| Composite with natural fiber as reinforcing material, and biodegradable polymer for the matrix, possess advantages as full biodegradability and renewable in its raw material, could imply the practical meaning in replacing petroleum based polymer materials to reduce the non-degradable plastic wastes, improve the environment and achieve sustainable development. Milling, extruding and other regular fibers and matrix melting mixing methods, are all limited to deal with the chopped fiber, mean while the preparing process make serious length and strength reduction of natural fiber, degradation of matrix and uncontrollable of fiber orientation, as a result, the composite is hard to meet higher stander application. In order to over come the shortcomings mentioned above, technology improvement must be made to optimize the preparing method of composite.We design an extruding-rolling mix machine to prepare premixied material of different fibers fraction. By adapting the gap and horizontal angle between the upper and the under synchronous, the conveyor belt can both pressing and rolling the premixture of fiber and the extruding matrix while transmit them. By preparing the extruding-rolling mixing SF/PLA composite, and compare with the mixing mill ones, reaserch on the influence of new technology and relevant parameters on composite’s performance.We compare with the extrusion-rolling mixing sisal/PLA composite and mixing mill ones. The rolling mixed composite of 40wt% fibers fraction has significant improvement in its mechanical strength and modulus, it’s tensile strength and flexural strength, notch impact strength reached 200.44 MPa,216.77 MPa and 54.470KJ/㎡ respectively, was 3.06 times, 2.02 times, 23.52 times as pure PLA, and was 5.48 times, 1.98 times,6.63 times as mixing composite, respectively. And the tensile modulus, flexural modulus was 6516.259 MPa, 13139.49 MPa respectively; compared with pure PLA was enhanced by 3.29 times and 2.72 times respectively, and was 2.13 times, 2.08 times as mixing composite. The tensile elongation at break was decreased, but still remanded 65.49% those of pure PLA.Compare with the composite made by premixed SF/PLA samples of different twist. In SF fraction of 40wt%, twist of premixed material has no significant difference between the tensile properties. But the bending strength and modulus of composite made of no twist samples are 20.2% and 30.6% higher than those of composite made by samples of 14r/m twist. Meanwhile, the impact strength of high twist composite is 35% enhanced than the no twist composite.We prepare the extrusion-rolling mixing composite of 40wt%, 50wt%, 60wt%, 70wt% fibers fraction respectively,the result proved that the max fiber fraction of SF/PLA is 60wt%, below which the composite could possess both favorable surface quality and mechanical strength. When the fibers fraction is 50wt%, the flexural strength, flexural modulus, notch impact strength of which are respectively increased 20.5%, 39.0%, 34.4% than composite of 40wt% fibers fraction. In addition, the tensile elongation at break retains 78.0% of that of pure PLA. The composites of 40wt%, 50wt%, 60wt% fibers fraction have no remarkable difference in tensile properties.Owing to the extruding-rolling mix processing, the length of fiber in premixing with matrix and preparing process was no longer limited, the processing not only shorten the thermal history of both plant fiber and labile matrix, but also avoid length and mechanical strength reduction to a great extent, and by which the composite was made possessed high current consistent in fiber orientation, uniform fiber dispersion, long fiber benefit in reducing the influence of stress concentration caused by the poor property of interface bonding function, thus bring about remarkable mechanical strength enhancement of SF/PLA composite. |
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