Thermal Analysis Quickly Assesses The Useful Life Of Food Contact Materials

Food contact materials that were common in life can be aging for a long time.This would not only affect their normal use,but also caused some harmful substances in the process of aging.My study selected the three common food contact materials which was PP microwave oven special food bowl,PET mineral water bottles,roasted mat silicone rubber for its thermal oxygen aging life assessment and thermal oxygen degradation kinetics parameters by DSC and TG method.Specific experimental content was as follows:（1）The accelerated aging experiment of polypropylene was carried out by TGA to measure the relationship between weight loss rate and time of polypropylene under constant temperature.Polypropylene’s using life was evaluated about 24.6 thousand times.DSC accelerated aging test to determine the relationship between the aging time and the oxidation induction period,it is presumed that the number of polypropylene meal boxes used in the microwave oven was about 6,000 times.Compared with the traditional methods of accelerating the aging of the thermal oxygen,the use of polypropylene in the microwave oven was estimated to be about 1.28 thousand times（2）Comparison of three methods of life evaluation of polypropylene: The life measured by the accelerated aging test of DSC was actually life for the antioxidants consumed in the material.the minimum measured life.The life time measured by the hot air aging method was the time experienced when a material’s performance drops to 50%,measured life center.TGA accelerated aging test,the measured life was the overall degradation loss of 5% of the life of the material,the longest life measurement.（3）The accelerated aging experiments of silicone rubber were carried out by TGA,and the relationship between the weight loss rate and time of silicone rubber under constant temperature was measured.The Arrhenius equation was used to estimate the number of silicon rubber used in the oven was about 1.66 thousand times.（4）The aging experiment of PET was carried out by TGA.It is estimated that the life expectancy at normal temperature is about 4.3× 109 years.PET has been tested for the traditional physical properties of thermal air aging and the life of PET bottles was assumed about 22.6 years.The results of the two experiments were very different.The TGA accelerated aging method is used to test the degradation of the polymer chain structure under high temperature and thermal oxygen conditions,and PET physical performance in normal temperature was affected by the molecular chain of degradation,in addition,the influence of factors such as the change of the crystal morphology is very big,so that the difference between two results is great.The results show that there are still many problems that need to be improved（5）According to the principle of thermal analysis,The kinetic parameters of thermal decomposition were measured through Freeman-Carroll method and Kissinger method by thermal analysis technique.The apparent activation energy of PP,silicone rubber and PET was 147.71,161.35,302.36 kJ?mol-1.The pre-exponential factor A was 7.98×10¹²,3.1×10¹²,4.2 ×1023min-1.The reaction order n was 1.5,0.5,0.5.This provided some theoretical support for the thermal stability of the materials and the mechanism of thermal aging.