Preparation Of Antioxidant GM Immobilized On Nanosilica And Its Application In Natural Rubber

Because of the effects of heat, oxygen, ozone, and mechanical stress, rubber is easy tosuffer from oxidation in the process of storage, processing and using. It results in crosslinkingor degradation of the molecular, and leads to performance degradation and service lifereduction. The phenomenon is referred to as the oxidative aging. Antioxidants are usuallyadded into the rubber to prevent or retard the oxidative reaction. However, traditional smallmolecule antioxidants are easy to volatilize, migrate or be extracted from the rubber duringprocessing and using, which makes the thermo-oxidative aging resistance of the rubber worseand could even result in environmental pollution. In recent years, the immobilization ofantioxidant on inorganic particles has increasingly attracted attention. On the one hand, thevolatility resistance, migration resistance and extraction resistance of small moleculeantioxidant could be improved through immobilization. On the other hand, through surfacemodification, the reinforcing effect of inorganic particles could be also enhanced due to bettercompatibility between the inorganic particles and the rubber.In this work,2-tert-butyl-6-(3-tert-butyl-5-methyl-2-hydroxyphenyl)-4-methylphenylacrylate (antioxidant GM) was grafted onto the surface of nanosilica through the connectionof γ-mercaptopropyl trimethoxysilane (KH590) to prepare antioxidant GM immobilized onnanosilica (SiO2-g-GM). Effects of SiO2-g-GM on the processing performances, mechanicalproperty, thermo-oxidative aging resistance of the natural rubber (NR) and its extractionresistance in NR were investigated. The main research contents and results are listed asfollows:Firstly, the intermediate (KH590-GM) with alkoxy and phenolic hydroxyl group wassynthesized by thiol-ene reaction between KH590and antioxidant GM. Then the alkoxygroup of KH590-GM reacted with the hydroxyl group of nanosilica to prepare SiO2-g-GM.Effects of reaction temperature, dosage of triethylamine catalyst on the reaction betweenKH590and antioxidant GM, and KH590-GM amount on the grafting ratio of antioxidantwere investigated. The product was characterized by FT-IR,1H-NMR, TG and SEM. Resultsshowed that the optimal reaction condition between KH590and antioxidant GM was that thedosage of triethylamine catalyst was10wt%, reaction temperature was40oC and reaction time was4.5h. When the amount of KH590-GM was30wt%, the highest grafting ratio ofantioxidant was13.4%.Secondly, the SiO2-g-GM was applied to the NR and its effects on processingperformance of the NR compounds and mechanical properties of the NR vulcanizates werestudied. Results showed that the SiO2-g-GM could promote the vulcanization, and themechanical property of SiO2-g-GM filled vulcanizates was superior to the SiO2filledvulcanizates. According to the RPA and SEM analysis, the Payne effect of SiO2-g-GM filledNR compounds was decreased, and the dispersibility of SiO2-g-GM in NR vulcanizates wasimproved.Thirdly, the thermostability of SiO2-g-GM, its effects on the thermo-oxidative agingresistance of the NR vulcanizates and its extraction resistance in NR were studied. Resultsshowed that the thermo-oxidative aging resistance, the extraction resistance andthermostability of SiO2-g-GM were all superior to the antioxidant GM. Compared with theantioxidan GM, the aging coefficient of SiO2-g-GM filled vulcanizates increased from0.58to0.66after aging at100oC for48h. The aging coefficient of the NR vulcanizates withSiO2-g-GM extracted in70oC water for48h was0.63after aging at100oC for48h, whilethe aging coefficient of the NR vulcanizates with the antioxidan GM was0.49.