Preparation, Structure And Properties Of Plant Fiber/ABS Composites

Wood-plastic composite (WPC) is a new type of environmental material, which ismanufactured from blends of thermoplastics and plant fibers with a special functionalmodified agent and other additives using plastic molding process. The plant fibers includewood flour, bamboo fiber, rice husk and straw. WPC synthesizes the advantages of plant fiberand polymers. It is a low carbon, green, renewable materials with a great developable future.Itcan substitute plenty of wood and efficiently mitigate the status of our country’s poor forestresources and demand. It will solve the problems in the recycling of waste plastics and woodresources. In recent years, research and development of WPC have been very popular inliterature, most of which were carried out using PVC, PE, and PP as matrix, but ABS asmatrix is very rare. The preparation of the WPC with ABS matrix has important practicalsignificance for improving its properties and broadening its application area.The characteristics of five kinds of plant fibers were explored in this thesis firstly. Theywere bamboo fiber (BF), eucalypt fiber, cypress fiber, pine fiber and camphor fiber. Thecontact angle, surface free energy and its components of plant fibers were determined by theWashburn equation with the thin-layer wicking technique. Then the bamboo fiber wasselected for further investigation because of its lower surface free energy. BF/ABS compositeswere prepared by melt compounding. Then the structure and performance of the compositeswere systematically investigated. The modification methods of bamboo fiber that strengthenthe bonding between bamboo fiber and ABS matrix were also studied. Furthermore, ainterfacial modifier was synthesized from ABS. The influence of the interfacial modifier onthe performance of BF/ABS composites was investigated. The interfacial modificationmechanisms were also discussed.The five kinds of plant fibers all contain a large number of hydroxyl groups, but theirthermal stability is not pretty well. Based on Washburn equation and the thin-layer wickingtechnique, the surface free energies of the plant fibers were calculated. Results demonstratethat eucalypt fiber has the highest surface free energy and non polar part; while bamboo fiberhas the lowest. As combined with the same plastics, the interfacial adhesion between eucalyptfiber and matrix is better than that of the others, so the mechanical properties of eucalyptfiber/ABS composites outperforms the other four.The poor compatibility between bamboo fiber and ABS matrix limited the performanceof BF/ABS composites. The mechanical properties of BF/ABS composites, including tensilestrength, flexural strength and impact strength, decreased with the increasing bamboo fiber loading, but its flexural modulus increased. The Vicat temperature of BF/ABS compositesincreased with the increasing bamboo fiber loading, suggesting that the incorporation ofbamboo fiber could extend the operating temperature range of composites. Besides, theaddition of bamboo fiber had negative influence on the thermal stability， processingperformance and water absorptivity of BF/ABS composites. As the bamboo particle sizeswere between80and180meshes, the mechanical properties of the samples, besides impactstrength, exhibited a creasing tendency. However, the mechanical properties showed adecreasing tendency when the particle size was40meshes.Oxazoline modified ABS(ABSm) improved the interactions between bamboo fiber andABS matrix and promoted better mechanical properties of the composites. The tensilestrength and flexural strength of BF/ABS composites were52MPa and91.4MPa whenABSm2was added, about17.6%and35.2%up. The conversion of the nitrile groups intooxazoline of ABSm2is about30%, the optimum dosage was7phr. Among three commerciallyavailable interface modifiers(SMA, PS-g-MAH, EVA-g-MAH), SMA has the best interfacemodified effect, but none of them is better than ABSm.Alkali treated of bamboo fiber at room temperature and high temperature cooking werestudied. The effects of time and concentration of NaOH on the chemical composition,crystallizing structure, thermal characteristic and surface morphology of bamboo fiber werediscussed. And the optimum processing of alkali treatments at room temperature,concentration of NaOH4%,1h, were obtained. The alkali treatment of the bamboo fiberspromoted the partial removal of the hemicelluloses, extractives, and lignin which present onthe surface of the fiber, and improved its thermal stability. The crystalline structuretransformation of cellulose I into cellulose II was observed by X-ray diffraction for bamboofiber, when NaOH concentration exceeded10%. This would decrease the crystallinity andthermal stability of the bamboo fiber, while the fiber bundles partially break down and appearshrinkage.The bamboo fibers after acetylation, alkali treated and high temperature alkali cookingwas used to prepare BF/ABS composite. Experiment result showed that different treatmentincreased the dynamic property of the composite by different degree.The two kinds of alkalitreatment had better effect on the BF/ABS composites, while the effect of acetylationtreatment was insignificant. Further studies showed that two kinds of alkali treatment usedtogether with SMA had synergistic effect, while they used together with ABSm andacetylation treatment used together with SMA had no synergistic effect.