*2.7. Fourier Transform Infrared Spectroscopy (FTIR)*

The FTIR analysis of the raw OPEFB, OPEFB-treated cellulose, OPEFB microcrystalline cellulose and nano-bentonite was performed by using the KBr pellet method. The functional groups of all the samples were analyzed using a Perkin Elmer spectrum 65 FTIR spectrometer (Waltham, MA, USA) with the wavenumber range of 650–4500 cm−<sup>1</sup> , 16 scans and resolution of 4 cm−<sup>1</sup> . FTIR transmitted infrared radiation through the sample and resulted in the infrared spectrum of the sample.
