Adhesives in the economy

Phenohc resins are produced by the condensation of phenol or a substituted phenol, such as cresol, with formaldehyde. These low cost resins have been produced commercially for more than 100 years and in the 1990s are produced by more than 40 companies in the United States. They are employed as adhesives in the plywood industry and in numerous under-the-hood appHcations in the automotive industry. Because of the cycHc nature of the automotive and home building industry, the consumption of phenol for the production of phenohc resins is subject to cycHc swings greater than that of the economy as a whole. 

Both melamine—formaldehyde (MF) and resorcinol—formaldehyde (RF) foUowed the eadier developments of phenol—, and urea—formaldehyde. Melamine has a more complex stmcture than urea and is also more expensive. Melamine-base resins requite heat to cure, produce colorless gluelines, and are much more water-resistant than urea resins but stiU are not quite waterproof. Because of melamine s similarity to urea, it is often used in fairly small amounts with urea to produce melamine—urea—formaldehyde (MUF) resins. Thus, the improved characteristics of melamine can be combined with the economy of urea to provide an improved adhesive at a moderate increase in cost. The improvement is roughly proportional to the amount of melamine used the range of addition may be from 5 to 35%, with 5—10% most common. 

Economies of production personnel can still be achieved today, and a unit cost reduction of 30-50% is possible. Physical properties of mouldings can be enhanced and the adhesion of the bond in a rubber-metal part is improved. Tool costs can be cheaper than for compression press methods because the throughput is greater. 

A wide range of adhesive and other binder systems is used in the manufacture of composite panels, dominated by formaldehyde-based systems. Growth in the composite panels industry has depended on adhesives with the required properties being available in sufficient quantities at a suitable eost. The industry requires considerable economies of seale for synthetie adhesive production. The materials are derived from oil (phenol) or natural gas (urea and formaldehyde). Recently in the face of environmental constraints and the inereasing eost of oil and natural gas there is renewed interest in adhesive systems derived from renewable resourees. 

Disadvantages include the high costs and environmentally harmful adhesives used to realize complex geometries with layered constructions. Wood is one of the few inexhaustible natural resources, assuming proper management, and has been one of the most important products in the human economy since earliest times. From the material point of view, wood is a composite consisting mainly of lignin, cellulose fibers, and hemicellulose. 

Amino resins have found applications in the fields of industrial and decorative laminating, adhesives, protective coatings, textile treatment, paper manufacture, and molding compounds. Amino resins are used in adhesive formulations for bonding plywood and furniture. The melamine resins give excellent boil-resistant bonds but for economy are usually blended with ureas. 

Several studies have examined the adhesive properties of LCTs. Ochi and Takashima, and Carfagna and co-workers both foimd an increase in the lap shear strength for an LCT epoxy compared to an isotropic LCT (85,86). However, Frich and Economy (87) found that the lap shear strength with a titanimn substrate for an LCT that cures by transesterification was lower than that for an isotropic resin. Given the limited data available, it is not clear whether these differences are due to the substrates, surface pretreatment, the type of cure reaction, the liquid crystalline phase, or some other factor. However, most of these studies did find... 

Today, thanks to the advent of chemistry and biotechnology, natural polymers can be tailored to meet specific needs since biopolymers are diverse types of materials that have potential applications in all sectors of the economy [1, 2], For example, they can be used as adhesives, absorbents, lubricants, soil conditioners, cosmetics, drug-dehvery vehicles, high-strength structural materials, in textiles, and even as computational switching devices, among other uses [1],... 

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