Лако-красочные материалы — производство

Mohamed Naceur Belgacem and Alessandro Gandini

Ecole Frangaise de Papeterie et des Industries Graphiques (INPG), St. Martin d’Heres, France

I. INTRODUCTION

The dwindling availability of fossil reserves constitutes a driving force towards finding alternative resources which can substitute them, totally or partially, in order to prepare chemicals and materials that are normally produced from petroleum and coal. In this context, vegetable biomass represents a very promising source since it offers a large variety of potential monomers, oligomers, and polymers, some of which can be extracted and used as such (namely, products such as terpenes, tannins, rosins, lignins, and cellulose) and others which can be suitably transformed to give monomers, solvents, surfactants, and a variety of polymeric materials (e. g., modified sugars, saponified oils, furfural and its derivatives, and cellulose acetates). We tried to show [1] that, besides its extensive use as a source of fibers for papermaking and textiles, vegetable biomass can also lead to interesting chemicals and materials. In a recent review [2], we focused on the use of furanic monomers for the preparation of polymeric materials and showed that different petro­leum-based monomers (especially aromatic derivatives) could be replaced by their furanic counterparts. Thus, a variety of totally furanic, aromatic-furanic, and aliphatic-furanic polymers display properties similar to (and sometimes better than) those of currently used polymers derived from petroleum, proving that a whole area of biomass-based materials can be developed from two first-generation compounds which are readily available from a wide spectrum of renewable resources.

Furanic monomers can be obtained from hemicelluloses which are among the main constituents of vegetal biomass and are abundant in trees and agricultural residues of annual plants, such as sugarcane bagasse, oat hulls, corn husks, rice, and wheat straw. The precursors of most industrial furan derivatives are obtained directly from hemicellu — loses through the acid-catalyzed hydrolysis of pentosans (e. g., xylans) followed by dehydration and cyclization of the ensuing pentoses leading to the formation of furfural (1), which is today the most important first-generation furan derivative, produced industrially at a rate of ca. 200,000 tonnes per year. This output is spread widely among numerous countries, including both industrialized and developing economies, because the process is particularly simple and the raw materials are available and plentiful virtually everywhere and are renewable often on short cycles. An additional advantage of this approach is that it calls upon a rational exploitation of agricultural wastes. Furfural

can be used as such, but is mostly (more than 80%) converted into furfuryl alcohol (2) using either liquid-phase or vapor-phase hydrogenation in the presence of copper catalysts which were found to be very selective in avoiding the hydrogenation of the heterocycle ring [3].

Furfuryl alcohol finds numerous applications as monomer (see below) and has, therefore, been for decades the most important second-generation furan derivative.

It is also used to prepare 2,5-bis(hydroxymethyl furan) (3) through its reaction with formaldehyde [3], namely:

Compound 3 can also be prepared by the hydrogenation of 5-hydroxymethyl furfural (4) which, in turn, is obtained from hexoses following the same acid-catalyzed process described above for furfural [2].

Compounds 1, 2, and 3 are among the most relevant monomers or co-monomers for furan-based adhesives, but so also are furfurylidene acetone (5) and its bis-adduct 6. The synthesis of 5 involves the base-catalyzed reaction between 1 and acetone [2] and, in the same context, the use of an excess of 1 leads to the formation of 6:

This chapter is devoted to adhesives and resins prepared from totally furanic monomers or formulations in which furanic compounds are added. In this realm, only
a few furanic monomers and resins are involved, namely: 1, 2, 3, 5, and 6, as well as liquid oligomers of 2 (poly2) and 3 (poly3). The properties of these monomers together with the mechanisms of their resinification and the composition of poly2 and poly3 will be briefly dealt with before discussing their use in the manufacture of resins for binders and adhesives.