Topochemistry of heat-treated and N-methylol melamine-modified wood of koto (Pterygota macrocarpa K. Schum.) and limba (Terminalia superba Engl. et. Diels)

Abstract

To broaden the knowledge about the chemical changes at the cell wall level of differently modified tropical hardwoods, heat-treated and N-methylol melamine (NMM)-treated samples of koto (Pterygota macrocarpa) and limba (Terminalia superba) were prepared. UV microspectrophotometry (UMSP) was applied at 278 and 240 nm as specific wavelengths to analyze chemical alterations of the samples caused by heat and NMM treatment, respectively. The absorbance of koto exceeded that of limba before and after treatment, potentially due to the higher extractive content of the former. Regardless of the wood species, the absorbance of the samples increased with increasing intensity of the NMM treatment. Additionally, the absorbance of lignin within the spectrum of 230–350 nm was altered due to the NMM treatment. The functionality of applying specific wavelengths for the analysis of different modification methods of wood was proven. However, the comparison with literature did not show differences in the absorbance, which could be assigned to the characteristics of tropical hardwoods.

Topochemical analyses of furfuryl alcohol-modified radiata pine (Pinus radiata) by UMSP, light microscopy and SEM

“…The highest absorbances occur in the area of the CML and the CC as previously described for W untr (Koch and Kleist 2001;Koch and Grünwald 2004) and also for thermally (Mahnert et al 2013) and hydrothermally modified wood (Andersons et al 2016). For the W untr tissue, the following UV absorption data (A 280 nm ) are typical: 1.22 for the CML, 1.48 for the CC and lower, slightly varying values for the S2 layer (0.69-0.95).…”

“…Compared to W untr , higher UV absorbances were also observed by UMSP on thermally modified wood (160°C-180°C) (Mahnert et al 2013). Andersons et al (2016) reported similar results at lower temperatures, but at 140°C for 1 h only a slight impact on the UV absorbance was seen.…”

“…The UV-A max data are lower in lignins with higher syringpropan unit participation, seen on the increasing OCH 3 /C 9 ratios (Musha and Goring 1975;Fujii et al 1987). Modified timbers, such as heat-treated and N-methylol melamine-modified hardwoods (Kielmann et al 2013;Mahnert et al 2013;Sint et al 2013), hydrothermal-modified wood (Andersons et al 2016) and degraded furfurylated softwood (Ehmcke et al 2016), were also studied by UMSP.…”

Chemical and ultrastructural changes in compound middle lamella (CML) regions of softwoods thermally modified by the Termovuoto process

“…The appearance of silver fir TMW 4 h, 220°C after staining with KMnO 4 is shown in Figure 2 Brought to you by | Sveriges Lantbruksuniversitet Authenticated Download Date | 8/6/15 3:11 PM studies in terms of the apparent lignin content increment in TMWs (Boonstra and Tjeerdsma 2006;Windeisen and Wegener 2008;Esteves and Pereira 2009;Mahnert et al 2013). Esteves and Pereira (2009) emphasized that the apparent high lignin content is the result of polycondensation reactions between lignin and other cell wall components.…”

“…The changes in the gross chemistry after TM were also extensively studied as reviewed by Esteves and Pereira (2009). Microredistribution of wood components caused by TM was observed by Fourier transform infrared (FTIR), nuclear magnetic resonance (NMR), X-ray photoelectron spectroscopy (XPS), and ultraviolet microspectrophotometry (UMSP) (Sivonen et al 2002;Tjeerdsma and Militz 2005;Kocaefe et al 2012;Mahnert et al 2013). However, these methods also have limitations concerning changes at the cellular level, particularly on individual cell wall layers.…”