Preparation And Properties Of Thermoplasticized Starch And Its Composites

In the face of the increasingly serious pollution problems and energy crisis,the demand for biodegradable materials continues to increase.However,due to their high price,the promotion and application of biodegradable materials are limited.Starch,which has the characteristics of wide sources,renewability,low price,and excellent degradability,is often used as a filler to mix with other synthetic biodegradable materials to reduce the price of biodegradable materials.When starch is added directly,the amount needs to be low due to its poor compatibility with synthetic biodegradable materials,leading to poor performance of the resulting composite materials.However,when starch is plasticized to obtain thermoplastic starch and then blended with other biodegradable materials for further processing,the added amount of starch and the mechanical properties of the blend can be greatly improved.Currently,starch plasticizers are mainly classified into two types:polyols and amides.The type of plasticizer has a significant impact on the properties of thermoplastic starch.For example,polyols such as glycerol can give thermoplastic starch a certain toughness,but with poor tensile strength and easy to precipitate,leading to poor storage stability and tendency to retrogradation.Amide plasticizers such as formamide can form stable hydrogen bonds with starch,effectively preventing retrogradation,but the resulting thermoplastic starch material is brittle with poor toughness.In actual production,the two types of plasticizers are often used in combination to achieve complementary advantages,but the drawbacks of plasticizing starch with different types of plasticizers still exist.Therefore,in this study,three plasticizers containing both amide and hydroxyl groups were selected: N-(2-hydroxyethyl)formamide(HF),N,N-bis(2-hydroxyethyl)formamide(BHF)and N-(2-hydroxyethyl)-N,N’-dimethylformamide(HEF)were used to prepare thermoplastic starches(HFTPS,BHFTPS,and HEFTPS)and their properties were compared with the traditional glycerol plasticizer(GTPS).Based on this,BHFTPS with better comprehensive properties was selected to prepare biodegradable composite materials BHFTPS/PBAT and BHFTPS/PBS by blending with PBAT and PBS,respectively.The results were compared and discussed with traditional GTPS/PBAT and GTPS/PBS by infrared spectra,X-ray diffraction patterns,micro-morphology,water absorption performance,and mechanical properties.The specific research content is as follows(1)Three types of composite organotin polymer plasticizers containing both amide and hydroxyl groups,HF,BHF,and HEF,were synthesized and characterized by Fourier transform infrared spectroscopy and nuclear magnetic resonance spectroscopy.A hot-melt extrusion process was used to prepare thermoplastic starch materials,and the effect of plasticizer type and amount on the properties of thermoplastic starch was analyzed and discussed.The study found that the addition of plasticizers altered the crystalline structure of starch.A plasticizer content of 30%was found to be the optimal proportion,and the tensile strengths of HFTPS,BHFTPS,HEFTPS,and GTPS were 13.2 MPa,12.2 MPa,8.5 MPa,and 14.8 MPa,respectively.BHFTPS exhibited the highest tensile strength.(2)Based on the above research results,BHF was chosen as the plasticizer to prepare thermoplastic starch and blended with PBAT to form BHFTPS/PBAT composite materials.The properties of the composite material were analyzed and discussed by Fourier transform infrared spectroscopy,X-ray diffraction patterns,micro-morphology,water absorption performance,and mechanical properties,which were compared with traditional GTPS/PBAT.The study found that increasing the amount of thermoplastic starch reduced the mechanical properties of TPS/PBAT composite materials.BHFTPS/PBAT had a higher tensile strength than GTPS/PBAT,and BHF was less likely to precipitate compared to glycerol,which improved the storage stability of materials.From micro-morphology images and dynamic thermodynamics analysis,it was observed that BHF could improve the compatibility between thermoplastic starch and PBAT compared to glycerol.(3)BHF was selected as the plasticizer to prepare thermoplastic starch,and the BHFTPS/PBS composite materials were prepared by extrusion.The properties of the composite material were analyzed and discussed by Fourier transform infrared spectroscopy,X-ray diffraction patterns,micro-morphology,water absorption performance,and mechanical properties,which were compared with traditional GTPS/PBS.The study found that increasing the amount of thermoplastic starch reduced the tensile strength but increased the elongation at break of TPS/PBS composite materials.BHFTPS/PBS had a higher tensile strength than GTPS/PBS.Compared with glycerol,BHF could increase the compatibility between thermoplastic starch and PBS,leading to better stability.