UHMWPE Fiber

Advantages of UHMWPE fiber?

Properties of UHMWPE Fiber

Production process of UHMWPE Fiber

The main production process of ultra-high molecular weight polyethylene fiber is as follows: preparation of raw materials - twin-screw extruder - spinning box - spinneret - extraction - drying - heating and stretching - winding.

Preparation of raw materials
At present, the preparation methods of raw materials at home and abroad are different, the solvents used are different, and the solid content is also different. Therefore, there is no fixed unified mode, and the equipment for production is also very different, and conventional melt spinning does not add solvent. But no matter which method is adopted, the desired effect can be achieved in the end. Because the production is continuous, the ratio of raw materials cannot fluctuate, and it is required to be uniform and consistent. Although the increase in solid content is one of the important means to increase production, the stretching ratio will also increase accordingly, and the overall speed will respond faster, which increases the difficulty of operation. The amount of hair is significantly increased, which is not easy to grasp. However, if the percentage of solid content can be controlled within an appropriate concentration, it is still possible. It should be done according to one's own situation. Increasing the speed of the metering pump is also one of the effective means to increase production.

Stirring materials
The screw extruder plays the role of conveying, stirring, heating, and pressurizing the material. First of all, the slurry before entering the "screw" must be degassed and must not contain water vapor. The material must be fully mixed and stirred during the conveying process. The heating temperature of each zone should be set in combination with the position of the kneading block on the screw, and a certain conveying pressure should be guaranteed. The setting of the screw kneading block is very theoretical, and different combinations will have different effects on the stirring of the material.

Spinning
The main function of the spinning box is to keep warm; control the temperature; and evenly distribute the material to each spinning component.

Spinning
The metering pump extrudes the material into filaments, which is achieved through the spinneret. The pore size and planing surface shape of the plate are its important technical parameters, which play a vital role in the molding and tensile properties of the fiber. The temperature at the spinning box and the spinneret is matched, and the temperature parameters are set by observing the molten state of the ejected filaments. However, in order to accurately control, some specific technical conditions and practical experience are also required.

Extraction
It is mainly to extract and replace a large amount of solvent in the filaments to obtain "pure" high-strength polyethylene fibers. The selection of extractants varies from manufacturer to manufacturer, and the production process is also different.
The molecules are wrapped and isolated by a large amount of solvent and cannot form molecular chains. If the molecular chains cannot be formed, the silk cannot have real strength. At this time, the inside of the fiber is actually like a circular tubular mesh body, and the molecular particles of polyethylene are in its pipe network. As the fiber is continuously stretched and thinned, the solvent is continuously precipitated, and the shape of the pipe network changes from round to long, from combed to dense, the density between the material molecules gradually increases, and the arrangement of the macromolecules gradually changes from a disordered state to a partially ordered state.

Drying
The main purpose of the drying process is to remove the extractant stuck on the filaments and dry them for drawing. This process seems simple to control, but it is actually difficult. If the process temperature and tension are not properly controlled, a large number of twisted and stiff filaments will be produced, resulting in the inability to continue processing the semi-finished filaments. The control of drying temperature and drying length is the key. This process should not be underestimated, as it is directly related to the quality of the post-drawing product.

Heating drawing
The drawing of ultra-high molecular weight polyethylene fiber is basically the same as the drawing process of conventional polyester staple fiber in form, but the control accuracy required is very different. This fiber must adopt a multi-stage drawing method to achieve high strength and high modulus characteristics. In each stage of under-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 orientation degree of the macromolecules of the fiber along the fiber axis increases, the number of macromolecular chains produced is large, the cohesion is greater, and the strength of the fiber is naturally higher. As the crystallinity of the fiber increases, the initial modulus also naturally increases. When the fiber is resisted by external forces, the smaller the elongation, the smaller the deformation.

Winding Forming
Requirements for silk roll forming: the silk tube has no collapsed edge, no burrs, and the silk bundle must be fixed in length and weight. The so-called fixed length and fixed weight do not simply refer to the requirements for the length and weight of the tow. It has a deep connotation and is very difficult to grasp accurately. It requires that all production processes must be normal and stable. Only when the fiber fineness is always uniform can it be guaranteed. If anyone can truly achieve the technical level of fixed length and fixed weight, he will reach the pinnacle in the field of high-strength fiber.