Title:structural Analysis And Functionalization Of Waterborne Polyurethane Based On Waste Pet Depolymerization Products

Waterhorne polyurethane(WPU)materials have good resistance to high and to low temperatures,flexibility and processability,and are therefore widely used as packaging materials and sealing materials.As an important raw material for the synthesis of waterborne polyurethanes,chain extenders can improve WPU performance and achieve WPU functionalisation.Currently,chain expanders are generally used in petroleum-based chemicals.however,in recent years,energy consumption and environmental pollution caused by the use of fossil raw materials have become increasingly prominent,and the development of new alternatives to fossil raw materials is particularly important.On the other hand,the development of self-healing waterborne polyurethane(SHWPU)has become a hot topic of research as it may crack during use due to external physical damage,which in turn affects the aesthetics and performance of the material.To address these issues,this study utilises the depolymerisation products(GOPs)of waste polyethylene terephthalate(PET)as chain expanders instead of fossil raw materials to produce WPUs with excellent overall performance.On the other hand,the addition of dihydroxyethyl disulphide(HEDS)chain expanders introduces dynamic disulphide bonds in the main chain of WPUs,giving the material higher self-healing properties.The main work and results are as follows:(1)Waste-based WPU were prepared using GOPs containing terminal hydroxyl groups as chain extenders.The effects of the introduction of GOPs and the chain extender coefficient on the structure and properties of WPU were investigated.The results showed that under the influence of GOPs,the hard segments of WPU were enhanced and stronger intermolecular hydrogen bonding was formed;the thermal stability of the samples was improved,with the initial degradation temperature of the sample with a 40%chain expansion coefficient(WPU2)being 31℃ higher than that of the sample without the addition of GOPs(WPU0);the mechanical strength of WPU was improved,with the tensile strength(1.15 MPa)and elongation at break(597%)of WPU2 being 261%and 709%higher than that of WPU0,respectively;in terms of transparency,the maximum light transmission rate of WPU2 was 92%.(2)HEDS chain extender was added to functionalize WPU for self-healing.The effect of HEDS and its content on the structure,basic properties and healing performance of SHWPU was investigated.The results showed that the disulfide bond was successfully embedded in the main chain of WPU,the glass transition temperature(Tgs)of the soft segment of SHWPU samples was below-50℃,and the strong intermolecular hydrogen bonding and good mobility of the molecular chain provided the basis for the self-healing property of SHWPU.The healing rate of SHWPU was quantified by tensile test,and the results showed that the samples exhibited better healing performance after superimposed dynamic exchange of disulfide bonds,and the maximum strain healing rate and tensile strength healing rate were 82.57%and 93.72%,respectively;comparing the healing rates of HEDS samples with different healing times and contents,the results showed that the healing rate was positively correlated with the healing time and disulfide bond content.The results showed that the healing rate was positively correlated with the healing time and the disulfide bond content.(3)The prepared WPU and SHWPU have good flexibility and self-healing properties,so we used them as the substrate of the flexible strain sensor and used Pyrrole(PPy)as the conductive phase to prepare the gas-liquid interface PPy/WPU(PPyG-L/WPU)and solid-liquid interface PPy/WPU(PPyS-L/WPU)with good electrical properties by the cladding method and deposition method,and assembled the flexible strain sensor.Flexible strain sensors were assembled to investigate the practicality of aqueous polyurethane-based flexible strain sensors.The results show that the sensors have good dynamic response and signal stability,and the healed SHWPU-based flexible strain sensors also have good electrical conductivity and electrical signal monitoring performance,which demonstrates their potential application in the field of apparently tapped packaging.