Differential scanning calorimetry of phenol–formaldehyde resols

Abstract

SynopsisDifferential scanning calorimetry was used on a range of synthesized phenol-formaldehyde (PF) resols to discover relationships between formulation parameters or physical properties of resols, and their thermal behavior during cure. The thermograms showed either one or two exothermic reactions. The lower exothermic peak temperature varied between 98 and 129°C with changes in the free formaldehyde content. This exotherm is caused by the addition of free formaldehyde to phenolic rings. The upper exothermic peak temperature varied from 139 to 151"C, with the higher temperatures occurring when the formaldehyde-to-phenol molar ratio was low or the total amount of sodium hydroxide relative to phenol was high. These two factors led to resins which contain a somewhat higher level of unreacted ortho or para aromatic ring positions and no free formaldehyde. Consequently, condensation is probably not solely by the faster self-condensation through hydroxymethyl groups, but also includes the slower condensation of hydroxymethyl groups with unreacted ring positions. Gel times show trends with changes of formulation parameters somewhat similar to trends of the upper exothermic peak temperatures.

Study on preparation and properties of phenol-formaldehyde-chinese fir liquefaction copolymer resin

“…Both of the exotherms obtained in the resin systems were attributable to the curing reaction. According to the previous research (Christiansen and Gollob 1985), the lower exothermic peak in the range of 141,4-144,8°C has been attributed to the addition reaction of free formaldehyde to phenolic ring, and the upper exothermic peak in the range of 143,8-157,5°C was associated with the chain-building condensation reactions, involving hydroxymethyl groups attached to various phenolic species. The appearance of single exothermic peak is mainly due to the F/P molar ratio below 2,3 that resulted in the overlapping of exothermic signals, two well-separated exothermic peaks are revealed when the F/P molar ratio was larger than 2,3 (Holopainen et al 1997).…”

Effect of alkalinity on the structure of phenol–formaldehyde resol resins

“…All spectra of the resins were run with a 90°pulse of 11.5 s in the previously optimized 12 NMR conditions of a 10-s pulse delay, 600 scans, and with 20 mM of the relaxation reagent, Cr(acac) 3 (97%, purchased from Aldrich, Milwaukee, WI.) DMSO-d 6 , 99 atom % deuterated dimethyl sulfoxide (Riedel-de Haën, Seelze, Germany), was used as a solvent.…”

“…The mechanism and kinetics of the alkali-catalyzed reaction of phenol with formaldehyde, the physical properties of resins under alkaline conditions, and the effects of the curing alkalinity on resins have been widely researched. [1][2][3][4][5][6][7][8][9][10][11] In this study, the effects of the methylation alkalinity (first-stage alkalinity after an initial addition of a NaOH catalyst) and the condensation alkalinity (second-stage alkalinity after subsequent addition of a NaOH catalyst) on the chemical structures and reactivity in two phenol-formaldehyde resin series were studied by 13 C-NMR spectroscopy and differential scanning calorimetry (DSC).…”

Rheological analysis of the phenolic and furfuryl resins used in the carbon materials processing

“…The knowledge of certain characteristics of the precursor polymer, such as molecular weight distribution, average molecular weight and rheological behavior, orientates the processing conditions in order to control the porous size and its quantity in the carbon matrix and, consequently, the final mechanical, electrical and thermal properties of the CM [8][9][10][11][12][13][14][15] . In this work, rheological characteristics of phenolic and furfuryl resins are determined and used to help the selection of the appropriate raw material and to establish the parameters for processing CRFC and glassy carbon.…”