| In modern society, humans are still troubled by a lot of serious problems such as environment pollution, global warming, energy shortage, desertification and etc. As the issue of environmental protection has received considerable concern, people have gradually realized the harms the solvent materials have done to the environment. The governments of various states have also paid much attention to this issue. Therefore, a more environmental-friendly solvent material has been created--Waterborne polyurethane (WPU). It is a new polyurethane system in which solvent is replaced by water, with the characteristics of environment protection, non-pollution, safety and excellent mechanical performance.At present, waterborne polyurethane dispersion is mostly synthesized by prepolymer dispersion process. Specifically, creating the polyurethane prepolyme with hydrophilic groups and then dispersing it in water. In this condition, using highly active polyamine chain extender to further extends water dispersible polyurethane which has already obtained high molecular weight. However, the chemical reaction is very complex for the chain extension happened under dispersed condition where water and polyamine chain extender react together. Therefore, the whole reaction system is in a dispersed condition. So far, little is known about how to study chain extension effectively. Research on prepolymer dispersed extender chain reaction is still in the blank stage. Therefore, in order to fill in the gap, our present study pioneered a quantitative determination method to measure waterborne polyurethane end amino. We adopted ninhydrin to colorate aqueous polyurethane. Next, the features of the dyed samples had been measured with visible absorption spectrum. At last, we acquired the residual data of aqueous polyurethane, and then analyzed the data quantitatively. (1) Research on the reaction conditions of water-soluble ninhydrin and amine and the measurement of working curveNinhydrin is a kind of reagent which is used for the quantitative determination of amino acids. It is also applied in criminal investigation to colorate fingerprint at the crime scene because of its sensitiveness to color. Besides, ninhydrin can be used in primary amine chromogenic reaction. The reaction product is a kind of violet compounds, with the visible absorption characteristic peaks at560nm.The present chapter mainly explored whether ninhydrin reacts with amine. If so, what are the reaction temperature, time, and dosage? When ninhydrin reacted with diamine, a blue color appeared immediately. Gradually, the whole solution turned into blue, which demonstrated that our hypothesis is feasible; we mixed ninhydrin with polyurethane emulsion, stirring them slowly with no heat, then part of the emulsion become blue. When heated slightly, the process speeded up. It showed that it is applicable to study how ninhydrin reacts on end group. The procedures were as follows:put diamine and ninhydrin together at90℃ for an hour. Use UV-vis ultraviolet visible photometer to test the reaction solution. Absorption peak appeared at about560nm which indicated that the experiment succeeded.The results revealed that ninhydrin can react with amine. With the help of UV vis ultraviolet visible photometer, the absorption peak appears at560nm. At a certain temperature, the same samples of two gram resin added with different amount of diamine, after joining about0.3grams of ninhydrin, the peak of dyed samples leveled off. Therefore, it is optimal to have0.3grams of ninhydrin when the sample amount is0.2grams. We used the same amount of2grams of resin and0.3grams of ninhydrin to make the dyed samples at different temperatures respectively:70℃、75℃、80℃、85℃、90℃. With the help of UV-vis ultraviolet visible photometer, the peak of ultraviolet visible spectrum basically leveled off when the temperature was higher than80℃. Therefore, the optimal reaction temperature of ninhydrin and resin is80℃-85℃; we used the same amount of2grams of resin and0.3grams of ninhydrin to make the dyed samples with different reaction time:5min、1Omin、15min、20min、25min、30minn、35min、40min. With the help of UV-vis ultraviolet visible photometer, the peaks leveled off when the reaction time was more than30min. The experiment showed that sample mass ratio of ninhydrin and resin is20:3, reaction temperature is80℃-85℃, reaction time is30min. Working curve determines whether we can do the quantitative analysis. Therefore, we used hexamethylendiamine to make the curve. With the completion of the working curve, it proves that quantitative analysis is feasible.(2) Research on the reaction of water and diamine chain extensionTo synthesize waterborne polyurethane, first we had polyisocyanate and polymer polybasic alcohol reacting with each other to form polyurethane prepolymer which acquired low molecular weight during this phase. Next, chain extension should be used here to increase the molecular weight of polyurethane. At this stage, the distinctions of reaction activity should be taken into account. Therefore, chain extension mainly used small molecule dihydric alcohol such as ethylene glycol,1,4-butanediol, diethylene glycol, propylene glycol. We chose different diol small molecule according to different nature of the materials. At present, the synthesis of polyurethane generally adopts the method of prepolymer dispersion, which requires a second time of chain extension. During this process, ethidene diamine, butanediamine, hexamethylendiamine, cyclohexanol dimethylamine were chosen. And the present chapter mainly focuses on the efficiency of diamine extender chain during the second time.In the present experiment, the first step was to synthesize a series of sample emulsions by adding different diamine into the initial synthesis during the process of post emulsification. Next, add ninhydrin to react with the above emulsion to colorate them. And then use UV-vis ultraviolet visible photometer to measure the Uv-vis absorption peak of the dyed samples. The current chapter aims to investigate the chain extension efficiency of water, ethylenediamine, butanediamine, hexamethylenediamine and cyclohexanol dimethylamine.Added some PTMG to a500ml three-necked flask, and adjusted the infrared lamp to heat it to90℃. After30minutes dehydration, the temperature felled to75℃. Then added a certain amount of HDI, controlling the reaction temperature to85℃.After two hours, when the temperature felled to75℃, added DMPA, TEG and acetone. At this moment, the temperature should be heated up to85℃. After reacting for an hour, when the temperature felled to75℃, added acetone and a certain amount of catalyst. After three hours’reaction, added a certain amount of acetone, waiting for the temperature dropped to the dispersion temperature. Put the prepolymer into scattered barrels, and added neutralizing agent-triethylamine and used water dispersion to form aqueous polyurethane dispersion. All the dispersed water in the current experiment was kept to0℃. Triethylamine thinning water was kept to0℃. According to the needs of the experiment, at last we added a certain amount of post chain extender to get the final product.The result indicated that we could do the chain extension of water with waterborne polyurethane polymer dispersion. Through measuring the visible light absorption of the dyed aqueous polyurethane dispersions end amino, amounts of end amino formed by water chain extension could be seen on the ultraviolet visible spectrum. However, the efficiency of the chain extension was poor. Interestingly, we found an unusual phenomenon that water chain extension could be very efficient when the reaction was carried out at a lower temperature of10℃-20℃or at a higher temperature of40℃-50℃. At a medium temperature of20℃-30℃, it had the lowest efficiency. We had repeated the experiments several times to test such unusual phenomenon but with the same result. Besides, with the same dosage of different diamines, the effect of ethidene diamine was the best in the chain extension, while the efficiency of butanediamine and hexamethylenediamine were the lowest.(3) Research on the efficiency of diamine chain extension and the effect of particle size on the chain extensionThis chapter mainly investigated the chain extension efficiency of ethidene diamine, butanediamine, hexamethylenediamine and cyclohexanol dimethylamine. At the meanwhile, the present chapter also explored whether temperature would affect the efficiency of chain extension when the dosage of diamine accounted for20%.40%、60%.80%、100%of the theoretical amount respectively.This chapter revealed that at different temperature, there were amino appearing on the end group of ethidene diamine, butanediamine, hexamethylenediamine and cyclohexanol dimethylamine. But the number of amino was lower compared with water chain extension. It showed that the efficiency of diamine chain extension was higher than that of water. In addition, we discovered a similar phenomenon that diamine chain extension had a high efficiency at a lower temperature of10℃-20℃or at a higher temperature of40℃-50℃. We had repeated the experiments several times but with the same findings. All the experiments reached the same result that chain extension efficiency was the highest when the dosage of post chain extender accounted for40%of the theoretical amount. |
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