Preparation And Performance Study Of PLA Based Antibacterial Materials

In recent years,as environmental pollution has become more prominent and people’s demand for food quality has increased,the development of biodegradable functional packaging materials has gradually become a trend in the food packaging industry.In this thesis,a fully biodegradable material,polylactic acid,was used as the substrate to prepare films with antioxidant or antibacterial properties,and the main research is divided into three parts.Firstly,seven PLA-based composite films were prepared by blending tea polyphenol(TP),tributyl acetyl citrate(ATBC)and poly(lactic acid)(PLA).Fourier transform infrared spectroscopy(FTIR)and scanning electron microscopy(SEM)test results showed that PLA,ATBC and TP were well compatible due to the presence of hydrogen bonds.Differential scanning calorimetry(DSC)results show that the addition of ATBC and TP reduces the crystallization temperature of PLA and increases the crystallinity of PLA.The mechanical properties tests showed that TP and ATBC toughened the PLA,and the addition of TP reduced the hydrophobicity of PLA/ATBC and weakened the water vapor barrier property of the composite films.In addition,the PLA film was relatively transparent,but the addition of ATBC tended towards a light yellow color and the addition of TP changed the color to red.With the addition of TP,the DPPH radical scavenging rate and the inhibition of S.aureus were improved.The overall migration test results showed that the overall migration increased with the addition of TP,but the overall migration results for all seven films were within the overall migration limit(10mg/dm~2),which were in line with the safety standards for food packaging materials.Secondly,to improve the mechanical properties and bacterial inhibition of the films,polylactic acid(PLA)and poly(butylene adipic acid/terephthalate)(PBAT)were used as substrates,and chitosan(CS),silver nanoparticles(Ag NPs),and zinc oxide nanoparticles(Zn ONPs)were used as substrates,respectively.Bacteriostats were blended with PLA and PBAT to prepare films,which were PLA/PBAT,PLA/PBAT/C1,PLA/PBAT/C3,PLA/PBAT/C5,PLA/PBAT/Z1,PLA/PBAT/Z2,PLA/PBAT/A1 and PLA/PBAT/A2.We investigated the effects of the bacteriostats on the FTIR,barrier properties,mechanical properties,chromaticity,transparency,bacterial inhibition and safety of the composite films.The results revealed that the addition of CS resulted in yellowing of the films,Ag NPs tilted the films towards black,and Zn ONPs possessed the effect of whitening the films.The FTIR results showed that no interaction occurred between the three bacteriostats and the PLA/PBAT substrate.The addition of all three inhibitors improved the oxygen barrier capacity of the films compared to the blank films,but the addition of Zn ONPs and Ag NPs increased the hydrophilicity of the films and reduced the elongation at break,while CS prevented crack extension in the blended films resulting in an increase in elongation at break.Bacterial inhibition results showed that the three bacteriostats were able to inhibit E.coli and S.aureus well,with Ag NPs being the most effective and chitosan being relatively weak.The overall migration test results showed that the films containing chitosan had higher overall migration in the 3%acetic acid food simulant and all films generally had higher overall migration in the 95%ethanol food simulant than the 10%ethanol food simulant.When the content of silver nanoparticles is high(PLA/PBAT/A2),there will be safety hazards.Finally,a bilayer biodegradable composite film was prepared to improve the barrier properties of the film.In this case,PLA/PBAT was the outer substrate and the inner barrier layer was a complex of three bacteriostats chitosan(CS),zinc oxide nanoparticles(Zn ONPs)or silver nanoparticles(Ag NPs)and sodium alginate(SA),which were laminated by starch adhesive to prepare a bilayer composite film PLA/PBAT/CS,PLA/PBAT/Zn ONPs,PLA/PBAT/Ag NPs.The FTIR,barrier properties,mechanical properties,UV absorbance and bacterial inhibitory properties of the bilayer composite films were investigated.It was found that the bacterial inhibitors in the composites did not generate new products with SA.UV absorption spectroscopy analysis revealed that the UV absorption peak of the PLA/PBAT/CS composite membrane appeared at 275nm,the absorption peak of the PLA/PBAT/Zn ONPs composite membrane was between 340-395,while the absorption peak of the PLA/PBAT/Ag NPs composite film was at 412nm.Compared to the PLA/PBAT membranes,the oxygen barrier and water vapor barrier of the bilayer composite membranes were improved,while the mechanical properties did not change significantly.In addition,the bilayers containing the three bacterial inhibitors were added to inhibit both E.coli and S.aureus.