Preparation Of Polytetrafluoroethylene Fiber Reinforced Poly(propylene Carbonate)/ Polylactic Acid Blends And Their Microcellular Foaming Behavior

Polypropylene carbonate?PPC?is an aliphatic polycarbonate made by the copolymerization of carbon dioxide and propylene oxide under the action of a catalyst.It is a rapidly developing and promising biodegradable bioplastic with a wide range of sources and very broad industrial value.Polylactic acid?PLA?is also a polyester and is completely biodegradable.The production process of PLA is environmentally friendly and helps to achieve the recycling of polymer materials in nature.However,PLA has the defects of poor crystallization performance and toughness,which greatly restricting the scope of its industrial application.Polytetrafluoroethylene?PTFE?has the reputation of"Plastic King"in the industrial.It'is mainly used for making plastic products with extremely high performance requirements and a widely used special engineering plastic at home and abroad.The purpose of this work was using the common processing methods and the characteristics of fiber-forming under the shear stress of PTFE to introduce PTFE fibrils into PPC/PLA blends.Through the microstructure design and the research of PPC/PLA two-phase composite material,the strength,stiffness and thermal properties of the PPC/PLA/PTFE composite material are further improved,which provides possible directions for more applications of PPC materials.Subsequently,PPC/PLA and PPC/PLA/PTFE composite foamed products were prepared by the laboratory self-made supercritical CO₂ intermittent foaming kettle using the intermittent foaming technology of supercritical fluid.Through the change of the microstructure of the composite material,the control of the foaming ratio and cell structure can be realized.Foam products significantly increase the compressive strength of PPC materials in the application of foam materials provide more ideas.Experimental results show:1.PPC/PLA composites have certain miscibility.The interface of the PPC/PLA composites shows the change of the composite from"island structure"to the bicontinuous phase with the change of PLA content.The tensile strength of the two-phase composites prepared by melt blending increased remarkably with the increase of PLA content.When the content of PLA was 50 wt%,the tensile strength of composites reached the highest value of31 MPa with an elongation at break of 62%,and its strength is superior to that of some conventional petroleum-based polyethylene?PE?materials.2.The PPC/PLA/PTFE composites were prepared by introducing PTFE fiber as the reinforcing structure between PPC/PLA.The tensile strength of 30 wt%PLA content increased from 21 MPa to 30 MPa under the action of 0.5 wt%PTFE,increased by 43%,which is equivalent to the tensile strength of two-phase composites with 50 wt%PLA.The elongation at break at this time was about 84%,better than the two-phase composite at 50wt%PLA.The tensile strength of 50 wt%PLA component in the presence of 0.5 wt%PTFE reaches nearly 43 MPa,and the elongation at break is about 24%,which is comparable to that of pure PLA material.3.Experimental results of supercritical CO₂ foaming show that a small amount of PLA has synergistic effect with PPC on foaming processs.The composites with PLA content of 10wt%achieved larger expansion ratio and larger cell size than the pure PPC and PLA under the corresponding process.With the increase of PLA content,the cell structure undergoes complex changes with the change of the phase structure.Among them,50 wt%PLA component obtained PFC/PLA blends with bimodal pores and special through-hole structure,which is equivalent to the expansion ratio of pure PPC material.Among them,the foaming material of 50 wt%PLA component obtains the equivalent expansion ratio of pure PPC material and the special through-hole structure with bimodal cells.The specific compressive strength of pure PPC material is about 2?MPa·cm³?/g.Under the action of PLA,the specific compressive strength of foamed products of composite material is significantly enhanced,reaching a maximum of 22 times that of pure PPC material,effectively expanding the application range of PPC-based composite materials.4.PTFE can effectively limit the cell growth.The cell size of the composite decreases to about 1?m under the action of PTFE,approaching the nano-scale.At the same time,PPC/PLA/PTFE composite foam products have further enhanced the specific compressive strength.