Editing Adhesive (section)

==Types==
{{See also|List of glues}}
Adhesives are typically organized by the method of adhesion. These are then organized into reactive and non-reactive adhesives, which refers to whether the adhesive [[chemical reaction|chemically reacts]] in order to harden. Alternatively they can be organized by whether the raw stock is of natural, or synthetic origin, or by their starting [[phase (matter)|physical phase]].<ref>{{Cite web|url=https://roofonline.com/mil-hdbk-691b-department-of-defense-military-standardization-handbook-adhesive-bonding|title=MIL-HDBK-691B - Department of Defense - Military Standardization Handbook - Adhesive Bonding|page=47|website=Roof Online|access-date=2020-05-08|archive-date=1 August 2020|archive-url=https://web.archive.org/web/20200801052433/https://roofonline.com/mil-hdbk-691b-department-of-defense-military-standardization-handbook-adhesive-bonding|url-status=live}}</ref>

=== By reactiveness ===
====Non-reactive====
=====Drying=====
There are two types of adhesives that harden by drying: ''solvent-based adhesives'' and ''polymer dispersion adhesives'', also known as ''emulsion adhesives''. Solvent-based adhesives are a mixture of ingredients (typically [[polymer]]s) dissolved in a [[solvent]]. [[Polyvinyl acetate|White glue]], contact adhesives and [[rubber cement]]s are members of the ''drying adhesive'' family. As the solvent evaporates, the adhesive hardens. Depending on the chemical composition of the adhesive, they will adhere to different materials to greater or lesser degrees.

Polymer dispersion adhesives are milky-white dispersions often based on [[polyvinyl acetate]] (PVAc). They are used extensively in the woodworking and packaging industries. They are also used with fabrics and fabric-based components, and in engineered products such as loudspeaker cones.

=====Pressure-sensitive=====
{{Main|Pressure-sensitive adhesive}}
''Pressure-sensitive adhesives'' (PSA) form a bond by the application of light pressure to bind the adhesive with the adherend. They are designed to have a balance between flow and resistance to flow. The bond forms because the adhesive is soft enough to flow (i.e., "wet") to the adherend. The bond has strength because the adhesive is hard enough to resist flow when stress is applied to the bond. Once the adhesive and the adherend are in close proximity, molecular interactions, such as [[van der Waals force]]s, become involved in the bond, contributing significantly to its ultimate strength.

PSAs are designed for either permanent or removable applications. Examples of permanent applications include safety labels for power equipment, foil tape for [[HVAC]] duct work, automotive interior trim assembly, and sound/vibration damping films. Some high performance permanent PSAs exhibit high adhesion values and can support kilograms of weight per square centimeter of contact area, even at elevated temperatures. Permanent PSAs may initially be removable (for example to recover mislabeled goods) and build adhesion to a permanent bond after several hours or days.

Removable adhesives are designed to form a temporary bond, and ideally can be removed after months or years without leaving residue on the adherend. Removable adhesives are used in applications such as surface protection films, [[masking tape]]s, bookmark and note papers, barcode labels, price marking labels, promotional graphics materials, and for skin contact (wound care dressings, EKG electrodes, athletic tape, analgesic and trans-dermal drug patches, etc.). Some removable adhesives are designed to repeatedly stick and unstick.<ref>{{cite web|last1=Barcode|first1=Barry|title=Rubber Acrylic Adhesive Labels|url=http://www.midcomdata.com/rubber-acrylic-adhesive-labels/|website=Midcomdata|date=23 July 2014|access-date=6 August 2014|archive-date=4 March 2016|archive-url=https://web.archive.org/web/20160304085930/http://www.midcomdata.com/rubber-acrylic-adhesive-labels/|url-status=live}}</ref> They have low adhesion, and generally cannot support much weight. [[Pressure-sensitive adhesive]] is used in [[Post-it note]]s.

Pressure-sensitive adhesives are manufactured with either a liquid carrier or in 100% solid form. Articles are made from liquid PSAs by coating the adhesive and drying off the solvent or water carrier. They may be further heated to initiate a [[cross-link]]ing reaction and increase [[molecular mass|molecular weight]]. 100% solid PSAs may be low viscosity polymers that are coated and then reacted with radiation to increase molecular weight and form the adhesive, or they may be high viscosity materials that are heated to reduce viscosity enough to allow coating, and then cooled to their final form. Major raw material for PSA's are [[acrylate]]-based polymers.

=====Contact =====
{{See also|Contact adhesives}}
''Contact adhesives'' form high shear-resistance bonds with a rapid cure time. They are often applied in thin layers for use with [[laminate]]s, such as bonding [[Formica (plastic)|Formica]] to countertops, and in footwear, as in attaching outsoles to uppers. [[Natural rubber]] and [[polychloroprene]] (Neoprene) are commonly used contact adhesives. Both of these elastomers undergo [[strain crystallization]].

Contact adhesives must be applied to both surfaces and allowed some time to dry before the two surfaces are pushed together. Some contact adhesives require as long as 24 hours to dry completely before the surfaces are to be held together.<ref>{{cite web|url=http://www.thistothat.com/glue/contact.shtml|title=Contact Adhesives|website=www.thistothat.com|access-date=25 September 2006|archive-date=12 September 2006|archive-url=https://web.archive.org/web/20060912043858/http://www.thistothat.com/glue/contact.shtml|url-status=live}}</ref> Once the surfaces are pushed together, the bond forms very quickly.<ref>{{cite web| url = http://composite.about.com/library/glossary/c/bldef-c1257.htm| title = Definition of ''contact adhesive'' on About.com| access-date = 25 September 2006| archive-date = 24 October 2006| archive-url = https://web.archive.org/web/20061024171339/http://composite.about.com/library/glossary/c/bldef-c1257.htm| url-status = dead}}</ref> [[Clamp (tool)|Clamps]] are typically not needed due to the rapid bond formation.<ref>{{Cite web |title=Contact Adhesive |url=http://www.woodworkbasics.com/contact-adhesive.html |access-date=4 January 2024 |website=woodworkbasics.com}}</ref>

=====Hot=====
[[File:Stanley-Hot-Glue-Gun-GR35K.jpg|right|thumbnail|A glue gun, an example of a hot adhesive]]
{{Main|Hot-melt adhesive}}

''Hot adhesives'', also known as ''hot melt adhesives'', are [[thermoplastic]]s applied in molten form (in the 65–180&nbsp;°C range) which solidify on cooling to form strong bonds between a wide range of materials. [[Ethylene-vinyl acetate]]-based hot-melts are particularly popular for crafts because of their ease of use and the wide range of common materials they can join. A glue gun (shown at right) is one method of applying hot adhesives. The glue gun melts the solid adhesive, then allows the liquid to pass through its barrel onto the material, where it solidifies.

Thermoplastic glue may have been invented around 1940 by [[Procter & Gamble]] as a solution to the problem that water-based adhesives, commonly used in packaging at that time, failed in humid climates, causing packages to open.  However, water-based adhesives are still of strong interest as they typically do not contain volatile solvents.<ref>{{Cite journal |last1=Bhakare |first1=Madhuri A. |last2=Lokhande |first2=Kshama D. |last3=Bondarde |first3=Mahesh P. |last4=Dhumal |first4=Pratik S. |last5=Some |first5=Surajit |date=2023-02-15 |title=Dual functions of bioinspired, water-based, reusable composite as a highly efficient flame retardant and strong adhesive |url=https://www.sciencedirect.com/science/article/pii/S1385894722059010 |journal=Chemical Engineering Journal |volume=454 |pages=140421 |doi=10.1016/j.cej.2022.140421 |bibcode=2023ChEnJ.45440421B |issn=1385-8947}}</ref>

====Reactive====

=====Anaerobic=====
Anaerobic adhesives cure when in contact with metal, in the absence of oxygen.<ref>{{cite web |title=About anaerobic adhesives |publisher=ThreeBond Holdings Co. |url=https://www.threebond.co.jp/en/technical/seminar/adhesion2.html |access-date=15 September 2018 |archive-date=16 September 2018 |archive-url=https://web.archive.org/web/20180916055843/https://www.threebond.co.jp/en/technical/seminar/adhesion2.html |url-status=live }}</ref> They work well in a close-fitting space, as when used as a [[Thread-locking fluid]].

=====Multi-part=====
''Multi-component adhesives'' harden by mixing two or more components which chemically react. This reaction causes polymers to cross-link<ref>{{Cite book|url=https://books.google.com/books?id=-Y2ykcUBWZsC&q=Multi-component+adhesives+harden+by+mixing+two+or+more+components+which+chemically+react&pg=PA83|title=Plastics: in Architecture and Construction|last1=Engelsmann|first1=Stephan|last2=Spalding|first2=Valerie|last3=Peters|first3=Stefan|date=2010-01-01|publisher=Walter de Gruyter|isbn=9783034611947|language=en}}</ref> into [[Acrylate polymer|acrylates]], [[Carbamate|urethanes]], and [[Epoxy|epoxies]] {{crossreference|(see [[:Thermosetting polymer]])}}.

There are several commercial combinations of multi-component adhesives in use in industry. Some of these combinations are:
* Polyester resin & polyurethane resin
* Polyols & polyurethane resin
* Acrylic polymers & polyurethane resins

The individual components of a multi-component adhesive are not adhesive by nature. The individual components react with each other after being mixed and show full adhesion only on curing. The multi-component resins can be either solvent-based or solvent-less. The solvents present in the adhesives are a medium for the polyester or the polyurethane resin. The solvent is dried during the curing process.

=====Pre-mixed and frozen adhesives=====
''Pre-mixed and frozen adhesives'' (PMFs) are adhesives that are mixed, deaerated, packaged, and frozen.<ref>{{cite book|url=https://books.google.com/books?id=XiRdDgAAQBAJ|title=Polymeric Thermosetting Compounds|publisher=Apple Academic Press|author=Ralph D. Hermansen|page=31|date=16 March 2017|access-date=27 October 2017|isbn=9781771883153}}</ref> As it is necessary for PMFs to remain frozen before use, once they are frozen at −80&nbsp;°C they are shipped with [[dry ice]] and are required to be stored at or below −40&nbsp;°C.<ref>{{cite web|url=http://www.adhesivesmag.com/articles/93547-repackaging-options-for-two-component-adhesives-sealants-and-coatings|title=Repackaging Options for Two-Component Adhesives, Sealants and Coatings|publisher=Adhesives and Sealants Industry|date=5 January 2015|access-date=27 October 2017|archive-date=12 September 2017|archive-url=https://web.archive.org/web/20170912070031/http://www.adhesivesmag.com/articles/93547-repackaging-options-for-two-component-adhesives-sealants-and-coatings|url-status=live}}</ref> PMF adhesives eliminate mixing mistakes by the end user and reduce exposure of curing agents that can contain irritants or toxins.<ref>{{cite book|title=Adhesives Technology for Electronic Applications: Materials, Processing, Reliability|publisher=Elsevier|author1=James J. Licari|author2=Dale W. Swanson|date=2011|page=121|access-date=27 October 2017|url=https://books.google.com/books?id=ZZ5kEWU5aHoC&q=Premixed+and+frozen+adhesives+history&pg=PA28|isbn=9781437778908}}</ref> PMFs were introduced commercially in the 1960s and are commonly used in aerospace and defense.<ref>{{cite web|url=http://www.appli-tec.com/adhesives/history-of-frozen-adhesives/|title=History of Pre-Mixed and Frozen (PMF) Adhesives|publisher=Appli-tec|access-date=27 October 2017}}</ref>

=====One-part=====
''One-part adhesives'' harden via a chemical reaction with an external energy source, such as [[radiation]], heat, and [[moisture]].

[[File:Steeldive SD8205-2.jpg|thumb|A watch with a date magnifying lens ("cyclops"). The cyclops is attached with transparent UV light curing adhesive to the top of the watch crystal.]]

''Ultraviolet'' (UV) ''light curing adhesives'', also known as ''light curing materials'' (LCM), have become popular within the manufacturing sector due to their rapid curing time and strong bond strength. Light curing adhesives can cure in as little as one second and many formulations can bond dissimilar substrates (materials) and withstand harsh temperatures. These qualities make [[UV curing]] adhesives essential to the manufacturing of items in many industrial markets such as electronics, telecommunications, medical, aerospace, glass, and optical. Unlike traditional adhesives, UV light curing adhesives not only bond materials together but they can also be used to seal and coat products. They are generally acrylic-based.

''Heat curing adhesives'' consist of a pre-made mixture of two or more components. When heat is applied the components react and cross-link. This type of adhesive includes [[thermosetting polymer|thermoset]] [[epoxy|epoxies]], [[polyurethane|urethanes]], and [[polyimide]]s.

''Moisture curing adhesives'' cure when they react with moisture present on the substrate surface or in the air. This type of adhesive includes [[cyanoacrylates]] and [[polyurethane|urethanes]].
{{See also|List of polyurethane applications#Adhesives}}

===By origin===
====Natural====
Natural adhesives are made from organic sources such as vegetable [[starch]] ([[dextrin]]), natural resins, or animals (e.g. the milk protein [[casein]]<ref name="cornell">[http://www.ccmr.cornell.edu/education/ask/index.html?quid=160 CCMR – Ask A Scientist!] {{webarchive|url=https://web.archive.org/web/20110928023201/http://www.ccmr.cornell.edu/education/ask/index.html?quid=160 |date=2011-09-28 }}</ref> and hide-based [[animal glue]]s). These are often referred to as [[bioadhesives]].

One example is a simple paste made by cooking flour in water. Starch-based adhesives are used in [[corrugated board]] and [[paper bag|paper sack]] production, paper tube winding, and [[wallpaper adhesive]]s. Casein glue is mainly used to adhere glass bottle labels. Animal glues have traditionally been used in bookbinding, wood joining, and many other areas but now are largely replaced by synthetic glues except in specialist applications like the production and repair of stringed instruments. [[Albumen]] made from the protein component of blood has been used in the [[plywood]] industry. [[Masonite]], a wood hardboard, was originally bonded using natural wood [[lignin]], an [[organic polymer]], though most modern particle boards such as [[Medium-density fiberboard|MDF]] use synthetic thermosetting resins.

====Synthetic====
Synthetic adhesives are made out of [[organic compound]]s.<ref>{{cite journal | last1=Mantanis | first1=George I. | last2=Athanassiadou | first2=Eleftheria Th. | last3=Barbu | first3=Marius C. | last4=Wijnendaele | first4=Kris | author1-link=George Mantanis |title=Adhesive systems used in the European particleboard, MDF and OSB industries | journal=Wood Material Science & Engineering | volume=13 | issue=2 | date=2018-03-15 | issn=1748-0272 | doi=10.1080/17480272.2017.1396622 | pages=104–116 }}</ref> Many are based on [[elastomer]]s, [[thermoplastics]], [[emulsion]]s, and [[Thermosetting plastic|thermosets]]. Examples of thermosetting adhesives are: [[epoxy]], [[polyurethane]], [[cyanoacrylate]] and [[Acrylic resin|acrylic]] polymers. The first commercially produced synthetic adhesive was Karlsons Klister in the 1920s.<ref>{{cite web| url = http://www.nyteknik.se/nyheter/innovation/article3208149.ece| title = Ny Teknik: Sverige fastnade tack vare åsnan| access-date = 15 August 2011| archive-date = 23 July 2011| archive-url = https://web.archive.org/web/20110723225324/http://www.nyteknik.se/nyheter/innovation/article3208149.ece| url-status = dead}}</ref>