{"id":92,"date":"2023-09-22T10:16:51","date_gmt":"2023-09-22T09:16:51","guid":{"rendered":"https:\/\/www.elastomer.kuraray.com\/in\/2023\/09\/22\/what-are-polymer-adhesives\/"},"modified":"2025-03-24T14:52:00","modified_gmt":"2025-03-24T11:52:00","slug":"polymer-adhesives","status":"publish","type":"post","link":"https:\/\/www.elastomer.kuraray.com\/in\/blog\/polymer-adhesives\/","title":{"rendered":"What are polymer adhesives?"},"content":{"rendered":"\n
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What are polymer adhesives?<\/h1>\n\n\n\n

Author<\/p>

Robin Conrad<\/a><\/p><\/div><\/div>\n\n

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How do polymer adhesives work?<\/h2>\n\n\n\n

Polymer adhesives make use of the two forces that are at play in any bonding process: Adhesion and cohesion.<\/p>\n<\/div>\n<\/div>\n\n\n\n

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Adhesion and cohesion<\/h3>\n\n\n\n

Adhesion<\/strong> is the force that sticks the molecules of two different substances together. For example, when a water droplet sticks to the surface of a glass, that is caused by the adhesive forces between the water molecules and the glass molecules.<\/p>\n<\/div>\n\n\n\n

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Water droplet sticking to the surface of glass (adhesion)<\/figcaption><\/figure>\n<\/div>\n<\/div>\n\n\n\n
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Cohesion<\/strong> is the force that keeps the same type of molecules together. For example, when you fill a glass of water all the way to the top and carefully add a few more drops, you can observe the water forming a dome-like structure above the rim of the glass. This phenomenon is called surface tension and caused by the cohesive forces of the hydrogen bonds between the water molecules. Due to these cohesive forces, light objects with a large surface area can stay afloat on the surface of the water such as water striders or this paperclip. Cohesion also explains why rain takes the shape of droplets rather than a fine mist.<\/p>\n<\/div>\n\n\n\n

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Water surface tension (cohesion)<\/figcaption><\/figure>\n<\/div>\n<\/div>\n\n\n\n
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Polymer adhesives need both adhesion and cohesion to work: If the adhesive forces are too weak the glue won\u2019t stick to the substrate in place (adhesive failure). If the cohesive forces are too weak the glue won\u2019t hold itself (cohesive failure).<\/p>\n<\/div>\n\n\n\n

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Adhesion and cohesion<\/figcaption><\/figure>\n<\/div>\n<\/div>\n\n\n\n
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Bonds<\/h3>\n\n\n\n

There are three types of bonds: Electrostatic bonds, mechanical bonds and chemical bonds.<\/p>\n\n\n\n

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Electrostatic bonds<\/h4>\n\n\n\n

Electrostatic bonds rely on \u201cadsorption\u201d forces between ions, i.e. charged molecules of the glue and inversely charged molecules of the substrate that attract each other like magnets. These forces are also called \u201cvan der Waals\u201d forces after the researcher who discovered them.<\/p>\n\n\n\n

Electrostatic bonds are relatively weak. The adhesion will only work if the glue is spread over the substrate with good surface wetting and the surfaces are very close to each other.<\/p>\n<\/div>\n\n\n\n

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Electrostatic and mechanical bonds are relatively weak, while chemical bonds are relatively strong.<\/figcaption><\/figure>\n<\/div>\n<\/div>\n\n\n\n
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Mechanical bonds<\/h4>\n\n\n\n

Mechanical bonds rely on the adhesive entering holes in the surface of the substrate to flow in or protrusions to cling onto. Such bonds are more effective if the substrate has a particularly textured or porous surface.<\/p>\n<\/div>\n<\/div>\n\n\n\n

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Chemical bonds<\/h4>\n\n\n\n

Chemical bonds rely on a chemical reaction between the molecules of the adhesive and the molecules of the substrate. This requires the adhesive and the substrate to be chemically compatible with each other, or else no reaction will occur.<\/p>\n\n\n\n

If the substances are compatible, they will form a very strong chemical bond compared to the much weaker electrostatic bonds.<\/p>\n\n\n\n

In some cases, otherwise incompatible chemicals can still chemically bond indirectly through the use of a coupling agent.<\/p>\n<\/div>\n<\/div>\n\n\n\n

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Good to know<\/h4>\n\n\n\n

Coupling agents have a similar role as compatibilizers in the sense that both improve the interactions between two different substances. However, coupling agents improve the bond ability while compatibilizers improve the miscibility.<\/p>\n<\/div><\/div>\n<\/div>\n\n\n\n

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Thermoplastic adhesives vs. thermoset adhesives<\/h2>\n\n\n\n

There are many ways to categorize adhesives. An important distinction to be made is between thermoplastic adhesives and thermoset adhesives based on their molecular structure.<\/p>\n<\/div>\n<\/div>\n\n\n\n

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Thermoplastic adhesives<\/h3>\n\n\n\n

Thermoplastic adhesives provide strong adhesion at normal temperatures and can be melted and reworked without degradation.<\/p>\n\n\n\n

Examples include:<\/p>\n\n\n\n