Effect of Silk with Different Length-Diameter Ratio on Mechanical and Electrical Properties of Polylactic Acid

In this study, the effects of SF with different length-diameter ratio on the mechanical properties and insulation strength of polylactic acid composites were investigated. The experimental results show that the tensile strength and impact strength of the composite can be improved by adding SF. Especially when the length of the SF reaches 4 cm, the tensile strength and impact strength of the sample increase by 41.86% and 39.63%, respectively. However, the bending strength is affected by different laws. The addition of SF decreases the bending strength at first, and then increases with the increase of fiber length to diameter ratio. In terms of insulation strength, the introduction of SF leads to a decrease in the breakdown voltage of the composite. However, removing the influence of impurities and defects, the larger length-diameter ratio of SF will promote the growth of larger crystals in the PLA matrix, thereby shortening the breakdown path and increasing the breakdown voltage. The final 4 cm SF has a breakdown strength of 30.24 kV/mm. The simulation results show that the horizontal energy gap of the lowest occupied molecular orbit-highest occupied molecular orbital (LUMO-HOMO) decreases from 4.72 eV to 2.39 eV and then rises to 3.19 eV. The breakdown voltage of polylactic acid material decreases first and then increases. The purpose of this study is to provide theoretical basis for the influence of SF with different length-diameter ratios on PLA materials.