This study aimed to evaluate reaction conditions for deposition of SiO2 nanoparticles on the surface of cellulose fibers and their influence on moisture adsorption of the hybrid organic-inorganic material formed. SiO2 nanoparticle deposition was carried out with the sol-gel process testing four reaction times (2, 12, 18, and 24h) and three contents of the tetraethyl-orthosilicate (TEOS) precursor (1.9, 4.2 and 8.4g g(-1) of cellulose fiber). Modification time and TEOS content directly influence the amount of Si deposited on the fiber surface, nanoparticle diameter distribution, thermal stability, and resistance to moisture adsorption. There is a tendency of slight increase of nanoparticle size and the amount of Si deposited with increasing reaction time. SiO2 nanoparticles were bonded on the surface of the cellulose fibers and are able to improve thermal stability of the material, increasing onset degradation temperature. The moisture adsorption capacity of the modified cellulose fiber was reduced up to 50%.

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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.

MDP (medium density particleboard) panels are normally graded in composition along their cross-section, using low-size particles and high concentration of adhesive on the particleboard surface (leading to improved physical and mechanical properties), and high-size particles in the particleboard core (interior), which provide higher porosity. Then, the aim of this study was to evaluate the impact of using different contents of bamboo particles in the particleboard core, on their physical and mechanical properties. The production of the panels was carried out using Pinusoocarpa (P) and Bambusavulgaris var. Vittata (B) particles in different contents (100% P, 100% B, 50% de B e 50% de P, 25% de B e 75% de P, 75% de B e 25% de P) in the core of the particleboards. The face of the particleboards were composed of P particles. The panels were produced with nominal density of 0.70 g/cm3, 40:60 face:core relation, 11% urea-formaldehyde adhesive in the faces and 8% adhesive for the core, specific pressure of 3.92 MPa, 160 °C temperature and pressing time of 8 min. After seasoning, the panels were submitted to evaluation of the thickness swelling (TS) and water absorption (WA) after 2 and 24 h of immersion, apparent density (AD), internal bonding (IB), modulus of rupture (MOR) and modulus of elasticity (MOE) under static bending. There was no statistical difference between the treatments for AD, IB, MOR and MOE values. Panels produced with high contents of bamboo particles (100% B, 75% B e 50% B) in the core, presented the lower WA and TS values, leading to improved dimensional stability than panels with only pinus particles. The present results show the important impact of using functionally gradation and bamboo particles on the physical properties of the MDP panels produced.

Eucalyptuspulp cellulose fibers were modified by the sol-gel process for SiO2superficial deposition and used as reinforcement of thermoplastic starch (TPS). Cassava starch, glycerol, and water were added at the proportion of 60/26/14, respectively. For composites, 5% and 10% (by weight) of modified and unmodified pulp fibers were added before extrusion. The matrix and composites were submitted to thermal stability, tensile strength, moisture adsorption, and SEM analysis. Micrographs of the modified fibers revealed the presence of SiO2nanoparticles on fiber surface. The addition of modified fibers improved tensile strength in 183% in relation to matrix, while moisture adsorption decreased 8.3%. Such improvements were even more effective with unmodified fibers addition. This result was mainly attributed to poor interaction between modified fibers and TPS matrix detected by SEM analysis.