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Some contact adhesives require as long as 24 hours to dry before the surfaces are to be held together. 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.
Anaerobic adhesives cure when in contact with metal, in the absence of oxygen. Multi-component adhesives harden by mixing two or more components which chemically react.
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This reaction causes polymers to cross-link  into acrylics, urethanes, and epoxies - See thermosetting polymers. There are several commercial combinations of multi-component adhesives in use in industry. Some of these combinations are:. 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 PMFs are adhesives that are mixed, deaerated, packaged, and frozen.
One-part adhesives harden via a chemical reaction with an external energy source, such as radiation , heat , and moisture. 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.
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When heat is applied the components react and cross-link. This type of adhesive includes thermoset epoxies , urethanes , and polyimides. 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 urethanes.
Natural adhesives are made from organic sources such as vegetable starch dextrin , natural resins, or animals e. 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 sack production, paper tube winding, and wallpaper adhesives.
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 MDF use synthetic thermosetting resins.
SPECS & DESCRIPTION
Synthetic adhesives are based on elastomers , thermoplastics , emulsions , and thermosets. Examples of thermosetting adhesives are: epoxy , polyurethane , cyanoacrylate and acrylic polymers. The first commercially produced synthetic adhesive was Karlsons Klister in the s. Applicators of different adhesives are designed according to the adhesive being used and the size of the area to which the adhesive will be applied. The adhesive is applied to either one or both of the materials being bonded.
The pieces are aligned and pressure is added to aid in adhesion and rid the bond of air bubbles. Common ways of applying an adhesive include brushes, rollers, using films or pellets, spray guns and applicator guns e. All of these can be used manually or automated as part of a machine. For an adhesive to be effective it must have three main properties. It must be able to wet the substrate.
Adhesion, the attachment between adhesive and substrate may occur either by mechanical means, in which the adhesive works its way into small pores of the substrate, or by one of several chemical mechanisms. The strength of adhesion depends on many factors, including the means by which it occurs. In some cases, an actual chemical bond occurs between adhesive and substrate.
In others, electrostatic forces, as in static electricity, hold the substances together. A third mechanism involves the van der Waals forces that develop between molecules. A fourth means involves the moisture-aided diffusion of the glue into the substrate, followed by hardening. The quality of adhesive bonding depends strongly on the ability of the adhesive to efficiently cover wet the substrate area. This happens when the surface energy of the substrate is greater than the surface energy of the adhesive.
However, high strength adhesives have high surface energy. Thus, their application is problematic for low energy materials such as polymers. To solve this problem, surface treatment can be used to increase the surface energy as a preparation step before adhesive bonding. Importantly, surface preparation provides a reproducible surface allowing consistent bonding results. The commonly used surface activation techniques include plasma activation , flame treatment and wet chemistry priming.
There are several factors that could contribute to the failure of two adhered surfaces. Sunlight and heat may weaken the adhesive. Solvents can deteriorate or dissolve adhesive. Physical stresses may also cause the separation of surfaces. When subjected to loading, debonding may occur at different locations in the adhesive joint.
The major fracture types are the following:. Cohesive fracture is obtained if a crack propagates in the bulk polymer which constitutes the adhesive. In this case the surfaces of both adherends after debonding will be covered by fractured adhesive.
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The crack may propagate in the center of the layer or near an interface. For this last case, the cohesive fracture can be said to be "cohesive near the interface". Adhesive fracture sometimes referred to as interfacial fracture is when debonding occurs between the adhesive and the adherend. In most cases, the occurrence of adhesive fracture for a given adhesive goes along with smaller fracture toughness.
As a general design rule, the material properties of the object need to be greater than the forces anticipated during its use. The engineering work will consist of having a good model to evaluate the function. For most adhesive joints, this can be achieved using fracture mechanics. Concepts such as the stress concentration factor and the strain energy release rate can be used to predict failure.
In such models, the behavior of the adhesive layer itself is neglected and only the adherents are considered. As the loads are usually fixed, an acceptable design will result from combination of a material selection procedure and geometry modifications, if possible.
In adhesively bonded structures, the global geometry and loads are fixed by structural considerations and the design procedure focuses on the material properties of the adhesive and on local changes on the geometry. Some glues and adhesives have a limited shelf life. Exposure to heat, oxygen, water vapor, freezing, etc.
From Wikipedia, the free encyclopedia. For other uses, see Glue disambiguation. For the band, see Adhesive band. Casein glue preparation. This section does not cite any sources. Please help improve this section by adding citations to reliable sources. Unsourced material may be challenged and removed. August Learn how and when to remove this template message.
See also: List of glues. Main article: Pressure-sensitive adhesive. Main article: Hot-melt adhesive. Main article: Adhesion. Retrieved 9 April London: Chapman and Hall. Journal of Archaeological Science.
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Scientific Reports. Bibcode : NatSR Bibcode : PNAS.. Current Anthropology. Amsterdam: Elsevier. Pizzi Handbook of Adhesive Technology 2nd ed.