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Table of contents
- Adhesives: Mechanical Properties, Technologies & Economic Importance by Dario Croccolo - monsstatadbar.tk
- 1. Introduction
- Adhesives - Mechanical Properties Technologies & Economic Importance Paperback
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 adhesives PSA form a bond by the application of light pressure to marry 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. 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 forces , become involved in the bond, contributing significantly to its ultimate strength.
PSAs are designed for either permanent or removable applications. 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.
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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 tapes , bookmark and note papers, barcodes labels, price marking labels, promotional graphics materials, and for skin contact wound care dressings, EKG electrodes, athletic tape, analgesic and transdermal drug patches, etc. Some removable adhesives are designed to repeatedly stick and unstick. Pressure-sensitive adhesive is used in Post-it notes. 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-linking reaction and increase molecular weight. Major raw material for PSA's are acrylate -based polymers. Contact adhesives are used in strong bonds with high shear-resistance like laminates , such as bonding Formica to a wooden counter, 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 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. 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.
Adhesives: Mechanical Properties, Technologies & Economic Importance by Dario Croccolo - monsstatadbar.tk
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.
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.
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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.
Adhesives - Mechanical Properties Technologies & Economic Importance Paperback
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. 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. The higher the percentage is the more important the application of primer coating and the less effective the surface treatment.
The negative values indicate that the results of samples without primer were better. Comparable results were achieved by physical modification. A different exposure period might have improved the adhesive properties of the surface even more. On the other hand, it seems to be that the selected chemical surface treatment was the least effective.