Abstract
The pretreatment process is an essential step for nanofibrillated cellulose production as it enhances size reduction efficiency, reduces production cost, and decreases energy consumption. In this study, nanofibrillated cellulose (NFC) was prepared using various pretreatment processes, either chemical (i.e., acid, basic, and bleach) or hydrothermal (i.e., microwave and autoclave), followed by disintegration using high pressure homogenization from oat bran fibers. The obtained NFC were used as an emulsifier to prepare 10% oil-in-water emulsions. The emulsion containing chemically pretreated NFC exhibited the smallest oil droplet diameter (d32) at 3.76 μm, while those containing NFC using other pretreatments exhibited d32 values > 5 μm. The colors of the emulsions were mainly influenced by oil droplet size rather than the color of the fiber itself. Both NFC suspensions and NFC emulsions showed a storage modulus (G′) higher than the loss modulus (G″) without crossing over, indicating gel-like behavior. For emulsion stability, microwave pretreatment effectively minimized gravitational separation, and the creaming indices of all NFC-emulsions were lower than 6% for the entire storage period. In conclusion, chemical pretreatment was an effective method for nanofiber extraction with good emulsion capacity. However, the microwave with bleaching pretreatment was an alternative method for extracting nanofibers and needs further study to improve the efficiency.
Highlights
Cellulose is a homopolysaccharide consisting of a β-1,4 linked glucopyranose unit which can have a polymerization degree from 300 to 15,000 [1,2]
We focused on the effect of the pretreatment process by chemical and hydrothermal techniques including microwave and autoclave treatments to facilitate the mechanical defibrillation of oat fiber and study the emulsion capacity of nanofibrillated cellulose (NFC) extracted from dried purified oat fibers
It is suggested that transmission electron microscopy (TEM) is a more suitable and effective method to observe the microstructure of NFC
Summary
Cellulose is a homopolysaccharide consisting of a β-1,4 linked glucopyranose unit which can have a polymerization degree from 300 to 15,000 [1,2]. In order to extract cellulose from plant sources regarded as lignocellulosic biomass, it is necessary to have a pretreatment process to remove noncellulosic materials (i.e., lignin, hemicellulose, pectin, and wax) that are embedded within the cellulose structure [12]. Intensive mechanical disintegration is a final step for producing NFC which consumes a lot of energy and time. Mechanical processes, such as grinding or high-pressure homogenizing, are the most common methods used to disintegrate and reduce cellulose fibril sizes [13]. Alkaline pretreatment is regarded as a chemical pretreatment and is an effective method used for removing the lignin, hemicellulose, and non-cellulosic substances from lignocellulosic materials [13]. Using hydrothermal pretreatment without chemical addition affected physical changes by the re-localization of lignin on the cellulose surface, solubilization of hemicellulose, and increased accessibility of the cellulose structure [18,19]
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