UHMW-PE
(Ultra High Molecular Polyethylene)
UHMW-PE(Ultra High Molecular Polyethylene) is a kind of thermoplastic engineering plastics with linear structure and excellent comprehensive performance, with molecular weight up to 1.5 million. Small density, good wear resistance, self lubrication, impact resistance, corrosion resistance and so on.
Performance:
The high molecular weight of UHMW-PE (the molecular weight of HDPE is usually
only 20 ~ 300 thousand) gives it excellent performance, and belongs to the
moderate price, excellent performance of thermoplastic engineering plastics, it
almost concentrates the advantages of all kinds of plastics, With ordinary
polyethylene and other engineering plastics incomparable wear resistance,
impact resistance, self-lubrication, corrosion resistance, impact absorption,
low temperature resistance, health and non-toxic, not easy adhesion, not easy
water absorption, small density and other comprehensive properties. In fact,
there is no single polymer material with so many excellent properties.
UHMW-PE material classification:
Processing molding technology is more complex, immature molding
technology will make the product performance is low or after molding can not
meet the requirements of products. UHMW-PE processing, performance of high ductility UHMW-PE, size
stability UHMW-PE, glass fiber UHMW-PE, anti-stick UHMW-PE, acid and alkali
resistance UHMW-PE, high weather resistance UHMW-PE, aging resistance UHMW-PE,
oil resistance UHMW-PE, anti-UHMW-PE, high transparency PE-UH MW, transparent UHMW-PE, medical grade UHMW-PE, food grade UHMW-PE,
high gloss UHMW-PE, folding UHMW-PE, flexural UHMW-PE, high thermal temperature
UHMW-PE, high tensile modulus UHMW-PE, high toughness UHMW-PE.
UHMW-PE material physical properties:
UHMW-PE has excellent impact energy absorption, impact energy
absorption value is higher in all plastics, so the noise damping performance is
very good, has an excellent whitening effect, UHMW-PE has excellent low
temperature resistance, in liquid nitrogen temperature (-169℃) still has
ductility, so it can be used as low temperature resistance components in the
nuclear industry. UHMW-PE health non-toxic, in line with the standards of the
Japanese Health Association, and the United States Food and Drug Administration
and the United States Department of Agriculture recognized, can be used to
contact food and drugs, UHMW-PE surface adsorption capacity is very weak, its
anti-viscosity ability is second only to plastic in the non-viscous PTFE, and
the surface of products and other materials are not easy to stick. UHMW-PE water absorption rate is very low; Compared with other engineering plastics, the density of UHMW-PE
is lower than that of PTFE, 33% lower than that of POM and 30% lower than that
of PBTP. So its products are very light. UHMW-PE has unmatched high tensile strength due to the
structural characteristics of tensile orientation, so it can be obtained by gel
spinning method with high elastic modulus and strength, tensile strength up to
3~3.5Gpa, tensile elastic modulus up to 100~125GPa; Fiber specific strength is so far has been commercialized in all
the higher fiber, 4 times larger than carbon fiber, 10 times larger than steel
wire, 50% larger than fiber, UHMW-PE also has excellent electrical insulation
performance, better than HDPE environmental stress cracking resistance, better
than HDPE fatigue resistance and r ray resistance ability.
UHMW-PE material characteristics:
--UHMW-PE processing melt viscosity is as high as 10 ^ 8 Pa. S,
poor fluidity, its melt flow index is almost zero, so it is difficult to
directly extrusion or injection molding. Its main forming characteristics are as follows:
(1) The material melting viscosity is high, not viscous flow
state, but in a high viscoelastic state. The extrusion process of UHMW-PE in extruder can be regarded as
the process from solid powder to molten rubbery high viscosity elastomer; Unlike ordinary high density ethylene, materials due to heating,
screw rotation of its shear and forward thrust, so that it moves forward while
mixing, gradually become a viscous fluid process. UHMW-PE in the conventional screw extruder processing, it is
difficult to push along the screw groove, but wrapped around the screw
rotation, falling into the state can not be extruded.
(2) Critical shear rate, low melt is easy to fracture. UHMW-PE may produce melt rupture when the shear rate is very low. For ordinary high density, melt rupture occurs when the shear
rate reaches 100/s. Therefore, when UHMW-PE is extruded, the extrusion speed can not
be fast, otherwise it will cause melt rupture and surface cracks. During injection molding, air holes and delamination are caused
by jet flow.
(3)UHMW-PE friction coefficient is low, so that the powder is easy
to hit the palm in the process of feeding, not easy to feed.
(4) Forming temperature range is narrow, easy oxidation
degradation. Because UHMW-PE these molding characteristics make it difficult
to use common thermoplastic processing method molding, and mainly use similar
to ptfe powder pressing sintering molding process. Since the 1980s, foreign research and design of extruder and
injection machine with special structure began, supplemented by the continuous
improvement and exploration of molding process conditions, achieved great
success, so that UHMW-PE has been able to use extrusion and injection and other
methods for molding.
UHMW-PE processing molding:
--UHMW-PE molecular weight is generally more than 1 million, the
density is 0.930-0.940g/CM3, with self-lubrication, excellent impact resistance
and fatigue resistance, when the molecular weight is more than 1.5 million, the
entanglement and intermolecular force of macromolecules are increased to the
extent of deformation and extension of macromolecules, resulting in the
reduction of impact strength. UHMW-PE self-lubrication is excellent, and the friction
coefficient is very low, even in the condition of no lubrication and steel or
brass surface sliding friction, it will not cause gel phenomenon because of
heat, can greatly reduce the energy consumption of equipment. UHMW-PE also has excellent low temperature resistance and can
maintain high impact strength even at -40℃. The film made of UHMW-PE is placed
in a liquid nitrogen bottle (-196℃), and the film is repeatedly folded 100
times in the liquid without the occurrence of brittle-cracking. In addition, UHMW-PE has better long-term mechanical properties,
chemical properties and environmental stress cracking resistance than LDPE and
HDPE. However, THE rigidity and hardness of UHMW-PEA are not high,
roughly equivalent to HDPE. UHMW-PE is difficult to be molded by general thermoplastic
molding equipment because of its high melt viscosity and poor melt fluidity. In addition, the critical shear rate of the melt is low. UHMW-PE processing is mainly similar to powder metallurgy method
for cold pressing sintering molding, sintering products can be machined, adding
processing additives, extrusion, spraying, lamination, hot stamping. UHMW-PEa is suitable for agricultural machinery, automobile,
textile, papermaking, chemical industry, food industry non-viscous, low noise,
self-lubricating parts, such as guide rails, valves, gaskets, bushings,
materials in contact with food, human internal organs, joints and other
devices, can also be used as film, large containers, large special-shaped tubes
and plates and other products.
UHMW-PE manufacturing process:
Polyethylene with a molecular weight of more than 1.5 million is
called "UHMW-PE" ultra-high molecular weight POLYETHYLENE (UHMWPE)
according to the division method of Lip Oil Company. Hoechst (Germany) company, Hercules (USA) company and Mitsui
Petrochemical Company are the world's three major companies in the production
of UHMW-PER, China's main manufacturers are Beijing Auxiliary No.2 Plant,
Shanghai Gaoqiao Petrochemical Company chemical Plant, China Petrochemical,
Qilu Petrochemical Company. High molecular weight polyethylene, can be used to produce
ordinary high density polyethylene by changing the process conditions to
control the molecular weight, production methods are Ziegler method, Solvay
method and solution method. Ziegler process is called low pressure polymerization. It uses titanium oxide and alkyl aluminum G aluminum ethyl or
diethyl aluminum gasification as catalyst, heptane or gasoline as solvent, at
60-90℃C and atmospheric pressure conditions for polymerization. Reactor or vertical tower reactor is generally used in the
reactor. Using tower type reactor, bottom should install multi-layer
mixing propeller, a suspension of ziegler method production technology is the
first solvent catalyst into the reaction with ethylene raw material plant in
polymerization, polymerization of exothermic reaction, reaction temperature
should be cool to regulation, then put to the product of polymerization
catalyst decomposition groove, joined methanol catalyst decomposition; After filtration and drying, UHMW-PE products with average
molecular weight of 1 million to 5 million were obtained. Solvay process is a new production process combining the ring
reactor used in the Phillips process with ziegler catalyst supported by
magnesium compounds. Solvay method uses titanium tetrachloride as catalyst and
alkylaluminum compounds as activators. MgCl2 or MgClOH with large pore size
after burning is mostly used as catalyst carrier. The characteristic of this method is that the catalyst is
adsorbed to the carrier larger than the surface, so that the crystal structure
is spread out, so that most of the transition metal atoms play the role of the
active center, the catalyst efficiency is up to 50-600KG4tio polymerization is
carried out in a closed-loop reaction tube, with cold water jacket outside,
with high-speed turbine agitator to make the catalyst complex. The reaction temperature was 80-90C, the partial pressure of
ethylene was 1.0mpa, and the reaction time was 2-3h. The resulting slurry was filtered by centrifugation, the filter
cake was stripped by steam to remove the residual solvent, and then dried by air
flow. UHMW-PE with average molecular weight of 1.5 million to 6 million could
be prepared. In the solution method, CrO3 was used as the catalyst,
Al7O7-SiO7 as the carrier, and C6 alkane was used as the solvent. The
polymerization was carried out at 170-180℃ above the melting point temperature
of the polymer, and the pressure was controlled in the range of 196-2.94MPa. Ethylene and a small amount of comonohexene as raw materials,
the polymerization of ethylene and polyethylene are dissolved in solvent to form
a homogeneous reaction system; After the polymerization, the ethylene is removed by flash
evaporation, and then the polymer is separated by centrifugation, concentration
and cooling. UHMW-PE with average molecular weight over 1 million can be
prepared by this method.
UHMW-PE applications:
-- Because UHMW-PE has excellent wear resistance, impact
resistance, it is widely used in the machinery manufacturing industry, can make
all kinds of gear, CAM, impeller, roller, pulley, bearing bearing bush,
bushing, cutting shaft, gasket, gasket, elastic coupling, screw and other
mechanical parts. Is given priority to with self lubrication and not sticky
application - UHMW PE can make coal, cement, lime and mineral powder, salt,
grain, powder material hopper, storehouse, the lining of the chute, due to its
excellent self-lubrication, not sticky, can make the powder material in storage
and transportation equipment is not adhesion phenomenon, to ensure stability of
coal, mineral powder, food, such as the hopper, In the past using stainless steel lining for packing
transportation, now use UHMW-PE lining, long-term use, can reduce the
phenomenon of heat, Baosteel transport ore hopper UHMW-PE, than the original
use of metal materials to improve the service life of 10~50 times, with UHMW-PE
hopper lining easy construction, low cost, Therefore, the large power plant conveying coal hopper is also
used in H MWPE, coal mining chute using UHMW-PE manufacturing, can reduce the
tilt Angle, so as to improve the amount of mining, transport 400,000 tons of
coal without the need for more refueling tank, its service life is 2 times
higher than magnesium alloy lining flow groove, UHMW-PE used in sand flow and
other solid conveying pipeline, Compared with steel pipe, the service life is increased 18 times
and the cost is reduced to 1/25. Compared with nylon pipe, the service life is
increased 3 times and the cost is reduced to 1/8. When conveying, the resistance in the tube is 25% smaller than
the metal tube, which greatly improves the conveying efficiency. In the case of chutes, buckets and lining of ore cars, materials
freeze on metal in cold and wet weather with traditional metal materials, while
UHMW-PE does not, thus greatly reducing unloading time. After lining a layer of UHMW-PE plate on the dump hopper of the
bulk carrier, the average unloading time is reduced to 8h from the original
16~20h, UHMW-PE self-moistening is excellent, the soil is easy to slide on its
surface, and will not happen to stick, and its impact resistance, wear resistance
is good, suitable for the production of agricultural and construction machinery
parts. Such as the sliding plate of the combine harvester, the outer
lining plate of the plough, the scraper of the back soil machine, the lining of
the excavator bucket, the lining of the dump car, etc., can greatly improve the
work efficiency and reduce energy consumption.
