Лако-красочные материалы — производство

According to Pedersen and Jul-Rasmussen [2], wood chips are mixed with 20 to 25% of their weight with a 50% technical SSL and pressed at 185°C for 30 min, giving a 12-mm — thick board that must be postheated at 195°C for 80min in an autoclave. The pH value of the SSL had been adjusted […]

According to its structure as a polyphenol, lignin as an adhesive should be similar to phenol-formaldehyde (PF) resins. This is true for native lignin in wood; to transfer them into insoluble resins, technical lignins (lignosulfonate and black liquor) have to be additionally cross-linked. However, condensation reactions in lignin by heat or mineral acids cannot be […]

When lignosulfonate is treated with strong mineral acids at elevated temperatures or heated at temperatures above 180° C, condensation reactions leading to diphenylmethanes and sulfones take place. The reactivity of lignosulfonates depends to some extent on the cation. Of the four lignosulfonates obtained technically, the calcium-based exhibit the lowest and the ammonium-based the highest reactivity; […]

Lignin is composed of phenylpropane (C9) units that are linked together by carbon-to- carbon as well as carbon-to-oxygen (ether) bonds. Our present knowledge of the lignin Figure 1 Phenyl propanoid units of lignin: R, R2 = H, OCH3; R3 = H, CH3, CH2; (f) = possible linkage to other phenyl propanoid units. structure is based […]

A. Pizzi Ecole Nationale Superieure des Technologies et Industries du Bois, Universite de Nancy I, Epinal, France I. INTRODUCTION The occurrence of lignin as a waste product in pulp mills has made it an attractive raw material for adhesives ever since the beginning of the sulfite pulping of wood. The first patents dealing with the […]

Various methods of analysis are available for the determination of tannin content. These methods can generally be grouped into two broad classes: 1. Methods aimed at the determination of tannin material content in the extract. The classical method of this type still used is the hide-power and derived methods. These methods were devised to determine […]

The autocondensation reactions characteristic of polyflavonoid tannins have only recently been used to prepare adhesive polycondensates hardening in the absence of aldehydes [70]. This autocondensation reaction is based on the opening under alkaline and acid condi­tions of the O1-C2 bond of the flavonoid repeating unit and the subsequent condensation of the reactive center formed at […]

Another application of condensed tannin extracts that has proved technically successful is as tire cord adhesives. Both thermosetting tannin formulations [68] and tannin-resorcinol — formaldehyde formulations have been experimented with successfully. A. New Concepts and Principles 1. Surface Catalysis As in the case of other formaldehyde-based resins the interaction energies of tannins with cellulose obtained […]

A series of different novolak-like materials are prepared by copolymerization of resorcinol with resorcinolic A rings of polyflavonoids, such as condensed tannins [62-64]. The copolymers formed have been used as cold-setting exterior-grade wood adhesives, com­plying with the relevant international specifications. Several formulations are used. The system most commonly used commercially relies on the simultaneous copolymerization […]

The adhesive developed for the manufacture of damp-ply-resistant corrugated cardboard are based on the addition of spray-dried wattle extract, urea-formaldehyde resin, and formaldehyde to a typical Stein-Hall starch formula of 18 to 22% starch content [60,61]. The wattle tannin-urea-formaldehyde copolymer formed in situ, and any free formaldehyde left in the glue line is absorbed by […]