Preparation And Study On The Performances Of Starch-based Biodegradable Foams

Nowadays, those traditional foams such as polystyrene, polyethylene, polypropylene, and so on, which are non-degradable, are confronted with serious environmental pollution issues. However, starch has excellent foaming performance, which is biodegradable, renewable, abundant and inexpensive. Once starch is made full use of as a kind of foaming material, the great pressure that foam industry is suffering, will be reduced tremendously. Thermal plastic starch (TPS) and TPS/biodegradable polymers with excellent physical and mechanical performances, which attracts a lot of attention, are ideal matrix to prepare biodegradable foams On the basis of referring to the previous papers, this paper prepared high-performance biodegradable foams with TPS and TPS/biodegradable polymers, using extruder.The performances of TPS foams are affected by various factors. On the basis of exploiting the best processing conditions including temperature, screw speeds, contents of foaming agents and contents of nucleating agent, the radial expansion ratios, apparent densities, water absorbing rate and micro structures were studied. It is suggested by Scanning Electron Microscopy (SEM) that the cell structures of NPTPS were more uniform than those of GTPS. As far as corn starch was concerned, glycerol/formamide (GL/FA) was a more effective plasticizer. Compared with GTPS,the radial expansion ratios of GFTPS were raised, its apparent densities were reduced and its micro structures were improved.High-performance biodegradable foams produced by using TPS/Poly(vinyl alcohol) composite as matrix, could overcome the drawbacks of great brittleness and hydrophilicity of TPS foams. Compared with GFTPS and the traditional GTPS/PVA, the radial expansion ratios of GFTPS/PVA were obviously raised, its apparent densities were reduced greatly, and its cushioning performance was improved dramatically. It is suggested by Differential Scanning Calorimetry (DSC) that the glass transition temperature (Tg) of GFTPS/PVA was raised compared with GFTPS and the traditional GTPS/PVA, thus its applied temperature was extended. SEM showed that the cell structures of GFTPS/PVA were smaller and more uniform, and its cell walls were thinner with less collapsed cells than those of GFTPS and the traditional GTPS/PVA. When it comes with Poly(lactic acid)(PLA), the effect of reinforcing was not obvious.Compared with GTPS/PVA, GTPS/CA/PVA with small percentage of Citric Acid (CA) has higher radial expansion ratios, lower apparent densities and improved cushioning performances. It was suggested by SEM that the cells of GTPS/CA/PVA were smaller, its cell structures more uniform and cell walls thinner with less collapsed cells than those of GTPS/PVA. It is also suggested by Fourier transform infrared spectroscopy (FTIR) that the specific peak of starch moves to lower wavenumber with citric acid. This suggested that the three carbonyls of citric acid had formed strong hydrogen bonds with the hydroxyl groups of starch and PVA. It is suggested that by X-Ray that citric acid could effectively restrain starch re-crystallization, which showed us that the hydrogen bonds formed by the three carbonyls of citric acid and the hydroxyl groups of starch and PVA are stronger than the hydroxyl groups of GL.