Effect Of Secondary Vulcanization On Safety Performance Of Silica Gel Products

- Sep 20, 2019-

September,20th,2019

        The purpose of the secondary vulcanization is to remove the volatile components generated by the decomposition of the additive, further improve the vulcanization cross-linking, and improve the strength and stability of the product. The main factors affecting secondary vulcanization are temperature and time.

              


          Fig. 7 and Fig. 8 respectively show the evaporation residue and the content of volatile organic compounds in the hexane-hexane soaking solution after the secondary curing for 8 hours.


         It can be seen from the figure that the evaporation residue and volatile organic matter content of the n-hexane soaking solution of the product decreases with the increase of temperature, which may be because increasing the temperature promotes further vulcanization of the product, the density of the product increases, and the network structure It is more stable, and at the same time, some volatile small molecular substances escape during the vulcanization process, so the amount of substances which migrate to the n-hexane soaking solution is reduced, and the content of volatile organic compounds is also gradually reduced. When the vulcanization temperature reaches 200 °C, the content of volatile organic compounds is less than 0.5%, which is lower than the reference limit of the regulation; on the other hand, if the vulcanization temperature is too high, the molecular chain of the silica gel will be cleaved, resulting in breakage of the crosslinks. The phenomenon of sulfur reversion causes the physical properties of the vulcanizate to decrease, so 200 ° C is a suitable temperature in consideration of product performance and production cost.


         Fig. 9 and Fig. 10 respectively show the evaporation residue and the volatile organic matter content of the silica gel plate of the secondary vulcanization at 200 °C as a function of time.

         It can be seen from the figure that the evaporation residue and volatile organic matter content of the n-hexane soaking solution of the product decreases with time, which may be because the vulcanization time determines the degree of vulcanization at a certain temperature, and the time is prolonged. The degree of cross-linking of the product is increased, and at the same time, part of the volatile small molecular substance continuously escapes during the vulcanization process, so that the substance which migrates to the n-hexane soaking solution is reduced, and the content of the volatile organic substance is gradually reduced. When the vulcanization time is 4h, the content of volatile organic compounds is less than 0.5%, which is lower than the reference limit of the regulations. Considering the production cost of the comprehensive enterprise, the time of 4h is more suitable.