In the process from spinning to extraction, filaments are drawn randomly and continuously. From the appearance, from coarse to fine, from translucent to semi-milky white, the ductility of filaments gradually improves, with a little "strength." From the inside of the silk, the molecular structure of the raw materials has not changed greatly, the macromolecules have no orientation, or are in a disordered state, and the molecules are wrapped and isolated by a large number of solvents, so that molecular chains cannot be formed. If the molecular chain is not formed, silk will not have real strength. At this point, the inside of the fiber is actually like a circular tubular network. Molecular particles of polyethylene are in its pipe network. With the continuous stretching and thinning of the fiber, the solvent is continuously precipitated, and the shape of the pipe network is also from round to long, from comb to dense, the density between the molecules of the material is gradually increased, and the arrangement of macromolecules is gradually changed from disordered state to partially ordered state. The drafting process of UHMWPE fiber is basically the same as that of conventional polyester staple fiber in form, but the required control accuracy is quite different. This kind of fiber must adopt multi-stage drafting method to achieve the characteristics of high strength and high modulus. At each stage of sinking, the intermolecular structure has changed greatly. With stretching, the macromolecules are arranged from disorder to order and orientation, and the crystallinity gradually increases. Only by improving the orientation of fiber macromolecules along the fiber axis, the number of macromolecular chains will be more, the cohesion will be greater, and the strength of fiber will naturally be higher. When the crystallinity of fiber increases, the initial modulus naturally increases. Under the action of external force, the smaller the fiber elongation, the smaller the deformation.
In the process of underexpansion, the underexpansion multiple should be as large as possible. The ordered orientation and high crystallization of macromolecules can only be promoted if the fibers are suddenly stretched. The internal crystallization of fibers occurs simultaneously with the formation of high orientation. Because of its large molecular weight and strong resistance to external force, this kind of fiber can only be produced by thermal drawing process. Therefore, in order to achieve high rate drawing, higher drawing temperature is needed. The temperature of each drawing is different, depending on the state of the filament in the previous process. There is no fixed quantity, but it must be within the temperature range that the optical fiber itself can withstand. In production, the temperature generally does not exceed 65438 055 degrees Celsius. Otherwise, there will be hard wires and stiff wires. (1) application of ropes and cables: ropes, cables, sails and fishing gear made of this fiber are suitable for marine engineering, which is the original use of this fiber. Widely used in negative force rope, heavy load rope, salvage rope, towing rope, sailing rope, fishing line and so on. The breaking length of rope made of this kind of fiber is 8 times that of steel wire rope and 2 times that of aramid fiber under its own weight. This rope is used as mooring anchor rope for supertankers, offshore platforms and lighthouses. It solves the problem that the cable strength is reduced and broken due to the corrosion of steel cable, the corrosion, hydrolysis and ultraviolet degradation of nylon and polyester cable, and it needs to be replaced frequently. (2) Sports equipment and supplies: in sports goods, helmets, skis, sails and wheels, fishing rods, rackets and bicycles, gliders, ultralight aircraft parts, etc. Their performance is superior to that of traditional materials.
(3) Used as biomaterials: Fiber reinforced composites are used as denture materials, medical implants, plastic sutures, etc. It has good biocompatibility, durability, high stability and no allergy, and has been used in clinic. It is also used in medical gloves and other medical measures.
(4) In industry, fibers and their composites can be used as pressure-resistant containers, conveyor belts, filter materials, automobile bumper plates, etc. In architecture, it can be used as a wall and partition structure. The toughness and impact resistance of cement can be improved by using it as a reinforced cement composite material.
Uses: bulletproof vests and helmets, light armor, sails, cables, optical cables to enhance parachutes and filter materials.