This kind of amazing plastic, recycling is so simple

Ultra-high molecular weight polyethylene (UHMWPE), a thermoplastic structural engineering plastic with excellent overall performance in a linear structure, generally has a molecular weight of more than 1.5 million, and has unmatched wear resistance, impact resistance, corrosion resistance, and low temperature resistance. The comprehensive properties of lubrication, absorption of impact energy, and hygienic non-toxicity are called "surprising plastics".

1 Melt characteristics

Although UHMWPE is a thermoplastic, because its molecular weight is too high, the properties exhibited during melting are quite different from those of ordinary thermoplastics, and therefore cannot be processed by conventional processing methods.

1 UHMWPE melts are rubbery, highly elastic, with very high viscosity and poor processing fluidity.

2 UHMWPE has a lower critical shear rate. At lower shear rates, slipstreams or jet flow phenomena occur; jets tend to appear porous or delaminated during injection molding.

3 The friction coefficient is small. In the feeding process, it is easy to slip in the feeding section and cannot be advanced.

2 molding methods

Due to the characteristics of UHMWPE, the promotion and application of UHMWPE are largely limited. However, in recent years, the processing technology of UHMWPE has developed rapidly, from the initial molding to the multi-branching method of extrusion, blow molding and injection molding and other special methods.

1 Molding

The oldest plastic molding method is characterized by: low cost, simple equipment, low investment, not limited by the molecular weight of the processed plastic; the disadvantages are: low production efficiency, labor intensity, prone to oxidation and degradation, unstable product quality, etc. . According to the specific process differences, they are divided into: pressing-sintering-pressing method, sintering-pressing method, press-sintering method, and rapid heating pressing method.

2 extrusion molding

Extrusion molding equipment mainly includes plunger extruder, single screw extruder and twin screw extruder. Among them, co-rotating twin-screw extruders are preferred.

a. Plunger extrusion

Plunger extrusion can be considered as a press-sinter method. This method has a long plasticizing time, a low production efficiency, and a limited product width.

b. Single screw extruder

At present, the single-screw extruder only accounts for 2% of UHMWPE's total processing volume, but the single-screw extrusion technology is the most valuable in terms of economy and practicality.

c. Twin-screw extruder

The twin-screw extruder overcomes the problem of UHMWPE powder slippage in the screw and greatly increases the feed capacity. The co-rotating twin-screw extruder has a small shearing effect on the material and minimizes the degradation of the material during the extrusion process.

3 injection molding

UHMWPE single-screw injection molding process is mainly through the high-speed shear to make the material evenly dispersed, and full of cavity. In contrast, plastic is injected into a molten fluid.

4 Blow molding

Blow molding of UHMWPE is mainly used for large hollow products such as automobile fuel tanks and cartridges.

5 other molding methods

UHMWPE other special molding methods are: jelly spinning, stamping, roll forming, forging, welding and other molding.

3UHMWPE product recovery method

Due to UHMWPE's ultra-high mechanical properties and non-processability, the recycling of UHMWPE products has also become an important problem. Even some waste stations refuse to recycle this product directly.

The current recycling methods are:

1 grinding method

The UHMWPE product is crushed and then made into powder by a granulator or other equipment and reused.

2 Shear Tear

For some fiber products, the fibers can be sheared and can be applied directly after cutting.

Application of 4UHMWPE

1 Ultra-high molecular weight polyethylene is widely used in trailers, silos, chute linings of powdery documents such as coal, lime, cement, mineral powder, salt, grain, etc.;

2 In defense and military equipment, a large number of protective clothing, helmets, bulletproof materials;

3 In aerospace engineering, ropes that can be used for the landing of a space shuttle and parachute suspensions for heavy objects on planes replace traditional steel ropes and synthetic fiber ropes, and their development speed is extremely rapid;

4 In the civilian sector, ropes, ropes, sails and fishing gear made are suitable for marine engineering;

5In industrial applications, it can be used as pressure-resistant containers, conveyor belts, filter materials, automotive buffer boards, etc. In construction, it can be used as walls, partitions, etc.

6 Safety helmets, snowboards, sail boards, fishing rods, rackets and bicycles, gliders, ultralight aircraft parts, etc. have been made on sporting goods;

7 In medicine, it has been used in dental materials, medical implants, and plastic and suturing applications. It has good biocompatibility and durability, high stability, and no allergic reactions. It has been used clinically.

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