Látex de borracha natural como adesivo alternativo para painéis de partículas de média densidade

Abstract

Formaldehyde emissions from urea-formaldehyde (UF)-based adhesives, widely used in wood panel production, have raised significant environmental concerns. This study evaluated the use of centrifuged natural rubber latex (NRL) as a partial substitute for UF in the manufacture of medium-density particleboard (MDP), in four proportions: T0%, T20%, T40%, and T60%. Analyses included moisture content, chemical structure, gel time, pH, rheology, solids content, optical and electron microscopy (SEM), density, swelling, water absorption, bending strength (MOR), modulus of elasticity (MOE), screw withdrawal resistance, thermogravimetric analysis, thermal conductivity, and formaldehyde emissions. Pinus oocarpa particles contained 5.61% extractives, 31.36% lignin, 62.89% holocellulose, 31.53% cellulose, and 0.14% ash, with thermal stability up to 250 °C. The UF and NRL adhesives had solids contents of 75 ± 0.04% and 66.6 ± 1.18%, viscosities of 28.3 ± 1.1 cP and 490 ± 24 cP, gel times of 55 ± 2.4 s and 53.19 ± 1.61 s, and pH values of 8.15 ± 0.3 and 10.22 ± 0.61, respectively. Rheological analysis showed that NRL altered the behavior of UF, forming a non-Newtonian hybrid fluid with initial fluidity and rapid solidification. The average panel density was 0.56 g/cm3 (M-2 class), with compaction ratios ranging from 1.06 (T0%) to 1.10 (T20%). The addition of NRL increased water absorption and swelling, reaching 50.9% after 2 h (T60%) and 48.8% after 24 h. The T20% treatment met the requirements of the ABNT NBR 14810-2 (2013) standard for MOR and MOE, while T20% and T40% remained within the regulatory MOE limits. T20% also met the standard for screw withdrawal resistance (ABNT NBR 14810- 2:2018). Thermal conductivity was maintained across all treatments, with a slight reduction in T40%. SEM analysis of the NRL treatments showed poor interaction between components, with clump formation and irregular adhesion, negatively affecting physical and mechanical properties. Formaldehyde emissions progressively decreased with increasing NRL content; all treatments were classified as E1 (most restrictive), with T60% showing a 99% reduction in emissions. It is concluded that NRL can replace up to 20% of UF without compromising panel performance, and that higher proportions progressively reduce formaldehyde emissions, representing a more sustainable solution for the industry.