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Technical parameters: the composite materials
Liquid crystal polymer in-situ composite materials
Liquid crystal polymer in-situ composites is refers to the mixture of thermotropic liquid crystal polymer (TLCP) and thermoplastic resin, which blends in melt processing, due to the rigid molecular structure of TLCP, under the action of a force field can be spontaneously orientated along the flow direction, produce significant shear thinning behavior, and in-situ in the matrix resin is formed with orientation structure strengthening phase, namely the in situ fibre, and thus serve to strengthen and improve the processability of the thermoplastic resin flowability effect. Thereby enhancing thermoplastic resin and improving the processing flow dynamic role. In Tsinghua university Zhao Anchi etc, using in situ composite technology, achieved significant effect to improve UHMW-PE processing performance.
Using TLCP on ultra-high molecular weight polyethylene (UHMW-PE) was modified, not only improves the liquidity of process, using usually thermoplastic processing technology and universal equipment can conveniently carry on the processing, but also keeps the higher tensile strength and impact strength, wear resistance have increased greatly.
Polymerization filled composite materials
In polymer synthesis, polymerization filling process is a new type of polymerization method, which is the filling material was processed to form the active center of the particle surface, so that ethylene, propylene and other olefinic monomers polymerized in the surface of the filler particles during the polymerization, forming a tightly packed particles of resin to obtain the final composite material with unique properties. Excepting for a mixed type of composite material performance, it has its own characteristics: first,it is not necessary a molten polyethylene resin, can maintain the shape of the filler and prepare powder or fibrous composite materials. Second, the composite filler/resin ratio is not restricted, generally the content of the filler can be arbitrarily set .Further, the resulting composite material is a homogeneous composition, not restricted by packing density, shape.
Compared with hot melt blending material, ultra-high molecular weight polyethylene (UHMW-PE) composite materials is produced by polymerization filling process, the filler particles are well dispersed, and the interface combination of particles and the polymer substrate is better also.This makes the composite materials tensile strength, impact strength and ultra-high molecular weight polyethylene (UHMW-PE) be similar, but far better than the blend type material, especially at high filling case, contrast is more obvious, the hardness and bending strength of the composite, especially the bending modulus increases many comparing with pure ultra-high molecular weight polyethylene (UHMW-PE), especially suitable for use as bearings, shaft housing and other force components.And thermodynamic properties of composite material has a better improvement: vicat softening point increased of nearly 30 ℃, thermal deformation temperature increased of nearly 20 ℃, the linear expansion coefficient decreased by more than 20%.Therefore, this material can be used in higher temperature, and suitable for manufacturing bearings, bushings, gear and other high precision mechanical parts.
By filling hydrogen or other chain transfer agent and controlling the molecular weight size of ultra-high molecular weight polyethylene (UHMW-PE), polymerization filling technology can make it easier for the resin processing.
U.S. patent with an acid and neutral surface of the filler material, hydrated alumina, silica, water-insoluble silicate, calcium carbonate, Basic aluminium sodium carbonate hydroxyl wollastonite and calcium phosphate made ​​of high modulus the homogeneous polymerization filled UHMWPE composite materials.Another patent pointed out that at 60 ℃, 1.3 MPa and the presence of catalyst, the ultra-high molecular weight polyethylene (UHMW-PE) aggregation on the surface of the alumina drying in heptane polymerization, then the high modulus of homogeneous composite material can be obtained. Using diatomaceous earth, kaolin as filler respectively, research institute of Qilu petrochemical company has synthesized ultra-high molecular weight polyethylene (UHMW-PE) composites.
Self-reinforced ultra-high molecular weight polyethylene (UHMW-PE)
Adding ultra-high molecular weight polyethylene (UHMW-PE) fiber in ultra-high molecular weight polyethylene (UHMW-PE) , since the matrix and the fibers have the same chemical characteristic, so the chemical compatibility, the strong interface binding force of the two components, then it is obtained that composite cmaterials owes good mechanical properties.Adding ultra-high molecular weight polyethylene (UHMW-PE) fiber,can greatly improve the tensile strength, modulus, impact strength and creep resistance of ultra-high molecular weight polyethylene (UHMW-PE).Compared with the ultra-high molecular weight polyethylene (UHMW-PE), adding in a volume content of the ultrahigh molecular weight polyethylene (UHMW-PE) for 60% of the ultra-high molecular weight polyethylene (UHMW-PE) fibers, the maximum stress and modulus can increase by 160% and 60%, respectively. This self-reinforced ultra-high molecular weight polyethylene (UHMW-PE) materials are particularly suitable for biomedical bearing on the occasion, and for the whole replace artificial joints is only in recent years much attention, the low volume wear rate of self-reinforced ultra-high molecular weight polyethylene (UHMW -PE) can increase the life of artificial joints.
In addition to form with plastic alloy to improve its processability, Ultra-high molecular weight polyethylene (UHMW-PE) can obtain other properties.Among them, the PP/ultra-high molecular weight polyethylene (UHMW-PE) alloy is most prominent.
Polymer toughening is usually in the introduction of flexible chain segment of resin to form compounds (such as rubber blend) ,its toughening mechanism for "multiple crazing mechanism." In the PP/ultra-high molecular weight polyethylene (uhmw-pe) systems, ultra-high molecular weight polyethylene (UHMW-PE) for PP has significantly toughening effect, this is the “multiple crack” can not explain.In 1993, the earliest reported using high molecular weight polyethylene (UHMW-PE) toughening PP is a success, when the content of ultra-high molecular weight polyethylene (UHMW-PE) was 15%, the notched impact strength of blend than pure PP increased by more than two-fold.There are reports recently, ultra-high molecular weight polyethylene (UHMW-PE) and PP blends containing ethylene chain segments in the ultra-high molecular weight polyethylene (UHMW-PE) content of 25%, the impact strength is more than double the PP. Explanation of the above phenomenon is "Network toughening mechanism"
The submicroscopic phase of PP / ultra-high molecular weight polyethylene (UHMW-PE) blend system is double continuous phase, ultra high molecular weight polyethylene (UHMW-PE) and long-chain molecules PP molecules together constitute a blended network, The remaining PP  constitutes a PP network, the two interwoven into a "linear interpenetrating network". Blended network which plays a role in skeleton in the material provides mechanical strength.When suffering external shocks, it will happen a larger deformation to absorb external energy, play a role in toughening; more complete network formation, the greater the density , the toughening is better.
In order to ensure the formation of the "linear interpenetrating network" structure,it must make ultra high molecular weight polyethylene (UHMW-PE) dispersed in PP matrix with excimer level, which puts forward higher requirements to the blending way. Beijing University of Chemical Technology studies have found, four-screw extruder will make ultrahigh molecular weight polyethylene (UHMW-PE) uniformly disperse in PP matrix, while the blending effect of the twin screw extruder is poor.
EPDM can play compatibilizer role to PP / ultra high molecular weight polyethylene (UHMW-PE) alloy . Since the EPDM have two primary links, respectively with PP and ultra high molecular weight polyethylene (UHMW-PE) the same, and thus the two materials have a relatively good affinity, easily dispersed in the two-phase interface when blended. EPDM play eutectic composite insert, segmentation and thinning effects, which increase the toughness of the material is beneficial, can greatly improve the notched impact strength.
In addition, ultra-high molecular weight polyethylene (UHMW-PE) may also form an alloy with the rubber, to obtain excellent mechanical properties than pure rubber, such as abrasion resistance, tensile strength and elongation at break. Wherein the rubber will be vulcanizing when the temperture reaches the softening point of ultra-high molecular weight polyethylene (UHMW-PE) during the mixing.
Ultra high molecular weight polyethylene (UHMW-PE) with a variety of rubber (or rubber alloy) curing the composite sheet made ​​of modified PE sheet by vulcanizing and complexing, these sheets can further be made of composite material and the metal sheet. In addition, ultra-high molecular weight polyethylene (UHMW-PE) can also be compound in the plastic surface in order to improve the impact resistance.
Above the ultra-high molecular weight polyethylene (UHMW-PE) softening point, under the condition of the temperature, the unvulcanized rubber sheet containing a vulcanizing agent and ultra-high molecular weight polyethylene (uhmw-pe) sheet pressed together, the high peel strength laminated products can be obtained, compared with the excluding of vulcanizing agent, its peel strength can improve dozens of times.In this way it can make the same of unvulcanized rubber and plastic alloy, such as EPDM/PA6, EPDM/PP, SBR/PE) and ultra-high molecular weight polyethylene (UHMW-PE) sheet bond tightly together.