This section on science is dedicated to provide a broader understanding of how adhesives and sealants are made, the handling precautions one should take and links to further information.

History: The use of adhesives and sealants goes back to thousands of years ago but nature was there first. Read the historical section and discover how you can make your own adhesives just like the Neanderthals.

► HISTORY OF ADHESIVES, GLUES AND SEALANTS

Safety: Adhesives and sealants are safe to use when following instructions. The section on health, safety and the environment will give you an understanding why minimal precautions are necessary to avoid possible difficulties.

► HEALTH, SAFETY & ENVIRONMENT

Science & Technology: Have you wondered why some materials stick and why some don't? This section is slightly more technical but tries to explain in layman language how adhesives and sealants work.

► UNDERSTANDING ADHESION

► MAKE YOUR GLUES AND SEALANTS

► CATEGORIES OF ADHESIVES, GLUES AND SEALANTS

► HISTORICAL GLUE FORMULARY

► FAMOUS GLUEING CASES

► SUCCESSFUL GLUEING

Glossary: The technically challenged will find in this section the meaning of some of the more specialized terms used.

► GLOSSARY OF TECHNICAL TERMS

Links: For the curious, there are other sources of information on adhesives. The managers of this site assume no responsibility for the content of other websites. If you find out that some of the links are out of date, please contact the managers.

► USEFUL LINKS

Introduction

For a long time humans have succeeded in joining or bonding materials together with several purposes in mind: home construction, tools, weapons, machines (probably quite rudimentary at the very beginning) and decoration.

As a result bonding techniques allowing binding together various substrates and elements have been developed. Adhesives (or glues) and sealants are one of them. Bonding by fusion and soldering is another as well as several other techniques like riveting, joining with mortise and tenon, ligaturing, using weights and counterweights, etc.

Bonding technologies were developed by humans first by being inspired by nature.  For example, insects, arachnids and birds are skilled at forming composites with natural fibres and their own secretions and several molluscs attach themselves strongly to rocks. We may reasonably speculate that the stickiness of birch tree tar or of latex issued from the hevea tree, eggs albumen or starch paste were soon put to use by the early humans. It’s also likely that the adhesive properties of blood were discovered a long time ago. Based on archaeological evidence, most probably the very first bonding attempts by humans are much anterior to the Neolithic period (circa 8000 B.C.), dating back to Paleolithic for which the first evidence of adhesive use has been discovered.

It is commonly accepted that the chronological evolution of adhesion knowledge acquisition is as follows:

Chronological Summary Adhesives Types and Evolution:

• 3 300 000 B.C.: Cell to cell bonding; mussels; spiders; bees and wasps; barnacles…
• 2 800 000 B.C. (Paleolithic): Birch tree tar ( first traces of use)
• 8 000 B.C. (Neolithic): Birch tree tar
• 5000 B.C. Mesopotamia (Babylon): Animal blood proteins, Plant resins (colophony) and Asphalt
• 3500 B.C. Egypt : Boiled Glues (Animal skins, etc.)
• 1500 B.C. Aztec : Animal blood and Natural rubber cement (Hevea Latex)
• 1841: Vulcanisation process >>> Synthetic adhesives development
• 1902: Bakelite
• 1921: Principles of Macromolecular Chemistry by Max Staudinger
• 1902-1940: Synthetic rubber (PolyButadiene); silicones; epoxy; polyurethanes…
• 1952: Cyanoacrylate (Super Glue)

An Ancient Art

1. Birch Tree Tar

In the Neolithic period, namely ca. 8000 BC, people frequently used a resin from birch trees to attach the heads of spears and axes.

The oldest production and use of Birch Tree Tar has been identified in Italy on the Acheulean (Lower Paleolithic) site of Campitello. This adhesive has also been used in the Middle Paleolithic, in the Mesolithic and more frequently in the Neolithic.

When the glacier man “Ötzi” was discovered, tools and pieces of clothing were found, including an axe made from yew whose blade was attached with birch pitch (adhesive) and strips of leather. 

Birch tree sap is an edible liquid collected from trees at the break of winter. Birch tar is not made from the sap, but from the bark heated in the absence of air, like charcoal. Black oil is collected at the bottom of the oven and cooled in water. Detailed recipes on how to make birch tar using readily available and inexpensive equipment are available on the internet. The oil should then be boiled down slowly in the open (because of the fumes) until it thickens, just before it carbonizes. After it solidifies, it can be stored indefinitely and melted just before use, just like modern thermoplastic glues commonly called hot melt adhesives.

Birch bark tar is a very effective adhesive with excellent resistance to humidity: it was used to seal leather seams on moccasins and boots. Not being brittle, it also has gap-filling properties like a sealant. It was extensively used to repair pottery and affix arrow points to shafts.

2. Animal Glues

In the warmer climates birch does not grow naturally and the need for alternatives developed.

There is archaeological evidence that proteins extracted by prolonged boiling and partial hydrolysis in water of skin, teeth, bones, horse hooves or tendons were used even by the Neanderthals. However, the oldest written evidence of such practices dates back to about 2000 B.C. in Egypt where their use in furniture and cabinet making probably first started.

Survival guides show how to make glue from raw hide. The hard hide must first be softened in boiling water, cut in small pieces and put back into the boiling water for several hours. After that, the remaining solids are filtered and the water is boiled down until it thickens. The thicker the solution, the faster it will dry. It can be dried up completely and if protected from humidity, it will keep for some time. Historically, hide glue was used to make composite bows.

Fish glue was invented in Ireland in the late 19^th century. Until the advent of epoxy adhesives, refined fish glue was advertised extensively for affixing metals to each other, although it may have been over promoted for that use. Its major deficiency was that after drying it remained water soluble.

Albumen from egg white is used to bond gold leaf.

Casein based glues are made by precipitating casein from milk using vinegar. The curds that form are neutralized with baking soda causing them to unclump and thicken. Low fat milk works best. Casein glue can be made into a powder by drying it first by squeezing in a towel and then in air, and finally by grinding. It will keep better in that state. Before use, mix with water to a honey-like consistency and apply. Casein glue works well on woodwork.

Waste animal blood is readily available from slaughterhouses. The adhesive component is the albumen contained in blood serum. Addition of lime and alkali to albumen-water mixtures improves adhesive properties. The plywood industry is an important user of blood-based adhesives, as they are relatively resistant to humidity once hot-pressed. Synthetic glues like melamine/ formaldehyde are today more used due to a much higher resistance to humidity and regular availability. Of course due to the growing concern for sustainable and biodegradable materials, one may speculate that the market share of animal glues may increase again until a biodegradable synthetic material is available in large volumes.

3. Mineral Glues and Cements

In Mesopotamia, natural bitumen resurgences were used to make asphalt. The volatile components of oil evaporate and leave a sticky or solid black residue. In 6000 B.C., naturally occurring asphalt was quarried and used as mortar between building stones. Later on, bitumen was used as caulking for ships, to make jewellery and to set mosaics and weapon parts. In North America, Amerindians were using asphalt to waterproof their baskets and secure arrowheads to shafts. Nowadays, asphalt is made industrially from crude oil or from coal distillation and is still used for binding insulation panels or shingles.

Historically, the first known mineral cements were extensively used by the Romans from burnt limestone, volcanic ash and pulverized brick (from clay), calcined together and then crushed. Mineral cements harden in the presence of water due to the formation of crystalline hydrates. Mortar is a combination of cement and sand while concrete is made from cement and aggregate. Cement is nearly exclusively used in construction.

By extension, dental cements are made by mixing powder and liquid together. This is where the similarity ends. The powder is a basic metal oxide and the liquid is acidic. The metal salt formed acts as the cementing matrix.

Mineral cements are not considered further in this website since many of their properties and uses are unlike most adhesives and sealants.

4. Natural Rubber

Natural rubber is made by coagulating latex sap from the Hevea tree. A stable viscous liquid is formed by mixing with hydrocarbon solvent and some alcohol. The first raincoats were made by Charles Macintosh by gluing two layers of cloth together with rubber.

The accidental discovery of rubber vulcanization with sulphur in 1841 by Goodyear overcame rubber’s propensity to soften in the presence of oil or fuel or when heated. This was the first time a natural product was chemically modified to improve its properties.

Rubber cements used to repair inner tubes in tires contain cross-linking chemicals that prevent melting in hot weather.

5. Synthetic Resins

In 1862, A. Parkes succeeded in making semi-synthetic celluloid, a mixture of nitrocellulose and of camphor. Cellulose was too brittle to be used as an adhesive.

The first totally synthetic resin was Bakelite, a thermosetting phenolic compound invented by Belgian-born Leo Baekeland in 1907. Bakelite is a hard mouldable material unsuitable as an adhesive, but the same chemistry was modified to impregnate fabrics or paper.

Nowadays particle boards and chipboards are made by binding under heat and pressure wood chips, shavings or saw dust with amino-formaldehyde resins. Since formaldehyde is classified as a potential carcinogen, any traces of unreacted residues are maintained within very strict limits.

Many new synthetic rubbers such as polychloroprene, Buna (polybutadiene) and silicones were first synthesized during and after the Second World War. Then followed epoxy resins, polyurethanes and after that methacrylate and cyanoacrylate adhesives (superglues). New drying technologies based on UV light and on electron beams were also developed to eliminate volatile solvents, requiring specially designed resins and additives.

Nature is Our Guide

The study of nature has revealed many examples of the use of adhesives that continue to be a source of inspiration.

1. Rubber latex

Good adhesive strength is dependent on the molecular weight of the binding resin. Unfortunately, higher molecular weights increase viscosity of the resins in solution making use difficult or weakening the glue’s properties. Latexes widely used today in modern paints for example were indeed invented a long time ago by nature, which indeed has shown the way of modern lattices such as acrylic paint or glue dispersions where the resin in the form of microscopic particles is mixed with water and surfactant, just like the sap of Hevea.

In the same register, there are also several other examples of adhesives or sticky material produced by plants. Probably the most known and spectacular are the sticky glues secreted by carnivorous plants. They are made of mucilage, a gluey substance produced by nearly all plants and some microorganisms. It is a polar glycoprotein and an exopolysaccharide. Nanofibres and nanoparticles were found in Drosera mucilage, probably contributing to the observed viscosity and stickiness.

2. Honey Bee hives

The naw (or hulusheng in China) is a mouth organ used in Northern Thailand. The reeds are glued to an emptied gourd with beeswax.

The wax used to build honeycombs in honey hives is applied as a liquid due to the warmth of the bee’s body, like a hot melt adhesive.

Wasps Nests: many social wasps make nests from materials collected nearby and then chewed and mixed with wood fibres. The nests are water-resistant due to the proline-rich nature of the mucoproteins in the saliva, similar to the wasps’ chitin exoskeleton, which dries irreversibly to a water repellent surface.

3. Birds’ Nests

Very well know, designed for a temporary use are the swallow nests for example. They are built with earth agglomerated by saliva which contains imucin, a glycoprotein.

The dried saliva of the White-nest Swiftlet (Aerodramus fuciphagus) and of the Black-nest Swiftlet (Aerodramus maximus) is edible and is used to make bird’s nest soup, a Chinese delicacy. The swiflets deposit interwoven strands of pure salivary laminae cement secreted by glands underneath their tongues.

4. Termites

Termite nests are sometimes attacked by other insects. Some termite species have evolved a defence mechanism where a sticky liquid is sprayed on the attackers using a frontal secretion. The liquid rapidly hardens in contact with air trapping ants and other termites. Sometimes the spraying contractions are so violent that the termites rupture themselves (autothysis).

5. Barnacles

Barnacles are known to strongly attach themselves to hard surfaces, whether rocks or ship hulls (biofouling) or whales. Barnacles produce the most durable and toughest connection in the aquatic world. These molluscs secrete polyphenolic proteins which are now being investigated for various dental and medical purposes because of their resistance to antibodies. An enzyme, polyphenol oxidase, reacts with protein with a diphenol producing tanned (insoluble) protein.

6. Geckos

Geckos attach and detach their adhesive toes in milliseconds while running up to 1 meter/second on nearly any surface. The adhesive on gecko toes differs dramatically from that of conventional adhesives. Conventional pressure-sensitive adhesives are difficult to remove after applied. In contrast, gecko toes bear angled arrays of branched, hair-like fibres (setae) formed from stiff, hydrophobic keratin that act as a bed of angled springs with an effective stiffness similar to that of pressure sensitive adhesives. Setae are self-cleaning and maintain function for months during repeated use in dirty conditions. Thus, gecko setae resist inappropriate bonding and are capable of easy and rapid attachment and detachment. According to scientists, engineered adhesive nanostructures inspired by geckos may become the glue of the future.

7. Rosin (or colophony or Greek pitch)

Rosin is a component of the pine tree exudation in response to a wound. Distilled rosin as such is a brittle material melting at around 80° to 90°C with some weak adhesion properties which are insufficient for practical binding usage. In mixture it can be used to protect trees from climbing insects or as sealing wax. By chemical transformations rosin derivatives enable synthetic modern adhesive formulations like the hot melts and contact adhesives widely used today, as well as for the prodution of paints and printing ink resins. Rosin as such is used to improve the adhesion of the bristles of the bow on the strings of the violin. The first utilsation of rosin for this purpose probably took place in Cremona (Italy) original town of Stradivarius.

8. Other Plant Adhesives

Starch extracted from many plants such as potato, rice, tapioca and the like is also useful as an adhesive although its poor resistance to humidity and mould formation are important limitations to their wider use. Starch adhesives are used to make corrugated board and wallpaper, for example. The ancient Chinese and Egyptians were quite adept at using starch-based adhesives in paper or papyrus making. When heated in water, native starch granules hydrate (absorb water), increase in size and thicken to form a viscous liquid, gel or paste. This paste can be used to bind wood and paper together. Once dried the paste becomes relatively hard while retaining some adhesives properties. One of the drawbacks is the poor resistance to humidity. Maybe some of us have already used this glue to build kites.

Sources

• THE ART OF MAKING VARIOUS KINDS OF GLUES. By M. Duhamel Du Monceau, of the Royal Academy of Sciences (1771).

• Adhesives.org
• Primitiveways.com
• Wikipedia.org

Introduction

Most countries have developed a fairly extensive legislation to identify chemical hazards and to control their uses when they can potentially put to risk human health and the environment. The legislation assumes that consumers or members of the general public are more at risk because they tend to be less educated about the hazards of the products they are using (do-it-yourself people also fall in that category). It also assumes that while professional users are potentially more exposed to adhesive ingredients from regular use, they tend to be better trained and therefore more likely to follow the necessary precautions.

Proper labeling of adhesives and sealants packaging is also a legal requirement, and manufacturers usually go beyond the minimum required to ensure safe use of their products as well as customer satisfaction. For example, the European CLP Regulation (EC) No. 1272 / 2008 on the classification, labelling and packaging of substances and mixtures provides pictogrammes and related codes signification aimed at warning about possible risks and hazards.

For obvious reasons when manufacturers have a choice between two adhesive ingredients that perform equally, they will select the less hazardous and less expensive one. However, if one is more expensive or if its hazard classification is higher, it will be necessary to consider a trade-off. Therefore, the presence of a hazardous ingredient reflected on the label's safety information, or in the product's safety data sheet (not supplied to the consumer, unlike to professional users, but available on the internet), may be necessary either for product performance or for cost reasons.

Regarding adhesives and sealants, several of the best performing are very reactive or contain organic solvents, which are linked to specific hazards. Therefore, their safe use requires a minimum understanding of these hazards and of the precautions to take during use.

Some would argue that the best precaution is to avoid using products containing hazardous ingredients, notably those that are classified as carcinogenic, toxic to reproduction, mutagenic or persistent in the environment. Given the current state of technology, they are likely to be disappointed by the results they will obtain unless the use is not demanding.

Others may also argue that the most environmentally-friendly adhesives or sealants are those derived from nature without much form of chemical transformation. That may be true for some uses, such as Gum Arabic gum for labels, but the overall performance trade-off may work out differently in practice. There are few life cycle analysis studies that would make such comparisons based on factual data.

Fortunately, most of the precautions to be taken when using adhesives and sealants are common sense:

1. Read carefully before use the information provided by manufacturers on the label
2. In case of doubt, ask the vendor or contact the manufacturer using the phone number generally provided on the label
3. Professional users should always read and understand the product's safety data sheet (called Material Safety Data Sheet or MSDS in North America)
4. Never apply an adhesive to a non-intended use
5. In particular, adhesives or sealants should never be used in contact with skin or food, or otherwise ingested unless specifically intended for skin contact or approved for food contact (ex. Gum Arabic) or medical applications (ex.: dental adhesives, bra or hosiery self-adhesives, self-adhesive bandage)

Hazard Codes and their signification

Precautionary Codes and their signification

General Safety Precautions

Fire/explosion

Substitution of chlorinated solvents (which have a low fire hazard) by other organic solvents has increased the risk of fire and/or explosion. To lower the risk (especially with aerosol products):

• Ensure good ventilation away from the work area
• Avoid sparks or open flames
• Prefer less volatile solvents if there is a choice

Inhalation Exposure

Organic solvents (acetone, methylated spirits or methanol, white spirit, etc.) are sometimes a necessary adhesive ingredient or are required for prior cleaning, or wiping excess adhesive.
Most solvents used today have a low toxicity but if exposure is prolonged, ventilation is inadequate or if the vapor concentration is high, some people may start getting dizzy or feeling sick especially if the solvent odor is strong.
Stop work immediately and ventilate area.

Dermal Exposure

Except if working with small amounts of glue, wearing gloves and protective glasses is necessary because glue cannot be easily removed by wiping or by washing with water.
Any trace of organic solvent based or solventless glue contacting the skin must be wiped off using cloth or cotton wool impregnated with solvent and then washed with soap and water. Applying a skin lotion may be necessary to restore the skin's fatty layer. This site offers tips on how to remove sticky residues using commonly available items such as peanut butter and toothpaste:

http://tipnut.com/25-helpful-items-to-remove-sticky-adhesive-goo/

Accidental contact of glue with the eye (especially glues that react with humidity such as cyanoacrylates and reactive polyurethanes) can be very dangerous and medical attention should be sought immediately.
For occasional use and delicate work latex gloves, or single use polyethylene gloves of the type used for painting jobs, are usually adequate. For heavier work the following compatibility chart should be taken into account (taken from Ansell Chemical Resistance Guide, 7th edition)

Glove Type and Common Solvent Use

Environmental Exposure

Unused glues should be given in their original packaging to chemical refuse collection points.

Given the need to lower volatile organic compounds (VOCs) emissions to the atmosphere, water-based or solventless adhesives should be preferred unless required by a specific performance need.

ABS

ABS is a thermoplastic polymer made from acrylonitrile (CH2=CH-CN), butadiene (CH2=CH-CH=CH2) and styrene (CH2=CH-C6H5). It is used to make moulded parts with a high impact resistance.

Polyvinyl acetate (PVA)

PVA is a polymer made from vinyl acetate (CH2=CH2-O-CO-CH3), usually in dispersion in water. It is used as a cement additive and in adhesives. Vinyl acetate is also polymerized with ethylene forming a copolymer called EVA (ethylene – vinyl acetate).

Acrylic

Term used to characterize a polymer made from acrylates and/or methacrylates, generally in water dispersion. Acrylic polymers are known to have good ageing properties and low yellowing. They are also used as binders in paints.

Acetone

Acetone is a volatile and flammable solvent with a strong smell, with good degreasing properties. Its chemical formula is CH3-CO-CH3.

Adhesive (from the ASC-CATIA-FEICA Adhesives and Sealants Classification Manual, 2012 Ed.)

An adhesive is a compound that adheres or bonds two or more substrates together. Adhesives may come from either natural or synthetic sources. Adhesive is a general term and includes, among others, cement, glue, mucilage, and paste. All of these terms are often used interchangeably.

Casein

Milk protein. It´s the fraction of milk that forms a skin when it is heated or boiled.

Catalysis

Term used to define conditions under which a chemical reaction is speeded up (like in a reactive glue) under similar temperature conditions. Heterogeneous catalysis uses active surfaces whereas homogenous catalysis uses a catalyst dissolved in the reactive mixture. Glues and sealants often use homogenous catalysts. For example, silicone sealants contain a small amount of tin derivatives to accelerate the reaction with humidity.

Cationic

Term used to characterize chemical groups carrying positive charges in molecules. To ensure electrical neutrality, the molecules are in the presence of anions of equal charge. The attraction between opposite charges facilitates adhesion to mineral surfaces such as teeth, for example.

Cellulose

Water-insoluble natural polymer found in plants. It is made from a chain of sugars (the repeating unit is ẞ-D-glucose). Cellulose can be chemically modified to make it water-soluble, for example in wallpaper adhesives. Cellulose is the main constituent of plants.

Cement (from the Free Dictionary)

a. A building material made by grinding calcined limestone and clay to a fine powder, which can be mixed with water and poured to set as a solid mass or used as an ingredient in making mortar or concrete.
b. A substance that hardens to act as an adhesive; glue.

Cohesion

Internal resistance to failure under external force. Contributes to maintaining the integrity of a bond.

Compound

A compound is a mixture of several chemical substances from synthetic or natural sources tailored to specific applications. It is used interchangeably with the terms "formulation", "mixture" or "preparation".

Contact Adhesive

An adhesive which is usually first coated on both sides of objects to affix to each other. After a short drying period, the objects form a strong bond when pressed together with light to moderate force.

Corona (Treatment)

Process of "cold combustion" consisting of exposing a polymer surface for a fraction of a second to an electrically ionised gas. The superficial oxidation of the polymer increases its surface tension making it easier to wet and therefore improves the adhesion to glues, paints or inks.

Curing

The chemical reaction taking place in a reactive adhesive.

Cyanoacrylate

Methyl cyanoacrylate (CH2=C(CN)-CO-O-CH3) has the property of polymerizing very quickly by a cationic mechanism in the presence of humidity. It’s the main component of cyanoacrylate glues.

Definition of Durability Classes (EN 204)

D1: Interior use, in which the moisture content of the wood does not exceed 15 %.

D2: Interior use with occasional short-term exposure to running or condensed water and/or to occasional high humidity provided the moisture content of the wood does not exceed 18 %.

D3: Interior use with frequent short-term exposure to running or condensed water and/or to heavy exposure to high humidity. Exterior use not exposed to weather.

D4: Interior use with frequent long-term exposure to running or condensed water. Exterior use exposed to weather but with protection by an adequate surface coating.

EN 14257 (WATT 91): Interior and exterior uses where the glue line could be exposed at elevated temperatures.

Emulsion

Very fine dispersion of a liquid insoluble in another liquid, stabilized with a surface-active agent (surfactant). The surfactant resides at the liquid/liquid interface preventing the less dense liquid from floating to the surface. For example, mustard’s surfactant properties help oil emulsifying in vinegar. Milk and hevea latex are examples of naturally-derived emulsions.

Epoxy

Term used to define chemical substances containing CH2OCH- groups. Epoxy resins react with amine groups forming highly cohesive polymeric networks. In two-component epoxy adhesives, the epoxy resin is mixed with an equal amount of amine-containing resin.

Ethylene

Flammable gas with sweet odour used as a raw material in the chemical industry, for example in the manufacturing of EVA or ethylene-vinyl acetate copolymer. This gas is also present in nature and serves to ripen fruit.

Fungicide

Fungicides are added to sealants used in wet or humid environments to prevent the superficial formation of moulds.

Glue

A sticky liquid preparation used to affix objects to each other.

Hot Melt

An adhesive in the solid state at room temperature, which converts to a liquid by heating during application and then solidifies again upon cooling.

Methyl Cellulose

A water-dispersible derivative of cellulose, frequently used in wallpaper adhesives.

Mucilage (from the Free Dictionary)

a. any of various, usually liquid, preparations of gum, glue, or the like, used as an adhesive.
b. a gummy or gelatinous substance present in plants.

Neoprene

Neoprene is a trade mark owned by DuPont since 1931. It is the first synthetic rubber. It is made in solution or in emulsion from chloroprene of formula CH2=CH-CCl=CH2.

Open Time

See Working Time

Paste

A thick liquid preparation used to affix objects to each other if it has adhesive properties.

Polyethylene

A thermoplastic polymer made from ethylene, a gas of formula CH2=CH2. Polyethylene is commonly made into films and is used to make bags. Its surface has a low surface tension and is generally difficult to glue. A Corona treatment increases surface activity and improves adhesion.

Polypropylene

A thermoplastic polymer made from propylene, a gas of formula CH2=CH-CH3. Polypropylene has a low surface tension making it difficult to glue unless special surface treatments are used, such as Corona. Polypropylene is used to make textile fibres (carpets, ropes, bags).

Polyurethane

Polyurethane resins are supplied either as finished products such as preformed insulating foams or as preparations containing reactive precursor chemical groups named isocyanates. When applied and in the presence of humidity, isocyanates form carbon dioxide gas. The resulting foam expands which make it particularly useful for caulking. In adhesives, isocyanates form very strong chemical bonds on some substrates such as wood.

Polyvinyl Chloride (PVC)

Chlorine-containing thermoplastic polymer, very resistant to ageing (with additives) and widely used in construction. It is used to make window frames and drain pipes. It is also used to make blood bags useful for surgery.

Pot Life

The time required for a reactive adhesive to double its viscosity.
It is an indication of working time.

Preparation

A mixture of natural and/or synthetic chemical substances. This mixture is prepared according to a formula.

Reactive Adhesive

Reactive adhesives will form strong bonds only when reacted with an external ingredient (a curative, a catalyst, moisture, a substance inactivating an inhibitor), or activated with an external energy source (light, heat, radiation).

Rolling

The operation consisting of mounting a sheet covered with adhesive by passing a roller back and forth or a brush or a sponge to the edges, to remove entrapped air.

Sealant (from the ASC-CATIA-FEICA Adhesives and Sealants Classification Manual, 2012 Ed.)

A sealant is a soft, pliable material that is used to seal cracks or joints where structural strength is not required. The sealant, initially a fluid or semi-fluid, or alternatively hot applied, placed between two opposing solid materials, becomes solid itself (by solvent evaporation, chemical reaction or both), and bonds to the surfaces to which it is applied. Thus, it accommodates joint movement without adhesion loss. The sealant purpose is to prevent excessive absorption of water, penetration of other liquids, gaseous substances, or airborne particulates. A sealant has the adhesive and cohesive properties to form a permanent seal.

Set Time

Set time is the time it takes to form an acceptable bond when two or more substrates are combined with an adhesive.

Silicone

Silicones are semi-inorganic polymers containing a silicon atom in the backbone. Their general formula is –(Si02-O)n-. Depending on their use, silicones are sold either as finished articles such as kitchenware or seals, as emulsions (haircare products) or as formed-in-use preparations such as sealants or dental mould products. Silicones are resistant to ageing but their low surface tension makes them difficult to paint or to glue. However, silicone glues are very effective in some cases.

Structural Adhesives

Structural adhesives are generally capable of making load-bearing structures; they are often stronger than the substrates being bonded.

Surfactant

Substance capable of ensuring the compatibility with water of an insoluble hydrophobic substance. Detergent surfactants work by lifting and by dispersing surface dirt.

Tack

The force necessary to separate objects coated with an adhesive immediately after contact.

Working Time or Open Time

Working time is the time after which a reactive adhesive can no longer be used. Pot life is a good indication of working time.
Open time is the time after adhesive is applied during which a serviceable bond can be made. Many factors affect open time and pot life, including temperature, substrate, adhesive, and amount of adhesive applied.