Characterization And Simulation Of Polyolefin Foaming Process

Microcellular foamed materials are widely used in all aspects of our life due to its large weight reduction and better comprehensive performance.The comprehensive properties of the micro-porous polymer depend on the pore structure,and the cell structure is determined by the evolution of the formation and growth of the micro-pores.Therefore,in order to obtain the high-quality micro-porous foamed product,the research on the characternzation and mechanism of the micro-porous foaming process is of great importance.At present,the research on the foaming process is mainly focused on the influence of the forming process parameters,additives,melt properties and the like on the foaming process,and the foaming behavior of the foaming process is studied through the characteristics of the initial state and the final state bubble pore morphology,And the dynamic characterization and quantitative description of the migration and stretching of the resin will have less impact on the morphology of the cells.In this paper,through the establishment of the model of the migration of the resin in the process of cell growth,the mathematical model of the degree of stretching of the molecular chain,and then the static and dynamic representation of the deformation behavior of the two adjacent cells under the two foaming modes of the actual injection and the free foaming,the rotation and deformation phenomena of different characteristic fibers around the cell are tracked,the influence range model of the cell growth on the surrounding resin and the correctness of the circumferential stretching model of the resin are verified,the cell formation,the growth and the deformation internal rule of the polymer foaming material are further proved,In ord to provide a theoretical guidance for preparing high-quality microporous foamed polyolefin material.The specific conclusions are as follows:(1)Establish a mathematical model for the influence of the resim around the hole during the growth of the cell:the thickness of the shell of the n-th resim outside the cell wall is ? rn = rn+1—rn =(3n+ 1—3n)r.The model shows that as the cell grows,the resin at the edge of the cell pushes outward in a layer.In the case of the same volume of the resin,the thickness of the shell decreases from the inside to the outside,and the outermost layer The area affected by the resin is the smallest,and the influence is the weakest,so that the affected area of different sizes can be quantitatively calculated.The mathematical model of radial migration can quantitatively calculate the degree of cell expansion around the hole.A mathematical model which shows that when the resin in the cell is completely pushed out into the nearest region outside the cell wall,the closer the resin molecular chain is to the center of the cell,the stronger the hoop stretching effect.It can be obtained by comparing the circumferential stretching and radial migration of different layers of resin outside the cell wall,and the closer to the cell,the stronger the resin molecular chain is subjected to the hoop stretching(2)Establish a mathematical model for the deformation of the cell growth process.When ? rn=k,the outer edge of the nth layer from the center of the cell to the outside of the cell wall is a cell.The surrounding resin deformation affected zone size is:r*= rn+1=(3n+1)r.For the foaming process of two adjacent cells,define r1*+r2*= L as the critical point of deformation of the two cells.When r1*+r2*<L,the two cells are far apart,and the adjacent two bubbles do not overlap each other when they grow up,and the adjacent cells will be alone.Continue to grow up,continue to produce a circumferential stretching and radial migration of the resin around the individual,the cells become regular spheres,and the cells will not be deformed.When r1*+ r2*?L,the two cells are close together,and the adjacent two bubbles overlap each other in the surrounding resin influence zone and the resin in the radial migration process around the adjacent two cells When squeezed,the cells are adapted to the deformation caused by the radial extrusion by the circumferential direction of the resin ring.As the cells grow,the overlapping area of the resin-affected zone around the two cells is larger.The greater the mutual squeezing effect during the radial migration,the more serious the circumferential stretching,and finally the more the deformation of the cells.The bigger it is(3)In the foaming process of CF tracer PS material,when the distance between the near-cell end of CF and the center of the cell is larger than the deformation zone of the resin molecular chain outside the cell wall.CF does not follow the bubble.The growth of the pores rotates or migrates;when the distance between the near-cell end of CF and the center of the cell is smaller than the deformation zone of the resin molecular chain outside the cell wall,the molecular chain will be deformed,and when the fiber ends When the degree of migration and hoop stretching is different,CF will rotate or migrate.The light microscope simulation visualized foaming process and the actual injection foaming process showed similar rules,which proved the influence range model of the cell growth on the surrounding resin and the hoop tensile model of the resin.(4)In the foaming process of the AF tracer PS material,when the cell is at the AF end and the AF is outside the deformation zone of the resim molecular chain outside the cell wall,the cell is not deformed;when the AF is in the cell wall When the outer resin molecular chain is in the deformation zone,the cells are deformed.During the growth of the cell,the fiber and the resin have a larger force due to the longer fiber length.The stretching and migration of the cell s local molecular chain by the cell does not cause migration or deformation of the entire fiber,and the cell can only be deformed.Adapt to the shape of the fiber.When the cell is at the AF end and the AF is within the deformation zone of the resin molecular chain outside the cell wall,the radial migration and hoop stretching of the resin around the cell will drive the migration and stretching of the end fiber.Eventually the fibers begin to curl and deform around the perimeter of the cell walls.The light microscope simulation visualized foaming process and the actual injection foaming process showed similar rules,which proved the influence range model of the cell growth on the surrounding resim and the hoop tensile model of the resin.