Cellulosic Fibers and Nonwovens from Solutions: Processing and Properties

Cellulose is a renewable and bio-based material source extracted from wood that has the potential to generate value added products such as composites, fibers, and nonwoven textiles. This research was focused on the potential of cellulose as the raw material for fiber spinning and melt blowing of nonwovens. The cellulose was dissolved in two different benign solvents: the amine oxide 4-N-methyl morpholine oxide monohydrate (NMMO•H₂0) (lyocell process); and the ionic liquid (IL) l-butyl- 3-methylimidazolium chloride ([C₄MIM]Cl). The solvents have essentially no vapor pressure and are biologically degradable, making them environmentally advantageous for manufacturing processes. The objectives of this research were to:

• characterize solutions of NMMO and [C₄MIM]Cl

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  develop processing techniques to melt blow nonwoven webs from cellulose using NMMO as a solvent

• electrospin cellulosic fibers from the (C₄MIM]Cl solvent

• spin cellulosic single fibers from the [C₄MIM]Cl solvent

Different concentration solutions of cellulose in NMMO and [C₄MIM]Cl were initially characterized rheologically and thermally to understand their behavior under different conditions of stress, strain, and temperature. Results were used to determine processing conditions and concentrations for the melt blowing, fiber spinning, and electrospinning experiments.

The cellulosic nonwoven webs and fibers were characterized for their physical and optical properties such as tensile strength, water absorbency, fiber diameter, and fiber surface. Thermal properties were also measured by thermogravimetric analysis, differential scanning calorimetry, and dynamic mechanical analysis.

Lyocell webs were successfully melt blown from the 14% cellulose solution. Basis weights of the webs were 27, 79, and 141 g/m² and thicknesses ranged from 0.3- 0.9 mm, depending on die temperatures and die to collector distance. The average fiber diameter achieved was 2.3 microns. The 6% lyocell solutions exhibited poor spinability and did not form nonwoven webs. The electrospun nonwoven webs obtained were evaluated for fiber diameter and surface/web structure using scanning electron microscopy (SEM). The fibers obtained were in the range of 17-25 microns and the fiber surfaces and shapes varied with spinning conditions. A capillary rheometer was used to spin single fibers from [C4MIM]Cl. Circular fibers in diameter ranging from 12-84 microns were obtained.

Potential applications of these melt blown and electrospun webs include hygiene and medical products where softness, moisture absorbance, and barrier properties are desirable. Apparel is a new and growing market for nonwovens and the aesthetics and drapeability of regenerated cellulosic fibers should have appeal.