On the behavior of mixed furfural‐formaldehyde phenoplaste
Authors: Mikes J. A. 
Published: November 2014

The hardening of phenolic resins depends on the presence of reactive hydrogen atoms in the ring. Usually it is admitted that these active atoms, such as the hydrogen atom are inorthoandparaposition. The phenoplasts composed of elements of identical structure, or of variable structure, contain two, and not more, hydrogen atoms per monomer molecule; they usually give only linear chains without any transverse network formation. In the condensation of phenol with furfural, there is a tendency toward crosslinking of the linear homologe; indeed, besides the presence of a bifunctional aldehydic group in the furan ring, there are 2–4 reactive positions (in agreement with the character of the reaction). This process of transverse reticulation is followed by the formation of brittle products; consequently, these furfurol‐phenol resins are with difficulty adopted for industrial uses. An attempt was made to obtain phenoplasts with good technical properties, by combining furan resins (of which the transverse crosslinking is characteristic) with resins of low hardening and low reactivity based on homologe of phenol. By condensing furfurol withortho‐eresol poor results are obtained, as well as with xylenol‐furfural resins. An attempt at condensation with a mixture of furfural and formaldehyde was also unsuccessful, because the most active constituents have reacted with the most reactive centers; this effect inhibits the incorporation of the residual constituent during the reaction. The product was heterogeneous and contained insertions of condensation products with only one constituent as well as un‐condensed products. An effective solution of the problem, which was discovered by the author, consists of mixing the furfural‐cresol resin at stage A with a formaldehyde resin at the same stage. The further condensation and hardening were carried out with this homogeneous mixture. The following properties were determined for these hardened or fusible resins: thermal stability, impact resistance, break tension and time of hardening, time necessary for the transformation of the mixture in a brittle material (on being heated in a bath at 160°C). The testing carried out on 50 mixtures has shown that in 23 cases the time of hardening of the mixture was shorter than that of any composing resin; in 13 cases an almost linear dependence was found from the composition of the mixture; in only one case more time was necessary than for the separate constituent. The change of dielectric properties varies linearly with the composition; the curve of the mechanical resistance shows a maximum. Because of the discoloration, the crosslinked structure, and the insolubility of the products, it was not possible to determine exactly the change in chemical structure; the modification is accompanied by simultaneous mutual reactions of various types, in which intervene the monomers, the intermediary products, and the reaction medium. The possibility of carrying out standard experiments with model substances in simple and well‐determined conditions is excluded in this case. The products presented in this paper have been used in the industry for a year, in order to avoid temporary difficulties with respect to the availability of raw materials.