The Role of Extractives in the Hydrophobic Behavior of Loblolly Pine Rhytidome
Keywords:
<i>I'inus taeda</i>, phellogen, phloem, wettability, contact angles, extraction, heating, agingAbstract
Wettability, as indicated by contact angle with water, of phellogen and old phloem surfaces of loblolly pine (Pinus taeda) rhytidome was determined after extraction, heating, and aging. These two tissues are the predominant surfaces exposed after milling pine bark into small particles.
Contact angles measured for bark surfaces were over 50% higher than those published for wood. Old phloem gave an average angle of 118° while phellogen was significantly more wettable with an average contact angle of 106°. Extraction of bark by diethyl ether and methanol increased wettability. Furthermore, large contact angles were measured on glass plates covered with condensed bark extractives. Heat treatments at 105 C for 78 hr increased the contact angle, thus decreasing wettability. The influence of heating time on contact angle was described by an exponential function whose coefficients were used for quantitative assessment of the treatment effects. Surface aging was shown to involve the same general physico-chemical processes as heating. Effects of heating were shown to be related to ether and methanol soluble extractives in loblolly pine bark.
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