Preparation And Properties Of Modified Cassava Starch/natural Rubber Composites

Modified cassava starch was prepared by microwave method, with cassava starch as raw materials, different chain length of the esterifying agents (such as acetic anhydride, octenyl succinic anhydride, sodium dodecyl benzene sulfonate) and cross-linking agent as modifying agent, under the corresponding catalyst conditions to get hydrophobic esterified and cross-linked cassava starch. The synthesis condition on the substitution or cross-linking degree was investigated, such as the amount of the esterifying agent or cross-linking agent, reaction time, reaction temperature and the dosage of the catalyst or pH value. The esterified and cross-linked cassava starch structure and thermal stability characterized by fourier transform infrared spectrophotometer (FTIR), polarizing microscope, X-ray diffraction (XRD), differential scanning calorimeter (DSC) and thermal gravimetric (TG) analysis.Optimal preparation conditions of the starch acetate as follow:reaction temperature of80℃, acetic anhydride dosage48.45g, reaction time3h, the amount of concentrated sulfuric acid0.1ml. Optimal preparation conditions of the octenyl succinate starch as follow:reaction temperature45℃, octenyl succinic anhydride dosage3.2g, reaction time4.5h, the pH value of9. Dodecyl benzene sulfonate starch preparation conditions:reaction temperature80℃, mole ratio of esterifying agent and glucose unit0.06:1, reaction time4h, the pH value of14. The cross-linked starch optimal preparation conditions:reaction temperature50℃, the amount of cross-linking agent for2.5%of the starch, reaction time2.5h, the pH value11.Under the polarization microscope, the crystal structure of starch was able to show a black partial cross light. But the crystalline region was damaged in whole or in part after modified, the black partial cross light was significantly reduced in starch granules. Crystalline structure was destroyed also can be proved by X-ray diffraction, starch acetate, octenyl succinate starch and sodium dodecyl benzene sulfonate starch’s diffraction peak from the four sharp diffraction peaks into one or several gentle diffraction peaks. But the diffraction peak of cross-linked starch’s change was not obvious. This may be the cross-linking occurred on the surface of the starch granules but not touched to internal which in the crystalline structure of starch. The thermal stability of the modified cassava starch show that each changed differently, acetate starch have a greater increase in the decomposition temperature (368.10℃), but octenyl succinate starch (292.17℃) and dodecyl benzene sulfonic acid esters starch(307.18℃) is decreased, While the cross-linked Starch little change.Different degree of esterification and cross-linking of the modified cassava starch was blended with the natural rubber latex in the emulsion state, and then subside to prepare the modified cassava starch/natural rubber composites. After vulcanized, the tensile and tear properties of different types esterification modified cassava starch/NR composite material were investigated by electronic tensile testing machine. The best performance of the composite materials were selected to test the structure and properties by TG, DMA, RPA, SEM.The results of mechanical behavior showed that:with the degree of substitution of various modified cassava starch increased, the performance of the composite materials were increased. But to get the cross-linked starch/NR composite material, must to choose the appropriate degree of cross-linking of cross-linked starch to fill NR. Because excessively cross-linked starch reinforcing effect was the worse. The results of the TG showed that esterified or cross-linked cassava starch/NR composites increased in thermal stability. DMA and RPA results showed that the starch acetate/NR, dodecyl benzene sulfonic acid ester starch/NR, and cross-linked starch/NR composite material’s tan8was lower than NR in the0℃and60℃, a slight decrease in wet skid resistance, but rolling resistance decreased significantly. Cassava starch/NR and octenyl succinate starch/NR composite’s tan δ was higher than NR, wet skid resistance and rolling resistance increased. The scanning electron micrographs of the tensile fracture shows that modified cassava starch improved the degree of dispersion of cassava starch particles in NR and the particle size tends to decrease, the roughness surface of the modified starch enhanced starch and rubber matrix interface role to improve the structure and properties of composite materials.