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Analysis of the phenomenon of whitening of silica gel after touching water

by:ORK      2022-10-29
Analysis of the main reasons for rubber whitening (blooming) 1. Overview of frosting is divided into unvulcanized rubber (hereinafter referred to as rubber material) and vulcanized rubber (hereinafter referred to as product). Frost. Bloom is a phenomenon in which liquid or solid compounding agents migrate from the inside of the rubber to the surface of the rubber [1]. It can be seen that the internal compounding agent of the rubber seals is precipitated, and the bloom is formed. The forms of rubber spraying can be roughly divided into three types. That is, powder spraying, wax spraying, and oil spraying (also called oozing). Powder spraying is a powdery compounding agent such as vulcanizing agent, accelerator, active agent, antioxidant, filler, etc. that precipitates on the surface of the rubber to form a layer of powder. Spray wax is paraffin, ceresin and other wax-like substances precipitated on the rubber surface to form a layer of wax film. Oil injection is a liquid compounding agent such as softener, tackifier, lubricant, and plasticizer that precipitates on the surface of the rubber to form a layer of oil. In practice, the form of frosting on the rubber surface sometimes occurs in one form, sometimes in two or three forms at the same time. (1) Improper formula design: Saturated ejection: common in sulfur, accelerators, active agents, antioxidants Migration ejection: common in processing aids, migratory antioxidants. Antistatic agent generation and ejection: common in sulfur vulcanization systems Medium accelerator combined with reaction product Retention: common in organic peroxide vulcanization system, low molecular material Excessive stress ejection: common in inorganic filler: such as calcium carbonate (2) Improper process operation caused poor dispersion due to uneven mixing The saturation temperature of rubber mixing is too high, which makes the local overweight of the compounding agent inaccurate (overweight, underweight, missed, and wrong) The vulcanization temperature is too high, and the macromolecule degradation causes the blooming and vulcanization temperature to be too low, resulting in an incomplete reaction The undersulfur frost spraying and vulcanization time is not enough, resulting in improper operation of the release agent or mold washing water sprayed by undersulfur spraying, resulting in whitening of the rubber surface (3) The quality of raw materials fluctuates due to different origin materials, different manufacturing methods, and different processes. Different raw materials in different batches are very different. The synthesis process of raw rubber: the difference in polymerization temperature, catalyst, synthesis monomer, etc., causes the difference in solubility. Purity, moisture, ash, pH value, physical properties, etc. change (4) Poor storage conditions Temperature: The solubility of compounding agents in rubber generally rises and falls with the rise and fall of temperature. Time (pressurehumidity): The pressure of the rubber during storage, the humidity of the surrounding air and time also affect the solubility of compounding agents , generally has little effect [6]. However, if the pressure is high, the compounding agent in the rubber at the pressure part will form crystal nuclei, which will precipitate on the surface of the rubber to form frost; The effect of polarity) is weakened, and the solubility of the compounding agent decreases, which leads to frosting; the longer the storage time, the more obvious the frosting on the rubber surface, because the temperature and humidity of the air in the storage environment vary with the seasons, and the difference is large, It is very easy to cause the solubility of the compounding agent to change, resulting in blooming. (5) aging Most of the aging of rubber leads to the destruction of the complete and balanced network structure of the vulcanizate, which also destroys the chemical or physical combination between various compounding agents in the rubber system and raw rubber molecules and compounding agents, reducing the The solubility of the compounding agent in the rubber system. Therefore, those compounding agents that are partially supersaturated will be freed from the rubber seals to form blooming. Company website:
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