Radiation processing of polyethylene

Radiat. Phys. Chem. Vol. 18, No. 1-2, pp. 267-280, 1981 Printed in Great Britain.

0146-5724/81/070267-14502.00/0 Pergamon Press Ltd.

RADIATION PROCESSING OF P O L Y E T H Y L E N E A. Barlow, J. W. Biggs and L. A. Meeks U.S. Industrial Chemicals Co., Research Div. 1275 Section Rd., Cincinnati, Ohio 45237 ABSTRACT This paper covers two areas

(a) the use of high energy radiation for the

synthesis and improvement of polymer properties and

(b) the formulation of

radiation curable compounds for automotive/appliance wire applications and high voltage insulation. The first part discusses

the use of gamma radiation for the bulk polymer-

ization of ethylene and the properties of the polymer produced.

The use

of low dose radiation to increase polymer molecular weight and modify polydispersity cost.

is also described together with its projected operational

An update is provided of the cost savings that can be realized w h e n

using radiation crosslinked heavy duty film, which expands its applications,

compared with noncrosslinked materials.

The second section of the paper considers the advantages and disadvantages of radiation vs. peroxide curing of wire and cable compounds. lation of a radiation curable,

cussed together with the interactions between the various i.e.,

base resin,

antioxidants,

The formu-

a u t o m o t i v e / a p p l i a n c e wire compound flame retardant filler,

coupling agents,

processing aids and radiation to achieve the desired product. tion,

is dis-

ingredients; In addi-

the general property requirements of a radiation curable polyethyl-

ene for high voltage efficiency,

insulation are discussed;

thermal stability,

electric properties.

these include c r o s s l i n k i n g

wet tree resistance and satisfactory die-

Preliminary data generated in the development of a

230KV radiation crosslinked polyethylene insulation are included. INTRODUCTION The increasing costs of fossil fuels coupled with governmental regulations which tend to slow down the development of new polymers has'helped to stimulate the d e v e l o p m e n t of energy saving processes and innovative modifications of readily available materials. of use in both of these areas,

High energy radiation has been

and this paper describes

some of the in-

vestigative work performed in both of them at U.S. Industrial Chemicals Co.

Most of the radiation work at this company has dealt with ethylene or

ethylene copolymers.

The first part of the paper covers some of the

processes and a p p l i c a t i o n s of radiation developed over the last 15 years at USI;

some projects have been completed whereas others are still under \

consideration.

The second part of the paper addresses

velopment of radiation curable wi~e and c a ~ l e ~ m p o u n d s

itself to the dethrough d e v e l o p -

ment of a specific material which is now a/cOmmerclal reality. cluded is p r e l i m i n a r y data obtained in developing a material high voltage

insulation.

267

Also in-

suitable for

268

A. BARLOWet al.

POLYMER M O D I F I C A T I O N Among

AND SYNTHESIS

the first attempts

ene for other

to utilize

than crosslinking

and Boyle (2) in an attempt It was d e t e r m i n e d short-chain stracted

hydrogen

sponding

paraffin.

from the polyethylene

was

further

that the method acetate

days

infrared

inhibited

radiolysis

in p o l y e t h y l e n e

corroborated

analysis.

With

is more

data

by Kamath

was generally

the ab-

as the corre-

analysis

which

of C-13

of

in those

nuclear

mag-

infrared

spectroscopy,

in p o l y e t h y l e n e

and comonomer

easier

and more rapid.

rise

to butyl

2:1, whereas

and equally

& Barlow (3) who also

fillers,

transform

it gives

the ethyl

cleaved radicals

for q u a n t i t a t i v e

structure

was made

rapid,

showed

these

quantitatively

the advent

and fourier

of short-branch

of polyethylene.

and could be analyzed

could be used

in filled copolymers

the C-13 NMR m e t h o d cause

structure

backbone,

on polyethyl-

by W i l l b o u r n (I)

preferentially

copolymers (4) containing

spectroscopy

the d e t e r m i n a t i o n analysis

of radiation

The fact that this occurred

ethylene-vinyl

netic resonance

the fine

radiation

from the polymer

for all sidechains demonstrated

to define

that high energy

branches

the effects

was the work performed

to another short

Although

question

chain branch

the new method

shows

be-

ratio

the

opposite. Of more practical ethylene. project

value

Research

Institute.

Their

in a flow-type

butanol (7)

struction

to those

(Cobalt-60)

desired

along

be seen.

similar

in polyethylene

require

sequently, countries

system

comonomers thus making

it d i f f i c u l t

Consequently,

weight

weight

initiation

could

and poly-

relatively

result

reactor the very

can

in a cost

whether

such

or in very intense

by the reactor

in highly

in this

properties

it is doubtful

where

of

as

in a commercial

dependent

in a tubular

of this process

the stirrer

produced

are likewise

than that provided

when polymerized

another

in the p r o d u c t i o n

molecular

molecular

However,

source

within

source

body.

Con-

industrialized

remote.

agents, levels.

i.e.,

the

in con-

can be controlled

The material

capacity

t-

so that the intensity

species

that this process

>250 liters

shielding

commercialization appears

The radioactive

in the d e n s i t y

production.

similar

concentrically

of the two materials

have shown

the p o l y m e r i z a t i o n

m e d i u m of aqueous

reactor

by peroxide

could be utilized

e.g.,

more

Certain

cessing

in structure;

i) but differences

large autoclaves; would

(Fig.l).

of initiating

to that produced

Calculations

an initiation

use

Energy

& Platz, (8) have examined

along the axis of the reactor

(Fig.2)

(Table

Greenberg

into the reactor

The properties

similar

investigated

using a reactor

the length of the reactor.

is fairly

reactor.

studies

of

on this

at the Japan Atomic

in an autoclave

in commercial

or c o n c e n t r a t i o n

dispersity

recent process

of ethylene

is inserted

and is moved

radiation

savings

of work has been performed

In other work at USI,

bulk p o l y m e r i z a t i o n

manner

amount

by T. Wada (6) and his colleagues

of ethylene

shaft

is the work done on the bulk p o l y m e r i z a t i o n

A considerable

with ethylene

to achieve

potential

of polyolefins

of a polymer.

behave

desired

as chain

molecular

application

of radiation

is its use

for increasing

A low dose of radiation

transfer

weight pro-

is employed

the which

Radiation processing of polyethylene is less than the gel point dose thus avoiding particles

into the product.

polydispersity

is c o n t r o l l e d

can penetrate the material using

about being

radiation

while

u s i n g a self shielded

molten

is % 0 . 7 ¢ / i b

Folymer

repelletizing

uses

or improved. improvement

FORMULATION

cable

large growth where

from ~ 1 0

such as Radiation

advantages

controls

processing

are showing

beam curing.

of r a d i a t i o n

Some

in 1979.

curing

lower

losses,

costly

process

scrap

Inc.

5 which

compares

extremely

well

materials

are being developed;

both of w h i c h r e p o r t e d l y ducing

energy

porous

insulation

Some

consumption

an economic

with per-

provides

greater

for this

advan-

extrusion

and is therefore

evidence

a less

is shown

costs with those

peroxide

salt,

advantage

for

cured materials

and new methods

are

for curing

these

or hot nitrogen,

over

In addition,

is decreased,

and dis-

compared

significant

use of molten

50% or more. (II)

to be produced

beam units

The most

curing

hand,

in the industry

offer

to be

manufacturers

electron

insulation

4.

radiation

i.e.,

benefits

idea of the benefits

Further

On the other

established

equipment

are now building

curing.

plants

beam units used for wire curing

In addition,

less power consumption

current

steam vulcanization. (I0)

of those

is in the wire and

the financial

are that the process

than peroxide

radiation

an update

idea of the growth of this area

can be seen in Table

tages of radiation

film was published

for steam generation

cured wire and cable

rates,

for

& CABLE COMPOUNDS

fuel costs

for this application.

cured m a t e r i a l s

in Table

WIRE

skyrocketing

Dynamics,

is more

are un-

3.

CURABLE

to % 7 0

For

allowing

strength

through

in that report,

from the growth of electron

in 1969

specifically

to be gained

area for radiation

with p o l l u t i o n from electron

can be judged

oxide

in Table

OF RADIATION

industry

coupled gained

is given

given

enhanced.

of the use of radiation

of polyethylene

advantages

were

and the impact

account

and in

at a dose of 10

such as heat sealability

and sterilization

The economic

of p o l y e t h y l e n e

calculations

Another

A more detailed

is in the

applications,

of the film are improved

applications properties

and

costs.

of p o l y e t h y l e n e

In addition,

the

in line on the

extruding

of heavy duty film are s i g n i f i c a n t l y

Furthermore,

previously. (9)

processing

properties

ex-

show that

the cost of u p g r a d i n g is performed

film for food wrapping

temperature

of the co-

are more

to the radiation

tubing.

to

of peroxide

Calculations

the cost of remelting,

of heat shrinkable

for "hot-fill"

processing

the irradiation

of

of these give

and both processes

for radiation

it to be used

property

The alternative

Neither

and

which

the thickness

the temperature

forces.

must be added

than doubled. changed

2.

weight

(250KV),

a low c o n c e n t r a t i o n

point of view.

Otherwise

of heat shrinkable

the high

electrons

E l e c t r o c u r t a i n ® processor, providing

the properties

example,

in Table

of intractable

in molecular

and by r e g u l a t i n g

or raise

as irradiation efficiency

stream.

the m a n u f a c t u r e Mrads,

as shown

the m i x t u r e

the material

One of the largest production

of polymer,

it to high shear

product

introduction

increase

low energy

to introduce

and heat

from an energy

material

by using

irradiated

exposing

such a u n i f o r m pensive

12 mils

is either

into the polymer polymer

The overall

269

steam by re-

the tendency

especially

for a

in the newer

270

A. BARLOWet aL

processes, very

since

little

they are performed

under

limitation

on wall

Formulating

a compound

for radiation

of removing

peroxide

ation

sensitizer. formulation

compound

influence

resultant

physical

YR 19505,

the interactive described The base

(12)

available

in Table

6 where a peroxide

flame retardant

the

in the develop-

radiation

wire

ingredients

in the

and consequently

The steps

and a p p l i a n c e

a matter a radi-

All components

with radiation

of compound

resin n a t u r a l l y

illustrated

has a significant

and ease of filler

that e t h y l e n e - v i n y l

crosslinked

curable

applications

com-

illustrate

and radiation.

and,

a series

of EVA copolymers,

because

copolymers

to the gel point dose. as having

good c r o s s l i n k i n g

easily

in Table

The material

(EVA)

acrylate

are more

shown

influence

They are

and is chosen

acceptance.

acetate

than e t h y l e n e - e t h y l

ethylene

well

to be

in the following.

ease of c r o s s l i n k i n g

readily

illustrated

is not merely

and introducing

of the material.

for automotive effects

recipe

in this manner.

the interaction

ment of a c o m m e r c i a l l y pound,

is clearly

was treated

properties

and there appears

crosslinking

from an e s t a b l i s h e d

This

curable

pressure

thickness.

The work of copolymers

copolymers filled

efficiency

was

are more

or homo-poly-

than homopolymers,

7, were evaluated

w h i c h accepts

for

N.M. Burns

with

filler most

subsequently

respect

easily

chosen

as

as the

base resin. Several

known

radiation

crosslinking

were

evaluated

in the chosen

peroxide

crosslinking. effective own w o r k

(Fig.3).

Following variety

this,

an evaluation

in an attempt

w i t h an EVA copolymer

none were used

are generally

and m a y

interfere

with the c r o s s l i n k i n g

and hence

not available

Consequently,

effectiveness

in retaining

after crosslinking. more critical compounds.

aged physical

Our work

for radiation

showed

cured

are required

were

i.e.,

that very

to provide

such as alumina

or be consumed at a

in two ways

gel formation

and

(a)

(b) their

of the c o m p o s i t i o n selection

in peroxide

specific

is far

crosslinked

concentrations

the least effect

employed

in this

system

of

on cure and best

is a water

trihydrate.

In order

properties,

it is necessary

to employ

a coupling

inforcement

of the compound

(Fig.4).

The vinyl

those coupling

ration

at a

of aged properties.

The flame retardant

ability

evaluated

properties

than

systems

protection

that a n t i o x i d a n t

systems

It was also d i s c o v e r e d

antioxidants retention

efficiency;

by our

free radical

process

to provide

the a n t i o x i d a n t s

impact on c r o s s l i n k i n g

is not a cost

in the compound.

was made of 20 antioxidant

Antioxidants

of

to enhance

by Burns, (12) and confirmed

irradiation

later date. their

Consequently,

as well as low levels

copolymer

as was m e n t i o n e d

of concentrations.

scavengers during

The use of promoters

proposition,

coagents

agents

to couple with of the vinyl

four most effective

found

through

into the polymer

silanes

releasing

were

examined

additive

satisfactory

physical

agent which

provides

alkoxy

the alkoxy network

group

of their

and incorpo-

on crosslinking.

at various

re-

silanes were among

to be most effective (13) because

the filler

group

to obtain

concentrations

The and

Radiation processing of polyethylene doses

to obtain

though

Silane

of resin)

the m a x i m u m

provides

al of choice required

because

In a commercial

ing equipment;

effect

ingredients time

can be critical;

in the mix cycle

in Table

9.

aluminum

stearate

fluence

a measurable

9 regardless itself

is also

important

however,

laboratories (14) has clearly this

stage,

insulation

the physical

curable

applications

compound Table

XL 7400.

i0 and,

was

despite

specially

formulated.

RADIATION

CROSSLINKED

Ion Physics

Inc.

have a minimal

properties

processing as shown

The mixing

of a satisfactory

that care must

as shown

stearate

be taken

aid

in Table

process

compound

to avoid

en-

shown

porosity

is eliminated

that unless

properties

or in-

work

similarity

is the primary which

crosslinked

for the project. to meet

in these at

of the finished

is directed

towards

cured

This covers

must be

insulation

for economy

material

would

crosslinked

the physical

be

polyethylene

and dielectric tree resistance insulation.

In

a high c r o s s l i n k i n g

and to prevent

void

formation,

et al (16) that Lichtenberg

cable

of a

is the materials

for high voltage

crosslinked

of Energy

the d e v e l o p m e n t

electrochemical/water

concentration

crosslinked

in con-

and processing

compounds

USI

for peroxide

shown by T. Sasaki

in radiation

they differ

for the Department

The radiation

both

curable

are shown

INSULATION

contractor

characteristics,

is required,

cured

and appliance

peroxide

silane content

cable.

for the radiation

it has been

a similar

two compounds

in properties,

loading,

the specifications

and void or c o n t a m i n a n t

for automotive

polyethylene

in AEIC CS5-79 (15) aging

of these

HIGH VOLTAGE

supplier

properties,

YR 19505,

to complement

filler

expected

formation

properties

use of a p r o p r i e t a r y

the fact that radiation

ET-78-C-01-3001

230KV radiation

since

tensile

such as calcium

in the mix cycle

and electrical

their

in base resin,

efficiency

aids

of the

aid at the w r o n g

Previous

tailored

emphasizes

addition,

as is well

in the compound.

The properties

siderably

listed

reduce

in tensile

insulation,

aid w h i c h

project

of the

will be unacceptable.

This radiation wire

Also,

the processing

to the production

of air or volatiles

the influence

in the mix cycle.

this o p e r a t i o n

satisfactory

are usually

they can have a significant 9 shows

adding

time

improvement

or to obtain

of the compound.

of processing

of time of addition

it is during

trapment

e.g.,

at the proper

to use a

the order and time of addition

can significantly

The addition

on the properties;

provides

since

industry,

at the

from the compound-

such materials

Table

aid on the cured properties

in the c o m p o u n d i n g

etc.

1 to 2 phr,

properties.

The dose

agent

necessary

of the material

Even though

at low concentrations,

Alparts

is the materi-

costs by 13¢/ib.

this coupling

it is frequently

release

roll mill,

rates.

4.

(Table 8).

operation

Banbury,

on the physical

processing known

e.g.,

extrusion

with

in Figure

per hundred

S-I at 3 phr

raw material

is 12.5 Mrads

to obtain

as shown (phr=parts

Silane

properties

compounding

aid either

end product present

this reduces optimum

concentration

processing

properties of 5 phr

the best properties,

to achieve

specified

physical

S-2 at a c o n c e n t r a t i o n

271

is likely

to occur

tree

if a high

A. BARLOW et al.

272 radiation

dose

is employed.

peroxide

and radiation

density,

hence

polyethylenes

properties

at d i f f e r i n g

physical

lent gel contents. (17)

It is also necessary

crosslinked

There are

some indications

to determine

whether

have the same crosslink temperatures,

at equiva-

that this may not be the

case.

Copolymers cation

such as e t h y l e n e - v i n y l

because

ethylenes

were examined

synthesized density

in both

and c o n s e q u e n t l y

synthesis resins

which

tubular

polyethylenes.

each resin

its melt

type are presented

exhibit

formulated

for the proposed

structure

voltage

properties.

and p o l y d i s p e r s i t y

performance

structure

Our p r e l i m i n a r y this compound

promoters;

e.g.,

The gel point dose

and description

The results

curing.

cured materials

modification

end use properties

It has been cyanurate)

but this material,

Sasaki (16) has a deleterious

it means

to provide

influence

to an economical

should

are efficient

effect

the

the re-

that molecuon high

of the polymer be attainable.

to be employed

level;

i.e.,

shown by Burns (12)

as well

the

must be specifically

synthesis

consequently,

the dose

triallyl

the structure

In other words,

In this context,

during

for

of

show the autoclave

indicating

show that a c o a g e n t m a y have

to reduce

less for 70% gel content.

quirements,

ii.

efficiency,

low

in structure

Prior work (18) has indicated

the desired

results

density

six polypolymers

as well as linear

significantly

have no significant

properties;

to achieve

reactors

differ

application.

has to be tailored

end product

lar weight

low density

for radiation

that radiation

in this appli-

conventional

to radiation.

in Table

type is preferred

be used

Therefore,

index,

the best c r o s s l i n k i n g

indicates

quired

six resins

differently

with

data again

resin

included

cannot

properties.

and autoclave

All

respond

together

of this resin

acetate

of their poor dielectric

dose

suecinate

on the d i s s i p a t i o n

or

that the common

at reducing

as dipropargyl

in

i0 Mrads

factor

re-

used by

of the

insulation. Future

work will

for r a d i a t i o n necessary, as well

diacetylenes

as other

retardants crosslinked ability

insulation

In addition,

compounds

strand

are

by Patel (19) will be tested

the effects

be studied.

various

types

of tree

of the radiation

Tree

of conductive

tree resistance

suggested

is determined

semiconductive

will

relationship

If coagents

and tree resistance

and growth

Electro-chemical

content

polyethylenes.

of the type suggested

initiation

by the procedure

density-gel

crosslinked

promoters.

to resist

resistance

the c r o s s l i n k

have on the properties

insulation. tory,

examine

and peroxide

resistance

pathways

is measured,

is the

through

in our

by A s h c r a f t (20) , and the electrical

by method

A S T M D-3756.

and insulation

shield

A radiation

tree

crosslinkable

is also being developed

as

part of the project. CONCLUSION The two primary i.

Radiation method

conclusions

processing

for improving

drawn

offers polymer

from this work

an energy

are:

efficient

properties.

the

labora-

and cost effective

Radiation processing of polyethylene 2.

273

Radiation curable compounds must be specifically formulated to take advantage of the economics offered by electron beam processing compared to the higher energy requirements of established processes.

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3.

Polymer 2,323,(1961).

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(1977).

for Thermoplastic and Crosslinked

Insulated Shielded Power Cables Rated 5 through 69 KV

(6th Edition).

274 16.

A. BARLOW et al. T. Sasaki, F. Hosoi, M. Hagiwara, K. Uesugi,

High Voltage Cable, 17.

E. Saito, H. Ishitani,

H. U. Voigt.

Radiat Phys Chem 14,821

Kunststoffe A. Barlow,

IEEE Trans on Electrical

Insulation EI-15,124

(1980).

G. N. Patel, A c c e l e r a t i o n of R a d i a t i o n - I n d u c e d Crosslinking Polyethylene by Diacetylenes,

20.

Kautschuk und Gummi

29,17(1976) C h a r a c t e r i z a t i o n of HMWPE Used for High Voltage

Insulation, 19.

(1979).

The Crosslink Density of Crosslinked Polyethylene

and the Problems with its Measurement, 18.

and

Development of Radiation Crosslinking Process for

A. C. Ashcraft, World December

Radiat Phys Chem 14,729

Factors Influencing Treeing Identified, 1,38

in

(1979). Electrical

(1977).

TABLE 1 PROPERTY C O M P A R I S O N OF PEROXIDE AND RADIATION POLYMERIZED POLYETHYLENE

Melt Index g/10 min Density,

g/cc

20.7

17.1

psi

0.918

1410

1230

psi

1240

1490

percent

520

Yield Strength, Modulus,

Radiation

0.913

Tensile Strength, Elongation,

Peroxide

psi

190

15,700

Low Temperature Brittleness

°C

Vicat Softening Point Stress Crack Resistance,

hrs

25,500

-55

-36

78

85

0.25

0.22

TABLE 2 CONTROLLED RADIATION M O D I F I C A T I O N OF ETHYLENE COPOLYMER Mw x 10 -4

Mn x 10 -4

Mw/Mn

Original Polymer

4.66

1.58

2.95

40 Mil Film

(i Mrad)

6.38

1.56

4.08

15 Mil Film

(i Mrad)

9.36

1.82

5.14

275

Radiation processing of polyethylene ~LE

3

COMPARISON C~ PRCEXJCTIflN COSTS* FCR NA%'JRAL ASD CROSSLINK~D HEAVY DUTY FILM

Fquipment

250 KV 30" Electrocurtain

Processor

$285,000

installed with web handling facilities. Hourly 15-yrAmortization Cost

$ 2.17/Hr

(Labor, Utilities, Maintenance, Etc.)

$ 9.34/Hr

Operating Cost

sn.51/Hr

Total RunningCost

Film Thickness ~is

Output

Production

Film Cost

Radiation

Total

Percent

Sq.Ft/Hr.

Cost

¢/Sq.Ft.

Cost

Cost

Savings

¢IS~.~.

¢l~.Ft.

$/~. 5

16600

304

1.831

4

20800

304

1.462

0.032

1.831 1.494

18.4

3

20800

257

1.236

0.032

1.268

30.7

* (Feb. 1980)

TABLE 4 ADIrANTAGES AND DISADVANTAGES CY RADIATION VS. PEROkqqgE CROSSLINKING CHARACTERISTIC Ccr~pound Formulation

RADIATION

PEROXIDE

Technology developing

Technology developed

Antioxidant Selection

Very critical

Less critical

Temp. Sensitive Additives

Few problems

Must be avoided

Have to avoid air

Have to avoid scorch

Co~und

Production

entrapment Wire & Cable Production Equipment Maintenance

Low

High

Extrusion Hate

~I000 Ft/Min

~350 Ft/Min.

Production Cost

Lower

(Pollution problems)

Curing

Off-line

Must be cured in-line

Safety/Employee Concern

Requires greater employee education

Product Properties Residual by-products

None

Polymer Degradation

Lichtenberg trees

Can be beneficial or harmful

Porosity

Possible

Cured under pressure

Insulation Thickness

~0.6" Max.

>i"

RPC Vol. 18. No. I - 2 - - T

A. BARLOWet ai.

276

~,BLE 5

C(]b~ARISON OF PRfIXICTION COSTS

FOR RADIATION VS P~OXIDE

CROSSLIN~D WIRE & CABLE OOMPOUNDS

Peroxide

Radiation

$

Capital Investment 3-1/2" Extruder, CV Line, Installation, Complete

280,000

4-1/2" Extruder, Thermoplastic Line - Installation ccaplete

300,000

1 MeV - 50 ~

Dynamitron O, Installation complete

900,000

Operating costs (Line operating 6000 hrs/yr) Labor, Utilities, Maintenance, etc. Equipment Amortization TOTAL OUTPUT

41.97/Hr

59.80/Hr

3.20/Hr

13.70/Hr

45.17/Hr

73.50/Hr

350 Ft/Min

1000 Ft/Min

$2.689/M Ft

$1.531/M Ft

TOTAL PRODUCTION COST Asstm%e 80% Efficiency Factor (Maintenance, * **

Reel Changes, Product Changes)

From Reference i0 (Feb 1980) Cc~pound with 1.33 g/cc density extruded onto 12 AWG copper wire with 30 mil wall thickness.

TKBLE 6 EFFEL~T CF CROSSLINKING PROCESS ON POLYMER & O3MPOUhD PPOPE~TIES

XL 7400 TYPE

POLYOLE~ IN RESIN

PROPerTIES

FO~MUIATICN Thermal

Radiation

Thermal

Radiation

Cure

Cure

Cure

Cure

0.938

0.938

1.39

1.39

3220

3400

2510

1370

Elongation, %

540

520

230

140

Swell Ratio

7.2

10.5

5.1

8.1

Extractables, Wh.%

5.7

13.5

7.3

20.7

Density g/cc Tensile Strength,

psi

Radiation processing of polyethylene

277

TABLE 7 RESIN CHOICE FOR RADIATION CROSSLINKID COMPOUhDS

Resin

Melt Index

Weight Percent

Gel Point Dose

Vinyl Acetate A

2.1

0

1.88

B

3.0

8.8

1.92

C

1.5

17.0

1.55

D

1.3

28.0

0.86

E

8

40.5

1.18

TABLE 8 DOSE FOR OPTIMIZATION C~ CURED PROPERTIES WITH SILANE S-I

Dose (Mrads)

0

Tensile Strength, psi Elongation,

10

12.5

15

17.5

1650

1730

1900

1840

1900

650

310

250

240

230

(percent)

TABLE 9 OF PROCESSING AID AND ADDITION T]2~ ON PHYSICAL PROPERTIES

Processing Aid

Time of*

Properties of Cured Cc~pound

Addition

Tensile, psi

Elon~ation, %

0

1360

210

Calcium stearate

1

1650

230

Aluminum stearate

1

1750

250

0 or 1

2350

260

Calcium

stearate

Proprietary Aid

*

0 = Start of mix cycle 1 = After flux

A. BARLOW et ol.

278

TABLE i0 C(IMPARISON OF PE~ROXIDE AND RADIATION APPLIANCE/AUTflMOTIVE WIRE INSUIATION XL 7400

YR 19505

Peroxide

Radiation

2510

2350

230

260

2830

2910

200

200

-46

-47

20

13

4.8 x 1015

1.6 x 1015

25

25

UL Appliance Wire Flame Test

Pass

Pass

SAE J 1128 Flame Test

Pass

Pass

Cure Type Original Properties Tensile Strength, psi Elcngation, percent Aged Properties (7 days @ 158°C) Tensile Strength, psi Elongation, percent Low T~llc~ratllre Brittleness F50 eC Water Absorption (7 days @ 82°C mg/sq in) Voltune Resistivity Ohm-an C~ygen Index

~%BLE ii RADIATION CROSSI/qTKIA~ E F F I C ~

OF POLYETHYI/~_~

FOR HIGH V O L ~ G E INSULATION Synthesis

Y~it Index

Density

Type

~/i0 min

g/cc

Autoclave

0.2

0.918

0.97

Autoclave

1.2

0.919

1.3

Tubular

0.3

0.919

3.9

Tubular

2.0

0.919

7.1

Linear

0.7

0.926

8.5

Linear

1.9

0.919

7.1

*

~ - P i n n e r ~

Gel Point Dose* Mrads.

Radiation processing of polyethylene

279

FIG 1 S C H E M A T I C D I A G R A M OF R E A C T O R FOR R A D I A T I O N P O L Y M E R I Z A T I O N OF E T H Y L E N E

STIRRER

CC F

REACT

I I FIG 2 C O M P A R I S O N OF P E R O X I D E AND R A D I A T I O N P O L Y M E R I Z E D P O L Y E T H Y L E N E

MwX 10-4 80

....

(PEROXIDE) (RADIATION)

21.9 24.8

MnX 10 -4

MwlMn

1.58 1.11

13.9 22.3

6C

:S (9 0 40 -J %%%% 2O

0 10 2

103

104

105

MOLECULAR WEIGHT M

108

107

280

A. BARLOW et aL FIG 3

E F F E C T OF P R O M O T E R S ON C R O S S L I N K I N G E F F I C I E N C Y OF EVA. ( 8 5 % GEL) 10.0

8.0

6.0 RADIATION DOSE,

(MEGARDS) m

4.0

2.0

EVA

1PHR VULCUP 4 0 KE

1 PHR SR351

1/0,5 PHR 1 PHR SR3501 SR350 V U L C U P 4 0 KE

FIG 4 E F F E C T OF S I L A N E AND S I L A N E L E V E L ON P H Y S I C A L P R O P E R T I E S

2200 2000"~ 1800"~ Z w

1600"~ 1400"~ z

1 2 0 0 " ~w 1000 CONC. PHR

0

1

3

5

1

5

3

5

3