The Effects of Resin Formulation Variables on the Dynamic Mechanical Properties of Alkaline Curing Phenolic Resins

Abstract

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

Effect of synthesis parameters on thermal behavior of phenol–formaldehyde resol resin

“…Another work showed that the percentage of wood failure increased up to a F/P ratio of 1.4 and then was relatively stable 7. Both ratios also affected the rigidity of the cured resins, showing that high F/P and NaOH/P ratios gave high relative rigidity 8…”

The effects of temperature and humidity on phenol-formaldehyde resin bonding

“…A number of indirect analytical techniques have been used to characterize the cure of PF resins by responding to either the chemistry or physics of the curing process. Such techniques include: (1) nuclear magnetic resonance (NMR) (Woodbrey et al 1965;Maciel et al 1984); (2) Fourier transform infrared (FTIR) spectroscopy (Myers et al 1991); (3) ultraviolet spectroscopy (Chow 1969;Chow and Hancock 1969;Chow and Mukai 1972); (4) differential thermal analysis (DTA) or differential scanning calorimetry (DSC) (White and Rust 1965;Burns and Orrell 1967;Kurachenkov and Igonin 1971;Chow 1972;Chow et al 1975;Kay and Westwood 1975;Christiansen and Gollob 1985); (5) torsional braid analysis (TBA) (Steiner and Warren 1981;Kelley et al 1986); and (6) dynamic mechanical analysis (DMA) (Young et al 1981;Young 1986a;Young 1986b;Geimer et al 1990;Kim et al 1991;Follensbee et al 1993;Christiansen et al 1993). The resin samples measured by these indirect methods are usually in the forms of pure liquid or solids, mixtures with various portions of wood powders, and resin-impregnated glass cloth or wood wafers.…”

Characterizations of Phenol-Formaldehyde Resol Resins

“…Dynamic mechanical measurements characterize the viscoelastic properties of the curing prepolymer resin. Kelley et al (1986) applied torsional braid analysis to study the dynamic mechanical properties of curing resols as a function of formulation variables. This method allowed study of the progression of reaction from the liquid polymer through gelation and on to vitrification, the point when the polymer becomes a molecularly immobilized amorphous glass.…”