Abstract
The biomass resources oil palm empty fruit bunch (EFB) and sugarcane bagasse, which are residues from the palm oil and sugar industries, continue to be investigated for more applications. With increasing concern for the environment, cleaner production has been a worldwide aim of researchers. In this study, thermomechanical pulp (TMP) from EFB and sugarcane bagasse was prepared with disc refining after steam pretreatment of the raw materials. Afterwards, refining and handsheet properties of TMP using various percentages of unbleached soda bagasse pulp (USBP) were studied. Fiber characterizations and handsheet properties showed that pulp of acceptable quality was obtained via thermomechanical pulping. Moreover, energy consumption during PFI refining of EFB TMP was higher than that of bagasse TMP. Physical properties were further enhanced through introduction of USBP. The results firmly support the feasibility of cleaner thermomechanical pulping of EFB and sugarcane bagasse.
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Chemical-free Thermomechanical Pulping of Empty Fruit Bunch and Sugarcane Bagasse
Kai Liu,a Peiqi Lyu,a Yang Ping,a Zheming Hu,b Lihuan Mo,a,* and Jun Li a,*
The biomass resources oil palm empty fruit bunch (EFB) and sugarcane bagasse, which are residues from the palm oil and sugar industries, continue to be investigated for more applications. With increasing concern for the environment, cleaner production has been a worldwide aim of researchers. In this study, thermomechanical pulp (TMP) from EFB and sugarcane bagasse was prepared with disc refining after steam pretreatment of the raw materials. Afterwards, refining and handsheet properties of TMP using various percentages of unbleached soda bagasse pulp (USBP) were studied. Fiber characterizations and handsheet properties showed that pulp of acceptable quality was obtained via thermomechanical pulping. Moreover, energy consumption during PFI refining of EFB TMP was higher than that of bagasse TMP. Physical properties were further enhanced through introduction of USBP. The results firmly support the feasibility of cleaner thermomechanical pulping of EFB and sugarcane bagasse.
Keywords: Empty fruit bunch; Sugarcane bagasse; Thermomechanical pulp; PFI refining
Contact-information: a: State Key Laboratory of Pulp and Paper Engineering, South China University of Technology, Guangzhou 510641, China; b: School of Law, Humanities and Sociology, Wuhan University of Technology, Wuhan 430070, China;
* Corresponding authors: lhmo@scut.edu.cn (L. H. Mo); ppjunli@scut.edu.cn (J. Li)
INTRODUCTION
The awareness of negative environmental impact has indirectly contributed to the revolution of the pulp and paper industry. While trying to maintain the strength of paper and paperboard products (Hubbe 2014), the pulp and paper industry has been seeking for new raw material to take the place of wood at the same time (Marín et al. 2009; Sharma et al. 2011; Ferhi et al. 2014; Ooi et al. 2017; Emmclan et al. 2018). Non-wood raw materials, such as bamboo, wheat straw, and sugarcane (Saccharum officinarum) bagasse, have already been utilized in practical production in China, e.g., the sugar industry in South China, where sugarcane bagasse has already been used as raw material for pulping and papermaking. The palm oil industry in South East Asia annually produces enormous biomass resources such as empty fruit bunch, palm kernel shell, oil palm trunk, etc. (Ooi et al. 2017). Among these biomass resources, empty fruit bunch (EFB) is an abundantly available fibrous residue left after the separation of palm fruits (Singh et al. 2013). It is wasteful if EFB is simply buried or combusted.
The application of sugarcane bagasse as a feedstock for soda pulping has reached a mature stage. As for EFB, various methods, such as soda-anthraquinone pulping, semi-chemical pulping, thermomechanical pulping, organic solvent pulping, and bio-pulping, have been investigated (Rodríguez et al. 2008; Jiménez et al. 2009; Risdianto and Sugesty 2015; Mulyantara et al. 2017). The studies mentioned above used chemicals that can give rise to environmental problems if not seriously treated.
Despite many studies that have reported on various pulping methods, there is still a lack of more environmentally friendly and less expensive methods for EFB application. Pulping by a mechanical method could maximize the yield with low production cost while maintaining the small impact on the environment. Mechanical pulping does have some advantages. The high bulk and stiffness of mechanical pulp are desirable in paperboard production (Liu et al. 2012). Additionally, the opacity of mechanical pulp is favorable in obtaining good printing products (Zhang et al. 2011). However, such advantages are achieved with compromised pulp quality. Normally, mechanical pulp, especially without chemical treatment, is used as a partial substitution of chemical pulp for papermaking. Because the fiber bond of mechanical pulp is not as strong as chemical pulp, the application of mechanical pulp is hindered by the low physical strength of the resulting paper (Zhang et al. 2011).
Therefore, one of the major research targets of all time is to enhance the pulp quality for higher value applications. Various methods, such as mild chemical pretreatment, steam treatment, enzymatic pretreatment, and biological pretreatment, have been utilized in the improvement of mechanical pulping (Ferraz et al. 2008; Ahmadi et al. 2010; Lei et al. 2012; Mulyantara et al. 2017). Among these solutions, steam pretreatment stands out as having the slightest influence on the environment and low manufacturing cost. The typical steam preheating temperature for wood chips before mechanical pulping is 120 to 130 ℃, accompanied with chemical treatment. The major applications of thermomechanical pulp (TMP) produced with steam pretreatment are used for making corrugating medium and packaging paper or paperboard, because of the high stiffness. Furthermore, TMP can be used in printing paper, coated paper, and some other applications.
To enrich the raw material selections with a cleaner production method, chemical-free thermomechanical pulping was performed with EFB and sugarcane bagasse. The objectives were to explore thermomechanical pulping with EFB and sugarcane bagasse as raw materials, without using any other chemicals, and to evaluate their mechanical properties. Furthermore, various amounts of chemical pulp were added to mechanical pulp to investigate the refining and papermaking behavior of pulp mixtures.
EXPERIMENTAL
Materials
The EFB was obtained from Heng Huat Group (Pulau Pinang, Malaysia). Sugarcane bagasse (without depithing) and unbleached alkaline bagasse pulp (USBP) were provided by Guangxi Boguan Environmental Products Co., Ltd. (Guangxi, China). The primitive form of the raw EFB was fiber strands several centimeters in length (> 10 cm) and diameter less than 1 mm (Fig. 1). Sugarcane bagasse was in the form of stubby fiber strands shorter than EFB and sometimes thicker than several millimeters (Fig. 1). The moisture content of USBP was measured after full disintegration. The chemical components of EFB raw material were analyzed following the determination of structural carbohydrates and lignin using NREL laboratory analytical procedures for standard biomass (Sluiter et al. 2008). The extractives content in organic solvents was measured according to TAPPI T204 cm-97 (1997) and ash as per TAPPI T211 om-93 (1993).