Parica cellulose nanofibrils (Schizolobium parahyba var. amazonicum) for films production and as an agent for paper coating

Abstract

The main objective of the study was to modify the Schizolobiumparahyba var. amazonicum (paricá) fibers by alkaline treatment (NaOH) and bleaching (NaClO2 + glacial acetic acid) for production of nanofibrillated cellulose (CNFs) and evaluate their application in films production and as agent for coating Writing & Printing (W&P) papers. The work was divided in 2 manuscripts. In the first article the treated fibers and CNFs were characterized, as well as the films produced from the generated CNFs. The characterization of the fibers and CNFs was done by FTIR spectra, thermogravimetry and scanning electron microscopy (SEM-FEG).The films generated from the CNFs were evaluated by the mechanical properties and surface wettability. The hemicelluloses content decreased with the sequence of treatments. The FTIR spectra showed that mechanical defibrillation caused the rupture of the fibers bonds. The thermal degradation temperature observed in the DTG analysis was increased by comparing the natural fibers (243°C) to the bleached fibers (255°C).The defibrillation process led to greater thermal stability for the bleached CNFs when compared to the fibers. The mechanical properties showed values of 6.93 ± 0.18 GPa for modulus of elasticity (MOE) for the films produced from the fibers submitted to the bleaching and 1.65 ± 0.08 GPa for films produced with only alkaline treated CNFs. These results showed a superiority of the films produced from the bleached CNFs. A more hydrophobic surface for the films produced with CNFs generated from the bleached CNFs was observed. In the second article, paricá cellulose CNFs were used as a coating agent for Writing & Printing (W & P) papers withgrammage75g.m-2 with layers 1 to 5. In the second stage of the study, the gelatinized cassava starch was used in alternation with the layers of CNFs. The layers of CNFs and starch were deposited on the base paper using the dip-coating technique and for each deposited layer, the paper was dried at 50 °C for 24h. The deposition of consecutive layers resulted in less degradation in water for papers covered with alkaline treated CNFs. The thermogravimetric analysis showed that the starch started to degrade in a higher temperature in comparison to the nanofibrils,however, it took less time to reach the maximum degradation temperature. The gelatinized starch layers resulted in a higher density increase to the papers. The degradation in water was low for all types of coated papers. The use of the gelatinized starch in alternation with the layers of nanofibrils with alkaline treatment resulted in papers with greater elongation at break. Samples produced with a layer of bleached nanofibrils and a layer of gelatinized starch obtained a tensile strength of approximately 20% greater than the W&P papers. The application of the gelatinized starch improved the surface properties of CNF coated papers, but the W&P papers showed better surface characteristics than all coated papers. The system of layer deposition and sequential drying may have caused damage to the structure of the paper fibers, causing lower mechanical strength for the coated papers in comparison to the commercial paper. In summary, the present work involving the 2 articles contributes with important information about coated papers using CNFs.