Preparation And Rheological Properties Research Of PLA/PBAT Composites System Filled With Modified Nano-SiO₂

Poly?lactic acid??PLA?has great market potentialities of an environment-friendly macromolecule materiagreat potential for its biodegradable property in numerous fields.However,like traditional plastic,PLA is quick-wearing,which limits its application in packing materials,the electrical industry,or automotive components.It is therefore necessary to provide toughening and reinforcing to PLA materials.In this thesis,the dynamic rheology properties,steady-state rheological properties and crystallization kinetics of PLA/PBAT composites were studied with filled nano-SiO₂.The main contents are summarized as follows:PLA/PBAT composites were partially compatible,viscoelasticity system and viscous dominated.Its impact strength and degradation property were improved for PBAT.PLA/PBAT composites showed stronger non-Newtonian as to pure PLA.Its MFR decreased and elasticity increased as PBAT added.PCL could improve compatibility of PLA and PBAT,when the content of PCL was 2%,the impact strength and tensile strength of composite reached to 6.87 kJ/m² and 63.44 MPa,respectively.Linear rheological properties showed the storage modulus,loss modulus andcomplex viscosity decreased as the content of nano-SiO₂ increased.Non-linear rheological properties indicated PLA/PBAT/SiO₂ composites were pseudoplastic fluid.When shear rate was lower and SiO₂ content was smaller,the Cox-Mert relationship was established.The steady-state rheological properties results showed,PLA and PLA/PBAT/SiO₂ composites were pseudoplastic fluid.Their non-Newtonian index n increased with increasing SiO₂ amount.After the temperature reacheds175 oC,the apparent viscosity of the composites was greater than pure PLA,but with the increase of SiO₂ filled amount,the apparent viscosity of the composite decreased.In addition,PLA and the composites melt has a relatively low viscous flow activation energy in the range of 175¹85 oC,which the melt had low sebsitivity to temperature.The isothermal crystallization kinetics of PLA and PLA/PBAT/SiO₂ composites were investigated by Avrami equation.The crystallization constant K_T,semi-crystallization time 2/1t and crystallization rate 2/1t were increased and then decreased with increasing crystallization temperature.The K_Tand 2/1t of PLA/PBAT/SiO₂ composites were higher than pure PLA at the same crystallization temperature.Simultaneously,the non-isothermal crystallization kinetics of PLA and PLA/PBAT/SiO₂ composites were investigated by Avrami equation with Jeziorny improvement,which 1n values range from 1.31 to 4.88,indicating that the growth of the crystal growth pattern were two-dimensional and three-dimensional growth coexist.The ,Z_c1 and Z_c2 of all samples were increased with increasing heating rate,and n₁ less than n₂.The results of Avrami equation with Jeziorny improvement and based on Mo equation were coincident.And the crystallization activation energy ?E of PLA/PBAT/SiO₂ composites was greater than pure PLA.