Лако-красочные материалы — производство

A RF novolak is produced according to the following schematic reaction (Formula 5): If paraformaldehyde and fillers, generally wood and nutshell flours, are added, the resin becomes capable of setting in 2 to 3h and curing in 16 to 24 h at ambient temperature.

The same chemical mechanisms and driving forces presented for PF resins apply to resor­cinol resins. Resorcinol reacts readily with formaldehyde to produce resins which harden at ambient temperatures if formaldehyde is added. The initial condensation reaction, in which A-stage liquid resins are formed, leads to the formation of linear condensates only when the resorcinol/formaldehyde molar […]

A. Pizzi Ecole Nationale Superieure des Technologies et Industries du Bois, Universite de Nancy I, Epinal, France I. INTRODUCTION Resorcinol-formaldehyde (RF), and phenol-resorcinol-formaldehyde (PRF) cold­setting adhesives are used primarily in the manufacture of structural, exterior-grade glulam fingerjoints, and other exterior timber structures. They produce bonds not only of high strength, but also of outstanding water […]

In 1965, W. Arnold [2] found that the pressing time of SSL particleboard obtained with sulfuric acid as catalyst (see the Shen procedure) can be reduced by 50% and the specific gravity of the boards by 7 to 10% if 10 to 30% of the SSL-blended wood chips are replaced by UF-blended wood chips. However, […]

The fundamental problem of lignin, slowing of the pressing time obtainable with PF resins, was partly eliminated by Sellers (1990) [19] and by Calve (1990) [20], who first reacted lignin with formaldehyde in a reactor for a few hours. A methylolated lignin (ML) equivalent to a PF resol was obtained. As in this case the […]

According to Forss and Fuhrmann (1972) [5,18], the amount of lignin in lignin-PF adhe­sives for particleboard, plywood, and fiberboard can be increased to 40 to 70% if a high — molecular-weight fraction (MW > 5000) of either lignosulfonate or black liquor, obtained from alkaline pulping of wood, is applied. Fractionation of SSL or black liquor […]

In 1971, Roffael and Rauch [14,15] claimed that the curing time of SSL particleboard could be reduced and, according to Pedersen, the postheating treatment in an autoclave avoided when phenolic resins of the novolak type were added to the SSL [15]. Due to coagulations between calcium-based SSL and PF, the calcium-based SSL has to be […]

The number of patents on lignin as a substitute or extender for phenolic wood adhesives during the past four decades is high [2]. Under certain conditions, up to 40% of PF adhesive can be replaced by lignosulfonate or black liquor without significantly extending the curing time or worsening board properties. Lignin-PF formulations have been used […]

The drawbacks inherent in the Pedersen and Shen procedures—high pressing temperatures and long pressing times or strong mineral acids—can be avoided if cross-linking of the lignin molecules is achieved by radical coupling instead of condensation reactions (Nimz et al. 1972 [2]). In this case, the formation of new carbon-carbon as well as carbon-oxygen bonds between […]

In 1973, K. C. Shen of the Eastern Forest Products Laboratory in Ottawa, Canada, pro­posed sulfuric acid as a curing agent for SSL waferboard. The pressing conditions were the same as those of conventional PF particleboard, when poplar wafers were first sprayed with 1% of 15 to 20% sulfuric acid and then with 4 to […]