Chemical Properties

Adhesives An adhesive is a substance that sticks to the surface of an object such that two surfaces become bonded.

A typical home improvement store carries many different adhesives for many different applications.

Why so many adhesives? The reason for so many adhesives has to do with how they’re formed

Depending on the type of adhesive selected, we will get different mechanical properties

Properties of Adhesives• It must "wet" the surfaces - that is it must flow out over the surfaces that are being bonded, displacing all air and other contaminates that are present.

• It must adhere to the surfaces - That is after flowing over the whole surface area it must start to adhere and stay in position and become "tacky".

• It must develop strength - The material must now change its structure to become strong or non-tacky but still adherent.

• It must remain stable - The material must remain unaffected by age, environmental conditions and other factors as long as the bond is required.

Adhesives function in multiple branches of technical engineering in which the phenomenon of adhesion appears: creating adhesive joints, sealing, applying protective or decorative coating (paint or varnish), printing, decorating and many others. Among adhesive bonding techniques these are adhesive joints which are used most often in various machine structure joints.

TYPES OF ADHESIVESAdhesive Type Sources/Properties Common Uses

Animal glue Obtained from animal byproducts such as bones, blood, and hooves

Binding of abrasives in sandpaper and other grinding materials

Casein Main protein in milk Labels on beer bottles that do not come off in ice water, yet are recyclable

Starch From corn and maize Corrugated cardboard bonding

Natural rubber Not "sticky enough" by itself but is used as an additive in other adhesives

Self-adhesive envelopes and other pressure-sensitive adhesives; adhesives that bond to substrates on contact (like tapes)

Butyl rubber/isobutylene It is elastomeric—it stretches Additive for hot-melt adhesives, window sealants, and pressure-sensitive adhesives

Amino resins Water-soluble adhesives Bonding of layers in plywood and the bonding of particles in particle board

Polyurethane A flexible adhesive Bonding soles to the bodies of shoes; also used in food packaging

Polyvinyl acetate Common "white" glue Book bindings and labelsPolyolefin/ethylene copolymer No solvents involved Hot melts

Acrylates or anaerobic adhesives Cure when air is removedAdhesive used to keep nuts tight on bolts, such as those within ATMs and heavy machinery

SiliconeBoth an adhesive and a sealant and only common adhesive that is based on silicon rather than carbon

Bathtub and shower sealants; also many car applications, such as oil pans and head gaskets

Coatings A coating, from a surface engineering point of view, is a layer of material deposited onto a substrate (surface) to enhance the surface properties for corrosion and wear protection

Coatings can also be used for decorative purposes

Example Paints and lacquers are coatings that mostly have dual uses of protecting the substrate and being decorative, although some artists paints are only for decoration, and the paint on large industrial pipes is presumably only for the function of preventing corrosion.

Factors Affecting Coating Choice Factors affecting the choice of a coating include service environment, life expectancy, substrate material compatibility, component shape and size, and cost.

A major consideration for most coating processes is that the coating is to be applied at a controlled thickness. Using a simple brush for painting a wall, to using some very expensive machinery to apply coatings in the electronics industry are examples of this.

A further consideration for 'non-all-over' coatings is that control is needed as to where the coating is to be applied. A number of these non-all-over coating processes are printing processes.

Typical examples of functional coatings are self-cleaning, anti-static, anti-reflective and anti-bacterial

Typical expectations of functional coatings include durability, reproducibility, easy application and cost effectiveness, and environmental friendliness.

Uses of Coatings Adhesive – adhesive tape, pressure-sensitive labels, iron-on fabric

Changing adhesion properties◦ Non-stick PTFE coated- cooking pans◦ Release coatings e.g. silicone-coated release liners for many self-adhesive products◦ primers encourage subsequent coatings to adhere well (also sometimes have anti-corrosive properties)

Optical coatings◦ Reflective coatings for mirrors◦ Anti-reflective coatings e.g. on spectacles◦ UV- absorbent coatings for protection of eyes or increasing the life of the substrate◦ Tinted as used in some coloured lighting, tinted glazing, or sunglasses

Catalytic e.g. some self-cleaning glass

Light-sensitive as previously used to make photographic film

Uses of Coatings Protective

◦ Most paints are to some extent protecting the substrate◦ Hard anti-scratch coating on plastics and other materials e.g. of titanium nitride to reduce scratching, improve wear

resistance, etc.◦ Anti-corrosion

◦ Underbody sealant for cars◦ Many plating products

◦ Waterproof fabric and waterproof paper◦ antimicrobial surface

Magnetic properties such as for magnetic media like cassette tapes, floppy disks, and some mass transit tickets

Electrical or electronic properties◦ Conductive coatings e.g. to manufacture some types of resistors◦ Insulating coatings e.g. on magnet wires used in transformers

Scent properties such as scratch and sniff stickers and labels

Additives Additives are most commonly found in foods

Food additives are substances added to food to preserve flavor or enhance its taste and appearance

Additives Some additives have been used for centuries; for example, preserving food by pickling (with vinegar), salting, as withbacon, preserving sweets or using sulfur dioxide as with wines.

With the advent of processed foods in the second half of the twentieth century, many more additives have been introduced, of both natural and artificial origin.

Categories Acids

◦ Food acids are added to make flavors "sharper", and also act as preservatives and antioxidants. Common food acids include vinegar, citric acid, tartaric acid, malic acid, fumaric acid, and lactic acid.

Antioxidants - Antioxidants such as vitamin C act as preservatives by inhibiting the effects of oxygen on food, and can be beneficial to health.

Food Colouring - Colourings are added to food to replace colours lost during preparation, or to make food look more attractive.

Categories Colour Retention Agents

◦ In contrast to colourings, colour retention agents are used to preserve a food's existing colour.

Emulsifiers - Emulsifiers allow water and oils to remain mixed together in an emulsion, as in mayonnaise, ice cream, and homogenized milk.

Flavours - Flavours are additives that give food a particular taste or smell, and may be derived from natural ingredients or created artificially.

Categories Glazing Agents - Glazing agents provide a shiny appearance or protective coating to foods.

Preservatives - Preservatives prevent or inhibit spoilage of food due to fungi, bacteria and other microorganisms.

Stabilizers, thickeners and gelling agents, like agar or pectin (used in jam for example) give foods a firmer texture. While they are not true emulsifiers, they help to stabilize emulsions.

Categories Sweeteners - Sweeteners are added to foods for flavouring. Sweeteners other than sugar are added to keep the food energy (calories) low, or because they have beneficial effects for tooth decay or diabetes

Thickeners - Thickening agents are substances which, when added to the mixture, increase its viscosity without substantially modifying its other properties.