X-ray diffraction, Fourier transform infrared spectroscopy, and thermal decomposition analyses of virgin cork elements in Quercus variabilis grown in Korea

The crystalline characteristics, chemical composition, and thermal decomposition of elements in Quercus variabilis (Qv) virgin cork were investigated using X-ray diffraction, Fourier transform infrared spectroscopy, and thermogravimetric methods, respectively, and compared with those of elements in Quercus suber (Qs) reproduction cork. Samples of cork elements, including pure cork, lenticular filling tissue (LFT), dark-brown zone (DBZ), and sclereids, were prepared. The X-ray diffractograms of pure cork from both species showed an amorphous pattern, whereas those of LFT, DBZ, and sclereid showed a crystalline cellulose I pattern. The relative crystallinity of DBZ was significantly lower than that of Qv LFT and the sclereid. In the FTIR spectra, Qv pure cork tended to show weaker band intensities for the suberin, lignin, and carbohydrate compounds than Qs pure cork. The pure corks of both species showed stronger suberin bands than LFT, DBZ, and the sclereid. In the thermogravimetric analyses, the peaks of hemicellulose and cellulose decomposition in both pure corks were weaker than those in LFT, DBZ, and sclereid, whereas the peaks of suberin decomposition in both pure corks were the highest among all elements.