Optimization of eucalyptus cellulose fiber using response surface methodology: Effects of sulfur content and refining time on the mechanical characteristics of paper pulp

Abstract

The purpose of this study was to examine the delignification of Eucalyptus camaldulensis fibers by the kraft chemical process using sodium hydroxide and sodium sulfide as fillers. To optimize the levels of factors influencing pulp yield and pulp content, a response surface approach with a central composite plane was used. Fourier transform infrared spectroscopy, X-ray diffraction, and thermogravimetric analysis were used to characterize the structure and thermal properties of cellulose fiber. Then, a dynamometer, a dechirometer, and an eclatometer adamel were used to evaluate the physico-mechanical properties (breaking length, tear resistance, and resistance to burst) of the paste. The results show that FTIR spectroscopy confirmed the structure of the cellulose fiber; the crystallinity index is 76.35%, the maximum degradation temperature is 368 °C and the kinetic energy of activation (75.45 kJ.mol-1) according to thermogravimetric studies. Subsequently, for the predicted optimal pulping conditions, the concentration of NaOH was 18.8% and 13.40% Na2S at 105 °C for 45 min. Finally, the results obtained for the evaluation of the papermaking properties of fibers during refining showed that the breaking length is 34% (2975 m–1958 m) with a sulfide concentration of 0%–30%, respectively, and that when the refining intensity is increased to 45°SR, the rupture length (5997-4088 m) decreases by approximately 31% under the same conditions. Then, the tear strength is 37.5% (53-33.1), the sulfide concentration is 0%–30%, and the refining intensity is 20°SR; the increase in the latter leads to a reduction in the tear index of approximately 19% (50-40.6) under the same conditions. Finally, the bursting index is 38.5% (18.4-11.3) at identical sulphide concentration and refining intensity, but the increase in the latter leads to a slight decrease in the burst index (37.7-23.6) which is about 37.40%. The results suggest that the valorization of Eucalyptus fibers for the production of well-delignified, high-yield, and resistant pulp is a promising approach. This research qualifies eucalyptus fiber as a potential reinforcement in composite materials.