Treating fibres especially alkali treatment removes lignin,hemicellulose and other impurities which are usually hydrophobic (water hating). After removal of these hydrophobic parts, the remaining cellulose is now able to take in more water.
depends on what kind of treatment, what fibres.
I assume there is a way to activate the fibre surface, i.e. provide more adsorption sites for water molecules. Loosening the fibres, i.e. creating more surface, might also help.
Thank you @Cornelia Hintze for your conversation, i'm using sugarcane bagasse fibre and NaOH treatment.
Hi gokul,
While treatment of fibers,surface of fiber tends to more rough then the untreated so it could be a one of the possible for more intake of water,and more thing high amount of cellouse leads to high intake of water.
Even without delignification, sodium hydroxide promotes an effect denominated "superswelling", that is, it promote high water absorption by hemicelluloses. As hardwoods, grasses, and canes have proportionally higher hemicelluloses content than softwoods, this effect is more noticeable in them.
Hello,
It depends on the applied treatment. While alkali and bleaching treatment increases hydophilicity by removal of hydrophobic substances that cover the fiber and by forming a rough fiber surface and increase surface area; acetylation and silanization decrease hydrophilicity.
The treatment conditions also are effective. If applied to harsh alkalization may result in loss of water binding sites and decrease hydrophilicity.
Below are some excerpts from (Yılmaz, N.D. “Agro-Residual Fibers as Potential Reinforcement Elements for Biocomposites”, Chapter 11, in “Lignocellulosic Polymer Composites: Processing, Characterization and Properties”, Ed. Thakur, V.K., Wiley -Scrivener, USA, ISBN 978-1-118-77357-4, s. 233-270. , 2015 ).
"11.7.2.1 Alkalization
Alkaline treatment (mercerization) is one of the most common chemical methods
applied to plant fibers which are used as reinforcement in biocomposites. Alkalization partially removes lignin, wax and oils covering the surface of fiber cell wall [3]. Thus, alkalization improves the surface adhesion of fiber to the polymeric matrix with the removal impurities which results in a rough surface topography [8].
...
Decrease in water absorption behavior is reported to occur with alkalizing of okra
bast and banana stem and bunch fibers [5,26]. Ganan et al. [26] reported an increase in contact angle and decrease in surface free energy. Yılmaz [11] also found a decrease in moisture content of corn husk fibers with the increase in concentration and duration of alkalization. The decrease in moisture content might be due to the reduction in hydroxyl groups.
...
11.7.2.4 Bleaching
Bleaching causes the fiber parameters to become more uniform [5]. Due to removal of some extra-cellular materials, the degree of chrystallinity increases [28], fibers acquire a whiter color and the inherent yellowness is decreased. Fibers lose some weight and become finer [12]. Increase in water absorption was reported to occur with bleaching of okra bast fibers. This might be due to the removal of hydrophobic substances which exposes hydrophilic cites [5].
...
11.7.2.2 Acetylation
The acetylation treatment decreases the hydrophilic nature of the plant fibers. During the acetylation treatment the hydroxyl groups in the cellulosic fiber are replaced with acetyl functional groups. The decrease in hydrophilicity results in lower moisture intake and stronger interfacial bonding [8]. De Rosa et al. [15] obtained lower water content in acetylated okra fibers compared to untreated ones.
...
11.7.2.3 Silane Treatment
By forming stable covalent bonds, the silane treatment would improve the contact
angle against water by increasing the hydrophobicity. The mechanism of this treatment can be explained as a silane chemical reacts with water and forms a silanol and an alcohol. With the moisture present, the silanol reacts with the hydroxyl groups of the cellulose and bonds itself to the cell wall [8].
Decrease in water absorption behavior is reported to occur with silanizing of banana stem and bunch fibers [26]. Ganan et al. [26] reported an increase in contact angle and decrease in surface free energy and polar component."
This is due to the increase in percentage of cellulose content during the treatments received, releasing free –OH groups ( each cellulose unit has 3 OH groups), allowing H linkage with H2O molecules, increasing the moisture content.
chemical treatment with Na-OH entails the substitution of the hydroxyl bonds ions sodium. prolonged treatment causes the storage of cellulose and therefore an increase of the porosity, therefore an increase in the water absorption
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