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Specifications for composites: phenolic and silicone resins
Snecif ications for comr>osites: phenolic and silicone resins V. EDWARDS
The published specifications for phenolic and silicone resins intended for use in the production of composites are confined to three US Military specifications and two issued by the German Ministry of Defence
There is no doubt that, of the thermosetting resins most widely used in the manufacture of reinforced composites, the epoxide and polyester resins have attracted most attention from the specification issuing bodies both in Europe and the United States. Phenolic resins have been and are still being used extensively in the reinforced plastics industry in combination with reinforcement materials such as paper, asbestos, wood. and both organic and inorganic fibres and fabrics. Silicone resins are more a speciality product but are now used in a wide variety of applications. However the need for specifications covering the supply of these resins has not generally been considered necessary by the majority of the national authorities. Standards for phenolic and silicone resins intended primarily for use in the production of composites have been issued only by the Defence Departments of Germany and the United States. PHENOL IC RESINS
Two specifications on phenolic resins have been issued by the US Department of Defence: MIL-R--3745 MIL---R-9299C
Resin,phenol-formaldehyde, laminating Resin, phenolic. laminating
MIL- RR9299C is the most comprehensive specification. It covers two grades of phenolic or modified phenolic resin used in the fabrication of laminates for structural applications. Grade A is described as having normal properties and Grade B as having improved properties. Both grades can be supplied in liquid form or as a prepreg with glass fabric No 18 1. In general, properties of the uncured resins or prepregs are left to agreement between the supplier and purchaser, as are the majority of the test methods to be used. On the other hand, the mechanical and physical properties of test laminates prepared from the resins are strictly controlled with a wide variety of tests. Laminates are made using 18 1 glass fabric finished in accordance with MIL-C-9084 and the test methods are those published in the Federal Standard FED 406.
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Flexural and compressive strengths, hardness, water absorption and flammability tests are required to be carried out on the laminates under normal atmospheric conditions. The allowable changes in strength after two hours immersion in boiling water are specified, and testing at 260” C (500°F) after subjection to b.5h and 1OOh at that temperature is also required. Also detailed are the permitted changes in weight, thickness and flexural strength after immersion in a number of liquids. Some of the main requirements of resins meeting this specification are shown in the table. MIL-R-3745 is a much simpler specification for a single grade of phenolic resin for use in the manufacture of laminates. The solids content must be 59-64% and resin properties such as pH, viscosity, specific gravity and gel time are also specified. However, there are no performance tests required to be carried out on laminates made from the resin. The Normenstelle Luftfahrt 5.3600 published by the German Ministry of Defence specifies a liquid phenolic resin which is generally equivalent to MIL-R-9299C Grade A. However in addition to tests on a cured glass cloth laminate as described above the general physical properties of the uncured resin are also specified. Resin content should be 68%, viscosity 150 mPas (= 15OcP) and hardening time should be lo-12 minutes at 130°C. SILICONE
RESINS
The US Department of Defence specification MIL-R-25506A(ASG) covers silicone resins suitable for use in fabricating laminates for aircraft and nonaircraft structural and external parts, aircraft radio and radar antenna housings and other applications. Three types of resin are described: Type 1 Type II Type Ill
General purpose Radio frequency Radar frequency
Each of these resins may be required to be supplied as a solid or liquid or in the form of a preimpregated glass mat or fabric. The physical properties of the uncured resin are left to mutual agreement between the supplier and the purchaser. Detailed testing of the properties of standard
COMPOSITES . MAY 1974
Properties of standard laminates made from phenolic and silicone resins Specification Resin type Grade Flexural strength N/mm* Tensile strength N/mm* Compressive strength N/mm* Flammability mm/min Water absorption % Barcol hardness
MI L-R-9299C Phenolic Grade A Grade B 350 510 280 320 245 400 25.4 25.4 + 1.25 + 1.25 55 55
MI L-R-25506A Silicone Types I, II and III 250 210 126 12.7 + 0.5 50
Tests under wet conditions* Flexural strength N/mm* Tensile strength N/mm* Compressive strength N/mm*
315 266 210
490 310 370
210 190 105
Tests after %h at 260°C (5OO’F) Flexural strength N/mm* Tensile strength N/mm* Compressive strength N/mm*
280 210 210
360 270 225
105 140 42
Tests after IOOh at 260°C (500°F) Flexural strength N/mm*
140
315
105””
* After 30 days in distilled water at room temperature * * Tested after 192h exposure at 260°C (500” F) Note: all figures for physical properties are minimum values
laminates made with 18 1 glass fabric conforming to MIL-C-9089 is required, however. Each resin type must meet minimum strength levels when tested under normal atmospheric conditions, after water immersion, after 3 months and one year outside weathering and after half an hour and 191, hours heating at 500°F. Some of the main quality requirements are shown in the table. Type II and Type III resins are differentiated by their electrical properties. A standard laminate of the Type II resin is required to have a dielectric constant of 4.2 and a maximum
COMPOSITES.
MAY 1974
loss tanpent of 0.0.3 when tested at 1 nqacyclc. Type III laminates are required to have a dielectric constant of 4.5 and a maximum loss tangent of 0.025 at 8 500 to IO 000 megacycles The resin covered by the Normcnstellc l.ui‘tl’ahrt 5.2400 will also meet the same quality requjrcmcnts as the US MIL -Km-25506A Type I resin when made into laminates. Additional clauses. however. specify that ir should bc a liquid resin with a viscosity of 5 000 to 10 000 1111’as (cl’) at ‘10°C.
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The published specifications for phenolic and silicone resins intended for use in the production of composites are confined to three US Military specifications and two issued by the German Ministry of Defence
There is no doubt that, of the thermosetting resins most widely used in the manufacture of reinforced composites, the epoxide and polyester resins have attracted most attention from the specification issuing bodies both in Europe and the United States. Phenolic resins have been and are still being used extensively in the reinforced plastics industry in combination with reinforcement materials such as paper, asbestos, wood. and both organic and inorganic fibres and fabrics. Silicone resins are more a speciality product but are now used in a wide variety of applications. However the need for specifications covering the supply of these resins has not generally been considered necessary by the majority of the national authorities. Standards for phenolic and silicone resins intended primarily for use in the production of composites have been issued only by the Defence Departments of Germany and the United States. PHENOL IC RESINS
Two specifications on phenolic resins have been issued by the US Department of Defence: MIL-R--3745 MIL---R-9299C
Resin,phenol-formaldehyde, laminating Resin, phenolic. laminating
MIL- RR9299C is the most comprehensive specification. It covers two grades of phenolic or modified phenolic resin used in the fabrication of laminates for structural applications. Grade A is described as having normal properties and Grade B as having improved properties. Both grades can be supplied in liquid form or as a prepreg with glass fabric No 18 1. In general, properties of the uncured resins or prepregs are left to agreement between the supplier and purchaser, as are the majority of the test methods to be used. On the other hand, the mechanical and physical properties of test laminates prepared from the resins are strictly controlled with a wide variety of tests. Laminates are made using 18 1 glass fabric finished in accordance with MIL-C-9084 and the test methods are those published in the Federal Standard FED 406.
QMC Industrial
122
Research
Ltd. 229 Mile End Road, London
El 4AA
Flexural and compressive strengths, hardness, water absorption and flammability tests are required to be carried out on the laminates under normal atmospheric conditions. The allowable changes in strength after two hours immersion in boiling water are specified, and testing at 260” C (500°F) after subjection to b.5h and 1OOh at that temperature is also required. Also detailed are the permitted changes in weight, thickness and flexural strength after immersion in a number of liquids. Some of the main requirements of resins meeting this specification are shown in the table. MIL-R-3745 is a much simpler specification for a single grade of phenolic resin for use in the manufacture of laminates. The solids content must be 59-64% and resin properties such as pH, viscosity, specific gravity and gel time are also specified. However, there are no performance tests required to be carried out on laminates made from the resin. The Normenstelle Luftfahrt 5.3600 published by the German Ministry of Defence specifies a liquid phenolic resin which is generally equivalent to MIL-R-9299C Grade A. However in addition to tests on a cured glass cloth laminate as described above the general physical properties of the uncured resin are also specified. Resin content should be 68%, viscosity 150 mPas (= 15OcP) and hardening time should be lo-12 minutes at 130°C. SILICONE
RESINS
The US Department of Defence specification MIL-R-25506A(ASG) covers silicone resins suitable for use in fabricating laminates for aircraft and nonaircraft structural and external parts, aircraft radio and radar antenna housings and other applications. Three types of resin are described: Type 1 Type II Type Ill
General purpose Radio frequency Radar frequency
Each of these resins may be required to be supplied as a solid or liquid or in the form of a preimpregated glass mat or fabric. The physical properties of the uncured resin are left to mutual agreement between the supplier and the purchaser. Detailed testing of the properties of standard
COMPOSITES . MAY 1974
Properties of standard laminates made from phenolic and silicone resins Specification Resin type Grade Flexural strength N/mm* Tensile strength N/mm* Compressive strength N/mm* Flammability mm/min Water absorption % Barcol hardness
MI L-R-9299C Phenolic Grade A Grade B 350 510 280 320 245 400 25.4 25.4 + 1.25 + 1.25 55 55
MI L-R-25506A Silicone Types I, II and III 250 210 126 12.7 + 0.5 50
Tests under wet conditions* Flexural strength N/mm* Tensile strength N/mm* Compressive strength N/mm*
315 266 210
490 310 370
210 190 105
Tests after %h at 260°C (5OO’F) Flexural strength N/mm* Tensile strength N/mm* Compressive strength N/mm*
280 210 210
360 270 225
105 140 42
Tests after IOOh at 260°C (500°F) Flexural strength N/mm*
140
315
105””
* After 30 days in distilled water at room temperature * * Tested after 192h exposure at 260°C (500” F) Note: all figures for physical properties are minimum values
laminates made with 18 1 glass fabric conforming to MIL-C-9089 is required, however. Each resin type must meet minimum strength levels when tested under normal atmospheric conditions, after water immersion, after 3 months and one year outside weathering and after half an hour and 191, hours heating at 500°F. Some of the main quality requirements are shown in the table. Type II and Type III resins are differentiated by their electrical properties. A standard laminate of the Type II resin is required to have a dielectric constant of 4.2 and a maximum
COMPOSITES.
MAY 1974
loss tanpent of 0.0.3 when tested at 1 nqacyclc. Type III laminates are required to have a dielectric constant of 4.5 and a maximum loss tangent of 0.025 at 8 500 to IO 000 megacycles The resin covered by the Normcnstellc l.ui‘tl’ahrt 5.2400 will also meet the same quality requjrcmcnts as the US MIL -Km-25506A Type I resin when made into laminates. Additional clauses. however. specify that ir should bc a liquid resin with a viscosity of 5 000 to 10 000 1111’as (cl’) at ‘10°C.
123