Overview of UHMWPE Fibre production
The main production process flow of Ultra High Molecular Weight Polyethylene Fiber (UHMWPE) are as follows: Preparation of Raw Materials - Twin Screw Extruder - Spinning Box - Spinneret - Extraction - Drying - Heated drawing - Winding Forming. It is mainly to extract and replace a large amount of solvent in the filament to obtain "pure" high-strength polyethylene fiber. The selection of extractant is different based on the manufacturer and the production process. So far, it is difficult to find an ideal extractant that is economical, practical, safe and environmentally friendly, good extraction effect, non-toxic and tasteless. Internationally, it is also a long-term problem that haven't been solved.
In the process from spinning to extraction, the strands are stretched randomly and continuously. From the appearance, from thick to thin, from translucent to semi-opalescent, the stretchability of the silk is gradually improved, with a little "strength" ". From the inside of the silk, there is no major change in the molecular structure of the raw material. There is no directional arrangement between the macromolecules, and the macromolecules are still in a disordered state. The molecules are separated by a large number of solvents, and the molecular chain cannot be formed. If the chain cannot be formed, the silk cannot have real strength. At this time, the inside of the fiber is actually like a tubular network, and the molecular particles of polyethylene are in the pipe network. As the fiber continues to stretch and become thinner, the solvent continues to precipitate, tubular network shape also changes from round to long, from comb to dense, the density between material molecules gradually increases, and the arrangement of macromolecules also gradually changes from a disordered state to a partially ordered state.
The drawing process of UHMWPE fiber is basically the same as the drawing process of conventional polyester staple fiber, but the precision required for control is very different. This fiber must be drawn in multiple stages to achieve high strength and high modulus. During each stage of drawing, the intermolecular structure changes greatly. With the stretching, the macromolecules change from disordered to ordered, directional arrangement, and the crystallinity gradually increases. Only when the degree of orientation of the macromolecules of the fiber along the fiber axial axis is increased, the number of macromolecular chains generated will be greater, the greater the cohesion force, and the higher the strength of the fiber will naturally be. The crystallinity of the fiber increases, and the initial modulus also increases naturally. Under the action of resistance to external force, the smaller the elongation of the fiber, the smaller the deformation.
During the drawing process of the fiber, the drafting ratio should be as large as possible, and the fiber must have a sudden stretching change, so as to promote the orderly orientation and high crystallization between macromolecules. While a high degree of orientation is formed, crystallization occurs and forms the internal crystal of the fiber. Due to the high molecular weight of this kind of fiber and strong resistance to external force, only hot drawing process can be used in production. Therefore, a higher stretching temperature is required to achieve high drawing. The temperature of each stage of stretching is different, and it depends on the state of the thread in the previous process. There is no fixed number, but it must be within the temperature range that the fiber itself can withstand. In production, the temperature generally does not exceed 155 degrees Celsius. Otherwise, there will be hard fibers and stiff fibers.
(1) Application of ropes and cables: ropes, cables, sails and fishing gear made of this fiber are suitable for marine engineering and are the original use of this fiber. Commonly used in negative force ropes, heavy duty ropes, salvage lines, drag lines, sailing lines and fishing lines. The breaking length of the rope made of this fiber under its own weight is 8 times that of the steel rope and 2 times that of the aramid fiber. The rope is used for the fixed anchor ropes of super tankers, marine operating platforms, lighthouses, etc., which solves the problem of the corrosion encountered in the previous use of steel cables and the corrosion, hydrolysis, and ultraviolet degradation of nylon and polyester cables that cause the strength of the cable to decrease and break, and need to be replaced frequently.
(2) Sports equipment supplies: helmets, snowboards, sailboards, fishing rods, rackets, bicycles, gliders, ultra-light aircraft parts, etc. have been made into sports goods, and their performance is better than traditional materials.
(3) Used as a biological material: The fiber-reinforced composite material is used in dental tray materials, medical implants and plastic sutures, etc. It has good biocompatibility and durability, and has high stability. It will not cause allergies and has been used in clinical applications. It is also used in medical gloves and other medical measures.
(4) In industry, the fiber and its composite materials can be used as pressure-resistant containers, conveyor belts, filter materials, automobile buffer boards, etc.; in construction, it can be used as walls, partition structures, etc. Improve the toughness of cement and improve its impact resistance. Uses: bulletproof vests and helmets, lightweight armor, sails, cables, fiber optic cable reinforcements, parachutes and filter media, etc.
