TYPES of ADHESIVES

TYPES of ADHESIVES

Post 448

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Adhesives join materially and dimensionally different materials. Adhesives can penetrate deep groves, closely spaced sides and other difficult to access forms to create a joint. Adhesives are very low viscosity or thin body materials so take up very little space. Even their overlapping joints do not add much to the thickness of the assembly. Adhesives allow uniform stress distribution, unlike screws and nuts which create localized stress points. Adhesive Joints may be designed as required, to be elastic or rigid. Adhesive joints can be demountable and very clean on removal.

Glues, Gums, Adhesives

Adhesives form a joint at ambient temperature and at very low processing temperature. Adhesive joining does not affect crystallographic structure of metals or plastics. Adhesives can create very extensive, multi layered laminar compositions without physically cutting or puncturing the materials.

Swanson_Shoe_Repair_26

Shoe sole joining with adhesive

Adhesives bonding are surface sensitive joining system. Adhesives require elaborate surface treatments, specific application conditions, curing procedures and sometimes considerable expense of time for setting. Screws, nut-bolts and other mechanical fixings nearly involve substantial mass of the material being joined, so often can join materials with weak surface components. But for adhesive bonding the integrity of the surface component, with the rest of the material is extremely important. Inspection of the joint is difficult. Joint design becomes very critical, compared with other mechanical and thermal processes. The adhesive itself may corrode the materials it is joining, or induce stresses during curing.

Plywood layers joined with Urea formaldehyde

Many of the adhesive products are used as sealants, masking pastes, caulking compounds, bulk fillers, water proofing materials, cracks and crevices filler, temporary to permanent holding compounds (such as for metal sheets, glass, etc.).

Senior Airman Collin Uvanni caulks the baseboards of the new post office at Bagram Air Field, Afghanistan, June 6, 2006.  The office, constructed entirely by the 1st Expeditionary Red Horse Group here, will nearly double the size of the existing post office.  (U.S. Air Force photo/Senior Airman Brian Ferguson)

Caulking

Adhesives have many formulations and forms, both of which are closely linked to the technique of applications, material surface types and shape configurations. Adhesives can be broadly defined by what they join, such as paper, wood, metals-ceramics-glasses, fibers-fabrics, plastics-elastomers, and biological entities like skin-bones-hairs. Adhesive joining technologies also are a method of categorization, such as liquid-paste spread, hot glues, tapes or patches, ambient temperature curing, baking, heat curing, fusing, surface softening or dissolving, pressure softening, instant bonding, contact adhesive, etc.

Solvent based adhesive

One of the largest markets for adhesives is for wood, paper and fibres. Wood adhesives are of basically two types: 1 Used for joining wood components by carpenters and workshops, these are Polyvinyl Acetate (PVA) and Acrylic emulsion-based adhesives, 2 Used for plywood composite manufacturing such as plywoods, particle boards, etc., such as the Amino resins made from Urea, Phenol and Melamine processed in combination with Formaldehyde.

Hockey stick reinforced with adhesive tape

For wood joinery workshops, and packing and labelling fields two major types of adhesives are used, Adhesives based on solvents and based on water. Water-based systems are mainly in the form of emulsions. Water-based formulations of Polyvinyl acetate (PVA), Ethylene vinyl acetates (EVA) and Methacrylate, are widely used. Solvent adhesives include acrylics and styrene-butadiene (SB) latex. Acrylic resins are used for removable and permanent pressure sensitive applications.

Super Glue

Neoprene or Polychloroprene was the first synthetic elastomer adhesive. It is widely used in shoe manufacturing. It is also used as a contact adhesive for attaching large surfaces and very quickly. It provides water and heat resistant bonds. Epoxy adhesives are widely used for structural applications. Epoxies offer reliable and good adhesion to all substrates. Urethane adhesives are environmentally tough, abrasion resistant and flexible adhesives. Instant adhesives such as cyanoacrylates provide an instantaneous bond and are called super glues. These are available as liquids, pastes, and gels, that set at normal or elevated temperatures. These are used for repair work of pipes, toys, ceramics, etc.

Scotch Tape

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NATURAL ADHESIVES (Bio-adhesives)

Post 224 –  by Gautam Shah

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Kerala_kathakali_makeup

Bio-adhesives are comparatively a recent nomenclature to distinguish a variety of Adhesive materials that are of natural origin. These materials are often only ‘primarily processed’ and so are believed to retain their natural characteristics. Synthetic adhesives pose environmental concerns of volatile organic compound (VOC) emissions, safe disposal and recycling problems (very long life cycles). The health and safety issues relating to hazardous ingredients, in foods, medicines and bio-implants, cause concerns.

tragacanth-gum-231301_640Bio-adhesives like other natural materials tend to be bio-compatible, and so there is increased commercial interest in them. There use in certain applications such as for biomedical and topical uses such as the bonding of skin and body tissues are being studied. The uses of bio-adhesives are being assessed, as food additives and supplicants, due to low level of toxicity. Secretions by microbes, marine molluscs and crustaceans, are being researched with a view to applications in bio-mimicry.

sandcastle_worm_colony_in_laboratory

In 2005, researchers from the University of California, Santa Barbara (UCSB) discovered that the glue used by the phragmatopoma to build its protecting tube was made of specific proteins with opposite charges. Those proteins are called polyphenolic proteins that are used as bio-adhesives. They succeeded in obtaining the sequence of these adhesive proteins and described the detailed mechanisms by which the adhesive sets. Inspired by these results University of Utah researchers reported in 2009 that they succeeded in duplicating the glue that the worms secrete and use to stick sand grains together underwater. The typical amount of glue that the worm produces at once is approximately 100 picoliters, requiring 50 million to fill a teaspoon. They believe the glue to have applications as a bio-compatible medical adhesive, for instance to repair shattered bones.    >>> from Wikipedia: http://en.wikipedia.org/wiki/Sandcastle_worm

Adhesives are primarily bonding materials, but many such substances are also used as thickening and homogenizing substances in foods and medicines and as fragrance giving gums. Bio-adhesives consist of a variety of substances, but proteins and carbohydrates form a large section.

Steri-Strip_-_01

Natural adhesives or bio-adhesives are of three broad classes: Plant materials and exudates, such as starches, plant saps and resins, natural rubber, gum arabic, colophons, oils like linseed oil, and wax like carnauba wax, proteins like the soybean, and carbohydrates like starch. Animal products like casein, milk proteins, wax, glue and other gelatinous substances, shellac. Mineral products like Pozzolana and other natural cement products, silicates, asphalt, bitumen pitch. To these can be added, a range of modified natural products, typically various derivatives like a chlorinated rubber, cyclized rubber and rubber hydro-chloride.

colophane

Natural adhesives of vegetable origin include plant exudates such as: Gum arabic, colophon; Oils and waxes like linseed oil, carnauba wax; Proteins like the soybean, and carbohydrates like starch.

Natural adhesives of animal origin include various glues and other gelatinous substances, milk casein, shellac and bees wax.

shellac_varities

Natural adhesive like mineral substances include silicates, Pozzolana, asphalt, bitumen etc.

Natural elastomers are natural rubbers and their various derivatives like a chlorinated rubber, cyclized rubber and rubber hydro-chloride.

Birkenpech

Proteins glues such as a gelatin, and carbohydrates such as starch, have been used as glues by man since very ancient times. Postal stamps have natural wet-able glue despite synthetic alternatives. There are several applications where cooked starch or flour adhesives are used, such as for book binding, corrugated board, paper-bag production, paper tube winding, kite thread colouring, and wallpaper fixing. Casein glue is mainly used to stick labels on bottle labels. Animal glues are traditionally used for leather work, bookbinding and wood joinery.

Morandi.glue_.pot.final_

Animal Glues: The term animal glue is usually confined to glue prepared from mammalian collagen, the principal protein constituent of skin, bone, and muscle. When treated with acids, alkalies, or hot water, the normally insoluble collagen slowly becomes soluble. If the original protein is pure and the conversion process is mild, the high-molecular weight product is called a gelatin which is used for food or photographic products. The lower-molecular weight material produced by more vigorous processing is normally less pure and darker in colour and is called animal glue. Animal glue traditionally has been used in wood joining, book bindery, sandpaper manufacture, heavy gummed tapes, leather shoes and luggage items and similar applications. Joints with animal glue work well in dry to moderately moist weather, but with high humidity (80 % or more) growth of micro organisms weakens the adhesive. In spite of its advantage of high initial tack (stickiness), animal glue is being replaced by synthetic adhesives.

kerria-lacca

Protein Glues: Casein glue is made by dissolving casein, a protein obtained from milk, in an aqueous alkaline solvent. The degree and type of alkali, influences behaviour of the product. In wood bonding, casein-glues generally are superior to animal-glues in moisture resistance and ageing characteristics. Casein also is used to improve the adhering characteristics of paints and coatings (calcimine, distemper coatings).  Casein is now getting replaced by urea formaldehyde resins.

True_sago_palm_starch_product,papeda,gata-gata(Hatusua,W.Seram,Maluku,ID_thu01oct2009-1324h)

Blood Albumin Glue is made from serum albumin, a blood component obtainable from either fresh animal blood or dried soluble blood powder to which water is added. Addition of an alkali to albumen-water mixtures improves adhesive properties. A considerable quantity of glue products from blood was used in the plywood industry.

Starch0

Starch and dextrine: Starch and dextrine, are extracted from corn, wheat, potatoes, tamarind or mango seeds or rice. They constitute the principal types of vegetable adhesives that are, soluble or dispersible in water and obtained from plant sources throughout the world. Starch, and dextrine, glues are used in corrugated board, packaging, and as a wallpaper adhesive.

Kite Strings

Natural Gums: Natural gums, are extracted from their natural sources, also are used as adhesives. Agar-agar, Calcium alginate, a marine-plant colloid (suspension of extremely minute-particles), is extracted by hot water and subsequently frozen for purification. Algin, is obtained by digesting seaweed in alkali and precipitating either the calcium salt or alginic acid. Gum arabic is harvested from acacia trees that are artificially wounded to cause the gum to exude. In India Babool, Neem, provide such gum exudates (Hindi-Gund), some of which are also used in sweets, and Ayurvedic-herbal preparations. Another exudate is natural rubber latex, which is harvested from Hevea trees. Natural gums are used chiefly in water-re-moistenable products.

cattien_ceramic_bowl

Bituminous Adhesives: Bitumen and coal tar derivatives are available as hot melt or softening, emulsion and solvent diluted materials. The hot melt or softening materials have a tendency to run at high temperatures. Bituminous materials are used for fixing waterproofing felt and roof insulation boards.

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ADHESIVES

Post 218 ⇒   by Gautam Shah 

ADHESIVES

Historical perspective

An adhesive is a substance that as an intervening agent binds two similar or dissimilar surfaces (or objects) together and resists their separation. The term adhesive is used for substances such as the glue, gum, cement, mucilage, mastic compound, sealant or caulking compound.

Plant exudate Gum

Plant exudate Gum

Surfaces stick or remain together when forces that cause attraction are operative. A force of attraction is any type of force that causes objects to come together even if those objects are not close to each other or not touching each other. Gravity is one such force. The electrostatic force cause attraction due to differential electrical charge. The magnetic force affects objects that have magnetic properties.

Using Natural Starch

Using Natural Starch

Adhesive substances are many types. It is a solid that is dissolved by heat or solvent, a natural liquid that remains wet, a substance that in the presence of a reactant shows binding capacity, and a material that forms a longer chain (polymerization) over age or with chemical action.

Adhesives are joining substances, and offer unique advantages. The use of adhesives offers superior binding or joining in many situations. Its advantages are evaluated against other joining systems such as seaming, stitching, tying, knotting welding, forging, soldering, fusion joining, mechanical fastening, etc.

The adhesive like substances are valued, for non-invasive joining (without drilling, melting), ability to join similar and non similar materials, capacity to distribute stress across the joint surface, often without damaging the visual aspects of the objects, in some cases for demountable joining, functionality over wide range of temperature and other environmental conditions and facility to work without heavy duty equipments or energy use.

Adhesive are disadvantageous, in varied stress conditions due to environmental as well as structural loading conditions, require a large surface for adequate bonding and do not allow assurance inspection of joint integrity.

Gold Foil fixing with adhesives

Gold Foil fixing with adhesives

Earliest adhesives were plant exudates like gums and resins, and of animal origin like hide gums. The adhesives were perhaps used for joining, dissimilar materials for tools making, broken ceramics, and for waterproofing boats and canoes. Many of the primitive applications of binding materials were similar to use of painting or surface coatings materials.

Bitumen

Bitumen

Adhesive materials like, gums, glues, starches, egg whites, casein and other proteins, have been used in art work painting to fix various types of colourants. The Egyptians have extensively used animal-glues in tombs, furniture, ivory and papyrus items. Many societies worlds over have used adhesive materials to fix decorations on adornments, ornaments, etc. In Europe during the middle ages, egg whites were used to decorate parchments with gold leaves. Adhesives made of starch were used by Egyptians dating back 3,300 years, for bonding non-woven fabrics from fibres of reed plant -papyrus, and as a sizing material.

Roman concrete Vault of Pozzolana cement

Roman concrete Vault of Pozzolana cement

Limes and natural cementing materials like Pozzolana (volcanic ash), calcium carbonate and sulphates, were used in masonry work. Bitumen, tar pitches, and beeswax were used as caulk or sealants and also as adhesive for fixing statues and other repair work.

Cement masonry

Cement masonry

Wooden objects were bonded with glues from fish, horn and cheese. Hide glue was extensively produced in Holland and Fish glue was produced by the British, in 1750s.

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