Thermal oxidative aging of butadiene rubber and its mechanism

Butadiene rubber (also known as polybutadiene rubber) has the advantages of high elasticity, cold resistance, abrasion resistance, flexural resistance and good dynamic performance. It is currently mainly used in tires, shoemaking, high-impact polystyrene and ABS resins. Modification and other fields. There are unsaturated bonds in the structure of butadiene rubber. Under the conditions of hot oxygen or ultraviolet light, it is susceptible to the attack of oxygen free radicals, causing its composition and structure to be destroyed, thereby greatly reducing its performance. At present, most studies on the aging of butadiene rubber focus on the changes in physical and mechanical properties [5-7], and there is almost no research on the changes in the chemical structure of the aging process. In this paper, butadiene rubber is used as raw material to conduct thermal and oxygen aging research, using hydrogen nuclear magnetic resonance spectroscopy (1H-NMR), Fourier transform attenuated total reflection infrared spectroscopy (ATR-FT-IR), and ultraviolet-visible light (UV -Vis) absorption spectroscopy focuses on exploring its chemical structure changes and aging mechanism. So far, there have been no reports on the methods and results of using nuclear magnetic resonance spectroscopy to study the aging of butadiene rubber. This is of great significance for the development of new formulas and protective measures to improve the storage and service life of butadiene rubber. 1 Experimental part 1.1 Raw material butadiene rubber (BR≥98%): commercially available; Deuterated chloroform (CDCl3): D>99.8%, TMS 0.03%, Sigma-Aldrich; Cyclohexane: analytical pure, Xilong Science Co., Ltd. Limited company. 1.2 Experimental instruments Nuclear magnetic resonance spectrometer: Bruker Avance 400 MHz, Bruker, Germany; Infrared spectrometer: Nicolet iS10, Nicolet Instruments, USA; UV-Visible spectrophotometer: UV-2550, Shimadzu Corporation, Japan. 1.3 Sample preparation and aging test Sample preparation: Dissolve 3 g of butadiene rubber in a three-necked flask containing 30 g of cyclohexane, heat and stir at 80 ℃ for 2 hours to fully dissolve it, cool to room temperature, and drop it quantitatively. Make a thin film on a glass slide. Put it in a fume hood and wait until all the reagents evaporate. The film thickness is about 0.02 mm. Thermal oxidative aging: According to the national standard GB/T3512-2001 [8] (hot air accelerated aging and heat resistance test of vulcanized rubber or thermoplastic rubber), put the finished butadiene rubber film in an electric heating constant temperature blast drying box, and set the temperature It is 120 ℃, aging for 0.5 d, 1 d, 2 d, 3 d, 5 d, 7 d, 10 d, 15 d, and then take it out for testing. 1.4 Test and Characterization 1.4.1 ATR-FT-IR test: using Attenuated Total Refraction (ATR) technology, scanning times 16 times, scanning range 500～4000 cm-1, direct infrared test on the butadiene rubber film [9]. 1.4.2 1H-NMR test: Cut about 10 mg of butadiene rubber film and dissolve it in 0.5 mL of deuterated chloroform, and carry out the proton nuclear magnetic resonance spectrum test. 1.4.3 UV-vis test: Cut out about 2 mg of butadiene rubber film, dissolve it in 10 mL cyclohexane, and perform UV spectrum test. The scanning range is 500～190 nm, the speed is medium, and the scanning gap is 0.5 mm. 1.5 Calculation of the reaction rate 2 Results and discussion 2.1 The infrared spectrum of the thermal oxidative aging process of the butadiene rubber Fig. 1 is the ATR-FT-IR spectrum of the butadiene rubber before and after 15 days of aging. Among them, in the infrared spectrum of unaged butadiene rubber, 3068 cm-1 is u003dCH2 antisymmetric stretching vibration, and 3004 cm-1 and 1654 cm-1 are cis-1,4-butadiene structural units- CH2u003dCH2 stretching vibration peak, 2939 cm-1 is the antisymmetric stretching vibration peak of CH on the methylene group -CH2, 1448 cm-1 is the swing vibration peak of CH on the methylene group -CH2-, 993 cm-1 And 911 cm-1 are the out-of-plane swing vibration peaks of -CH2, and 736 cm-1 is the repeating unit -CH2-CH2- in-plane swing vibration peaks, which are also characteristic bands of cis-1,4 butadiene rubber structure [10]. When the butadiene rubber was thermally and oxidized at 120 ℃ for 0.5 d, it was observed that the infrared spectrum began to change, and obvious new material peaks appeared.

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