Effects Of Ion/acidification On The Structure And Properties Of Thermoplastic Starch And PBAT/TPS Blends

Starch currently ranks versatile applications in renewable biodegradable polymers based on its abundance,renewable,easy modification and so on.However,there are many hydroxyl on glucose units in starch,forming strong hydrogen bonds between the molecular chains,which cause the poor processability and the application limit of starch.With the plasticization of glycerin and the shear of the screw,the thermoplastic starch?TPS?are prepared via destroying the hydrogen-bond force of starch,which can't be widely used due to its high brittleness,low water resistance and heat resistance and other drawbacks.Therefore,ionic modification was developed for the fabrication of TPS with chelation structure by coordination bond,improving the thermal and mechanical properties of TPS.Based on the phase morphology and interface bonding strength of regulation mechanism,TPS was acidified to reduce the melt viscosity.Then it extruded with PBAT and TPS/PBAT blends were prepared,providing a new methods and theoretical guidance for the preparation and application of high-performance TPS.In this paper,the effect of different kinds of calcium salt on TPS performance was studied.Calcium maleate,calcium chloride,calcium gluconate?CG?with the Ca²⁺contents of 1 wt.%?based on starch?extruded with mixture?starch and glycerol?70:30 wt.%??at 145°C,respectively.The results of DMA and tensile test revealed that only CG could reinforce TPS;The influence of CG content?5-20 wt.%?on TPS performance was further investigated.FTIR,XPS,SEM and EDS results showed that the chelation structure of TPS was formed by the coordination bonds between Ca²⁺and starch.The influence mechanism of Ca²⁺contents on thermal and mechanical properties of TPS-CGs was investigated by TG-IR and DMA.The results revealed that the T_g of TPS-CGs increased from 48.1°C to 66.8°C;Decomposition temperature of starch increased from 314°C to 326°C and the release of CO,furan and other gases were greatly reduced.The tensile strength and notch impact strength of TPS-CGs were increased from 4.7 MPa,2.1 J/m to 7.4 MPa,3.2 J/m,respectively.Therefore,the chelation structure formed by ionic bonds via reactive extrusion will improve the thermal and mechanical properties of TPS.The effects of organic acids on the structure of TPS were studied by the method of acidification.Acidified TPS were prepared via reactive extrusion at 145°C by adding 1 wt.%?based on starch?of acidifier A?A?,acidifier B?B?,succinic acid,stearic acid and lactic acid,respectively,then it blended respectively with PBAT and PBAT/TPS?70:30 wt.%?were prepared.The results of intrinsic viscosity,dynamic rheology and SEM showed that A reduce the molecular weight of starch in TPS from 18.6×10⁴ to 9.6×10⁴,and improved the compatibility between PBAT and TPS,making the phase structure of PBAT/TPS blends show the homogenous phase;The effects of A content and TPS content on the structure and properties of PBAT/TPS were further studied.The results of intrinsic viscosity,FTIR and capillary rheological showed that A reduced the molecular weight of starch and the shear viscosity of TPS,without esterification reaction with starch.SEM,dynamic rheological test,DMA and contact angle test revealed that A acted as a compatibilizer,effectively improving the interface adhesion between the two phases and the interaction between PBAT and starch molecular chain,which was beneficial for TPS in the form of micro-nano particles dispersed in PBAT,making its average particle size reach 184 nm with the A content at 0.5 wt.%;The results of mechanical and degradation properties showed that the toughness of PBAT was increased by TPS-A.Elongation at break of PBAT/TPS-A-0.5?70:30 wt.%?increased from 942%to 1131%and its degradation rate increased by 38.9%.Therefore,A acidified TPS during the process of extrusion,significantly reducing the shear viscosity of molecular weight of starch and shear viscosity of TPS.Thus it reduced the size of TPS-A in PBAT and formed micro/nano dispersed phase.A acted as a compatibilizer,so that PBAT/TPS-A presented a homogeneous morphology and had good biodegradability.This new blend will have a wide application prospect in the blown film materials.PBAT,PBAT/TPS?70:30 wt.%?and PBAT/TPS-A-0.5?70:30 wt.%?films were prepared by extrusion blow at 160°C with different blow-up ratio.In order to investigate the influence of stretch orientation and film blowing on properties of the films,SEM,mechanical and barrier properties were used and the results showed that PBAT/TPS-A-0.5 film formed a microstructure of PBAT wrapped TPS with the blowup ratio at 3.75 and TPS-A was distributed along the stretching direction.Compared with the PBAT/TPS,transverse/longitudinal tensile strength of PBAT/TPS-A-0.5 increased by 83.2%and 44.0%and the air permeability and water permeability were decreased from 5.3×10^-9 cm³·cm·cm^-2·s^-1·Pa^-1?5.4×10^-6 g·m·m^-2·s^-1·Pa^-1 to3.7×10^-9 cm³·cm·cm^-2·s^-1·Pa^-1?5.3×10^-6 g·m·m^-2·s^-1·Pa^-1.Thus the PBAT/TPS-A-0.5 film prepared by acid-modified extrusion has excellent mechanical and barrier properties,showing a wide prospect for commercial application.