Abstract
Cellulose nanocrystals (CNCs) were prepared from kraft pulps of eucalyptus, birch, and softwood. The different kraft pulps were hydrolyzed using strong sulfuric acid in order to obtain colloidally stable CNCs. The CNCs were studied using flow cytometry (FCM). The light scattering properties of the CNCs in side direction and forward direction were documented. The use of a selective staining agent in combination with FCM analysis enabled detection of the hydrophobic particle populations within the CNC suspensions. The hydrophobic particles were seen clearly in the CNCs from the eucalyptus and birch kraft pulps, but not in the CNCs from softwood pulp. These particles were shown to be linked with the content of lipophilic extractives, especially sterols, present in the kraft pulps. From this fact, it was concluded that FCM analyses offer useful information about the properties of CNCs in suspension. It was also concluded that the content of lipophilic extractives in different raw materials should be determined and considered prior to CNC production. Pre-extraction steps might be needed in order to produce high-quality CNCs from various raw materials, even from kraft pulps.Graphical abstract
Highlights
Cellulose nanocrystals (CNCs) have received a lot of attention in research due to their physical and chemical properties, renewability, sustainability, and usefulness in composite materials (Favier et al 1995a, b; Ruiz et al 2000; Habibi et al 2010; Wang et al 2012)
It is known that the acid methanolysis procedure cannot hydrolyze crystalline cellulose, and it is commonly used to analyze the hemicelluloses and pectins in various lignocellulosic materials (Sundberg et al 1996a)
The presence of hydrophobic particles were seen clearly in the CNCs from the eucalyptus and birch kraft pulps; i.e. the CNCs consisted of a hydrophilic and a hydrophobic particle population
Summary
Cellulose nanocrystals (CNCs) have received a lot of attention in research due to their physical and chemical properties, renewability, sustainability, and usefulness in composite materials (Favier et al 1995a, b; Ruiz et al 2000; Habibi et al 2010; Wang et al 2012). CNCs are a strong contender for various future applications in composite materials, due to their low cost and abundancy. The crystallites of CNCs are, similar to the crystallites of the cellulose fiber raw materials. The cellulose raw material is normally hydrolyzed by addition of strong acid, in combination with controlled reaction conditions, i.e. temperature, agitation, and time (Revol et al 1994; Dong et al 1998; Wang et al 2014)
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