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The temperature index (TI) of epoxy resin based laminated sheet was studied using thermogravimetric point slope method (TPS). The main difference with standard JB/T 1544 is that a kinetic method is applied to describe the thermal gravimetric process and to calculate the activation energy. The final TI results comply with the insulation level of commercial laminated sheets under evaluation, indicating that this method can be used to study the TI of resin based laminated composites. However, its accuracy needs to be further studied. 1.Introduction The thermogravimetric point slope (TPS) method was established as a standard test procedure in China (JB/T 1544 [1]) for thermal endurance characterization of impregnated varnishes and coated fabrics. The main advantage of applying this method would be a remarkable reduction in the total testing time below that required by IEC 60216 [2]. Nowadays, its use has been extended to several other kinds of insulating materials as an alternative to the standard IEC 60216. Zhang Yingsuo [3] compared the reliability of conventional and rapid ageing methods based on the theoretical analysis test data and consider that the reliability of TPS may well be identical with, or even better than conventional ageing (CA) to determine the thermal endurance properties of insulating materials. Gian etc. [4] further discussed the limits of application and the interesting characteristics of the TPS method and suggested of rearrangement of categories of insulating materials used for TPS application, which could improve the estimates and accuracy of the thermal endurance indices. According to TPS, the whole test procedure for thermal endurance characterization shall consists of two parts: one is the realization of a thermal gravimetric (TG) test to determine the activation energy at a selected heating rate; the other is the realization of a conventional thermal endurance test at a temperature chosen in order that the time to the selected end point is large enough to ensure good accuracy for TI estimation, but not so large as in IEC 60216. That is, one TG analysis and one life test, with the total time in practice determined by the length of the life test. In this paper, the thermal endurance characterization was performed by TG tests at three or more rates of temperature rise and analyzed by kinetic methods [5] to get the activation energy, according to the relationship as below: ( ) α β α f e A dT d RT E / − = (1) Where E is the activation energy, R is the gas constant, α is a temperature function of conversion and β is the heating rate, equal to dT/dt. The TI of epoxy resin based laminated sheet was then calculated and discussed using the TPS method. 2.Experimental details 2.1 Materials Two kinds ofepoxy resin basedlaminated sheets reinforced by glass fiber cloth were tested and discussed. The detail information can be seen in Table 1. International Conference on Automation, Mechanical Control and Computational Engineering (AMCCE 2015) © 2015. The authors Published by Atlantis Press 404 Table 1: Materials Supplier Material Insulation level Shanghai Electrical Insulation Material Co., Ltd 1 # H Sichuan EM Technology Co., Ltd 2 2.2 Thermogravimetric Analysis (TGA) TG measurements of fiberglass laminated sheet samples were performed using a TA Q-50 thermogravimetric analyzer at different heating rates of 5, 10 and 20oC/min. The laminate samples were crushed into powder then screened with 100 mesh standard sieve before test as in accordance with JB/T 1544-1999 [1]. 2.3 Mechanical Properties The bending strength was chosen as the diagnostic property. Sufficient samples with a size of 80 mm×10 mm×4 mm were put into ovens under selected ageing temperature, as shown in Fig.1a. At least 5 samples were taken out to test flexural strength at each timepoint until its value declined to 50% or even lower, as shown in Fig.1b. The bending test was performed according to GB/T 9341 [6] by Electronic universal materials testing machine (Shimadzu, AG-X) with a testing speed of 2 mm/min. The length of span between supports is 64 mm and the radius of the loading edge is (5±0.2) mm. For the initial value, at least 10 specimens were tested to get an average value. Fig.1 a) Aging oven; b) Flexural test 3.Results and Discussion 3.1 Apparent Active Energy (E). The Kissinger method [7], which is based on the following equation was applied to calculate the apparent active energy: ) /( ) / ln( ) / ln( max 2 max RT E E AR T − = β (2)

Rapid evaluation on temperature index of epoxy resin based laminated sheet using thermogravimetric point slope method