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.

side-chain reorientation, it seems necessary to discuss these two factors separately in a more quantitative approach concerning the side-chain motion. Lipari, G.; Szabo, A. J. Am.

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Torsional braid analysis (TBA) was used to study the effects of formulation variables on the properties of phenol-formaldehyde resins. These variables were the mole ratio of formaldehyde to phenol (F/P), the ratio of initial and total sodium hydroxide to phenol (i-NaOH and t-NaOH, respectively), and presence or absence of a Iow temperature (60°C) hold during the resin cook. Analysis of the resins during eure showed that the initial relative rigidity and mechanical damping were determined by the molecular weight and viscosity of the resin. The relative rigidity of the fülly cured resin was strongly influenced by the F/P, t-NaOH and the presence of a Iow temperature methylolation step. A high F/P (2.5) and a high t-NaOH (0.75) both promoted a high relative rigidity in the cured resin. Einfluß der chemischen Zusammensetzung auf die dynamisch-mechanischen Eigenschaften von alkalisch härtenden Phenol-Formaldehydharzen ZusammenfassungDer Einfluß der chemischen Zusammensetzung von alkalisch härtenden Phenol-Formaldehydharzen auf die Harz-Eigenschaften wurde mittels Torsionsanalyse untersucht. Die Variablen waren das Formaldehyd/Phenol Molverhältnis (F/P) und das Verhältnis von ursprünglichem zu Gesamt-Natriumhydroxid (i-NaOH und t-NaOH) bei einer niedrigen Harzkondensationstemperatur von 60°C. Die Harzanalyse während der Härtung zeigte, daß die ursprüngliche relative Sprödigkeit und mechanische Dämpfung vom Molekulargewicht und von der Viskosität des Harzes bestimmt werden. Die relative Sprödigkeit des vollständig ausgehärteten Harzes wurde stark vom F/P Verhältnis, vom Gesamt-NaOH-Gehalt und von der Temperatur bei der Methylolierungsstufe beeinflußt. Ein hohes F/P Verhältnis (2,5) und ein hoher Gesamt-NaOH-Gehalt bewirkten relativ hohe Sprödigkeit im ausgehärteten Harz. IntroductionTorsional braid analysis (TBA) is useful in studying the mechanical and chemical reactions of thermosetting resins. This technique is suited to a study of the curing reactions äs the resin progresses from a liquid, to a gel, to a solid (Gillham 1979).' In addition, TBA is useful in studying the mechanical transitions of a fully cured thermoset resin. A review of TBA and its applications to the study of cross-linked Systems is given by Gillham et al (1974). With TBA the sample is suspended under tension and enclosed by an oven to control the temperature. A