Study On Maleic Anhydride Melt-grafted Ethylene Vinyl Acetate Copolymer And Its Entoughness In Modified Nylon 66 Blends

Nylon is one of the most important engineering plastics, which has pretty mechanical strength, high melting point, good heat resistance and excellent resistant performance to wear, oil and other common solvents. But some disadvantages narrow application fields of nylon. Many modification techniques have been widely studied aiming at minimizing the defects of nylon, of which blending modification is the most effective one. In order to prepare toughened nylon alloy, polyolefins have been used to blend with nylon. Primal problem of this technique is poor compatibility between the polar nylon and the nonpolar polyolefins. A simple and effective method could be adopted to solve the problem.Small molecules, usually maleic anhydride (MAH), which can react with amino group or acrylamino group of nylon, were grafted onto the backbones of the polyolefins. During the process of melt extrusion, insitu copolymer was formed, which helped to improve the interfacial binding force as well as minimize the size of the disperse phase while widen its distributing range in the polymer matrix. These led to remarkable improvement in the performance of the composite.Due to its high melting point, strong polarity and poor processability, it's difficult to choose a proper impact modifier or compatibilizer for PA66. EVA was a better choice compared with PE and PP since its vinyl acetate (VA) contents contributed to increasing the polarity of the copolymer, which led to better miscibility between EVA and the strongly polar nylon66.In this study, MAH was melt grafted onto EVA in twin-screw extruder in the presence of peroxide. It was confirmed, by chemical titration and FTIR, that the graft reaction did take place. The polarity of EVA, which was proportional to its VA content, had great influence on the grafting reaction. Graft ratio of EVA-g- MAH was higher than that of PE and PP. Type of peroxide also had effects on grafting reaction. It was found that initiator dicumyl peroxide (DCP) was more efficient in playing the role of initiation than benzoyl peroxide (BPO). The feed rate of initiator should be limited toavoid the possible cross-linking side reaction. Appropriate dosage of DCP should be 0.05~0.1phr(EVA 100phr). In order to obtain higher graft ratio and lower degree of cross-linking, dosage of MAH should also be carefully determined. If 100 phr EVA and 0.1 phr DCP were used, ratio of MAH/DCP should be adjusted to 20/1. Processing condition had great influence on grafting reaction. The optimal recipe condition was found to be 205 with screw rotating rate of 60 rpm.In order to prepare toughened nylon66, EVA-g-MAH was blended with nylon 66 in a twin-screw extruder. Since PA66 and EVA were immiscible, the interfacial morphology of the blend was poor. During the process of melt blending, insitu reaction between PA66 and EVA-g-MAH took place and copolymer (PA66-EVA) was formed at the interface. The resulted copolymer improved the dispersion of the dispersed phase in the polymer matrix and increased the compatibility of the blend. The interfacial binding power was also enhanced, which aided to transfer the stress between the two phases. As a result, the change of interfacial morphology directly improved the material's macroscopical mechanical properties. Compared with PA66 and PA66/EVA, the maximum impact strength of the PA66/EVA-g-MAH (70/30) blend was about eleven times higher, which led us to the conclusion that the EVA-g-MAH content had great influence on morphology and performance of the blend. As the content of EVA-g-MAH increased, interfacial morphology and impact strength continuously improved. The blend composed of PA66/EVA-g-MAH 70/30 (mass ratio), a transition from brittle to ductile occurred and impact strength reached its peak. Further increasing the dosage of EVA-g-MAH would decrease the phase adhesion, which caused the impact strength to fall. It can be concluded that the toughening effect of EVA-g-MAH exceeded that of PE-g-MAH and PP-g-MAH.Both EVA and EVA-g-MAH increased the crystallized temperature (T...