The preparation of PVA spinning dope

At present, in the mass production with water as solvent for preparing Polyvinyl Alcohol ( PVA ) spinning dope. The process of it is as following:

1. Washing and dewatering:

The objective of washing is to reduce the water content of Sodium Acetate in Polyvinyl Alcohol material, and is make it not more than 0.05 % to 0.2 %, otherwise, it will make the fiber alkaline coloring occur during heat treatment. Through washing, it also can remove the material part of low relative molecular mass Polyvinyl Alcohol, improve its relative molecular mass and polydispersity. In addition, the process of washing, PVA occurred moderate swelling, facilitates the dissolution. The process of washing is the main regulating the temperature of washing and washing water. Content of sodium acetate as in long net type washing machine mainly depends on the regulation to control the temperature of washing water after washing the Polyvinyl Alcohol, the groove binding type washing machine is to regulate the washing water quantity, water temperature should not exceed 30 to 40 ℃, water consumption is about 10t / T  (PVA). Polyvinyl Alcohol need to dewatering after washing and to ensure that the water content of sodium acetate Polyvinyl Alcohol after washing and stable rate. The former in order to avoid alkaline coloring fiber during heat setting, the latter in order to avoid the concentration of dissolved when the control is difficult. The control index of moisture or crush rate.

2. Dissolution:

After washing the Polyvinyl Alcohol through intermediate storage and weighing distribution is fed into a dissolving machine, dissolved with hot water. Concentration of PVA water solution wet spinning with 14% to 18%, dry spinning dope concentration is 30% to 40%. Sometimes in the Polyvinyl Alcohol dissolved while also adding appropriate additives, to meet the needs of different types of Polyvinyl Alcohol fiber production.

In the actual production of Polyvinyl Alcohol, dissolved generally under pressure in the 95 to 98 ℃. According to the different concentration of solution preparation, dissolution time can be varied from 2 to 8h. The concentration of the solution is dissolved, the longer the time required.

Liquid viscosity is the need for strict control of the dissolution process parameters. The average degree of polymerization of 1750 soil 50 Polyvinyl Alcohol, with concentration of 15% aqueous solution, the viscosity of 135s, the concentration of aqueous solution of 16% of the viscosity is of 180s.

3. Mixing, filtering and deaeration;

After dissolving Polyvinyl Alcohol spinningsolution was not immediately used for spinning, must be in constant temperature (96 to 98 ℃) by mixing, filtering and deaeration. Mixed in a large capacity equipment, filtration by filter press; deaeration still static batch deaeration, such as the use of high efficient continuous defoaming, it must be in the protection of saturated steam, to prevent excessive evaporation of surface level and crust.