Adhesive Technology

Development of suitable adhesives continues to be an important R&D activity of the Institute.
Research on the project "Modification of phenolic and amino resins suitable for bonding veneers from non-durable species treated with fixed type of preservatives" was completed and the research report published. The Institute has developed two phenolic resin adhesive systems to bond preservative treated veneers (using Acid Copper Chrome and Copper Chrome boric) has given adequate bond quality plywood indicated by predominant wood failure in the panels when tested in dry state as well as in wet after immersion in boiling water for 8 hours and 72 hours, condition. Field tests carried out on the panels by subjecting them to grave yard test for 6 months also gave satisfactory results indicating the long-term durability of the panels.

Studies on the analysis of formaldehyde emission in urea formaldehyde resin adhesive bonded wood particleboards made in the laboratory have been completed. Formladehyde emission was measured in terms of formaldehyde content of particleboards, determined at different intervals of time by perforated method. Results have shown that formaldehyde content in the boards reduces gradually and attain the minimum level of 10 mg /100 gram board in about 90 days. The formaldehyde content seem to stabilize at this level.

Evaluation studies carried out on the use of extenders like Tapioca flour, maize starch and maida extenders under the project "Evaluation of extenders for synthetic resins" have shown that these extenders can be efficiently used up to 30% with urea formaldehyde resin for the manufacture of MR grade plywood.

Work is under progress for the improvement of fire retardancy of plywood by treating veneers with fire retardant chemicals as well as glue line treatments. Few panels made in the laboratory using phenol formaldehyde resin incorporated with fire retardant chemicals, and veneers treated with fire retardant chemicals are being tested.

Adhesive is a substance capable of holding materials together by surface attachment. Use of adhesive in wood bonding is an important means of improving utilization of wood and also other lignocellulosic materials.

Adhesives play an important role in the wood based panel industries and are backbone of panel industries. The use of right type of adhesive is very important from the point of view on the quality of the resin, products aswell as its cost.

The earliest commercial adhesives were generally of plant or animal origin. These adhesives were widely used but seldom had durable properties. The scenario changed with the introduction of synthetic polymers in 1930’s. Though synthetic resin adhesives were introduced in the wood processing industry in the early 1930’s great progress in their development and acceptance on a large scale began in mid 1940’s and since then developmental activities were continuing aiming to improve process and performance resulting in replacement of the glues from plant or animal origin.

Development of synthetic resin adhesives has lead to development of various engineered panel products from wood and other lignocellulosic materials.

The formaldehyde based synthetic resin adhesives are more widely used and among them the most important are viz. Phenol formaldehyde(PF) – Urea formaldehyde (UF), Urea Melamine formaldehyde (UMF), Melamine formaldehyde(MF), Resorcinol formaldehyde(RF), Phenol-resorcinol formaldehyde(PRF) resins are the most widely used in panel industries for making wood based panels and wood laminates.

Among the available synthetic resin adhesives the phenolic resin adhesives finds wide acceptance for exterior grade applications as they produce strong and durable joints that can be used with confidence where service requirements are severe i.e. Exposure time is higher.

The basic raw material for phenolic resin ie. Phenol AND formaldehyde which are derived from crude oil and natural gas. Due to the hike in the cost of petroleum, there was remarkable increase in the cost of phenole which influences the cost of phenolic resin adhesives and ultimately the product made out of it. Cost of these resins have increased significantly during the last two decades. The shortages and the price increase of the basic raw material has lead to search for alternative lower cost materials based on non-petrochemical resources which can find partial or full substitution of phenol in phenolic resin adhesives. However phenolic resins are still used in large quantities for specialty grade of panel products.

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