Richard H. S. Wang

Flakeboards made from aspen and southern pine wood flakes reacted with gaseous ketene

Abstract Southern pine and aspen wood flakes were chemically modified by reaction at ca. 55°C with ketene in the absence of solvent. Reactions were relatively slow, with weight gains of up to 17% and 20%, respectively, obtained. Acetyl content correlated with weight gain only up to the 12% level. Water and solvent extraction of ketene-modified southern pine and aspen flakes showed very little loss in acetyl. Flakeboards made from southern pine and aspen flakes treated with ketene showed a greatly reduced rate and extent of swelling resulting from liquid water sorption as compared to control boards. Similar results were obtained in swelling tests done in water vapor. Ketene modification had a much greater effect on improving dimensional stability properties of aspen flakeboards than on southern pine flakeboards.

Effects of Titanium Dioxide on the Weatherability of Thermoplastic Polymers

Titanium dioxide is used widely as an opacifying agent for paper, fibers, coatings, and plastics. Our data show that this white pigment functions as either a weathering stabilizer or sensitizer, depending on its concentration or treatment during manufacture and use. Lifetimes of oxidizable polymers, such as polypropylene and cellulose esters, can be reduced greatly by the presence of photoactive titanium dioxides; oxidation-resistant polymers, such as poly(tetramethylene terephthalate), are affected to a much lesser extent. The undesirable effects of titanium dioxides can be reduced greatly by the presence of certain additives. The large effects of temperature on the lifetimes of certain polymers indicate that considerable care must be exercised in the design of accelerated test methods.