DEVELOPMENT AND EVALUATION OF A TOUGHENED PHENOLIC RESIN FOR

MINING APPLICATIONS

I SIGALAS, R HOHENDORF AND P TRUTER

CSIR

DEVEIDfl.1ENT AND EVALUATION OF A 'roUGHENED PHENOLIC RESIN

FOR MINING APPLICATIONS

I Sigalas, R Hohendorf and P Truter J Oi vision of Materials Science and

Technology, CSIR

This work describes some of the work done recently at the CSIR in the area

of development of toughened phenolic resins. A novel type of plasticiser

was used to improve the impact resistance of a commercially available

resole phenolic resin by a factor of 5. '!he properties of the plasticised

resin, as well as those of the resulting glass f.i.bt'e reinforced laminates

are reported.

1. INTRODUCl'ION

As several speakers have already mentioned in this COlloquium, composites

have a great number of present and, potential applications in the South

African mining industry. '!heir combination of high specific strength and

stiffness I coupled to their high resistance to corrosion, makes them the

ideal material involved in the solution of a great number of problems

encountered in the mining environment.

However, fibre reinforced plastics can burn. This, particularly in view of

the sensitivity of the industry to the hazard of yet another fire, makes

the utilisation of composites in the mining industry problematic in some

instances. one particular category of composites allows the design

engineer to overcome this problem. Phenolic resins are inherently fire

resistant.

Phenolic resins are used in a large variety of composites applications in

the electrical , automotive, construction and appliance industries.. '!hey

were commercialised in the early days of this century.

2/

- 2 -

Inherent characteristics of phenolic resins that make them attractive

include low flammability, low smoke production on burning, high char yield

and good thermal stability. However, phenolic resins also have several

major deficiencies that limit their use, namely release of volatiles

during curing and brittleness of cured products. Addition of

thermoplastics inproves toughness rut reduces the service temperature

limit of the phenolic carg;x>site and enhanCes flammability [1-4]~

In view of the above, new chemistry is needed to chain extend and cross

link phenolic resins to: reduce volatiles production during curing and, at

the same time, achieve ~ter toughness without significantly increasing

flammability, enhancing smoke production, or reducing thermal

stability of the finished product.

lhis paper describes some of the work done recently at the CSIR in the

area of developuent of toughened. phenolic resins. A plastiCiser was developed, suitable for the above purpose. In what follows, the properties

of the plasticised resin, as a function of the amount of plasticiser

utilised are reported. Glass fibre reinforced laminates were also made ~

and evaluated as far as mechanical properties and fire resistance are

conoerned.

2. EXPERIMENTAL

.2.1 .Phenolic resin

'Ibe phenolic resin used was a resole Beetle resin type 17"'1393 supplied by

British Industrial Plastics. '!he cost of the plasticiser developed was

less than R8jKg.

3/

- 3 -

2.2 Resin test specimens

Different phenolic plasticiser mixtures ratios were prepared and cured at

60 C for 6 hours. standard test specimens were cast in polycarbonate

moulds according to ASIM 0638-86 on an Instron model 1122 at a speed rate

of 5mmjrnin.

'!he impact test is used to measure the toughness or shock resistance of a

specimen and was done according to ASIM D3029-78.

2.3 Glass fibre reinforced resin specimens

In order to obtain results relating to materials locally available, it was

decided to use AF1 glass fabrics in the preparation of all the GRP samples

studied in this work. An AF1 non balanced woven fabric 250 gin? in area!

density, with 90% rovings in the warp and 10% in the weft directions was used to determine the "unidirectional" properties of glass fibre

reinforced composites made with the plasticised phenolic resin. AFI 450

g/m2

balanced plain weave glass fibre fabric was used to obtain a

complimentary set of properties.

'.Ihe tensile properties were obtained according to ASIM D3039-76 at a speed

of 2mmjrnin . '!he compressi ve properties were obtained according to ASIM

03410-75 at a speed of lmmjrnin. '!he 10sipescu shear test [5,6] was used to

determine the in plane shear properties, at a speed of lll1mjrnin. As impact

resistance is one of the most important properties of phenolic (;RP that

could benefit through the introduction of a toughened phenolic resin, the

End Notch Flexure (ENF) test [7] was also performed in order to determine

the Mode 11 critical strain energy release rate for the "unidirectional"

laminates. Smoke tests were performed on the balanced weave specimens to

determine the behaviour of the composites as far as fire hazard is

concerned. The failed "t.midirectional" specimens were examined in a

scaning electron microscope.

41

- 4 -

3. RESULTS

3.1 Resin smcimens

Table 1 shows the values obtained for the tensile and impact strength of

the phenolic resin, as a function of the amount of plasticiser used.

A graphic representation of the results is give in figures 1 and 2.

As can be seen I the tensile strength of the plasticised resin peakS at

+-10%, at an absolute value 130% higher than that of the 'IJt'llOOdified one. A

significant improvement is achieved in the impact strength of the

plasticised resin, that pl.""Operty increasing fivefold at a 30% plasticiser

addition level.

3.2 Glass fibre reinforced, §PeC1.mens

Table 2 and Figure 3 shows the variation of the tensile properties of the

"unidirectional if laminates as a function of resin plasticiser content. A

decrease in tensile strength, coupled to a drop in tensile strain was

obtained. A slight increase in the tensile modUlus is obserVed.

Table 3 and Figure 4 show the variation of the compressi ve properties of

the "unidirectional ut laminate. A sharp decrease in the value of this

matrix dominated property is observed. '!he strain to failure is also seen

to decrease. '!he oode of filu.re changed from that of oompressive shear to buckling preceeded by de:\.amination. No significant effect on the modultJS is

observed.

Table 4 and Figure 5 show the variation of the in plane shear properties

of the Unidirectional If laminate as a function of plasticiser content.

Table 5 and Figure 6 show the variation of the in plane shear properties

of the woven fabric. In both cases a sharp drop in strength and modulus is

observed. 'llle strain to failure on the othe:t' hand shows a marked increase

with increasing plasticiser content.

= 5 -

Table 6 and Figure 7 show the variation of the Mode II critical strain

energy release rate as a function of plasticiser content. A drop in this

property is observed.

3.3 Microscopic evaluation

Photographs 8 to 10 show micrographs of the 0% to 30% plasticised resin

respecti vel y. The following observations can be made:

All samples are wet through, Le the fibres are surrounded by resin.

However, the bonding of resin to the fibres is rather poor. This is the

case even for the non plasticised resin. Specifically, the following

observations can be made:

No plasticiser (Figure 8): The wet out here is \<JOrse than the one attained

at 10% plasticiser content (figure 9). Fibre pull-out, with the fibres

clean of resin can be seen

10% plasticiser (Figure 9). This composition seemed to offer the best

bonding to the fibres. Note that fibres are not clean as before. Voids in

the ~in, possibly a result of the phenolic curing condensation reaction

can be seen.

20% plasticiser content (Figure 10). Clean fibres and resin flakes,

indicating poor adhesion.

30% plasticiser content (Figure 11). The resin is seen here to wet the

fibres, but not to adhere to them. This can be seen in the areas of voids

where the resin has lifted off the fibre surface.

6/

- 6 -

3.4 Smoke test

Table 7 shows the variation of the smoke density as Cl function of

plasticiser content and time. As can be seen, up to plasticiser content of

20% the plasticised laminates show no higher smoke emission than the

laminates made with plain resin.

4 DIsaJSSION

Although the strength of the plasticised phenolic resin shows a peak in

magnitude at 10% plasticiser content, this does not have a marked effect

in the properties of the resul tin<] laminates. This is due to the very low

strain to failure of the pureas well of the plasticised resin.

'!be drop observed in the tensile strength of the phenolic laminates

(Figure 3) may be attributed to the decrease in stiffness of the resin

with increasing plasticiser content. As :mentioned above, the elongation to

failure of the resin remains less than 0.5% throughout the plasticiser

range. At the same time, as shown by our scanning electron microscopy

observations, resin to fibre adhesion is not very good. in this system. It

is therefore expected that the load at failure is carried almost

exclusively by the glass fibres at that stage. However, even under those

conditions one expects the matrix to transfer some of the load from one

fibre to the next. Clearly this function is impaired with decreasing

matrix stiffness, a sure result of the plasticising process.

'Ihe drop in compressi ve strength is as should be expected for this matrix

dominated property when the matrix suffers a decrease in stiffness. '!be

same decrease in stifness causes the change in failure mode from

cornpressi ve shear to microbuckling and delamination.

f7

- 7 -

'!he small variation in Mode 11 strain energy release rate indicates that

the prsent resin is probably not going to offer a greatly inproved impact

resistance. Again this behavour can be attributed to the fact that resin

to fibre adhesion is not very good to start with, nor does it improve with

increasing plasticiser content.

5 CONCWSIONS

'Ibe present plasticised resin system, altough promising as far as strength

and ilnpact resistance are concerned, does not transfer too many obvious

advantages to the resulting laminate, although the increase in shear

strain to failure is certainly very encouraging. However I before a final

conclusion is reached as to the advantages of this system it will be

necessary to evaluate the impact resistance of the resulting laminates, as

well as. perform comprehensive fire tests on them.

It is felt that a bet'ter adhesion of fibre to resin 'WOuld improve the

behaviour of this system to a very significant extenI:i.

- 8 -

1. Knop, A. and Pilato, L.A., "Phenolic Resins, Chemistry, Applications

and Performance", Springer-Verlag, 1985.

2. Postel, S. L. f The Society of Plastic Industry, Inc., June 3 - 4,

Cincinnati Conference Proceedings, p. 58 - 61, 1987.

3. Grupta, M.K., Hoch, D.W., and Keegan/ J.F., Modern Plastics, p. 70,

1987.

4. CUlbertson, B.M., and Tufts, T.A., D.S. Pat. 4,430, 491 to Ashland

oil, Inc. f Feb. 7" 1984.

5. Walrath, D. E. and Adams ID. F ., The Iosipescu Shear Test as applied to

Composite Materials, Experimental Mechanics, March 1983, p. 105 - 110.

6. Broughton I W. R. Mixed Mode Fracture of carbon Fibre Reinforced

cO~1site Materials, A. Dissertation, Darwin College, Cambridge, June

1986, p. 32 - 37.

7 • Car lsson, L. A., Gillespie Jr., J. W., and Pipes, R. B., Fini te Element

Analysis of the End Notched Flexure (ENF) specimen. Comp. sci. & Tech.

Vol. 26 (1986).

TE~~SILE STRENGTH (MPa)

28

24

20 L / 15

12

o ,5 10 20 25 30 35 40

PLASTiCIZER ADDITiO~4 cm

Figure 1 Tensile strength versus the percent plasticiser addition

PLASTICIZER ADDITION (%)

Figure 2 Lmpact strength versus the percent plasticiser addition

I I-e!)

Z W 0:: I-Ul

w .-J H Ul Z W I-

Z H

650

575

500

1 .8

& 1. 5 I­Ul

Ul :::J .-J

1.2

48

:::J 4 1 r:::I o L

35

TENSILE PROPERTIES OF UD GLRSS FIBRE/PLRSTICISED PHENOLIC Resin Content Range: 24 - 27 % by Mass

Long i tud i n a 1 Tens i 1 e St rength [MPaJ

I

I o % 10 % 20 % 30 %

Ultimate Longitudinal Tensi le Strain [ % J

--

--

--

-'--

o % 10 % 20 % 30 %

Longitudinal Tensi le Modulus [GPaJ

I I I

o % 10 % 20 % 30 %

PLRSTICISER RDDED TO PHENOLIC Figure 3.

I I­o Z W IX I­U!

700

w 400 > H U! U! W IX Cl. L o U

Z H

a: IX I­U!

U! :J ..J

100

2

o

55

:J 45 ~ o L

35

COMPRESSIVE PROPERTIES OF UD GLRSS FIBRE/PLRSTICISED PHENOLIC Resin Content Range: 22 - 24 % by Mass

Longitudinal Compressive Strength [MPaJ

I

I I

I

I j o % 10 % 20 % 30 %

Ultimate Longitudinal Compressive Strain [ % J

I I I I

o % 10 % 20 % 30 %

Longitudinal Compressive Modulus [GPaJ

I I I I o % 10 % 20 % 30 %

PLRSTICISER RDDED TO PHENOLIC Figure 4.

INPLRNE SHERR PROPERTIES OF UD GLRSS FIBRE/PHENOLIC Resin Content Range : 22 - 23 % by Mass

Iosipescu She ar Strength [MPaJ 80

I I ~ 19 Z W 0::: ~ 50 U1

0::: I a: w

L I U1

I 20

0 % 10 % 20 % 30 %

Ultimate Shear Strain <calculated) [MPaJ 4

Z I H a: 0:::

I ~ U1 2 0::: a: w

I I I U1

0 0 % 10 % 20 % 30 %

Iosipescu Shear Modulus [GPaJ 6

I U1

I :J ...J :J r::l 0 L 3

0::: a: w I I U1

o o % 10 % 20 % 30 %

Figure 5. PLRSTICISER RDDED TO PHENOLIC

INPLRNE SHERR PROPERTIES OF HOVEN GLRSS FIBRE/PHENOLIC Resin Content Range : 2 1 - 27 % by Mass

Iosipescu Shear Strength [MPaJ 60

I I I I-

I 19 Z W er:: I- 35 tn

er:: cc w I tn I

10 o % 10 % 20 % 30 %

Ultimate Shear St r a in (calculated) [ % J 4

z I H CC er:: l-tn 2 er:: I CC

I w I I tn

o o % 10 % 20 % 30 %

5 Iosipescu Shear Modulus [GPaJ

[J) I :J --1 I :J (::l

0

I L.: 2 er:: CC W I tn

o o % 10 % 20 % 30 %

Figure 6. PLRSTICISER RDDED TO PHENOLIC

900

u H 650 H 19

400

800

u H 500 H 19

200

E N F TEST OF UD GLASS FIBRE/PHENOLIC TO DETERMINE GIIc Resin Content Range: 28 - 29 % by Mass

Critical Strain Energy Release Rate GIIc [kJ/m A 2J

-r- I -- I o % 10 % 20 % 30 %

E N F TEST OF WOVEN GLASS FIBRE/PHENOLIC TO DETERMINE GIIc Resin Content Range: 22 - 25 % by Mass

Critical Strain Energy Release Rate GIIc [kJ/m A 2J

I I I

0 % 10 % 20 % 30 %

PLASTICISER ADDED TO PHENOLIC

Figure 7.

Table 1 Mechanical properties of the resin plasticiser systems

Plasticiser Addition

0 5 10 15 20 25 30 35

Tens; le Strength (MPa) 11 ,42 16,52 27,75 26,86 19,31 21,65 22,64 24,16

Impact Strength 1,9 3,7 5,1 (J/mmxlO-2)

6,2 7,6 9,3 10,3 11,3

Tabl

e 2

: M

echa

nica

l Pr

oper

ties

of U

nidi

rect

iona

l G

lass

Fib

re I

Phen

olic

.

Con

ditio

n: R

oom

Tem

pera

ture

l 40

-50

% R

elat

ive

Hum

idity

PROP

ERTY

I

RESIN

I

MEAN

:ST

ANDA

RD :

COEF

FICI

ENT

: NO

. OF

I

I !

lDEV

IATI

ONloF

VAR

IATI

ONiSP

ECIM

ENS

! Phe

nolic

I

iPlast~ciser\

I "

-I

I six

I

I '0

I '6

I x

I s

I i

i i

I I

I i

I

I Lon

gitu

dina

l Te

nsile

stre

ngth

I

I I

I I

100

0 60

7 13

.2

0.02

1 I

10

I I

I I

90

10

561

31.0

,

0.05

5 10

I

I 80

I

20

536

25.3

I

0.04

7 I

10

I I

I I

I I I

I ,

\Ulti

mat

e Lo

ngitu

dina

l Te

nsile

Stra

in

I 10

0 I

0 15

400

1079

I

0.06

9 I

10

'I 90

I

10

1560

0 16

25

I 0.

103

I 10

I

I 80

I

20

1410

0 14

49

I 0.

102

! 10

I

I I

I I

I I

I iL

ongi

tudi

nal

Tens

ile M

odulu

s 10

0 I

0 41

.3

1.57

,

0.03

8 I

10

90

10

40.4

1.

97

I 0.

048

10

I 80

I

20

43.2

0.

99

I 0.

022

I 10

!

i I

I

Tabl

e 3

Mec

hani

cal

Prop

ertie

s of

Uni

dire

ctio

nal

Gla

ss F

ibre

/Ph

enol

ic.

Con

ditio

n :

Room

Tem

pera

ture

, 40

-50

% R

elat

ive

Hum

idity

PROP

ERTY

I

RESI

N ME

AN

STAN

DARD

:C

OEFF

ICIE

NT :

NO.

OF

: I

! I

DE\iIATIOI~IOF V

ARIA

TION

i SPE

CIM

ENS I

I

lPlast

~ciser

\ i P

heno

lic

-I

-I

;c x

~

I si

x ;

I ~,

I I

" I

I I

I

I I

\---1

I

Long

itudi

nal

Com

pres

sive

Stre

ngth

10

0 I

0 i

613

I I

I 10

I

I 29

.11

I 0.

047

i 90

I

10

I 43

4 56

.04

I 0.

129

I 10

3D

20

!

353

10

I I

23.0

3 I

0.07

9 I

70

30

1 13

4 22

.02

I 0.

119

I 10

I

I U

ltim

ate

Long

itudi

nal

Com

pres

sive

Stra

in

100

I 0

I 14

400

1636

I

0.11

3 10

I

I 90

1

10

I 12

300

4083

,

0.31

8 10

80

I

20

3000

13

13 i

0.

165

10

70

I 30

43

00

653

I 0.

151

10

(Lon

gitu

dina

l Co

mpr

essiv

e M

odul

us

100

0 44

.2

I 0.

073

10

3.46

I

, 90

10

43

.9

2.02

I

0.04

6 10

3D

20

42

.5

2.11

I

0.04

9 10

70

30

44

.3

2.93

!

0.06

6 10

Tabl

e 4

Hec

hani

cal

Prop

ertie

s of

Uni

dire

ctio

nal

Gla

ss F

ibre

jPh

enol

ic.

Cond

ition

: R

oom

Tem

pera

ture

, 40

-

50

% R

elat

ive

Hum

idity

PROP

ERTY

Iosip

esCl

l Sh

ear

stre

ngth

Ulti

mat

e Io

sipe

scu

Shea

r St

rain

-m

easu

red

Ulti

mat

e Io

sipe

scu

Shea

r St

rain

-ca

lcul

ated

Iosip

escu

She

ar M

odulu

s

. P.

ESIN

i

HEAN

[S

TAND

ARD

iCO

EFFI

CIEN

T 1

NO.

OF

! i

. i

+,.

: iD

EVIA

TION

,OF

VARI

ATIO

NjSP

ECIM

ENS\

,Phe

nOllc

IP

laSc

lClse

ri _

I I

. I

I I

~; I

%

; x

! s

11 si

x I

. I

I!

i i----\

I i-

--i

.1 _

_ _

" ..

I

! 10

0 0

I 6~.

9: 4

.31

: 0.

067

i 10

90

10

i

5.).~!

1.41

I

0.02

6 I

10

80

20

i 43

..:;

, 3.

05 i

0.07

0 I

10

70

30

i 28

.4

I 1

.82

, 0.

064

I 10

100 90

80

70

100 90

80

7()

100 90

80

70

o 10

20

30 o 10

20

30 o 10

20

30

I ,

1020

00

4362

0 iD

. 42

7:

10

1290

00

2549

0!

0.19

7 j

10

1460

00

3791

0 \

0.26

0 i

10

1180

00

3101

0 I

0.2

62

: 10

I

[

1133

0 18

32 !

0.

161!

10

11

800

1738

'!

0.14

7 I

10

2112

0 31

71 !

0.14

9 l

10

2990

0 35

64 i

0.11

9 I

10

I ,

5.25

0.

56 i

0.10

6 I

4.07

0.

37

i (L

090

1.78

0.

22 I

0.12

2 0.

83

0.09

I

0.10

8

10

10

10

10

Tabl

e 5

Mec

hani

cal

Prop

ertie

s of

Wov

en F

abric

Gla

ss f

ibre

jPn

enol

ic,

Con

ditio

n :

Room

Tem

pera

ture

, 40

-50

% R

elat

ive

Hum

idity

\ i I I

PROP

ERTY

Iosip

escu

She

ar S

treng

th

[Ulti

mat

e Io

sipe

scu

Shea

r St

rain

-m

easu

red

1 1 I i [Ulti

mat

e Io

sipe

scu

Shea

r St

rain

-ca

lcul

ated

I I Iosi

pesc

u Sh

ear

Mod

ulus

RESH

!

! Phe

nolic

iP

:ast

icis

er

, ~

! )

o I

" ---1

-----

100 90

80

70

101) 90

80

70

100 90

80

70

100 90

80

70

o 10

20

30 o 10

20

30 o 10

20

30 o 10

20

30

MEk~

ST

ANDA

RD

COEF

FICI

ENT

NO.

OF

DEVI

ATIO

N OF

VAR

IA'rIO

N SP

ECIM

ENS

x s

sF;;

51 ~

'1

48.0

41

. 7

19.6

1100

0e

1520

00

1430

00

1590

00

1240

0 13

000

1540

0 27

700

3.72

3.

18

: i+4

0.

63

2.61

5.

86

4.28

1.

81

I

5035

0 I

2862

0 43

300

3820

0

1953

26

33

3124

59

47

0.25

0.

20

0.28

0.

11

-_

._

------

0.05

0 0.

121

0.10

2 0.

092

0.45

6 0.

188

0.30

3 0.

240

0.15

7 0.

203

0.20

2 0.

214

0.06

7 0.

062

0.11

4 0.

174

10

10

10

10

10

10

10

10

10

10

10

10

10

10

10

10

TABLE 6 Mode II critical Shear In Energy Release Rate.

r"-"-,,~ Plasticiser =l I '~Content

i ''''" % 0 10 20 , ~

'l'ype of Fabr~J I

Unidirectional 650 (92) 708 (77) 552 (67)

c--'

Woven roving 642 (60) 533 (80) 311 (30)

Ti\BLE 7

r-------.

I ~----.---. I PLAIN

L--.----.-­I

30% ADD

*

20% ADD

* -------

I 5 MIN. Ds

13

30

--

25

20

----- ------.~

--

I 10 MIN. 15 MIN. DIn Ds Ds

-21 23 23

15 min.

60

I 64 64

15 min. --

20 14 26 8 min.

25 22 26 7 min.

.- - --

Figure 8 Fracture surface micrograph of unplasticised resin laminate

Figure 9 Fracture surface of 10% plasticised resin laminate

Figure 10 Fracture surface of 20% plasticised resin laminqte

Figure 11 Fracture surface of 30% plasticised resin laminate