CONDENSED

TANNIN-RF$ORCINOL ADDUCTS AND

THEIR USE IN WOOD-LAMINAnNG

ADHFSIVES:

AN EXPLORATORY STUDY

R.W. HEMINGWAY SouthernForestExperiment Station, 2500 ShreveportHighway, Pineville,Louisiana 71360 R.E. KREIBICH ResearchDivision, Weyerhaeuser Compony,Tacoma, . Washington,98401

SYNOPSIS The reaction of a tannin extract (containing about 30"/0carbohydrate) from loblolly pine (Pinus taeda L.) bark (two parts) and resorcinol (one part) at 12O"C for 24 h with acetic acid catalyst gave a product containing predominantly oligomeric procyanidin-4-resorcinol adducts (3Wo), unreacted resorcinol (22%). carbohydrate (20010).the resorcinol adduct 2R,3R,4S 4-(2.4-dihydroxyphenyl).fIavan-3,3',4',5.7-pentaol(80;0),its 2,3-transisomer (40;0).and catechin and epicatechin (7%). The above mixture was used as a resorcinol replacement in a conventional phenolresorcinol-formaldehyde laminating adhesive as used in the manufacture of laminated wood beams. Preliminary gluing results suggest that. with some modification of adhesive formulation and resin synthesis conditions. room-temperature curing adhesives for wood-laminating purposes could be produced successfully using such condensed tannin-resorcinol adducts to replace more than (JJ'foof the resorcinol requirement.

INTRODUcnON The increasingcost and scarcity of resorcinol required for the synthesisof cold-setting wood-laminating adhesivesprompted our consideration of the use of condensedtannins extractable from conifer barks as a source of inexpensivebut highly reactivephenols.The condensedtannins in loblolly pine bark are polymeric procyanidins (1) that are composedpredominantly of 2,3cis-procyanidin units terminated with the 2,3,-trans-flavan-3-ol(+ )-cata:hin (Fig. I) [1]. Both C(4)-c(6) and C(4)-C(8) interflavanoid bonds are present in thesepolymers [2,3]. Condensedtannins isolated from a broad s~trum of plants, including bark of the southern pines, exist as mixtures of procyanJournal or Applied Polymer Science:Applied Polymer Symposium40. 7~90 (1984) Published by John Wiley & Sons. Inc. Not subj~t to copyriaht within the United States CCC 0570..4898/84/030079-12$04.00

HEMINGWAY AND K.REIBICH

80

HO

OM FIG. 1. Polymeric procyanidins (I) .A = 4.8-8.3 units,8=4.8-6. I unit. M. ,..;., 9 flavanunits.

idins of a comparatively broad molecular-weight distribution with numberaveragemolecular weights centeringon 2

Wood failure ('Yo) All valua are averaaes of (mly)

two specimens.

m 78

HEMINGWAY AND KREIBICH

90

and related approachesto the developmentof resorcinol replacementsfrom bark extracts. The authors thank Dr. J. J. Karcbesy, Department of Agricultural Chemistry, Oregon State University, Corvallis. Oregon, for someof the spectra reported in this paper.

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