| Nowadays, with the improvement of people’s living standard, there is an increasing demand of fruit, vegetable and frozen food. In order to reserve the original flavors and nutritive ingredients, these goods need to be kept in low temperature condition. Due to the lack of enough cold-chain capacity and the breakage of the cold-chain logistics of temperature-sensitive goods, the quality of these goods is seriously affected which may cause a threat to people’s health. To solve these problems, it is quite necessary to choose the moderate temperature controlled packaging which includes cool storage agents to make sure the required temperature that the goods need. The temperature controlled packaging consists of two important parts: insulating materials and cool storage agents. In order to maintain the moderate temperature of the insulating system, it is of great significance to choose the cool storage agents with moderate temperature and high latent heat which can extend the shelf life of goods and reduce the loss before consumption.According to the domestic and international research on phase change cool storage materials, sodium sulfate hydrated salt was chosen as the main energy storage. The sodium sulfate hydrated salt is cheap and abundant which has relatively high latent heat and high thermal conductivity. But it has great disadvantages, such as the serious problems of super cooling and phase segregation which limits the scope of its application. It is effective to diminish the super cooling and phase segregation by adding the moderate nucleating agents and thickening agents into the sodium sulfate hydrated salt.The high salt-tolerance super absorbent polymer was selected as the substrate of the cool storage agents, which could also act as the thickening agent of the sodium sulfate hydrated salt to diminish the phase segregation. The high salt-tolerance super absorbent polymer was synthesized by corn starch, acrylic acid and acrylamide. In the process of preparation, the water absorption and salt absorption were used as the evaluation index to make sure the influence of different factors. Through orthogonal test, a high salt-tolerance super absorbent polymer with the best proportion was prepared under the optimum reaction conditions, and the properties of the super absorbent polymer were characterized through a serious of detection. Besides, the degradation property of the super absorbent polymer was tested by using the mold-degradation method and the soil burial method. These two methods both showed that the super absorbent polymer was an environment-friendly material which had a good property of degradation.The sodium sulfate hydrated salt was chosen as the main energy storage. Besides, the borax was selected as the nucleating agent to diminish the super cooling of the system. At the same time, in order to get a neutral system, it was necessary to add boric acid as neutralizer. Then the high salt-tolerance super absorbent polymer and fumed silica were added as the thickening agents of the system. In order to get a moderate temperature, different proportion of potassium chloride and ammonium chloride were added as cooling agent. At last, the sodium hexametaphosphate was added into the system as the crystal habit modifier and the free water was used to increase the latent heat of the system. Finally, the phase change temperature of the system is 6.9℃, and the latent heat was between 120J/g and 130J/g.At the end, the amount of cool storage agents was calculated by the formula under different temperatures such as 22℃, 25℃, 30℃ and 35℃ for different storage time such as 12 h, 24 h and 48 h. Then by testing the real cooling time of the cool storage agents in 25℃, the paper verified the good cooling performance of the cool storage agents. Besides, the result of the experiment also showed the formula used in the paper could forecast the amount of cool storage agents for certain storage conditions. |
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