KR100387771B1 - Thermoplastic composition with enhanced abrasion - Google Patents

Abstract

A self-lubricating polymeric composition suitable for forming a low friction shaped article, which comprises 70 to 99.5 wt% of a thermoplastic polymer and 30 to 0.5 wt% of a melt blend of a lubricating system comprising ultra high molecular weight polyethylenes, pentaerythritol stearate and a calcium carbonate.

Description

Thermoplastic Compositions with Enhanced Abrasion

Thermoplastic polymers such as polyamides, polyesters, polyphenylene sulfides, polyoxymethylenes, polyolefins, styrene polymers and polycarbonates have been identified as polymers that exhibit good moldability and chemical resistance and also exhibit exceptional mechanical and electrical properties. do. However, these polymers may exhibit inadequate friction properties when utilized in some frictional environments, such as plastic to metal and plastic to plastic contact surfaces. Many lubricating compositions have been applied to thermoplastic polymers to enhance the friction and abrasion of moldings made from thermoplastic polymers, but in some applications, for example, the use of some lubricants is prohibited, for example in food processing, garment manufacturing, and the like It was due to the pollution that could be caused and the pollution caused by its volatility.

Attempts have been made to incorporate lubricating oil directly into the polymer matrix prior to producing the moldings in order to enhance the friction performance and reduce the surface wear of articles made from thermoplastic polymers. Solid lubricants and fibers (eg graphite, mica, silica, talc, boron nitride and molybdenum sulfide), paraffin wax, petroleum and synthetic lubricating oils, and other polymers (eg polyethylene and polytetrafluoroethylene Many materials, including), have been added to thermoplastic polymers to enhance friction and wear properties. However, various combinations of additions of these additives to thermoplastic polymers have improved frictional properties while reducing other desirable physical and mechanical properties. Some additives have been found to be satisfactory for a short period of time at low speeds and during degradation. However, the frictional properties of most of these lubricants deteriorate considerably over time under increased load.

There is a need to provide a non-toxic self-lubricating thermoplastic composition having surface wear resistance and low friction properties even under increased load over a long period of time. Suitable compositions are those which retain the desirable mechanical and physical properties associated with thermoplastic polymers when made into moldings and should be safely utilized in the food processing and garment manufacturing industries.

Summary of the Invention

The present invention relates to a self-lubricating composition suitable for forming low friction moldings, wherein the present invention is a melt mixture of about 70 to about 99.5 weight percent thermoplastic polymer and about 30 to about 0.5 weight percent lubrication system. Ultra high molecular weight polyolefin, pentaerythritol tetrastearate (PETS) and calcium carbonate. Processing aids that do not affect the properties of the present invention can be added to the composition to improve physical properties and processing such as, for example, dispersing a lubrication system in the polymer matrix.

The composition is a self-lubricating molding that is useful in many applications where low friction and reduced wear properties are desired and exhibits good frictional properties such as bearings, gears, cams, rollers, sliding plates, pulleys, levers, guides, conveyor links. And the like.

The present invention relates to a self-lubricating low wear composition containing a thermoplastic polymer and a lubrication system suitable for use as a molding resin for forming moldings. Moldings made from this composition exhibit reduced surface wear under load and exhibit low friction.

The present invention relates to self-lubricating compositions that can be made into moldings that exhibit good frictional properties. Generally, the composition may be characterized as a mixture of about 70 to about 99.5 weight percent thermoplastic polymer and about 30 to about 0.5 weight percent lubrication system. Typically, the composition may contain about 85 to about 99 weight percent thermoplastic polymer and about 15 to about 1 weight percent lubrication system. Preferably, the composition contains about 98% by weight thermoplastic polymer and about 2% by weight lubrication system based on the total weight of the composition.

Thermoplastic polymers useful in the self-lubricating compositions of the present invention may generally be selected from polyamides, polyesters, polyphenylene sulfides, polyolefins, polyoxymethylenes, styrene polymers and polycarbonates. Particularly preferred thermoplastic polymers of the invention are polyoxymethylene, ie acetal polymers or oxymethylene polymers. Polyoxymethylenes exhibit physical and mechanical properties that make them suitable for a variety of industrial applications.

Polyoxymethylene, ie polyacetal or oxymethylene polymers useful in the present invention are generally characterized as having repeating oxymethylene units of the formula (1).

[Formula 1]

Polyoxymethylenes useful for preparing the compositions of the present invention generally have a fairly high content of oxymethylene units, ie generally at least 85%. These materials are marketed by various manufacturers as homopolymers, copolymers, terpolymers and the like. These high crystalline acetals, which will be briefly described below, are well known in the art and have been extensively reviewed. For example, information on acetal polymers under the heading “Acetal Resins” written by TJ Dolce and JA Grates is described in the Second Edition of Encyclopedia of Polymer Science and Engineering, John Wiley and Sons, New York, 1985, Vol. 1, pp. 42-61. Additional information on acetal polymers can be found in French patent no. 1,221,148 and US Patent No. 3,027,352, 3,072,069, 3,147,234 and 3,210,318.

Typically, acetal homopolymers can be prepared by polymerizing anhydrous formaldehyde or trioxane. Oxymethylene homopolymers are typically capped with esters or ether groups such as those derived from alkanoic anhydrides (eg acet anhydride) or dialkyl ethers (eg dimethyl ether), or stabilizing compounds within the homopolymer Incorporation to stabilize against thermal decomposition. Commercially available acetal homopolymers are prepared by polymerizing anhydrous formaldehyde in the presence of an initiator and then end-capping the polymer by acetylating the hemiacetal end group with acet anhydride in the presence of a sodium acetate catalyst. Methods for preparing end-capped acetal homopolymers are described in US Pat. 2,786,994 and 2,998,409. Acetal homopolymers are well been known in the art and are commercially available under the trade name DELRIN ^R and ^R TENAC.

Acetal polymers that have been found to be particularly suitable for use in the compositions of the present invention are crystalline oxymethylene copolymers having repeating units consisting essentially of oxymethylene groups mixed with oxy (higher alkylene) groups of formula (2).

[Formula 2]

Wherein R ₁ and R ₂ are each hydrogen, lower alkyl group, or halogen-substituted lower alkyl group, and R ₃ is methylene, oxymethylene, or lower alkyl or haloalkyl-substituted methylene, or lower alkyl or haloalkyl- Substituted oxymethylene, n is 0 or the integer of 1-3. Each lower alkyl group preferably contains one or two carbon atoms. The oxymethylene group will generally comprise 85 to 99.9% of the repeat units in the copolymer and are generally incorporated by ring-opening polymerization of trioxane in the presence of an acid catalyst. The oxy (higher alkylene) groups copolymerize cyclic ethers or cyclic formals having at least two adjacent carbon atoms in the ring in addition to trioxane and incorporate them into the polymer. Cyclic ethers or formal are incorporated by breaking the oxygen-carbon linkage. Preferred oxy (higher alkylene) groups are oxyethylene having the structure of formula (3).

[Formula 3]

Oxyethylene can be incorporated into the polymer by copolymerizing ethylene oxide or 1,3-dioxolane with trioxane.

Preferred crystalline acetal copolymers described above having a structure consisting essentially of oxymethylene and oxyethylene groups are thermoplastics having a melting point of at least 150 ° C. They may be molded or processed at temperatures in the range of about 175 ° C. to 230 ° C. in normal times. These copolymers exhibit about 40% to about 90% or more polymer crystallinity as normal high crystalline.

Typically, the oxymethylene copolymers, after preparation, decompose and stabilize polymer chain-labile unstable molecular ends to a degree that can prevent degradation of both ends of the polymer chain by relatively stable carbon-carbon bonds. For example, Berardinelli, US Patent No. As disclosed in 3,219,623, the cleavage of the labile molecule ends is carried out by general hydrolysis. The oxymethylene copolymer can also be stabilized by end-capping, well known to those skilled in the art, for example by acetylation as acet anhydride in the presence of sodium acetate catalyst.

Particularly preferred series of oxymethylene copolymers are the commercially available acetal copolymers under the trade name CELCON ^R. CELCON acetal copolymers are typically a copolymer of about 98% by weight trioxane and about 2% dioxolane. CELCON is a registered trademark of Hoechst Celanese Corporation. The compositions of the present invention can be prepared using other industrial grade CELCON acetals, including U-10, M-25, M-90, M-270 and M-450. CELCON M-25 acetal copolymer has an application index of about 2.5 g / 10 min when tested according to ASTM D1238-82. CELCON M-90 acetal copolymers have a much lower molecular weight and melt viscosity than CELCON M-25.

In addition, oxymethylene terpolymers can be used to prepare the self-lubricating compositions of the present invention. These terpolymers contain oxymethylene groups, oxy (higher alkylene) groups such as those corresponding to formula (2), and a third other group that is polymerized with the oxymethylene and oxy (higher alkylene) groups.

Formula 2

The terpolymers described above are typically prepared by reacting trioxane with a cyclic ether or cyclic acetal and a third monomer which is a bifunctional compound such as diglycidide of formula (4).

[Formula 4]

Z is a carbon-carbon bond; Oxygen atom; Oxyalkoxy having 1 to 8 carbon atoms, preferably 2 to 4 carbon atoms; Oxycycloalkoxy groups having 4 to 8 carbon atoms; Or an oxypoly (lower alkoxy) group, preferably a lower alkoxy group having 1 to 2 carbon atoms each is repeated 2 to 4 times. Examples of suitable difunctional compounds include diglycidyl ethers of ethylene glycol, 1,2-propanediol and 1,4-butanediol, with diglycidyl ethers of 1,4-butanediol. Generally, when preparing the terpolymer, 99.89 to 89.0 weight percent trioxane, 0.1 to 10 weight percent cyclic ether or cyclic acetal, based on the total weight of monomers used to form the terpolymer It is preferable that it is 0.01-1 weight% of a functional compound. Particularly preferred oxymethylene terpolymers are prepared from about 0.05% by weight of 1,4-butanediol diglycidyl ether crosslinker, 2.0% by weight of dioxolane and 97.95% by weight of trioxane, based on the total weight of the terpolymer Acetal polymer under the trade name CELCON U10, which is commercially available from Hoechst Celanese Corporation. Oxymethylene-based terpolymers are prepared and stabilized by methods well known to those skilled in the art, such as adding antioxidants and formaldehyde and acid scavengers. More detailed descriptions of the oxymethylene-based terpolymers and methods of preparing their compositions can be found in the patents cited above.

These oxymethylene polymers can be combined in various ratios by melt mixing in an extruder or similar apparatus forming a suitable polymer for the preparation of the self-lubricating compositions of the present invention. In general, polyoxymethylene polymers are easily mixed with the lubrication system and processing aids when the polymer is in the molten state, ie at a temperature of at least about 170 ° C.

The lubrication system of the present invention is characterized by containing ultra high molecular weight polyolefin, pentaerythritol tetrastearate and calcium carbonate. Ultra high molecular weight polyolefins have an inherent crystallinity of about 40%, a weight-average molecular weight of at least about 3x10 ⁶ (typically from about 5x10 ⁶ to about 6x10 ⁶ ), at least about 28 dl / g (measured by ASTM No. D4020) Straight chain polyethylene exhibiting a viscosity, a bulk density of at least about 0.5 g / cm 3 (measured by ASTM No. D1895) and a specific gravity of about 0.93 g / cm 3. Particularly preferred ultrahigh molecular weight (UHMW) polyethylenes that comply with FDA / USDA regulations include Hostalen ^R GUR 415 UHMW polyethylene, distributed by Hoechst Celanese Corporation, Somerville, NJ. In general, the lubrication system of the present invention is characterized by containing at least 0.1% by weight UHMW polyethylene, 0.25% by weight PETS and at least about 0.25% by weight calcium carbonate, based on the total weight of the composition. Typically, the lubrication system is characterized by containing from about 0.2 to about 10.0 weight percent UHMW polyethylene, from about 0.25 to about 2.0 weight percent RETS and from about 0.25 to about 4.0 weight percent calcium carbonate based on the total weight of the composition do. Preferably, the lubrication system is characterized by containing about 1.5% by weight UHMW polyethylene, 1.0% by weight PETS and about 1.0% by weight calciumate, based on the total weight of the composition.

Several additional ingredients may be added to the compositions of the present invention to assist in lubrication and processing. In general, the additives can be proportionally combined with the lubrication system and mixed as a package with the thermoplastic polymer, or added directly to the composition. These additives may comprise (a) at least about 0.25 weight percent polyoxymethylene terpolymer, based on the total weight percent of the composition; (b) at least about 0.25 weight percent sterically hindered phenol; (c) at least about 0.05% by weight of calcium ricinoleate or calcium hydroxystearate. Typically, these additives comprise (a) about 0.25 to about 2.0 weight percent polyoxymethylene terpolymer, based on the total weight percent of the composition; (b) about 0.25 to 0.75 weight percent of hindered phenols; (c) can be admixed with the self-lubricating composition in an amount selected from about 0.05 to 0.3 weight percent calcium ricinoleate or calcium hydroxystearate. Preferably, these additives comprise (a) about 0.5 weight percent polyoxymethylene terpolymer, based on the total weight of the composition; (b) about 0.4 weight percent sterically hindered phenol; (c) can be admixed with the composition in an amount of 0.01% by weight of calcium ricinoleate or calcium hydroxystearate. By adding these processing aids the amount of thermoplastic will typically be consistently controlled. Other processing aids known to those skilled in the art can be used to assist in molding, such as silicone or fluoropolymer molding sprays.

Calcium carbonates useful in the present invention are characterized by a particle size of about 0.6 μg, a surface area of about 7 m 2 / gm, a bulk density of about 25 lb / ft ³ , and a specific gravity of about 2.7. Preferred calcium carbonate is Pfizer, Inc. Super-Pflex ^R 200 available from.

The hindered phenols useful in the present invention are generally known as antioxidants or free radical inhibitors. Useful hindered phenols include 2,2'-methylenebis (4-methyl-6-t-butylphenol), hexamethylene glycol-bis (3,5-di-t-butyl-4-hydroxyhydrocinnamate ), Tetrabis [methylene (3,5-di-t-butyl-4-hydroxyhydrocinnamate)] methane, triethyleneglycol-bis-3- (3-t-butyl-4-hydroxy-5- Methylphenyl) propionate, 1,3,5-trimethyl-2,4,6-tris (3,5-di-t-butyl-4-hydroxy-benzyl) -benzene, p-octadecyl-3- ( 4'-hydroxy-3 ', 5'-di-t-butyl-phenol) propionate, 4,4'-methylenebis (2,6-di-t-butylphenol), 4,4'-part Thilidene-bis- (6-t-butyl-3-methylphenol), 2,2'-thiodiethyl-bis- [3- (3,5-di-t-butyl-4-hydroxyphenol)] Propionate, di-stearyl-3,5-di-t-butyl-4-hydroxybenzylphosphonate and 2-t-butyl-6- (3-t-butyl-5-methyl-2-hydrate At least one of oxybenzyl) -4-methylphenylacrylate may be used, but is not limited to these compounds. Other steric hindrances or spatially hindered phenols of the same kind as those described above are effective. Among them, hexamethylene glycol-bis (3,5-di-t-butyl-4-hydroxyhydrocinnamate), for example Irganox ^R 259, tetrabis [methylene (3,5-, available from Ciba-Geigy) Di-t-butyl-4-hydroxyhydrocinnamate)] methane, for example Irganox 1010 and triethylene glycol-bis-3- (3-t-butyl-4-hydroxy- produced by Ciba-Geigy 5-methylphenol) propionate, for example Irganox 245 manufactured by Ciba-Geigy, is effective. Preferred hindered phenols are hexamethylene glycol-bis (3,5-di-t-butyl-4-hydroxyhydrocinnamate).

The following examples are general illustrations of the process for preparing the polymer compositions of the present invention. They are provided solely for the purpose of supporting the detailed description.

Example 1

To prepare a mixture of self-lubricating compositions containing 7.9% by weight of lubrication system, the following components are used:

The compounds are mixed in a vat and then mixed rapidly in a Henschel mixer for 30 seconds to make a mixture. The mixture is extruded into strands in a Werner and Pfleiderer twin screw ZSK extruder, heated and purged with polyacetal pellets. The extruder zone is operated at 372 to 387 ° F, the melting temperature is 415 ° F, under vacuum of 27 in mercury and the rotational speed is 150 rpm. Strand of the extrudate is produced at a rate of 38 lbs / hr. The strand is then quenched in cold water and cut into pellets. The pellets are injection molded at typical pressure, speed and rotational speed settings, nozzle temperature settings from 360 to 420 ° F and barrel temperature settings from 350 to 420 ° F to 1.25 diameters, each weighing about 7 mg for mechanical and friction analysis. To form a disk.

A disc, washed in a methanol bath, dried in air and weighing about 0.1 mg, is prepared for surface abrasion resistance and torque analysis. These disks are tested according to the Pin-on-Disk Wear Test. In performing this test, a mechanical Nylatron Nylon pin with a spherical tip of 0.187 inch radius was mounted on the upper layer of the Falex Friction and Wear Test Machine, Model Multi-Specimen, located 0.469 inch from the center of the test disc mounted on the lower spindle. Mount on the spindle. A 20 pound load is applied to the test disc by an air cylinder that presses the disc against a spherical pin tip. The rotation speed is 425 rpm (104.3 ft / min). During the test, the air stream is directed away from the disc surface at a distance of 2 inches and 40 standard cubic feet per hour to remove debris. The test time is 0.5 to 65 hours. After the test, the pin tip is disconnected from the disk, the disk is taken out and shaken in air to remove debris, and the lost weight, ie surface wear, is measured.

The torque (Γ) measured during the test is converted into a friction coefficient f by applying the following equation.

[Equation 1]

2.137 The factor is a specific factor for this machine. The results for surface wear and coefficient of friction are shown in Table 1.

Comparative Example 2

As a comparative example, the lubrication system of Example 1 was replaced with 1.5 wt% polytetrafluoroethylene (PTPE) to prepare a polymer composition, using the following components:

The composition is mixed, extruded and molded into 7 gm discs according to the process of Example 1 for weight loss and friction coefficient analysis. The analysis results are shown in Table 1.

Comparative Example 3

As a comparative example, the lubrication system of Example 1 was replaced with 3.0 wt% PTPE to make a polymer composition, using the following components:

The composition is mixed, extruded and molded according to the process of Example 1 to form a 7 gm disk for weight loss and friction coefficient analysis. The analysis results are shown in Table 1.

From the analysis results, after a 0.5 hour test according to the Pin-on-Disk Wear Test, the sample of Example 1 shows an average weight loss of 1.1 mg; After a 17 hour test, the disks exhibited an average weight loss of 4.3 mg and a coefficient of friction of 0.075; After a total of 65 hours of testing, it can be seen that the disks show an average weight loss of 5.4 mg.

Abrasion test results for discs made from compositions containing PTFE as a lubrication system show significantly higher surface wear and coefficient of friction than the present invention.

In order to show the wear performance of the composition in the presence and absence of lubrication system components, several formulations are prepared according to the method of Example 1 above, which are as follows:

Example 4

Example 5

Example 6

Example 7

Example 8

Example 9

Example 10

The compositions of Examples 4-10 were molded into test disks and the wear rate was tested according to the Pin-on-Disk Wear Test in Example 1. The test results are shown in Table 1.

The table shows that the compositions of Examples 4, 9 and 10 containing UHMW polyethylene, calcium carbonate and PETS provide good abrasion properties after 17 and 65 hours of abrasion testing as compared to compositions containing less of these three components. .

Claims (20)

Suitable for forming low friction moldings comprising about 70 to about 99.5 weight percent thermoplastic polymer and a melt mixture of about 30 to about 0.5 weight percent lubrication system comprising ultra high molecular weight polyolefin, pentaerythritol tetrastearate and calcium carbonate Self-lubricating composition. The composition of claim 1 wherein the thermoplastic polymer is selected from the group consisting of polyamides, polyesters, polyphenylene sulfides, polyoxymethylenes, styrene polymers and polycarbonates. The composition of claim 2 wherein the thermoplastic polymer is polyoxymethylene. 4. The composition of claim 3 wherein the polyoxymethylene is selected from the group consisting of (i), (ii), (iii) and (iv) below. (i) oxymethylene homopolymers; (ii) an oxymethylene copolymer consisting of about 85 to about 99.9% of an oxymethylene repeating unit having a repeating unit represented by Formula 2; Formula 2

Wherein R ₁ and R ₂ are each selected from the group consisting of hydrogen, lower alkyl radicals and halogen-substituted lower alkyl radicals, each lower alkyl radical having 1 to 2 carbon atoms, and R ₃ each being methylene , Oxymethylene, lower alkyl and haloalkyl-substituted methylene, and lower alkyl and haloalkyl-substituted oxymethylene radicals, n is an integer from 0 to 3.) (iii) an oxymethylene terpolymer that is the reaction product of trioxane and cyclic ethers and / or cyclic acetals, and diglycidyl ether crosslinkers of formula (4); Formula 4

Wherein Z is selected from the group consisting of carbon-carbon bonds, oxyalkoxy units of 1 to 8 carbon atoms of oxygen, and oxypoly (lower alkoxy) units. (Iv) (i), (ii) and mixture of (iii). The composition of claim 4 wherein the polyolefin is a straight chain, ultra high molecular weight polyethylene. The composition of claim 5 wherein the polyethylene exhibits at least about 40% crystallinity, a molecular weight of at least about 3 × 10 ⁶ , an intrinsic viscosity of at least about 28 dl / g, a bulk density of about 0.5 g / cm 3, and a specific gravity of at least about 0.93. 7. The composition of claim 6 consisting of about 85 to about 99 weight percent polyoxymethylene and about 15 to about 1 weight percent lubrication system. 8. The composition of claim 7, wherein the lubrication system comprises at least about 0.1 wt% ultra high molecular weight polyethylene, at least about 0.1 wt% pentaerythritol tetrastearate and at least about 0.1 wt% calcium carbonate. 9. The composition of claim 8, comprising (a) about 0.1 weight percent polyoxymethylene terpolymer, based on the total weight percent of the composition; (b) about 0.1% by weight of sterically hindered phenols; And (c) about 0.05% by weight calcium ricinoleate or calcium hydroxystearate. Molds made from the self-lubricating composition according to claim 9, exhibiting a weight loss of about 4.2 mg and a coefficient of friction of about 0.075 due to abrasion after 17 hours at a rotational speed of 104.3 ft / min and an applied load of about 21 lbs. . (a) preparing a melt mixed composition consisting of about 70 to about 99.5 weight percent of a thermoplastic polymer and about 30 to about 0.5 weight percent of a lubrication system comprising ultra high molecular weight polyolefin, pentaerythritol tetrastearate, and calcium carbonate; (b) preparing the composition into a molding which exhibits an improved coefficient of friction and surface wear resistance. 12. The process of claim 11 wherein the thermoplastic polymer is selected from the group consisting of polyamides, polyesters, polyphenylene sulfides, polyoxymethylenes, styrene polymers and polycarbonates. 13. The method of claim 12, wherein the polyoxymethylene is selected from the group consisting of (i), (ii), (iii) and (iv) below. (i) oxymethylene homopolymers; (ii) an oxymethylene copolymer consisting of about 85 to about 99.9% of oxymethylene repeat units in which repeat units of formula (2) are mixed; Formula 2

Wherein R ₁ and R ₂ are each selected from the group consisting of hydrogen, lower alkyl radicals and halogen-substituted lower alkyl radicals, each lower alkyl radical having 1 to 2 carbon atoms, and R ₃ each being methylene , Oxymethylene, lower alkyl and haloalkyl-substituted methylene, and lower alkyl and haloalkyl-substituted oxymethylene radicals, n is an integer from 0 to 3.) (iii) an oxymethylene terpolymer that is the reaction product of trioxane and cyclic ethers and / or cyclic acetals, and diglycidyl ether crosslinkers of formula (4); Formula 4

Wherein Z is selected from the group consisting of carbon-carbon bonds, oxygen, oxyalkoxy units of 1 to 8 carbon atoms, and oxypoly (lower alkoxy) units. (Iv) (i), (ii) And a mixture of (iii). The method of claim 13, wherein the composition consists of about 85 to about 99 weight percent polyoxymethylene and about 15 to about 1 weight percent lubrication system. 15. The method of claim 14, wherein the polyoxymethylene is an oxymethylene copolymer consisting of about 85 to about 99.9% of oxymethylene repeating units in which repeating units of formula (2) are mixed. Formula 2

Wherein R ₁ and R ₂ are each selected from the group consisting of hydrogen, lower alkyl radicals and halogen-substituted lower alkyl radicals, each lower alkyl radical having 1 to 2 carbon atoms, each of R ₃ Methylene, oxymethylene, lower alkyl and halo alkyl-substituted methylene, and lower alkyl and haloalkyl-substituted oxymethylene radicals, n being an integer from 0 to 3.) The method of claim 15, wherein the lubrication system comprises at least about 0.25 weight percent ultra high molecular weight polyethylene, at least about 0.25 weight percent pentaerythritol tetrastearate and at least about 0.25 weight percent calcium carbonate. The method of claim 16, wherein the lubrication system comprises about 0.1 weight percent ultra high molecular weight polyethylene, about 0.1 weight percent pentaerythritol tetrastearate, and about 0.1 weight percent calcium carbonate. 18. The composition of claim 17, wherein the composition comprises (a) about 0.5 weight percent polyoxymethylene terpolymer, based on the total weight percent of the composition; (b) about 0.4 weight percent sterically hindered phenol; And (c) about 0.1% by weight of calcium ricinoleate or calcium hydroxystearate. A molding made according to the method of claim 18, exhibiting a weight loss of about 4.3 mg and a friction coefficient of less than about 0.05 after 17 hours at a rotational speed of 104.3 ft / min and an applied load of about 20 lbs. 20. The molding according to claim 19 selected from the group consisting of bearings, gears, cams, rollers, sliding plates, pulleys, levers, guides and conveyor belt links.