development and evaluation of a toughened phenolic … · - 2 - inherent characteristics of...
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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