NATIONAL BUREAU OF STANDARDS REPORT

6134

Structural Epoxy Adhesives

by

Irma G. Callomon

Desmond A. George

and

Frank W. Reinhart

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
THE NATIONAL BUREAU OF STANDARDS

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NATIONAL BUREAU OF STANDARDS REPORT

MBS PROJECT WBS REPORT

/^&~J>Z~¥SO/

-1QQ3. 13" *1883:- NBS No. 6134

July 30, 1958

Structural Epoxy Adhesives

by

Irma G. Callomon

Desmond A. George

and

Frank W. Reinhart

Plastics Section

Organic and Fibrous Materials Division

NATIONAL BUREAU 0

Intended for use w.ithln To additional evaluation

listing of" this Report, ei the Office of the Dlrectr however, by the Govern

to reproduce additional

IMPORTANT NOTICE

Approved for public release by the

Director of the National Institute of

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on October 9, 2015.

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Is form&Sly published It is subjected

ntijvg, reproduction, or opart-literature termicslcn is obtained In writing frorr,

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<NBS>

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

TABLE OP CONTENTS

page

1. Introduction ........ 1

2. Chemistry ........ 1

3. Manufacturers ........ 4

4. Applications ........ 4

5. Bonding Procedures ....... 6

6. Spe cificktiojae and Methods . . . . . 14

7. Properties ........ 17

8. Bibliography ........ 24

9. Additional References ...... 30

iii

FOREWORD

Th© information in this report is taken from

the literature references listed in Section 8

Bibliography.

Structural Epoxy Adhesives

by

Irma G. Callomon

Desmond A. George

and

Frank ¥. Reinhart

1. Introduction

Although the epoxy resins 'were discovered as early as

1863, it was only during World War II that manufacturing

and processing techniques for this interesting type of

resins were developed. The manufacture and consumption of

epoxy resins increased from none prior to 1950 to about

90 million pounds in 1956. This includes molding,

laminating, potting, casting, coating^and adhesive compounds.

The resins possess outstanding adhesive properties which

can be improved selectively by the addition of suitable

fillers, diluents, and/or resinous modifiers thus, proyiding

a class of adhesives of great versatility. Depending on

the formulation the adhesives may be either rigid or

flexible, and for certain applications, short-time

temperatures af about SOCPGjnay be tolerated. Most of

the research on epoxy adhesives has been in the development

of those for metals, reinforced plastics, glass, and

combinations of these.

This report is primarily concerned with room-temperature

setting structural epoxy adhesives for bonding wood and

metal. The literature reviewed is discussed under the

headings of chemistry, manufacturers, applications, bonding

procedures, test methods, and properties.

2. Chemistry

Epoxy adhesives are based on resins made by the reaction

of epoxides or oxiranes with other materials such as amines,

alcohols, phenols, carboxylic acids, acid anhydrides, and

unsaturated compounds. The chemistry to produce the final

adhesive material involves two steps. The first step, usually

2

carried out in a chemical manufacturing plant or laboratory,

involves the production of a thermoplastic resin or high

molecular weight liquid that contains epoxide terminal

groups. An example of this step is the reaction of epichlorohydrin with a polyhydric material such as bisphenol-A.

In this typical basic reaction, epichlorohydrin reacts with

bisphenol-A at temperatures of 60°-120 o C in the presence of . aqueous sodium hydroxide in the following manner:

CH 2^CH-CH2C1 / HO- <£> -j-OCH- CH-

/

OH NaOH^ CH2-CH-CH 2

i CHOH ^

I OCH^-CHCH,

CH- o

/\

0CH2-CH-CH

2

n

/ NaCl /HO

CHBy varying the operating conditions and the proportions of

epichlorohydrin and bisphenol-A the n in the above formula

can be changed to produce resins with molecular weights from

400 to 8000. When bisphenol derived from cashew nut shell

oil is used in place of the bisphenol-A, epoxies are obtained

that are more flexible. Other modifiers may produce similar

or totally different results.

The second step results in the bond formation and is

carried out in the final bonding processes. This step

is often called curing of the adhesive. The liquid resin

and the curing agent are mixed in the proper proportions

immediately before applying to the surfaces to be bonded.

In this step the thermoplastic or liquid resin is converted

into a crosslinked or thermoset polymer. This hardening

or "curing'’ procedure may involve a variety of chemical

reactions in which the epoxy groups take part. Simple

heating does not cure epoxy resins; they do not contain heatreactive groups which will permit efficient conversions

into infusible resins as do the phenolics and other formaldehydebased resins. Modifying resins, coupling agents, or catalysts
" .. <

*: *
- 3 -

are required for cure. Secondary and tertiary amines

are used to cure epoxy materials at room temperature. The

terminal epoxy groups on each molecule of the thermoplastic

or liquid resin furnish the necessary crosslinking sites.

The curing of the resin is exothermic and is

accelerated by heat. Because of this heat effect, many

catalysts, are too reactive for genera] use. For example

Lewis acids such as borontrifluoride and stannic chloride

give gelled products during mixing with liquid epoxy resina

and hence are unsuitable.

In practice the resins are normally blended with a

specific hardener or curing agent so that 'the desired

physical and ‘working properties are obtained. Therefore,

since the unmodified epoxy resin made with bisphenol-A , is hard and brittle when cured by catalysts, it is

often modified with a polysulfide, polyamide, or other

flexible coupling resins to, impart higher peel and impact

strength. These chemical modifiers also affect other

chemical and physical properties and compromises must be

made in order that important properties are not adversely

affected. But with proper modification the epoxy resins

can almost, be called the universal adhesive.

A filler is often incorporated into the epoxy resin

during its formulation as an adhesive. Usually these fillers

are chemically inert materials that are incorporated

to increase the impact strength, increase or decrease the

electrical resistance, improve the heat resistance and water

vapor transmission rate, or change some other property.

Some common fillers are mica, asbestos, silica, talc,

aluminum oxide, and titanium oxide.

Detailed information on the chemistry, curing reactions,

relations between structure and properties, and formulation

of epoxy resinous products are given by Lee and Neville

(l) a Bruin (a), Kirk and Othmer ( 3 )* and Stivala ( 4 ).

cT Numerals in parentheses apply to cited references

starting in Chapter 8.

3. Manufacturers

A large variety of epoxy adhesives are commercially

available, and manufacturers and suppliers are constantly

developing new formulations with different properties.

Tables 1 and 2 contain the names of manufacturers, suppliers,

and trade names of epoxy resin adhesives and polyamideepoxy resin adhesives, respectively. Both tables are taken

from the Adhesive Chart, published in the 1957 Modern

Plastics Encyclopedia (5). These lists , may not be entirely,

complete. , Some of the manufacturers are also formulators

and will assist the prospective user with detailed information; others sell the raw materials to formulators who

will perform the same assistance. References 6 through 13

contain information and data on room—temperature setting

epoxy adhesives published by some manufacturers and

suppliers.

4. Applications

Dietz (14) reports on the use of epoxy resin adhesives

in the "House of the Future", developed under a project

sponsored by the Monsanto Chemical Company by the

Massachusetts Institute of Technology. The house is now

located in Anaheim, California. It consists of a core

with projecting reinforced plastic wings which are attached

to the central supporting core by overlapping joints

in which the strength is largely supplied by epoxy

adhesives put initially under pressure by bolts. No

mention is made of the kind of epoxy adhesives used. Dietz

states that there has been no indication of adhesive

failure after the wear and stress produced by over a

million visitors in a year.

General information on epoxy resins and their

applications as adhesives are described by Preiswerk

and associates (15)* two German Publications (16, 17)*

Preiswerk (18), Modern Plastics (19)* Carey and Nock (20), and

Carey (21). The Interscience Encyclopedia (3) in addition to

their chemistry gives a survey of applications in laminates,

encapsulation, adhesives, etc. The relative merits of epoxide.

polyester* and phenolic resins are discussed by Vaughan ( 22 )

Lee and Neville (l) in their book on epoxy resins give

a comprehensive review of the present status of applications

and technology. In 1956* symposia on epoxies were conducted

by the Diamond Ordnance Fuze Laboratories (23) and the

Journal for Industrial and Engineering Chemistry (24).

Adhesives as such were not discussed but the excellent

adhesive properties of the epoxies account to a large extent

for their applications as coatings* laminating resins,

sealers* castings* potting* etc. Elam and Hopper ( 25 ) report on structural epoxy-resin laminates. Moss (26)

reports on applications in the engineering industries of

hot-setting and room-temperature setting epoxies for

joining metal -to-metal and dissimilar materials* such as

glass-to-metal. Zolin and Green ( 27 ) report on epoxy

resins as engineering materials for the chemical industry.

Narracott ( 28 ) discusses applications of some epoxy

resins in the plastics industry. Rudoff and Rzeszotarski

(29) report on applications of epoxy resins for electrical

applications. The bonding of cementitious materials with

epoxy resins ‘is described by Goeke (30). High-temperature

setting epoxy resins were tested at low temperature for

evaluation as cryogenic structural adhesives by the

National Bureau of Standards (31). Modern Plastics (32)

describes an epoxy adhesive for bonding quick curing

concrete to the base which it contacts. Farr (33) joined

pipes with epoxy adhesives. Another article reports on

the reduction of rejected grinding wheels due to the

application of epoxy resins (34). Epoxy resins used as

sealants for high vacuum systems are reported by Stivala and

Denniger (35).

Since the greatest interest in epoxy adhesives has been

in the aircraft industry the literature in this field is

quite voluminous. DeBruyne (36)* Epstein (37)* Bandaruk( 38)

Black and Blomquist (39* 40) to name only a few* have

investigated presently available adhesives* the possibility

of developing new epoxies with higher heat-resistance* bonding

techniques* etc. The Forest Products Laboratory* Wright Air

Development Center* and the manufacturers have been extremely

active in this field. A general survey of data on the

reliability of metal bonding adhesive processes was made

by Eickner (41). Most of the investigations in this field have

- 6 -

been on high-temperature curing epoxy adhesives.

No published data have been located on the application of

epoxy adhesives for wood-tO-wood and wood-to-metal . The lack

of activity in 'the field of wood adhesives is attributed to

the fact that other adhesives- are available in greater

abundance and at much lower prices. While epoxy adhesives

can be used to bond other materials to wood or to itself,

this type product has not been generally used in the wood

working industry. The economics of melamine, urea, or

polyvinyl acetate adhesives are more favorable.

Stark and Glickman (42) investigated the use of epoxy

resins in bonding polystyrene foam to Douglas fir, but the

resulting shear strengths data of 29 to 31 psi at 70°F and

24 to 25 psi after 16 hours at 120°F are not indicative

of the properties of the adhesive because the failure

occurred in the foam material at very low stresses.

Marmion (43) reports that epoxy adhesives are mostly

used in the aircraft industry for metal-to-metal bonding

but that they will join almost any combination’ of polar

materials.

5. Bonding, Procedures

The choice of any particular epoxy composition for

an adhesive application depends on the desired strength properties, the temperature to which the bond will be subjected,

the. configuration of the bonded parts, the adherends, etc.

Factors influencing the bonding techniquea in. general

are discussed by Delmonte (44), by Koehn (45) and by

Thielsch (46). Tompkins (47) discusses the selection of the

proper epoxy compound.

The following bonding qualities are characteristic

of epoxy adhesives:

1. One hundred percent solids, no volatile solvent present.

2. Lovir pressure curing, only contact pressure is required.

3. Low-temperature and high-temperature curing.

4. Versatility, high bond strength with many different

materials.

5. Thermosetting, good heat and solvent resistance.

6. Low-shrinkage.

- 7

-

The latter quality is one of the shortcomings of the

presently used wood adhesives, according to Marra (48).

One major limitation of the epoxy adhesives is the

relatively limited pot life of the liquid resin after it

is mixed with the curing agent or hardener. Been (49)

states that the use of a room-temperature curing epoxy

adhesive usually imposes the following important

limitations:

1. A two-part system, consisting of resin plus

hardener (there are no one-component room-temperature

curing epoxy adhesives).

2. Limited pot life of the mixed material,

3. Long curing time to achieve optimum bond

characteristics

.

4. Limited high-temperature service.

A relatively limited pot life is inherent in most of these

systems. If the curing agent used gives a fast cure, it

will start the curing action just as soon as it is mixed

with the resin. This, in turn, means short working life of

the mixed material. If a longer pot life in the mixed

adhesive is essential for the production cycle, a sloweracting hardener must be used. This retards the curing

action and development of strength in the bond.

The following rules should be observed to obtain the longest

pot life:

1) Start with a cool mixture and work in a cool room.

2) Mix no more than necessary at one time. In other

words, mix small batches.

3) Mix the materials in a shallow, oversize metal

container and work from this container.

The curing of an epoxy resin is a chemical reaction that

liberates heat. Unless this heat can escape from the

resin to the surroundings, it increases the temperature of

8

the resin and the curing reaction goes faster. As the

curing reaction goes faster, the rate at which heat is

evolved increases, the mixture gets even hotter, and so on.

The problem is to hold down the rate of curing in the

mixing pot. This can be achieved by starting cfrut at a

low temperature, by keeping the total amount of heat

generated to a minimum, and by making it easy for this

heat of reaction to escape. Thus the work should be done

with a small total volume, this volume should be spread

over a large area of contact with the surroundings, the

surroundings should be kept cool, and the transfer of

heat should be speeded by using metal containers.

The curves in fig. 1 show the viscosity of the mixed

resin versus time for three different batches. Curve A

represents the behavior of a 330-gram batch of Bondmaster

M648 mixed at 77°F. In 1 hour it reaches a viscosity of

75*000 centipoises. Curve B, representing a 1000-gram

batch of the same resin mipced at the same temperature,

rises more steeply and after 60 minutes has a viscosity of

over 400,000 centipoises. Curve C^ representing a 330-gram

batch mixed at 100° P rises even more steeply than the

others. A viscosity of 30,000 centipoises is about maximum

for easy application by brush. While these graphs are

typical of a great many epoxy adhesives, it should be kept

in mind that many factors affect pot' life. Examples of these

are the composition of the resin, the type of curing agent,

and the ratio of mixing. Many large users of epoxy adhesives

find it more economical to mix several small batches per

shift than to risk premature "setting-up" of the adhesive

that might be encountered in one large batch.

One different approach to the pot life problem would

be to develop a method for continuously metering, mixing,

and dispensing the adhesive as needed. Equipment to do

this especially for materials having short pot lives is

being developed.

Since the pot life of the epoxy adhesives is limited,

the curing agent or hardner should not be added to the

resin solution or liquid resin until immediately before use.

- 9

-

Most of the epoxy adhesive systems are the two-container

type and may be applied either as liquids by spraying,

brushing, dipping^ or rolling. However, other systems may

be used, as listed below.

1. Latent curing agents give bonds of good adhesive strength

and permit the formulation of extremely convenient onecontainer1 100 percent solids systems, where the high curing

temperatures can ‘be accommodated.

2. One-container adhesive solutions may be formulated with high

molecular weight epoxy resins. The retained solvents in the

adhesive layer will blister the adhesive la>er unless handled

properly. The reduction in bond strengths may be as high

as 15 percent, when compared with the strengths obtained

with a similar hot-melt system.

3. Both supported and unsupported tapes may be employed.

The tapes virtually eliminate handling difficulties and ' provide highly reproducible results in production situations.

Tape formulations, however, have limited shelf lives at room

temperature and may require storage under refrigeration.

4. One-container adhesive powders are available and are useful for a limited amount of adhesive work, such as bonding

larger areas and in special production situations.

5. Solid heat-flowing adhesives are useful for a number

of structural applications.

6. Solid two-part adhesive systems may be formulated for

special applications. These formulations involve the

preparation of ‘high molecular weight resin curing agent

soluble in acetone. This is applied in solution to one

bonding surface. A coating of a high molecular weight

homolog of diglycidyl ether of bisphenol —A is applied

to the second bonding surface. The prepared system is

indefinitely stable at room temperature, but if the two

layers are joined under heat and pressure, good bonds

may be obtained (l).

10

The development of an aluminum- epoxy adhesive for roomtemperature curing Is reported by Modern Plastics (50).

This adhesive comes in two tubes. Other epoxy pastes are

described by Gould (51) and Delmonte (52).

Another important factor in the bonding process is

the proper surface preparation of the adherends. Epoxy

adhesives will give excellent bonds to steel, aluminum, brass,

copper, and most other , metals; to most thermosetting plastics

(phenolics, polyesters, epoxies) and most thermoplastics (vinyl,

chlorides, cellulose acetate butyrates, styrenes, etc.), though

here formulation may become increasingly critical; and to glass,

wood, concrete, paper, cloth, etc. For many applications,

thorough degreasing with solvents, wire brushing, or sandblasting, will provide a satisfactory surface. However,

when higher adhesive strengths are required, attention should

be given to chemical means of surface preparation. Careful

preparation has resulted in up to a fourfold increase in

bond strengths. The following treatments may be recommended.

Where appropriate, they are followed by a neutralizing rinse

and drying. In some cases, however, it may be necessary to

apply a primer coat to the adherends if inservice moisture

and vibration are severe.

Steel . Sandblast with clean grease-free sand or wire brush,

and degrease with a 10 per cent solution of sodium metasilicate for 10 minutes at 60°C.

Stainless Steel . Dip for 10 minutes at 65°C in the following

Cleaning solution, parts by weight:

Concentrated hydrochloric acid . . 50 parts

30$ hydrogen peroxide 2 parts

Formalin solution 10 parts

Water 45 parts

in the following solution, parts by volume:

42^ ferric chloride 15 parts

Concentrated nitric acid .... 30 parts

Water 197 parts

Titanium Alloys. Dip for 20 minutes at 50°C in the following

solution; parts by volume:

Concentrated, nitric acid 9 parts

50^ hydrofluoric acid ...... 1 part

Water 30 parts

This treatment will provide increased bond strength, but it does

not appear to be optimum.

11

Glass and Aluminum, Dip for 10 minutes at 70° C in the following

solution* parts lay we igh t

:

Sodium dichromate 66 parts

9

6

^ sulfuric acid 666 parts

Water . . 1*000 parts

Rubber . Immerce for 10 (± 5 ) minutes at room temperature in

concentrated sulfuric acid* or apply a sulfuric acid paste

made by 'adding barytes to' sulfuric acid. Bonding strengths

can frequently be improved by flexing the rubber to produce

tiny surface cracks.

Plastics . Sanding* buffing* or flame treatment is recommended

in some cases.

Wood . Freshly planed surfaces are recommended.

Porous Surfaces. Porous surfaces* such as concrete, do not

require special treatment * but sufficient adhesive should

be used to allow for absorption (1).

For most other adhesives* the thickness of the adhesive

layer is a critical factor for che bond strength. However*

the epoxy resins appear to be somewhat unique in that the

thickness of the adhesive layer may be varied from 1 to 12

mils* although narrower limits may be required for more

complex joints* without seriously affecting the joint

strength. For supported tapes, thicknesses up to 30 mils

may be used* depending on the nature of the bond. The t production tooling will to a very considerable degree

dictate the thickness for a specific application .(1). • The

difference in behavior between epoxy and other adhesives may

be attributed in part to difference in the degree of . shrinkage on curing.

The open assembly time* the period during which freshly

coated surfaces are permitted to remain open to the air

before as semblyj depends on the curing agent* which is usually

a somewhat volatile amine. It is therefore recommended

that this time be held to 20 minutes or less. With longer

open assembly times* sufficient curing agent is lost

to give lower bond strengths after curing (28).

12

Although, one of the chief advantages of epoxy adhesives

is that no solvent is required, there are occasions .when

the use of solvents may he helpful, for example in applying

the adhesive over a large area. In such case a fast-evaporating,

active solvent is desired to minimize the amount of solvent

used and .shorten the open-assembly time. Methylal, methylene

chloride, and the low-boiling aromatic solvents have been

found satisfactory for this use. Although ketones and

esters make excellent solvents for epoxy resins, they tend

to remain in the adhesive film. Esters may also react with

amine curing agents' and thus inhibit cure to sdme extent

( 10 )

.

The curing pressure for unsupported epoxy adhesives

is usually contact pressure. Contact pressure is that required

to just achieve good contact of the adhesive layer to the adherend

surfaces being bonded. The usual range for supported tapes

is from less than 5 to 50 psi, although in special cases

pressures up to 100 psi may be needed. In all cases pressure

should be sufficient to assure complete wetting of the adherend

surfaces and even distribution of the adhesive over the

bonding surface but not high, enough to give starved areas.

The selected pressure must be maintained throughout the

initial phase of the cure (l). The smoothness ’ and flatness

of the adherend surfaces is a factor influencing the

magnitude of the pressure.

Curing of room-temperature setting epoxy adhesives begjns

as soon as the resin and catalyst are mixed and in many

cases the bond will be strong enough to withstand handling

and stocking within 6 to 24 hours. This rapid gain In

strength in the early hours of a week-long cure is called

"handling time" and often goes unmentioned in the manufacturers* data sheet. Optimum strength requires a curing time

from 120 to 144 hours. (28, 49). The cure can of course

be accelerated by raising the temperature. The strength

properties of room- temperature curing epoxy adhesives can be

increased considerably by postcuring at temperatures not

exceeding 120°C. When larger volumes of fillers are

employed, such as 100 parts per hundred or more, a roomtemperature cure of about 6 days or more is required to

obtain maximum shear strengths, with heat and chemical

resistance Increasing even more slowly, (l).

- 13 -

Been (49) investigated the relation of the curing time

required to develop 85 percent maximum strength versus

curing temperature, and the strength as a function of

temperature for some epoxy-based adhesives. The results

are shown in figures 2 and 3* respectively. The curve

in figure 2 slopes very steeply at the lower temperatures

and gradually becomes less steep at the higher temperatures.

If the cure were carried to exactly the same degree of

completion at all temperatures, it would be expected from

the theory of chemical reaction rates that the curve would

be nearly straight like the dashed line. However, some

of the amine hardener is lost by vaporization at the higher

temperatures, and the rate is affected. Another factor

is the partial permanent loss of strength of some resins

due to degradation at the higher temperatures. To offset

this loss of strength, the resin must be more highly cured

at the higher temperatures to reach the same strength. For

these reasons, the actual curing time is considerably ‘ longer

than would be expected from extrapolation of the lowtemperature rates. ‘ But in spite of degradatibn and' loss of

hsi'dener, the curing time can be sharply reduced by raising

the temperature.

The majority of the manufacturers' data sheets provide

information on the effect of curing temperature of roomtemperature setting epoxy adhesives on their physical

properties. *

The retention of high strength in the cured* bonds at

elevated temperatures requires the use of special heatresistant adhesives. The curves in figure 3 show the

strengths of three epoxy adhesives at elevated temperatures.

The ones having higher resistance at elevated temperatures

are more expensive than the others (49),.

The hardening or curing agent is generally an organic

amine. Hence, precautions similar to those for other

strong alkalies or amines should be observed in handling

it. Ventilation should be adequate to prevent inhalation

of the vapors, and contact with the skin should be

avoided to prevent dermatitis and burns.

Precautions should also be taken in handling the liquid

epoxy resins* especially to avoid skin contact which may

give rise to dermatitis in some sensitive individuals.

- 14 -

In general, operators should observe strict personal

hygiene in the handling of both the resin and the curing

agent. The resin is generally less toxic and less

dangerous than the hardening agent.

During curing, the hardening agent is almost entirely

consumed in the reaction with the epoxy resin and

ceases to be a health hazard (4). The epoxy resin also

loses its harmful properties at this time. Dermatosis

with respect to epoxy resins is discussed by Dorman (53).

Because the epoxies are extremely resistant to

solvents, they are difficult to remove from surfaces

once they are cured. Excess uncured adhesive or adhesive

that is dropped during application should be cleaned off

Immediately with solvent. Thoroughly cured and filled

systems must be soaked for long periods in special solvents

before they can be removed. A proprietary solvent that

works well with aliphatic amine cured systems is DeSolv

292 (Ram Chemical). From a practical standpoint, it

is often less expensive to scrap small components than

to remove the epoxy resins particularly on aromaticdiamine cured systems. The resin on larger components

can be removed by sandblasting or burning off at

temperatures above 400°C (l).

6. Specifications and Test

Methods

No Federal or ASTM materials specifications or

standards have been issued for epoxy adhesives. Military

specification MIL-A-8623 (54) covers structural heat-curing

epoxy resin adhesives for metal-to-metal adherends;

MIL-A-l4042 (Ord) (55) covers room- temperature curing

adhesives.

General testing methods for adhesives have been issued

by the American Society for Testing Materials. They are

constantly being revised and new ones are being developed.

The latest issue "ASTM Standards on Adhesives (With

Related Information)", (56), published December 1957

contains specifications, physical tests, and definitions.

- 15 -

A.S.T.M. adhesive standards are under the jurisdiction

of Committee D-l4. Federal Test Method Standard No. 175

(57) contains the Federal standard methods for testing

adhesives. MIL-A-5090B (58) contains the requirements

that can at present only be met by high-temperature curing

epoxy adhesives. Military Qualified Products List (QPL)

for MIL-A-928A (59) does not specify epoxy resins for

structural metal-to-wood adhesives.

Test method for adhesives suffer from many limitations

due to the multitude of variables encountered in the

problem., such as the variety of chemical types involved

(resin, filler, catalyst, etc.), the difference in the

thermal expansion of adhesive and adherend, the bonding

process itself, effect of temperature and humidity,

geometry of the bond, and a host of others. All the

standard test methods for strength properties of adhesive

bonds adopted by Committee D-14 on adhesives carry a long

preamble defining many of the variables involved and

specifying that bonding conditions shall be as described

by the manufacturer who shall 1 furnish numerical values

and other specific information for all the variables

named in the preamble.

All destructive test methods for adhesives give strength

values that usually show a high degree of variation in

replica test specimens. As a result, a rather large number

of specimens must be prepared and tested, and the data have

to be treated statistically before reliable comparisons

can be made. AL1 these limitations make it evident

that no one single test method is sufficient to characterize

the strength properties of an adhesive. Tensile shear

strength tests at various temperature and exposure conditions

( ASTM D 1002-53T and Federal Standard Method 1033. 1-T),

peel strength (ASTM D 903-49 and Federal Standard Methods

1041.1 and 1042-T), impact strength (ASTM D 950-54 and

Federal Standard Method 1051 and fatigue strength (Federal

Standard Method 106l) are some of the most commonly specified

test methods for the strength properties of adhesives.

The epoxy adhesives being primarily used as structural

adhesives for metals are generally tested to meet the

requirements of MIL-A-5090B, Adhesive: airframe structural,

metal-to-metal . Most of the manufacturers 5 data for epoxy

adhesives are based on this military specification. It

contains a bend test where a 1-inch wide specimen is loaded

- 16 -

at the center of the bonded area as a simple beam with

a 1 1/2-inch span. The loading block and end supports

contact the full width of the specimen and are rounded

at the line of contact with the specimen to a specified

radius. The load required to produce failure in the

bond is reported.

Dietz (14) points out that for the application of

adhesives in building the pressing problem in the

evaluation of new materials is to find a completely

reliable method of accelerated testing which accurately

oredicts the long-time behavior of materials in building

because here the time scale is long compared to airplanes

or automobiles, for instance. This is not an easy task.

The complexities of' weather with the many subtle interactions of ultraviolet, visible, and infrared radiation

with the components of the atmosphere, changing temperatures

and moisture in vapor, liquid, and frozen form make

laboratory reproduction, especially in accelerated form,

a most difficult problem. Add to this the extreme

variability of the weather itself even in a given locality

and the wide departure in a given location on a given

building from the mean weather for the locality, and the

problem becomes a formidable one. This problem has been

considered by Reinhart (60).

Merriman (6l) states that in any bonded structure

complete inspection of the finished assembly is difficult.

Therefore, to produce bonded structures with any degree of

reliability, it is very important to follow correct*

procedures and to maintain rigorous control through every

step of the process. This Includes control during

fabrication and final inspection of the finished assembly.

A process control chart for adhesive bonding of sandwich

construction is shown in figure 4. Although the use of

this assembly requires complete reliability, the process

control chart for the assembly indicates items that should

be considered. Less rigorous applications than’ this

aircraft use will require less control.

In 1956 Eickner (4l) made a statistical analysis of data

obtained during a survey of fabricators of epoxy bonded metal

constructions. The .data were obtained from individual

adhesive-bonded lap joints which had been tested for

the purpose of production control, laboratory control,

adhesive acceptance tests, and storage tests. The number of

specimens tested ranged from 15*000 for production control to 44

for adhesive acceptance tests. The coefficients of variation for

the joints bonded with epoxy adhesives varied from 7 to 29 percent.

The individual means varied from 1700 psi to 39°0 psi for the tensile-

- 17 -

lap-shear strength of joints made with Individual adhesives.

Another approach to better production control is the development

of non-destructive tests. An early evaluation of adhesion by ultrasonic vibrations was made by Moses and Witt (62). Dietz (14) reports that

especially in sandwich constructions actual voids in a bond are not

particularly difficult to detect. Tapping , the ultrasonic reflectoscope

,

or vibrating a horizontal panel with a layer of powder on the surface,

where unbonded areas are revealed from the pattern developed, will be

sufficient to locate actual voids. The difficulty is to locate weakly

bonded areas. Dietz, Closman, Kavanagh, and Rossen ( 63 ) found on a

laboratory scale with laboratory specimens that the dynamic modulus of

elasticity of adhesive bonds, as determined at ultrasonic frequencies,

is roughly related to strength. In general, the higher the modulus of

elasticity, the stronger the bond. This method is applicable to adhesiveadherend systems in which the modulus of elasticity of the adhesive is

markedly different : from that of the adherend.

Arnold (6k) developed the so-called STUB-Meter (STanford Ultrasonic

Uond-meter). This instrument is based on the use of sonic methods in the

evaluation of structural adhesive bonds. Although it has been used in

some production control the requirements for highly trained observers and

standard panels limit its usage also to laboratory controls.

The University of Louisville Institute of Industrial Research ( 65 ) developed methods for the non-destructive testing of wood laminates for

the Office of Naval Research. The investigation included an ultrasonic, a

sonic, and a "brittle lacquer" method, none of which are very promising.

7. Properties

The Information on general properties of epoxy adhesives in

the Adhesives Chart in the 1957 Modern Plastics Encyclopedia ( 5 ) may

be summarized as follows:

Bond formation of epoxy resins takes place through chemical

reaction either at room temperature (70° - 80 °P), moderate temperatures

(I5O0 - 200° F) , or at elevated temperatures (275° - 310°F). Enoxy

adhesives have excellent resistance to water, solvents, heat, cold,

and fungus. They form excellent bonds with wood, metals, glass,

leather, paper, textiles, and ceramics, and good bonds with rubber.

No solvents are needed.

Another group of epoxy adhesives listed in this chart are the

phenolic-epoxy resins. They are cured only at elevated temperatures,

require no solvents, and have excellent resistance to water, solvents,

heat, cold, and fungus. They form excellent bonds with wood, metals,

rubber, glass, leather, textiles, and ceramics, and good bonds with

paper.

18

The third group listed in the chart are the polyamideepoxy adhesives. They form bonds by curing at room or

elevated temperatures or by solvent release. The solvents

may be alcohols or ketones. These adhesives have excellent

resistance to water, solvents, cold, fungus> and good

resistance to heat. They form excellent bonds with wood,

metals, glass, leather, paper, textiles, and ceramics,

and good bonds with rubber.

The average bond strength of some epoxy adhesiveadherend systems is given in table 3 (66). The effect

of fillers on the tensile-shear strength of epoxy

adhesive formulations is given in table 4 (l). The effect

of the amount of filler on the tensile— shear strength

is shown in table 5 (1, 67). Lee and Neville (1)

state in this connection that the specific loading volume

is somewhat dependent on the viscosity of the resin used

and also will be a function of cure time, since higher

volumes of filler lengthen the cure time required for

optimum bonding values. Engineering data for some

proprietary room-temperature 1 curing epoxy adhesives for

aluminum, brass, and steel are given in table 6(6).

Eickner (68) made extensive tensile-shear tests with

aluminum joints bonded with 3 heat-cured epoxy (Epon ) adhesives. The original shear strengths, the shear

strengths after various laboratory exposure conditions, and

after exposure to several climatic conditions are listed

in table 7. Exposures in Wisconsin, Alaska, and New

Mexico although much less severe than those in Florida

and the Canal Zone caused appreciable deterioration of

the stressed Epon VIII specimens. The stressed and

unstressed Epon VI and Epon VIII specimens generally

showed appreciable deterioration after 1 year of

exposure, averaging less than 30 to 40 percent of their

original strengths. Not dll the exposure tests with the Epon

422J adhesive tape are complete.

Stivala’s investigation (4) was directed toward

improving the impact characteristics of room-temperature

curing epoxy resins while simultaneously retaining or not

appreciably altering the valuable properties of the rigid

system. It was found that an epoxy resin (Cardolite 7019)

based on a bisphenol derived from cashew nut oil is

superior in impact strength, shear strength, and tensile

- 19 -

strength to epoxy resins based on bisphenol A-epichlorohydrin. Comparative strengths of some commercial epoxy

resins at 73 * 5°F are shown in table 8. The effects of

plasticizer on the shear., impact, and tensile strengths of

Epon 828 and Cardolite 7019 are shown in table 9.

The development of experimental resorcinol epoxide resins

as high strength, room- temperature curing, structural

adhesives for metals is reported by St. Clair and Moult

(69, 70). They confirmed the findings reported previously

that the strength of an epoxy bond whether tested at room

temperature or at 180°F 3s directly proportional to the

temperature and pH of the rinse water which is used

after aluminum has ‘been degreased and etched. They ascribe

this to the oxide film formed after these cleaning

operations. Figure 5 shows that the bond strength is

proportional to the rinse water temperature up to l60°F.

When the resorcinol epoxides were cured with liquid

aliphatic polyamines, the adhesives were brittle and the

pot life short. Solid polyamines ground with Thiokol

plasticizer gave longer pot lives but the adhesive was

still too brittle. Optimum bond strengths were obtained

with an adhesive having a resin/resorcinol glycidyl ether

ratio in mol/mol of 50/50 as shown 'in figure* 6. This

experimental room-temperature curing epoxy-resorcinol

resin met all the requirements for a heat-curing metal

structural adhesive of the type specified in MIL-A5090B (58), except for pot life which was only' 1.7

hours instead of the specified 4 hours. Average tensile

shear strength and bond strength for three specimens

of 2024 T3 clad aluminum bonded with this ' adhesive are

as follows:

Tensile shear strength. ps3 Fend strength

Room temperature 180°F -65 F lb

2865 2005 2550 160

Naps (71) reports on new experimental elevated

temperature-resistant epoxide adhesives developed for

the Air Force. The shear strength properties of five of

these adhesives are given in figures 7 and 8. The

aluminum bonded assemblies were cured at 330°F.

20

Merriman and Goplen (72) conducted a very thorough

investigation of structural adhesive properties

over a wide temperature range. The adherends were 0. 064-

inch thick, type 301, 1/2-hard, 2D finish stainless steel and

0. Q64-inch thick 2024-T3 alclad aluminum. Epon VIII epoxide

(Shell Chemical Corp.) and 422 J epoxide-phenolic (Shell

Development Co.) were among the adhesives tested for tensile

shear, creep rupture, impact, cleavage, tensile, bend, peel,

and fatigue tests. The peel tests were conducted at room

temperature in a climbing drum apparatus similarly to

Federal Test Method 1042T. As expected, the epoxy resins

had poor peel strength: Epon VIII 7.0 in. -lb; Shell 422J

4.2 in. -lb. It should be noted that the peel strength obtained

is a function of the surface preparation method equally as

much as it is a function of the adhesive being tested.

Therefore, comparisons of peel strength of various adhesives

may be made only when a highly controlled surface preparation

method is used for all test specimens. Note also that peel

strength represents the load required to continue failure.

The peel strength of an adhesive may be roughly defined

as its resistance to further failure. This implies that

some failure has already occurred. Thus the load required

to initiate failure in an adhesive will not necessarily be

in ratio to its peel resistance (72). The peel resistance of

unmodified adhesives can be improved by changing the

formulation, as is also the case with impact resistance.

Compression data for epoxy adhesives are not available

although this test is often performed with wood-to-wood

adhesives.

One manufacturer (13) quotes a compressive strength of

14,000 psi. without reference to the test method used. This

same manufacturer gives the value for the refractive index

as 1.562 which is in good agreement with data obtained for

this property in tests made at the National Bureau of

Standards. This property is of importance for bonding

glass and/or quartz where optical clarity is required.

The sales literature for the epoxy adhesives quotes

specific gravities in the range of 0.90 to 1 . 2 , depending on the composition and formulation.

The chemical resistance of the epoxy resin adhesives

is reported as very good in the literature, but it is

dependent on the curing agent. The chemical resistance

for an epoxy resin adhesive cured with amine-resin adduct

tested at room temperature as reported by Lee and Neville (l)

is presented in Table 10,

21 -

Military Specification MIL-A-509OB (58) requires a

minimum of 2,500 psi tensile shear strength after

exposure to various liquids. St. Clair and Moult (69, 70)

state that their formula 761 meets these requirements. No

data were given to substantiate this claim.

Table 11 gives tensile shear strength data for four Thiokolepoxy resin adhesives after immersion in solvents for 30

days (11).

Fillers may affect the moisture resistance, the moisturevapor transmission, and the solvent resistance either adversely

or advantageously. The effects of several fillers on these

properties are presented in figures 9 , 10, 11 (66).

The electrical properties of epoxies used as adhesives

proper are not reported in the literature. Data for electrical

properties of straight epoxy and modified epoxy resins are

found in the symposium on Casting Resins (23). The data i,n

table 12 (73) show the electrical properties of various epoxy

resins. The typical electrical properties of resin cured

with diethylene triamine are given in table 13 (7*0. The

volume resistivity versus temperature is given in figure

12 (7*0. Linden (750 also reports on the effect of

temperature on the electrical properties of encapsulating

materials.

Borders (76) investigated the effect of nuclear

irradiation on structural adhesives. The deteriorating

effect on the tensile shear strength of three epoxy adhesives

is shown in figure 13 and the effect on bend strength

in figure 14. The tests were made at room temperature

in accordance with methods 4.3. 2.1 and 4.3. 2.9 of MIL-A5090B, respectively, on standard 1-inch 2024T3 aluminum

alloy lap joints. The tests showed considerable

deterioration except in the case of the high-tempe rature

curing epoxy-phenolic tape 422J.

Mixer (77) reports that attempts have been made to

improve the irradiation resistance of* commercially

compounded adhesives with protective agents. Epon VIII

was chosen because of its ease of handling and the east with

which the additive can be incorporated into the adhesive.

Without additive tensile shear specimens from Epon VIII

lost 40$ of their original strength. Additions of Nvinylcarbazole at concentrations of one and nine percent

showed a deleterious effect on the adhesive. One percent

- 22

of 2* 5-diphenyloxazole showed no change in the properties of

the adhesive. Nine percent of 2£>-diphenyloxazole, however

showed a marked improvement in the radiation resistance of

the adhesive which lost only 11% of its initial strength

at> 800 megarep.

Lee and Neville (1) report that the low temperature

strength of epoxy resins at -50 °C can he improved by flexibilizers.

They appear to offer no immediate promise for improving

performance at temperatures much above 100°C because of the

loss of strength of such modified resins at these temperatures.

Phenolic resins* in higher loading volumes* have been used

with limited success in epoxy adhesives for operations in the 250°C

range. Considerable effort is being directed toward extending

the upper operating temperature limits to even higher values.

Three approaches are being followed to achieve adhesives for

higher-temperature operations: development of more

satisfactory resinous modifiers* development of better curing

agents* and synthesis of epoxy resins with improved temperature

resistance. For intermediate-range work* "bodying” resins

with phenolics and anhydrides has been suggested* but little

work has been accomplished.

Even below 250°C* the upper temperature limit i3 critical

for many compounds. With systems suitable for operation in

the 150 to 200°C range* there is usually a moderate increase

in bond strength as temperature rises; but thereafter* the

bond strength decreases with further temperature increase to

a drop-off point beyond which loss of properties is rapid.

A single batch of adhesive for a single application will give

loss in strengths that vary over a 5 to 10°C range.

Because the high* compared to metals* coefficient of

thermal expansion of the unmodified epoxy resins tends to

disrupt the adhesive bond with Changes in temperature*

reductions in this value have the effect of extending the

upper operating temperature limit.

Fillers are most effective in reducing the value*

as shown in figure 15* Ideally* the coefficient of thermal

expansion should be lowered to match that of the material

being bonded, or* in the case of like-on-unlike bonds* to a

value between the two materials. In practice* however* it

is often not possible to employ a sufficiently large loading

volume. High loading volumes increase viscosity to the

point where thin* regular glue lines cannot easily be obtained
-
and in other ways tend to degrade , rather than improve, the

bond. For some applications and 3ome fillers, loading volumes up

to 200 parts per hundred may be employed, but optimum shearstrength values are usually obtained with lesser amounts.

Suggested loading volumes for some good adhesive fillers

are mica, 14 parts per hundred; short-fiber asbestos, 25 parts

per hundred; aluminum oxide, 50 parts per hundred; talc, 80

parts per hundred; and zinc dust, 100 parts per hundred.

These, of course, are not optimum for all applications or in

all formulations.

Turner and associates (78, 79) considered the filler

problem in heterogeneous materials from a more basic viewpoint, When temperature limits permit, it is useful to

compensate for differentials in the coefficient of thermal

expansion by the use of flexibilizers to absorb the internal

stresses during thermal cycling. For short periods at higher

temperatures, supported tapes will somewhat improve performance

by more uniform distribution of stresses.

Table 14- summarizes expansion coefficients for some

commonly used building materials. For purposes of comparison

the dimensional changes of a 10-foot length of material

accompanying a 100°F temperature change are also shown.

Dietz (14) states that such changes in dimensions of materials

with changes in temperature, moisture, and other factors are

of crucial importance in the application of adhesives. Although

the changes may be relatively small in comparison to the

structure as a whole, they are extremely large compared to

the dimensions of the adhesive.

8, - 24 - Bibliography

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... - „ . '

•••' - 1 '.
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~ 29-

70. St. Clair, W. E., and Moult, R. H., Room-temperature-cured

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76. Borders, D. F., Nuclear deterioration of structural adhesives.

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77. Mixer, R. Y. , Nuclear deterioration of structural, adhesives.

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78. Turner, P. S., Doran J., and Reinhart, F. W., Fairing

compositions for aircraft surfaces. NACA Tech. Note No.

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79* Turner, P. S„ and Thomason, R. H., Correlation between

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- 30 - 9.

Additional References

1. Adhesion and Adhesives; Fundamentals and Practice. John

Wiley and Sons, Inc., New York. 1954 -

2. Allen, F. J., and Hunter, W. M. , Some characteristics

of epoxide resin systems; hardening of epoxide resins with

amines. J. Applied Chem. 7* 86 (Feb. 1957).

3. Anonymous. Plastics make the sandwich. Modern Plastics

100 (Dec. 1954).

4. Charlton, J.j Alloying with epoxies. Modern Plastics 32, 155

(Sept. 1954).

5. Dearborn, E. C., Fuoss, R. M. and White, A. F., Acid

acceleration of epoxide condensations. J. Polymer Sci.

16, 201 (1955).

6. DeBruyne, H. A., Adhesive properties of epoxy resins. J.

Applied Chem. 6j_ 303 (1956).

7. Eickner,H.WJ, Basic shear strength properties . of metal -bonding

adhesives as determined ' by lap-joint stress -formulas of

Volkersen and .Goland and Reissner. Forest Products Lab.

Report No. 1850 (1955).

8. Fisch, W., and Hofmann, W., The hardening mechanism of epoxy

resins. J. Polymer Sci. 12, 497 (1954).

9.

Floyd, D. E., Ward, W. J., and Minarik, W. L.^ Polvamideepoxy resins. Modern Plastics 33* 238 (June 1956 )

10. Greenlee, S, 0., Pearce, J. W., and Kawa , J., Film curing

by simultaneous esterification and olefin polymerization.

Ind. Eng. Chem. 49_, IO85 (1957).

11. Greenspan, F. P., Epoxidation-hydroxylation reactions.

Modern Plastics _31, 123 (Mar, 1954).

12. Hoerner, A. H„, Cohen, M., and Kohn,L. S„, Heat distortion

temneratures of epoxy resin-catalvst combinations. Modern

Plastics 35* 184 (Sept. 1957).

13. Jorcsak , j. S., and Belisle, J. A., Liquid polymers combined

with epoxy resins. SPE J. 10, 23 (Feb. 1954).

14. Kilduff, T. J a , and Benderly, A. A .j Conductive adhesive for

electronic applications. Electrical Mfg* .61*., 148 (June

1958).
<i

fi ; i
-31 -

15. Manfield, H. G.^ Applications of epoxy resins in the

electrical industry and in electronics. Polymer Progress

(Shell Chemical Corp.) No. 4 (Feb. 1957)

16. Parry, H. L., Carey, J. E., and Anderson, M. D 0 , Effect of

fillers on high humidity insulation resistance of epoxy

resin systems. SPE J. 13 . 45 (Oct. 1957)*

17 • Parry, H. L., and Hewitt, R. W., Effect of fillers on

epoxy resins. Ind. Eng. Chem. 49, 1103 (1957)

18. Peerman, D. E., Tolberg, and Floyd, D.. E., Reaction of

polyamide resins with epoxy resins. Ind. Eng. Chem, 49

,

1091 (1957). '

19* Robitschek , P., and Nelson, S. J., Flame- and heat-resistant

epoxy resins. Ind. Eng. Chem. 48, 1951 (Oct. 1956).

20. Shell Chemical Corp,, Technical Bull. SC: 57-134. Bibliography

of magazine articles for epoxy re-sins.

21. Smith, et al.^ Room-temperature curing of metal -to-metal

adhesives, U. S. Rubber Co. 1951 * Available from. Office

of Tech. Services, Dept, of Commerce as PB 108755.

22 . Sorg, E. H., and McBurney, C. A., Polysulfide-epoxy

compositions. Modern Plastics 34, 187 (Oct. 1956).

23. Stifter, J. A., A control program for epoxy-caused

dermatitis. Plastics Tech. _4^ 138 (Feb. 1958).

24. Walb, T. A., Epoxy resins, Tappi 37 - (July 1954).

Table 1

List of Manufacturers* i 01? cincl

Adhesives

Trade Names of Epoxy Resin

Firm name and address Trade name

Adhesive Engineerings San Carlos* Calif,

Adhesive Products Corp.* l660 Boone Ave.*

New York 60* New York

Alkydol Labs. 3242 S, 50th Ave.* Cicero

50^-Illinois

Am, Latex Products Corp.* Hawthorne* Calif

Angler Adhesives* Div. of Interchemical

Corp.* 120 Potter St.* Cambridge 4-2* Mass.

Armstrong Cork Co.* Lancaster* Pennu.

Armstrong Products Co.* P.0. Box 1*

Warsaw* Ind.

Atlas Mineral Products Co.* Metztown* Pa.

Atlas Synthetics Corp.* Long Island City

1* New York

Bakelite Corp.* Div. of Union Carbide Corp.*

30 E. 42nd Street.* New York 17 j, N. Y.

Carl H. Biggs Co.* Inc.* 2255 Barry Ave.*

Los Angeles 64* Calif.

Bloomingdale Rubber Co.* Aberdeen* Md.

Bond Adhesives Co„* Box 406 Main P.0.)

Jersey City 4* N. J.

The Borden Co.*Chem. Div.* 350 Madison

Ave.* New York 17* New York

Brit. Resin Products* Ltd. Devonshire

House* Picadilly* London* England

Carboline Co., 331 Thornton Ave* St.

Louis 19 j Mo.

Chemical Coatings and Eng. Co.* 2633

Westchester Pike* Edgemont* Pa.

Chemical Development Corp.* Endicott

St.* Danvers* Mass.

Ciba Co.* Inc.* Plastics Div. . Kimberton*

Pa. , Cordo Chem. Co.* 34 Smith St.*

Norwalk* Conn.

Cycleweld -Cement Prod. Div.* Chrysler

Corp.* 5437 W. Jefferson* Trenton*

Michigan

Emerson and Cuming* Inc.* 869 Washington

St.* Canton* Mass.

Epoxylite Corp.* 10829 E. Central Ave.*

El Monte* Calif.

Ferrington Texol Corp. *2000 Main St.*

Walpole* Mass

Metalfil

Adgrip

Alk-0-Flex

Staybond

Alfane* Amphesive*Nepoxide

Bakelite

Bonding Agent

BRC

Bond

Epiphen

Cellcbond

Carboline

Corrocote

C, D. Cement

Araldite

Cordo -Bond

Cycleweld

Ecco

Epoxylite

Firm name and address

Paisley Products., Inc., D^v, Morning star

Nicol, Inc .> 630 W. 51st Street, New York

19 ^ New York

Poly Resins, 11661 Wicks St., Sun Valley,

Calif.

Polymer Chemical Co., 9920 Carthage Ave.,

Cincinnati 12, Ohio

Polymer Industries, Inc. Springdale, Conn.

Reichhold Chemicals, Inc., 525 N« Broadway,

White Plains, New York

Ren Plastics, Inc., 5422 S, Cedar St.,

Lansing 17, Mich.

Rubber and Asbestos Corp., 234 Belleville

Ave., Bloomfield, New Jersey

Shell Chemical. Corp. , 380 Madison Ave.,

New York 1 < , New York

Siemens Labs. > Inc.* 31-27 Thomson Ave.,

Long Island 1, New York

Thiokol Chem. Corp. 780 N. Clinton St.,

Trenton 7 , New Jersey

United States Stoneware Co., Talimadge

Ave., Box 350, Akron 9 » Ohio

Willross Products Co,, 20 4th Ave,,

Hawthorne, New Jersey

Trade name

Paisley

Poiypreg

Polyox, Polytool

Ren

Bondmaster, Brushmaster, Plymaster

Epon

Thiokol

Tygofil, Tygoweld

Table O

List of Manufacturers, Suppliers, and Trade Names of ModifiedEpoxy Resin Adhesives

Firm name and address

Polyamide Modified

Adhesives Engineering, San Carlos, Calif.

Adhesives Products Corp., 1660 Boone Ave.,

New York 60, New York

Angler Adhesives, Div. of Interchemical

Corp., 120 Potter St., Cambridge

42, Mass.

Bond Adhesives Co., Box 406 Main P.O.,

Jersey City 4, N. J,

The Borden Co,, Chem. Div., 350 Madison

Ave., New York 17 * New York

Chem, Coatings and Eng, Co., 2o33 Westchester Pike,Edgemont, Penna.

Dennis Chemical Co., 2701 Papin Street,

St. Louis 3j Mo.

General Mills, Inc., Chem. Div., So.

Kensington Rd., Kankakee, 111.

Gordon-Lacey Chem. Prod, Co., Inc., 57-02

48th St., Maspeth 78, N, Y.

Houghton Labs., Inc., 322 Houghton Ave,,

Clean, N. Y.

Hughes Glue Co., 3500 Aubin Srreet.,

Detroit, Michigan

Trade name

Metalfil, Aerobond

Adlok

Bond

Arcco, Placco, Reslac

Corrocote

Hysol

Lawrence Adhesives and Chem. Co., Inc.,

19 S. Canal St., Lawrence, Mass* Epolac

Midland Adhesives and Chem. Corp.,

2600 Goodrich, Ferndale 20, Mich. Midland

Miracle Adhesives Corp., 250 Petit Ave.,

Bellmore, L. I., N. Y. Miracle

Narmco Resins and Coatings Co., 600

Victoria St., Costa Mesa, Calif. Narmco

National Adhesives Div,, National

Starch Products, Inc., 270 Madison

Ave., New York 16, N. Y, Duro-lok

Nureco, Inc .} 1100 Pontiac Ave.,

Cranston 10, R. I. Nureco

Ohio Adhesives Corp., Maple Ave., Ext.

New Philadelphia, Ohio Ohio

Rubber and Asbestos Corp,, 234 Belleville

Ave., Bloomfield, N. J. Bandmaster

Willross Products Co., 20 4th Ave., Hawthorne 3 New Jersey ---

Table 2 (continued)

Phenolic Modified

Adhesives Engineering, San Carlos, Calif.

Bloomingdale Rubber Co., Aberdeen, Md.

Lebec Chemical Corp., Paramount, Calif.

Narmco Resins and Coatings Co., 600

Victoria St., Costa Mesa, Calif.

Plastics Engineering Co., 1607

Geele Ave., Sheboygen, Wis.

United States Stoneware Co., Tallmage

Ave., Box 350, Akron 9 j Ohio

Polysulfide Modified

Aerobond

BRC

Lebec

Metlbond

Plenco

Tygoweld

Adhesive Engineering, San Carlos, Calif Aerobond
; V

- -

*

*• •" *

. •••••'

i: -

I
Table 3° Strengths of Typical E: Adhesive-Adherend Systems

Formulation Parts

Average tensile-lap- shear strength

Steel Brass Aluminum

psi psi psi

_ . a Epoxy resin 100 720 1400 1570

Hardener l b 25

Epoxy resin 100 1500 1950 — —

Hardener 1 25

Filler^ 35

Epoxy resin 100 1750 2650 4500

Hardener 2C 5

Epoxy resin 100 2050 3025 4750

Hardener' 2 5

Filler 90

Epoxy resin 100 2400 4500 5400

Resin modifier6

5

Hardener 2 5

Filler 90

a. Epoxy resin BRR 18795 (Bakelite Co.)

b. Hardener 1 BRR 18793 ( do a ) c. Hardener 2 (pyrrolidine)

d. Filler Titanium oxide

e. Resin modifier polyvinyl acetal

Table 4

Effect of Various Fillers on Tensile-Shear Strength

of Aluminum Assemblies Bonded with Epoxy Adhesives a

Filler

Ignited AI 2O3

Short-fiber asbestos15 Carbon black

Silica OBI

Zinc dust

Tensile-shear strength

room temp 105"C

psi psi

1650 1150

2130 3910

2000 1170

1530 600

4080 3865

a. Room temperature curing adhesive of the following

composition: Mixed polyrner/epoxy resin: 100 parts; allyl

glycidyl ether: 10 parts; filler: 100 parts; triethylamine 12, 5 parts,

b. 24 parts.
i
Table 5

Effect of Filler Loading Volumes on Tensile *

’ Shear Strength of Epoxy Adhesive

Filler

Tensile-shear strength for

Amount, aluminum assemblies

parts/100

23° C 60°C

None

Aluminum

Aluminum oxide

Mica

Silica

psi psi — 1,030 1,205

40 2,525 3,725

60 2,525 3,580

80 2,390 2,620

30 2,505 2,805

50 3,615 3,600

70 2,555 2,665

6 2,210 1,810

14 2,360 2,815

26 1,055 1,210

40 600 610

90 1,460 1,225

30 1,870 2,360

60 2,650 0,655

80 2,520 2,400

Talc

Table 6

Strengths of Some Room-Temperature Curing Epoxy

Adhesives^ for Various Metals

EC-1294 with EC-1294 with EC-1474 with EC-1472

EC-1295 acce- EC-1468 acce- EC-1475 acce- EC-1473

Properties lerator lerator lerator lerator

Working life 15 min 2 hr 2 hr 1 hi

Tensile—shear

strength, psi

To aluminum"13

After 7 days* < curing at room

temperature

tested at room

temp. 2,700 1,600 2,000 3,400

tested at -65°F 810 1,100 530 2,000

tested at 180°F 180 890 430 660

After 7 days in

tap water 4,200 2,200 2,000 3,100

After 30 days '

: )\'0 V ' ) do. 3,000 3,300 2,900 2,700

After 7 days at

120°F + 100

% relative

humidity 3,200 3,300 4,700 2,200

After 30 days

do. 2,900 3,000 4,000 1,400

After 0.5”hr

curing at 200 °F

tested at room

temperature 4,500 3,500 2,100 1,800

tested at -65°F 2,800 2,700 690 3,800

tested at 180°F 960 1,500 750 190

After 7 days in

tap water 4,400 4,ioo 2,400 1,300

After 30 days

do.: 4,400 4,ooo 3,400 1,100

After 7 days at

120°F at 100%

relative

humidity 3,300 3,700 4,300 740

After 30 days

do. 2,500 3,100 3,600 410

with

acce-

Table 6 (continued)

EC-1294 with EC-1294 with EC -147 4 with EC-1472 with

EC-1295 acce- EC-1468 acce- ECr-1475 acce- EC-1473 acceProperties lerator lerator lerator lerator

After 7 days'

curing at room

temperature

To brass 29O 1,000 980 1,500

To steel 540 800 790 1,200

Bend strength,

ib c To aluminum13 After 7 days

curing at room

temperature 280 100 130 260

After 0.5 hr

curing at 200 °F 270 160 150 200

a Proprietary adhesives.

b 1/2-inch overlap specimens of 24ST3 alclad aluminum

c Probably tested in accordance with method 4. 3. 2.9 in MIL-A-5090B (58).

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Table 8

Comparative Strengths of Commercial Epoxy Resins at 73.5°F

Resin Tensile, a

. ^

v Te^il.e * Shear 49V/ 1 .'-' 4

' a psi Ai-to-Ai steei-to-steej.

psi psi • ft -It/inCycleweld

C-14 2713 1314 1872 11.7

Araldite CN

502 3095 940 1706 11.3

Araldite

CN 503 3890 728 1298 4.0

Epon 828 3640 960 1743 7.7

Cardolite

7019 3760 1058 2524 6.2

a. Steel-to-steel
:

'

4',; r; *.*. -

; *

c
Properties

of

Epon

828

and

Cardolite

7019

Adhesives,

Both

Plasticized

with

Cardolite

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CO

A oo OJ 0 oo p • P A 0 O

VO

A 0 S3 0 0 0 0 P 5: • X P P P 0 o 1 OJ £ P C \ • P 1 P* G ta P to S3

to 0 0 S3 0

co , 0 X ft CM »p-f « ft «f o O

ft

p

VO P CM'!O P co

•;1 to

p \ p d i—

p- Sh

C ft

p * p 0 O o • p • t— i—

co

ftffl

02

O 02 o • 0

p'd c

p- co co 0 X • • • Sh GO o

poo P 0 0 p

ft 0 p

Sh

p 0 bO

OJ CO

A S3 0 d • 9 • p d C • p CO -=j- £ 1 0«~>

(3 Sh Sh =

Sh

O 9 0 C0 P ftp p\ 0 0 0 d t

P • vo P > 0 0 • O • P * AP A 0 to ra d

S3 0 l C = 0 o O 0 co P 0 P \ P^ft 1 p Sh pc - P 0 0. <

1 0 CO 0 P • P P X O 0

Sh P CO CO P P C p 0 < P ft

A CO • w- 0 Sh

A • O

p • CO 0 0

VO AVO Sh 0 0 P 0 02 1 PP 0 X 0 C 0

ft 0 0 P A ho 0 O O 0 C

t- 5 ft> P p vo d POP ftVO C P % 0 0 (j— O P P | 1 • ft

•H

CQft

ft0

aj0P

co

d003o0>

ft

020pd< G

ft 0 S3 0 ft 0p pcOO 0 o 0 • ftO £0 o p p o p

p

O ft

O

C

O S3 ft ft

a3 0 0 0 0 0 0 0 0 0 A 0 AP A

co o to 0 0 ft 0 C £ S3 OHO 0 pod

Table 10

Chemical Resistance of an Epoxy Resin

Cured with Amine-Resin Adduct

System tested in gain in weight,

7 days’ immersion

j

10$ caustic Negligible

Ethyl alcohol do.

Kerosene do.

Toluol do.

Ethyl acetate do.

30$ sulfuric acid 0.88

Ethyl ether 0.55

Chloroform 1.81

Acetic acid 2.88

Acetone 0.83

Trichlorethylene 0.13
' ’ . • i .'•/

r ! \ ' ' .
Table 11

Tensile Shear Strengths after Optimum Cure at 250°F

and Solvent Immersion at 80°F, for 30 Days

Formulation

Solvent T- T-120-2 T‘-T20TM3 T-12'0"

psi psi psi psi

Tap water 3200 800 1200 2700

Sba water 2900 1100 700 2800

Type III fuel 3300 3400 3200 3600

JP-4 fuel 3400 3200 2800 3400

Engine oil 3500 3200 3100 3100

Isopropyl alcohol 3700 3200 2800 3500

Ethylene glycol 3400 3700 3600 2900

10$ soln. Alp

(so,). 3200 2000 1800 2800

10$ soln.

Na2

C03 3500 2800 1400 3600

Methyl ethyl

ketone 2700 400 disintegrated 2600

Dibutyl phthalate 3200 3400 3500 4100
: . f t ' 1
Table 12

Electrical Properties of Various Epoxy Potting Resins

Potting resin Formulation Dielectric

Component

Dissipation

Parts by wt constant factor at

at 105 cycles 105 cycles

per sec per sec

Volume

resistivity

ohm- cm

Epoxy 60 4.69 .0476 5X101- Polysulfide 40

DEAPAa 6

Epoxy 50 6.181 .0560 3X1011

Polysulfide 50

DET° 5

Epoxy 100 3.65 .0089 IO16

DETb 10

a. DEAPA = Diethylaminopropylamine

b. DET = Diethylene triamine

Table 13

Typical Electrical Properties of Epoxy Resin Cured with

Diethylene Triamine

Frequency, cycles/sec

Property C\J 0

1

—

1

io3 10^ 105 106

t- 0

1

—

1

Power factor:

-40°C 0.0220 0.0200 0.0195 0.0175 O.OI65 0.0170

-20°C 0*0300 0.0500 0.0500 0.0700 0.0900 0.1000

20 °C 0.0O90 0.0400 0.0480 0.0800 0.1000 0.1300

60°C 0.0045 0.0100 0.0600 0.0750 0.1100 0.1500

100°C 0.0175 0.0165 0.0300 0.0600 0.1200 0.2000

Dielectric constant:

-40°C 3.4 3.35 3.3 3.3 3.2 3.1

-20°C 3.8 3.8 3.75 3.7 3.6 3.4

20° C 4.1 4.2 4.2 4.1 4.2 4.1

60°C 4.3 4.4 4.6 4.6 4.5 4.4

100°C 4.5 4.6 4.7 4.8 4.9 5.0

25°C

50°C

T5°C

100°C

125°C

x 10?\ ohm-cm

x 10“-^ ohm-cm

x 10-3 ohm-cm

x lOr^r ohm-cm

x 1011 ohm-cm
. .

..i 4*
Table 14

Expansion and Contraction of Some Building Materials

Material

Thermal

.sJL

Coefficient

io n

m5W

Aluminum Alloys, Wrght.

Copper Alloys

Glass

Plastics

Steel, * carbon 0.20C

M stainless 18-8

Brick

Concrete

Wood, parallel to grain

perp. to grain

Brick

Concrete (ly^ar at 50°_

relative humidity)

Wood, parallel to grain

" perp, to grain

11.1-13*5

9

* 0- 11*8

4

-

5*1

5

-

210

6*7

0*6

5

fc7

4-6.5

1*1-5*

3

14*6034*1

Moisture, Expansion

and Contraction

5-150x10^ in ../in.

250-ll60xl06 in, /in.

0*1-0* 2 percent

2-14 percent

Dimensional Change

b. in) 10 ft for

: - 0 TOO °F « hTemp

,

Change

inches

0*133-0*162

0*108-0*142

0*053-0*061^

0*069-2*51

0*081

0*105

0*060-0.084

0*048-0*078

0*013-0*063

0*175-0*410

Dimensional Change

in 10 ft.

0*0006-0*0126

0*018-0*139

0*120-0*240

2*40-16*8

Viscosity,

cp

i'ig. I Pot life of mixed epoxy resin

800

600

400

300

200

100

80

60

40

30

20

101

<

F

p —

.

L

.. .. 1\

- - t \

\\

l ^

i j l

1,

\

\

... \

\

\

\

\

t 40 80 120 160 200 240

Curing, temperature, F

ig. 2 Curing time versus temperature for epoxy

adhesive
.

.

1
Tensile

shear

strength,

p

si

Fig. 3 Strength versus temperature tor epoxy

adhesives

SEMI- h

temp.

TOOL I

Fig. 4

Process

control

for

adhesive

bonding

Tensile

shear

strength,

psi

Figure 5. Influence of surface condition of aluminum on bond strength using resorcinol epoxy adhesive

C]

lesled

at

room

temperature

O

Tested

at

180

°

|sd ‘l]j6u9J|S J09ljS 9|ISU9j_

Fig.

6

Effect

of

resin

“resorcinol

ratio

on

bond

strength

o O O o o

o o o o o

o oo vO

on fM

cz

jsd ‘lj|5u0JJS >ID9L|S 0|ISU0J_

Room

temp

500

°F

500°F

600°F

Aged

ZOO

hr

at

500° F

Fig.

7

Comparison

of

three

epoxy

adhesives

containing

polyvinyl

formal

rest

3000 o o o

o o o

SO o 40

<Ni r—

ISd ‘HlONddlS dV3HS 3HISN31

FIGURE

8.

COMPARISON

OF

TWO

EPOXY

ADHESIVES

CM

O

- CO

CD

CM

00 CM

% 'uie§ iqSieM

j

Time,

days

FIG.

9

Water

adsorption

at

40°Cfor

filled

epoxy

adhesives

r—4

Q)

01

OJ

ro CO o

>-> OO

p

o

CO

o o !k— Q O M

o-°

S^P 0^

O O O LO

ro LO LO CO

+ “h +- f*

c\i re 'sf lO

C\j

C\i OO LO

o

00

’'t

eg

o

eg

VD eg oo

%

4 uid 6 |i|5i8M

L

ld

ro

eg

ro

oo

eg eg

Time,

days

FIG

10

Benzene

adsorption

at

40°C

for

filled

epoxy

adhesives

CM

00

MD

CM

%‘uio6 jqbi 0/\/\

Time,

days

Fig.

11

Ethyl

alcohol

adsorption

ot

40°C

for

filled

epoxy

adhesives

VOLUME

RESISTIVITY

,

OHM

-

CM

Fig 12 Volume resistivity as a function of temperature for epoxy

and modified epoxy resins- Resin A, epoxy cured with

diethylene triamine, Resin B, IOO parts epoxy- 60 parts

polysulf ide rubber, Resin C, 100 parts epoxy - 100 parts

polysulfide rubber, Resin D, epoxidized polybutadiene

SSd '.H19N3H1S d V 3HS 31ISN3X

FIGURE

13.-

EFFECT

OF

NUCLEAR

RADIATION

ON

TENSILE

SHEAR

STRENGTH

OF

EPOXY

ADHESIVES

AT

ROOM

TEMPERATURE

003 o

roOO </5 m z

Hio

§~z

yjO o cco

LJ©o o

ro ZqH<Q<

jr oo o o o o o ^ W oo <$* SOI l HI9N3UiS 0N3Q

X

h"

e>z

Idoc

sTM yj

(/) tr3 Q2

bJ

h-<

DC

yj

£D

X2 O Id

F- zo 2 H o < o Q QC < H X <

IT CO < yj

yj >

CO o yj 3 X Z Q

Ls_ < o >~ HO Xo

Ld CL

Ll, Ld

Ll. k_

Ida

G 5

LdX3

e>

u.

CD

CDO

Bb— if) <D

CD fO

T3 o c

O) £ c o

”Q

>

O

CL E

X)

CD 3 CD O

CL

&W, E3

c

T3

£C

CD

E

o

E

a> CL 3

CL

Ql E C

3

IE

rou JJ

a o -}—

*— CD

o < -J CO O

o o

LO

o

C\J

Oo/

u !/' u ! ‘0.09+ OJ 0.09-

uoisuedxa leuuaqj jo luapijpoo aSejaAy

0

20

40

60

80

100

Filler

content,

%

by

weight

FIG.

15

Eftect

of

various

fillers

on

coefficient

of

thermal

expansion

of

epoxy

adhesives

s>

. U S. DEPARTMENT OF COMMERCE

Sinclair Weeks, Secretary

NATIONAL BUREAU OF STANDARDS

A„ Y. Asiin, Director THE NATIONAL BUREAU OF STANDARDS

The scope of activities of the National Bureau of Standards at its headquarters in Washington,

D. C„, and its major laboratories in Boulder, Colo,, is suggested in the following listing of the

divisions and sections engaged in technical work, In general, each section carries out specialized

research, development, and engineering in the held indicated by its title. A brief description of

the activities, and of the resultant publications, appears on the inside front cover. WASHINGTON, D. C.

Electricity and Electronics. Resistance and Reactance. Electron Devices. Electrical Instru- ments. Magnetic Measurements, Dielectrics. Engineering Electronics. Electronic Instrumentation. Electrochemistry.

Optics and Metrology. Photometry and Colorimetry. Optical Instruments. Photographic

Technology. Length. Engineering Metrology,

Heat. Temperature Physics. Thermodynamics. Cryogenic Physics. Rheology. Engine

Fuels. Free Radicals Research,

Atomic and Radiation Physics, Spectroscopy, Radiometry, Mass Spectrometry. Solid State Physics, Electron Physics. Atomic Physics. Neutron Physics. Nuclear Physics, Radioactivity. X-rays. Betatron. Nucleonic Instrumentation. Radiological Equipment.

Chemistry, Organic Coatings. Surface Chemistry. Organic Chemistry. Analytical Chemistry. Inorganic Chemistry. Electrodeposition. Molecular Structure and Properties of Gases. Physical Chemistry. Thermochemistry. Spectrochemistry. Pure Substances.

Mechanics. Sound. Mechanical Instruments. Fluid Mechanics. Engineering Mechanics.

Mass and Scale. Capacity, Density, and Fluid Meters, Combustion Controls.

Organic and Fibrous Materials. Rubber. Textiles. Paper. Leather. Testing and Specifications. Polymer Structure. Plastics. Dental Research.

Metallurgy. Thermal Metallurgy. Chemical Metallurgy. Mechanical Metallurgy. Corrosion.

Metal Physics.

Mineral Products. Engineering Ceramics. Glass. Refractories. Enameled Metals. Concreting Materials. Constitution and Microstructure,

Building Technology. Structural Engineering. Fire Protection. Air Conditioning, Heating,

and Refrigeration. Floor, Roof, and Wall Coverings. Codes and Safety Standards. Heat

Transfer.

Applied Mathematics. Numerical Analysis. Computation. Statistical Engineering. Mathematical Physics.

Data Processing Systems, SEAC Engineering Group. Components and Techniques. Digital

Circuitry. Digital Systems, Analog Systems. Application Engineering.

® Office of Basie Instrumentation, * Office of Weights and Measures. BOULDER, COLORADO

Cryogenic Engineering. Cryogenic Equipment. Cryogenic Processes. Properties of Materials.

Gas Liquefaction.

Radio Propagation Physics. Upper Atmosphere Research. Ionospheric Research. Regular

Propagation Services. Sun-Earth Relationships. VHF Research.

Radio Propagation Engineering. Data Reduction Instrumentation. Modulation Systems.

Navigation Systems. Radio Noise. 'Tropospheric Measurements. Tropospheric Analysis.

Radio Systems Application Engineering. Radio Meteorology.

Radio Standards. High Frequency Electrical Standards. Radio Broadcast Service. High

Frequency Impedance Standards. Calibration Center. Microwave Physics, Microwave Circuit

Standards.
I