Low-Alpha-Cellulose-Based Membranes

Abstract

Depending on the method of cellulose production, the proportion of alpha fraction in it can vary significantly. Paper pulp, unlike dissolving cellulose, has an alpha proportion of less than 90%. The presence of cellulose satellites in the system does not impede the formation of concentrated solutions of N-methylmorpholine-N-oxide (NMMO). In the current study, spinning solutions based on cellulose with a low alpha fraction (up to 90%) (pulp cellulose) are investigated. The morphological features and rheological behavior of such solutions are examined. It is suggested to roll the obtained solutions in order to obtain cellulose membranes. X-ray diffraction, IR spectroscopy, AFM and SEM were used to investigate the resulting structure and morphology of the obtained membranes. It is shown that the degree of crystallinity for the membranes varies based on the impurity content in the sample. The morphology of the films is characterized by a dense texture and the absence of vacuoles. The highest strength and elastic modulus were found for membranes made of bleached hardwood sulfate cellulose, 5.7 MPa and 6.4 GPa, respectively. The maximum values of the contact angle (48°) were found for films with a higher proportion of lignin. The presence of lignin in the membranes leads to an increase in rejection for the anionic dyes Orange II and Remazol Brilliant Blue R.

Keywords: N-methylmorpholine-N-oxide; alpha fraction; biodegradability; cellulose; cellulosic membranes; hemicellulose; morphology; permeability; transport properties.

Figure 1

Photograph of cellulose powders. Cell 1 (bleached sulphate hardwood pulp grade “NS-Extra”), Cell 2 (unbleached sulphate softwood pulp grade “Extra”), and Cell 3 (unbleached sulphate softwood pulp grade “Fiber”) (from left to right).

Figure 2

IR spectra of cellulose powders Cell 1 (a), Cell 2 (b) and Cell 3 (c).

Figure 3

Morphology of cellulose solutions: Cell 1 (a), Cell 2 (b) and Cell 3 (c) in NMMO (oval inclusions—air).

Figure 4

Flow curves of 18% cellulose solutions for Cell 1 (a), Cell 2 (b) and Cell 3 (c) in NMMO at different temperatures.

Figure 5

G′ and G″ as a function of oscillatory frequency (18% cellulose solutions in NMMO: Cell 1 (a), Cell 2 (b) and Cell 3 (c)).

Figure 6

Photographs of cellulose films Cell 1 (a), Cell 2 (b) and Cell 3 (c).

Figure 7

SEM micrographs of cellulose membranes Cell 1 (a), Cell 2 (b) and Cell 3 (c).

Figure 8

Diffraction patterns of cellulose membranes Cell 1 (a), Cell 2 (b) and Cell 3 (c).

Figure 9

IR spectrum of membranes Cell 1 (a), Cell 2 (b) and Cell 3 (c).

Figure 10

AFM images for membrane samples Cell 1 (a), Cell 2 (b) and Cell 3 (c).

Figure 11

Contact angle (a) and drying time (b) of cellulose samples.