Process requirements for solvents used in spinning stock solution

Process requirements for solvents used in spinning stock solution

1. From a technical point of view

（1）The solvent must give the concentrated solution good rheology.

（2）The less viscous an isocratic solution is or the more concentrated an isoviscosity solution is.

2. Considering economic effect and labor protection

（1）The boiling point should not be too low or too high, and it is usually better if the boiling point of the solvent is within the range of 50-160°C; if the boiling point is too low, it will cause waste due to volatilization and pollute the air; if the boiling point is too high, it will be inconvenient to recycle.

（2）Solvents need to have sufficient thermal and chemical stability so that they are not easily decomposed during recycling.

（3）The solvent is required to be low in toxicity and less corrosive to equipment.

（4）The solvent does not cause damage to the polymer or other chemical changes during the process of dissolving the polymer.

Some solvents currently used in production have more or less disadvantages such as instability, toxicity, difficult recovery, and high price. A substitute for volatile solvents, ionic liquids, is being researched and developed.

Ionic liquids are organic liquids composed entirely of ions at room temperature and adjacent temperature ranges. Ionic liquids have excellent characteristics such as strong polarity, non-volatile, non-oxidative, non-flammable and explosive, good solubility to inorganic and organic compounds, and stability to most reagents, so they are called green solvents.

The solubility of polyacrylonitrile in concentrated brine shows that concentrated brine is a polar solvent, which is generally a good solvent for polar polymers; and its solubility to polyacrylonitrile reaches the optimum value at a certain concentration, At this point the ions of the salt are almost completely solvated.

In addition, adding some additives to the solvent can also increase the solubility of polyacrylonitrile. For example, adding zinc chloride, calcium chloride and other electrolytes to the solution can increase the solubility of polyacrylonitrile and reduce the viscosity of the solution. A similar effect can also be obtained by adding some ethanol to the aqueous solution of sodium thiocyanate.

Solvents commonly used for several fiber-forming polymers