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Preparation and Properties of Modified Starch/Nature Rubber Composites

Author: AiJunWei
Tutor: LiuFang
School: South China University of Technology
Course: Materials Science
Keywords: starch nature rubber Si69 epoxidized natural rubber in-situ modification coating modification
CLC: TQ330.1
Type: Master's thesis
Year: 2011
Downloads: 79
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Abstract


In this thesis, starch and natural rubber were used to prepare environmental friendly starch (St)/natural rubber (NR) composites materials with excellent performance by a simple modification method. This research is of great theoretical significance and the material has good application prospects. Starch is one kind of natural material with large particle size and crystal structre, and there is a great amount of hydroxyl group on its surface. The starch could be used to reinforce rubber after modified by small reactive molecule and macromolecular modifier.First, Si69 in-situ interface modification and coating modification St/NR composite materials were prepared by directly blending. By incorporating Si69, the scorch time extended, the optimum cure time was delayed. It also decreased the Payne effect of compound and improved the dispersion and processing properties of starch in the rubber. The peak value of tanĪ“and the loss factor of vulcanized rubber decreased with increasing the amount of Si69. The adhesion between starch and rubber matrix increased because of the improvement of starch surface properties by Si69 modifying, which led increasing of mechanical properties of St/NR composites especially after post-curing. Compared with in-situ modification method, coating modification method made starch dispersing much more sophisticatedly, leading stronger interface reaction. Therefore, adding starch, which was treated by Si69 through coating modification method, into rubber could get a better reinforcing effect. A little amount of coating Si69 could make an effective modification, and also efficiently improved the compression of natural rubber composites heat fatigue performance. The mechanism research of coating Si69 modification of St/NR indicated that the crosslink density of St/NR vulcanized rubber which modified by the air film cladding Si69 increased significantly, the post-cured crosslink density continued to rise significantly. In the normal blending and curing temperature, adding Si69 could damage the crystal structure of starch. Siloxane of Si69 reacted with hydroxyl of starch, and participated in vulcanization of NR to increase the comprehensive properties of St/NR composite materials.ENR is an effective modifier for the St/NR composites. By incorporating ENR, the mechanical properties of the composites are significantly enhanced, the rolling resistance is effectively lowered and the wet-skid resistance is obviously improved. When the mass ratio of ENR-25 is 5phr, relative St/NR had the best comprehensive properties. During the mixing and vulcanization, epoxy groups in ENR might react with hydroxyls in starch to form covalently bond and produce large amount of hydrogen bond interaction, which could strength the interface bond between starch and NR. Meanwhile, covulcanization of NR and ENR could enhance the bond between starch and NR further. Therefore, dispersion of starch in NR and the comprehensive properties of St/NR composites could be improved by adding ENR in it.Based on the above studies, the starch which was coated by Si69 partly replacing carbon black was promoted in NR/CB system. In comparison with unmodified St/NR/CB composites, the results revealed that the mechanical properties of modified St/NR/CB composite were improved remarkably to approach that of NR/CB composite. The rebound resilience of vulcanizates increased and the rolling resistance decreased. The hot air aging resistance and the dynamic compression fatigue property were improved, which were even higher than that of NR/CB composites. However the density of St/NR/CB is less than that of NR/CB composite. This research has great theoretical and practical significance in manufacturing green tires materials.

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