Лако-красочные материалы — производство

The purity of vegetable tannin extracts varies considerably. Commercial wattle bark extracts normally contain 70 to 80% active phenolic ingredients. The nontannin fraction, consisting mainly of simple sugars and high-molecular-weight hydrocolloid gums, does not participate in the resin formation with formaldehyde. Sugars reduce the strength and water resistance in direct proportion to the amount added. […]

The word tannin has been used loosely to define two different classes of chemical com­pounds of mainly phenolic nature: hydrolyzable tannins and condensed tannins. The former, including chestnut, myrabalans (Terminalia and Phyllantus tree species), and divi-divi (Caesalpina coriaria) extracts, are mixtures of simple phenols such as pyrogallol and ellagic acid and of esters of a […]

Lignin is a phenolic polymer that is one of the main polymeric constituents of wood formula (1). It is generally produced in great quantities as waste from paper pulp mills. It is composed of repeating phenylpropane units. Considerable research has been carried out on lignin adhesives and binders. While for certain applications, such as binders […]

A. Pizzi Ecole Nationale Superieure des Technologies et Industries du Bois, Universite de Nancy I, Epinal, France I. INTRODUCTION The loose term renewable resources adhesives has been used to identify polymeric com­pounds of natural, vegetable origin that have been modified and/or adapted to the same use as some classes of purely synthetic adhesives [1]. At […]

Only a small amount of work has been done up to now concerning the prediction of bond strengths and other properties based on the results of the analysis of the PF resin. Correlation equations evaluating the chemical structures in various PF resins with differ­ent formaldehyde/phenol molar ratios and different types of preparation on the one […]

The use of TMA techniques has allowed for the first time the determination of time- temperature-transformation (TTT) and continuous-heating-transformation (CHT) dia­grams for UF and PF [59,60] adhesives and for MUF and phenol-resorcinol-formalde­hyde (PRF) [41] adhesives hardening directly within wood joints and allowed the quantification of the wood/adhesive interface characteristics and parameter limits. Until then, such […]

The characteristics of PF resins and the reactive chemical groups they present render them particularly suitable for the preparation of binders by coreaction with other resins. This is still a relatively young field, and the most interesting and relevant co-resins that are being used or explored in this respect are the aminoplastic resins, in particular […]

Phenolic resins are also extensively used in the binding of foundry molds. Both resol and novolak resins are used for this application. The sand is coated with the phenolic resin at a rate of 3 to 4%. The PF resin can be used both as an organic solvent solution and in powder form. Coating of […]

One of the more common difficulties in bonding pine veneers and chips is adhesive dry­out. Dry-out is associated with the high liquid absorbancy of pine sapwood and it appears especially during long assembly times. This problem can be overcome by using resins modified through reaction with alkylated phenols, especially 3,4-xylenol [52]. Another technique used to […]

In the case of the application of phenolic adhesives to the manufacture of exterior-grade particleboard, the closest attention must be focused on the application of the resin rather than on its formulation. A good phenolic resin for plywood can be used successfully for the manufacture of particleboard once the various conditions of application have been […]