Wood resin acids

Sizing chemistry is critically linked to the pH of the paper-making system, and the oldest and most established sizing system involves the use of wood resin acids and aluminium sulfate. The presence of aluminium sulfate gives rise to an acidic pH ( 4.5), because the aluminium ion in aqueous solution exists as a hexahydrated complex capable of dissociation according to the equilibria shown in equations 7.1-7.3. Further equilibria are also possible. 

Wood also contains 3—10% of extraceUulat, low molecular weight constituents, many of which can be extracted from the wood using neutral solvents and therefore ate commonly caUed extractives. These include the food reserves, the fats and their esters in parenchyma ceUs, the terpenes and resin acids in epitheUal ceUs and resin ducts, and phenoUc materials in the heartwood. Resin materials occur in the vessels of some hardwood heartwood. 

Wood is the raw material of the naval stores iadustry (77). Naval stores, so named because of their importance to the wooden ships of past centuries, consist of rosin (diterpene resin acids), turpentine (monoterpene hydrocarbons), and associated chemicals derived from pine (see Terpenoids). These were obtained by wounding the tree to yield pine gum, but the high labor costs have substantially reduced this production in the United States. Another source of rosin and turpentine is through extraction of old pine stumps, but this is a nonrenewable resource and this iadustry is in decline. The most important source of naval stores is spent sulfate pulpiag Hquors from kraft pulpiag of pine. In 1995, U.S. production of rosin from all sources was estimated at under 300,000 metric tons and of turpentine at 70,000 metric tons. Distillation of tall oil provides, in addition to rosin, nearly 128,000 metric tons of tall oil fatty acids annually (78). 

Furfural is a colourless liquid which darkens in air and has a boiling point of 161.7°C at atmospheric pressure. Its principal uses are as a selective solvent used in such operations as the purification of wood resin and in the extraction of butadiene from other refinery gases. It is also used in the manufacture of phenol-furfural resins and as a raw material for the nylons. The material will resinify in the presence of acids but the product has little commercial value. 

Tall oil rosin is obtained from crude tall oil obtained from the Kraft (sulphate) pulping of various coniferous trees in the paper manufacturing industry. During the Kraft pulping process the fatty acids and the resin acids from the coniferous wood are saponified by the alkaline medium. On concentration of the resulting pulping liquor, the sodium soap of these mixed acids rises to the surface from where they are skimmed out. By acidification of this material with sulphuric acid, the crude tall oil is obtained. Fractional steam distillation of the crude tall oil allows the separation of the tall oil fatty acids and the tall oil rosins [21]. 

The resin acids found in rosins are generally of the abietic- and pimaric-type. Rosins of various pine species differ in their content of abietic vs. pimaric-type acids. Rosins from species exhibiting high abietic-type acid compositions are preferred for production of rosin derivatives. However, the differences in properties of rosins are often associated with their non-resin acid content instead of their chemical compositions. On the other hand, the compositions of rosins from different sources greatly differ [22]. Table 8 shows a typical distribution of resin acids in rosins obtained from gum, tall oil and wood sources. 

Resin acid Tall oil rosin Wood rosin Gum rosin... 

Tannenbaum, m. fir tree pine tree, tannenbaumartig, a. arborescent, dendritic. Tannen-baumkristall, m. arborescent crystal, dendrite, -harz, n. fir resin, -harzsaure, /, fir-resin acid, specif, abietic acid, -holzstoff, m. fir (wood) pulp, -nadelol, n. fir-needle oil (loosely) pine-needle oil. -zapfen, m. fir cone, -zapfenol, n. fir-cone oil (loosely) pine-cone oil. 

Water emissions from paper production softeners (BPA), other phenolic compounds (NPE, APE), other surfactants (LAS), biocides (benzothiazoler, dibromo compounds), wood extractions (terpenoids, resin acids) and more... 

Copals, sometimes referred to as immature amber, originate from Africa, Asia or central American countries and derive from the Araucariaceae and Leguminosae families. Polymerised communic acid and agathic acid are found as the main compounds in these fossil resins. The extreme hardness of copal results from polymers of resin acids such as ozoic acid, an enantiomer of communic acid that can polymerize and thus enable fossilization [86]. They are still commonly used today for varnishing and protecting wood. 

Wood contains a small proportion (usually less than 5%) of components which are extractable by organic solvents such as ethanol or dichloromethane. The proportion of these extractives varies in hardwoods and softwoods and also between species. Although many of these substances are removed during the chemical pulping process, some may still be retained in the final sheet of paper. Their chemical composition is very varied, and they include alkanes, fatty alcohols and acids (both saturated and unsaturated), glycerol esters, waxes, resin acids, terpene and phenolic components. The proportion which remains in pulp and paper depends upon the pulping process used. In general, acidic components such as the resin and fatty acids are relatively easily removed by alkali by conversion to their soluble... 

The resin acids present in pulps, particularly those from softwood, have also been found to be significantly toxic to aquatic organisms. The amount in wood varies greatly between species (Table 10.4). Between 0.3 and 3.6 kg/tonne is extracted during pulping. 

Table 10.4 Resin acid content of various woods.

Species Total resin acids (kg/tonne of dry wood) References... 

Tricyclic diterpenes-resln acids. Wood resin constituents, e.g. abietane derivatives, have also been implicated in pest resistance (Figure 4). Among the conifer-associated sawflles many prefer to feed... 

Air-entraining Neutralized wood resins Fatty acid soaps Alky-aryl sulfonates -3 to 0... 

The oleoresinous exudate or "pitch of many conifers, but mainly pines, is the raw material for the major products of the naval stores industry. The oleoresin is produced in the epithelial cells which surround the resin canals. When the tree is wounded the resin canals are cut. The pressure of the epithelial cells forces die oleoresin to the surface of die wound where it is collected. The oleoresin is separated into two fractions by steam distillation. The volatile fraction is called gum turpentine and contains chiefly a mixture of monoterpenes but a smaller amount of sesquiterpenes is present also. The nonvolatile gum rosin 5 consists mainly of llie dilerpenuid resin acids and smaller amounts of esters, alcohols and steroids. Wood turpentine, wood rosin and a fraction of intermediate volatility, pine oil are obtained together by gasoline extrachon of the chipped wood of old pine stumps. Pine oil is largely a mixture of the monoterpenoids terpineol. borneol and fenchyl alcohol. Sulfate turpentine and its nonvolatile counterpart, tall oil, 5 are isolated as by-products of the kraft pulping process. Tall oil consists of nearly equal amounts of saponified fatty acid esters and resin acids. 

Phenolic resin treatment imparts considerable decay resistance to wood as do other dimension stabilization treatments (17). The treatment increases the electrical resistance materially (49). It also gives wood considerable acid resistance (45) and heat resistance (50). Treated specimens have been subjected to cyclic heating to"T05°C followed by cooling more than 50 times without visual harm, whereas untreated controls charred and disintegrated badly after a few heating cycles. Phenolic resin treatment, however, does not impart true fire resistance to wood, but it does improve the integrity of the char, thus cutting down on fire spread (45). 

Wood et al. [174] analysed long-chain fatty hydroxy acids. After esterification with diazomethane, hydroxyl groups were silylated with HMDS. DEGS and Apiezon L were used as the stationary phases and even the partial resolution of some diastereoisomers was achieved. TMS esters have similarly been applied to the analysis of resin acids, and retention data have been reported for several of them on SE-30, Apiezon L, QF-1, etc. [175]. 

Sometimes terms pathological and physiological resin are used. Pathological resin, located in resin canals, is mainly composed of resin acids and monoterpenes and protects the wood against biological damage. Physiological resin, located in the ray parenchyma cells, is rich in fats and constitutes a supply of reserve food. Hardwoods contain only this type of resin. 

The resin content of wood and its composition vary considerably, depending on such factors as place of growth, age of the tree, and genetic factors. For example, the resin content of Norway spruce (P/cea abies) is considerably higher for stems grown in the northern than in the southern parts of Scandinavia. The resin content within the same stem also varies, but in a very irregular manner. In all pines, the heartwood contains much more resin than the sapwood, whereas the opposite seems to be true for P/cea species as indicated by data for Norway spruce. The heartwood extractives in both pine and spruce contain resin acids and free fatty acids as main components,... 

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