Furan Resins from Furfural

In perfect analogy to the formation of phenol/formaldehyde resins, phenol reacts with furfural to form phenol/furfural resins. In phenol, due to its hydroxyl group, the hydrogen atoms in ortho and para positions are highly reactive. Consequently, phenol reacts with furfural to form phenol fiirfurylol  

These processes can continue as on account of its three highly reactive hydrogen atoms, the phenol can form not only phenol monofurfurylol but also phenol difurfurylol, and phenol trifurfurylol, the latter being shown below, thus permitting the formation of arbitrarily 

Instead of phenol, one of the cresols can be used as well [100]. In the cases of o-cresol and p-cresol, with one of the reactive ring positions taken up by a methyl group, it is readily understood why the polymerization rate is slowed down. By contrast, with m-cresol the reaction rate is unchanged. 

The principal advantages of phenol/furfiiral resins as compared to phenol/form-aldehyde resins can be summarized as follows  

The initiation of the reactions between phenol and furfural to form the resin can be catalyzed by both acid or alkali. As these reactions are exothermic, heat must be withdrawn at this stage. The final curing of the resin is universally triggered by the application of heat. 

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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. 

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. 

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. 

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. 

A number of very reactive compounds can be obtained from carbohydrates. Furfural, a furan, is one such compound that is produced by reacting a pentose carbohydrate under acidic conditions. Bill McKillip (Chapter 29) gives an excellent overview of furan resin chemistry and the use of furans for the production of polymeric materials such as adhesives. Furans, in particular furfural,... 

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 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 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... 

Furan resin is a generic term for a thermoset resinous product that contains a heterocyclic unsaturated furan ring in its molecular structures. Pentosans from com cobs and rice hulls are the main sources for the key ingredient, furfural. Commercially, the furfural alcohol polymer is the most important. All furan resins are dark in color and have a reddish-black appearance when catalyzed to cure they become black. 

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

Group of plastics composed of resins in which the furane ring is an integral portion of the polymer chain made from polymerization or polyconden-sation of furfural, furfural alcohol and other compounds containing furane rings also formed by reaction of furane compounds with an equal weight or less of other compounds. 

Furfural (furan-2-carbaldehyde Scheme 1) arises from the decomposition of sugars and is a commercially important raw material used in furfural-phenol resins and as a synthetic intermediate (see CHEC 1.15). 

Furan derivatives remained commercially insignificant until about 1920, when furfural was prepared in bulk from acid digestion of the pentosans of oat hulls and corn cobs for use as an industrial solvent and in the preparation of synthetic resins. How this change was wrought is one of the epics of industrial chemistry (B-56MI31000). 

The furan aldehydes were also affected differently by the resins. The fractions from the strong anion exchangers showed decreased concentrations of furan aldehydes, whereas the weak anion exchangers showed increased concentrations of furan aldehydes in the fractions used for fermentation. The lowest concentrations of furan aldehydes were observed in fractions from the strong anion exchangers with styrene-based matrices, Dowex 1x4 and Dowex 2x8, which displayed a decrease in the concentrations of furfural and HMF to approx 60-70%. 

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. 

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