Distribution and curing reactions of melamine formaldehyde resin in cells of impregnation-modified wood

Abstract

Wood modification improves the properties of wood as a building material by altering the wood structure on a cellular level. This study investigated how dimensional changes of wood on a macroscopic scale are related to the cellular level chemical changes on the micron level after impregnation modification with melamine formaldehyde (MF) resin under different heat curing conditions. Our results showed that the curing conditions affected the polycondensation reactions and the morphological structure of the MF resin within the cell lumen. The diffusion of the resin into the cell wall was estimated based on the triazine ring vibration of melamine in the Raman spectrum at 950-990 cm −1. Thereby, it was shown that macroscopic changes in wood dimensions do not provide a reliable estimate for the cell wall diffusion of the resin. The removal of cell wall constituents during the modification, which was facilitated by the alkaline pH of the impregnation solution, counterbalanced the cell wall bulking effect of the resin. This was particularly evident for wet cured samples, where diffusion of MF resin into the cell wall was observed by confocal Raman microscopy, despite a reduction in macroscopic wood dimensions.

Bundling of cellulose microfibrils in native and polyethylene glycol-containing wood cell walls revealed by small-angle neutron scattering

“…Due to the chemical similarity of PEG and the cell wall constituents, observing the interactions between PEG and the wood cell wall nanostructure suffers from similar challenges as studies of the native cell walls. In such situations, highly useful information can be obtained by spatially-resolved spectroscopic methods such as Raman imaging combined with multivariate image analysis 26 . Moreover, combining spectroscopic imaging with scattering methods offers a powerful set of tools for resolving the penetration depth of PEG in the hierarchical structure of wood.…”

“…Wavenumbers outside the region were excluded. Cosmic ray removal, baseline correction and vector normalization were performed as described previously 26 . Principal component analysis was done after mean-centering of the spectra and the first principal component was used to exclude pixels in the cell lumen based on a score value threshold.…”

Hyperspectral imaging and chemometrics reveal wood acetylation on different spatial scales

“…Raman microspectroscopy has also been extensively utilized in studying wood chemistry, with typical applications involving the visualization of cellulose and lignin distributions on a cellular and subcellular level in different types of natural and treated samples [9,17]. Raman images have also been used to study the distributions of wood extractives [18] and various wood modification agents [19][20][21].…”

Incorporation of In Situ Synthesized Nano-Copper Modified Phenol-Formaldehyde Resin to Improve the Mechanical Properties of Chinese Fir: A Preliminary Study

“…Comparison of the curves of the FTIR spectra indicated that the C=O stretching vibration at 1724 cm −1 disappeared after nano-copper modification, while the C–O stretching vibration of aliphatic C–OH, aliphatic C–O, and methylol C–OH at 1270 cm −1 increased in the modified PF resin curves (green and blue spectra). These changes revealed that the modified PF resin reacted with acetyl groups in the hemicelluloses [ 42 ]. The modified PF resin samples showed a relatively larger ratio at 1600 cm −1 , which was attributed to the enhanced condensation reaction of the methylol in the PF resin in the presence of nano-copper to form methylene (–CH 2 –) [ 42 ].…”