Conifer bark extracts

These results may be compared with viscosities obtained in a similar way from conifer bark extracts which, while heterogeneous, contain polymeric pro-cyanidins or mixed polymeric procyanidins and prodelphinidins as their predominant components (2). For example, Weissman (25) reported a viscosity of 65 mPa-s for a 30% solution of the water extract from Pinus oocarpa bark, and Dix and Marutsky (26) obtained a value of 31 mPa-s for a similar solution from Picea abies bark. These viscosities are similar to those observed for the 30% procyanidin polymer solutions. They indicate that the viscosities of these bark extract solutions are dominated by the proanthocyanidins and that there is little influence from any accompanying polysaccharides-as already suggested by Weissmann (25)-in contrast to wattle extracts where gums play an important role in determining solution viscosities (7). 

If this method proves to be commercially feasible, a renewable and abundant waste product of forest products manufacture could replace expensive petrochemicals. Additionally, use of an inexpensive waste product from processing of forest products could materially reduce adhesive costs and expand opportunities for manufacture of structural materials from low-quality wood. This benefit is particularly important since the difficulty in producing large, strong, structural members from timber resources of declining quality is growing exponentially with time. The cost-benefit ratios of replacing PRF resins with extracts from conifer barks are, therefore, quite favorable in a honeymoon system. 

When P. radiata bark is extracted by sulfite-carbonate, the solution viscosities are much lower. For example, Woo (30) reported a viscosity of 1,600 mPa-s for a 45% solution of Tannaphen, a commercial tannin extract from P. radiata bark that contains approximately 70% proanthocyanidins. When extracted with sulfite-carbonate, the proanthocyanidins will be partly depolymerized 31), which will cause a fall in viscosity. Whether the very high viscosities observed for aqueous extracts by Yazaki and Hillis 29) are due to the P, radiata proanthocyanidins being of much higher molecular weight than other conifer tannins or due to complexation of the proanthocyanidins with the polysaccharide fraction 32) remains to be shown. 

If polymeric procyanidins extractable from conifer tree barks are to be used in adhesive formulations requiring condensation with phenol-formaldehyde prepolymers, these reactions must be performed at acidic pH conditions, and because of solubility limitations, this will probably require the use of sulfonate derivatives. 

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. 

Arabinogalactan occurs in high concentration (5% to 35%, dry weight basis) in the heartwood of many species of Larix, a deciduous conifer native to the temperate and subarctic zones of the Northern Hemisphere in fact, the presence of this water-soluble, easily extractable polysaccharide is characteristic of Larix spp. Larch arabinogalactan will accumulate in masses under the bark as a result of injuries however, this supply is limited and its collection is difficult. 

Condensed tannins are excellent clay dispersants. Sulfite extracts from conifer tree barks are very effective in reducing the viscosity and increasing the gel strength of muds used in well drilling (72, 92, 145, 246, 248). Condensed tannins still face strong competition from lignosulphonates for this application, particularly because of the comparatively low thermal stability and salt tolerance of the tannin (96). However, reaction of tannins with chromium increases their thermal stability considerably to permit their use in muds for wells drilled as deep as 6000 feet (208). Sulfonated condensed tannin derivatives have found use as dispersants in other specialty applications, such as ceramic clays, pigments, carbon black, and pesticides (93, 96). 

The most important natural feedstock is turpentine. It can be produced by tapping suitable conifers, a process that involves making an incision in the bark and collecting the exudate in cups. Such turpentine is called gum turpentine. Wood turpentine is extracted mainly from tree stumps but the major source of turpentine is known as crude sulphate turpentine (CST) as it is a by-product of the Kraft paper process. 

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