Extraction and Characterization of Hemicelluloses from a Softwood Acid Sulfite Pulp

Hemicelluloses were extracted from a softwood acid sulfite pulp in a three-step procedure. Further delignification step resulted in a holocellulose pulp containing only 1.7 wt.% of the lignin left. Cold caustic extraction (CCE) with 18 wt.% NaOH at 60 degrees C for 1 h was performed to solubilize hemicelluloses of the holocellulose. An unbleached cellulose pulp was then obtained 97% pure, which indicates that 89% of the hemicelluloses were removed. After purification, extraction yields between 1.1 wt.% and 9.5 wt.% were obtained from the delignified pulp and the hemicelluloses' chemical compositions and structures were investigated by H-1, C-13 nuclear magnetic resonance spectroscopy (NMR) and two-dimensional NMR by correlation spectroscopy (2D-COSY) and proton-detected heteronuclear single-quantum correlation (2D-HSQC), high-performance anion-exchange chromatography coupled with a pulsed amperometry detector (HPAEC-PAD), size-exclusion chromatography coupled with a refractive index detector (SEC-RI) and thermogravimetric analyses (TGA). Hemicelluloses were obtained with a purity of 96%, with short cellulosic chains as the only residue. Sulfite pulping modified the hemicelluloses' structure, and it was found that two types of hemicelluloses were isolated, glucomannans, predominant at 67%, and methylglucuronoxylans. Finally, alkali-soluble hemicelluloses displayed relatively narrow size distributions and low molar masses, M-w varying between 18,900 and 30,000 g/mol after acid sulfite pulping.

Automated summary

Hemicelluloses were extracted from a softwood acid sulfite pulp in a three-step procedure, resulting in a holocellulose pulp with minimal lignin content. Various analytical techniques were employed to study the chemical compositions and structures of the extracted hemicelluloses, revealing modifications in their structure due to sulfite pulping.