Research on Ultra-High Molecular Weight Polyethylene Fiber in China

Ultra-high molecular weight polyethylene fiber (UHMWPE fiber), also known as high-strength and high-modulus polyethylene fiber, usually refers to the fiber spun from ultra-high molecular weight polyethylene resin with a molecular weight of 1 million to 5 million. It is the fiber with the highest specific strength and specific modulus in the world. It is the third generation of high-performance fiber after carbon fiber and aramid and has the lowest density. It has a series of excellent characteristics such as low density, high strength, high modulus, corrosion resistance, and impact resistance. Among the various preparation methods of ultra-high molecular weight polyethylene fibers, only the gel spinning-super-stretching method is the most mature and has achieved industrial production.

Raw materials UHMWPE resin, solvents and spinning aids such as antioxidants

The mechanism is that ultra-high molecular weight polyethylene has a very long polyethylene macromolecular flexible chain, which is very easy to cause chain entanglement. It is dissolved in a certain solvent, and the distance between the macromolecules is pulled apart by the dilution effect of the solvent. After the stock solution is extruded into fibers, gel precursors with moderate macromolecular entanglement points are obtained. After super-multiple thermal stretching and molecular orientation, UHMWPE fibers with straight chain structures are finally obtained.

The main process steps of the process flow include spinning solution preparation, gel fiber forming, gel fiber desolventization and multi-stage super-multiple thermal stretching of dry gel fibers.

Dry and wet processes Depending on the solvent used, the gel spinning-superheat stretching method mainly includes two different processes: 

(1) Dry process, that is, the dry gel spinning process using high-volatile solvents; it can be directly removed by flash evaporation-evaporation, and then directly stretched. Domestic Yizheng Chemical Fiber uses dry process to produce UHMWPE fiber.

 (2) Wet process, that is, the wet gel spinning process using low-volatile solvents. It is necessary to use extraction spinning to remove, and then dry to remove the extractant before hot stretching. Domestic UHMWPE fiber manufacturers except Yizheng Chemical Fiber all use wet gel spinning process to produce UHMWPE fiber.

Dry process VS wet process

Dry process: short process flow, the prepared fiber has a smooth surface, few defects, softness, high crystallinity, high fiber density, high melting point, and low solvent residue. 

Wet process: high strength, thicker single filaments, low solvent cost, safety, relatively simple and mature, so it has become the mainstream process of domestic and foreign fiber companies.