Research On The Preparation And Mechanical Properties Of Continuous Sisal Fiber Reinforced Polylactide Laminated Biocomposites

Sisal fiber(SF)has the advantages of low cost,renewable,biodegradable and high specific strength,which can be used to reinforce polylactic acid(PLA)to make fully biodegradable composite materials.This can not only reduce the cost of PLA and improve its properties,but also can alleviate the increasingly serious environmental problems and achieve sustainable development.Due to the short length and uncontrollable orientation of chopped fiber,the composite is hard to meet higher stander application.In order to overcome the shortcomings mentioned above,this paper prepared continuous sial fiber reinforced PLA composites(PLA/LSF)by laminating process.PLA/LSF was compared with the chopped sisal fiber reinforced PLA composites(PLA/SSF)to study the enhancement effect of continuous sisal fiber.At the same time,the rule of maxiture of tensile properties of fiber reinforced polymer composites was introduced and the applicability of this rule was discussed.After that,the effects of different fiber layers,fiber angles and fiber layer thickness on the mechanical properties of PLA/LSF were studied,and the different failure mechanisms of composites were also analyzed.The experimental results show that:Under the same fiber content,the mechanical properties of PLA/LSF were better than PLA/SSF,which illustrated that continuous plan fiber as an enhancement can greatly improve the mechanical properties of composites.Taking into account the porosity,the modified curve fitted with the experiment results better than the original one.Therefore,when predicting the tensile properties of continuous plan fiber reinforced composites,the volume of porosity cannot be ignored.The number of fiber layers had different effects on the tensile properties,flexural properties and impact properties of composites.With the increase of fiber layer,the tensile and impact properties of composites increased,but the flexural properties increased first and then decreased.Fiber orientation had a great effect on the mechanincal properties of composites.As for the composites with different fiber layers,when the fiber orientation of each fiber layer was 0°,the mechanical properties of composite was the best.As for the unidirectional fiber reinforced composite with single fiber layer,the failure mode of composite with 0° fiber orientation was fiber breaking,composites with 45° or 90° fiber orientation were matrix breaking and interface failure.As for the composites with multi fiber layers and multi fiber angles,the failure of composite was more complex.Each individual fiber layer had an independent form of failure,and the failure of composite was the result of combined effect of various failure modes.As for composite with one fiber layers,there was a critical fiber angle of 9.1°.When the fiber orientation was less than the critical angle,composite had good tensile properties.Alkalitreatment could improve the interfacial strength between matrix and fiber,and increase the tensile properties of composite whose fiber angle was greater than the critical angle.Fiber layer thickness affected the flexural properties of composites with two fiber lyares seriously.When the ratio of fiber layer thickness was 3:2,the composites had the best flexural properties,whose flexural strength and flexural modulus were 271.58 MPa and 18250.06 MPa respectively.When the ratio of fiber layer thickness was 0:1,the flexural strength and flexural modulus of composite were relatively poor,which were 132.95 MPa and 5106.31 MPa respectively.