No 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

INTRODUCTIONmerizable monomer, hence, not of the repeating unit of the polymer itself. Thus, while the equation is useful to forecast the values of m in a network (and vice versa Recently, an equation and simpler regressions, also, of E) from a polymerizable monomer, it must be realcorrelating the relative deflections obtained by thermoized that the limitation of the number of degrees of mechanical analysis with the sum of the interfacial enfreedom to account for the constraints introduced by ergy of interaction of a synthetic polymer with wood the formation of the network itself had to be introduced plus the internal cohesive strength of the hardened synat the level of m and a. thetic polymer has been obtained.1-2 Namely, f Å 0km/ While interesting conclusions on polymer net-(aE) (or f Å km/(aE), according to the convention working 1,3 and good network forecasting have been obused for E), where k is a constant depending on the tained already with such an approach, the validity of testing conditions used, m is the average number of the same equation can be checked for molecular medegrees of freedom between crosslinking nodes of a chanics calculations in which the repeating unit of the hardened network, E is the sum of the energy of interacpolymer, rather than the monomer, is considered. Thus, tion at the interface synthetic polymer-substrate and the validity of the equation can be checked by decreasof the internal cohesive energy of the synthetic polymer ing the number of degrees of freedom m directly in the (the internal energy of the substrate is not considered molecular mechanics calculations. This can be done by because the deflections measured are relative to the introducing constraints in the repeating unit of the substrate alone), and a is Flory's coefficient of polymer, namely, with the reactive groups of the monobranching for polycondensates. The above equation has mer already reacted and fixed in the position of minibeen shown to work also for radical hardening polymum energy found for the monomer alone, hence, with mers, with the provision that the coefficient a is not the crosslinking nodes fixed. This can then be used to Flory's coefficient of branching anymore but a coeffireproduce directly in the molecular mechanics calculacient calculated in a similar manner, 3 and also for nontion the situation a repeating unit finds itself in a covacrosslinked entanglement networks.