An underrated variable essential for tailoring the structure of xerogel: the methanol content of commercial formaldehyde solutions

Abstract

Resorcinol-formaldehyde xerogels are polymers whose porosity can be designed for a specific application by the selection of appropriate physical and chemical synthesis variables. Until recently, the methanol content of commercial formaldehyde solutions has never been considered as a chemical variable that must also be taken into account. However, it has been demonstrated that the proportion of methanol might be even more important than other variables for tailoring the porosity of xerogels.Different reaction mechanisms are proposed to explain this heavy dependence of the final structure of RF xerogels. Organic and carbon xerogels synthesized with low concentrations of methanol showed a higher porosity with much larger pore sizes (up to two orders of magnitude) than when using formaldehyde with high concentrations of methanol. This means that extra caution needs to be shown in choosing these commercial products since formaldehyde solutions differ greatly in methanol content from one supplier to another.

Selective Control of Ion Transport by Nanoconfinement: Ionic Liquid in Mesoporous Resorcinol–Formaldehyde Monolith

“…Hence, the resulting gel is influenced by multiple parameters. These can be summarized as five main variables: (i) the dilution ratio of R and F to the total solution; (ii) the R/F ratio; (iii) the catalyst concentration, i.e., the pH value of the solution; (iv) the drying conditions, as they affect the shrinkage of the resulting porous polymer, and (v) the amount of organic solvent added and its polarity − (methanol is used as a stabilizer in formaldehyde solution and thus always present in small quantities). By varying these parameters, it is possible to adjust the porosities and surface areas of the resulting polymer monoliths as well as other characteristics, i.e., thermal conductivity or flexibility .…”

“…In this work, a hydrochloric acid-catalyzed route , was employed in which the pore size generated is controlled by the amount of ethanol added to the starting solution. Usually the pH and the dilution of the reactants are the main factors used to control the final porosity, but the addition of an organic solvent (e.g., methanol , or ethanol ,, ) surmounts these factors and makes it even simpler to adjust and predict the resulting pore size. Combined with subcritical drying, a washing step for the removal of the catalyst or a solvent exchange is not required, making the synthesis route very simple and easy to handle.…”

Hybrid Proton-Exchange Membrane Based on Perfluorosulfonated Polymers and Resorcinol–Formaldehyde Hydrogel

“…Regarding the solvents, one can note that alcohol opens up membrane pores better than water, facilitating the gelation process. The downside of ethanol is that it may react with formaldehyde, generating hemiacetal and acetal molecules that do not react with resorcinol [ 32 , 33 , 34 ].…”

Exploring the application of carbon xerogels as anodes for sodium-ion batteries

“…According to previous studies, these polymeric materials, produced from the same monomers (i.e., resorcinol and formaldehyde), present analogous chemical compositions irrespective of their textural properties [36]. Therefore, in order to assess the performance of carbon xerogels as anodes for SIBs, first the textural properties of the materials are discussed (Table 2).…”