CA1134538A

CA1134538A - Polymeric compositions

Info

Publication number: CA1134538A
Application number: CA000325173A
Authority: CA
Inventors: Paul Tamplin; Malcolm D. Heaven; Raymond Clarke
Original assignee: Raychem Ltd
Current assignee: Raychem Ltd
Priority date: 1978-04-07
Filing date: 1979-04-09
Publication date: 1982-10-26
Also published as: IT7921670A0; FR2432535A1; AU533616B2; BR7902145A; NL191123B; NL7902745A; DE2914014C2; AU4593479A; DE2914014A1; ES484220A1; ES479382A1; FR2432535B1; IT1115166B; NL191123C

Abstract

ABSTRACT

Cross-linked polymers are disclosed which comprise a linear low density ethylene homo - or copolymer which, prior to cross-linking is characterised by a density at 25°C of 0.940 gm/cm3 or less and a linearity expressed in terms of pendant methyl groups per 103 carbon atoms of the polymer chain of less than 30 with a substantial absence of long chain branches. These polymers possess higher .DELTA.T values than conventional branched, low density polyethylenes and are characterised by high elongation versus modulus performance.

Description

The present invention relates to crosslinked polymers, especially blends of polymers, and shaped articles constructed therefrom. In particular, the present invention relates to crosslinked polyethylenes.

It is known that the properties of polymers may be considerably modified by crosslinking of the polymer chains. This is particularly true of polyethylenes which, in crosslinked Eorm, I;
have found important commercial applications.

The present invention is based on the finding that a certain class of polyethylenes, when crosslinked, exhibits substantial advantages.

Accordingly, the present invention provides à substantial~y cross-linked polymeric material (sometimes referred to herein as a polymeric composition~ comprising a linear low density ethylene homo - or copolymer which, prior to crosslinking, is characterised by a density at 25C of 0.940 gm/cm3 or less and a linearity expressed in terms of pendant methyl groups per 10 carbon atoms of the polymer chain of less than 30 with a substantial absence of long chain branches.

, ~3~1~3~ r~9 1 For the avoidance o doub-t, the term "copolymer" as emplo~ed herein i.s used i.n -l broacl sense to mcan polymers produced xom at leac;~ two cliffererit monorlleric species ancl to include terpo:Lynlexs and the li.ke.

The ethylcne homo or copolymer pxeferably has a density at 25C ~rior to crossli.n]~.ing of from 0.916 to 0.940 c~n/cm3, particularly ~rom 0.919 to 0.940 gm/cm3 especiall.y less t'nan 0.930 gm/cm3 e.g. from 0.919 to 0.930 gm/cm3.

The deyree of bxanciling of the po:L~neric chains pr.io.r to cross-linking i5 expressed in terms of the average number of pendarlt methyl groups per 103 carbon atoms of the eth~lene homo -- or copol~ner chain wh:Lch, as will be appreciated, is ~ mea~sure of all slde gxoups ~lhich contain a meth~l group~
e.g. any alkyl group and may be determined in accordance with kno~m analytical procedures, for example the infra-red analytical -technique reported by A.H. Willbourn in J~ Poly.
Sci 1~59 34 559. Preferred polymers are those haviny 10 less pendant meth~71 groups per 103 carbon atoms of the pol~nex chain and those having 15 to 30 pendant methyl ~xoups per 103 carbon atoms c~ the po].~ner chain. Preferabl-~7 the pol-~mer contains on average less than 20 pendant methi71 groups pex 103 ca.rbon atoms o the pol~7mex chain.

~ 3 ~

;3~
~K~3.

The e~hylerle holno or copolymel-s are characte~isea by a subs~ant1.al absellce of long chain b.ranches and pxe~erab].y have no more than 5 long chain branches and more preferably nc morc than 1 long chaln branch, on average E~er 103 carbon atoms o:E the polymeL- chain. By long chain branches as employed herein is preferably meant branches yreater in length than C~ more preferably greater in length than C6.

The degree of long chain branching may, for example, be established by computing the differences between the number of shor~ hranches, determined for example, hy 13C nuclear ma~netic resonance spectroscopy, in accordance witth the method reported by M.E.A. Cuddy and ~. Bunn in Polymer, 1976 Vol, 17 April page 345, and the total number of branches determined as pendant methyl groups by infra-red spectroscopy.

! .

Of particular interest are those polymers wherein substanti.ally all branches are C2 to C6 branches especially C2 branches.

The linear low density ethylene homo or copolymers of the invention may be distingui.shed from the conventional~ i.e.
hranched, low density polyethylencs by their higher ~T
values where ~T as employed herein is defined as the difference in C between the temperature at which the po]~er melts and the temperat.ure at which the onsett of crystallisa~ion occurs.
Typically ~1~ values of greater than 15C, for example 15 to 20C particularly 16 to 20C, are observed in the linear low density ethylene homo or copolymers employed in the com- '~
positions of the invention.

The linear low density ethylene homo or copolymers employed in the compositions of the invention may be characterised by their molecular weight distribution index (Mw rn) as measured by standard methods (e.g. GPC). Thus the preferred polymers are characterised by a molecular wei~ht distribution index of below 8 and preferably in the range 3 to 8 e.g. 3 to 7. A
related parameter is the stress exponent, the preferred poly-mers being characterised by a stress exponent in the range 1.20 to 1.40 where ~tress exponent is defined as 1 _ melt index usinq 6480q at 190C. I
0.477 log10 melt index using 2160g at 190C

A further characteristic feature of the polymers employed in the compositions in accordance with the invention is their ~egree of unsaturation particularly in terms of terminal vinyl groups per 103 carbon atoms of the polymeric chain, values of at least 0.2, particularly 0~2 to 1.5 for example 0.3 to 1.5 as measured for example by infra-red spectroscopy being preferred.

~he degree of cross-linking of the compositions may be expressed in terms of the gel content (A~SI/ASl'M D2765-68).
Preferably the gel content of the cross-linked compositions , ~ 91 is at leasl~ ~0.., nlo]e prefel-ably abovc 50~, pal^~iculc:rly abovc fi5~, and up to ~5%, of the polymeric componerlts of the coml,~os:ition .

The cross-lin}~ed compositions of the invention may be further characterised by their higll elongation versus modulus performance. Thus typical elon~ation at brea}c values at 150C exceed 300~, or example 300 to 1000~, for filled and unfilled cross-linked compositions having a. 100~ secant modulu.s at 150C in the range ~.5 to 4 K~/cm2 measured in accordance with As~rM n 1708-66. Preferred composi.tions are ch~r.lcterised by elongatiorl at break values at 150C o at least 300%, parti.cularly at least 500%, for exarnpl.e at least 600%, 700%, 800%, and often 900% for cross-linked compositions havinq at 100% secant modulus at 150C in the range 3.5 to 4 Kg/cm2. I
.. , , ~

Ethylene copolymers which may be employed in the composi-~ions of the invention are pxeferably low density copolymers o ethylene wi~nh ol.efinically unsaturated monomers po1.ymeri.~a.~le therewith. Suitable such monomers are C3 to C20, preferably C3 to C~, olef.ins, preferabl~ olefins such as n--propyl~
ena, n-but~l~ene,. n-pent-l-ene, n--hex-l enej n-hept-l-ene and n-oct-l ene, or olefin;.cally unsatura-ted esters such as C2 C8 alkenyl. C~ - CB c~rboxylic acid esters for example .:

-.

~ ,3~3 RIC91 v.inyl aceta~.e anc~ CI~C~ alky]. C3 - C~ al~enoate~; or example ~hyl acJyl.aJ~e~. Copol~yrner; preferably cont.a.irI greater than ~Q weight per cent r more preferahI.y greclter than 60 weicJht per cent, ~or exarnple ~rea~er than 70 ~eight per cent, especi.ally ~r~ater ~han 85 ~reig]lt per cent, for e~clmple 95 ~o 9$ weicJht per cent, et.hylene, the optimum amount depend;ng o cour;se on ~he cornonomer employed.

~n~om, block or graft copol~ners may bë employe~, particularly r~ndom cspol~ners.

O:E speci.al in~erest in the composi.tions of the invention are b~en~s sE ~he linear ethylene homo or copol~ners with other homo ~ or c~pclymcrs hlended prior to cross~linking. Examples o~ ~uitable ~Iomo - or copolymers which may be blended .into the c~mpositions include therrnoplastic polymers, particularly other polyethylenes, for example branched low density pol~ethylcnes especially those having at least 5 more preferably a~ least 10 lvn~ cha.in branches (e.g. greater than CIO
pre~erably greater than C20) per 103 carbon atoms of the p~l~ethylen~ chain such as those having on avexage at least 5 more preferably at least 10 especi.all-y at least 15 pendent methyl gxo~lps per 103 carbon atoms of the polyethylene chai.n (par-ticularly those polyethy].enes having at least 20 more preferab].y at leas~ ~.0 branches greater i..n ].ength than C200 per ~erage molecule), and a density at 25C below 0~9~0 .- 7 .

`3 -- -gm/cm3 for example i.n the :rarl~e 0.910 to ~,940 cJm/cm3, or linear higll densi~y polye~}ly]elles haviny on avera~e less than 20 preferabl.y less than 15, :Eor example less than 10, especiall~r 0.5 to 5, pendent methyl cJroups pe~ 103 carbon atoms oE -the polyethyleIl2 chain and a density at 25C
greater than 0,940 gm/cm3 for example 0.941 to 0.960 gm/cm3, otheî pol~olefills for e~ample polypro~ylene, a~d copolymers for example ethylene/propylene copolymers and EPDM terpolymer.

Further e~:amples of suitable hlend polymers include elastomeric polymers particularly silicone elastomers as well as copolymers of ethylene wi.th ethylenically unsaturated a].iphatic esters, especially such copblymers when substantia:lly ~ree of halogen-containing subs'cituents. Preferred el.astomerlc polymers are those e~hibiting a characteristic ru~ber-like elastic deformabili'ty under the action of comparatively small stress the m~terial returning substantially to its undeformed state on the removal of the applied.stressr particularly those which in the uncross-].inked state havc an elastic modulus of 30N/mm2 or less, measured at room temperature in accordance with the method described in AST~ D638 - 72.

The preferred elastomers for use in the present invention are ethylene/acr~l.ic ester copolymers and ethylene/vinyl acetate copolymers, especi.all~y those containin~ a~ least 3.6 mo7es of etllylene per 1000 ~rams of polymer. Examp].es o~
suitable e].as',omers include:

;~

~.3~ Rl~]

a) ~n et}lylenc/allcyl acr~late or ethylene/;llJcyl rnc1:.nacry.].clt:e copolymer, wherein t.h~ al~;~rl cJroup nc~ car:bon atoms; the proportion of the acrylic ester being about

2.5-8.0 moles o ester groups per kiloyram of ~he copolymer .

b) ~ terpol~ner o~ ethylene with an alkyl acrylate or methacrylate wherein the alkyl group has 3.~4 carbon atoms alld a third copolymeri.zable monomer, which may ~e, for eYam~le one of the ~ollowing:

.
i~ a Cl-C12 a].kyl monoester or diester of a ~utenedioic acid, ~.
ii~ acrylic acid, iii) methacrylic acid~ ..
: iv) carbon monoxide, ~) acrylonitrile, vi.) a v nyl ester, vii) an alkyl acrylate or alkyl me-thacryl.ate, 'che alkyl group having at least fi.ve carbon atoms; and viii)maleic anhydride; or c~ ~thylene/vi.nyl acetate copolymers especially tho~e containing at least 35~ by weight vinyl acetate.

In the above terpolymer the proportlon of the acry.l.ic ester ls r~quivalent to about 2.5-8.0 moles of est.er yroups per kiloyram of the pol~ner, and the proportion of the third monomer is no hlgher tllan about 10 welght per cent cf tlle polymer .

RKQl The e~.ClS~Olne]^ can be a simple copol~ner o~ ethylene with methyl acryl.~e, eth~l acry]at.e, propy]. acrylate isopropyl ac:rylat:e, a butyl acry]..lte, methyl mcthacryla~e, ethyl methacrylate, propyl methacr~:Lclte, isopropy:l methacrylate, a butyl. metllacry].ate or vinyl acetate. Such copolymers that are not commereially ava:llab].e can be made by conventional and well known methods. These copo]ymers preEerably have a melt index within the ran~e of 0.1-70 at 190C, more preerably 0.5-15 as measured by ASTM method number D-1~38-52T, or the suhstantially equi.valent method A5TL~ D-1238-73.

The terpolymer o~ el~hylene with an acrylic ester and a third monomer may contain as the third monomer an ester or half ester of fumaric aci.d or maleic ac:id J wherein the alcohol moiety ean be, for e~ample, methyll ethyl, propyl, isopropyl, various isomers of butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl and the like~ The third monomer may also be, among others, a vinyl ester such as, for exampl.e, vinyl acetate or vinyl butyrate. It can also be an aerylie ester such asr for example, various isomeric ~orms of pentyl, hexyl~ heptyl, octy]., nonyl, decyl, undesyl, dodeeyl~ pentadeeyl and oetadecyl aerylate and methaerylates.
It is not practical to use as the third monomer an aery]lc ester i.n ~mieh the alcohol moiety contains more than 18 earl~on atoms.

}~9l Exoe]l~nL re;~.~.3.l:s !~clve be.~en ol-~t:ained using as l.he e].astome].
componen~ o~ ~hc~ pol.ylner composi-ti.on a terpolymer o~ eth~lerle, methyl acryla~e and a cure~site monomer comprls.i.ng carbo~yl gro-~ps availablc .rom Du ~?on-t unc1er the trade name Vamac.

Physical properties and other deJ;ails concerni.ng this material are to ~e found in a brochure available from Du Pont entitled "Vamac ethylene/a~rylic Elastomers - A new Class of Heat &
Oi.l Resistant ~ubber" by J.F. ~Iaymon, R.E. Fuller, W.X. Witsiep~
and R.~. Greene under ref-erence ~A-0002, the disclosure of which i5 incorporated herei.n by reference, correspondirlg essenticllly to articles appearing in Rubber Age, May 1~76, ~nd De Nederlands Rubberindustrie No. 7177.

Mixtures of any 03-. the above mentioned elastomers with each ~ther or with o-ther.elastomers may be used where appropriate al~hougll it has been found that the presence 03 hydrocarbon elastomers has a deleterious effect upon the oil resistance of the polymer composition and thus these are preferably not included, or if present, are prefe3:ably incorpordted in an amount of not more ~han 5% by weight based on the tota].
w~ight of the polymer compositionu It is be.li.eved to be advantageous for the solubi].i1~ parameter of the e]astomer to be greater than 9, and, in advanta~20us cvmposJ.tions according ~o the invention, it i.s further ~referred that the soluhili. ty paramet:ers of tlle polvmeYi.c componeTlts o the hlend should b~ similar, e.g. Wley w.~11 r,~ PL~

RY~q 1 di.,~er by not more thcln 0~5, preferably by not ~ore tllan 0.25.

For the purposes o~ thi-s 5pec; E.icat-..ion, solu~i.lity parameter i.s defined a5 that: measl1red by tne method o~ Brandrup ~
I~nergut, Polymer Handbook Chapter 4 page 340 (2nd ~dition) and is expressed as (cals/cm3)~.

Some types of polymer ma~erials inherently have a soluhility paramet:er greater than 9 whereas others can have solubil:ity parameters gr~ater than or less than 9 depend.ing on their prccis~ che~l].cal composi.cion. Still others, of course, have solubility parameters which are inherently less than 9.

The cross-linked polymeric compositions of the inventi.on whicil have be.~n derived from hlends of linear low dens:ity homo or copolymers with thexmoplastic or elas-tomeric homo -or copolymers offer ~arious unforeseen advanta~es and are accordinyly of special interest. Thus reduced hot creep and hot t-ensic)n se-t ph~nomena are typically exhibited by the blend compos..tions, paxticularly the blends with other polyethylenes, considerably facilitating moulding of ~he compositions. In addition cross-linking may be more readi.l~
achie~red, particu:larly the hlends with other polyet:hylenes such as branched low den~it~l ~olyetllylenes, fOL e~arnP1e ~ 12 ~

is~

after incorporating from 5 to 50 we:ight per cent of the blend polymer.
l`he blend polymers frequently offer increased thermal ageing and resistance to hydrocarbon fluids particularly where the solubility paramete~ of the blend component exceeds 9, for example blends with elastomers such as ethylene/vinyl acetate.
Preferably the weight ratio of the blended polymeric component or components to the linear low density ethylene homo - or copolymer in the composition lies in the range O to 20~ articularly O to l:lS more preferably O to 0.5 : 1, especially O to 0.2 : 1, for example O to 0.15 : 1 respectively.
The preferred blends have a density at 25C below 0.960 gm/cm3, especially below 0.940 gmtcm3 with branched low density polyethylenes. In some cases blends with a density at 25C of below 0.925 gm/cm3 exhibit particularly interesting properties especially high elongation at break versus 100% secant modulus at 150C properties.
Particularly interesting linear low density ethylene homo or copolymers, including blends, are the resins commercially available from .I. Du Pont de ~emours (Canada), Corruna, Ontario under the trade name "Sclair" and in particular the resins listed below in Table 1 under type reference

3~3.~

Du ~ont~ Scl.~ n~,il y ~,m/cm Ind~lx Exponent q~y~ r~llc~
8 405 0 ~ 937 2 ~ 26 .].]~-1 0~ 9190~ S0 1~ 40 llW 0. 919O~ J0 lo37 lLS 0. 920 1.40 1.35 . ~
llU 0. 92151~ ~0 1.35 llY 0. 924 5.1 1.26 2107 0. 924 5~ 26 8107 0~ 924 5~ 26 210~Vl V. 92~ 8~ 5 1.26 2109 1 0~ 92410~ 0 ~
2113 ~ 0~ 92429 ~0 211a 0~ 924~ 53~ 0 ~ -8307 0~ 930 5~0 1~ 2 8305 1 0~ 932 3~0 1.26 44F . 0~ 935 1. 5 1. 67 15B 0~939 0~35 1~69 8506 0~ 9403 ~ 8 1.26 8109 0.92]. 12.0 1.26 ~309 0~ 93012 r 0 1.26 2316 Ou930 73~0 8507 0~ 940 5~0 1~ 26 ~51~ 0. 940~5 . 0 ~91.4 ~ 92~ 50~0 ~105 0 ~ 9222 ~ 7 .

~ P P ~

,.. . .

~3~3~ ~Kgl :

E.~amples of linear low density l~olyethylene homo - or ::opolymers including blends of special interest are further characterised in Table 2.

Du Pont De~ree of Pendant S~.ort No. of double bonds per 103 Sclair CrystallinityMethyl Chain C atoms ~ype % groups branches ~ef per 103 per 103 ---- tennnal pen~ t C ato~ns C atomsYinylenevinyl methylene 8107UVl 44 7 ~7 ~.23 ~.48 ~.0~
83û7 64 ll ~ll 0.19 0.55 ~.08 83Q5 5~ 9 - 9C2 ~.16 -0.48 Q.07 8105 47 l~ 16C2 0.16 0.46 ~.09 8705 ~g 4 l -2C2 û . 0~ 3 0.~6 ~4û5 ~5 7 ~7 --0.1l 0.52 0.07 46 17 17C2 ~.26 o.a.9 o~g . ., -~ llW 53 27 ~27 0.23 û.23 ~.12 . . .

~h~'~3 .~'J

~ 3~

For most purposes, it is preferred that the compositions in-corporate at least 10 weight per cent filler, either reinforc-ing fillers (e.g. of particle size from 0.01 to 1 micron) or non~reinforcing fillers (e.g. of particle size from 1 to 120 microns). It is generally found that a higher degree of rein-forcement is secured by the use of reinforcing fillers such as high surface area carbon blacks or silicas than would be obtained with other types of polyethylenes and that usually no significant detriment to physical properties is observed with non-reinforcing fillers such as calcium carbonate or thermal black, as would be observed in other types of polyethylenes.
The compositions of the invention may include other additives, such as stabilizers, for example W stabilisers and anti-oxidants, flame retardants, anti-tracking fillers and pigments, the nature and amounts of additives included depending naturally on the specific use for which the com positions are intended.
The compositions of the invention may be produced in conventional manner e.g. by milling the components in a Banbury mixer. ~hey may then be processed into shaped articles e.g. by extrusion or moulding. Shaped articles so produced also form part of the present invention. When it is proposed to cross-link the compositions of the invention in the solid s-tate, e.g. by exposure to ionising radiation, preferably the compositions are quenched after the hot shaping stage, at least across the crystalline melting point of the composition. Pre-ferably quenching rates of at least 5 C/sec, e.g. at least 10/Sec, more preferably at least 20C/sec and, in the case of thin articles such as films, advantageously at least 100C/sec, are employed. Quenching may be achieved by contacting the shaped article with a heat exchange fluid such as water. It has been found that quenching achieves a decrease in crystal-linity and thereby an increase in modulus e.g. 2 per cent secant modulus, in the cross-linked material. Il ~
Cros~-linking preferably takes place at or sub- ~;
sequent to the shaping stage, depending - 16a ~

~ 3 ~ ~ c~ ~
1~9~-on l.he manller o~ cros~ ;,.ncJ and the natul-e ~E the shaped art.icle. It may ~e ef:ectecl by tl~e i.ncorporatj.on of ~rom 0.2 to 5 weiyht per cent of a cross--l.inkiny agent such as a free radi.cal ini~iator for exarnple an oryani.c perox.ide, such as dicumyl perox:icle or 2,5-d.i-(~butyl~pero~y) hexane~ alone or i.n com~ina~ion with a co-eur:ing agent such as a poly ~unctional vinyl or allyl compound, for examp~.e tria].lyl eyanurate, triallyl isocyanurate or pentaerythritol tetra-methacrylate. One preferred mocle oE chemically cross-linklny invol.ved graftin~ a hydrolysable silanP or silane de~:iva~ives e.cJ. an alkoxysilane such as vinyl trimethoxysilane to the polyeth,71ene base structure and subsequently hydrolysing to effect cross-linking by silanol condensation in manner known per se. Catalysts may be employed to ~acili~ate silanol condensation e.y. organotin catalysts such as dibutyltindilaurate.
. .

Alternatl~ely, cross-linking may be effected by exposure to high encr~y irra~iation such as an electron beam or y-rays.
Dosages i.n the range 2 to 80 Mrads, preferably 5 to 50 ~rads r e.g. 8 to 20 Mrads are appropriate r For the purposes of cross-linkincf by irradiation, preferably Erom 0.2 to 5 ~7eiyht per cent or a pro-rad SllCh as a poly-functional vinyl 0~ allyl compo~ d/ for example triallyl cyanurate or triallyl isocyanura~e are!incorporated i.nto the compositi.on prior to ~lle c.oss-linkln~ ~.reatment.

: ~- .t7 ~ $~ 91 The above mentioned -.on-cl^oss l~.nked compositi.ons incorporatj.ny an ecc~i~e ~llount of a cross-lin~in~J a(~ent or pio~:a~l are new ard also form parl~ o the present: :inventlon.

The composi.lions oE the present inventi.on are particu.l.clrly suitable for ~he production of dimensioncllly recovera~hle articies that is to say articlesJ ~he dimensional coniyurati.o.
v which may be made substantially to chanye wh~n sub~ected to an ~ppropriate ~.rea~menc. Of particular interest are - -heat recoverable articles the dlmensi.onal confiyuration of which may be made substantially to chanc~e when subjected to hea.t ~crea~nent. ~leat recoverable articles may be produced by deorm.ing a dimensiollally heat stable conf~guration to a heat unstable con~iguxation in whi.ch case the articla tends to assume t.he original heat stable confi~uration on the application of heat alone. As is made clear in US Patent No. 2 027 962 however the orlginal dimensionally hed C
stable con~iguration may be a transient form in a continuous process in which ~or e~ample an extruded tube i.s expanded whilst hot to a di.mensionally heat-unstahle form~ Alternatively a preformed dimensionally heat stable ar-cicle may be deforlned t~ a dimerlsional].y heat-~nstaDle form in a separate staye In the pxoduction of di.mensior)ally recoverable articles the compositior; may be c~oss-li.nked at any stage in the production process t}lat will accomplish the desired climensional recovera}~ility ~ 18 ~ 3~ K91.

e.y. prior to l:he shap:in~ oE the dl.mensiollal.l.y ~nstable confl(~uration. One manner o:E producin~ a heat recovcrable article comp.rises shaping thc pre-cross-linked composit.ion into the desired heat stable forln, subsecluently cxoss-lin~incJ the composition, heating the article to a temperature above the crystalline melting point of the composit.ion, deforming the artlcle and cooling the article whilst in the deformed state so that the deformed shape of the artlcle is retai.ned. In use, since the deformed state of the article is hea~ unstable, application of heat will cause the article to assume its original heat stable shape. Such di.mensionally recoverable articles may be employed as sleeves for cove~.ng and sealing splices and terminations in electri.cal conductors, for environmentally sealing damaged regions or joints in utili~y supply systems, e.g. gas or water pipes, di.strict heating systems, ventilation and heatlng ducts and conduits Oî pipes carrying domestic or industrial ef~luent.

The compositions of the present invention are also particularly suitable for the produc-t.ion of insulation materiai., particularly jacketing materiais for wi.res and cables. Such materials may be ~roduced in conventional manner, for example by extrusion onto conductors to form wires or onto wires to form cables with simultaneous or subse~uent cross-linking.

1~ ~

RK9~

I'hey ~re also usefuL as lli~h volta~e insulation i.ncQrporating an anti-tracki.ll~ fi.~.~er sucll as alumina trih~dr~te especially to ~Ich:i.eve all ini.ti.al ~rack,ng vo].ta~e zccorcli.llcJ to I~STM
D2303 o ~re.lter tharl ~.5 ]cV ancl/or when includin~ as a bl.enc1 componcll~, in the l~.ne~.r low density e-thylene homo -or copolylncr, silicone el.as-~omers or ethylene copol~mers.
Suitable an~i.-tracking ~illers and blendahle silicone elastomers and ethy~.ene copolymers are described by R.J. Penneck and .J.T. Cl~bburn in l'Heat Shrin~ab].e Cable Terminati.on System for High Voltage Cables" Proc. 10th Electrical Insulation Con~erence, Chicago USA September 20 - 23 1971, page 292 -297 and in U~ "Patent Nos. 1,303,43~ and 1,137,952 the contents of which are incorpor~ted herein by reEerence.

Furthermore, by the incorporation o;E app~opriate illers, e.g. carbon black, the compositions may be rendered se~
. eondueting or corlducting and in such form are particularly .~ suitable ~s semi conducti~e Oï conductive polymers for use in electxical heating ma-terials, e.g. in the form of heating tapes, stri.ps or pane].s, in the elec-trical screening of electrical power cables or in the electrical stress relief of splices and termination in high voltage electric cables.

~nother important app~.ication of the cross linked compositions o~ the invention is in the produc~ion of semi~permeable mem}.)ralles. Yor such use the composi~.ions of the invention are produced in ~ilm ~orm preferably with a film thickness o less 1han l.V~m, mo-e prefera~ly in the ran~e 0.001 to 0.5 mm. The ilm is a~.sc) prefcrably gra~ed with monomers des;.gne~ ~o moclifv ~:ile selecl.-ivity of thc membr2ne to ~clr~

~0 !

RI~'31 the perme~.~?~li.t~ t~he.r.eo:~` to val:ious iOlliC s~ecies . ~xaml?lc-'s o:E grai~t:able Inonomers :i.rlclude olef illica.l~ly unsatura-ted acicls or deriva~-.ives thereof, parti.cularly met.h;-lcryllc and acryli.c ~eids. .Sllch graft;.ncJ may be accompli.shed in known manner by sub-jectin~ the film to hi~h energy radiatio}l, e.s. to an elect3^0n heam, U.V. or y-radiation in the presence of the monomeric species to be cJrafted. The film may be in non-cross lin};ed form prior to exposure to the xadiation such that the radiation treatment serves also to cross-link the eomposition. Preferably, however, the fi.lm is cross-li.nked prior to c~rafting to achieve bet-ter ion selectivity ~lembranes produceæ in accordance ~7ith the inventi.on are particu:Larl~ useful as separators in electrochcrnica]. processes, for example as separators in electrolytic cells and particularly ba-~teries such as Ag/Znr Hg/æn/ Ni/Cd and Ni/Zn cells. Such mem~ranes possess several advantac~es such as longer service li~e in electroli-tic cell environrnents, irnproved wet strength and lower swelLing tendency than convent.ional. polyethylene melr,brane s .

The compositi.ons are particularly useful in any of the above applications in view of their notable ability to accept loadings of a~ditl~Tes, particularly fillers, e.g. 10 weight per cent or more, without detriment to the properti.es of the eomposi.t-.on, theLr notahle mechani.cal properties in cross-3~ R~

linked form, e.CJ, elonga~i.on at breakr hot modulus, abrasionresis~clnce c~.nd t_nsi.le s~rength, and/or theil chemical res.istance, e.g. to solvents, particularly orcJanic sol.vents such a~: o.il and pel:roleum jelly.

The in~rention is i.llustrated by the followillg examples wherein par~s and percenta~es are by weight and ternperatures are in C.

EX~MPLE 1 - Chemically cross-linked systems _ _ Various cross-linked compositions are produced by mi.lling the ingl-edients of~each Eormulation (see belcw) togetller on a ~win roll mill to form a hide. The hides are pressed in~o unifo~n p].aques ~na cured at 200C for 10 minutes. The ingredi.ents of the various formulations emp'oyed are set out . below: -;

- ~2 ,~ ' ' .

~3~ 3~ R~

FORM _~'I'ION l Sclair~aO5 61.75 Wh:it-:in~J G'100 30.00 (yroulld calc:ium carbonate) ~.illC s~eara~e 1.50 Macflite D 1.50 (hi~h surface area magneslum oxide com!nercia].ly availab]e ~rom Merc]c Chemlcals Inc) Irganox~Y1010 1.25 pentearithritol tetra~is -3-(3,5 ai-tert~but.yl-4-nydro~y phenyl)~?ropionate, antioxidant commerci.ally availab1e from ~iba Geigy A..G.
Tr.ia:Llyl cyanurate 0.20 Varox~ 0.80 2~5~dimethyl--2,5--di-(ter-t-~utyl-peroxy)hexane .
FOPU~U A~ ON 2 %
Sclai~ 8105 55 Elvax ~50 15 ~an ethylene/vinyl acetate copo]ymer containing 25% vinyl ac~tate commercially available from Du Pont de Nemours) Whitincj G400 21.5 Maglite ~ 1.5 Vulcan~9 (a ~q~O~ bl~) 2 . 7 Irgano~ 1010 1.25 ~inc stearate 1.75 Tr:ia11.yl cyanurclte ; 0.30 Varo~ 1.00 .

~ I ,..... , ~"

.

- - i ~3~3~ , _ Sclair 8305 55 Elvax 360 15 Whiting G400 21.5 Maglite D 1.5 Vulcan 9 2.7 Irganox 1010 1.25 Zinc stearate 1.75 Triallyl cyanurate 0.30 Varox 0.80 The tensile properties of the resultant plaques are set out below and determined by standard test methods:

Formulation Formulation Formulation Tensile Property l 2 3 1 0CP/o Secant Modulus 150~
(~g/c~ ) S.6 4.8 ~8 Tensile strength 15~C
(kg/cm ) 7.5 6.0 8.5 Elongation at break 150C
(%) ~450 ~420 ~450 Tensile strength 23 C 2 (kg/cm ) 220 230 214 Elongation at break 23 (%) >500 ~500 ~00 ~.

:

~' 3~

~ .[,E 2 ~ ^o~ d ~ mc The followlrl~ E~rmulations ~ and B were melt exkruded at 19S at ~hicll -Lempel-ature ~ra~tincJ o the silaIIe onto the polyetl~lene base structure is init:i.ated via the decom~ositior o~ the peroxide.

FOl~~UI,~TIOM A
part.s Sclair 8105 ~ ,~ a r /~
pal-~s ~YI~I-I 3 (trade ~ a branched low density polyethylene available from Union Carbide) ~ parts Vir-yltrimethoxysilane 0.1 p~rts Vicu.nyl peroxide FoRMl;lr?~trIo-N B

100 parts VYNH 3 2 parts Vinyltrimetho~ysilane 0.2 parts Dicum~1 peroxide The re~ultiny material was cooled and pelletised.

The following fo:-mulation C was also melt extruded and p~lletised:

FORMULAT~:O~J C

100 parts ~YNH-3 1 part Vi.butyltindilaurate ~ arK
paxts Salltanox R (tracle ~ n ant:ioxidant c~vailable from Monsallto LL-d) _. ~ r~

3~
95 parts of pelletised formulation A were blended with 5 parts of pelletised formulation C and injection moulded into short tube sections. The resulting tube sections were allowed to cool, and then immersed in water at 80 for 24 hours, The procedure was repeated for a blend of formulations B and C.

m e materials produced form formulation A were found to possess substantially superior elongation at 150 than those produced from formulation B.

EXAMPLE 3 - Radlation cross-linked sy~stems Pla~ues are made up in analogous manner to that described in Example 1 from commercial grade Sclair linear low density polyethylenes (11W, 11D, 8105, 8305 and 8405) in the absence of any additives other than any already present in the commercial grade product. Instead of the heat cure step of Example 1, the plaques are exposed to electron beaming at radiation dosages of 10, 15, 20 and 25 Mrads. Thereafter, the various plaques are examined to determine their 100% secant modulus at 150. For comparison purposes, the procedure was repeated with the following commercially available branched low density polyethylenes i.e. DY~H-3, PN220 (BXL) and CARLO~A
30-002BA (Shell). The results are set out graphically in Figures 1 and 2 and define two envelopes, one characteristic of the linear low density polyethylenes and the other charac-teristic of the branched low density polyethylenes. These figures demonstrate the greater ability of the linear low * trade mark - 26 -~L~.3~
density polyethylenes -to crosslink at any given radiation dosage khan the branched low density polyethylenes (E'igure 1) and th~ superior hot properties of the crosslinked linear low density polyethylenes than the crosslinked conventional branched low density polyethylenes (Figure 2~. In Figures 1 and 2 the units for th~ 100% secant modulus are Mæa~

~me~ ' m e procedure of Example 3 is repeated incorporating 0.2% of triallyl cyanurate as prorad in each product prior to cross-linking. Re~ults are slightly improved o~er those obtained in Example 3.

~e~
In order to demonstrate how ethylene homo and copolymers employed in the compositions of the invention are distinguished from branched low density polyethylenes, accompanying Figure 3 shows a plot of ~T (Tm ~ Tc) versus density at 25C values for the linear low density Dupont Sclair resins 11W1, 81052, 81073, 83074, 83055 and 84056 against commercially available branched low density polymers DY~H-37 (Union Carbide), P~ 2208 (BXL) Carlona 25-002GA9 (Shell), Carlona 30-002BA~O (Shell), EXXON LT-117 1 ~EXXON) and Gulf 2604M (Gulf Oil), the materials being represented on the Figure by the superscripts 1 to 12.

Example 3 is repeated at radiation dosages of 10, 15 and 20 trade mark - 27 -~3~3~

Mrads on plaques made up from blends of commercial grade Sclair linear low density polyethylenes with varying amoun-ts of a conventional branched low density polyethylene and the 100% secant modulus at 150C determined for each plaque.
The results are shown graphically in Figure 4 indicating a synergistic effect in 100% secant modulus properties at 150 for cross-linked mixtures of linear and branched low density .
polyethylenes. In Figure 4 the 10~/o secant modulus at 150C
is given in MPa.

EXAMPLE 7 - Heat Shrinkable Sleeve A formulation of the following composition: ¦
Sclair 8405 62.55 parts Whiting G400 30.00 parts Vulcan 9 3.00 parts Zinc stearate 1.50 parts Maglite D 1.50 parts Irganox 1010 1.25 parts and Triallyl cyanurate 0.20 parts is formed into tubing ln a laboratory ex~ruder under the following operating conditions~
barrel temperature zone 1 120-130 barrel temperature zone 2 130-140 die temperature 140-150 die diameter 25+ lmm wail thickness 1~ O.Ol mm haul off speed 0.4 metres/minute The extruded tubinK is subjected to a dosage of 10 Mrads electron beaming in an electron accelerator and then cut into 20cm lengths. Each length is expanded after heating, on a former to give 500% expansion as measured by change in wall thickness. The resulting heat shrinkable product is suitable for shrinking onto a substrate of from 26 to 120mm diameter without danger of splitting.
The example is repeated with the additional stag~ of quenching the extruded tube by immersion in water as soon as it leaves the extruder thereby achieving an increase in modulus of the material after cross-linking.
xample 8 - Heat Shrinkable Sleeve The procedure of Example 7 is repeated employing the following formulation.
Parts Sclair 8105 39.98 Commercially available ethylene/ 15.99 vinyl acetate copolymer containing 25% vinyl acetate melt flow index 2 Commercially available branched 19.49 low density polyethylene ~ density at 25C 0.918 and melt flow index 0.1 G~00 Whiting 13.00 Maglite D 1.5 Zinc Stearate 1.0 Irganox 1010 1.25 Vulcan 9 6.49 Triallyl cyanurate 0.30 Varox 1.00 100 . 00 - :, .:
.

~ ~ ~ 3 RK91 l'he slecvc so l?t:oduc~od could he e~:panclec~ t:o yreater than 600~ tllout e~ ltillg split se~llsit:iv:i.ty and in ad~it.ion an e~cellcnt- balallce o proper-ti.cs is achi.eved. Typi.cal ~:L^o~?~ arc set out helow.
150C Pro~?er~it~s lOO~o secant modulus 0.35 - 0.40 MPa Tens.ile strength O.g5 MPa Elongatlon >~30 %
Room Tel~erat,~lre l'roperties Tensile strength 24.5 MPa Elongation 590 %
2~ Secant, modulus 130.0 MPa -40 ~ ,ertles Tensile ~t,rength ' 29.0 ~Pa Elongation 365 %
eat, At~eint L68 houl^s_ t 150C
- Tensi.le strength 22.4 MPa Elongation 525 ., .
......
Solvent Resistance 168 hours Petroleum Jélly 70C
Tensile streng~h 1CJ~5 MPa E~ongation 532 %
E_ c~ri al Prop_~ties ~lectrical strenc~th 161 Kv~cm Permat,lvit~ 3.L4 Volume Resistivity 7.7 x 1013ohm cm Wate~ ak.e 0.21~
~ecific Gravity 1.057 g/cm3 f~ K91.

~ MI~ 9 - ';eJni-corlcll:lc~ ive ~leat: _h in]~a~]e S_eeve The procedure of J',xamp~.e 7 .i.s repeated employing'a formulatlor of ~the following compos:itioll Scla:ir 8105 61.55 parts Thermax (trade ~e a thermal.30.00 part-s carbon b:Lack availcLble rom VanderbiJ.t I.td) Zinc stearc~-te 1.50 parts Magl.i~e D lo50 parts Irganox 1010 1~25 parts q'r.iallyl cyanurate 0.20 parts The resultillg semi-conductive heat shrinkable tube may be em.ployed in the stress gracling o the termination in a screened h.igh voltage cable.

EXAMPLE lo _- Conducti.ve Heat Shrinkable Sleeve '~ The pxocedure of Example 7 is xepeated employing the following formulation , Sclair 8105 51.70 Comrilet-cially availabl.e eth~lene/ 17.25 vinyl ace-tate copolyrner contai.ni.ng 25% vinyl acetate - melt flow index w~ r ~t Ketjen EC (trade ~- a conductive 17.00 carbon black avaiIable from AKZ0 I.td) The~ma~ 6.65 .

f '?3 f ~
R1~91 Z inc .stearc;it 2 '. OQ
Ma~li.te D 1~50 Ayeri.te resin D 1.50 T.r~ allyl cyan~lrate 0. '10 ma~,Y
Lupero~ 130 (trade ~ ~ a peroxide 1.00 available from l,u~erco) head fumarate _.1.00 100 . 00 The conductive sleeve so produced possesses an excellent balance of properfies, allowing its use as a screen or elec-tr~cal cables, typical properties being set out below Tensile strength (MPa~ 19.57 : . Elongation (%) 325 150C ' , .. . ~ .
Tensile streng~h ~MPa) 2.3 Elongation (%) 365 100~ secant modulus (MPa~ 0.8 Heat- Shoc~ : 4;hrs @ 200C
EloncJation (%) 275 Heat ac3einc~ 7 days @ 150C
E;.lonc~aticn 1%) 225 Solvent Reslslance : 7 days ___ _ .__ _ Trans~ormer Oil E].o~ya tiOIl ( % ) ~ 7 0 j ~ 32 ~-.

RK9.l ~)ecific Grav.i.ty 1.086 Volume 1~esis-tivi-ty ohm cm 6.0 __ _ __ __. __ EXAMI~I,E 1~ _ _ lliqh Voltaqe A_t~- trtl ckin~ Sleeve The procedure o~ ample 7 is repeated ~mploying -the following hi~h volta~e anti~tracking insulation ~ormulations:

Formulation 1 Formulation 2 Component Parts Parts __ . __ __ Sclair 8105 23~10 DPD 6169 (~rade ~ ~ 22.73 22.73 ~n et.hyleIIe/e~hyl acrylate copolymer available from UYIion ~,arbl.le ) Sllastic~437 (Silicone ~elastomer 22.73 22.73 availab~.e from Dow ~ornin~) A~nina trihydrate 24.99 24.99 Ferric oxide ' 3.79 3.79 ~gerite Resin D ~ 1.52 1.52 Triallyl cyanurate 0.76 0.60 2rS~bis~tert-butyl-peroxy-2,5- 0.76 0.55 dimethyl heY~yne DYNH~3 22.73 ~-.' .... --- - " .

~ ~R~ ~ ~ 3~

, .

~' .
' 3¢~
The sleeves so produc ~ were found to have the following properties.

Formulation 1 Formulation 2 Tansile stren~th 23 (MPa~ 9.48 9.7 Elongation a~ break 23 (%~ 425 , 482 10~/o secant modulus 150C ~MPa~ 0.62 0~67 Elongation a~ break 150 (%~ 189 299 Tensile strength 150 (MPa~ 1~16 1.55 Failure time (mins~ according >200 > 200 to ASTM D 2303 involving progressive increase of stress starting at 2~5 kV with increment~ of 0.25 kV~hour and .
determination of the time to failure As will be ohserved, the sleeve produced ~rom the linear low density polyethylene (Formulation 2~ is significantly superior in all its physical propertie~ particularly elongation at break at 150, to that produced ~rom the branched low density polyethylene (Formulation 1~ whilst retaining the high anti-tracking property according to ASTM D 2303u EXAMPLE 12 Wire Jacket A formulation having the composition:
Sclair 8405 74.5 parts Timinox (antimony trioxide~ 8.0 parts Chlorowax (Hoechst)16.0 parts Agerite Resin D (Vanderbilt) 1.5 parts (a commercially available antioxi-dant~

* trade mark ~ 34 ~

~3~

was ex~rucled onto a he~tecl copper conductor (110C) to yield a -iac~e~ }lavincJ excelle~nt: insulation characteristics and particulclrly good mecllallical p~opel^t:ies e.y~ hi~h abrclsion rec,:is-~ance.

EXAMPLE 13 -- 5emi-permeable membrane Sclair llD was extruded as a film 0.025 mm thick under the ~ollo~A7i.llg extrusion conditions:

one 1 140 Zone 2 165 Zone 3 175C' Die I ' 175 Blow up ratio 2.5:1 -~'he resulting film is immersed in a solution comprisiny by volume 55O benzene, ,5% carbon,tetrachloride and 40% acrylic acid and irradiated with y~radiation to a dosage Ot- O, 5 Mrads at a dosaye rate of 0.05 Mrads per hour. ~he film is washed with a 40% aqueous solution of potassium hydroxide.
The resulting film i.5 emmlnently suitable for use as a bai'ter~ separator ha~iny all areal resistivity in 40,; aqueous potassium hydro~id~ of 0.1 to 0.2 ohm/cm2 and excellent mechanical properti~s, for example tensile s~renyth.

~L~

EX~ TlrJ ~ t)~ c.~ . E3~ r~

Th~. ~ollow.i.ng cc~mposi~.;.on~ were blet-lde~d employi.ncJ a 1.aboratory P,allhur~ i.nt.c~J^ncll. mi.xer.

Vamac N3.23 (Trade name ~ an ethyl.erie/ 30 methyl acrylclte elastQmer ava.i.].able from L~upc,nt and having a soluhi.lity parame-t:er o~ 9.1) Carbvn black Antimony trioY~ide 6 Dec~ahromodiphenylether 12 Cxodami.ne II-~T (Trade ~ a release 0.37 a~en~ avai.lable from (Crode Ltd) I.rganox 1010 0.375 Triallyl cyanu.rak.e WI~Lting G400 16 Sclair resi.n 30 .
The Sclair resin, Vàmac N123 and Irganox 1010 were loaded inko the mixer and ~nixed at room temQerature ~or 1 minuteO
The carbon black, alltimony trioxide, deca~romod.iphe.nylether ~nd c~].cium carbona~e were then added and ~.ixed unt:i.l temperature of the mix .ro~e to 1~0. Crodamine IHl~ and '~ri.allyl cyailurate ~ 3'~ RK91 ___ were the~n intrc)duced and mixed i.n fox ~5 seconds. This mi.x was thell put on-to a mi.l]. and sheeted off. Compression mo~l.cl.ecl plaqlles wert? maclc l-rom the sheetecl matc!rial and irradiated with an elect:ron ~eam to a dosage oE 12 ~rads.
The plaqucs were tested for heat shock resistance (4 hours at 200C) and for resisttance to l-,STM Oil No. 2 and diesel oil by immersion i.n the fluids for 24 hours at 90. The resu:Lts are set out below. As a coMparison the sclair resin is replaced by DYNH-3.

.

. ' , , ' ' ' ' , .. . \ ~

. ` .

. ~

3~

~a, r-l t~C) r~ o In ~ ~l Q) d~ t~ r--lt`~ t~
Q~ ! "
r~ r~
f~ ___..____ _~ __ r~ n ~ :~' O ~- ln ~ t~o ~D
a) ~ ,_ ''~ rS
~____ .___ _ ____ _ r~O
1~ m o In O o In O
tn O t~ ~fl r-l ~I r-l n ~s~
a) o ~ ~ t~ r~
.,~ ~I O ~
~ ~J ~ o\o ~td __ __ __~_ 5~ ~1 ~--~, ~ ~ ~
O ~ f~
~ d~ h ~~ r,~ t~ I_ ri tn tO r; O r-lt) O r~
a~ .In ~ r-l r-lr~~ -1 P~ ~1 r~ , , rS ~ td, ~ ' . Co___._ ~

t~ o o O O m ~n U~ ~\ o\, r-l ~D t~ n c~
~r-l r-l~t~ t77 ~ t~) P-! ~ _ ~
PiO~n ~ .
r-l t~ a tY- o In L~ ~D
~r-l tJ~ 'tl~ 7 tn ,t~ r~ ~r-~ r~ r-l r-l tn .

~ .
._~ _ l~or~ O t~
. I ~r~ 1.') t~lr~) r~ ~ ~
r lm ~t~ ~ ~ ~i~ .
)~I-) O O O O O ~r) ,r, l ____ ___ _ _ rl X
,1 1) al t- t- ~ ~1 U) o ~ n r.~lr~

- 3~ -~

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A substantially cross-linked polymeric material comprising a linear low density ethylene homo- or copolymer which, prior to crosslinking is characterised by a density at 25°C of 0.940 gm/cm3 or less and a linearity expressed in terms of pendant methyl groups per 103 carbon atoms of the polymer chain of less than 30 with not more than 5 pendant chains greater in length than C8 per 103 carbon atoms of the polymer chain.

2. A material according to claim 1 wherein the degree of cross-linking of the material expressed in terms of gel content (ANSI/ASTM D 2765-68) is at least 40%.

3. A material according to claim 1 wherein the ethylene homo- or copolymer prior to cross-linking is characterised by a .DELTA.T value as hereinbefore defined of greater than 15°C.

4. A material according to claim 1 wherein the ethylene homo- or copolymer prior to cross-linking is characterised by a molecular weight distribution index of less than 8.

5. A material according to claim 1 wherein the ethylene homo- or copolymer has substantially no chain branches greater in length than C6.

6. A material according to claim 5 wherein sub-stantially all chain branches of the ethylene homo - or copolymer are ethyl branches.

7. A material according to claim 6 wherein the ethylene homo - or copolymer has from 15 to 30 ethyl branches per 103 carbon atoms of the polymer chain.

8. A material according to claim 6 wherein the ethylene homo - or copolymer has no more than 10 ethyl branches per 103 carbon atoms of the polymer chain.

9. A material according to claim 1 wherein the ethylene homo - or copolymer is, prior to cross-linking, characterised by a degree of unsaturation expressed in terms of terminal vinyl groups per 103 carbon atoms of the polymer chain of at least 0.2 10. A material according to claim 1 wherein the ethylene polymer is a copolymer of ethylene with an olefinically unsaturated monomer.

11. A material according to claim 10 wherein the olefinically unsaturated monomer is a C3 to C8 .alpha.-olefin.

12. A material according to claim 11 wherein the .alpha. - olefin is n-but-l-ene.

13. A material according to claim 1 wherein the ethylene copolymer is a random copolymer.

14. A material according to claim 1 wherein the ethylene homo - or copolymer has a density of less than 0.930 gm/cm2.

15. A material according to claim 1 wherein the ethylene homo - or copolymer is present in the form of a blend with a blendable homo or copolymer prior to cross-linking.

16. A material according to claim 15 wherein the blendable polymer is a branched low density polyethylene or a linear high density polyethylene.

17. A material according to claim 15 wherein the blendable polymer is an ethylene/unsaturated aliphatic ester copolymer.

18. A material according to claim 17 wherein the ethylene/unsaturated aliphatic ester copolymer is an ethylene/
vinyl acetate copolymer.

19. A material according to claim 1 including at least 10 weight per cent of a filler.

20. A material according to claim 19 wherein the filler is a non-reinforcing filler.

21. A material according to claim 20 wherein the filler has a particle size of from 1 to 120 microns.

22. A material according to claim 19 wherein the filler is a reinforcing filler.

23. A material according to claim 22 wherein the filler has a particle size of from 0.01 to 1 microns.

24. A substantially cross-linked polymeric material comprising a linear low density ethylene homo - or copolymer which, in cross-linked form, is characterised by a polymer density at 25°C and a linearity and chain type as defined in claim 1.

25. A material according to claim 24 wherein the ethylene polymer in cross-linked form has a .DELTA.T value of greater than 15°C.

26. A cross-linkable material comprising a linear low density ethylene homo - or copolymer as defined in claim 1 incorporating an effective amount of a cross-linking agent or a prorad.

27. A dimensionally recoverable article comprising a material according to claim 1.

28. An article according to claim 27 which is heat shrinkable.

29. An article according to claim 28 which is hollow.

30. A hollow heat-shrinkable article of monolithic construction consisting wholly of the material defined in claim 1.

31. An article according to any one of claim 22, 28 and 30 in the form of a sleeve.

32. Electrical insulation for a wire or cable comprising a material according to claim 1.

33. Electrical insulation which comprises a material according to claim 1 incorporating an anti-tracking filler and having an initial tracking voltage according to ASTM
D2303 of greater than 2.5 kV.

34. A semi-conductive or conductive polymeric material comprising a material according to claim 1 having incorporated therein an effective amount of a conductive filler.

35. A stress grading tube for the electrical stress grading of the termination of high voltage cables comprising a semi-conductive material according to claim 34.

36. An electrical screen for wire or cable which comprises a semi-conductive or conductive material according to claim 34.

37. A semi-permeable membrane comprising a material according to claim 1 in semi-permeable film form.

38. A membrane according to claim 37 wherein the film has a thickness of between 0.001 and 0.5mm.
39. A membrane according to claim 37 wherein the film has been grafted with monomers to modify the selectivity thereof to ionic species.
40. An electrolytic cell or battery separator comprising a membrane according to claim 37.
41. A material according to claim 1 having been quenched across the crystalline melting point thereof prior to cross-linking.
42. A material as claimed in claim 17 wherein the blend-able polymer is an ethylene/methyl acrylate elastomer having a solubility parameter of 9.1.
43. A shaped article comprising a material according to

claim 1.