Cb. Vick et al., STRUCTURAL BONDING OF ACETYLATED SCANDINAVIAN SOFTWOODS FOR EXTERIOR LUMBER LAMINATES, International journal of adhesion and adhesives, 13(3), 1993, pp. 139-149
The bonding properties of a resorcinol-formaldehyde (RF), a phenol-res
orcinol-formaldehyde (PRF), a crosslinking polyvinyl acetate (PVAX) an
d an emulsion polymer-isocyanate (EPI) adhesive were determined in lam
inates of acetylated and unmodified Scandinavian pine (Pinus silvestri
s L.) and spruce (Picea abies Karst.). The effects of different degree
s of acetylation in adjacent laminae were also examined. The effective
ness of adhesion was determined by measuring delamination after three
cycles of vacuum-pressure soaking in water and drying, and by measurin
g shear strength and wood failure in dry and water-saturated condition
s. Acetylation stabilized laminates so that essentially no stress frac
turing developed in the wood during severe cyclic delamination tests.
Bonds to acetylated and unmodified wood with RF and PRF adhesives resi
sted delamination well, whether adjacent laminae were of equal or uneq
ual degrees of acetylation. Acetylation affected adhesion of both adhe
sives as indicated by lower percentages of wood failure after water sa
turation. The PVAX adhesive also resisted delamination well in acetyla
ted wood so long as individual laminae had equal acetyl content. Acety
lated laminates with PVAX effectively resisted stress fracturing near
bondlines and within the wood, but the unmodified laminates fractured
severely. The EPI adhesive bonded the unmodified laminates so well tha
t no delamination and remarkably little stress fracturing developed du
ring cyclic delamination tests. Acetylation affected adhesion of the E
PI adhesive as indicated by low wood failure in wet shear tests, howev
er, shear strength and wood failure were high in acetylated wood in th
e dry condition.