| Plant fibers have many advantages compared with conventional petrochemical fibers,such as low density,high specific strength,renewable,degradable,extensive sources,and low cost.Biodegradable polymer materials represented by polylactic acid(PLA)are of great significance to ease the oil crisis and reduce environmental pollution.However,polylactic acid is expensive and has poor comprehensive mechanical properties.Thus the preparation of plant fibers reinforced PLA composites can not only reduce the cost but also increase the mechanical properties of polylactic acid.However,the strength of the plant fibers is not as good as that of the conventional synthetic fibers,and the plant fibers are susceptible to moisture absorption,which greatly limits the further application of plant fiber reinforced PLA composites.Because of the defects of single sisal fiber(SF),this paper introduces a new type of environmentally friendly basalt fiber(BF)into the sisal fiber-reinforced polylactic acid(PLA)composites which prepared the sisal fiber/basalt fiber reinforced PLA interlaminar hybrid composites and sisal fiber/basalt fiber reinforced PLA sandwich hybrid composites by molding.The effects of fiber content,fiber hybrid mode,fiber layup angle and fiber layup position on the mechanical properties of fiber-reinforced PLA composites were studied by comparing with continuous sisal fiber reinforced PLA composite and continuous basalt fiber reinforced PLA composites.The water absorption,thermal and crystallization properties of the composites were also investigated.In order to study the effect of interfacial properties on the mechanical properties of continuous fiber-reinforced PLA composites,the alkali treatment and a silane coupling agent of the fibers was carried out.Scanning electron microscopy(SEM)was used to analyze the morphology of the fiber before and after treatment and the cross section of the composites.The reseach results are as follows.The mechanical properties of the composites show an upward trend with increasing fiber content in the research range of fiber content and reach a maximum at a fiber content of 40 wt%.Besides,the fiber hybrid method has a great influence on the flexural strength and flexural modulus of hybrid fiber reinforced PLA composites,and has little effect on tensile modulus and impact strength.The hybrid fiber-reinforced PLA composites in which the BF is outside and the SF is located in the core has better comprehensive mechanical properties.The addition of BF can improve the thermal stability and crystallinity of the composites and decrease the water absorption of the composites.To a certain extent,it can make up for the lack of mechanical properties and high water absorption of plant-fiber-reinforced PLA composites.The angle of fiber has a great influence on the mechanical properties of the composites.When the angles of the fibers are all 0°,the composites have the best longitudinal tensile properties,bending properties and impact properties.The sandwich hybrid composites in which the BF lay angles on both sides are 0° and the core SF lay angle is 90° have higher longitudinal and transverse strengths.The adjacent SF and BF of multi-directional SF and BF hybrid reinforced composites should be avoided in the same direction to improve the mechanical properties of composites.The difference in the position of the fiber layer in the composite would make the composites different mechanical properties.When the fiber layer is on the center layer of the composite,the composite has better tensile properties and impact strength;when the fiber layer is located on the lower surface,the composite has better bending performance.The effect of the fiber surface treatment on the composite varies depending on the type of fiber.After the fiber surface treatment,the interfacial bonding strength between the fiber and the matrix is improved,and the sisal fiber-reinforced polylactic acid composites tend to be brittle fracture which is relatively smooth and the tensile strength is reduced when tensile properties is tested,while the comprehensive mechanical properties of basalt fiber reinforced PLA composites were improved.Moreover,the tensile strength of hybrid fiber-reinforced composites decreased to a certain extent due to the influence of SF,but the bending performance was improved.It shows that comprehensive consideration needs to be made based on the characteristics of the fiber while fiber surface treatment is used to improve the mechanical properties of hybrid fiber-reinforced composites. |
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