The Development Of The Structure And Dynamic Viscoelastic Properties Of Natural Rubber Vulcanizates During Dynamic Fatigue And Hot Air Aging

The development of the structure and dynamic viscoelastic properties of the unfilled Natural Rubber （NR） vulcanizates, the NR vulcanizates filled with varying contents of carbon black and silica during dynamic fatigue and hot air aging were investigated by magnetic resonance crosslink density spectrometer （MR-CDS）, FTIR-ATR, dynamic mechanical analysis （DMA）, atomic force microscope （AFM） and scanning electron microscope （SEM）. The results showed that:The FTIR-ATR spectra of the unfilled NR vulcanizate changed obviously before and after tensile fatigue, the height of the peak at 1598 cm^-1, 1414 cm^-1, 1017 cm^-1 increased apparently with the fatigue time, Initial analysis suggested that diene and triene conjugation were formed; the AFM results showed that the surfaced roughness of the fatigued sample increased, the SEM photo of the fatigue surface showed that micropore with diameter of 10-100 nanometers were formed; on the DMA curve, the storage modulus E’ in the high elasticity region decreased apparently, tanδincreased obviously. After hot air aging, the crosslinking density of the unfilled NR vulcanizate decreased obviously with the aging time, the E’ in high elasticity region decreased relatively high, the tanδshowed greatest increase after aged by 72 h.For carbon black filled NR vulcanizate, the tensile strength decreased obviously; on the DMA curve, the peak value of tanδincreased, in the high elasticity region, the E’ decreased obviously, but change of the tanδwas minors; the AFM results showed that the fatigued sample had raised and hollow surface; the SEM photo of the fatigue surface showed that micropore with diameter of 10-100 nanometers were formed. After hot air aging, the peak of the tanδmoved to higher temperature, the tanδin high elasticity region increased obviously, the E’ decreased apparently at the latter stage of aging.For silica filled NR vulcanizate, the tensile strength of the specimen after fatigue decreased obviously; in the FTIR-ATR spectra the height of the peak at 1598 cm^-1 increased apparently, that showed that diene conjugation structure was formed in the fatigued sample; the peak value of tanδincreased, the E’ in the high elasticity region decreased obviously, tanδin the high elasticity region increased. After hot air aging, on the FTIR-ATR spectra, the peak at 2848 cm^-1 and 2916 cm^-1 decreased gradually, the peak at 1712 cm^-1 increased apparently, which indicated that the amount of methylene decreased and C=O group was formed; on DMA curve, the peak value of tanδdecreased, the peak temperature move to higher temperature, the tanδ, E’ and E" in high elasticity region increased.The tensile fatigue and hot air aging showed different influence on the tensile properties, crosslinking density and dynamic viscoelastic properties of the unfilled and filled NR with and without anti-aging agent 4020, but the dynamic viscoelastic properties of them changed apparently. Generally, the addition of the 4020 improved the anti-dynamic fatigue and anti-hot air aging properties of the unfilled and filler filled NR vulcanizate, but this protection effect of 4020 was only on the early stage of the aging or fatigue, and the anti-dynamic fatigue effect of 4020 was better than anti-hot air aging effect.