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Compimide bismaleimide resins — high performance thermosetting systems
Compimide Bismaleimide ResinsHigh Performance Thermosetting Systems
M . S . C a I113i 11g, Marketing Manager, Resins, The Boots Company plc, Nottingham, NG2 3AA, UK. Dr. H. S t e l l z e l l b e r g e r , Research Director, Technochemie TMBH, Verfahrenstechnik, D-6901 Dossenheim, West Germany. Abstract The use is described of Compimide bismaleimide resins in a variety of demanding performance applications, particularly where low flammability and resistance to high temperatures are important. Introduction Polyimide resins have, over the years, attracted a great deal of attention because of their unique properties at elevated temperatures and in extreme environments. However, until recently the history of polyimide resin development has been one of materials difficult to process but with outstanding performance. In these circumstances the designer has been prepared to accept such difficulties in order to obtain the benefits of high temperature performance. Commercially available polyimides may be classified into three distinct groups: condensation, addition and thermoplastic. Condensation polyimides, although amongst the best in elevated temperature performance, can only be processed via the precursor polymer route. Their use is limited to films and fibres. Addition polyimides which generate no volatiles during cure, like bisnadic acidimides and bismaleimides are easier to fabricate and are successfully used for fibre reinforced composites because of their epoxy-like processing. Real thermoplastic polyimides have become available recently, but their processing temperatures are still too high in relation to the temperature capability achieved. Compimide bismaleimide resins are a family of thermosets showing an outstanding balance between processability and high temperature performance. By high temperature performance we mean the retention of an acceptable proportion of room temperature properties either during sustained exposure to high temperatures or during excursions to perhaps even higher temper-
atures. In this context, the term "high temperature" refers to the 200-300°C region.
Bismaleimide Resin Chemistry Bismaleimides of the general formula:-
0
0
0
0
R = --CH2--,--0--,S-are the main building blocks for commercial resin formulations, and they can be cured thermally to high temperature resistant materials. However, they suffer from a lack of processability and therefore have to be formulated into resins which are suitable for a variety of processes. This means solution and hot-melt prepregging, low and high pressure curing, filament winding, resin injection moulding and injection moulding, Such formulations may include copolymerisation with other thermosetting resins and the use of reactive diluents and catalysts. The cure ofbismaleimide resins proceeds by a complex addition and polymerisation reaction which generates no volatiles, thus allowing void-free finished parts to be produced. The design of a resin system is always to some extent a compromise between processability and performance. However, Compimide bismaleimide resins have a very acceptable working temperature range and many hours of service are possible at temperatures up to 250°C.
MATERIALS & DESIGN Vol. 7 No. 4 JULY/AUGUST 1986
Processing of Compimide Resins Low pressure autoclave cure The production of complex shaped laminates is possible using conventional low pressure autoclave techniques with the exception that higher postcure temperatures are required to develop fully the resin's high temperature properties. The resins are of interest to the aerospace industry for large area carbon fibre composite components when autoclave moulding is commonly used. The high glass transition temperature of Compimide bismaleimide resins (around 285°C) is responsible both for the excellent retention of mechanical properties at elevated temperatures and the superior hot/wet environmental stability. These features are important where external surfaces may be subjected to stringent environmental conditions, e.g., hot spots on aircraft. Typical laminate properties for various types of carbon fibres are given in Table I. The fibre - resin interface is of major importance for the development of the expected mechanical properties. Commercially available fibres are designed for compatibility with epoxy resins and therefore not optimised for polyimide matrix resins. The outstanding hot-wet performance of Compimide 800 resin in combination with Celion 6000 fibres after ageing at 70°C and 94% relative humidity is shown in Table II and Fig. 1~1).
High pressure laminate moulding High pressure platen press techniques may be used for the production of laminates for printed circuit boards, thermal insulation plates and structural
207
Table I Mechanical Properties of C o m p i m i d e 8 0 0 carbon fibre laminates Property
FD
T 300/ 6000
Unit
Fibre Content
v/o
Celion 6000 Pl-finish (1) IM-6
63
61
63
Besfight HTA-7
Commercial Prepreg Epoxysized Besfight HTA-7
65,7
64
Fiexural Strength
20°C 250°C
0 0
MPa MPa
1892 1432
1884 1250
1839 1150
2253 1374
2069 1360
Flexural Modulus
20°C 250°C
0 0
GPa GPa
121 127
118 120
142 144
127 130
121 121
Flexural Strength
20°C 250°C
90 90
MPa MPa
85 -
80 35
56
73
48
-
33
-
20°C 250°C
90 90
GPa GPa
-
ILSS
20°C 250°C
0 0
MPa MPa
113 53
108 53
92 46
98 -
99 45
ILSS
20°C 250°C
0--- 45 0_+ 45
MPa MPa
63 37
58 47
43 35
50 38
50 36
Gtc
20°C
0
J/m2
ca. 90100
254
374
Flexural Modulus
8.26
7.92 5.4
7.17
8:24 5.28
-
8.05 -
-
225
(1) Finished based on N R 150 Polyimide Resin FD Fibre Direction
Table II Hydrothermal ageing of Celion 6000/Compimide 800 undireetional laminates (Fibre Size: Polyimide NR 150) Ageing condition: Temperature 70°C, 94% relative humidity.
Property
Test Temp. °C
Fibre content
Flexural modulus
Horizontal shear (5 : I)
208
0 % b y volume
Property Retention Ageing T i m e H o u r s 100 500 1000
58.7
-
-
-
%
-
1.19
1.49
1.66
20
MPa
1917
1749
1777
1756
150
MPa
1515
1327
1303
1319
20
GPa
111
112
111
112
150
GPa
112
114
112
112
20
MPa
90
76
84
82
150
MPa
74
56
54
52
Moisture absorption Flexural strength
Unit
MATERIALS & DESIGN Vol. 7 No. 4 JULY/AUGUST 1986
parts. Prepregs based on Compimide 183 can be used for these processes and the characteristics of such prepregs can be adjusted to meet the conditions being employed for composite moulding. The degree of B-staging, type of catalyst & its concentration and solvent employed can all be used to influence the cure kinetics. The low thermal expansion coefficient of Compimide bismaleimide resins is important in high performance printed circuit boards. Initial results indicate that a UL94 V-O flammability rating can be obtained with 2mm thick laminates. Typical properties for glass fabric laminates moulded from US-style 2116 prepregs using a simple cure cycle are given in Table III. Interestingly, the good flexural properties at room temperature and 250°C are almost fully developed even without postcure(2).
ageing conditions 70~C, 94% relative humidity
.c
0
0 100
500
1000
100" t E 7
~.--
50"
RT 150°C
(/3
0 --
1
0 100
500
1000
2000
~--
RT 150°C
,7gz
Honeycomb sandwichpanels
1000 0 100
500
1000
ageing time (hours)
Fig. 1
Hydrothermal ageing of Celion 6000/Compimide 800 unidirectional laminates.
Table III Mechanical Properties of Compimide 183 Glass Fabric Laminates Glass Fabric: US-Style 2116, Size A1100 Prepreg resin content: 42% by weight Solvent for prepregging: Methylglyeolaeetate Catalyst concentration: 0.35% (DABCO) Test Temperature (°C) Property
Unit
23
Fibre Content
% by weight
59
Flex Strength (1)
MPa
Flex. Modulus (1)
GPa
Flex. Elongation
%
Flex Strength (2)
MPa
Flex. Modulus (2)
GPa
474
17.1
2.84 481
19.6
(1) no post cure : --" green laminates (2) post cure : 2 hours at 200°C, Tg > 240°C
MATERIALS & DESIGN Vol. 7 No. 4 JULY/AUGUST 1986
15012001250
424
17.6
2.56 -
-
361
16.2
2.39 372
16.2
288
15.1
2.15 299
15.3
Thermosetting resins are widely used in face sheets for composite sandwich panels in aircraft interiors. Compimide bismaleimide resins offer improved fire resistance and, upon combustion, produce less smoke and toxic gases and thus meet all regulatory requirements Tables IV - VI. Such panels may be produced in a one-shot process with an adhesive layer by using a low pressure (3 bars) cure cycle. Glass fabrics may be the reinforcement chosen for such applications although carbon fibre face sheets will offer a significant weight saving. The low flammability of Compimide resins is also an advantage in other aircraft interior applications such as ventilation pipes.
Injection mouMing Compimide 15 MRK is the resin which has been designed for the injection moulding process. The resin is supplied as a powder containing the required catalyst homogeneously dispersed. It has been developed for processing with a wide range of reinforcements such as glass, carbon, aramid & mineral fibres and with particulate fillers such as PTFE, graphite powder & molybdenum disulphide for friction and wear property modification. Compounding, blending and kneading may be easily performed using standard compounding equipment. Moulding is achieved at a temperature of 180 - 200°C for 20 secs/mm thickness. A postcure is required (5 hours at 210°C plus 5 hours at 250°C) to achieve the optimum high temperature properties. Typical properties of Compimide 15 MRK containing 20% P T F E powder are given in Table VII. The strength property retention up to 250°C is 50% but the flexural modulus decreases
209
Table IV Burn Length of Compimide Glass Fabric Laminates Sample Description
Time of Test
Burn Length
Limit ATS 1000.001
(see.)
(ram)
(mm)
Compimide 183/7628
15
32
152
3 Layers
60
38
200
Table V N B S - Smoke Chamber : Smoke Densitities of Compimide Composites Sample Description
Compimide 183/7628
a)
3 Layers
Time of Test (mins)
SOD
Spee. Limit ATS 1000.001
1.5
< 1.5
100
4.0
< 1.5
200
1.5
1.5
100
4.0
2.3
200
1.5
< 1.5
100
4.0
2.3
200
1.5
4.5
100
4.0
11.0
200
L 1384)
b)
Sandwich Panel
a)
Compimide 183/7628, 3 Layers HT 424 Core: 4.8-96-8.8
b)
HT424 Compimide 183/7628, 3 Layers SOD Specific Optical Density. (a) non flaming conditions 2.4 W/cm2 (b) flaming condition
Fig. 2
210
Alpha Jet Speed Brake made by Dornier, West Germany based on Compimide 800 resin supplied by BootsTechnochemie
MATERIALS & DESIGN Vol. 7 No. 4 JULY/AUGUST 1986
significantly due to the PTFE filler. The outstanding friction coefficient and wear rate makes this combination an excellent candidate for friction parts.
Table Vl Toxicant Emission (Model Sandwich Panel) Toxicant
Results (ppm)
Proposed limited a~er (ppm) (ATS 1000.001)
1.5 mins
4 mins
1.5 mlns
4 rains
CO
8
10
3000
3500
HCN
2
2
100
150
NO + NO 2
2
2
50
100
SO 2
-
-
50
100
HF
-
-
50
50
HC1
-
-
50
500
Sandwich 1 2 3 4 5
Compimide 183/7628 3-layers HT 424 Core 4.8-96-8.8 HT 424 Compimide 183/7628 3-layers
Table VII Properties of Compimide 15 M R K / 2 0 % PTFE compound Property
Unit
Value 23 °C
200~ 250°C
Density
g/cm 3
Flexural Strength
MPa
Flexural Modulus
GPa
3.18
1.62
1.28
Flexural Strain
%
3.4
3.65
3.92
Moulding Shrinkage
%
0.1
Water Absorption
% 24 hrs cold water immersion
1.25
Glass Transition Temperature
°C
1.83 100
> 250°C
MATERIALS & DESIGN Vol. 7 No. 4 JULY/AUGUST 1986
50
40
New Developments Much has been said recently about the need to improve the toughness of bismaleimide matrix resins. In recognition of this demand from the market place we have developed some very exciting new toughening agents which show dramatic improvements in fracture toughness when compared to bismaleimide resins currently in use. The technologies of filament winding and resin injection moulding are growing in importance and in recognition of this Compimide bismaleimide resin was launched in April 1986 which is designed for use in both processes. At the same time, we have introduced a Compimide bismaleimide resin which has been rubber toughened. This will be available to adhesive formulators as the basis for a high temperature stable adhesive (3). Conclusions Bismaleimides are crystalline chemicals which can be modified and formulated into products which meet a wide variety of processing requirements. The designer has, with the Compimide resins family, the capability of gaining a significant improvement in performance over structures or components fabricated from other commonly used resin systems. Both in new product design and in the enhancement of existing product performance, the qualities of these resins are now undoubtedly recognised. References 1. H.D. Stenzenberger,M_Herzog,W. Roemer, R. Scheiblich,N.J. Reeves, S. Pierce, 29th National SAMPE Symposium No. 29, p.1043-1059 (1984). 2. I-LD.Stenzenberger,M. Herzog,W. Roemer, K. Fear, M,S. Canning, S. Pierce, SPE ANTEC 1985, Proceedingsp.1246 (1985). 3. S.J. Shawand A.J. Kinloch,Int. J. Adhesion & Adhesives Vo. 5 No. 3 p.123-127 July 1985.
211
M . S . C a I113i 11g, Marketing Manager, Resins, The Boots Company plc, Nottingham, NG2 3AA, UK. Dr. H. S t e l l z e l l b e r g e r , Research Director, Technochemie TMBH, Verfahrenstechnik, D-6901 Dossenheim, West Germany. Abstract The use is described of Compimide bismaleimide resins in a variety of demanding performance applications, particularly where low flammability and resistance to high temperatures are important. Introduction Polyimide resins have, over the years, attracted a great deal of attention because of their unique properties at elevated temperatures and in extreme environments. However, until recently the history of polyimide resin development has been one of materials difficult to process but with outstanding performance. In these circumstances the designer has been prepared to accept such difficulties in order to obtain the benefits of high temperature performance. Commercially available polyimides may be classified into three distinct groups: condensation, addition and thermoplastic. Condensation polyimides, although amongst the best in elevated temperature performance, can only be processed via the precursor polymer route. Their use is limited to films and fibres. Addition polyimides which generate no volatiles during cure, like bisnadic acidimides and bismaleimides are easier to fabricate and are successfully used for fibre reinforced composites because of their epoxy-like processing. Real thermoplastic polyimides have become available recently, but their processing temperatures are still too high in relation to the temperature capability achieved. Compimide bismaleimide resins are a family of thermosets showing an outstanding balance between processability and high temperature performance. By high temperature performance we mean the retention of an acceptable proportion of room temperature properties either during sustained exposure to high temperatures or during excursions to perhaps even higher temper-
atures. In this context, the term "high temperature" refers to the 200-300°C region.
Bismaleimide Resin Chemistry Bismaleimides of the general formula:-
0
0
0
0
R = --CH2--,--0--,S-are the main building blocks for commercial resin formulations, and they can be cured thermally to high temperature resistant materials. However, they suffer from a lack of processability and therefore have to be formulated into resins which are suitable for a variety of processes. This means solution and hot-melt prepregging, low and high pressure curing, filament winding, resin injection moulding and injection moulding, Such formulations may include copolymerisation with other thermosetting resins and the use of reactive diluents and catalysts. The cure ofbismaleimide resins proceeds by a complex addition and polymerisation reaction which generates no volatiles, thus allowing void-free finished parts to be produced. The design of a resin system is always to some extent a compromise between processability and performance. However, Compimide bismaleimide resins have a very acceptable working temperature range and many hours of service are possible at temperatures up to 250°C.
MATERIALS & DESIGN Vol. 7 No. 4 JULY/AUGUST 1986
Processing of Compimide Resins Low pressure autoclave cure The production of complex shaped laminates is possible using conventional low pressure autoclave techniques with the exception that higher postcure temperatures are required to develop fully the resin's high temperature properties. The resins are of interest to the aerospace industry for large area carbon fibre composite components when autoclave moulding is commonly used. The high glass transition temperature of Compimide bismaleimide resins (around 285°C) is responsible both for the excellent retention of mechanical properties at elevated temperatures and the superior hot/wet environmental stability. These features are important where external surfaces may be subjected to stringent environmental conditions, e.g., hot spots on aircraft. Typical laminate properties for various types of carbon fibres are given in Table I. The fibre - resin interface is of major importance for the development of the expected mechanical properties. Commercially available fibres are designed for compatibility with epoxy resins and therefore not optimised for polyimide matrix resins. The outstanding hot-wet performance of Compimide 800 resin in combination with Celion 6000 fibres after ageing at 70°C and 94% relative humidity is shown in Table II and Fig. 1~1).
High pressure laminate moulding High pressure platen press techniques may be used for the production of laminates for printed circuit boards, thermal insulation plates and structural
207
Table I Mechanical Properties of C o m p i m i d e 8 0 0 carbon fibre laminates Property
FD
T 300/ 6000
Unit
Fibre Content
v/o
Celion 6000 Pl-finish (1) IM-6
63
61
63
Besfight HTA-7
Commercial Prepreg Epoxysized Besfight HTA-7
65,7
64
Fiexural Strength
20°C 250°C
0 0
MPa MPa
1892 1432
1884 1250
1839 1150
2253 1374
2069 1360
Flexural Modulus
20°C 250°C
0 0
GPa GPa
121 127
118 120
142 144
127 130
121 121
Flexural Strength
20°C 250°C
90 90
MPa MPa
85 -
80 35
56
73
48
-
33
-
20°C 250°C
90 90
GPa GPa
-
ILSS
20°C 250°C
0 0
MPa MPa
113 53
108 53
92 46
98 -
99 45
ILSS
20°C 250°C
0--- 45 0_+ 45
MPa MPa
63 37
58 47
43 35
50 38
50 36
Gtc
20°C
0
J/m2
ca. 90100
254
374
Flexural Modulus
8.26
7.92 5.4
7.17
8:24 5.28
-
8.05 -
-
225
(1) Finished based on N R 150 Polyimide Resin FD Fibre Direction
Table II Hydrothermal ageing of Celion 6000/Compimide 800 undireetional laminates (Fibre Size: Polyimide NR 150) Ageing condition: Temperature 70°C, 94% relative humidity.
Property
Test Temp. °C
Fibre content
Flexural modulus
Horizontal shear (5 : I)
208
0 % b y volume
Property Retention Ageing T i m e H o u r s 100 500 1000
58.7
-
-
-
%
-
1.19
1.49
1.66
20
MPa
1917
1749
1777
1756
150
MPa
1515
1327
1303
1319
20
GPa
111
112
111
112
150
GPa
112
114
112
112
20
MPa
90
76
84
82
150
MPa
74
56
54
52
Moisture absorption Flexural strength
Unit
MATERIALS & DESIGN Vol. 7 No. 4 JULY/AUGUST 1986
parts. Prepregs based on Compimide 183 can be used for these processes and the characteristics of such prepregs can be adjusted to meet the conditions being employed for composite moulding. The degree of B-staging, type of catalyst & its concentration and solvent employed can all be used to influence the cure kinetics. The low thermal expansion coefficient of Compimide bismaleimide resins is important in high performance printed circuit boards. Initial results indicate that a UL94 V-O flammability rating can be obtained with 2mm thick laminates. Typical properties for glass fabric laminates moulded from US-style 2116 prepregs using a simple cure cycle are given in Table III. Interestingly, the good flexural properties at room temperature and 250°C are almost fully developed even without postcure(2).
ageing conditions 70~C, 94% relative humidity
.c
0
0 100
500
1000
100" t E 7
~.--
50"
RT 150°C
(/3
0 --
1
0 100
500
1000
2000
~--
RT 150°C
,7gz
Honeycomb sandwichpanels
1000 0 100
500
1000
ageing time (hours)
Fig. 1
Hydrothermal ageing of Celion 6000/Compimide 800 unidirectional laminates.
Table III Mechanical Properties of Compimide 183 Glass Fabric Laminates Glass Fabric: US-Style 2116, Size A1100 Prepreg resin content: 42% by weight Solvent for prepregging: Methylglyeolaeetate Catalyst concentration: 0.35% (DABCO) Test Temperature (°C) Property
Unit
23
Fibre Content
% by weight
59
Flex Strength (1)
MPa
Flex. Modulus (1)
GPa
Flex. Elongation
%
Flex Strength (2)
MPa
Flex. Modulus (2)
GPa
474
17.1
2.84 481
19.6
(1) no post cure : --" green laminates (2) post cure : 2 hours at 200°C, Tg > 240°C
MATERIALS & DESIGN Vol. 7 No. 4 JULY/AUGUST 1986
15012001250
424
17.6
2.56 -
-
361
16.2
2.39 372
16.2
288
15.1
2.15 299
15.3
Thermosetting resins are widely used in face sheets for composite sandwich panels in aircraft interiors. Compimide bismaleimide resins offer improved fire resistance and, upon combustion, produce less smoke and toxic gases and thus meet all regulatory requirements Tables IV - VI. Such panels may be produced in a one-shot process with an adhesive layer by using a low pressure (3 bars) cure cycle. Glass fabrics may be the reinforcement chosen for such applications although carbon fibre face sheets will offer a significant weight saving. The low flammability of Compimide resins is also an advantage in other aircraft interior applications such as ventilation pipes.
Injection mouMing Compimide 15 MRK is the resin which has been designed for the injection moulding process. The resin is supplied as a powder containing the required catalyst homogeneously dispersed. It has been developed for processing with a wide range of reinforcements such as glass, carbon, aramid & mineral fibres and with particulate fillers such as PTFE, graphite powder & molybdenum disulphide for friction and wear property modification. Compounding, blending and kneading may be easily performed using standard compounding equipment. Moulding is achieved at a temperature of 180 - 200°C for 20 secs/mm thickness. A postcure is required (5 hours at 210°C plus 5 hours at 250°C) to achieve the optimum high temperature properties. Typical properties of Compimide 15 MRK containing 20% P T F E powder are given in Table VII. The strength property retention up to 250°C is 50% but the flexural modulus decreases
209
Table IV Burn Length of Compimide Glass Fabric Laminates Sample Description
Time of Test
Burn Length
Limit ATS 1000.001
(see.)
(ram)
(mm)
Compimide 183/7628
15
32
152
3 Layers
60
38
200
Table V N B S - Smoke Chamber : Smoke Densitities of Compimide Composites Sample Description
Compimide 183/7628
a)
3 Layers
Time of Test (mins)
SOD
Spee. Limit ATS 1000.001
1.5
< 1.5
100
4.0
< 1.5
200
1.5
1.5
100
4.0
2.3
200
1.5
< 1.5
100
4.0
2.3
200
1.5
4.5
100
4.0
11.0
200
L 1384)
b)
Sandwich Panel
a)
Compimide 183/7628, 3 Layers HT 424 Core: 4.8-96-8.8
b)
HT424 Compimide 183/7628, 3 Layers SOD Specific Optical Density. (a) non flaming conditions 2.4 W/cm2 (b) flaming condition
Fig. 2
210
Alpha Jet Speed Brake made by Dornier, West Germany based on Compimide 800 resin supplied by BootsTechnochemie
MATERIALS & DESIGN Vol. 7 No. 4 JULY/AUGUST 1986
significantly due to the PTFE filler. The outstanding friction coefficient and wear rate makes this combination an excellent candidate for friction parts.
Table Vl Toxicant Emission (Model Sandwich Panel) Toxicant
Results (ppm)
Proposed limited a~er (ppm) (ATS 1000.001)
1.5 mins
4 mins
1.5 mlns
4 rains
CO
8
10
3000
3500
HCN
2
2
100
150
NO + NO 2
2
2
50
100
SO 2
-
-
50
100
HF
-
-
50
50
HC1
-
-
50
500
Sandwich 1 2 3 4 5
Compimide 183/7628 3-layers HT 424 Core 4.8-96-8.8 HT 424 Compimide 183/7628 3-layers
Table VII Properties of Compimide 15 M R K / 2 0 % PTFE compound Property
Unit
Value 23 °C
200~ 250°C
Density
g/cm 3
Flexural Strength
MPa
Flexural Modulus
GPa
3.18
1.62
1.28
Flexural Strain
%
3.4
3.65
3.92
Moulding Shrinkage
%
0.1
Water Absorption
% 24 hrs cold water immersion
1.25
Glass Transition Temperature
°C
1.83 100
> 250°C
MATERIALS & DESIGN Vol. 7 No. 4 JULY/AUGUST 1986
50
40
New Developments Much has been said recently about the need to improve the toughness of bismaleimide matrix resins. In recognition of this demand from the market place we have developed some very exciting new toughening agents which show dramatic improvements in fracture toughness when compared to bismaleimide resins currently in use. The technologies of filament winding and resin injection moulding are growing in importance and in recognition of this Compimide bismaleimide resin was launched in April 1986 which is designed for use in both processes. At the same time, we have introduced a Compimide bismaleimide resin which has been rubber toughened. This will be available to adhesive formulators as the basis for a high temperature stable adhesive (3). Conclusions Bismaleimides are crystalline chemicals which can be modified and formulated into products which meet a wide variety of processing requirements. The designer has, with the Compimide resins family, the capability of gaining a significant improvement in performance over structures or components fabricated from other commonly used resin systems. Both in new product design and in the enhancement of existing product performance, the qualities of these resins are now undoubtedly recognised. References 1. H.D. Stenzenberger,M_Herzog,W. Roemer, R. Scheiblich,N.J. Reeves, S. Pierce, 29th National SAMPE Symposium No. 29, p.1043-1059 (1984). 2. I-LD.Stenzenberger,M. Herzog,W. Roemer, K. Fear, M,S. Canning, S. Pierce, SPE ANTEC 1985, Proceedingsp.1246 (1985). 3. S.J. Shawand A.J. Kinloch,Int. J. Adhesion & Adhesives Vo. 5 No. 3 p.123-127 July 1985.
211