Cellulose nanocrystals extracted from okra fibers in PVA nanocomposites

Cellulose nanocrystals (CNC) were extracted from okra bahmia (Abelmoschus Esculentus) bast fibers and inserted in different tenors (1, 2, 5, and 10 wt %) as the reinforcement of a poly(vinyl alcohol) (PVA) matrix. The extraction of cellulose was carried out in a two-step procedure: the first chemical treatment led to the production of holocellulose by the gradual removal of lignin, while the subsequent sulphuric acid hydrolysis process allowed obtaining cellulose nanocrystals in an aqueous suspension. The dispersion of CNC in the composite appeared effective at low cellulose content (1 wt %), while it presented more problems for higher contents. However, a 5 wt % cellulose content proved ideal to promote a direct mechanical interaction between the PVA and cellulose structures. Thermal analysis demonstrated that the presence of okra did not have a large effect on glass transition temperature, while it sensibly modified the melting temperature of the PVA matrix, as well as the crystallization temperature, due to the nucleating action of the nanofillers. FTIR spectroscopy performed during the exposure to UV light underlined that no oxidative reactions occur after a short-time exposure and that a longer irradiation times are required to produce oxidation on neat matrix and PVA/CNC nanocomposites. The results confirmed that the presence of CNC does not affect the stability of the neat PVA matrix to the photodegradation after UV irradiation. (c) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013