Polyester has good thermoplastic properties and produces different changes at different temperatures. The thermal changes of polyester are between the thermal changes of amorphous and crystalline polymer compounds. Above the glass transition temperature, only certain segments with small interactions between molecular chains in the amorphous region can move. Molecular segments with large interactions between molecular chains are still difficult to move. Of course, molecular chains in the crystalline region cannot move. , so the fiber only appears to be relatively flexible, but does not necessarily have as good elasticity as the highly elastic state.
When it continues to be heated to 230-240℃, the softening point of polyester is reached, the movement of the molecular chains in the amorphous region of polyester intensifies, and the forces of intermolecular interaction are dismantled. At this time, it is similar to a viscous flow state, but the chain segments in the crystallization zone have not been dismantled, so the fiber only softens rather than melts. However, the use value of the fiber has been lost at this time, so it is not allowed to exceed during printing and dyeing processing. this temperature.
Transfer printing of polyester is achieved by utilizing the movement of heated molecular chains in the amorphous region. However, the temperature must be strictly controlled. If it exceeds the allowable range, the fabric will feel rough and hard; when polyester is exposed to high temperatures of 258-263°C, the molecular chain segments in the polyester crystallization zone also begin to move, and the fiber melts. This temperature is polyester melting point.
The principle of heat setting of polyester
When polyester is heat set, due to the different heat received, the microstructure of the fiber also changes. Are not the same. When the setting temperature is 170-180°C, the absorption capacity of polyester for disperse dyes in exhaust dyeing is very low. When it exceeds 180°C, the absorption rate of polyester for dyes is proportional to the increase in temperature, which is related to the crystallization properties of polyester. This is related to the fact that at 170-180°C, polyester crystallizes quickly. Since more crystals are formed, less dye is absorbed. As the temperature increases, the degree of orientation of macromolecules may decrease, so the absorption of dye increases.
Polyester will undergo hydrolysis under the action of high-temperature steam for a long time, and the strength and dyeing performance of the fiber will decrease. However, it can withstand 140% in water and dye baths using water as the medium. ℃ high temperature.