Assessment of Bleached and Unbleached Nanofibers from Pistachio Shells for Nanopaper Making

Abstract

Cellulose and lignocellulose nanofibrils were extracted from pistachio shells utilizing environmentally friendly pulping and totally chlorine-free bleaching. The extracted nanofibers were used to elaborate nanopaper, a continuous film made by gravimetric entanglement of the nanofibers and hot-pressed to enhance intramolecular bonding. The elaborated nanopapers were analyzed through their mechanical, optical, and surface properties to evaluate the influence of non-cellulosic macromolecules on the final properties of the nanopaper. Results have shown that the presence of lignin augmented the viscoelastic properties of the nanopapers by ≈25% compared with fully bleached nanopaper; moreover, the hydrophobicity of the lignocellulose nanopaper was achieved, as the surface free energy was diminished from 62.65 to 32.45 mNm−1 with an almost non-polar component and a water contact angle of 93.52°. On the other hand, the presence of lignin had an apparent visual effect on the color of the nanopapers, with a ΔE of 51.33 and a ΔL of −44.91, meaning a substantial darkening of the film. However, in terms of ultraviolet transmittance, the presence of lignin resulted in a practically nonexistent transmission in the UV spectra, with low transmittance in the visible wavelengths. In general, the presence of lignin resulted in the enhancement of selected properties which are desirable for packaging materials, which makes pistachio shell nano-lignocellulose an attractive option for this field.

Lignin and Xylan as Interface Engineering Additives for Improved Environmental Durability of Sustainable Cellulose Nanopapers

“…Hasen et al (3) demonstrated a very high elastic modulus, reaching 7.6 GPa for carboxymethylated NFC/Xylan NP prepared 50/50 ( w / w ) [ 51 ]. Pistachio shells (6) were mildly treated to process them into dimensions closer to microfibrillated cellulose than NFC [ 78 ]. The authors obtained relatively high elastic modulus, but the dimensions of cellulose contributed to lower stress and elongation values.…”

“…(5) Bacterial cellulose nanofibrils and nanocrystals film [ 77 ]. (6) Bleached and unbleached pistachio shell MFC film [ 78 ]. (7) Cellulose nanowhiskers (CNW) and NFC nanopapers [ 79 ].…”