Nonequilibrium phenomena influencing the wetting behavior of plant fibers

It is examined whether useful information on plant fiber surfaces can be re trieved from wetting experiments such as dynamic contact angle (DCA) analys is by use of the Wilhelmy technique and the Lifshitz-van der Waals acid-bas e theory. It is argued from a theoretical point of view that plant fibers m ay give rise to various complex phenomena during wetting experiments, pheno mena which are typically not found for synthetic fibers, and that these phe nomena can be a source of invalidation of experimental techniques which are commonly thought to supply information on equilibrium (or quasi-equilibriu m) properties of plant fiber surfaces or of surface-liquid interactions, Th e nonequilibrium phenomena are studied experimentally by DCA analysis of 10 sisal fibers, 10 coir fibers, and 5 polyacrylate-coated glass fibers. The fibers are immersed in deionized water at 10 different speeds ranging from 2 to 100 mum s(-1) and the relationship between immersion speed and contact angle is examined, In contrast to what is found for the coated glass fiber s, the results indicate that the (aqueous) wetting behavior of sisal and co ir fibers is qualitatively far from the behavior which should ensure the me aningful interpretation of the wetting data as (quasi-)equilibrium data. Fr om both a theoretical and a practical basis it is hence concluded that none quilibrium phenomena necessitate a more severe form of precaution toward su rface energy component theories when these are used for interpreting plant fiber wetting than what is currently at issue. (C) 2001 Academic Press.