Study On Preparation And Mechanism Of Post-chain Extension Of Internal Crosslinking Waterborne Polyurethane Adhesive

Due to the events of poisonous plastic tracks, the non-toxic environment-friendly aspects for sports fields have drawn much attention, but the adhesives used in domestic plastic runway are mainly single component moisture-curing solvent-based polyurethane, which contain free TDI monomers and solvent hazards harmful to human health and environment. In consideration of waterborne polyurethane(WPU) with good adhesion to numerous substrates as the versatile eco-friendly materials, based on the structure -property relationship, a series of aromatic TDI-based waterborne polyurethane adhesives were prepared through select of raw materials and functional monomers, formulation design and synthesis process control, which met environmentally friendly, low-cost and high adhesion requirements for plastic tracks.Besides, the process mechanism of post-chain extension of WPU had also been studied.Internal crosslinking waterborne polyurethane emulsions were prepared using toluene diisocyanate (TDI), polyether diol, trimethylolpropane (TMP) and dimethylol propionic acid (DMPA) as the main raw materials, and then the effect of number of hydrophilic groups, degree of internal crosslinking , amount of solvent and catalyst used in the synthesis process, microphase separation and amount of curing agent on the properties of WPU emulsions and films had been fully studied through FT-IR infrared characterization, viscosity, water absorption and peel strength tests. The results show that with the increase of DMPA content, the water absorption of WPU films increase and the peel strength increases first and then basically keeps the same. When the content of TMP raises from 0.5 % to 2 %, the water absorption of WPU films decrease first and then increase, while the peel strength increases first and then decreases. With the augment of catalyst, the stability of WPU emulsions reduce, but the water absorption of WPU films keep reducing and the peel strength improves first but decreases later. As the amount of solvent increases, the stability of WPU emulsions increase, as well as the peel strength of the films. The increase of hard content doesn’t benefit the peel strength of WPU; Besides the addition of curing agent significantly enhances the adhesion strength of WPU. As Wt (DMPA) = 5 %, Wt (TMP) = 1 %, Wt (Catalyst) = 0.2 %, Wt(Solvent) = 30 %, and the dosage of curing agent with 2 % to 3 % as to the mass of WPU emulsion, the overall performance of the WPU is optimal.On the basis of the upper part , the process and mechanism of the post-chain extension of waterborne polyurethane with ethylene diamine (EDA) as the chain extender was investigated, which involved the factors of H2O, temperature of post-chain extension, molar ratio of -NCO/-OH and chain extension ratio. FT-IR results show the post-chain extension process of polyurethanes with EDA can be affected by H2O in aqueous dispersion through the competitive reactions of H2O and EDA with the residual groups of -NCO encamped in the polyurethane chains. Testing of the molecular weight of polyurethanes, the particle size and Zeta potential of polyurethane dispersions before or after the chain extension indicate that the chain extension by H2O results in the instability of polyurethane dispersions, and that H2O in aqueous dispersion has a significant influence on the post-chain extension process with EDA as the chain extender at the low chain extension ratio, while the molecular weight of the chain-extended polyurethanes lowers at the high ratio. In this process, with the chain extension temperature rising, the molecular weight of the polyurethanes chain-extended by EDA decrease, but the particle size increases. So when the molar ratio of -NCO/-OH is 1.20, the chain extension temperature is 30 ℃ and the chain extension ratio is 60 %,the impact of H2O on the post-chain extension of polyurethanes with EDA is reduced effectively.