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The mechanism of adhesion of phenolic resins to cellulosic and lignocellulosic fibers has been explored using a nonpolymerizable bromine-labelled benzyl alcohol as a model for the adhesive. Bromine analysis by neutron activation techniques is sufficiently sensitive to show that reaction occurs much more extensively with the lignified fibers. This is attributed to the formation of covalent linkages between the model adhesive and the guaiacyl units in the lignin. The excellent general performance of phenolic adhesives on cellulose and lignocellulosic substrates can therefore be in part ascribed to the existence of high enthalpy covalent chemical bonds between adherend and adhesive.

synopsisThe use of surface tension measurements is proposed as a simple method for the determination of copolymerization ratios. The procedure depends on the parachor of the copolymer in the liquid state (n), which is defined by II = II,for solutions and II = [ D P ] Do for liquid or molten polymers, where II, is the parachor of the solvent of molecular weight M,; w p and w, are the weights of the polymer and solvent in solution; while IIo and Mo are the parachor and molecular weight of the repeating unit of the copolymer, respectively. The validity of this relationship is demonstrated by analysis of the surface tension properties of liquid silicone polymers, polystyrene-Decalin solutions, and molten polymers as well as by the calculation of the composition of some characterized tetrahydrofuran-propylene oxide copolymers. The application of surface tension measurement is also suggested as a means of estimating the degree of chain branching in a polymer.The establishment of the ratio of the constituent units in a copolymer is a common problem often encountered in macromolecular research. While the complete armamentarium of modern analytical chemistry can be brought to bear to resolve such questions, the procedures required may be cumbersome and tedious or they may involve the use of costly instrumentation not always readily ac~essible.~The simple physical measurement of the surface tension4J of a solution of the copolymer or the molten material is now proposed as a rapid, straightforward and inexpensive technique for securing this information without destruction of the sample. Thus, for example, rather precise (=k0.250/,) determinations of surface tensions can be made using the ubiquitous analytical laboratory balance. The overall procedure ultimately depends on the evaluation of the parachor II of the copolymer. The parachor was originally introduced as a physical constant by Sugden6 nearly half a century ago and defined by eq. (l), in which y is the surface tension of a substance of molecular weight M having a density of D L and d , for the liquid and vapor, respectively: 999