Thermal analysis of the stability of polyvinylchloride

ThermochimicaActa, 93 (1985) 183-185 Elsevier

Science

Publishers

B.V.,

Amsterdam

THERMALANALYSIS OF THE STABILITY OF,POLYVINYLCHLORIDE

T.R. Manley, A. Guy, L.J. Newcastle

Polytechnic,

Newcastle

Clark,

Ellison

Place,

upon Tyne NE1 8ST

U.K.

ABSTRACT

DTA correlates well with the standard congo red test for the thermal Thermogravimetry is not sufficiently stability of polyvinylchloride (PVC). sensitive and the heat stability test is the least useful of all.

INTRODUCTION Polyvinyl is

unstable

above

(PVC) is

at evelated

70°C,

producing

one of

. .

modrflers,

processing

aids,

chloride

and normal of

pigments,

can radically

and stabilisers,

the most widely

PVC degrades

temperature. hydrogen

150°C and ZOOOC. The addition

between

isers

chloride

by an unzipping processing

compounding

fillers,

used plastics.

effect

the thermal

it

mechanism

temperatures

ingredients:

lubricants,

but

are

impact

extenders, stability

of

plasticthe

material. The inclusion stability current of

of

to heat work is

part

the molecular

chloroparaffins

and light of

structure

The experimental

of

an attempt of

into

both

PVC significantly

stabilised to classify

the organic

techniques congo

chosen

stability

were a modified

red

stability

(ORS) and thermogravimetry.

test

reduces

and unstabilised

the

compounds.

the stabilising

effect

The

in terms

additive. to investigate (CRT),

the change

isothermal

in thermal

DTA, oven heat

EXPERIMENTAL :,67/113 is

is

a medium mol,wt.suspension

a chlorrnated

paraffin

extender

homo-polymer,

giving

Cereclor

good low temperature

S45 (I.C.I.) properties

in

PVC. The stabilisers

used were:-

mono ethanolamrne (MEA) ; di ethanolamine (DEA) ; ; mono-n-propanolamine (MPA) ; di-N-methyl aniline (DMA); hexamine (REX) ; melamine (MEL) ; pentaerythritol (PENTA) ; tri-n-butylamine (TBA) ; tri

ethanolamine

(TEA)

diphenyl

amine (DPA);

carbinol

(TPC) ; hexamethylmethylolmelamine

The other

Proceedings

ingredients

triphenylamine were all

(TPA);

laboratory

of IClA 85, Bratislava

triphenylmethane

(TPM);

(HMMM) ; trimethylolmelarmne standard

materials.

triphenyl(TMM).

The formulations

used were:Formulation

PVC Corvic

S67/113

(I.C.I.)

parts

100

100

50

25

S45 4.5

Antioxidant

(Bisphenol

The sheets

B

25

Stabiliser

155’C

Formulation

parts

D.O.P. Cereclor

A

were

A)

prepared

4.5

0.25 on a laboratory

0.25

2 roll

mill,

heated

by steam to

to 165’C. The congo

red test

was based

2782 Part

on B.S.

1 Method 130A (1976).

ISOTHERMALDIFFERENTIAL THERMALANALYSIS A DuPont 900 Differential using

the high

temperature

Thermal Analyser cell.

Silica

was used

was used as the reference

The sample was heated

to 200°C at the maximum rate

of nitrogen

rate

had been

at a flow

the heat

stability

of

possible

When all

150 mlsfminute.

consumed an exothermic

beginning

peak was visible.

up to the peak of

isothermally

under

the stabiliser The time

the exotherm

was taken

at 200°C material.

an atmosphere in the PVC

taken

from

as a measure

of

the

the sample.

OVENHEAT STABILITY TESTS Samples were heated

in a forced

180 + l°C

and removed at regular

determine

the relative

air

convection

stabilities

of

oven at either

The colour

intervals.

changes

200 + l°C

or

were used to

the samples.

RESULTS The results

The correlation

(CR). “t”

are given

test

is

0.171

between

which

Thermogravimetry pvc but

is

In the early

has been used

that

than DTA; this

calorimetric The congo

ability tool

days of

to process in screening

test

very

to investigate

were obtained.

the thermal

analysis

TG was claimed

was shown to be erroneous are

has the

and congo

The value

of TG was much lower

results claim

data

good.

for

red

tests

students

at the 10X level.

thermal

a number of a large

the isothermal is

the sensitivity

techniques red

1 for

the tests

significant

in our experiments

the DTA and so no further accurate

in Table

to be preferred advantages

samples

of

simultaneously,

number of possrble

addrtrves.

than that

of of

to be potentially and current

to gravimetric

simplicity,

degradation

methods.

cheapness hence

more

work confirms

and the

making it

Reproducibility

a useful of

-

185 -

results is good. The oven stability test is cormnonly used in industry.

The results could be

misleading because of the use of colour changes to determine when degradation had taken place.

It was difficult to differentiate between those that had given

slightly different congo red times because an additive or stabiliser system which gives good colour hold is not necessarily congo red time.

the one that gives a long

The general trend of stabilities is similar for both the congo

red test and oven stability test.

CONCLUSIONS Isothermal DTA correlates well wrth the standard congo red test and could provide the basis for a more convenient quality control test. the DTA sample however makes the obtarning of a homogeneous

The smallness of

sample more

difficult and this will militate against the adoptron of DTA as a standard, Inhomogeneous

specimens may also contribute to the poor reproducibility

of

thermogravimetry. The colour change on heating has little to recommend it apart from simplicity and should be discontinued.

TABtE 1

Comparison of the congo red test and isothermal dta on the reductron in stability of PVC caused by the addrtion of S45.

Additive

Congo red test

None

-61

-54

MEA

-46

-57

DEA

-39

-39

TEA

-35

-29

MPA

-39

-41

DNA

-56

-53

HEX

-11

-33

MEL

-34

-36

PENTA

-55

-55

TBA

-51

-57

DPA

-60

-62

TPA

-65

-61

TPM

-64

-64 -53

TPC

-64

HMMM

-37

-38

TMM

-37

-35