide and urea could effectively restrain the retrogradation and prevent urea from crystallization. On the other hand, both the thermal stability and water resistance of UFPTPS was better than those of TPS plasticized by each single plasticizer (including glycerol). The TPS properties mentioned in this paper were ameliorated by the mixture of formamide and urea(10 % / 20 % weight based on starch), mainly for it could form more strong and stable hydrogen bonds with starch hydroxy groups than glycerol could. As a novel plasticizer, the mixture of formamide and urea would be potential in extending the application scopes of TPS.