Development of dynamic mechanical methods to characterize the cure state of phenolic resole resins

Abstract

SYNOPSISWe are interested in using dynamic mechanical analysis (DMA) to measure the degree of cure achieved by aqueous phenol-formaldehyde (PF) resole resins as a result of previous exposures to various temperature-humidity-time regimes. We developed procedures that permit the obtaining of data that properly characterize and quantify the DMA behavior of these aqueous systems. Particularly important factors are substrate selection, sample clamping geometry, and sample humidification prior to analysis. In this report, we illustrate the problems encountered and the steps that we adopted to resolve them. We also present preliminary DMA data that illustrate some approaches for measuring the degree of cure achieved during previous resin exposures. One especially promising approach employs the area under the tan delta curve during isothermal scanning as an inverse measure of precure.

Investigating the nanomechanical behavior of thermosetting polymers using high-temperature nanoindentation

“…4b, the peak of PF adhesive shifted to higher temperature after mixing with wood, meaning that the retardation of condensation reactions shows a more obvious effect than does the acceleration on PF adhesive. This finding agreed with the results of dynamic mechanical analysis (DMA) that PF adhesive with low curing degree could have post-curing reaction during heating [42]. In theory, polymeric diphenylmethane diisocyanate (pMDI) adhesive should react with water or hydroxyl groups to form a cross-linking network during the curing [43,44].…”

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.…”

High temperature performance of soy-based adhesives

“…DSC/TGA/DMA DSC and TGA have been used in the polymer industry for decades to characterize thermal transitions (DSC) and thermal decomposition (TGA). For wood adhesives, DMA has been particularly useful to describe bond strength development either in a veneer sandwich tested in bending [20][21][22] or on a glass fiber support (either torsion or tension) [23,24]. The veneer sandwich DMA technique is well suited for adhesive layers whose stiffness is much less than that of wood, for example, during curing or to detect softening of the adhesive relative to the wood veneer.…”

“…Therefore, we also used glass fiber support to compare cured soy adhesives because, in this method, the glass fiber retains its original modulus, while the mat is weak enough that only the material response of the adhesive is measured. This test is suitable for adhesives that are fluid enough to penetrate into the structure of the mat and are relatively stiff during testing, such as PF [23,25]. We also attempted to form films of the soy products without support, but the films fractured or crumbled.…”