Identifying Juncus plant as viable source for the production of micro- and nano-cellulose fibers: Application for PVA composite materials development

With the aim of identifying new, renewable and sustainable sources for the production of bio-nano-materials, cellulose microfibers (CMF) and cellulose nanofibrils (CNF) were successfully produced from the widely available Juncus plant. CMF with average microfibers diameter of 3.5 mu m were produced by conventional alkaline and bleaching treatments with a yield of around 36 %. CNF with average nanofibrils diameter of 2.5 nm were isolated from CMF by a combination of TEMPO-oxidation and mechanical disintegration processes. The morphology and physico-chemical properties of raw Juncus plant stems, CMF, TEMPO-oxidized CMF (T-CMF) and CNF were evaluated using several characterization techniques. It was found that the applied chemical treatments were effective in producing pure CMF and CNF materials having typical cellulose I structure, high crystallinity and good thermal stability. The as-extracted CNF were utilized to develop CNF-reinforced PVA nanocomposite films, and their transparency, thermal stability and mechanical properties were investigated and compared with the CMF and T-CMF reinforced PVA composite materials. It was found that the PVA nanocomposite material containing 5 wt% CNF exhibited a tensile modulus and strength of 3.3 GPa and 110 MPa, respectively, which are higher than those observed for neat PVA and PVA composites reinforced with 5 wt% CMF or T-CMF (modulus of 1.9 and 3.1 GPa and strength of 52 and 97 MPa, respectively). In contrast to CMF and T-CMF reinforced PVA composites, that displayed a reduced optical transmittance (ca. 57-70 % at 600 nm), the CNF-reinforced PVA nanocomposite material maintained the same transmittance of the neat PVA film (ca. 90 % at 600 nm), suggesting the good dispersion of CNF at the nanometric scale. These newly developed CNF could be considered as a potential nanofiller candidate for the preparation of PVA-based nanocomposite materials of high transparency and good mechanical properties.