Preparation Of Humic Acid-based Nucleating Agent And Its Effect On The Performance Of Poly(Lactic Acid)

Poly(lactic acid)(PLA)is a new type of biodegradable polymer material from renewable plants.PLA has good application prospects due to its good thermoplasticity and non-toxicity,but it still has technical problems such as low crystallization rate,poor crystallinity and machinery tougheness,which restrict the development of the PLA industry.In this dissertation,amidated humic acid was used as crystallization nucleating agent of PLA,which were prepared with humic acid(HA)as raw material by two different HA amidation modification methods.The microstructure of PLA composites was characterized.And the effect of amidated humic acid on the mechanical,thermal stability,rheological behavior and non-isothermal crystallization kinetics of PLA materials were studied,respectively.Moreover,the effects of nucleating agents on the antibacterial properties and the degradation properties of PLA were also investigated,respectively.The main contents are as follows:(1)Firstly,amidated humic acid(AHA-A)which was introduced into the benzene ring was prepared using a phosphorus trichloride method and PLA composite(PLA/AHA-A)was prepared using melt-blended.Thermogravimetric analysis(TG),differential scanning calorimetry(DSC),polarized optical microscopy(POM),rheological analysis and other methods were used to study the mechanical properties,thermal stability and crystallization properties of the PLA composites.The mechanical properties and thermogravimetric analysis showed that the tensile properties,impact resistance and thermal stability of PLA composites were improved.The cross-sectional morphology of the fracture surface showed that the addition of nucleating agents significantly changed the crystallinity of PLA;DSC results showed that the crystallinity of PLA composites was increased from 4.19% to 35.36% after the introduction of nucleating agents.The POM of the PLA composites showed that AHA-A increased the crystallization rate of PLA.The increase of maximum torque and apparent viscosity of the PLA composites proved that the nucleating agent changed the lattice structure and stiffness of the PLA matrix;the non-isothermal crystallization kinetics showed that AHA-A provided a large number of heterogeneous nucleation sites and increased the crystallization rate of the PLA.(2)Then,the long-chain amidated humic acid(AHA-D)was prepared by the carbonyldiimidazole(CDI)method,and PLA composite(PLA/AHA-D)was prepared.The characterization results showed that the PLA’s mechanical properties,heat resistance,nucleation density and stiffness had been significantly increased,and the crystallinity increased from 4.19% to 25.67% with the addition of the nucleating agent AHA-D.The non-isothermal crystallization kinetics of PLA composites showed that there were differences in crystallization behavior of PLA materials at different cooling rates,and the crystallization rate of PLA/AHA-D composites was increased.(3)Finally,the antibacterial properties of AHA-A and AHA-D and the degradation performance of PLA/AHA-A and PLA/AHA-D composites under different media were tested,which showed that the modified humic acid had inhibitory effects on Penicillium,Aspergillus niger,Escherichia coli and Bacillus subtilis.The inhibitory effect of the modified humic acid on the bacteria was stronger than that of molds with the value of the inhibition zone and the minimum inhibitory concentration.The degradation performance test results showed that the addition of nucleating agents could promote the degradation of PLA materials,and the degradability of PLA was particularly evident in the UV and alkaline(p H = 12)medium.