CLIL CLIL CLIL LANGUAGE IMMERSION MECHANICAL TECHNOLOGY ADHESIVES An adhesive, also known as paste or glue, is a material, usually liquid or semi-liquid, that adheres or bonds items together. Adhesives come from either natural or synthetic sources. Adhesives harden by either evaporating a solvent or by chemical reactions that occur between two or more constituents. Adhesives are useful for joining thin or dissimilar materials, minimizing weight, and providing a vibration-damping joint. The disadvantage of most adhesives is that most of them do not form an instantaneous joint, unlike many other joining processes, because the adhesive needs time to cure. 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. There are two types of adhesives that harden by drying: Solvent based adhesives are a mixture of ingredients, typically polymers dissolved in a solvent. White glue, contact adhesives and rubber cements 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 (PDA) are milky-white dispersions often based on polyvinyl acetate (PVAc). They are used extensively in the woodworking and packaging industries as well as being 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. PSAs are designed for either permanent or removable applications. Removable adhesives are designed to form a temporary bond, and ideally can be removed after months or years without leaving residue on the adherend. Some removable adhesives are designed to repeatedly stick and unstick. They have low adhesion and generally cannot support much weight. Contact adhesives are used in strong bonds with high shear-resistance like laminates, such as bonding Formica to a wooden counter and in footwear. Natural rubber and Neoprene are commonly-used contact adhesives. Contact adhesives must be applied to both surfaces and allowed some time to dry before the two surfaces are pushed together. Hot adhesives are thermoplastics applied in molten form (in the 65-180 °C range) which solidify on cooling to form strong bonds between a wide range of materials. They are particularly popular for crafts because of their ease of use and the wide range of common materials they can join. A glue gun 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. GLOSSARY to adhere: aderire barrel: serbatoio bond: legame to bond: legarsi counter: bancone crafts: artigianato 172 to cure: indurire ease: facilità fabric: tessuto glue gun: pistol per colla a caldo to harden: indurire to marry: (qui) abbinare molten: fuso rubber cement: mastice to stick: attaccare vibration-damping joint: giuntura anti vibrazioni