Synthesis Of Chitosan Modified By Catechol And Multifunctional Flame Retardancy Of Poly (L-Lactic Acid)-Based Composite

While polymer materials bring us convenience,they also pose a challenge to the natural environment on which human beings depend for survival.Every year,the world produces tens of millions of tons of plastic waste that is difficult to decompose and putrefy,becoming an increasingly important constraint on urban and social development.Poly（Lactic Acid）（PLA）is a biomaterial with good biocompatibility and biodegradability from a wide range of biological sources.However,PLA is flammable and produces a large number of molten droplets during combustion,which easily causes secondary combustion and severely limits the application of PLA in automotive interiors,electronic devices,wires and cables.Halogen-containing flame retardants are commonly used in industry to enhance the flame retardant performance of PLA,but these flame retardants release toxic fumes and gases during combustion,causing great harm to human body and the environment,so bio-based environmental flame retardants have become the focus of attention in recent years.The most commonly used halogen-free flame retardant Ammonium Polyphosphate（APP）is biocompatible,although it can improve the flame retardant performance of PLA to a certain extent,its flame retardant performance still needs to be improved,and it is difficult to meet the public demand for multifunctional flame retardant products.In this paper,a modified chitosan was synthesized by grafting chitosan（CS）with 3,4-Dihydroxyhydrocinnamic Acid（HCA）,a biometabolic intermediate,and compounded with ammonium polyphosphate（APP）to prepare PLA-based flame retardant composites to study the synergistic flame retardant（C-CS/APP）on the thermal stability,combustion process and pyrolysis behavior,crystallization behavior,hydrophilic properties,bacterial inhibition and UV absorption of PLA,and further discussed the flame retardant mechanism.The main research results are as follows:The successful synthesis of flame retardant C-CS was verified by FTIR,XPS and WAXD analysis,and the surface morphology of C-CS was observed by SEM,which showed irregular smooth spherical shape;LOI,UL-94 and TGA test results showed that compared with pure PLA,the LOI of composite PLA/5%C-CS/10%APP was increased to 28.6%,with The results of CONE test showed that the p HRR of PLA/5%C-CS/10%APP was 309.5k W/m²,THR was 56.9MJ/m²,TSP was 6.5 m² and EHC was16MJ/Kg,which were all reduced to some extent compared with pure PLA.The residue after conical calorimetry can be found by SEM,EDS,FTIR and LRS spectra,the carbon layer of the residue after combustion of pure PLA is less graphitized,the surface is full of holes and brittle and thin,which is conducive to gas exchange between the material and the outside world to promote combustion;the surface of the residue after combustion of composite PLA/5%C-CS/10%APP is full of dense and compact phosphorus-rich carbon layer,which helps to isolate the material from heat exchange with the outside air and plays the role of cohesive phase flame retardant,and the graphitization degree is higher and the thermal stability is better.TG-IR and PY-GCMS tests showed that PLA composites produced non-combustible gases such as NH₃ and CO during the combustion process,diluting the concentration of combustible gases,while free radicals such as PO·and PO₂·could trap the more reactive H·radicals and HO·radicals during the combustion process occurring in PLA,thus interrupting the chain reaction and further inhibiting the pyrolysis of PLA composites and playing the role of gas-phase flame retardant.The DSC test showed that the addition of C-CS and APP to PLA can significantly shorten the crystallization time of PLA,reduce the glass transition temperature of PLA,and effectively improve the crystallization performance of PLA.The WCA test found that the addition of C-CS and APP to PLA can enhance the hydrophilic performance of PLA,and the improvement of hydrophilic performance of C-CS on PLA is better than that of APP.The antibacterial test found that An obvious antibacterial circle appeared around the composite PLA/5%C-CS/10%APP,indicating that C-CS can improve the antibacterial property of PLA.Finally,UV-vis test found that pure PLA has 96%light transmission at 400nm,while composite PLA/5%C-CS/10%APP has only 4%light transmission at 400nm,which has excellent UV resistance.