Study On PBAT/modified Chitosan Flame Retardant Composite With Eco-friendliness And Multifunctions

In recent years,due to the large-scale production of plastic products,plastic pollution in the environment has become increasingly serious,and biodegradable materials have received widespread attention.Poly(butylene adipate-co-terephthalate)(PBAT),one of the most widely used environmentally friendly materials with good biodegradability and outstanding tensile performance,is a random copolymer which is composed of butylene adipate(PBA)and butylene terephthalate(PBT).It was documented that PBAT has been widely used in various fields,such as packaging and food preservation films.However,due to the following disadvantages,such as easy ignition,large amounts of molten droplets and toxic smoke during combustion,poor crystallizability,weak antibacterial performance and anti-UV property of pure PBAT,there are significant limitations in application.Therefore,it is necessary to modify PBAT.In response to the green environmental protection concept,biobased flame retardants have gained much attention in order to prepare environmentally friendly flame retardant materials in recent years.The chitosan(CS)is a crustaceans-derived antibacterial bio-based carbon-rich macromolecule.Large amount of hydroxyl-and amide-groups endow the CS with good hydrophilicity.3,4-dihydroxyphenylpropionic acid(HCA)is a natural metabolic intermediate substance extracted from Gynura Bicolor,and shows excellent reactivity(with hydroxyl-and carboxyl-rich groups)and UV resistance.In this thesis,a bioderived flame retardant C-CS was synthesized using the CS and HCA,and the PBAT/C-CS composites was prepared with a twin-screw extruder.The effects of C-CS on the thermal stability,combustion behavior,flame retardant properties,crystallization properties,antibacterial properties,UV absorption properties,and hydrophilicity of PBAT were analyzed by various characterization techniques,and the flame retardant mechanism was proposed and discussed in depth and thoroughly.The main experimental results are as follows:The composition and chemical structure of C-CS were analyzed using Fourier transform infrared spectroscopy(FTIR),X-ray photoelectron spectroscopy(XPS),and wide-angle X-ray diffraction(WAXD).It indicated that the C-CS was fabricated successfully.Scanning electron microscopy(SEM)results showed that the C-CS has a small block-like structure.Through various testing methods such as vertical combustion(UL-94),limiting oxygen index(LOI),CONE calorimetric test(CONE)and thermograys analysis(TGA),in-depth research has been conducted on the combustion characteristics,flame retardancy,and thermal stability of PBAT and its composite materials.It suggested that after adding 3%C-CS,the LOI of the PBAT/3%C-CS composite(PC3)materials increased by 7.30%,the UL-94 rating reached V-0.Its thermal stability increased and the residue amount at 800 ℃ increased by 30.80%.In CONE experiment,the peak heat release rate(p HRR)reduced by 39.80%,the total heat release rate(THR)decreased by 14.86%,and the total smoke release(TSP)declined by 6.80%.The residues generated after the CONE test were analyzed using SEM,energy dispersive spectroscopy(EDS),Fourier transform infrared spectroscopy(FTIR),and Raman spectroscopy(LRS).The results showed that the addition of C-CS significantly increased the char residue and improved the degree of graphitization.A continuous dense and stable char layer formed in the PBAT composite residue,serving as a physical barrier.The residual amount after combustion increased to5.44%,effectively preventing oxygen and heat from diffusing into the substrate.Among the PBAT-based composites,PC3 exhibited the best condensed phase flame retardant effect.The pyrolysis gas products were analyzed using thermogravimetric infrared(TG-IR)and pyrolysis gas chromatography/mass spectrometry(PY-GC/MS).It revealed that the C-CS reduced the amount of volatile gas products of PBAT composite materials.It is attributed to the decomposed N-containing non-combustible gas protective layer(such as ammonia,nitrogen),which significantly dilute the oxygen content and bring away the heat from the PBAT matrix.In addition,the nitrogen-containing free radicals and aromatic compounds generated during pyrolysis could capture the ·H,·OH,·O and other free radicals produced in the pyrolysis of PBAT,inhibiting the combustion process of the PBAT.The results of differential scanning calorimeter(DSC)showed that the C-CS significantly improved the crystallizability of the PBAT.The E.coli inoculation experiments indicated that the C-CS enhanced the antibacterial performance of the PBAT.UV-Vis spectroscopy analysis showed that the C-CS effectively improved the UV absorption performance of the PBAT.Water contact angle experiments showed that the addition of the C-CS helped to improve the hydrophilicity of the PBAT-based composite,and the higher the content of the C-CS,the higher the hydrophilicity.