Furan Resins from Furfuryl Alcohol

When furfuryl alcohol is mixed with a small quantity of an aqueous acid solution, the alcohol group of one molecule of the furfuryl alcohol reacts with the active hydrogen from the ring of another molecule of furfuryl alcohol to yield water and a furan ring linked to a furfuryl alcohol molecule by a methylene bridge  

In the same fashion, further furfuryl alcohol molecules can be added indefinitely. 

Alternatively, the entire reaction can be carried out in situ , for instance by impregnating a porous material such as graphite or brick with properly acid-catalyzed furfuryl alcohol, and by then submitting this material to a temperature program devised so as to permit the water of the catalyst as well as the reaction water to escape as vapor before the final heat hardening takes place. 

To top off the appeal, the polymerization of furfuryl alcohol can be made to run with almost any partner containing reactive hydrogen. Thus, furfuryl alcohol can be reacted with formaldehyde to give a series of thermosetting resins featuring more methylene bridges than are obtained by the resinification of furfuryl alcohol alone. Such resins are commonly used for the bonding of wood. 

The most important application of furan resins from furfuryl alcohol lies in the foundry industry. Sand bonded with clay is usually used for molds, but for cores and for more stringent molding applications, a stronger more rigid chemical binder is required. One of these chemical binders is furan resin made from furfuryl alcohol. 100 parts by weight of sand are 

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FIGURE 4.10 Synthesis of furan resins from furfuryl alcohol. 

One of the most important furan resins from an industrial standpoint is undoubtedly that obtained from 2-furfuryl alcohol. The final cross-linked product displays outstanding chemical, thermal and mechanical properties8. ... 

Euran Furan resins are thermosetting polymers derived from furfuryl alcohol and Furfural. The cure must be carefully controlled to avoid the formation of blisters and delaminations. To obtain optimum strength and corrosion resistance, furan composites must undergo a postcure schedule at carefully selected temperatures depending upon the laminate thickness. Equipment made with furan resins exhibits excellent resistance to solvents and combinations of acids and solvents. These resins are not for use in strong oxidizing environments. 

The most commonly used furan resins are those obtained from furfuryl alcohol and/or furfural ... 

Uses. Furfural is primarily a chemical feedstock for a number of monomeric compounds and resins. One route produces furan by decarbonylation. Tetrahydrofuran is derived from furan by hydrogenation. Polytetramethylene ether glycol [25190-06-1] is manufactured from tetrahydrofuran by a ring opening polymeri2ation reaction. Another route (hydrogenation) produces furfuryl alcohol, tetrahydrofurfuryl alcohol, 2-methylfuran, and 2-methyltetrahydrofuran. A variety of proprietary synthetic resins are manufactured from furfural and/or furfuryl alcohol. Other... 

Other furan compounds, best derived from furfural, are of interest although commercial volumes are considerably less than those of furfural, furfuryl alcohol, furan, or tetrahydrofurfuryl alcohol. Some of these compounds are stiU in developmental stages. Apphcations include solvents, resin intermediates, synthetic mbber modifiers, therapeutic uses, as well as general chemical intermediates. 

The two intermediates of commercial furan resins are furfural and furfuryl alcohol. Furfural occurs in the free state in many plants but is obtained commercially by degradation of hemicellulose constituents present in these plants. There are a number of cheap sources of furfural, and theoretical yields of over 20% (on a dry basis) may be obtained from both com cobs and oat husks. In practice yields of slightly more than half these theoretical figures may be obtained. In the USA furfural is produced in large quantities by digestion of com cobs with steam and sulphuric acid. The furfural is removed by steam distillation. 

Furanic black resins arising from furfural, furfuryl alcohol and furfurylidene acetone 3a are characterized by highly conjugated structures (6-8) their inhibiting power as radical scavengers was tested and turned out to be extremely nigh even in heterogeneous conditions, e.g. with the resin suspended in a monomer solution. 

Furans. The last statement is certainly true of furans derived from sugars (142,143), particularly furfural and furfuryl alcohol, which is readily derived from furfural (144)- Dr. McKillip of QO Chemicals discusses furan resin chemistry and furan polymers in Chapter 29. Dr. Stanford and his colleagues at the University of Manchester Institute of Science and Technology discuss the use of a diisocyanate derived from furfural for polyurethane production in Chapter 30. 

An adjunct to the understanding of this mechanism is the evidence obtained that polymerization of 2,5-bis(hydroxymethyl) furan produces no 2,2,-difuryl methane or higher homologues (35). Analysis by thin-layer chromatography shows such resin having greater than 95% difunctional components (terminal hydroxymethyl groups) as compared to less than 50% for the resin from a conventional furfuryl alcohol polymerization (35). 

Furfural 69, which can be manufactured from hardwood waste, is used for the manufacturing of a furfural-acetone monomer <2000MI15>. This monomer is then used to obtain furfural resins which are suitable as binders for the production of particleboards. In a further application, these furan resins of low toxicity have been used as adhesives in the manufacture of plywood <1999MI24>. The use of such resins is recommended as it leads to products with advantageous economic and ecological indicators. The result is plywood with good physiomechanical properties when the Monomer furfuryl alcohol (FA) was used as the adhesive. 

Furan resins can be obtained from both furfural and furfuryl alcohol. 

Furan polymers are based on furfuryl alcohol, which is derived from agricultural residues such as corncobs, rice hulls, oat hulls, or sugar cane bagasse. The furan prepolymer is usually cross-linked with furfuryl alcohol, furfuraldehyde, or formaldehyde to yield thermosetting polymers, highly resistant to most aqueous acidic or basic solutions and strong solvents such as ketones, aromatics, and chlorinated compounds. The important characteristic of furan resins is their ability to be stored for long periods of time (up to 5 years), even at low temperatures. 

From the above survey, it appears that the industrial use of furanic monomers such as furfuryl alcohol and furfural, i.e., chemicals based on renewable resources, as binders in foundry molds is highly successful. Similar furan-based resins can also be used as efficient adhesives in wood particle composites and thus are interesting alternatives to petroleum-based counterparts. The fact that the substitution of formaldehyde by furfural has not yet met with a reasonable industrial success probably stems from the higher cost of the furan aldehyde. The increasing pressure on the reduetion of formaldehyde emission and the renewable character of furfural should play in its favor in the near future. 

Furan polymers are derivatives of furfuryl alcohol and furfural. With an acid catalyst, polymerization occurs by the condensation route, which generates heat and a by-product of water. The exotherm must be controlled to prevent the water vapor from blistering and cracking the laminate. Furan resin catalysts should have exotherms above 65°F (18°C) but not over 85°F (30°C). 

FURAN Combination resins of Phenol Urea Furfuryl alcohol Formaldehyde Particulate matter - soot from the incomplete combustion of the carbon based resins Carbon oxides Phenol, cresols and xylenols Formaldehyde Aromatics (inc. polycyclics) Sulphur dioxide Ammonia Aniline Isocyanic acid Methyl isocyanate Odour may occasionally be a problem... 

Furan This is a condensation product involving furfuryl alcohol which may compete with phenol formaldehyde in industrial processes. The advantage stems from the raw material furfural that originates in plants such as straw, com, sugar cane or wood. It is not however much in use in developed covmtries. The polymer itself shows good chemical resistance and serves in special coatings, adhesives and laminates. It is supplied as a relatively cheap fluid resin, hardened by the use of an acidic catalyst. 

Furan resins. Thermosets manufactured from furan derivatives such as furfural, furfuryl alcohol, tetrahydrofurfuryl alcohol. Applications foundry resins and core binders, acid-proof coatings, putties. 

Furan resins are also a low-volume consumption resin like amino resins, and are used as supplements to phenolic resins [33,34]. They are prepared by the reaction between a phenol and furan compounds such as furfural, furfuryl alcohol, and furan. Furan compounds can be used in place of formaldehyde in the conventional production of phenolic resins. The most popular and viable furan resins are prepared from furfuryl... 

Recently, UP made partly from biomass resources have been developed for commercial applications. Eor example, Japan U-PICA Co. Ltd [57] has recently patented the synthesis of UP resin made partly of monomers from inedible biomass resources. The resulting resin is proven to exhibit better processability and performance comparable to that of conventional UP. Bamboo, hemp, and kenaf fiber mat-reinforced composites of this particular resin have exhibited high specific bending strength and stiffness comparable to those of glass fiber mat-reinforced composites. Another biosynthetic resin that has been recently gaining more attention in the biocomposite industry is poly(furfuryl alcohol) (PEA), or furan resin. 

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