Contents lists available at ScienceDirect Industrial Crops & Products journal homepage: www.elsevier.com/locate/indcrop Enzymatic and cold alkaline pretreatments of sugarcane bagasse pulp to produce cellulose nanofibrils using a mechanical method Shuangxi Nie a,b, ⁎ , Chenyuan Zhang a , Qi Zhang a , Kun Zhang a , Yuehua Zhang a , Peng Tao a , Shuangfei Wang a,b, ⁎ a College of Light Industry and Food Engineering, Guangxi University, Nanning 530004, China b Guangxi Key Laboratory of Clean Pulp & Papermaking and Pollution Control, Nanning 530004, China ARTICLE INFO Keywords: Cellulose nanofibrils Enzyme Cold alkaline Thermal stability ABSTRACT Lignocellulosic biomass is the most abundant renewable resource on the earth. With the development of related fields, the high value utilization of lignocellulosic biomass has gradually become a new avenue for research. In this study, unbleached bagasse pulp was pretreated with xylanase and cold alkali to partially remove hemi- cellulose and convert to some cellulose I into cellulose II. Cellulose nanofibrils (CNF) were then obtained through ultra-micro grinding and high-pressure homogenization. The prepared CNF were characterized by TEM, Zeta potential, ATR-FTIR and XRD, and a thermogravimetric analyzer was used to analyze the thermal stability of CNF. The results show that xylanase pretreatment can improve the dispersion of fibers during mechanical treatment and can enhance the crystallinity of CNF. With an increase in alkali concentrations, the proportion of cellulose II structures increased, while cellulose crystallinity levels decreased due to the folding of cellulose chains. Under the common influence of crystallinity and crystal structures, the thermal stability of the CNF prepared after cold alkali pretreatment underwent an increasing trend. This shows that the influence of crystal structures on the thermal stability of CNF gradually plays a dominant role as alkali concentrations increase. 1. Introduction With the continuous development of human society, demands for energy, materials and other resources are increasing (He et al., 2016; Nie et al., 2016). The large-scale use of traditional fossil energy had serious environmental ramifications, rendering research on renewable resources particularly important (Fan et al., 2017; Nie et al., 2014; Yao et al., 2017). Cellulose is the most abundant natural polymer compound found on earth; it is highly biocompatibile and biodegradabile, and it can be biosynthesized (Lin et al., 2018). With the rapid development of materials science, research on cellulose-based materials has gradually become a major topic of research (Song et al., 2016). The application of nanotechnology has greatly extended the application of cellulose-based materials. Products composed of cellulose nanofibrils (CNF) products are characterized by their strength, low density, and low coefficient of thermal expansion due to their high aspect ratio and mesh-like en- tangled structure (Fukuzumi et al., 2010), which offers application potential in the field of high-performance products. Various changes in CNF observed under heated conditions directly affect the thermal stability of nanocellulose-based materials. The thermal stability of CNF refers to their ability to maintain their own performance at high temperatures. This trait can be evaluated by the change in temperature observed at breakage or under heated condi- tions, and thermal transition temperature or decomposition tempera- tures are often used to characterize the thermal stability of CNF (Lavoine et al., 2016). A traditional wood fiber begins to degrade at roughly 230 ℃. Cellulose is the most thermally stable component of wood fibers (Gardner et al., 2008; Goring, 1963). According to the “Broido-Shafizadeh” cellulose pyrolysis model proposed by Bradbury et al. (Bradbury et al., 1979), the pyrolysis process undergone by cel- lulose can be divided into two stages. The first stage occurs at 150–300 ℃. At 150 °C, the cellulose glycosidic bond begins to break down, and the degree of polymerization decreases to about roughly 200. When temperatures further increase to roughly 300 ℃, cellulose enters the second stage of pyrolysis. The severe depolymerization of cellulose results in the formation of intermediate cellulose, which is mainly composed of dehydrated sugar, and this is transferred into tar by evaporation or aerosol. With an increase in temperature, dehydration, dehydrogenation, deoxygenation, decarboxylation and other reactions occur in cellulose molecules to generate thermally degraded small https://doi.org/10.1016/j.indcrop.2018.08.033 Received 6 July 2018; Received in revised form 31 July 2018; Accepted 10 August 2018 ⁎ Corresponding authors at: College of Light Industry and Food Engineering, Guangxi University, Nanning 530004, China. E-mail addresses: nieshuangxi@gxu.edu.cn (S. Nie), wangsf@gxu.edu.cn (S. Wang). Industrial Crops & Products 124 (2018) 435–441 0926-6690/ © 2018 Elsevier B.V. All rights reserved. T