handling of adhesives and sealants and their components.
Completely cured adhesives
and sealants are generally considered safe and non-toxic, although caution must
be exercised when machining or grinding joints due to airborne particles. Also,
decomposition products may exhibit substantial vapor pressures that present
health and safety issues. However, it is exposure to uncured components that
can be the most harmful, and that is the subject of this article.
Four primary factors must be considered in all adhesive bonding or sealing
operations: toxicity; flammability; hazardous incompatibility; and equipment.
Resins and catalysts must be carefully considered because they not only present
health and safety issues within the factory or worksite, but they also present
issues within the community relative to the release of volatiles and waste
disposal. These materials could be toxic or flammable, or they could be skin
irritants. Formulators should ensure that these raw materials are compounded in
a safe environment. Once formulated, the end user also has responsibilities
with regard to safe handling and disposal of adhesive and sealant products.
Some materials are more dangerous than others, and some affect certain parts of
the body while others do not. Amine curing agents, for example, generally
irritate the skin and eyes. They are also considered to be strong caustics and
will produce serious local injury on short exposure. Their fumes pose
additional hazards in hot work environments.
In a two-component product, the resin and curing agent are packaged separately
and must be mixed together just before use. Each component can be hazardous. In
a single-component product, the resin and curing agent are supplied in
pre-mixed form. Single-component systems are generally safer for end users
because the hazardous chemicals are already partly combined into less-toxic
mixtures, and because they do not evaporate as readily into the air.
Solid adhesives, such as powder, preforms or film, are the least toxic because
they have very low vapor pressures. However, they may still present a hazard
when heated to a more volatile state to cure.
Accessory materials and equipment used to process and apply adhesives or
sealants can also be hazardous. Solvents that are used to either dilute the
product or to clean equipment after use can be both dangerous and toxic. Mixing
equipment can run at very fast speeds, and caution should be used when
operating such equipment. Curing equipment often runs at high temperatures,
which can create a fire or explosion hazard.
Because of the variety of materials, equipment and processes used with adhesive
and sealant systems, the following information provides only a general guide.
For more detailed information, contact the manufacturer of each material used.
Effects of Exposure to Adhesive and Sealant Materials
All product components,
solvents, chemical treatments and the like must be handled in a manner that
prevents toxic exposure to the workforce. Methods and facilities must be
provided to ensure that the maximum acceptable concentrations of hazardous
materials are never exceeded. These values are prominently displayed on the
material’s Material Safety Data Sheet (MSDS), which must be maintained and
readily available for the workforce.
There is no medical or laboratory test that can quickly measure the amount of a
foreign material in the human body, and most of the chemicals found in adhesive
and sealant systems are not stored in the body. Regional environmental
regulators will set and enforce workplace exposure limits. These limits are
generally set for some, but not all, of the components that one may come into
Table 1 shows legally permissible exposure limits (PEL) for some chemicals
commonly found in epoxy adhesive systems. These particular levels have been set
by the California Division of Occupational Safety and Health (Cal/OSHA), though
it bears mentioning that maximum permissible exposure limits may change from
region to region. Also, an individual’s exposure may be above the PEL at times,
though requirements can be met if the individual’s exposure level is below the
PEL value at other times, thus ensuring that the average exposure for any
eight-hour work shift is not greater than the PEL for the specific chemical.
PELs are measured as parts of
chemical per million parts of air (ppm). The chemicals in adhesive and sealant
systems can affect health when they come into contact with the skin, or if they
evaporate and form a mist or vapor in the air. The main effects of overexposure
are irritation of the eyes, nose, throat, and skin; skin allergies; and asthma.
Solvent additives and other high-vapor-pressure materials can cause other
effects, such has headaches, dizziness, and confusion. The effects of these
chemicals on various parts of the human body are summarized in the Chart.
Materials Used and Their Effect on Health and Safety
The main components of adhesive
and sealant materials may be hazardous and/or affect the health of those who
come into contact with them. In general, these products have hazardous
properties but can be handled safely. The hazards associated with the specific
product being handled depend upon the nature of the components.
Because different material components have different properties and health and
safety characteristics, one should always try to find out what chemicals are in
the products that are being used. This can be done by consulting the specific
An MSDS lists the hazardous chemical contents of a product, describes its
health and safety hazards, and details methods for its safe use, storage, and
disposal. It also includes information on fire and explosion hazards,
reactivity, and first aid, and lists procedures for handling leaks and spills.
Generally, environmental regulations require that an employer have all MSDSs
for any workplace product that contains hazardous substances, and these must be
made available to employees on request. MSDSs can also be obtained from the
manufacturer of the material, or sometimes over the Internet.
Most liquid resins can be mild to moderate irritants to the skin, eyes and
mucous membranes. The irritant potential is increased by their sticky nature,
which tends to lead to prolonged skin contact. These resins are generally
mild-to-moderate dermal (skin) sensitizers in susceptible individuals.
Solid resins are not readily absorbed through the skin and present a low risk
of skin irritation. Direct contact with solutions of these resins can cause
mild-to-moderate irritation of the skin and eyes, principally because the
solvents remove the protective layer of fat on the skin’s surface. When crushed
into a fine powder, most resins should be considered an irritant dust, and
inhalation and skin contact should be avoided. Solid resins are generally
considered to be low-to-mild sensitizers.
Resins that are modified by the addition of reactive diluents or solvents can
be more serious irritants. These resins should be handled with the same
precautions used with chemical solvents. Their sensitizing potential tends to
increase with decreasing molecular weight. Components with significant
volatility could cause irritation to skin, eyes and the respiratory tract, but
inhalation usually is not a hazard, except under certain conditions of use,
such as heating, spraying, or applications with large surface areas.
Reactive curing agents are generally more of a health hazard than unmodified
resins. Catalytic-type curing agents are difficult to generalize because of
differences in chemical makeup. Specific information on these, as well as all
materials used in adhesives and sealants, should be requested from the
manufacturer prior to use.
Certain curing agents, such as aliphatic amines, cycloaliphatic amines and
anhydrides, may cause irritation or damage to the skin, eyes, and lungs. Other
curing agents may be considered to be skin sensitizers. Certain curing agents
may absorb through the skin and cause damage to organs, such as the liver, and
interfere with the blood’s ability to carry oxygen.
Solvents commonly used in adhesive or sealant applications present a flammability
hazard. In addition, these solvents present other special health hazards.
Contact with solvents will cause “de-fatting” and drying of the skin, which
increases the chance of skin irritation. Some solvents are absorbed directly
though the skin, and absorption may be increased if the skin is abraded or
irritated. These solvents also have the ability to dissolve other epoxy resin
system chemicals and carry them through the skin. The inhalation of solvent
vapors or mists may cause respiratory irritation and depression of the central
The hazardous nature of fillers depends on the type of filler and how it’s
handled in production. Some inorganic fillers are considered to be essentially
nonhazardous. However, dusts of glass, silica-bearing powders and powdered
metals may present a serious risk of inhalation and/or explosion. The explosion
hazard is due to the high surface areas of finely divided fillers.
Fillers present a potential inhalation and dermal contact hazard. They can
cause mechanical damage to the skin, which may aggravate the irritant effect of
other chemicals and additives. When fillers are handled in a liquid matrix or
in a cured matrix, their inhalation hazard is low. However, inhalation exposure
to fillers can occur when they are handled in the dry state or when machining
or grinding cured products. Inhalation exposure to fillers such as crystalline
silica or fiberglass may result in delayed lung injury. Asbestos fillers have
long been abandoned from use for these reasons.
Potential exposure to
chemicals will vary with the type of process or task. Closed systems with
engineering controls are used to prevent workers from overexposure. However,
occasionally open areas with limited controls are encountered, and the potential
for exposure increases.
Dermal exposure is the most likely route of exposure; this generally occurs in
tasks involving hand contact with the adhesive or sealant. However, if certain
volatile components or solvents are being used, inhalation exposure may also be
a problem. Inhalation and dermal risks are most significant with any task
involving the use of solvents or curing agents. The risk of exposure from the
ingestion of materials is generally minimal.
Several of the more common processes that occur with the formulation and
end-use of adhesives and sealants are described in Table 2. Potential exposure
risks for these processes are characterized by dermal, inhalation or ingestion.
Comments regarding the effect of a given process on potential exposure are also
Workplace Practices to Limit Exposure
A number of practices can be
used to limit the exposure to chemicals commonly used in formulating and
processing these products. Generally, employers are required to protect workers
from exposure to any hazardous chemical over the permissible exposure level.
Chemical manufacturers, formulators and distributors must make health, safety,
and environmental protection an integral part of the product lifecycle. Several
guides have been created to help develop and implement policies and practices
that ensure protection through the product lifecycle. For example, the Epoxy
Resin Formulators Group of the Society of Plastics Industry has developed an
The workplace processes that can be used to limit or prevent potential exposure
to hazardous chemicals usually include the following.
- Engineering controls
- Protective equipment and clothing
- Good housekeeping
Companies that formulate or use adhesives or sealants should conduct continuing
training programs for all personnel involved in the handling of epoxy materials
or those who may come in contact with them. Planning for employee and plant
safety has value only when it is interpreted and practiced by the people
Continued instruction of all employees must be given concerning the
consequences of contact, as well as the precautions necessary for safe operation
(storage, handling, compounding, packaging and disposal). The training program
should address the following items at minimum.
- Labels, MSDSs and product information bulletins
- Health and safety hazards
- Emergency procedures
- First aid
- Workplace controls
- Personal protective equipment
- Safe handling procedures
Specific elements in the training of individuals to work with chemicals should
include several areas that are unique to adhesives and sealants.
When flammable products or solvents are used, they must be stored, handled and
used in a manner preventing any possibility of ignition. Proper safety
containers, storage areas and well-ventilated workplaces are required.
Certain adhesive materials are hazardous when mixed together. Epoxy and
polyester catalysts, in particular, must be well understood, and the user
should follow the manufacturers’ recommended procedure for handling and mixing.
Certain unstabilized solvents, such as trichloroethylene and perchloroethylene,
are subject to chemical reaction on contact with oxygen or moisture. Only
stabilized grades of solvents should be used.
Certain adhesive systems, such as heat-curing epoxy and room-temperature curing
polyester, can develop very large exothermic reactions upon mixing. The
temperature generated during this exotherm is dependent on the mass of the
materials being mixed. Exotherm temperatures can get so high that the adhesive
will catch fire and burn. Adhesive products should always be applied in thin
bond lines to minimize the exotherm until the chemistry of the product is well
understood. Never use elevated-temperature-curing sealants or adhesives for
casting or for application in excessively thick cross-sections without first
consulting the manufacturer. These materials are formulated to be applied and
cured in thin cross-sections so that the heat generated by exotherm can easily
Safe equipment and proper operation are crucial to a workplace. Sufficient
training and safety precautions must be established in the factory before any bonding
process is activated.
The most effective way to reduce hazardous chemical exposure is to use a safer
chemical, if available. Unfortunately, this is also one of the most difficult
methods of control.
Substitution is a difficult task because the specific materials will control
the application and end-use properties of the adhesive or sealant. Any
substitution of material generally requires that the complete product be
re-verified with production and prototype service testing. Of course, the
health and safety issues of any alternative material must be carefully
considered to ensure that it is actually safer.
Several elements should be considered when looking for a substitute material or
when selecting materials for original formulation. For example, one may be able
to choose an alternative system that:
- Contains higher-molecular-weight resins and has a lower vapor
pressure. High-molecular-weight resins are less likely to be vaporized and
transported through air streams, thus causing inhalation problems.
- Has a reduced solvent content or is solvent-free to minimize health
effects due to solvents. There have been significant recent efforts in
developing waterborne and UV/EB-cured adhesives for the purpose of reducing or
- Does not contain fillers in a dry form.
In addition to training, engineering controls are the most effective way of
minimizing exposure to harmful chemicals. Engineering controls include process
or equipment modifications that reduce the amount of potentially hazardous
materials to which an employee may be exposed. Isolation and ventilation are
the primary methods of control. Engineering controls also include maintenance,
policing and changing when necessary for work practices.
Isolation, or enclosure of a process or work operation to reduce exposure, is a
standard industrial hygiene method. The use of suspect resins, for example,
could be isolated to designated areas that are separate from the remainder of
the plant. Examples of isolation include spray booths, enclosed curing and
mixing rooms, and glove-bag systems. Isolation is an ideal method for use with
adhesives systems since the isolation can also prevent unwanted materials
(generally contamination [e.g., moisture, mold release, dust]) from getting to
the work piece and degrading the strength of the finished joint.
Ventilation is the standard method of controlling exposure to airborne vapors
of resins and solvents. Ventilation involves controlling air flow to reduce
exposure. Local exhaust ventilation systems capture the contaminant at the
source and either filter or remove it from the work area. The ventilation
system needs to be designed so vapors, aerosol and dusts are pulled away from -
and not into - workers’ breathing zones. A constant supply of fresh,
non-contaminated air should be available at all times.
Examples of local exhaust ventilation system include draw-down exhaust tables,
slot hoods, dust-extraction systems and portable vapor and dust collectors.
Care must be taken to ensure that the ventilation systems are used and
maintained as designed. The condition of the filters and the air-flow rate
should be checked periodically, as well as the condition of the duct work,
motors, belts, etc.
Certain work processes, such as heating or curing, can be isolated, enclosed or
automated to reduce exposure. Heating during compounding or cure can cause
components to evaporate more quickly. The higher the temperature, the greater
the amount of contaminant released into the air. Therefore, the lowest possible
temperatures for performing the functions should be used, and adequate
ventilation should be maintained around these areas. Electrostatic spray
systems can reduce the amount of workplace contamination and waste from sprayed
Equipment and Clothing
When engineering controls cannot sufficiently reduce exposures, protective
personal equipment and clothing must be used. An industrial hygienist or
another knowledgeable person should be consulted to ensure that the equipment
is appropriate and is used correctly. The most common forms of personal
protective equipment include eye protection, gloves, clothing and respirators.
Eye protection can be provided by safety glasses with side shields, chemical
goggles, full-face respirators and face shields with glasses or goggles. The
type of eye protection required will depend on the hazard assessment of the
specific application. When there is danger of vapor, aerosol or dust exposure,
such as when mixing, spraying, or pumping materials under pressure, the eyes
must be protected by chemical goggles at a minimum.
Cotton, leather or rubber gloves should be worn to protect the hands from
repeated contact with the materials. There is not much acute danger with many
of these systems, but repeated contact over long periods of time can sensitize
the skin and produce unpleasant reactions such as itchiness, redness, swelling,
Selecting the appropriate glove material involves matching the characteristics
of the glove with the requirements of the production task. Glove resistance
characteristics can be classified as either physical or chemical. Physical
characteristics of production tasks are dexterity, wet grip and cut, tear,
puncture, and abrasion resistance. Chemical characteristics depend upon the
aggressiveness of the resins, solvents and other materials being used.
The most common chemical characteristics to consider when selecting protective
gloves are permeation and degradation. For example, glove materials that
provide excellent resistance to epoxy resins, curing agents and solvents
commonly used with epoxies are ethyl vinyl alcohol laminate and butyl rubber. Nitrile
and neoprene gloves have less resistance to solvents and certain curing agents.
Gloves should be replaced whenever signs of degradation are noticed. Typical
signs of chemical degradation include swelling, softening, cracking or
discoloration of the glove material.
Similarly, protective clothing should be made of materials that will provide
protection from the chemicals in the product or chemicals used in associated
processing. The same chemical resistance characteristics that apply to gloves
apply to chemically resistant clothing. An assortment of disposable aprons,
coveralls, lab coats and sleeves is also available.
Respirators come in two primary types: air-supplied or air-purifying.
Air-supplied respirators provide the user with an external supply of clean
breathing air, while air-purifying respirators make use of adsorbents and
fillers to remove chemical vapors and particulates from the air. Respirators
are generally required where solvent or dust levels are high, where irritating
odors are present, and where materials that are respiratory sensitizers are
Personal hygiene is also important in minimizing exposure levels to harmful
chemicals. Contaminated clothing should be immediately removed and laundered or
discarded. Absorbent articles of clothing, such as belts and shoes, are
particularly troublesome. Provisions should be made for storage, laundering and
disposal of contaminated clothing.
When one comes into contact with a resin or any of the chemicals used with
adhesives or sealants, he or she should immediately wash off any components
that touch the skin. Do not use solvents for personal cleanup; use soap and
water or a commercial cleaner. Particular attention needs to paid to
fingernails and the area around the nail bed. After washing, a skin conditioner
or lotion should be used to help keep the skin in good condition.
Good housekeeping also dictates that eating, drinking and smoking facilities be
maintained separate from the workplace. Refrigerators and freezers used for the
storage of epoxy adhesive components must not be used to store food or drinks.
First aid should be an important component of any training program. First-aid
materials and facilities should also be maintained in a nearby but isolated
area, away from hazardous operations and materials. The specific type of first
aid for a given problem is generally indicated on the MSDS.
If skin or clothing becomes contaminated with chemical components, remove the
contaminated clothing and wash the exposed area with soap and water for at
least 15 minutes. Seek medical attention immediately if irritation or other
If the eyes become contaminated, they should be washed out with copious
quantities of clean water, and medical advice should be sought. Eye-wash
facilities should be provided in areas of the workplace where such accidents
have a potential to occur. Medical advice should be sought immediately after
washing the eyes.
If respiratory distress is experienced, immediately remove the individual from
the contaminated area to fresh air. If the person is not breathing, artificial
respiration should be provided. Again, seek immediate medical attention. If
breathing is difficult, transport the individual to a medical care facility for
treatment and, if available, give the individual supplemental oxygen.
If a chemical is accidentally ingested, seek immediate medical attention. If
the victim is conscious, give them water. Do not induce vomiting unless
directed to do so by a physician, or as directed by the MSDS. Emergency
Emergency procedures are generally required with respect to flammability, spill
contamination and cleanup of adhesives and sealants.
Most resinous materials are organic and will burn when sufficient heat and
oxygen are supplied. A common measure of a material’s flammability is its
flash-point temperature. This value indicates the minimum temperature at which
flammable conditions are produced in controlled laboratory experiments at
atmospheric pressure. Solvents, diluents and other materials used with
adhesives and sealants commonly increase the hazard of flammability and/or
Fires involving adhesives and sealants can generally be extinguished with foam,
dry powder or carbon dioxide. Water is not normally an effective extinguishing
agent for organic resins. When burning, some resins give off toxic byproducts,
such as carbon monoxide gas. Therefore, avoid breathing fumes or gases
resulting from a fire. Firefighters should use an organic vapor respirator or
self-contained breathing apparatus.
Any spills should be cleaned up immediately. The immediate concern in any spill
is to protect personnel, prevent a possible fire hazard and contain the spill until
it is cleaned up. Persons engaged in spill cleanup should be protected from
vapors and from skin contact by wearing the appropriate protective clothing and
equipment. Persons engaged in spill cleanup should also be aware of proper
disposal techniques for the materials in question.
For small spills, apply an absorbent material or a high-surface-area material
such as sand to the spill. Shovel the mass with absorbed epoxy into a suitable
container. The residue should then be cleaned with hot, soapy water or steam.
For material spills containing solvent, keep spark-producing equipment away
form the spill site and shut off or remove all potential sources of ignition.
For larger spills, employees should stay upwind of the spill to avoid
inhalation of components. Evacuate and rope off the spill area, and shut off
all potential sources of ignition. The spill should be contained with a dike,
and excess material should be collected in suitable containers for final
disposal. Hot, soapy water or steam may be used for cleaning up the residue
from floors or equipment. The use of solvents during cleanup should be avoided
because of their hazardous nature.
The spilled material must be prevented from entering sewers or drains, or any
body of water, including rivers, streams, or lakes. Flexible emergency dikes,
sometimes known as “pigs,” can be used to prevent spills from entering sewers
and drains. If spilled materials do enter drains or waterways, notify local
Dealing with Environmental Regulations
In the adhesives and sealants
industry, which has historically trailed other industries in regulation,
environmental regulations have spurred significant development on several
fronts. Some, however, see this as a plague of regulations and added cost.3
Whatever your position on the matter, your strategic business plan should be
adjusted to respond to these factors.
When setting strategy, it is important to look at the big picture. A number of
alternative materials and processes should be considered when trying to reduce
emissions or waste. However, there are several erroneous assumptions made by
companies when using government regulations as the sole basis for strategy
development (see Table 3).
Traditional factors must also be considered when setting business strategy.
These include assessment of competencies relative to growth opportunities. A
“SWOT” (strength-weakness-opportunities-threats) analysis will aid in this
activity. Above all, the strategy must be aimed at providing a sustainable
Strategic plans must be routinely evaluated to address the best opportunities
and market segments for growth. For those with the highest priorities, one must
identify: 1.) the potential to deliver and capture value; 2.) alternative paths
to market; 3.) alternatives or the elimination of processing steps and the
reduction in scrap or waste (both for the supplier and the customer); and 4.) a
complete value chain solution that takes into consideration how one can provide
value to both suppliers and customers that benefits everyone. In most cases,
this traditional approach to developing a strategic plan will, out of
necessity, also incorporate environmental factors.