Abstract: nano silica prepared by gas phase method is the best filler for reinforcing high temperature vulcanized silicone rubber. The effect of nano silica structure on the properties of silicone rubber was studied in this paper. The results show that silica aggregates dispersed into 100-200 nm scale have a good reinforcing effect on silicone rubber. Nano silica powder is added to silicone rubber to form a microcrystalline region with silica as crystal core, which increases the physical cross-linking point and is more prone to crystallization.
Key words: nano silica silicone rubber reinforcement
The mechanical strength of pure silicone rubber is very low. When the reinforcing filler is mixed, the tensile strength of vulcanizate can be increased from 0.35Mpa to 14MPa, and the reinforcing rate is up to 40 times, which is far higher than that of other rubber (1.4-10 times). It can be seen that the use of filler plays a decisive role in the final performance of silicone rubber [1]. Wang’s research shows that the formation of interparticle network structure improves the effective volume of filler reinforcement, so as to increase the modulus of elastomer [2]. Wu Jihuai of Huaqiao University studied talc, quartz α- Silicon fossils β- Silica fossils, kaolin, pyrophyllite, sericite and heavy calcium are used as fillers to strengthen silicone rubber vulcanizates. It is found that the tensile strength and resilience of vulcanizates filled with crystalline quartz are higher than that of silica prepared by precipitation method, but lower than that of silica prepared by gas phase method [3], indicating that nano silica prepared by gas phase method has excellent reinforcing performance for silicone rubber. In this paper, the effects of the structure of nano silica on the properties of silicone rubber were studied.
- Experimental part
1.1 main raw materials
Methyl vinyl silicone rubber (VMQ), with molecular weight of 600000 and vinyl content of 0.17%, is the product of dongjue Fine Chemical Co., Ltd. Nano silica A-200 prepared by gas phase method, product of Degussa company in Germany; M-5, products of Cabot company in the United States; ECUST, pilot product of East China University of technology. Hydroxyl silicone oil, containing 10% hydroxyl, is a product of Changshu reagent factory. Vulcanizing agent double-25, product of aczo company in the Netherlands.
1.2 sample preparation
The raw rubber, hydroxyl silicone oil and gas-phase nano silica are mixed evenly on the double roll rubber mixer according to the formula proportion. The thin pass out sheet of the mixed rubber is returned after heat treatment at 170 ℃ for 2h, vulcanizing agent is added, and the thin pass out sheet is molded on the vulcanizer the next day. The curing condition is 175 ℃ × t90。 T90 is the positive vulcanization time of vulcanizate measured by lh-90 vulcanizer.
1.3 performance test
The hardness shall be determined according to the national standard GB / T531. The ag-2000a Shimadzu universal testing machine is used, and the tensile speed is (500 ± 50) mm / min. the tensile and tear properties are measured according to the national standard GB / T528 and GB / t529 respectively. The positive vulcanization time and vulcanization temperature of vulcanizate were measured by lh-90 rubber vulcanizer. Use ls-230 particle analysis particle size analyzer to analyze the particle size distribution range of powder under ultrasound (0.04 ~ 2000) μ m) Particle size distribution of powder.
- Results and discussion
2.1 structural forms of nano silica by gas phase method
As shown in Fig. 1, the primary particles of nano silica are spherical particles of 2-20nm, and the spherical particles are connected into branched aggregates of 50-500nm pearl string structure through chemical bonds. The aggregates of this structure cannot be dispersed by mechanical forces such as shear, which is the most basic unit for reinforcing silicone rubber [4]. Loose network agglomerates are formed between the aggregates through hydrogen bonds.
