| Nitrile butadiene rubber is a kind of material which has high elasticity and be widely used in a sealed, oil and other fields, but the aging of rubber is a widespread problem in storage and use processing of the rubber and rubber products. Layered double hydroxides (LDH) are typical layered double hydroxide anionic clay materials, having thermal stability, ion-exchange, the memory effect, flame resistance, which makes it an popular filler to preparerubber composites. It is critical, however, to improve the dispersion of LDH in rubber and to impact the aging properties ofrubber are still problems to be solved. Aiming to address these issues, this dissertation focuses on the functionalization of LDH, and studies on the mechanical properties and aging properties of NBR/LDH composites and explores the aging mechanism of NBR/LDH composites.The parent LDH with nitrate as counter anion (LDH-NO3) was prepared by a typical coprecipitation method. The pH, temperature, whether the absence of air and other conditionsof the reactionduring the preparationhave noticeable effects on the product. NBR/LDH-NO3 composites were prepared by two-roll mill mixing. SEM and mechanical property tests show that isolated microvoid around dispersed LDH are formed as a result of the energy absorbing process (similar crazing phenomenon) during tensile deformation. This leads to higher tensile strength and elongation at failure for NBR/LDH-NO3 before aging, compared to the unfilled NBR and NBR/LDH-SSS. Nevertheless, the LDH-NO3 compound can form aggregation easily when added into rubberexceed 7 phm. The ATR spectra of the NBR composites before and after aging are shown that the C=C content from 1.91 to 2.10 in LDH-NO3/NBR, the methylene remains almost unchanged (from 4.56 to 4.60), and the aging mechanism of NBR/LDH-NO3 composite is the favored crosslinking. When the cleavage occurs at the the methylene of the NBR main chain, C=C double bonds can be generated. Since LDH-NO3 can facilitate the crosslinking, C=C will be transformed to C-H. This balances the C=C and C-H content and consequently deteriorates the aging property, which ultimately makes the aging NBR/LDH-NO3 composites performance becomes poor, the retention rate of tensile strength of the after aging from 86.7%?to 67.0%?and the retention rate of elongation at failure of after aging from 60.2%to 46.4%.The LDH-SSS is prerared by ion exchange method with LDH-NO3 precursor and Sodium p-Styrenesulfonate Hydrate (SSS). X-ray diffraction, infrared spectroscopy and thermal gravimetric analysis tests showed the successful intercalation of SSS and LDH-SSS was obtained successfully. The LDH-SSS could better disperse into NBR and generate stronger interaction compare with LDH-NO3, because of SSS is organic. The ATR spectra of the NBR composites before and after aging are shown that the content of C=C in the LDH-SSS/NBR composite decreased from 4.97 to 3.94 after aging, where as the content of methylene increased from 3.73 to 5.49 after aging and the aging mechanism of NBR/LDH-SSS composite is the inhibit crosslinking. This might be related to the fact that LDH-SSS is a depressant for sulfur vulcanization and the crosslinking between C=C and LDH-SSS during aging of composites, which leads to tensile strength of the sample after aging is 1.3 times of that of the sample before aging, when the amount of LDH-SSS moderate is 7 phr.The LDH-SAS is prerared by ion exchange method with LDH-NO3 precursor and Sulfanilic Acid Sodium salt (SAS). X-ray diffraction, infrared spectroscopy and thermal gravimetric analysis tests showed the successful intercalation of SAS and LDH-SAS was obtained successfully. The aging rate of composites is delayed caused by LDH-SAS capture oxygen radicalsat the aging of composites and aging properties of the composites is improved from 85%?to 100%. |
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