# US 10,118,998 B2 · Process for producing high molecular weight polyethylene

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- Number: US 10,118,998 B2
- Document ID: US10118998B2
- Status: Granted
- Kind: B2
- Application number: 15/393,194
- Filed: 2016-12-28
- Published: 2017-04-20
- Granted: 2018-11-06
- Earliest claimed: 2007-11-06
- Assignees: Dsm IP Assets B.V.
- Applicants: Dsm IP Assets B.V.
- Inventors: Harold Jan Smelt; Pieter Gijsman; Martin Van Duin
- Web page: https://patentgrep.com/patent/US10118998B2

## CPC

- C08J 3/24: Crosslinking, e.g. vulcanising, of macromolecules (mechanical aspects B29C35/00; crosslinking agents C08K)
- A61L 27/16: obtained by reactions only involving carbon-to-carbon unsaturated bonds
- A61L 27/505: {Stabilizers}
- C08F 8/00: Chemical modification by after-treatment (graft polymers, block polymers, crosslinking with unsaturated monomers or with polymers C08F251/00 - C08F299/00; of conjugated diene rubbers C08C)
- C08J 3/28: Treatment by wave energy or particle radiation
- C08K 5/3435: Piperidines
- C08K 5/3492: Triazines
- C08K 5/34926: {also containing heterocyclic groups other than triazine groups}
- C08L 23/06: Polyethylene
- C08J 2323/06: Polyethene
- C08J 2323/36: by reaction with nitrogen-containing compounds, e.g. by nitration
- C08L 2201/08: Stabilised against heat, light or radiation or oxydation
- C08L 2203/02: for biomedical use
- C08L 2207/068: Ultra high molecular weight polyethylene
- C08J: WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H (working, e.g. shaping, of plastics B29)
- A61L: METHODS OR APPARATUS FOR STERILISING MATERIALS OR OBJECTS IN GENERAL; DISINFECTION, STERILISATION OR DEODORISATION OF AIR; CHEMICAL ASPECTS OF BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES; MATERIALS FOR BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES (preservation of bodies or disinfecting characterised by the agents employed A01N; preserving, e.g. sterilising, food or foodstuffs A23; preparations for medical, dental or toiletry purposes A61K)
- C08F: MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
- C08K: Use of inorganic or non-macromolecular organic substances as compounding ingredients (paints, inks, varnishes, dyes, polishes, adhesives C09)
- C08L: COMPOSITIONS OF MACROMOLECULAR COMPOUNDS (compositions based on polymerisable monomers C08F, C08G; artificial filaments or fibres D01F; textile treating compositions D06)

## Abstract

Processes for producing an (ultra) high molecular weight polyethylene (HMWPE) article include incorporating into the HMWPE resin a Hindered Amine Light Stabilizer (HALS) and cross-linking the (U)HMWPE during or after molding the (U)HMWPE resin.

## Claims

### Claim 1

A process for making a cross-linked article from (ultra) high molecular weight polyethylene ((U)HMWPE) comprising steps of:
(i) forming a composition by incorporating at least one Hindered Amine Light Stabilizer (HALS) compound in a (U)HMWPE resin, wherein the (U)HMWPE is a substantially linear ethylene homopolymer or copolymer with a molecular weight distribution (Mw/Mn) of between 2 and 18;
(ii) adding an initiator to the composition; and
(iii) molding the composition to form an article having a cross-link density of 0.09 mol/dm3 or more.

### Claim 2 (depends on 1)

The process according to claim 1 comprising the steps of:
a) forming a composition by incorporating in the (U)HMWPE a HALS compound according to one of the following general formulas or combinations hereof:
wherein R1 up to and including R5 are herein independent substituents selected from the group consisting of hydrogen, ether groups, ester groups, amine groups, amide groups, alkyl groups, alkenyl groups, alkynyl groups, aralkyl groups, cycloalkyl groups and aryl groups, wherein the substituents may in turn contain functional groups selected from the group consisting of alcohol groups, ketone groups, anhydride groups, imine groups, siloxane groups, ether groups, carboxyl groups, aldehyde groups, ester groups, amide groups, imide groups, amine groups, nitrile groups, ether groups, urethane groups and any combination thereof;
b) adding an initiator and optionally a coagent to the composition;
c) molding or extruding the composition to form a cross-linked article or stock shape;
d) optionally further cross-linking and/or sterilizing the article or stock shape via gamma radiation or electron beam radiation;
e) optionally, if step c) results in a stock shape, machining the stock shape into an article, wherein
step d) and step e) can be performed in either order.

### Claim 3 (depends on 1)

The process according to claim 1, wherein the (U)HMWPE has an intrinsic viscosity of 8 dl/g or more.

### Claim 4 (depends on 1)

The process according to claim 1, wherein the (U)HMWPE comprises one or more comonomers.

### Claim 5 (depends on 1)

The process according to claim 1, wherein the HALS is present in an amount of between 0.01 and 2% by weight, based on the total weight of the (U)HMWPE.

### Claim 6 (depends on 1)

The process according to claim 1, wherein the HALS has a molecular weight of 1000 g/mol or more.

### Claim 7 (depends on 1)

The process according to claim 1, wherein the HALS compound is selected from the group consisting of N,N′″-[1,2-ethanediylbis [[[4,6-bis[butyl(1,2,2,6,6-pentamethyl-4-iperidinyl)amino]-1,3,5-triazine-2-yl]imino]-3,1-propanediyl]]-bis[N′,N″-dibutyl-N′,N″-bis(1,2,2,6,6-pentamethyl-4-piperidinyl) or poly{[[6-[(1,1,3,3-tetramethylbutyl)amino]-s-triazine-2,4-diyl][(2,2,6,6-tetramethyl-4-piperidinyl)imino]-hexamethylene [(2,2,6,6-tetramethyl-4-piperidinyl) imino]]}.

### Claim 8 (depends on 1)

The process according to claim 1, wherein the HALS is incorporated in the (U)HMWPE by mixing the HALS with (U)HMWPE resin or (U)HMWPE melt, by impregnating (U)HMWPE resin with a solution comprising the HALS, or by spraying a solution comprising the HALS on (U)HMWPE resin.

### Claim 9 (depends on 1)

The process according to claim 1, wherein the initiator is a peroxide selected from the group consisting of tert-butyl cumyl peroxide, tert-butyl peroxybenzoate, di-tert-butyl peroxide, 3,3,5,7,7-pentamethyl-1,2,4-trioxepane,1,1-di(tert-butylperoxy)-3,3,5-trimethylcyclohexane, butyl 4,4-di(tert-butylperoxy)valerate, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexyne-3, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, di(4-methylbenzoyl) peroxide, dibenzoyl peroxide, di(2,4-dichlorobenzoyl) peroxide, dicumyl peroxide, 3,3,5,7,7-pentamethyl-1,2,4-trioxepane, 1-(2-tert.-butylperoxyisopropyl)-3-isopropenyl benzene, 2,4-diallyloxy-6-tert-butylperoxy-1,3,5-triazine, di(tert-butylperoxyisopropyl)benzene, diisopropylbenzene monohydroperoxide, cumyl hydroperoxide, and tert-butyl hydroperoxide.

### Claim 10 (depends on 1)

The process according to claim 1, wherein the initiator is present in an amount of between 0.001 and 2.5% by weight based on the total weight of the (U)HMWPE.

### Claim 11 (depends on 1)

The process according to claim 1, wherein the initiator is present in an amount of between 0.01 and 1% by weight based on the total weight of the (U)HMWPE.

### Claim 12 (depends on 2)

The process according to claim 2, wherein the coagent is selected from the group consisting of divinylbenzene, diallylphthalate, triallylcyanurate, triallylisocyanuarate, triallyltrimellitate, meta-phenylene bismaelimide, ethyleneglycol dimethacrylate, ethyleneglycol diacrylate, trimethylopropane timethacrylate, trimethylopropane, timethacrylate, pentaerytritol tetramethacrylate, zinc diacrylate, zinc dimethacrylate, and polybutadiene.

### Claim 13 (depends on 2)

The process according to claim 2, wherein the co-agent is present in an amount of between 0.001 and 2.5% by weight based on the total weight of the (U)HMWPE.

### Claim 14 (depends on 2)

The process according to claim 2, wherein the co-agent is present in an amount of between 0.1 and 1% by weight based on the total weight of the (U)HMWPE.

### Claim 15 (depends on 1)

The process according to claim 1, wherein the step of molding or extruding comprises compression molding, ram-extrusion, direct compression molding, or hot isostatic pressing.

### Claim 16 (depends on 2)

The process according to claim 2, wherein the step of further cross-linking and/or sterilizing is performed with an irradiation dose of from 10 to 40 kGy.

### Claim 17 (depends on 2)

The process according to claim 2, further comprising annealing the cross-linked article or stock shape at a temperature below the melting temperature of (U)HMWPE.

### Claim 18 (depends on 2)

The process according to claim 2, further comprising annealing the cross-linked article or stock shape at a temperature of between 60 and 140° C.

### Claim 19 (depends on 1)

A crosslinked (U)HMWPE article obtained by the process according to claim 1.

### Claim 20 (depends on 19)

The article according to claim 19, having a thickness of at least 2 mm.

### Claim 21 (depends on 19)

A medical implant which comprises the article according to claim 19.