Waxes extraction from bark

Compounds which fit the broad definition of wax have been found in extracts of suberin-rich barks (Martin and Juniper, 1970). The wax associated with suberin, because of its physical location, cannot be as readily removed as cuticular wax, and therefore the exact location of the extracted wax is not clear. However, it seems likely that a major portion of the waxes extracted from barks are associated with the polymeric material suberin. 

Waxes, fats and fatty aeids, oils and resins are all readily extraeted from bark using non-polar solvents, while tannins, gums, peetin, soluble earbohydrates and sugars ean be removed by aqueous extraction. The amount of extraetives that ean be removed diminishes signifieantly after seasoning of the bark. 

In the search for the paper factor, extracts from several gymnosperms were assayed on P. apterus fifth instars (Table 1) [83, 84, 85]. Extracts of wood and bark of a number of these conifers were also injected into pupae of the wax moth, Galleria mellonella a localized scaleless patch was observed in the pupal cuticle at the site of injection with these extracts. However, no abnormal effects on development were observed [86]. The authors speculated that this absence of activity may be attributable to the dilute concentration of active ingredients in the extracts. 

Cuticular waxes are removed from surface layers of intact tissues by washing with organic solvents such as hexane or chloroform. It is very important to use redistilled solvents particularly since compounds such as hydrocarbons are natural components of most waxes. Internal waxes are extracted from tissues following homogenization by the usual methods (Section 6.3.1). Waxes have also been extracted from suberin-rich barks (Martin and Juniper, 1970). 

Fig. 6.4.1. Chain-length distribution of the alkanes in the wax from periderm (solid bars) and leaf cuticle (open bars). The periderm wax was extracted from underground storage organs of vegetables (116) and from the bark of trees (440)...

Trocino s concept of total utilization of the raw material, Douglas-fir bark, to produce several salable products was good, and earned Bohemia the 1976 Environmental Award from the American Paper Institute and the American Forest Products Institute. Unfortunately a certain amount of solvent losses is inevitable. Thus, efficient solvent extraction and recovery of solvent to obtain the primary product in a 3% yield, based on bark, could only be expected to be cost effective if the product sold in the dollars per kilogram range, such as carnauba wax imported from Brazil or Mexico. Unrefined Douglas-fir wax is soft because of the presence of terpenes, unsaturated fats, etc., and is subject to discolorization by iron salts because of the presence of ferulate esters, which promote the formation of complexes. As in the case of the polyphenolic extractives from redwood and hemlock bark, the product end-use was not sufficiently unique to ultimately justify a price that would support production and operating costs, and generate a reasonable profit. 

Trocino F S 1974 Method of extracting wax from bark. US Patent 3789058... 

Some commercial hope was directed towards Dou-glas-fir wax, which is extracted from the bark. It is mainly an ester wax (m.p. 59.2 °C). A small plant in the northwestern United States was shut down in 1970 because of poor economy. 

Weighed amounts of prepared wood particles were tumbled in a laboratory blender and a wax emulsion (1 percent solids oven-dry basis) was added from a spray gun, after which concentrated bark extract (8 percent solids oven-dry basis) was sprayed onto the tumbling mixture. Powdered paraformaldehyde (1 percent oven-dry basis) was added slowly to the stirred mixture. 

All these lipophilic components perform a function for the living tree. The exact function is not understood for all substances. The composition of the lipophilic wood extractives varies from species to species, and is far from homogeneously distributed in the tree. All woods contain sterols, waxes, glycerides and other aliphatic extractives. However, softwood contains considerable quantities of rosin acids (e.g. abietic acid), but these acids do not exist in hardwood (e.g. birch and aspen). Certain components are predominantly located in the bark of the tree. The sterol fraction from birch and aspen bark comprises almost exclusively beta-sitosterol by way of example. 

Waxes are usually isolated by extracting the tissue with a nonpolar solvent such as chloroform or hexane. Cuticular waxes can be extracted by a quick dip into the solvent at room temperature, but suberin-associated waxes are more difficult to remove because they are embedded in the suberized cell wall (232). Wax from the suberized cells of bark has to be isolated by Soxhlet extraction of dried and powdered tissue to assure its complete removal. Isolated wax can be subjected to GC/MS analysis either after separation into various classes by thin-layer or column chromatography or directly after derivitization of the functional groups (232, 253, 459, 460). 

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