ABSTRACT Background: The aim of this study was to investigate near infrared (NIR) spectroscopy ability to estimate nanofibril concentration, physical and mechanical properties of Kraft paper reinforced with cellulose nanofibrils (CNF). For this purpose, paper sheets were prepared by mixing unbleached Eucalyptus fibers and cellulose nanofibrils. Twelve treatments result from the combination of the nominal grammages 75, 85, 95 and 105 g m-² with the nanofibril concentrations of 1, 5 and 10wt%, with 7 sheets per treatment. NIR spectra measured directly on paper specimens were correlated with physical and mechanical properties values obtained through conventional laboratory analyzes. Results: Principal component analysis (PCA) revealed no separation among specimens related to nanofibril content. Partial least squares regression (PLS-R) models for estimating nanofibril content, tensile index, stretch and resistance to air passage yielded R 2cv ranging from 0.73 to 0.98. Partial least squares - discriminant analysis (PLS-DA) correctly classified up to 93% of the paper specimens both by grammage and nanofibril content using NIR spectra. Conclusion: This approach appears to be suitable for predicting physical and mechanical properties of Kraft papers and can detect cellulose nanofibril content in the cellulose handsheets.

Abstract The effect of planting density on the anatomical characteristics of wood is still matter of debate. The aim of the study was to investigate the influence of planting density on the variation of wood anatomical elements in Eucalyptus and Acacia trees cultivated in areas of high planting density (monospecific) and low planting density (mixed) stands. The fiber length, fiber width, fiber lumen diameter, cell wall thickness, vessel diameter and vessel frequency were evaluated. The measurements were made from wood discs taken from five Eucalyptus urophylla x E. grandis trees and five Acacia mangium trees grown in high planting density (monospecific plantations, 1667 trees/ha) and in low planting density (mixed stands, 500 trees/ha), totalizing 20 trees at 4.5 years old. Eucalyptus and Acacia produced wood with shorter fibers and smaller vessels in high density stands, when compared to its equivalent in low density. Acacia presented more frequent vessels and fibers with walls thicker than its equivalent in low planting density. Eucalyptus presented longer and thinner fibers and vessels more frequent than Acacia, regardless of planting density. On the other hand, in high planting density, Acacia presented fibers with walls thicker than Eucalyptus and in low density of planting their vessels were larger.

Resumen El efecto de la densidad de plantación sobre las características anatómicas de la madera aún es tema de debate. El objetivo de este estudio fue investigar la influencia de la densidad de plantación sobre la variación de elementos anatómicos de la madera de árboles de Eucalyptus y Acacia, creciendo en áreas de alta densidad de plantación (monoespecífica) y en rodales de baja densidad de plantación (mixta). Se evaluaron: longitud, ancho y diámetro de lumen de la fibra, grosor de pared celular, diámetro y frecuencia de vasos. Las mediciones se hicieron en rodajas de madera tomadas de cinco árboles de Eucalyptus urophylla x E. grandis y cinco de Acacia mangium, creciendo en alta densidad de plantación (plantaciones monoespecíficas, 1667 árb/ha) y de otro tanto igual de árboles creciendo en baja densidad de plantación (rodales mixtos, 500 árb/ha), lo que hace un total de 20 árboles de 4.5 años de edad. Eucalyptus y Acacia de rodales de alta densidad produjeron madera con fibras más cortas y vasos más pequeños en comparación con sus equivalentes en baja densidad de plantación. Eucalyptus presentó fibras más largas y delgadas y vasos más frecuentes que Acacia, independientemente de la densidad de plantación. Acacia presentó vasos más frecuentes y fibras con paredes más gruesas que su equivalente en plantación de baja densidad. Por otro lado, en alta densidad de plantación, Acacia presentó fibras con paredes más gruesas que Eucalyptus y en baja densidad de plantación sus vasos fueron mayores.

RESUMO O interesse em nanocristais de celulose obtidos a partir de recursos naturais tem crescido principalmente devido a características que esses materiais fornecem quando inseridos em matrizes poliméricas. O presente estudo teve como objetivo avaliar o efeito da adição de nanocristais de celulose nas propriedades mecânicas dos biofilmes feitos a partir de hipromelose (ou hidroxipropil metilcelulose - HPMC) e misturas com amido de mandioca (CS). Os nanocristais de celulose foram produzidos por hidrólise ácida e caracterizados por microscopia óptica (OM), microscopia eletrônica de transmissão (TEM), difração de raios X (XRD) e termogravimetria (TG). Os filmes foram feitos por fundição (ou “casting”) com CS puro, hipromelose pura e também com misturas de CS e hipromelose. Em seguida, os nanocristais de celulose foram adicionados às misturas nas concentrações de 1, 3 e 10% (m/m). As avaliações dos filmes incluíram a resistência a tração e a superfície da fratura por microscopia eletrônica de varredura (SEM). Observou-se que o reforço com nanocristais de celulose melhorou as propriedades mecânicas, e as observações da superfície de fratura dos filmes testados mostraram que os nanocristais promoveram uma melhora na coesão da hipromelose e do amido na mistura e promoveram uma superfície mais homogênea.

ABSTRACT Interest in cellulose nanocrystals obtained from natural resources has grown mainly because of features that such materials provide when inserted into polymeric matrices. The present study aimed to evaluate the effect of cellulose nanocrystals addition on mechanical properties of biofilms made from hypromellose (or hydroxypropyl methylcellulose - HPMC) and cassava starch blends (CS). The cellulose nanocrystals were produced by acid hydrolysis and characterized by optical microscopy (OM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and thermogravimetry (TG). Films were made with pure CS, pure hypromellose and also with blends of CS and hypromellose by casting. Then cellulose nanocrystals were added to the blends in the concentrations of 1, 3 and 10% (m/m). Evaluations of the films included tensile performance and fracture surface by scanning electron microscopy (SEM). It was observed that the reinforcement with nanocrystals improved the mechanical properties of the films, and their fracture surface showed that cellulose nanocrystals promoted an improvement in the cohesion of the hypromellose and starch molecules in the blend, and created a more homogeneous surface.