Research On In Situ Fibrillation Reinforced Biodegradable Composite Microcellular Foaming And Properties

Polymer foaming material has excellent properties such as light weight,high specific strength,heat insulation,etc.It is widely used in packaging,life products and other fields.Compared with traditional petroleum based foam such as polyethylene,foamed PLA/PBAT(polylactic acid/poly terephthalic acid-butylene adipate)as a biodegradable composite material has the characteristics of green environmental protection.However,due to the low melt strength and poor foaming ability of PLA and PBAT,PLA/PBAT foaming material has a little number of foaming cells and poor structure.Material modification can improve its foaming performance,but the general modification methods have defects:the dispersion effect of nano fillers is poor,the environmental protection of chemically modified materials will be affected,and the material properties of blending polymer will depend on the form of dispersed phase,which limits the application prospect of PLA/PBAT foaming materials.In situ fibrillation is a kind of composite modification technology which can regulate the morphology of the dispersed phase of polymer.For the foaming defect of PLA/PBAT,this paper adopts in situ fibrillation technology to enhance and modify it.The experiment studied and analysed the impact of PTFE(polytetrafluoroethylene)fiber relative to PLA/PBAT composite basic physical properties and foaming behavior.Paper studied the relationship between the foaming behavior and the macroscopic properties of foaming materials,to explore the application potential of foamed PLA/PBAT/PTFE in-situ fiber composites in lightweight,heat insulation.The main research results are as follows:1,PLA/PBAT was in situ fibrillation modified by using PTFE and twin-screw extrusion blends.The effect of PTFE microfiber morphology on the crystallization and rheological properties of the composite was revealed.PTFE was sheared to form microfibers in PLA/PBAT system.The microfibers with large specific surface area provide the attachment point for matrix crystallization.The experimental results showed that introduction of PTFE microfibers improve the crystallinity of the composites.Because the PTFE microfiber network formed by in situ fibrillation limits the large-scale movement between molecular chains,the melt relaxation time increases and the material exhibits solid-like properties.The results show that the storage modulus,loss modulus and complex viscosity of PLA/PBAT/PTFE composites increase with the increase of PTFE content at low rheological frequency.2,PLA/PBAT/PTFE in situ fibrillation composites were foamed by microcellular foaming injection molding process.The foaming behavior and mechanical properties of the composites with different PTFE content were analyzed.It was found that PTFE microfiber network promoted the heterogeneous nucleation effect and melt strain hardening behavior.Compared with the microcellular foamed PLA/PABT composites,the cell size of the microcellular foamed PLA/PABT/PTFE in situ fibrillation composites was smaller and the cell density was higher.For 3%wt PTFE content composites,the cell average size of the foamed material decreases by about 50%,the cell density increases by an order of magnitude,the distribution range of the cell size becomes more concentrated,and the defects of the foamed material are inhibited.The fine cell inhibits the internal defects of the material,so with the introduction of PTFE,the tensile strength,compression strength and impact strength of microcellular foaming materials are improved.3,By changing the gas injection content and using the micro opening mold process,the effect of foaming injection process on the thermal conductivity of PLA/PABT/PTFE foaming material with 3%PTFE content was studied.The work laid a foundation for the application of biodegradable foaming material in the field of heat insulation.Experiments show that the increase of gas injection content can improve the cell nucleation rate,improve the foaming ratio.The increase of cell volume accounted decrease heat conduction in the solid path,so the thermal conductivity coefficient will be decreased with the increase of gas injection content.For this experimental,the thermal conductivity coefficient is 158 mW/m·k-1 with the largest gas injection content.But restricted by gas solubility and foaming space,a large amount of gas cannot participate in the foaming when the gas injection content is too high,and the foaming rate tends to be stable.The micro mold opening action provides pressure drop power and a large amount of foaming space for the formation and growth of the cell.The experiments show that with the increasing of the mold opening distance,the foaming rate increases,the heat conduction path becomes narrow and tortuous,and the thermal conductivity decreases significantly.The thermal conductivity decreases to 85.7mW/m·k-1 with the maximum mold opening distance.