Abstract
In addition to their lower cost and more environmentally friendly nature, cellulose nanofibers isolated from unbleached pulps offer different surface properties and functionality than those isolated from bleached pulps. At the same time, nanofibers isolated from unbleached pulps keep interesting properties such as hydrophilicity and mechanical strength, close to those isolated from bleached pulps. In the current work, rice straw nanofibers (RSNF) isolated from unbleached neutral sulfite pulp (lignin content 14%) were used with polysulfone (PSF) polymer to make membrane via phase inversion. The effect of RSNF on microstructure, porosity, hydrophilicity, mechanical properties, water flux, and fouling of PSF membranes was studied. In addition, the prepared membranes were tested to remove lime nanoparticles, an example of medium-size nanoparticles. The results showed that using RSNF at loadings from 0.5 to 2 wt.% can significantly increase hydrophilicity, porosity, water flux, and antifouling properties of PSF. RSNF also brought about an increase in rejection of lime nanoparticles (up to 98% rejection) from their aqueous suspension, and at the same time, with increasing flux across the membranes. Tensile strength of the membranes improved by ~29% with addition of RSNF and the maximum improvement was obtained on using 0.5% of RSNF, while Young’s modulus improved by ~40% at the same RSNF loading. As compared to previous published results on using cellulose nanofibers isolated from bleached pulps, the obtained results in the current work showed potential application of nanofibers isolated from unbleached pulps for improving important properties of PSF membranes, such as hydrophilicity, water flux, rejection, and antifouling properties.
Highlights
Polysulfone (PSF) is one of the attractive polymers due to its good mechanical properties, thermal stability, chemical resistance, transparency, and flexibility [1]
It has been shown that rice straw nanofibers (RSNF) with high lignin content (~14 wt.%) could be isolated from rice straw xylanase-treated unbleached sulfite pulp with a width of ~14 ± 7 nm, as seen in Figure 1 [31]
Similar features due to addition of cellulose nanofibers were interpreted by the accelerated phase inversion trend was observed in membranes prepared from cellulose nanofibers isolated from bleached pulp process by the hydrophilic cellulose nanofibers, which results in formation of more pores and better with polysulfone/sulfonated polysulfone mixture [24]
Summary
Polysulfone (PSF) is one of the attractive polymers due to its good mechanical properties, thermal stability, chemical resistance, transparency, and flexibility [1]. Some inorganic additives have been used to improve the hydrophilicity and performance of PSF membranes such as Al2 O3 [10], TiO2 [11], and silica [12,13] Another route to overcome the hydrophobicity of PSF and to produce high-flux membranes is to blend it with other relatively higher hydrophilic polymers. The use of lignin, which produced as a byproduct from pulping processes, is another attractive route for improving hydrophilicity of polysulfones due to the presence of polar groups in the lignin structure in addition to the aromatic skeleton, which helps in achieving good compatibility between lignin and polysulfones [28,29]. The use of cellulose nanofibers isolated from unbleached rice straw neutral sulfite pulp (containing ~14% lignin) by ultrafine grinding for improving hydrophilicity, porosity, and ultrafiltration performance of PSF membrane was investigated. The effect of the isolated nanofibers on mechanical properties was investigated
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