Pine bark tannin, purified

The purified pine bark tannin was obtained in the following manner. The phloem of freshly felled loblolly pine trees was removed by carefully peeling the outer bark away at the cork cambium and then peeling the white phloem from the xylem cambium. Strips of phloem were cut into sections of about 2 to 5 in2 and immediately immersed in acetone-water (70 30, v/v). The extraction flasks were kept at ambient temperature, protected from exposure to light, for 48 hr, after which the solvent was recovered by filtration. The acetone was removed under vacuum on a rotary evaporator, and the aqueous solution was extracted four times with an approximately equal volume of ethyl acetate to remove low molecular weight phenolics. The remaining water-soluble extract was freeze-dried. Aliquots (about 50 gm) were redissolved in methanol-water (1 1, v/v), and the solutions were applied to 2.4 X 90 cm Sephadex LH-20 columns packed in this same solvent. The columns were eluted with methanol-water until no more colored material was eluted. The condensed tannin polymers absorbed... 

Figure 2. Pullout forces of polyester cords for various tannin-containing adhesive dips as a function of percent resorcinol. 1, pecan pith sulfite extract 2, purified pine bark tannin 3, pine bark sulfite extract 4, peanut skin tannin.

Figure 5. Comparison of the pullout forces of polyester and nylon cords for dips containing purified pine bark tannin.

In the second approach (120), condensed tannins were purified of co-occur-ring carbohydrates and used as resorcinol replacements in a honeymoon system (116) as described previously in use of wattle tannin adhesives. One surface was spread with a commercial phenol-resorcinol-formaldehyde laminating adhesive, to which additional formaldehyde was added. The other surface was spread with pine bark tannin extract in sodium hydroxide solutions. Bonds meeting the requirements of the American Institute of Timber Construction were also obtained using this approach. It was necessary to remove the carbohydrates, however. Addition of the separated carbohydrates at comparatively low levels (about 10%) resulted in bonds with low wood failure. 

Four types of condensed tannins were studied in the adhesive dips 1) extracts from pecan nut pith obtained by digestion with aqueous sodium sulfite-sodium carbonate solutions, 2) purified tannins from southern pine bark, 3) extracts from southern pine bark obtained by digestion with aqueous sodium sulfite-sodium carbonate solutions, and 4) tannins extracted with acetone-water solutions from peanut skins. 

The pecan pith extract was the best of the tannin extracts examined in bonding to polyester cord. Pullout forces using this extract to totally replace resorcinol were nearly twice as high as in the standard dip. The purified pine bark extract also gave very good results. One commonality in these two extracts... 

It has been observed many times that aqueous condensed tannin extracts, especially from pine barks, sometimes display very high viscosities. This is usually attributed to the high MW of the tannin species. Direct measurement with purified condensed tannin from Pinus radiata inner bark in water at 20 °C showed that the polymer had a low intrinsic viscosity ([ /] = 3.5), which could not account for such behavior (L. J. Porter, unpublished observations). 

---