Hemlock bark extract

The chemical reaction of western hemlock bark extract with... 

Herrick, F.H. Chemistry and Utilization of Western Hemlock Bark Extractives. J. Agric. Food Chem. 28, 228 (1980). 

Condensed tannins constitute more than 90 per cent of the total world production of commercial tannins (200000 tons per year) [11]. Their high reactivity towards aldehydes and other reagents renders them both chemically and economically more interesting for the preparation of adhesives, resins and other applications apart from leather tanning. The main commercial species, such as mimosa and quebracho, also yield excellent heavy duty leather. Condensed tannins and their flavonoid precursors are known for their wide distribution in nature and particularly for their substantial concentration in the wood and bark of various trees. These include various Acacia (wattle or mimosa bark extract), Schinopsis (quebracho wood extract), Tsuga (hemlock bark extract), Rhus (sumach extract) species, and various Pinus bark extract species, from which commercial tannin extracts are manufactured. 

Herrick F W 1980 Chemistry and utilization of western hemlock bark extractives. J Agric Food Chem 28 228-237... 

Anderson A B, Wong A, Wu K-t 1975 Douglas-fir and western hemlock bark extracts as bonding agents for particleboards. For Prod J 25(3) 45-48... 

Steiner P R, Chow S 1975 Factors influencing western hemlock bark extracts use as adhesives. West For Products Lab Rept VP-X-153 Vancouver B C, 25 p... 

This paper is a report on preliminary studies evaluating the suitability of bark extracts from four West Coast softwood species as bonding agents for particleboard. The barks investigated include white fir (Abies concolor), ponderosa pine (Pinus ponderosa), Douglas fir (Pseudotsuga menziesii) and western hemlock (Tsuga heterophylla) ... 

Attempts to make adhesive formulations by direct reaction of formaldehyde or its equivalent resulted in products that were excessively viscous, and the working time was too short for commercial application (57). It was concluded that formaldehyde, although readily reactive with the tannin molecule, provided much too short linkages to connect the bulky tannin molecules. This problem was circumvented by the preparation of a polymethylolphenol reagent that, when put in solution with the bark extract, formed a combination that was stable for several weeks at room temperature. When heated, the polymethylolphenol and bark extract reacted rapidly to form an infusible resin. Commercial trials were made to produce exterior-grade Douglas-fir plywood. Widespread use of the extracts for this purpose, however, was inhibited by a drop in the price of phenol below what the bark extracts could be manufactured for. (The best extract for adhesive purposes was an ammonia extract of hemlock bark converted to a sodium derivative prior to spray drying, a more costly extraction procedure than simple sodium hydroxide extraction of bark.)... 

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. 

The tannins are synthesized by plants and are abundantly distributed in many different forms of plant life. Common sources of tannins include for example, the bark, leaves, fruit and roots of many plants most tannins, however, have been and are still derived from the bark of a few trees and shrubs, such as oak, chestnut, hemlock, mangrove, quebracho, and wattle, from which they are generally extracted with water. 

Fraser H S, Swan E P 1979 Phenolic character of sequential solvent extracts from western hemlock and white spruce barks. Can J For Res 9 495 - 500... 

Two examples are illustrative Shortly after the turn of the century, one of the ten largest companies in the United States was totally dependant upon extractives for its raw material (23). The Central Leather Company, successor to the United States Leather Company, had tanneries scattered all over the state of Pennsylvania, each of which extracted tannin from the bark of the eastern hemlock Tsuga canadensis). Today not only is it the only one of the ten companies no longer in existence, but there is not a single producer of native tannin in North America. 

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