Molecular Simulation Of Mechanical Properties And Foaming Behavior Of Functionalized GNS/PLA Composites

Polylactic acid(PLA)is an excellent degradable biomaterial.In order to solve the problem of fragile fracture in medical stents and engineering applications,it is modified to improve its mechanical and thermodynamic properties.Compared with other domestic and foreign researches,this article focuses on the microcellular injection foam molding process and reinforcement materials of PLA from the atomic and molecular level,and analyzes and studies the foaming behavior and the microscopic mechanism of reinforcement,in order to improve the various aspects of PLA products.Item performance provides theoretical support.The main research contents are as follows:(1)The molecular simulation method is used to study the influence of shear stress and temperature on the diffusion behavior of CO₂ in PLA during the molding process.The CO₂ diffusion model in PLA is constructed.Simulation analysis shows that when the shear rate is 0,the higher the temperature is,the stronger the CO₂diffusion ability in the matrix is;when subjected to shear,the shear rate and diffusion ability are positively correlated;temperature and the shear rate affect the diffusion behavior of CO₂ in the polymer matrix by affecting the activity of the PLA main chain and the system energy.(2)Graphene(GNS)is one of the most ideal reinforcing materials.In order to reduce the agglomeration phenomenon,the PLA matrix is reinforced with surface functionalized GNS.Construct PLA,GNS/PLA and hydroxyl,carboxyl,amino functionalized GNS/PLA models.Simulation analysis shows that the surface modification of functional groups on GNS can improve the material,and the surface modification of carboxyl has the best thermodynamic enhancement effect;surface functionalization makes the combination of GNS and PLA matrix more tight,which improves the cohesive energy density of the composite material and enhances the mechanical properties.(3)To explore the effect of surface functionalized GNS on the diffusion behavior of CO₂ in composites during the molding process.The diffusion model of CO₂ in GNS/PLA and three functionalized GNS/PLA is constructed.Simulation analysis shows that:surface functionalization significantly increases the free volume fraction of the system,thereby improving the diffusion capacity of CO₂,and accelerating the transformation of the diffusion behavior from abnormal diffusion to normal diffusion increases the foaming rate during the microcellular injection molding process;the surface modified hydroxyl has the best diffusion capacity enhancement effect,and the amino group has the worst effect.