(1) cotton fiber: is a kind of cellulose fiber, relatively short (10~15mm), the strength of the cord mainly relies on the role of friction between the fibers twisted together, so the strength of cotton cord is only 55%~58% of its fiber strength. Due to its chemical composition of cellulose, the cellulose surface contains a large amount of -OH, with polarity, has a relatively high chemical reactivity, high surface activity, and rough surface, the surface has many lint and cellulose ends. In the case of dynamic fatigue, the fibers of the cotton cord will gradually loosen and spread apart, which not only reduces the twisting cooperation and the strength of the cord, but also further reduces the strength of the cord due to frictional heat generation. Therefore, the dynamic fatigue strength of cotton cord is 7~12 times lower than that of rayon cord.
(2) Rayon: The fiber is long and the strength of the cord is mainly determined by the strength of the fiber, which is 72% of the fiber strength. Rayon fiber surface is relatively smooth, fiber ends less, contains a moderate amount of -OH, chemical activity is relatively low, and rubber bonding effect is less than cotton fibers.
(3) nylon fibers: polyamide fibers, containing groups; smooth surface, few ends, the end contains a small amount of -OH, -COOH, and the bonding between the rubber is more difficult than rayon. Nylon fibers have high strength and good fatigue resistance, but the thermal shrinkage deformation is large, the use of hot stretch treatment before.
(4) polyester fiber: fiber surface is very smooth, containing groups, low activity, the surface is made in the molecular weight end contains a small amount of -OH, the surface has hydrophobic, and the bonding between the rubber is very difficult, the need for special treatment of fibers. Polyester fiber has high tear strength, small fixed load elongation, small deformation, good impact resistance and heat resistance, low water absorption, but easy amine solution, hydrolysis, poor light resistance, high heat generation.
(5) aramid fiber: aromatic polyamide fiber, more than 85% of its amide bond with the two aromatic groups directly combined. , although the amide bond has a certain activity, single is shielded by the benzene ring, so the reaction activity is very low, the surface is very smooth, and the bonding with rubber is very difficult. However, the lightness of aramid fiber is 6~7 times of the same diameter steel wire, fatigue resistance is much better than steel wire, good dimensional stability and small hysteresis. The affinity with rubber is better than steel wire, and it can replace steel wire in tires, and its application effect depends on the bonding effect of aramid fiber and rubber.