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Technical parameters: modification
Improvement of physical and mechanical properties
Compared with other engineering plastics, high molecular weight polyethylene (UHMW-PE) having a low surface hardness heat distortion temperature and flexural strength, and poor creep performance shortcomings. This is influenced by the molecular structure and morphology of ultra-high molecular weight polyethylene (UHMW-PE).It can be improved by filling and crosslinking methods.
Filling modification
Using glass beads, glass fiber, mica, talc, silica, aluminum oxide, molybdenum disulfide, carbon black, etc. on ultrahigh molecular weight polyethylene (UHMW-PE) for modifying, the surface hardness, stiffness, creep resistance, flexural strength, heat distortion temperature can be better improved. After coupling agent treatment, the effect is more pronounced. After filling the treated  glass beads, it can make the heat distortion temperature increase by 30 ℃.
Glass beads, glass fiber, mica, talc, etc. can increase the hardness, stiffness and temperature resistance; molybdenum disulfide, silicone oil and special wax can reduce the self-lubricating property, then further inprove the self-lubrication property; can improve the anti-static. Conductivity and heat resistance can improve by carbon black or metal powder. However, the impact strength decreased slightly after filler modified, if the content is controlled within 40%, ultra-high molecular weight polyethylene (UHMW-PE) still has very high impact strength.
Crosslinking is to improve the morphological stability, creep resistance and environmental stress cracking resistance. By cross-linking, crystallinity of ultra-high molecular weight polyethylene (UHMW-PE) decreased, masked toughness show again. Crosslinking can be divided into chemical crosslinking and radiation crosslinking. Chemical crosslinking is that  ,after adding the appropriate crosslinking agent in the ultra-high molecular weight polyethylene (UHMW- PE), the cross-linking occurs in the melting process. Radiation crosslinking is the use of electron beam or γ-rays directly to the ultra-high molecular weight polyethylene (UHMW-PE) products for molecular crosslinking irradiation. The Chemical crosslinking of ultra-high molecular weight polyethylene (UHMW-PE) is divided into peroxide crosslinking and coupling agent crosslinking.
Peroxide crosslinking
Peroxide crosslinking process is divided into mixing, molding and crosslinking three steps.When mixing the ultra-high molecular weight polyethylene (UHMW-PE) and superoxide melt blending, ultra-high molecular weight polyethylene (UHMW-PE) produce free radicals under the effect of peroxide, radical coupling and crosslinking.This step is to ensure the temperature not too high, so as to avoid resin crosslinked completely.After mixing, obtaining low crosslinking degree can continue to crosslink ultra-high molecular weight polyethylene (UHMW-PE), under the higher temperature than the mixed molding parts, cross-linking processing again.
After oxide crosslinking, the structure of ultra-high molecular weight polyethylene (UHMW-PE) is different from  thermoplastics, thermosets and vulcanized rubber, it has a body shape that is not completely crosslinking structure, therefore, both of the three characteristics in the performance, namely both hot plasticity and excellent hardness, toughness and resistance to stress cracking properties.
Abroad have been reported with 2,5-dimethyl-2,5 peroxide t-butyl hexyne-3 as the crosslinking agent, but it is difficult to find inland. Tsinghua University conducted a study with cheap and readily available dicumyl peroxide (DCP) as a crosslinking agent and found that: DCP amount is less than 1%, can impact strength than pure high molecular weight polyethylene (UHMW -PE) increased by 15% to 20%, especially DCP amount is 0.25%, the impact strength can be increased by 48%. With the amount of DCP increases, heat distortion temperature increase that can be used to heat pipe in water-based heating systems.
Coupling agent crosslinking
Ultra high molecular weight polyethylene (UHMW-PE) is mainly used two silane coupling agent: vinyl siloxane and allyl vinyl siloxane, are commonly used vinyl trimethoxysilane and vinyl triethoxysilane. Coupling generally rely peroxide initiator, commonly used DCP, organic tin derivatives generally uses to be catalysts.
Forming process of silane crosslinked with ultrahigh molecular weight polyethylene (UHMW-PE) make the thermal decomposition of the peroxide obtain the high chemical activity of free radicals firstly. These free radicals capture the hydrogen atoms from polymer molecule, then the polymer backbone becomes active radicals. Secondly, these active radicals occur grafting reaction with the silane, after grafting, ultra-high molecular weight polyethylene(UHMW-PE) takes place hydrolysis and condensation under the action of water and silanol condensation catalyst   , derived crosslinks to form a silane crosslinking ultra-high molecular weight polyethylene (UHMW-PE).
Radiation crosslinking
Under the effect of certain dose electronic rays or γ rays, parts of the molecular structure of the main chain or side chain in the molecular structure of ultra-high molecular weight polyethylene (UHMW-PE) may be cut by rays, a certain amount of free radicals comes into being. These free radicals combine with each other to form a cross linking chain, so that the macromolecular structure of ultra high molecular weight polyethylene(UHMW-PE) from a linear structure into a net-like macromolecular structure. After a certain dose of radiation, the physical properties of ultra-high molecular weight polyethylene (UHMW- PE), such as creep resistance, immersion oil and hardness, are improved to some extent.
Artificial high molecular weight polyethylene (UHMW-PE) joints radiate with γ-rays, while it is disinfecting,it is in the crosslinked, artificial joint can be enhanced hardness and hydrophilicity, and the creep resistance can be improved, thus extending its life.
Studies have indicated that the PTFE graft combined with irradiation, the wear and creep behavior of ultra-high molecular weight polyethylene(UHMW-PE) can also be improved. This material has a tissue tolerance, suitable for transplantation in vivo.