Study On Starch Plasticization And Composite Materials

Starch has wide choices of sources and low price.It is one of potential materials in biodegradable materials from nature.Starch contains a large number of hydrogen bonds,which lead to a higher melting temperature and poor processability.By adding the plasticizer,the hydrogen bond between the starch molecules can be destroyed.So the melting temperature of the starch can be lower to make it thermoplastic.On the other hand,starch has poor water resistance and mechanical properties,which also limits the use of starch products.By blending starch with polyester having excellent properties,the water resistance and mechanical properties of starch can be improved.Previous work mainly focused on the effect of starch as a filler on the properties of biodegradable polyester.However,there are few studies on starch-based biodegradable materials.In this work,glycerol thermoplastic starch(GTPS),sorbitol thermoplastic starch(STPS)and glycerol/sorbitol composite thermoplastic starch(GSTPS)were prepared by adding glycerol or sorbitol as the plasticizers into.The plasticizing efficiency of the two plasticizers,their effect on mechanical properties,processability,and hydrophilicity of starch and the plasticizing mechanism were studied.In addition,poly(terephthalic acid-co-adipic acid-co-butylene glycol)(PBAT)and polycaprolactone(PCL)was blended with TPS.The effect of two plasticizers on the processing,mechanical and crystallization properties of the blends were studied.The results were listed briefly in the following paragraphs.The plasticizing mechanism of polyols on starch was studied.The results showed that glycerol and sorbitol can be improved the plasticity by destroying the hydrogen bonds between starch molecules and reducing the polarity of starch molecules.The hydrogen bonding force between glycerol and starch was less than that of sorbitol.The plasticizing efficiency of glycerol starch was higher than that of sorbitol.The plasticizing time of glycerin is 130 seconds,and the plasticizing time of sorbitol was1066 seconds.The mechanical properties of sorbitol plasticized starch were better than glycerol,and the tensile strength of 30 wt% sorbitol was 20.88 MPa,while that of 30wt% glycerol was only 5.29 MPa.TPS/PBAT composites were prepared by melt blending.The results show that the mechanical properties of the composites were the lowest when the PBAT content was10 phr,and the tensile strength was 5.18 MPa;PBAT can improved the hydrophobicity of the composite and reduced the water absorption.The water absorption of the composite with 30 phr PBAT was reduced from 138.6% to 16.7%.The results of DSC and XRD showed that plasticizer and PBAT had a great effect on the crystallization behavior of the blends.Glycerol decreased the crystallinity of PBAT.The results also illustrated that PCL improved the processing performance,mechanical property,thermal stability and water resistance of TPS.PCL improved the fluidity,reduced the equilibrium torque and improves the processing performance of the blends.As PCL was 15 phr,the tensile strength reached 11.63 MPa,which was 120%higher than that of GTPs.It was found that TPS had promoted heterogeneous nucleation and crystallization of PCL.