Cold resistance of rubber refers to the ability to maintain rubber elasticity and normal operation at the specified low temperature. At low temperature, the relaxation process of vulcanized rubber slows down sharply, the hardness, modulus and intramolecular friction increase, and the elasticity decreases significantly, resulting in the decline of the working capacity of rubber products, especially under dynamic conditions. When the temperature drops to the elastic limit service temperature, the rubber will harden and shrink, resulting in leakage failure of seals. The cold resistance of vulcanizates mainly depends on two basic properties of polymers: glass transition and crystallization. Both will make the rubber lose elasticity at low temperature.

The selection of raw rubber with good cold resistance is the key to cold resistance. The cold resistance of rubber mainly depends on the variety of rubber. For amorphous rubber, the glass transition temperature is low and the cold resistance is good. For crystalline rubber, the glass transition temperature and crystallization shall be considered for cold resistance. Increasing the flexibility of rubber molecular chain, reducing intermolecular force and steric hindrance, and weakening the regularity of macromolecular chain are conducive to improve the cold resistance of rubber. Rubber blending is a common method of adjusting cold tolerance in rubber formulation design. For example, SBR and BR, NBR and NR, CO and ECO can improve the cold resistance of rubber.

The type of crosslinking bond affects the cold resistance of rubber. When the traditional vulcanization system is used for natural rubber, the shear modulus increases and the glass transition temperature increases with the increase of sulfur content until 30 phr (up to 20 ~ 30 ℃). The glass transition temperature of rubber is 7 ℃ lower than that of traditional vulcanization system. Therefore, NR, SBR and DCP have the best cold resistance. When vulcanized with thiuram, the cold resistance is reduced, while the cold resistance of vulcanization with sulfur / subsulfonamide accelerator is the worst. The reason for the above difference is that when sulfurized with sulfur, it not only generates polysulfide bonds, but also generates intramolecular cross-linking bonds, and cyclization reaction occurs. Therefore, the activity of chain segments is reduced, the elastic modulus is increased, and the glass transition temperature is increased. When the amount of sulfur is reduced and the semi effective or effective vulcanization system is used, the number of polysulfide bonds is reduced, mainly single sulfur bonds and disulfide bonds are generated, and the possibility of sulfur binding in the molecule is reduced. Therefore, the glass transition temperature increases more and the sulfur bonds are small. When vulcanized with peroxide and radiation, its cold resistance is better than that of effective vulcanization system and traditional vulcanization system, because the volume expansion coefficient of peroxide vulcanizate is large. The large volume expansion coefficient can increase the free space of chain segment activity and reduce the glass transition temperature. In addition, during peroxide vulcanization, a firm and short C-C cross-linking bond will be formed, while when sulfur vulcanization is used, a polysulfide bond with small firmness and large length will be formed. Therefore, in case of deformation, the intermolecular force to be overcome will be greater, and the weak bond will be distorted, which will increase the lag loss and increase the creep rate, The viscosity resistance of vulcanizate is greater than that of peroxide vulcanizate. In other words, the intermolecular force is much greater in the rubber vulcanized with sulfur, which is the reason for the poor cold resistance of vulcanized rubber.

The effect of filler on the cold resistance of rubber depends on the structure formed by the interaction between filler and rubber. Increase the rubber content and reduce the amount of filler. The addition of filler will hinder the change of chain segment configuration and increase the rigidity of filler. Therefore, filler can not be expected to improve the cold resistance of rubber.

In addition, the reasonable selection of softening and plasticizing system is an effective measure to improve the cold resistance of rubber products. The addition of plasticizer can reduce the glass transition temperature of rubber. Polar rubbers such as nitrile rubber and chloroprene rubber with poor cold resistance mainly improve their cold resistance by adding appropriate plasticizers. Because the plasticizer can increase the flexibility of rubber molecules, reduce the intermolecular force and make the molecular chain segments easy to move, the plasticizer with similar polarity and solubility parameters should be selected for polar rubber. The type and amount of softening plasticizer are very important to the cold resistance of rubber.