13C-NMR study on cure-accelerated phenol-formaldehyde resins with carbonates

Abstract

Both liquid‐ and solid‐state carbon‐13–nuclear magnetic resonance (13C‐NMR) spectroscopies were used to investigate the cure acceleration effects of three carbonates (propylene carbonate, sodium carbonate, and potassium carbonate) on liquid and cured phenol‐formaldehyde (PF) resins. The liquid‐phase 13C‐NMR spectra showed that the cure acceleration mechanism in the propylene carbonate‐added PF resin seemed to be involved in increasing reactivity of the phenol rings, whereas the addition of both sodium carbonate and potassium carbonate into PF resin apparently resulted in the presence of ortho–ortho methylene linkages. Proton spin‐lattice rotating frame relaxation time (T1ρH) measured by solid‐state 13C cross polarization/magic‐angle spinning NMR spectroscopy was smaller for the cure‐accelerated PF resins than that of the control PF resin. The result indicated that the cure‐accelerated PF resins are less rigid than the control PF resin. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1284–1293, 2000

Performances of larch (larix gmelini) tannin modified urea–formaldehyde (TUF) resin and plywood bonded by TUF resin

“…Figure shows the 13 C‐NMR spectrum of cured TUF resin. In addition, the assignments of chemical shifts are tabulated in Table according to the literatures . The sharp and high peak at 159 ppm is typical of the presence of carbonyl carbon.…”

“…In addition, the assignments of chemical shifts are tabulated in Table II according to the literatures. [14][15][16][17][18][19] The sharp and high peak at 159 ppm is typical of the presence of carbonyl carbon. These weak peaks at 116 ppm, 130 ppm, and 145 ppm were assigned to larch tannin.…”

Novel two‐stage phenol–formaldehyde resol resin synthesis

“…The 13 C-NMR signals and the signal areas of resol resins were identified with the help of the literature. 14,[16][17][18][19][20][21] The alkalinity of the samples affected the ppm range of the phenoxy carbon region. Higher alkalinity shifted the phenoxy area to a lower field.…”

Chemical Structure and Curing Characteristics of Phenol Formaldehyde Resins Catalyzed with Calcium Oxide

“…There have been many attempts to cure PF resins faster, including mixed with various resins [3] , adding accelerators and different catalysts such as ester [4,5] , copolymerized urea [6][7][8] , carbonate [9,10] and amides [11,12] .…”

“…This type of resin have been widely used as industrial impregnating resins and adhesives in various applications for more than 50 years [1,2] . One of the drawbacks of PF resin is its slow cure which requires longer hot-pressing time and higher hot-pressing temperature for the manufacture of composite products.There have been many attempts to cure PF resins faster, including mixed with various resins [3] , adding accelerators and different catalysts such as ester [4,5] , copolymerized urea [6][7][8] , carbonate [9,10] and amides [11,12] .Faster curing PF resins may also be prepared by metallic ion catalysis, which increases the proportion of the free higher reactive para positions available for the reaction during curing of the resin. It was investigated that the valence and ionic radius of hydrated cations of basic catalyst on the mechanisms and kinetics of phenol formaldehyde…”