Preparation And Mechanical Properties Of Cellulose Reinforced Polymer Composites

Cellulose is one of the most abundant natural polymers on the earth, which has been taken for renewable and biodegradable material. The growing environmental awareness and increasing scarcity of natural resources have provoked a hot research of cellulose composites. The mechanical properties of cellulose reinforced polymer composites is strongly limited by the dispersion of cellulose and the interface bonding strength between cellulose and matrix. In order to improve the mechanical properties of cellulose composites, several investigations were carried out.The bamboo cellulose fiber was applied to reinforce the thermosets epoxy. The epoxy composites filled with different content of bamboo cellulose fiber were prepared and their mechanical properties were characterized. In order to improve the interfacial properties between cellulose and matrix, the bamboo cellulose fiber was separately treated with alkali and coupling agent. Compared with untreated cellulose/epoxy composites, significant increases in the tensile strength and elongation percentage were obtained after 4% NaOH or KH560 modification, while impact toughness decreased slightly. The composites modified with KH560 displayed best mechanical properties among all the three kinds of composites.Bacterial cellulose, microcrystalline cellulose and bamboo cellulose fibers were applied to reinforce poly(L-lactic acid) (PLLA) based bio-composites, the mechanical properties and crystallization of the composites were studied. The incorporation of all three kinds of cellulose increased the stiffness of the composites compared to pure PLLA. However, the tensile strength of the composites reinforced with bamboo cellulosic fiber or bacterial cellulose was lower than PLLA. The reinforcing effect of the microcrystalline cellulose in the composites is most significant. The tensile strength of the microcrystalline cellulose/ PLLA composites was increased to 71 MPa from 61 MPa of PLLA. The Young’s modulus and impact toughness of the microcrystalline cellulose/PLLA composites were increased by 44.4 and 58.8%, respectively.Three kinds of modifications, say alkali soaking or silane coupling cellulose and maleic anhydride grafting PLLA were applied before the preparation of cellulose/PLLA composites. The effects of pre-treatments on the mechanical properties of the cellulose/PLLA composites were comparatively studied. The results demonstrated that the alkali soaking provided the composites with highest values of strength and Young’s modulus. The highest values of impact toughness and elongation were obtained by the silane agent pretreatment. Maleic anhydride grafting on PLA given moderate effects on both the stiffness and the ductility, exhibiting best over-all properties.Using straw cellulose as the raw material, all-cellulose composites were prepared by partially dissolving cellulose in LiCl/DMAc, and the structures, morphologies and mechanical properties were characterized and the effects of dissolution time on their mechanical properties were investigated. The all-cellulose composites prepared with dissolution time of 4 h obtained best mechanical properties, with tensile strength of 269.9 MPa. Further increasing the dissolution time, the mechanical properties of the composites declined. With increasing of the dissolution time, the continuity of the matrix increased but the content of cellulose I crystalline decreased.Using straw cellulose and microcrystalline cellulose as raw materials, all-cellulose composites were prepared by a two-step process. The effects of activation and alkali treatment of the straw cellulose on the structures, morphologies and mechanical properties of the all-cellulose composites were studied. Adding untreated straw cellulose to the dissolved microcrystalline cellulose decreased the mechanical properties of composites. The mechanical properties of the composites were significantly improved after activation treatment, and the tensile strength is 650 MPa, increased nearly six-fold than unmodified composites, and the composites had a Young’s modulus of 11.17 GPa and an elongation of 10.4%. The composites with alkali treatment had tensile strength of 568 MPa, Young’s modulus of 5.48 GPa and elongation at break got 10.2%. Both the activation and alkali treatment improved the dispersion of the straw cellulose and the interfacial interaction between straw cellulose and microcrystalline cellulose.