Obtenção de microfibrilas de celulose fosforiladas e sua aplicação com látex de borracha natural reticulado no recobrimento de papel cartão

Abstract

Cellulose is a natural material, renewable, abundant, and through their processing cellulose microfibrils (MFCs) are obtained which can be used in different ways, such as packaging paper coating. However, the high energy demand is still a limiting factor for industrial scale production. Thus, the phosphorylation pretreatment of cellulosic fibers is an alternative that seeks to facilitate the process of obtaining MFCs. The objective of this study was to assess the effect of phosphorylation pretreatment on unbleached Eucalyptus sp. Kraft pulps to obtain cellulose microfibrils (MFC) and its further application with crosslinked natural rubber latex on paper coating to enhance barrier properties. The pretreatments were applied in the proportions of 1.0 g of fiber/1.2 g of (NH4)H2PO4/4.9 g of CH4N2O (molar mass of 1:1:1) and 1.0 g of fiber/2.5 g of (NH4)H2PO4/10.0 g of CH4N2O (molar mass of 1:2:2). In addition, the material was subjected to heat treatment at 150°C in an oven for 20, 40 and 60 min for both proportions (1:1:1) and (1:2:2), to activate the phosphorylation process on the fibers. The pretreated pulps were washed and the pH was corrected to approximately 7 by adding NaOH solution. Pulps without pretreatment were analyzed as control samples. The pulps were diluted to 2% (w/w), for subsequent mechanical fibrillation. For the characterization of MFCs suspensions, the following analyzes were performed: turbidity, stability in water, scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), energy consumption and tensile strength of the films. In addition, the MFCs (5% w/w) from the best phosphorylation pretreatment were mixed with natural rubber latex to coat paperboard, by applying two layers with a 15 g/m² grammage. Along with this mixture, the use of photoinitiator Darocur 1173 (4% v/v) was tested by UV curing, aiming to improve the spreading and adhesion properties on the surface of the papers. For coated papers, the following analyzes were evaluated: characterization of suspensions/solutions, thickness and weight, scanning electron microscopy (SEM), oil resistance, water vapor permeability rate (WVPR) and water vapor permeability (WVP), water absorption capacity (coob test 120) and contact angle/wetting. The phosporylated unbleached Eucalyptus sp. kraft pulp reduced the energy consumption of mechanical fibrillation, as well as increased the quantity and quality of the obtained MFCs. Coating the papers with natural rubber latex and phosphorylated MFCs has helped to improve barrier properties of papers against external agents, and with data support for further theoretical studies. The coating of papers with biopolymers is a search for environmentally friendly processes, applicable on an industrial scale in a more sustainable way.