Nanofiber Composites of Polyvinyl Alcohol and Cellulose Nanocrystals: Manufacture and Characterization

Abstract

Cellulose nanocrystals (CN) were used to reinforce nanofibers in composite mats produced via electrospinning of poly(vinyl alcohol) (PVA) with two different concentrations of acetyl groups. Ultrathin cross-sections of the obtained nanocomposites consisted of fibers with maximum diameters of about 290 nm for all the CN loads investigated (from 0 to 15% CN loading). The electrospinning process did not affect the structure of the PVA polymer matrix, but its degree of crystallinity increased significantly together with a slight increase in the corresponding melting temperature. These effects were explained as being the result of alignment and enhanced crystallization of PVA chains within the individual nanofibers that were subjected to high shear stresses during electrospinning. The strong interaction of the PVA matrix with the dispersed CN phase, mainly via hydrogen bonding or bond network, was reduced with the presence of acetyl groups in PVA. Most importantly, the elastic modulus of the nanocomposite mats increased significantly as a consequence of the reinforcing effect of CNs via the percolation network held by hydrogen bonds. However, this organization-driven crystallization was limited as observed by the reduction in the degree of crystallinity of the CN-loaded composite fibers. Finally, efficient stress transfer and strong interactions were demonstrated to occur between the reinforcing CN and the fully hydrolyzed PVA electrospun fibers.

Effect of Moisture on Electrospun Nanofiber Composites of Poly(vinyl alcohol) and Cellulose Nanocrystals

“…Previous work demonstrated that the incorporation of CNs in dry PVA electrospun fibers induced a significant improvement of mechanical properties. 27,28 However, the complex and strong interactions that exist between PVA chains, water molecules, and CNs in less dry composites are expected to influence markedly their mechanical properties and, as will be shown later, may compromise their performance. Therefore, a leading question relevant to this subject pertains to the role of the CN reinforcing phase.…”

“…27 A unique effect was observed at high relative humidity (i.e., 98%); by loading the composite with CN, up to levels of ca. 10% in weight, a significant increase in the elastic modulus was observed; however, at higher loadings, beyond 10%, a drop in the mechanical strength occurred.…”

“…24 The presence of hydroxyl groups in CNs makes them suitable for the production of composites with polar, hydrophilic polymers such as PVA, and the benefit of improved mechanical and thermal properties has been reported in the case of cast films 25,26 and electrospun fiber mats. [27][28][29] The aim of the present contribution is to study the effect of water as well as humidity treatments on the morphological integrity and the mechanical properties of electrospun PVA fibers reinforced with CNs. Water uptake and the interactions between water and the PVA matrix were considered.…”

Orientation of cellulose nanocrystals in electrospun polymer fibres

“…Peresin et al [8] have successfully electrospun CNC-reinforced poly(vinyl alcohol) (PVA) fibres with improved morphological and thermomechanical properties. It was shown that the increase in the CNC concentration in the fibres led to a significant enhancement of mechanical properties [9].…”

Chitin-chitosan nanocomposite gels: reinforcement of chitosan hydrogels with rod-like chitin nanowhiskers

“…20 As these nanowhiskers are anisotropic nanoparticles with extremely high modulus and strength along their long axes, their utilization as fillers for nanocomposites, that is, composite materials with internal nano-ordered structures, has been widely investigated, [2][3][4]15 since the pioneering report by Favier et al 21 In addition to their high strength, the polysaccharide nanowhiskers have several useful advantages in comparison with conventional inorganic fillers, including facile chemical modification via surface hydroxyl or primary amino groups, and high degree of biodegradability. Although some of the previous studies 20,21 have employed nanocomposite films in which nanowhiskers were dispersed without directional order, more recent studies have produced several new types of nanocomposites, including an electrospun non-woven mat of poly(vinyl alcohol) containing cellulose nanowhiskers, 22 and a drawn poly(vinyl alcohol) fiber in which cellulose whiskers are uniaxially oriented. 23,24 In the present study, use of chitin nanowhiskers for reinforcement of chemically cross-linked hydrogels was investigated.…”