CN101486250B - Low-temperature and low-pressure extrusion method of ultra-high molecular weight polyethylene - Google Patents

Abstract

The invention discloses an ultrahigh molecular weight polyethylene low-temperature and low-pressure extruding method, which comprises the following steps: loading ultrahigh molecular weight polyethylene powder raw materials with the molecular weight more than or equal to 150 millions into an extruder, and pressing the raw materials for 3 to 5 minutes at a temperature of between 125 and 130 DEG C and a pressure of between 25 and 50MPa; melting the ultrahigh molecular weight polyethylene powder for 0.5 to 1.0 hour at a temperature of between 150 and 200 DEG C; cooling the molten fusant to the temperature of between 150 and 160 DEG C at a plunger speed of between 0.005 and 0.1 millimeter/second, and extruding the cooled molten fusant from an opening mold with the length-diameter ratio of between 2:1-4:1 so as to obtain an ultrahigh molecular weight polyethylene rod with a smooth surface and without distortion, wherein the extruding pressure is between 3 and 13MPa. The ultrahigh molecularweight polyethylene low-temperature and low-pressure extruding method utilizes common plunger extruding equipment to achieve continuous extrusion molding in one step without other changes, and low-temperature and lower-pressure processing reduces the energy utilization, and saves the cost.

Description

Low-temperature and low-pressure extrusion method of ultra-high molecular weight polyethylene

technical field

The invention relates to an extrusion method of ultra-high molecular weight polyethylene for producing plastic products such as various rods and pipes by using ultra-high molecular weight polyethylene as a raw material.

Background technique

Ultra-high molecular weight polyethylene (UHMWPE) is a thermoplastic with extremely high molecular weight. The average molecular weight of UHMWPE defined by ISO 11542 and ASTM D4020 is greater than 1 million and 3.1 million, respectively. Compared with many polymer materials, UHMWPE has outstanding characteristics such as self-lubrication, small friction coefficient, low wear, impact and stress crack resistance, chemical corrosion resistance and biocompatibility, and is the material of choice for artificial joints. However, clinical follow-up has found that the wear resistance of UHMWPE still cannot meet the requirements of long-term use, and improving its wear resistance is one of the key and difficult research directions in the biomaterials industry. Among them, cross-linking modification is a research hotspot. Although this method improves the wear resistance, the inevitable chain scission degradation and free radical oxidation during the cross-linking process reduce other mechanical properties of UHMWPE, so it is still being improved. Improving wear resistance by particle-reinforced UHMWPE is also one of the exploration directions. However, due to uneven particle dispersion and poor particle/UHMWPE interface, the particles fall off during the friction process, causing severe abrasive wear, so it is not suitable for artificial joints. In conclusion, modification has not solved this difficult problem.

A study of the wear mechanism of artificial joints found that melting defects in ultra-high molecular weight polyethylene (UHMWPE) were an important factor leading to lower-than-expected wear performance. At present, UHMWPE is usually processed by melt extrusion and mold forming. During melt processing, UHMWPE ultra-long chains form a high-density disordered entanglement network, and its molecular segments respond slowly to thermal motion, and the chain diffusion between resin powders is extremely slow, resulting in the formation of defects in the powder morphology. Loose along the interface and become wear particles. Secondly, UHMWPE has almost no fluidity. Using the conventional melt extrusion method, melt fracture is prone to occur. It is difficult to control the heat release and heat storage during the extrusion process, which leads to the degradation of macromolecules, making the molecular weight of the product less than one million, resulting in Various excellent properties of UHMWPE also weaken and disappear. In addition, the fluidity of UHMWPE in the molten state is extremely poor. In order to increase its fluidity, a large amount of various internal and external lubricants, nucleating agents and other processing aids are usually added to UHMWPE raw materials, and even relatively low molecular weight polymers. vinyl. However, this kind of doping will also greatly reduce the inherent excellent characteristics of UHMWPE, and the "solvation" effect of these substances will affect the stability of the product. Therefore, instead of modifying UHMWPE, it is better to improve its processing method to fundamentally solve the problem of wear resistance. Since the existing molding processing methods severely restrict the popularization and application of this high-performance plastic, it is necessary to explore new processing principles and develop new processing methods.

The processing performance of ultra-high molecular weight polyethylene (UHMWPE) depends on the motion state of its long chains. In the molten state, the long chains are entangled and the relaxation is slow; in the crystalline state, the entanglement points are reduced. Polyethylene (PE) has three crystal forms: orthorhombic, hexagonal and monoclinic. The hexagonal crystal structure is an extended chain structure, the platelet thickness is large, and the chain fluidity is higher than other phases. However, during the equilibrium process, hexagonal crystals only exist stably at high temperature and high pressure (>240°C, >360MPa), and it is difficult to meet such harsh conditions in actual processing. Considering the huge size of UHMWPE molecular chains, its phase transition is much slower than that of small molecular materials, and its final thermodynamic stable state is often difficult to reach, so there may be a metastable state during the phase transition process. According to the chain entanglement and kinetic theory in polymer condensed matter physics, the phase and phase transition behavior are closely related to the properties of materials, and the properties of materials change significantly when phase transitions occur. If the processing parameters can be controlled to form a metastable state with better fluidity, melting defects can be reduced and wear resistance can be improved. Therefore, the present invention proposes to use the metastable phenomenon to process UHMWPE in a metastable state with good fluidity, and open up a new way to solve the problem of difficult processing.

Contents of the invention

The purpose of the present invention is to overcome the above-mentioned deficiencies in the prior art and provide a low-temperature and low-pressure extrusion method for ultra-high molecular weight polyethylene. The present invention realizes through following technical scheme:

A low-temperature and low-pressure extrusion method for ultra-high molecular weight polyethylene, comprising the steps of:

(1) Feed ultra-high molecular weight polyethylene powder raw materials with molecular weight ≥ 1.5 million into the extruder, and compact them for 3 to 5 minutes at 125°C to 130°C with a pressure of 25 to 50MPa;

(2) Melting the ultra-high molecular weight polyethylene powder at 150-200°C for 0.5-1.0 hours;

(3) Cool the molten melt to 150-160°C and extrude it from a die with a length-to-diameter ratio of 2:1-4:1 at a plunger speed of 0.005-0.1mm/s, and the extrusion pressure is 3 ~13MPa, to obtain ultra-high molecular weight polyethylene rods with smooth surface and no distortion.

In the above low-temperature and low-pressure extrusion method for ultra-high molecular weight polyethylene, the barrel diameter of the extruder is 15mm.

In the above low-temperature and low-pressure extrusion method of ultra-high molecular weight polyethylene, the pressure when the ultra-high molecular weight polyethylene powder is melted in step (2) is 0-50 MPa.

In the above low-temperature and low-pressure extrusion method of ultra-high molecular weight polyethylene, the extrusion speed of ultra-high molecular weight polyethylene in step (3) decreases with the increase of extrusion temperature. (The extrusion temperature increases with the molecular weight of ultra-high molecular weight polyethylene)

In the above low-temperature and low-pressure extrusion method for ultra-high molecular weight polyethylene, in step (3), the extrusion pressure decreases as the aspect ratio of the extrusion die increases.

In the above low-temperature and low-pressure extrusion method for ultra-high molecular weight polyethylene, in step (1), the ultra-high molecular weight polyethylene powder raw material with a molecular weight of 3.5 million is fed into an extruder with a barrel diameter of 15 mm, and the Pressure, compact for 3 minutes.

In the above low-temperature and low-pressure extrusion method of ultra-high molecular weight polyethylene, in step (2), the ultra-high molecular weight polyethylene powder is melted at 200° C. and 45 MPa for 1.0 hour.

In the above-mentioned ultra-high molecular weight polyethylene low-temperature and low-pressure extrusion method, in step (3), the melted melt is cooled to 155°C at a plunger speed of 0.1mm/s, and the length-to-diameter ratio is 10mm/5mm from the die Extrusion, the extrusion pressure is 9.5MPa.

In the present invention, the UHMWPE powder raw material with a molecular weight ≥ 1.5 million is fed into the extruder, compacted at 25-130°C for 3-5 minutes, and then melted at 150-200°C for 0.5-1.0 hour to eliminate the initial boundary of the powder raw material structure. Ultra-high molecular weight polyethylene (UHMWPE) that can keep the molecular weight of the extruded material substantially unchanged or more than one million; the present invention controls the extrusion temperature of UHMWPE to be about 10-20° higher than the theoretical melting point of polyethylene crystals ℃, that is, 150-160 ℃, while controlling the extrusion plunger speed to 0.01-0.1mm/s, to induce the formation of metastable polyethylene with high fluidity, thereby significantly reducing the extrusion pressure, reducing the melting defects of UHMWPE, and improving the quality of UHMWPE Wear resistance, the above-mentioned metastable phase polyethylene is at the solid-melt transition boundary, its aggregated structure is similar to the equilibrium hexagonal crystal under high temperature and pressure, and its fluidity is much higher than that of molten polyethylene or chains with entangled ultra-long molecular chains. Slow-moving solid polyethylene (including orthorhombic and amorphous); the present invention controls the processing parameters, especially the melting process, extrusion temperature and speed, according to the molecular weight and mold of ultra-high molecular weight polyethylene (UHMWPE), so as to control The thickness of the lamellae and the extensional flow field in the mold make the metastable phase of UHMWPE with good fluidity stable.

The present invention generally has the following beneficial effects: the present invention heats the ultra-high molecular weight polyethylene (UHMWPE) in the extruder to a temperature slightly higher than its melting point by controlling the heating temperature, so that UHMWPE will not be degraded during extrusion , so that the molecular weight of the extruded material is guaranteed to remain basically unchanged, so that the product can still maintain the excellent characteristics of UHMWPE; secondly, the present invention extrudes UHMWPE at low pressure by inducing a metastable phase with high fluidity, without using processing aids, avoiding the quality of the final product due to the "solvation" effect of the processing aids; in addition, the present invention utilizes common plunger extrusion equipment to realize one-step continuous extrusion molding, and only needs to accurately control the temperature (±1 ℃), no other modifications are required, and low-temperature and low-pressure processing reduces energy utilization and saves costs.

Description of drawings

Figures 1a to 1c are scanning electron microscope (SEM) photos of ultra-high molecular weight polyethylene (UHMWPE) commercial samples (GUR1050, Ticona Ltd.) processed by conventional plunger extrusion methods, with a molecular weight of 4.9 million.

Fig. 2 a～Fig. 2 c is the scanning electron microscope (SEM) photograph of the ultrahigh molecular weight polyethylene (UHMWPE) sample (Basell 1900, Montel Ltd.) processed by low temperature and low pressure plunger extrusion method in the embodiment of the present invention, and its molecular weight is 600 Ten thousand. Among them, Figure 1a and Figure 2a are the surface morphology after ultrathin sectioning, Figure 1b and Figure 2b are the surface morphology after freeze fracture, and Figure 1c and Figure 2c are the surface morphology after mechanical polishing and corrosion.

Detailed ways

Embodiment one

Feed ultra-high molecular weight polyethylene (UHMWPE) powder with a molecular weight of about 3.5 million into the barrel of a plunger extruder (15mm in diameter), compact it at 120°C with a pressure of 45MPa for 3 minutes, and then melt at 200°C for 1.0 hour. Then cool to 150°C, extrude from a die with a length-to-diameter ratio of 10mm/5mm at a plunger extrusion speed of 0.01mm/s, and extrude at a pressure of about 10.5MPa to obtain UHMWPE rods with smooth surfaces and no distortion .

Embodiment two

Feed ultra-high molecular weight polyethylene (UHMWPE) powder with a molecular weight of about 3.5 million into the barrel of a plunger extruder (15mm in diameter), compact it at 120°C with a pressure of 45MPa for 3 minutes, and then melt at 200°C for 1.0 hour. Then cool to 155°C, extrude from a die with a length-to-diameter ratio of 10mm/5mm at a plunger extrusion speed of 0.1mm/s, and extrude at a pressure of about 9.5MPa to obtain a UHMWPE rod with a smooth surface and no distortion .

Embodiment three

Feed ultra-high molecular weight polyethylene (UHMWPE) powder with a molecular weight of about 3.5 million into the barrel of a plunger extruder (15mm in diameter), compact it at 120°C with a pressure of 45MPa for 3 minutes, and then melt at 200°C for 1.0 hour. Then cool to 160°C, extrude from a die with an aspect ratio of 10mm/5mm at a plunger extrusion speed of 0.005mm/s, and extrude at a pressure of about 9.0MPa to obtain a UHMWPE rod with a smooth surface and no distortion .

Embodiment four

Feed ultra-high molecular weight polyethylene (UHMWPE) powder with a molecular weight of about 2.5 million into the barrel of a plunger extruder (15mm in diameter), compact it at 120°C with a pressure of 45MPa for 3 minutes, and then melt at 200°C for 1.0 hour. Then cool to 155°C, extrude from a die with a length-to-diameter ratio of 10mm/5mm at a plunger extrusion speed of 0.1mm/s, and obtain a UHMWPE rod with a smooth surface and no distortion.

Embodiment five

Feed ultra-high molecular weight polyethylene (UHMWPE) powder with a molecular weight of about 4.9 million into the barrel of a plunger extruder (15mm in diameter), compact it at 120°C with a pressure of 45MPa for 3 minutes, and then melt at 200°C for 1.0 hour. Then cool to 160°C and extrude from a die with a length-to-diameter ratio of 10mm/5mm at a plunger extrusion speed of 0.005mm/s to obtain a UHMWPE rod with a smooth surface and no distortion.

Embodiment six

Feed ultra-high molecular weight polyethylene (UHMWPE) powder with a molecular weight of about 3.5 million into the barrel of a plunger extruder (15mm in diameter), compact it at 120°C with a pressure of 45MPa for 3 minutes, and then melt at 150°C for 0.5 hours. Extrude from a die with a length-to-diameter ratio of 10mm/5mm at a plunger extrusion speed of 0.01mm/s, and the extrusion pressure is about 10MPa to obtain a UHMWPE rod with a smooth surface, small outlet expansion, and no distortion .

Embodiment seven

Feed ultra-high molecular weight polyethylene (UHMWPE) powder with a molecular weight of about 3.5 million into the barrel of a plunger extruder (diameter 15mm), compact it at 120°C with a pressure of 45MPa for 3 minutes, and then melt it freely and without pressure at 200°C 1.0 hour, then cooled to 155°C, extruded from a die with a length-to-diameter ratio of 10mm/5mm at a plunger extrusion speed of 0.05mm/s, and the extrusion pressure was about 12.5MPa to obtain a smooth surface and no distortion. UHMWPE rods.

Embodiment Eight

Feed ultra-high molecular weight polyethylene (UHMWPE) powder with a molecular weight of about 3.5 million into the barrel of a plunger extruder (15mm in diameter), compact it at 130°C with a pressure of 25MPa for 3 minutes, and then melt at 160°C for 0.5 hours. Then cool to 155°C, extrude from a die with a length-to-diameter ratio of 20mm/5mm at a plunger extrusion speed of 0.035mm/s, and the extrusion pressure is about 3.3MPa to obtain a UHMWPE rod with a smooth surface and no distortion material.

Embodiment nine

Feed ultra-high molecular weight polyethylene (UHMWPE) powder with a molecular weight of about 3.5 million into the barrel of a plunger extruder (15mm in diameter), compact it at 25°C with a pressure of 50MPa for 5 minutes, and then melt at 200°C for 1.0 hour. Then cool to 155°C, extrude from a die with a length-to-diameter ratio of 10mm/5mm at a plunger extrusion speed of 0.05mm/s, and obtain a UHMWPE rod with a smooth surface and no distortion.

Embodiment ten

Feed ultra-high molecular weight polyethylene (UHMWPE) powder with a molecular weight of about 6 million into the barrel of a plunger extruder (15mm in diameter), compact it at 127°C with a pressure of 50MPa for 5 minutes, and then melt it at 200°C for 1.0 hour. Then cool to 157°C, extrude from a die with a length-to-diameter ratio of 10mm/5mm at a plunger extrusion speed of 0.05mm/s, and obtain a UHMWPE rod with a smooth surface and no distortion. Comparing the scanning electron micrographs of the commercial samples processed by the traditional plunger extrusion method (Fig. 1a-1c) and the samples processed by the low-temperature and low-pressure extrusion method (Fig. 2a-2c), the UHMWPE processed by the patented method has obvious melting defects. reduce.

Comprehensive analysis of all implementation methods, draw the following conclusions:

The extrusion processing temperature of ultra-high molecular weight polyethylene (UHMWPE) in the present invention is slightly higher than its melting point, and far lower than the traditional processing temperature (>200°C), which can prevent high-temperature degradation, thereby reducing the molecular weight of UHMWPE, and correspondingly loses UHMWPE has excellent properties due to its ultra-high molecular weight.

The extrusion process of the present invention forms the UHMWPE without using processing aids, and avoids affecting the quality of the final product due to the "solvation" effect of the processing aids.

The present invention utilizes ordinary plunger extrusion equipment to realize one-step continuous extrusion molding, only needs to precisely control the temperature (±1°C), and does not require other modifications, and the low-temperature and low-pressure processing reduces energy utilization and saves costs.

Claims (4)

1. The low-temperature and low-pressure extrusion method of ultra-high molecular weight polyethylene is characterized in that it comprises the following steps: (1) Feed ultra-high molecular weight polyethylene powder raw materials with molecular weight ≥ 1.5 million into the extruder, and compact them for 3 to 5 minutes at 125°C to 130°C with a pressure of 25 to 50MPa; (2) Melting the ultra-high molecular weight polyethylene powder at 150-200°C for 0.5-1.0 hours; (3) Make the melt temperature after melting be 150～160°C and extrude from a die with an aspect ratio of 2:1～4:1 at a plunger speed of 0.005～0.1mm/s, and the extrusion pressure is 3-13MPa, to obtain ultra-high molecular weight polyethylene rods with smooth surface and no distortion. 2. The low-temperature and low-pressure extrusion method for ultra-high molecular weight polyethylene according to claim 1, characterized in that in step (2), the pressure when the ultra-high molecular weight polyethylene powder is melted is 0-50 MPa. 3. the low-temperature and low-pressure extrusion method of ultra-high molecular weight polyethylene as claimed in claim 1, is characterized in that extrusion temperature also increases with the increase of ultra-high molecular weight polyethylene molecular weight in step (3), and ultra-high molecular weight polyethylene The extrusion speed decreases with the increase of extrusion temperature. 4. The low-temperature and low-pressure extrusion method for ultra-high molecular weight polyethylene as claimed in claim 1, wherein the extrusion pressure decreases as the aspect ratio of the extrusion die increases in step (3).

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