Study On Fabrication Of Porous Product From Co-Continuous Poly (Lactic Acid)/Polystyrene Blends

A number of researchers have been conducted to fabricate three-dimensionalporous products composed of biodegradable polymers. Ideal biological porousproducts not only have good biocompatibility and appropriate degradationperformance, but also should guarantee controllable pore size, high connectivity andsuitable shape.This paper explored co-continuous poly(lactic acid)/polystyrene (PLA/PS) meltblending properties, the fabrication methods of PLA porous products and themorphology of the products. The novel PLA porous products were manufactured withcontrolling pore size, highly connected porous structure and appropriate shape byselecting suitable PLA/PS blending method and rational fabrication technique. Themain work is as follows:1. Investigate the influence of blending methods and annealing on phasemorphology of PLA/PS blends. The dried PLA and PS at a50/50weight ratio weremelt-mixed in twin-screw extruder and torque rheometer, respectively. A preliminaryassessment of co-continuous structures formation was obtained by examining themass loss process of selective extract PS from film sample. The experimental resultsshow that the co-continuous structures of PLA/PS blends can be both obtained by thetwo blending methods. In addition, a bimodal distribution of porous structure waspresented after extracting the PS phase from the samples prepared by two blendingmethods.2. Explore effect of compression molding ways and process conditions on poresizes and distribution of PLA products. Two different compression molding ways,contact annealing and compression annealing, were explored in the experiments. Thepore sizes and distribution, internal connectivity and water absorption of the PLAporous products were observed by varying the processing conditions includingmolding temperature, plasticizing time and surface properties of mold. The resultsindicate that compression molding ways and process conditions both affected pore distribution and sizes of PLA porous products. That is, the former mainly impact onthe surface morphology of porous products, including pore distribution and sizes;with the rise of the molding temperature and the extension of plasticizing time, theinternal pore sizes of products were increased apparently.3. The multi-scale voids PLA porous products were fabricated by injectionmolding technique. The temperature and shear flow field of molding process werestudied to investigate influence on the morphology of the porous structure fromdifferent thickness and filling direction. The internal connectivity and waterabsorption of final PLA porous products were also evaluated. Eventually, the optimalPLA porous products with a gradient porous structure, highly connectivity and asuitable shape were obtained. In addition, thin PLA skin with thickness about0.2mmwas observed on the products. The skin may be generated by the viscosity differencebetween PLA and PS. It has been reported that the low viscosity component in apolymer blend during shear flow tends to migrate to the mold–blend interface tominimize the total system free energy.