Preparation And Properties Of Photothermal Initiation Self-Healing Waterborne Polyurethane

Waterborne polyurethane has the advantages of traditional solvent polyurethane,non-toxic and environmental protection.However,after long-term use,these materials are prone to generate imperceptible cracks under the environment,load,friction and other factors,which affects the integrity of the material matrix and ultimately leads to potential safety hazards.The concept of self-healing in nature provides a good solution for crack repair.Due to the low energy of the disulfide bond,mild reaction conditions and the possibility of reversible exchange dynamic equilibrium reaction,the materials can achieve good self repair.At the same time,the waterborne polyurethane modified by polyacrylate can form an environment-friendly acrylate polyurethane with low cost and high solid content,achieving the effect of complementary advantages.Therefore,this paper selects polyacrylate to modify waterborne polyurethane,and introduces disulfide bond to prepare a composite material with excellent comprehensive performance and self-healing ability.The detailed research contents are as follows:Firstly,a series of heat-initiated self-healing waterborne polyurethane/polyacrylate composites(SWPUA)with different HEDS content on the main chain were synthesized from isophorone diisocyanate,dimethylol propionic acid,polyether diol and di-(2-hydroxyethyl)disulfide(HEDS),and their structures were characterized.The effects of different HEDS content on the dispersion stability,mechanical properties and self-healing properties(including tensile strength and elongation at break)of SWPUA were studied.The results show that the prepared SWPUA has excellent dispersion stability,thermal stability,self-healing efficiency and certain hydrophobicity.Among them,SWPUA-1 and SWPUA-2 products with HEDS content of 0.0025 mol and 0.0050 mol have the best repair efficiency.They can recover 101.03% and 102.18% respectively after3 hours of repair at 75℃.Due to the influence of physical entanglement and chain link,SWPUA-1 has the highest repeated repair efficiency.At the same time,the addition of polyacrylate makes SWPUA-1 film show good hydrophobic property,which provides a good comprehensive guarantee for its use,storage or application.Secondly,this chapter continued to explore the effects of different kinds of hard and soft segment materials on the repair performance and comprehensive performance of heat-initiated self-healing waterborne polyurethane.In different hard segment experiments,because HDI is linear symmetric structure,the molecules are prone to roll in,and HMDI is six membered ring symmetric structure,which is relatively rigid,so that IPDI isocyanates can not be gathered well and block the movement of the chain segment,making the thermal stability and repair efficiency of HDI and HMDI doped films decreased compared with SWPUA-1,and their tensile strength repair efficiency is 94.58% and 91.69%respectively.In different soft segment experiments,it is found that the thermal stability and repair efficiency of all samples are also reduced compared with SWPUA-1.Because the polarity of polyester polyol is higher than that of polyether polyol,the repair efficiency of polyether diols with the same molecular weight is higher,so SWPUA-1 film shows good comprehensive performance and self-healing ability.In order to further improve the low temperature positioning repair ability of self-healing waterborne polyurethane,reduce the material aging phenomenon caused by high temperature,polypyrrole nanoparticles(PPy)were used as a photothermal conversion agent and mixed with SWPUA-1 emulsion to prepare uniform waterborne polyurethane/polypyrrole nano composite material(SWPUA/PPy).The effects of different PPy content on thermal stability,mechanical properties and repair effects of SWPUA/PPy nanocomposites were studied by converting light energy into heat energy to achieve remote designated area repair.The data show that the addition of PPy has little effect on the chemical structure of SWPUA-1,and a small amount of PPy can improve the thermal stability of the material in low temperature regions.For SWPUA/PPy samples,the mechanical properties increase significantly,and the repair efficiency increases first and then decreases with the increase of PPy content.Among them,SWPUA/PPy-2 shows the best self-healing performance,with the tensile strength self-healing rates of 86.98% and89.25% respectively after 30 and 40 minutes of repair.