Rheological Properties Of PCL/PLA Blends And Its Effect On The Cell Morphologies Of Microcellular Materials

In the preparation of tissue engineering scaffolds,supercritical fluid micro foaming method,without using harmful solvent gas as foaming agent,had been developed by many scholars.In the molding process of microcellular foamed products,the proportion of polymer materials determines the phase morphology of the blend material,and thus further determines its rheological properties,and the viscoelastic response of the polymer is closely related to the molding process conditions.Therefore,in the polymer micro foaming process of polymer micro foaming,the viscoelasticity of polymer directly determines the formation and growth process of the bubble profile.Analysising the viscoelasticity of polymer blends with different phase morphology and process parameters,and studying its influence on the cellular structure of microcellular materials can optimizing the foam process and improve the quality of products.In this paper,the polylactic acid（PLA）and polycaprolactone（PCL）blends were selected,and the rheological properties of the blends with different process parameter were measured by using a rotary rheometer.Based on the batch microcellular foaming technology,the PCL/PLA blends was foamed to explore the influence of the rheological properties of the materials on the morphology of the microcellular foam materials.Main work and conclusion are as follows:1.Morphology and rheological properties of PCL/PLA blendsThe phase morphology and rheological properties of PCL/PLA blends with different proportions were characterized,the effects of material proportions on the viscosity,modulus of PCL,PLA and their blends were investigated,and the cross model was used to analyze the viscoelasticity of materials.The results showed that in PCL or PLA based blends,with the addition of the dispersed phase,the particle size distribution of dispersed phase is denser and the diameter is larger.In PCL/PLA blends,the addition of PLA can increase the viscosity,modulus,and also improve the internal deformation resistance of the material.Moreover,the loss factor tanδ_max of PCL/PLA（30/70）blends is the lowest,the elasticity is better.2.The effect of process technology on the rheological behavior of PCL/PLAblendsThe influences of shear rate,scanning frequency,temperature and stress loading time on the rheological behavior of PCL,PLA and their blends were analyzed.The results showed that the apparent viscosity of PCL/PLA blends decreased with the increase of shear rate and temperature.The viscosity,storage modulus and loss modulus of PCL/PLA blends decreased with the increase of temperature.The internal deformation of polymer increases with the increase of time and temperature.3.The effect of rheological properties of PCL/PLA blends on the cell structure of microcellular materialsBased on the single factor experiment,the batch microcellular foaming experiment of PCL/PLA blends was carried out,and the effect of rheological properties of PCL/PLA blends on the morphology of cells was studied.The results showed that in the blends with high PCL content,small amount of PLA increased the viscoelasticity of the blends,which was beneficial to the cell formation,PCL/PLA samples with PLA content of 30%had the most uniform and dense cell distribution;However,when PLA content is 40%,the formation of"island"structure made the different phase relaxation state different greatly,which is not conducive to the cell formation.In the blends with higher PLA content,with the increase of PCL content,the viscosity and modulus of the blends decreased,and the ability of the blends to inhibit gas diffusion and bubble growth was reduced.Therefore,the addition of PCL increased the cell size and decreased the cell density.The higher temperature,the lower viscosity and modulus of PCL/PLA blends,which can not effectively inhibit the cell growth and maintain the cell structure,and made the cell size smaller and the cell density larger.