Preparation And Applications Of Citrate Chitosan Composite Films

According to the relevant policies issued by National Development and Reform Commission,the use of non-degradable petroleum-based plastics will gradually decrease from 2022,and biomass resources are the top priority to achieve sustainable development.Chitosan is a promising marine resource,and chitosan-based films have a host of advantages compared to other polymer films.But chitosan is essentially hydrophilic,which led to the inferior mechanical properties and poor thermal stability of chitosan-based films,far from petroleum-based films.Therefore,improving the all-around performance of chitosan-based films has always been the research focus and difficulty.The purpose of the present work was to fabricate feasible chitosan(CS)composite films that were modified with physical filling and chemical cross-linked;the chitosan composite films were mainly incorporated with nano Na+-montmorillonite(MMT)and citric acid(CA).The effects on the performances and structure of the prepared films were evaluated comprehensively.Further,the films were applied to cherry tomatoes preservation.Firstly,the properties of water resistance(moisture content,solubility,swelling degree),tensile strength,and elongation at break were compared to analyze the influences of drying temperature,addition amount of CA,MMT and glycerin.The results demonstrated that the MCS/CA-c film performed well with the formation conditions that added 80%w/w CA,5%w/w MMT,0.25 mL/g glycerin,and dried in a ventilated oven 60℃ for 12 h.Secondly,based on the above conditions,light transmittance,Fourier transform infrared spectroscopy,X-ray diffraction,electron microscope,and thermogravimetric were carried out to explore the influence of the CA amount on properties and microstructure of the prepared films.The results revealed that,with the incorporation of CA,the film’s moisture content was lower,the solubility was high,the swelling degree reduced from 58%to 29%sharply;the light transmittance increased by 2 times;the tensile strength was lower;the elongation at break increased from 30%to 64%,almost 2 times of the original.When adding 70%-90%w/w of citric acid,citric acid played the role of plasticizer and crosslinker.The film’s internal structure was changed and the interaction was enhanced,which were helpful to the dispersion and compatibility of MMT,and electron microscopy analysis showed that there was still much improvement in compatibility.Besides,the peaks took place at a relatively higher temperature than that of original film when they reached the maximum degradation rate,suggesting thermal stability was reinforced with the addition of CA and MMT.The second and the third thermal degradation stage temperature had increased by 83℃ and 63℃,respectively,and the residual increased.The MCS/CA-c film was applied to extend cherry tomatoes’ shelf life,and the consequence showed that it maintained superior fresh-keeping indexes,weight loss rate was lower than that of the control group,and the contents kept at a higher level in the soluble solids,titratable acid,and ascorbic acid.Finally,curcumin(CUR)was added to modify the film further.When the amount of CUR was in the range of 0.5%-2%w/w,the film MCA/CUR0.5 with 0.5%w/w CUR addition showed more improvement.With the addition of CUR,the film’s water-resistance slightly dropped;the light transmittance was increased by 15%continually;and the enormous tensile strength was increased by 44.4%.The physical interaction formed between CUR and CS molecules,film’s structure was undermined,the hydrogen bond became weakened,the crystalline decreased;and the thermal stability became worse with temperature on the third stage reduced by 14℃.However,the compatibility was much improved on the surface.Cherry tomatoes were preserved by coating film-forming solution with 0.5%w/w CUR addition or wrapping MCA/CUR0.5 film,it worked in freshness with these two methods,and they were better than the control group.This study provides a reference to use chitosan,the citric acid chitosan composite film’s performance has been improved,and has the potential in fruit and vegetable packaging applications.