Extension of simple polycondensation gelation theories to simple radical and mixed polycondensation/radical gelation

Considerations on the interface between lignocellulosic materials and tannin-based and other thermosetting adhesives

“…The results shown in Table 1 are the TMA-derived experimental deflection values f of beech wood joints bonded with the indicated polycondensation resins, thus the minimum deflection obtained for the joint at the end of the 'in situ' hardening of the adhesive; the energy of interfacial interaction E calculated by molecular mechanics [18][19][20][21][22], with the value of the average number of degrees of rotational freedom of the segment of the polymer between two consecutive cross-linking nodes m calculated according to the formula [14][15][16][17] …”

“…These and other results have already been used to adapt even the equations of Carrothers and Flory through the use of the average number of degrees of freedom of polymer segments between cross-linking nodes to describe the course of the polycondensation after the gel point and up to complete, stable networking 'in situ' in the lignocellulosic joint. Peculiarities in gel-point-forecasting by Flory's and Carrothers theories have been resolved on a theoretical basis, and by combination of the two theories into a single, simple equation, which can really be used with ease at the applied level, leading to much better precision of forecasting of the gel point than any of the two theories from which the equation is derived [14,15] and than any of the more complex theories in this field. Furthermore, the same approach has given a different theoretical basis to the observation that the intrinsic fracture energy at a lignocellulosic interface varies between being equal to, or equal to the square of the thermodynamical work of adhesion of an adhesive on a lignocellulosic substrate [26].…”

“…Indications were also obtained that such a relationship is also valid for polycondensation resins [14][15][16]. In this paper such a relationship is used firstly to show that correlation between these different parameters indeed exists also for polycondensation resins hardened directly in a wood joint, and secondly that regression equations correlating directly m with E and m with f can be derived for hardened phenol-formaldehyde (PF), resorcinol-formaldehyde (RF), melamine-formaldehyde (MF) and tannin-formaldehyde (TF) resins.…”

“…The values of m, E and α for the resins presented in Table 1 were known from previously reported work, and the relationship used between them was the phenomenological equation f = km/αE which has already been reported [14][15][16][17].…”

“…Recently work on the formation of polymer networks by photopolymerisable and polyester surface finishes on wood has yielded a mathematical relationship [14][15][16][17] between the energy of interaction (E) at the finish/ wood interface calculated by molecular mechanics (work of adhesion), the number of degrees of freedom (m) of the segment of the synthetic polymer between two cross-linking nodes, the coefficient of branching α hence the functionality of the starting monomer and the relative deflection (f ) obtained by thermomechanical analysis (TMA) of wood specimens coated with the photopolymerizable finish through the expression f = km/αE where k is a constant [14][15][16][17]. Indications were also obtained that such a relationship is also valid for polycondensation resins [14][15][16].…”