Study On The Synthesis And Properties Of Waterborne Polyurethane Based On Novel Chain Extenders With Several Sulfonic Groups

At present,the increasing global environmental protection requirements have greatly promoted the global industry to move towards green direction.Waterborne materials have become the "darling" of all industries,which has become the mainstream of global industrial development.In recent years,under the guidance of national support and policy,the waterborne polyurethane(WPU)with environmental safety and low emissions of VOCs has been developed rapidly.As compared with the traditional solvent-based polyurethane(PU),however,the problems of water resistance and long curing time,as a result of the introduction of hydrophilic ionic groups and low solid content respectively,are still greatly restrict the application of WPU in our country.Currently,sulfonate chain extender is an important means to improve the emulsifying property of WPU,but sulfonate chain extender used in the market and reported only contains one sulfonic acid group.Increasing the amount of the chain extender to improve the emulsification property of polyurethane will inevitably reduce the water resistance of the material.To solve these problems,a class of novel secondary amine chain extender with several sulfonic groups is proposed in this project.The multiple ionic groups can improve the charge density of chain extender,which can enhance the ion strength of chain extenders and regulate the distribution of ionic charge and the proportion of hydrophilic chain segment on the PU molecular chain.Firstly,secondary amine chain extenders containing two or four sulfonic acid ions were obtained through aldimine condensation and reduction reaction based on fatty diamine with different carbon chain length and benzaldehyde-2-sulfonate or benzaldehyde-2,4-disulfonate sodium.WPU was prepared by hydrophilic monomer chain extension method,which was confirmed by NMR and FT-IR.The emulsification test showed that the minimum content of chain extender required for effective emulsification of WPU prepared from the chain extender with four sulfonic acid groups was much lower than that of WPU prepared from the chain extender with two sulfonic acid groups.On this basis,the effects of the number of ions,the length of carbon chain and the amount of chain extender on the Emulsifying properties,mechanical properties,thermal property and water resistance of WPU were further discussed.The results show that under the same type of chain extender,with the increase of chain extender content,the emulsion stability,mechanical properties and heat resistance of WPU are improved,but the water resistance and crystallinity of WPU are gradually weakened.With the same content of chain extender,the crystallinity and emulsion stability of WPU decreased and the elongation at break increased with the increase of the length of fatty diamine carbon chain.With the same number of ionic groups,WPU prepared with four sulfonate ions has improved emulsion stability,mechanical properties,heat resistance and crystallization properties,but decreased water resistance.With the same content of chain extender,WPU prepared with four sulfonic acid ions showed better performance in heat resistance,mechanical properties,emulsion stability,water resistance and crystallinization than that prepared with two sulfonic acid ions.Secondly,using the synergistic action of ionic groups and non-ionic ether chain fragments reported in the literature,another class of sulfonate chain extender was synthesized based on ether diamine,which further reducing the minimum amount of chain extender required for WPU emulsification.WPU was also prepared by the hydrophilic monomer chain extension method,and the effects of the number of ions and the amount of chain extender on the emulsifying properties,mechanical properties,thermal property and water resistance of WPU were further discussed.The results show that in terms of the influence of the number of ions and the amount of chain extender on the emulsification property,mechanical property,thermal property and water resistance of WPU,sulfonate chain extender prepared from ether diamine shows a similar trend to that prepared from fatty diamine.However,the level of thermal resistance and mechanical properties of WPU prepared from ether diamine is slightly lower than that prepared from fatty diamine.