Adhesives for Wood and Lignocellulosic Materials. R. N. Kumar. Читать онлайн. Newlib. NEWLIB.NET

Автор: R. N. Kumar
Издательство: John Wiley & Sons Limited
Серия:
Жанр произведения: Техническая литература
Год издания: 0
isbn: 9781119605669
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       Library of Congress Cataloging-in-Publication Data

      ISBN 978-1-119-60543-0

      The dramatic increase in the production of reconstituted wood products over the past 100 years has been made possible through the systematic development of new adhesives devised to meet the growing challenges of the times. Originally, large-diameter trees were available, but as their availability decreased, followed by a corresponding increase in price, the wood industry had to meet the challenge by attempting to use small-diameter trees and comminuted wood particles, fibers and pulp mill waste. This resulted in the development of reconstituted wood produced from the comminuted particles bound together with adhesives. This development had a significant impact on meeting challenges. The development of new types of adhesives—both synthetic petroleum-based adhesives as well as adhesives of natural origin—occurred during this period.

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      This concept established the future trends in the wood-based industry, namely, (1) use of smaller trees, (2) use of waste from other wood processing, (3) removal of defects, (4) use of rare and hitherto unused wood species, natural lignocellulosic fibers, (5) creation of more uniform components, (6) development of composites stronger than the original solid wood, (7) ability to make composites of different shapes and (8) glulams, OSB, LVL, etc., (9) development of natural-fiber polymer-matrix composites, (9) development of more sophisticated engineered wood products and structural elements, such as wooden I-Joist box beams, aided by the availability of new or improved wood adhesives, (10) development of sandwich composites of wood and non-wood materials such as metal- and plastic-faced wood panels, paper and metal honeycomb sandwiches, etc.

      The above developments markedly increased the percentage of adhesives used for the production of glued wood products. It should be mentioned in this context that a high percentage, maybe 80% or more, of all wood products produced today are glued, and that about 70% (by volume) of all the adhesives produced in the world today are used for application to wood [3]. These developments have led to an increase in the functional efficiency of wood products as well as an efficient utilization of wood resources, thus constituting an essential tool to directly or indirectly affect the sustainability of forestry and wood-based industries.

      The first chapter of the book deals with the distinctiveness of wood as an adherend in the midst of other substrates such as metals, polymers, inorganic adherends like glass, etc. In contrast to other substrates, wood presents adhesives with hierarchical structural elements of different sizes which, along with its unique chemical and physical characteristics, greatly influence the wood-adhesive interaction.

      Knowledge of the fundamentals of adhesion is extremely important for researchers as well as technologists in the industry, both for adhesive formulations and troubleshooting during production. The importance of establishing an intimate contact between the adhesive and wood has been emphasized for an effective performance and durability of the bonded wood products in actual service. Therefore, mechanical interlocking, coulombic (ionic) interaction, hydrogen bonding, and apolar interactions are discussed in Chapter 2. In addition, electronic or electrostatic theory, adsorption (thermodynamic) or wetting theory, diffusion theory, chemical (covalent) bonding theory, theory of weak boundary layers and interphases and interfacial forces based on specific donor-acceptor (acid-base) interactions between adhesive and substrate molecules are also discussed.

      In Chapters 3 to 7, the chemistry and technology of urea-formaldehyde, melamine formaldehyde, phenol-formaldehyde, resorcinol-formaldehyde, and polyurethanes are discussed in detail. Special mention is given to non-isocyanate polyurethanes