Research On Preparation And Properties Of Ecological Self-healing Nanocomposites

Self-healing polymers and their composite materials,as a member of new intelligent materials,have become one of the research hot spots in this field.The self-healing materials consist of extrinsic self-healing material and intrinsic self-healing material.And,,extrinsic self-healing materials mainly use non-reversible dynamic covalent bonds to form self-healing functions,the number of self-healing is limited,and the preparation process is complicated,resulting in limited development.However,another material,the intrinsic self-healing material,can be indefinitely healed with multiple heal capabilities in theory,promoting it to become a focus of related researchers.Therefore,in this dissertation,it is of a great significance to explore this type of self-healing material.In view of the intrinsic self-healing polymer,considering that its reversible dynamic covalent bond has a higher bond energy than the non-reversible dynamic covalent bond,so it is beneficial to introduce into the polymer,which can bring higher mechanical properties to the polymers.In this thesis,polylactic acid/cellulose nanofilament(PLEG-FA-CNFM)composite materials with reversible dynamic covalent bonds were prepared by(Diels-Alder)crosslinking nanocellulose with lactic acid-ethylene glycol copolymer,and the structure and properties of polylactic acid/nanocellulose composite was studied;at the same time,based on the plasticity of the polycarbonate polyurethane structure,a polyurethane/nanocellulose composite with self-healing room temperature and good mechanical properties was prepared,and its structure and performance and heal mechanism was studied.First,using plant fibers as raw materials,using physical and chemical methods to prepare cellulose nanofilament(CNF).FTIR,XRD,SEM,TG,etc.were used to characterize the structure of cellulose nanofilament.XRD test showed that:some cellulose I in BAM-CNF,BAG-CNF and EUC-CNF were converted into cellulose II,and the relative crystallinity of EUC-CNF,BAG-CNF and BAM-CNF were 64.3%,58.2%and 61.3%.SEM shows that nano-cellulose with higher length of BAG-CNF and BAM-CNF makes the former two more flexible than EUC-CNF short fiber cellulose.Thermogravimetric tests show that the initial decomposition temperature of BAG-CNF is 252°C,which is higher than that of BAM-CNF and EUC-CNF;and that the content of cellulose II in BAG-CNF is higher,which results in the lowest thermal decomposition residue(19.9%);Therefore,BAG-CNF has better thermal stability.Secondly,the(Diels-Alder)bond is used as a cross-linking point,and lactic acid-ethylene glycol copolymer(PLEG)and nanocellulose are cross-linked together to produce a PLEG-FA-CNFM composite material with a network structure.GPC,FTIR,DSC,POM,tensile and swelling experiment tests are used to characterize the structure and performance of the composite.For the polylactic acid-based Diels-Alder bond cross-linked nanocellulose composite material,GPC test showed that the material has a number average molecular weight Mn=3200 and a molecular weight distribution index PD=1.49.DSC test results show that the material has a glass transition temperature of 20.5°C and a high elasticity at room temperature.An exothermic peak appears at 43.6°C to 60.3°C and DA reaction occurs:PLEG-FA-CNFM composite material is at 80.4?to 109.3°C;the swelling experiment shows that the PLEG-FA-CNFM composite only swells and does not dissolve in the DMF solvent at 60°C,while at 100°C,the PLEG-FA-CNFM composite can be completely dissolved in the solvent.The tensile test shows that the maximum tensile strength of the composite material after healing at 100?for 24h is 8.63MPa,and the maximum self-heal efficiency of the maximum tensile strength is as high as 92.4%,and the composite material has multiple heal capabilities,and its secondary healing efficiency is 63.5%.Third,this topic innovatively uses disulfide bond-containing alcohol as a chain extender to prepare the IPPC-HDS/CNF polyurethane elastomer;by infrared characterization,by observation It can be found that the intensity of the corresponding-NCO absorption peak at 2272cm^-1of IPPC,IPPC-HDS,IPPC-HDS/CNF and other substances is continuously weakening,indicating that IPPC-HDS,IPPC-HDS/CNF and other substances have been successfully synthesized,indicating that IPPC-HDS,IPPC-HDS/CNF and other substances were successfully synthesized.The elastomer exhibits tough characteristics at room temperature,with a maximum tensile strength of 16.5 MPa and an elongation at break is 861%;and after the specimen is healed at room temperature for 24 hours after cutting,the tensile strength and self-heaed The efficiency can be restored to 8.4MPa and 51.1%respectively,showing a certain room temperature self-healing ability.Through POM observation,it was found that the cracks of IPPC-HDS/CNF elastomer basically disappeared after being kept at 60?for 24 hours.And through the tensile test,the maximum tensile strength of the IPPC-HDS/CNF elastomer after healing at 60?for 24h is 15.4MPa,and the maximum self-healing of the maximum tensile strength is as high as 93.3%.At the same time,the elastomer has many times healed capacity,the secondary heal efficiency is 63.7%.