Preparation And Properties Of Gradient Structural Microcellular Polymer Foam

Polymeric foams with gradient of cell size attract more and more attention and have shown significant potential in many applications,but,the fabrication of such foams is difficult.By producing blowing agent concentration or temperature gradient inside the sample,some recently developed methods have successfully prepared gradient polymer foams,whereas,precise control system and/or delicate operation are highly needed.Herein,this paper studies in a simple method to obtain cell size gradient in polymer foams by a batch foaming of the polymers on a substrate with nanopore structure.Anodized aluminum oxide?AAO?film modified with a fluorinated silane wasused as the substrate.Then,polystyrene was compressed onto the modified AAO film,and then foamed by a batch foaming process using sc CO₂ as blowing agent.SEM characterizations on the foam morphology revealed that for the samples,the size of cell near the substrate was smaller and gradually increased along the distance from AAO surface.What's more,we found that under the condition of AAO film's size was 150 nm,foaming temperature and saturation pressure were 100 oC and 13.8 MPa with pressure drop time was 0.3 s,the gradient of cell size was perfect.In the study of different modifications of AAO film,we also found that AAO film resulted in heterogeneous nucleation of polystyrene,which was important to gradient structure.Besides,homogeneous pore structure by foaming of PS-G nanocomposites on AAO film had also well confirmed it.AAO film had nano confinement effects to polystyrene which was also a determining factor of cell size gradient in polymer foams.Due to the brittleness of AAO film in the market,reusing and preparing big cell size polymer foams are not available.Thus,we used electrolytic method to prepare AAO film for studying polymer foams.After foaming,gradient of cell size was structured and the pore structure of AAO film was covered by polymer matrix.In addition,cell size gradient in polymer foams was not obvious after AAO film being used repeatedly or even occurred a two-pole pore structure.By measuring the tensile strength,we found that the bulk density of polymer foams was increased by AAO film,and the tensile strength was improved.In order to verify the versatility of the method in different polymers,we used polymethyl methacrylate and polylactic acid as polymer matrix and found that different polymer has different cell size gradient and the cell size gradient of PMMA was poor.To specially mention,the cell size gradient in polylactic acid was more perfect and the cell size gradient range was over 1 mm.What's more,polylactic acid has good biocompatibility,so we got on in vitro cell culture experiments of polylactic acid foams with gradient of cell size and we found that mouse fibroblast cell has a good adhesion effect and can easily survive in bigger pore structure.