Molecular Mechanics/Experimental Methods Applied to Varnish/Primer/Wood Interactions

Abstract

Molecular mechanics modelling is used to calculate the energies of interaction, hence the molecular level energy of adhesion at the interface with crystalline cellulose I of three different photopolymerisable primers and of a polyester varnish at the interface with the primer/cellulose assembly. The energy of interaction for just one of the primers with the statistically most common conformation of amorphous cellulose has also been obtained for comparison. Experimental results of adhesion by a standard peel test and by thermomechanical analysis, in which the effect of energy dissipation by crack tip propagation has been respectively minimised or is not present, hence in which the energy of interfacial interaction is nothing else than the work of adhesion, correlated well with the energies of interaction calculated by molecular mechanics. An equation correlating energy of interaction at each finish/cellulose interface with the deflection and flexibility derived by thermomechanical analysis, and with the number of bond rotational degrees of freedom as well as degree of networking of the finish has been derived and is presented. Discussion of the relationship of the effects found with the glass transition temperature of the finish is also presented.Holzforschung / Vol. 51 / 1997 / No. 5 © Copyright 1997 Walter de Gruyter · Berlin · New York Brought to you by | University of Queensland -UQ Library Authenticated Download Date | 7/12/15 5:50 AM

Lignocellulosic substrates influence on TTT and CHT curing diagrams of polycondensation resins

“…Recently, an equation, and simpler regressions also, correlating the relative deflections obtained by TMA with the sum of the internal cohesive strength and interfacial energy of the interaction of a synthetic polymer with wood was obtained. 6,10,11 Interesting conclusions on a variety of aspects in UF and PF polyconden- sation and other networks have already been obtained 6,10,11 by this approach. However, it also appeared that at least in one region of the curing process on wood of formaldehyde-based polycondensates some lack of correspondence might exist with what already has been described from epoxy resins on glass fiber for the generalized form of the CHT (and TTT) diagram itself.…”

“…6 The only experimental data needed to calculate in this manner is the deflection in m obtained by TMA for a given network on wood at its different relevant stages of advancement which is readily obtainable by methods already reported. 6,10,11 This means that substituting T gmax for T gϱ will adjust the value of m end to T gmax and accordingly adjust the value of , validating the alternative DiBenedetto equation based on T gmax .…”

On the correlation of some theoretical and experimental parameters in polycondensation crosslinked networks. II. Interfacial energy and adhesion on cellulose substrates

“…lated in the same manner by substituting the number of reactive carbon atoms to the functionality [i.e., for each C|C present this gives two reactive carbons, and Molecular mechanics in the broader sense of the term thus a Å 1/( f 0 1 ), where f is 2 rather than 1 as it is a computational technique that is, among its other would be in polycondensates 8 ]. applications, particularly suited for determining at the Although interesting conclusions about the covalent molecular level the interactions at the interface of monetworking of polymers, both polycondensates and othlecularly well-defined polymers.…”

“…modulus E for each of the cases tested. Since the deflections D f obtained were proven to be constant and repro-DISCUSSION ducible, 8 and they are proportional to the flexibility of Table I presents the computational results of the energthe assembly, the relative flexibility as expressed by ies of interaction between different synthetic polythe Young's modulus of the two primers can be calcumers and crystalline cellulose I derived from previous lated for the two finishes through the relationship E 1 / work. 1 -6,8 -10 It must clearly be pointed out that the mo-…”

“…interfacial energy problems. Recently, an equation, as well as its simpler regressions, correlating the relative deflection obtained by thermomechanical analysis with the sum of the interfa-EXPERIMENTAL cial energy of interaction of a synthetic polymer with wood plus the internal cohesive strength of the hardMaterials ened synthetic polymer has been obtained, [8][9][10] namely Three photopolymerizable primer monomers, namely E Å 0km/(af ) the linear hexanediol diacrylate (HDDA ), the branched trimethylol propane triacrylate (TMPTA) and the linwhere k is a constant dependent upon the testing condiear tripropyleneglycol diacrylate (TPGDA), supplied tions used, m is the average number of degrees of freeby CIBA-GEIGY, Basel, Switzerland, and a model of a dom between crosslinking nodes of a hardened network, linear unsaturated polyester -alkyd varnish repeating E is the sum of the energy of interaction at the interface unit, were used for the study. The following polycondenof the synthetic polymer and the substrate and of the sation resins were used: (1 ) An industrial pure resorinternal cohesive energy of the synthetic polymer (the cinol-formaldehyde (RF) cold set resin having a solids internal energy of the substrate is not considered becontent of 53%, a pH of 8.3, and a manufacturing molar cause the deflection measured is relative to the subratio R : F of 1 : 1.5, to which was added one further strate alone ), and a is Flory's coefficient of branching molar proportion of paraformaldehyde as hardener to for polycondensates.…”