Abstract
This work concerns a study on the effects of fiber types and content of cellulose nanofiber on mechanical, thermal, and optical properties polyvinyl alcohol (PVA) composites. Two different types of cellulose nanofibers, which are nanofibrillated cellulose (NFC) and bacterial cellulose (BC), were prepared under various mechanical treatment times and then incorporated into the PVA prior to the fabrication of composite films. It was found that tensile modulus of the PVA film increased with nanofibers content at the expense of its percentage elongation value. DSC thermograms indicate that percentage crystallinity of PVA increased after adding 2–4 wt% of the fibers. This contributed to the better mechanical properties of the composites. Tensile toughness values of the PVA/BC nanocomposite films were also superior to those of the PVA/NFC system containing the same fiber loading. SEM images of the composite films reveal that tensile fractured surface of PVA/BC experienced more ductile deformation than the PVA/NFC analogue. The above discrepancies were discussed in the light of differences between the two types of fibers in terms of diameter and their intrinsic properties. Lastly, percentage total visible light transmittance values of the PVA composite films were greater than 90%, regardless of the fiber type and content.
Highlights
Cellulose, a linear chain polysaccharide of β-(1 → 4)-Dglucopyranose units, is one of the most abundant natural biopolymers in the world [1,2,3]
The diameter of the fibers is relatively small as compared to their length, implying that the cellulose nanofibers are of high aspect ratios
Our results suggest that it was possible to enhance mechanical and thermal properties of poly(vinyl alcohol) (PVA), without scarifying large visible light transparency, by blending it with a suitable type and content of the cellulose nanofibers
Summary
A linear chain polysaccharide of β-(1 → 4)-Dglucopyranose units, is one of the most abundant natural biopolymers in the world [1,2,3]. NFC is a high aspect ratio cellulose fibril with diameters of 10–100 nm and with lengths of tens of microns [3, 11, 12, 14,15,16] Another type of nanocellulose can be produced by the fermentation of sugar by the Gramnegative bacteria Acetobacter xylinumor Gluconacetobacter xylinus sources [5, 6, 17, 18]. The effective modulus of BC filaments investigated using Raman spectroscopy [17, 20] and atomic force microscopy [18] has been reported to be in the range of 79–114 GPa, which is close to a value of 138 GPa for the crystal modulus of cellulose I [21, 22] This is due to its higher degree of crystallinity
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