How to deal with the problem that water enters the radiator
Rubber products often work in a variety of harsh weather conditions, and in this case it is undoubtedly important to expand the range of their use temperature by improving the heat resistance and cold resistance of the rubber. As a professional rubber product manufacturer, we will introduce how to improve the heat resistance and cold resistance of rubber.
Above a certain temperature, the rubber loses its elasticity due to aging; at temperatures below a certain temperature, the rubber loses its elasticity due to vitrification. Therefore, to improve the heat and cold resistance of rubber, we must start from these two aspects.
1. Improve high temperature and aging resistance and improve heat resistance
(1) Change the main chain structure of rubber
(a) the main chain does not contain double bonds;
(b) butyl rubber (isobutylene and isoprene) having less double bonds in the main chain;
(c) a polysulfide rubber containing S atoms in the main chain;
(d) a polyether rubber containing O atoms in the main chain;
(e) dimethyl silicone rubber having a non-carbon atom in the main chain;
(2) changing the substituent structure
Rubber with electron-donating substituents is easily oxidized: natural rubber, styrene-butadiene rubber
Rubber with electron-withdrawing substituents is not easily oxidized: neoprene, fluororubber
(3) Changing the structure of the crosslinked chain
Principle: The cross-linked chain bond with less sulfur is larger, and the heat resistance is good. If the cross-linking bond is C-C or C-O, the bond energy is larger and the heat resistance is better. (The chloroprene rubber is vulcanized and crosslinked with ZnO as -C-O-C-, the natural rubber is crosslinked with peroxide or radiation, and the crosslink is -C-C-)
2. Reduce the glass transition temperature and improve cold resistance
Any measure that increases the mobility of the molecular chain and weakens the interaction between the molecules will lower the glass transition temperature. Any measure to reduce the crystallization ability and crystallization rate of the polymer will increase the elasticity of the polymer and improve the cold resistance (because crystallization is a regular arrangement of polymer chains or segments, which greatly increases the intermolecular interaction force and increases the strength of the polymer. , the elasticity is reduced) There are several methods.
(1) Add plasticizer: weaken the intermolecular force
Such as neoprene Tg-45 ° C, adding dibutyl succinate Tg (-80 ° C) can make it Tg-62 ° C;
If used with cresyl phosphate (-64 ° C), it can be made Tg-57 ° C.
It can be seen that the plasticizing effect is not only related to the plasticizer structure, but also to its own Tg. The lower the plasticizer, the lower the plasticizing polymer.
(2) Copolymerization
Polystyrene has large side groups, so the rotation in the main chain is difficult, relatively rigid, Tg is higher than room temperature, but the styrene-butadiene rubber after copolymerization is -53 ° C, and the polypropylene is polar, so the rotation in the main chain is difficult. More rigid, Tg is higher than room temperature, butadiene rubber copolymerized with butadiene and acrylonitrile is -42 ° C
(3) reduce the ability of polymer crystallization
The linear polyethylene molecular chain is very soft and has a low Tg. However, due to the high degree of regularity, it is difficult to use it as a rubber. It is difficult to use polyethylene as a rubber, and a small amount of a non-polar substituent methyl group is introduced to destroy the regularity of the polyethylene molecular chain. Sex, thereby destroying its crystallinity, which is the ethylene and propylene copolymer rubber Tg = -60 ° C.
By destroying the regularity of the chain, the crystallization ability of the polymer is lowered, and the elasticity is improved, but the side effect is detrimental to the strength.learn more about rubber product.
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