RU2791530C1 - Extruded anti-friction composite based on ultra-high molecular weight polyethylene - Google Patents

Abstract

FIELD: manufacture of wear-resistant polymer products.

SUBSTANCE: extrudable polymer composite material for use in additive technology to create parts and assemblies includes a matrix of ultra-high molecular weight polyethylene and fillers. Low-pressure polyethylene, stearic acid and carbon fiber are used as fillers.

EFFECT: invention makes it possible to reduce the melt flow rate, the coefficient of friction and increase the wear resistance of products made of a composite material.

1 cl, 2 tbl

Description

The invention relates to the field of polymer materials science, to the production of a polymer material with improved performance properties based on ultra-high molecular weight polyethylene by extrusion. The material can be used for the manufacture of various parts of friction units of machines and mechanisms, for lining equipment surfaces, as well as in additive technologies.

Due to their unique properties, such as high frost resistance, impact strength, chemical resistance, thermal stability and wear resistance, polymer composite materials (PCM) based on ultra-high molecular weight polyethylene (UHMWPE) have a wide range of applications in mechanical engineering and medicine. However, despite the high physical and mechanical properties of UHMWPE, the industrial development of the production of products is associated with a number of insurmountable difficulties associated with its ultra-large molecular weight and ultra-high viscosity, which does not allow the use of conventional and most effective processing methods for thermoplastics, such as extrusion and injection molding. . For the widespread introduction and consumption of PCM based on UHMWPE, it is necessary to develop technical solutions without degrading the performance characteristics inherent in UHMWPE, but at the same time improving the technological properties and the possibility of processing products by methods of both injection molding and extrusion, which will significantly expand the scope of these polymeric materials. , for example, in 3D technologies for obtaining parts and assemblies of complex shape.

Known polymer nanocomposite material for tribotechnical purposes based on ultra-high molecular weight polyethylene with an oriented structure and multi-walled carbon nanotubes as a filler, patent RU 2625454, C08L 23/06, C08K 3/04, C08K 7/04, C08J 5/16, B82Y 30/00, publ. July 14, 2017 [1]. The polymer material contains a matrix of ultra-high molecular weight polyethylene with an oriented supramolecular structure with a molecular weight of 5·10 ⁶ g/mol and a filler of multi-walled carbon nanotubes with a diameter of 4-15 nm and a length of more than 2 μm in an amount of 0.1-1 wt.%. The presented material is distinguished by a uniform distribution of the filler in the volume of the polymer matrix and an oriented structure of the polymer matrix, which made it possible to obtain a material with an increased tensile strength and good tribological properties. The disadvantage of this polymeric material is the low elongation at break in the range of 60-70% and the high labor intensity of the production process (three stages). The well-known invention does not imply an increase in the manufacturability of this composite, but an increase in tribomechanical characteristics (strength, wear resistance).

Known hierarchically reinforced heteromodular extrudable solid lubricant nanocomposite based on ultra-high molecular weight polyethylene and a method for producing it, patent RU 2674258, C10M 107/04, C08L 23/06, B82B 3/00, C08K 3/04, C08K 7/04, C08J 5/16, B82Y 30/00, publ. December 6, 2018 [2]. In the polymer nanocomposite, ultra-high molecular weight polyethylene with a molecular weight of 4.5⋅10 ⁶ g/mol and a particle size of 5-15 μm is used as a matrix; a high-density ethylene copolymer grafted with HDPE-g-SMA maleic anhydride in the form of ground granulate is used as a filler with a particle size of 160-250 microns (in the amount of 5-10 wt.%), as well as nanometer-sized carbon fibers with a diameter of 60 nm (in the amount of 0.3-0.5 wt.%) and a millimeter dimension with a length of about 2 mm (in amount of 2-5 wt.%). The invention relates to the field of obtaining high-strength, wear-resistant and extrudable polymer nanocomposites based on ultra-high molecular weight polyethylene for tribounits, including those operating in extreme conditions of the Far North. The technical result of the invention is to obtain a nanocomposite with high strength and tribological properties and satisfactory fluidity for additive manufacturing technologies. The specified technical result is achieved by the fact that the hierarchically reinforced heteromodular extrudable solid lubricant nanocomposite based on UHMWPE includes, wt.%: carbon fibers of nanometer dimension 0.3-0.5, carbon fibers of millimeter dimension 2-5, high-density ethylene copolymer HDPE-g-SMA 5-10 , UHMWPE - the rest. The method for producing the proposed nanocomposite consists in mixing the initial components and obtaining a nanocomposite sample by hot pressing at a pressure of 10±0.5 MPa, a temperature of 200±5°C with a subsequent cooling rate of 3-4°C/min.

Known extrudable anti-friction composite based on ultra-high molecular weight polyethylene, patent RU 2674019, C08J 5/16, C08L 23/06, C08L 51/06, C08K 3/04, C08K 7/06, publ. December 4, 2018 [3]. The invention relates to an extrudable anti-friction composite based on ultra-high molecular weight polyethylene and can be used to obtain anti-friction products in friction units in mechanical engineering and medicine using additive technologies. The composite contains ultra-high molecular weight polyethylene with a molecular weight of 4⋅10 ⁶ g/mol, a copolymer of high density ethylene with grafted vinyltrimethoxysilane (HDPE-g-VTMS) or a copolymer of high density ethylene with grafted maleic anhydride (HDPE-g-SMA) in the form of ground granulate with particle size 160-250 microns and reinforcing carbon fibers having a diameter of 7.5-15.0 microns and a length of 75-200 microns. The resulting composite is characterized by a uniform distribution of the filler in the volume of the polymer matrix and a spherulite supramolecular structure, and also has an increased tensile strength and good tribological properties. In this case, a high density vinyltrimethoxysilane grafted ethylene copolymer (HDPE-g-VTMS) or a high density maleic anhydride grafted ethylene copolymer (HDPE-g-SMA) is used to reduce the viscosity of UHMWPE composites.

The method for obtaining this hierarchically reinforced composite includes the following steps:

1) Drying of UHMWPE and HDPE-g-VTMS and HDPE-g-SMA copolymers at a temperature of 100-110°C for 1.5 hours. The mineral filler carbon fibers are dried at a temperature of 200-210°C for 1.5 hours. The drying process is carried out in a drying cabinet under the included exhaust ventilation.

2) To achieve a uniform distribution by volume and eliminate the agglomeration of fillers in an alcohol solution, an ultrasonic disperser with a submersible indenter UZDN - A with an operating frequency of 22 kHz is used; dispersion time from 1 to 5 min.

3) The resulting suspension is combined with UHMWPE powder and additional homogenization is carried out in an ultrasonic bath PSB-Hals for 7-10 minutes.

4) Mixing is carried out in a high speed (12000 rpm) homogenizer MP 302 for 2 minutes.

5) Then the mixtures are dried in an oven at a temperature of 100-110°C for 2 hours to evaporate the solvent under the included exhaust ventilation.

6) The mold is placed in a hydraulic press MS - 500. The dimensions of the resulting blanks are approximately 65 * 55 * 12.7 mm. Heating is carried out using a split furnace, consisting of two heaters. The heating process is regulated by means of the RPN control device - 4; the heating and cooling rate is 2-3°C/min. The samples are pressed out when the oven is cooled to a temperature of 60-80°C.

Thus, it has been shown that the process of obtaining a powder composite is energy-intensive and labor-intensive, and although the authors claim this material as an extrudable anti-friction composite based on ultra-high molecular weight polyethylene, in essence it is obtained by hot pressing. This invention is the closest in technical essence to obtaining the material we claim, however, this material cannot be a prototype, because it is impossible to compare physical-mechanical and tribotechnical indicators due to different modes of sample testing.

Known works on the modification of UHMWPE carbon fibers brand "Belum", obtained by hot pressing [4]. The described material based on UHMWPE, modified with 5 wt.% HC, although obtained by hot pressing, was taken as a prototype, because the conditions for carrying out physical-mechanical and tribological characteristics are the same.

The technical objective of the present invention is to obtain a polymer composite material with high tribotechnical properties, and having satisfactory fluidity for the production of products by extrusion.

To obtain the proposed polymer composite material, the following powders were used:

- UHMWPE brand GUR‑4113 with a molecular weight of 3.9·10 ⁶ g/mol manufactured by Ticona (China);

- low-pressure polyethylene (HDPE) grade PE2NT11 manufactured by OJSC Kazanorgsintez (Russia);

- stearic acid (SA) wt. a share of at least 99.30% of the production of Component-Reaktiv (Russia);

- filler - "Belum" - carbon fiber (CF) brand LO-1-12N / 40, on the surface of which a layer of organofluorine compounds was deposited by plasma-chemical processing (JSC "SvetlogorskKhimvolokono", Belarus).

The selection of the quantitative contents of the initial components of the extrudable polymer matrix was established experimentally according to the criteria for increasing wear resistance and the value of the melt flow index (Table 1). Since all the considered matrices are in the region of the index required for extruded materials (0.3–12 g/10 min), the choice of the composition of the composition 85 wt.% UHMWPE, 5 wt.% PE, 5 wt.% SC is due to according to the criterion of maximum reduction in the rate of mass wear, in comparison with the other options considered.

Table 1

Material under study ε _p ,% σ _r, MPa MFR, g/10 min I, mg/h UHMWPE + 5 wt.% HDPE + 3 wt.% SC 849 29.1 7.02 0.40 UHMWPE+ 5 wt.% HDPE + 5 wt.% SC 765 30.7 4.14 0.20 UHMWPE+ 10 wt.% HDPE + 3 wt.% SC 722 30.8 0.29 0.43 UHMWPE + 10 wt.% HDPE + 5 wt.% SC 658 24.8 0.48 0.53

Note: ε _p , % - relative elongation at break; σ _p , MPa - tensile strength; MFR, g/10 min – melt flow index; I, mg/h - mass wear rate.

Based on the selected extrudable matrix (85 wt.% UHMWPE, 5 wt.% PE, 5 wt.% SC), a composite reinforced with carbon fibers in an amount of 5 wt.%.

The novelty of the invention lies in the fact that the proposed composition of an extrudable anti-friction polymer composite material based on UHMWPE, containing low-pressure polyethylene and stearic acid in the stated quantitative ratios to reduce the viscosity of the composition, as well as carbon fiber as a reinforcing additive.

An example of obtaining the claimed composite material.

The initial components were weighed on an analytical balance with an accuracy of 0.0001 g.

The starting components were placed in portions in a rotary mixer of a plastic order PL2200 from Brabender (Germany) and mixed at a temperature of 180 ± 5°C and a roll speed of 30 rpm for 5 min. The resulting solid mixture was mechanically crushed and then extruded into ribbons 2-2.5 cm wide and 1.4-2 mm thick and cylindrical molds 10 mm in diameter.

Physical and mechanical characteristics in tension (relative elongation at break (ε _r ) , ultimate tensile strength (σ _r ) were studied according to GOST 11262-80 on a UTS-20K testing machine (Germany) at room temperature and a gripper extension speed of 50 mm/min Type 5 paddles were used as samples.

The tribotechnical characteristics were determined on an II-5018 friction machine according to the “finger-disk” scheme (the sample is a cylinder with a diameter of 10 mm and a height of 16 mm, the counterbody is a steel shaft with a hardness of 45–50 HRC and a roughness R _a = 0.06–0.07 µm), at a load of 200 N, a linear sliding velocity of 0.5 m/s, and a test time of 3 h. The wear rate ( I) was estimated from the weight loss of the samples per unit time.

The melt flow rate by mass was studied according to GOST 11645-2021 on a device for measuring melt flow XNR-400B

Table 2 presents the physical, mechanical and tribological properties of PCM based on the selected polymer matrix, modified with 5 wt.% carbon fiber, obtained by extrusion.

table 2

Material under study ε _p ,% σ _r, MPa I, mg/h f MFR, g/10 min UHMWPE + 5 wt.% HDPE + 5 wt.% SC 765 30.7 0.2 0.20 4.14 UHMWPE + 5 wt.% HDPE + 5 wt.% SC + 5 wt.% HC 664 29.5 0.14 0.19 0.30 UHMWPE+5 wt. %HC (analogue) 290 36.0 0.16 0.27 -

Note: ε _р , % – relative elongation at break; σ _r , MPa – tensile strength; I, mg/h – mass wear rate; f is the coefficient of friction; MFR, g/10 min – melt flow index.

It has been established that the reinforcement of the selected extrudable matrix with carbon fibers leads to a decrease in the mass wear rate by 1.5 times while maintaining the physical and mechanical parameters of the matrix. It is shown that the melt flow index decreases by 14 times, but remains in the region of the index required for extruded materials.

Compared with the analogue, the claimed composite is characterized by a 2.2-fold increase in relative elongation with a slight decrease in strength, which is apparently associated with a decrease in viscosity. From Table 2 it can be seen that the reinforcement with carbon fibers leads to some reduction in the mass wear rate, while the friction coefficient decreases by 1.4 times.

Thus, the developed composition is an effective solution that makes it possible to obtain extruded materials with improved tribotechnical parameters, which will increase the service life of products and expand their scope.

Literature

1. Patent RU 2625454, C08L 23/06, C08K 3/04, C08K 7/04, C08J 5/16, B82Y 30/00, publ. 07/14/2017.

2. Patent RU 2674019, C08J 5/16, C08L 23/06, C08L 51/06, C08K 3/04, C08K 7/06, publ. 04.12.2018.

3. Patent RU 2674258C1, C10M 107/04, C08L 23/06, B82B 3/00, C08K 3/04, C08K 7/04, C08J 5/16, B82Y 30/00, publ. 12/06/2018.

4. Kolesova E.S., Gogoleva O.V., Petrova P.N., Markova M.A., Chirikov A.A. Development of tribotechnical composites based on ultra-high molecular weight polyethylene // Materialovedenie. - 2020. - No. 9. - P. 34-37.

Claims (2)

An extrudable polymer composite material for use in additive technology to create parts and assemblies, including a matrix of ultra-high molecular weight polyethylene with a molecular weight of 3.9 10 ⁶ g/mol and fillers, which are low-pressure polyethylene, stearic acid and carbon fiber in the following ratio of components, wt.%: Low-pressure polyethylene 5 Stearic acid 5 Carbon fiber 5 Ultra high molecular weight polyethylene rest