The Thermo-oxidizing Aging Study On Natural Rubber Vulcanizate

With the development of spaceflight and aviation project, the higher storage reliability of vulcanizate was required. At present, the important task is exploring aging rule and mechanism, and seeking the life estimation and calculation method. In this paper, research object is NR vulcanizate which is a key part of missile engine flexible joint, and the structural reliability of engine is directly related to its adaptability to environment and storage life. So evaluating the properties of NR vulcanizate, especially researching the aging of NR, is very important. The aging mechanism, crosslink structure and mechanical properties of NR vulcanizate was investigated systemically by using heat air-oven method, the thermal analysis, FTIR and pyrolysis gas chromatograph-mass spectra (PGC-MS). It is the first time to predict their storage life.In this paper, the crosslink structure and mechanical properties of aged NR vulcanizate were researched firstly. The results show: At the initial stage of aging, compression permanent distortion, tensile stress, crosslink density and hardness increased, while resilience rebound, tensile strength and elongation at break decreased;With the aging time increasing, degradation effect became more superior, mechanical property and crosslink density decreased, while Compression permanent distortion increased.The dynamic mechanical properties of NR vulcanizate were also investigated: With the aging time increasing, lower loss storage modulus, higher loss modulus and tangent(tanδ) can be observed from the experimental result at 160℃(DMA experimental temperature),while storage modulus and loss modulus increased, the change of tan8 has no rule at 150℃.Some pyrolysis mechanism of NR was proposed that the main chain with double bond was cracked at first, which led to a series of chain reaction, and the products are polyisoprene monomer, 1,4-methyl-4-ethylene hexamethylene and some fragments.From the evaluation results, it is achieved that the storage life of missile engine which uses NR rubber vulcanizate can be fast worked out by using the hot accelerated age test. And by the comparing the result of calculation with thermo-gravimetricanalysis, it is proved that the evaluation results coming from accelerated age test is more reliable. Finally, we can make such a conclusion that the twelve year life of missile engine is feasible.From the research, the aging mechanism of natural rubber vulcanizate that is used in missile engine was found out, and achieved the life estimation and calculation method. What is more, provide the test data for the storage life, using life and reliability of missile system. All of these can be the theoretical basis of another material storage life research.