Adesivo PVAc/NFC para laminação de papel kraft: otimização de dosagem e impacto no desempenho mecânico

Abstract

The present study was structured into two complementary parts. The first consisted of the development of a theoretical framework on poly(vinyl acetate) (PVAc)-based adhesives, cellulose nanofibrils (CNF), and multilayer kraft paper laminates, addressing aspects related to adhesion, glue-line formation, reinforcement mechanisms, mechanical properties, and the influence of nanocellulose on aqueous adhesive systems. The second part consisted of the experimental evaluation of the mechanical and physical performance of multilayer kraft paper laminates produced with PVAc adhesive modified with cellulose nanofibrils containing residual lignin. Formulations containing 0% (control), 1%, and 1.5% (w/w, dry basis) CNF were mechanically dispersed into a commercial PVAc adhesive and applied between twenty sheets of 200 g·m⁻² kraft paper, forming laminates with 19 glue lines. After curing at room temperature for seven days, the specimens were subjected to four-point bending tests to determine the modulus of rupture (MOR), limit of proportionality (LOP), and modulus of elasticity (MOE), as well as water absorption tests after 1 h and 24 h of immersion. The results indicated that CNF incorporation did not promote statistically significant increases in flexural strength or stiffness of the laminates under the evaluated conditions. The formulation containing 1% CNF exhibited mechanical behavior close to that of the control, along with lower result dispersion, indicating greater uniformity of the adhesive system. In contrast, the formulation containing 1.5% CNF showed a reduction in LOP and a tendency toward decreases in MOR and MOE, suggesting an earlier end of the linear elastic regime at higher reinforcement contents. Regarding water absorption, no statistically significant differences were observed among treatments after 1 h and 24 h of immersion. The results suggest that, within the evaluated concentration range, CNF containing residual lignin was not sufficient to significantly modify the hygroscopic behavior of the PVAc/kraft paper system. It was concluded that the incorporation of CNF into PVAc adhesive allows modulation of the balance between stiffness, deformability, and mechanical uniformity of multilayer kraft paper laminates, although the observed effects strongly depend on reinforcement content, fibrillar dispersion, and adhesive processing conditions.