Development and application of the hottest UHMWPE

2022-10-18
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Development and application of ultra high molecular weight polyethylene (V)

4 alloying of ultra high molecular weight polyethylene (UHMW-PE)

in addition to forming alloys with plastics to improve its processing properties (see 3.2.1 and 3.2.3), ultra high molecular weight polyethylene (UHMW-PE) can also obtain other properties. Among them, pp/ultra high molecular weight polyethylene (UHMW-PE) alloy is the most prominent

generally, the toughening of polymers is to introduce flexible segments into the resin to form composites (such as rubber plastic blends), and its toughening mechanism is "multiple crazing mechanism". In pp/ultra high molecular weight polyethylene (UHMW-PE) system, ultra high molecular weight polyethylene (UHMW-PE) has obvious toughening effect on PP, which can not be explained by the "multiple cracks" theory. It was first reported in 1993 that the toughening of PP with ultra-high molecular weight polyethylene (UHMW-PE) was successful. When the content of UHMW-PE was 15%, the notch impact strength of the blend was more than 2 times higher than that of pure PP [29]. Recently, it has been reported that when ultra-high molecular weight polyethylene (UHMW-PE) is blended with copolymerized PP containing ethylene segments, its impact strength is more than twice that of PP when the content of UHMW-PE is 25%. The explanation of the above phenomenon is that "customers must carefully consider the complex toughening mechanism when purchasing experimental machines" [31]

the submicroscopic phase state of pp/ultra high molecular weight polyethylene (UHMW-PE) blend system is a bicontinuous phase. Ultra high molecular weight polyethylene (UHMW-PE) molecules and long-chain PP molecules form a blend complex, and the rest of PP forms a PP complex. The two interweave into a "linear interpenetrating complex". Among them, the blending complex plays a role of skeleton in the material, providing mechanical strength for the material. When impacted by external forces, it will deform greatly to absorb external energy and play a role of toughening; The more complete the complex formed, the greater the density, the better the toughening effect

in order to ensure the formation of "linear interpenetrating" structure, ultra high molecular weight polyethylene (UHMW-PE) must be dispersed in PP matrix at the excimer level, which puts forward higher requirements for blending methods. A study by Beijing University of chemical technology found that the four screw extruder can evenly disperse ultra high molecular weight polyethylene (UHMW-PE) in PP matrix, while the blending effect of the twin screw extruder is poor

epdm can increase the compatibilization of pp/UHMW-PE alloy. EPDM has the same two main chain links as PP and ultra high molecular weight polyethylene (UHMW-PE), so it has good affinity with both materials and is easy to disperse on the two-phase interface during blending. EPDM can insert, divide and refine the composite eutectic, which is beneficial to improve the toughness of the material and greatly improve the notch impact strength

in addition, ultra high molecular weight polyethylene (UHMW-PE) can also be alloyed with rubber to obtain better mechanical properties than pure rubber, such as friction resistance, tensile strength and elongation at break. Among them, rubber is vulcanized above the softening point of ultra high molecular weight polyethylene (UHMW-PE) in the mixing process

5 compounding of ultra high molecular weight polyethylene (UHMW-PE)

ultra high molecular weight polyethylene (UHMW-PE) can be vulcanized and compounded with various rubbers (or rubber plastic alloys) to make modified PE sheets, which can be further compounded with metal plates. In addition, ultra high molecular weight polyethylene (UHMW-PE) can also be compounded on the plastic surface to improve impact resistance

under the temperature above the softening point of ultra-high molecular weight polyethylene (UHMW-PE), pressing the unvulcanized rubber sheet containing vulcanizing agent and ultra-high molecular weight polyethylene (UHMW-PE) sheet together can produce laminated products with high peel strength, which can be dozens of times higher than that without vulcanizing agent. In this way, unvulcanized rubber and plastic alloys (such as epdm/pa6, epdm/pp, sbr/pe) and ultra high molecular weight polyethylene (UHMW-PE) sheets can also be firmly bonded together

how to choose high-quality plastic hoses

hoses, which are convenient and economical, are widely used and popular in the field of daily chemicals. A high-quality hose can not only protect the contents, but also improve the product grade, so as to win more consumers for daily chemical enterprises. Then, for daily chemical enterprises, how to choose high-quality plastic hoses suitable for their own products? We will introduce several important aspects below

selection of materials

the quality of materials is the key to ensure the quality of hoses, which will directly affect the processing and final use of hoses. The materials of plastic hoses include polyethylene (for pipe body and head), polypropylene (pipe cover), color masterbatch, barrier resin, printing ink, varnish, etc. Therefore, the selection of any kind of material will directly affect the quality of the hose. However, the choice of materials also depends on health requirements, barrier (requirements for oxygen resistance, water vapor, fragrance retention, etc.), chemical resistance and other factors

1. Selection of pipes:

first, the materials used should meet the relevant health standards, and the harmful substances such as heavy metals and fluorescent agents should be controlled within the specified range. For example, polyethylene (PE) and polypropylene (PP) used in hoses exported to the United States should meet the U.S. Food and Drug Administration (FDA) standard 21cfr117.1520

secondly, the barrier property of the material. If the contents of the packaging of daily chemical enterprises are products that are particularly sensitive to oxygen (such as some whitening cosmetics) or whose fragrance is very volatile (such as essential oils or some oils, acids, salts and other corrosive chemicals), five layer co extruded tubes should be selected at this time. Because the oxygen transmission rate of five layer coextrusion pipe (polyethylene/bonding resin/EVOH/bonding resin/polyethylene) is 0.2 ~ 1.2 units, while the oxygen transmission rate of ordinary polyethylene single-layer pipe is 150 carbon, which has the function of absorbing sound waves and various small vibrations ~ 300 units. In a certain period of time, the weight loss rate of CO extruded tubes containing ethanol is dozens of times lower than that of single-layer tubes. In addition, EVOH is an ethylene vinyl alcohol copolymer, which has excellent barrier and fragrance retention (the effect is ideal when the thickness is 15 ~ 20 microns)

third, the stiffness of the material. Daily chemical enterprises have different requirements for hose stiffness, so how to obtain the desired stiffness? Polyethylene commonly used in hoses is mainly low-density polyethylene, high-density polyethylene and linear low-density polyethylene. Among them, the stiffness of HDPE is better than that of LDPE, so the desired stiffness can be achieved by adjusting the ratio of HDPE/LDPE

fourth, the chemical resistance of the material. High density polyethylene has better chemical resistance than low density polyethylene

fifth, the weather resistance of the material. To control the short-term or long-term performance of the hose, factors such as appearance, pressure resistance/drop performance, sealing strength, environmental stress cracking resistance (ESCR value), fragrance and loss of active ingredients need to be considered

2. Selection of color masterbatch

Color Masterbatch plays an important role in hose quality control. Therefore, when choosing color masterbatch, user enterprises should consider whether it has good dispersion, filtration and thermal stability, weather resistance and product resistance. Among them, the product resistance of the color masterbatch is particularly important in the use of the hose. If the color masterbatch is incompatible with the installed product, the color of the color masterbatch will migrate to the product, and the consequences will be very serious. Therefore, daily chemical enterprises should test the stability of new products and hoses (do accelerated tests under specified conditions)

3. Types of varnish and their respective characteristics

the varnish used in the hose can be divided into ultraviolet UV type and heat drying type, which can be divided into bright and matte from the appearance. Varnish can not only provide beautiful visual effects, but also protect the contents, and has a certain blocking effect on oxygen, steam and fragrance. Generally speaking, heat drying varnish has good adhesion to subsequent bronzing and screen printing, while UV varnish has better gloss. Daily chemical enterprises can choose appropriate varnish according to the characteristics of their products. In addition, the cured varnish should have good adhesion, and the surface should be smooth without pitting, folding resistance, wear resistance, corrosion resistance, and odor. There should be no discoloration during storage

requirements for pipe body/head

1. The surface of the pipe body should be smooth, without stripes, scratches, strains, shrinkage deformation, the pipe body should be straight and not bent, the thickness of the pipe wall should be uniform, and the tolerance of pipe wall thickness, pipe length and diameter should be within the specified range

2. The tube head and tube body of the hose should be firmly connected, the wiring should be neat and beautiful, the width should be uniform, and the tube head should not be skewed after injection

3. The pipe head and the pipe cover should be well matched, the screw in and screw out should be smooth, there should be no tooth sliding within the specified torque range, and there should be no water and air leakage between the pipe and the cover

printing requirements

hose processing usually uses dry offset printing (offset), and most of the inks used are UV dried, which usually requires strong adhesion and color change resistance. The printing color should be within the specified depth range, the overprint position should be accurate, the deviation should be within 0.2mm, and the font should be complete and clear

requirements for plastic covers

plastic covers are usually made of polypropylene (PP) injection molding. High quality plastic covers should have no obvious shrinkage lines and sharp edges, the clamping line should be smooth, the size should be accurate, and it should be smoothly matched with the pipe head. During normal use, there should be no structural damage such as embrittlement and cracks. For example, when the opening force is within the range, the flap should be able to fold more than 300 times without fracture

I believe that from the above aspects, the majority of daily chemical enterprises should be able to select high-quality hose packaging products with appropriate elongation

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