Efeitos dos componentes químicos de duas espécies de madeiras amazônicas na hidratação do cimento Portland

Abstract

The production of bio composites from lignocellulosic residues from legalized sawmills in the Amazon region is an alternative to improper disposal in the environment. These materials can be used for the production of agglomerated panels of cement - wood used for rapid construction and at low residences cost. However, the wood chemical components (cellulose, hemicelluloses, lignin, extractives, minerals) may react adversely with the cement phases during hydration, causing the retardation / inhibition of the setting, characterizing the incompatibility between both materials. In order to analyze the chemical compatibility of the two materials, the contents of cellulose, hemicelluloses, lignin, total extractives and ashes, respectively, were isolated from the sawdust of two species of Amazonian woods: Dizinia excelsa (38.53% ± 1.14; , 24.95% ± 0.35%, 17.80% ± 0.58, 0.70% ± 0.05) and Dipteryx odorata (41.22% ± 0.35, 29.32% ± 0.64, 37.61% ± 0.39, 14.22% ± 0.38, 1.15% ± 0.03). The extractives were removed by cold water, hot water in a water bath, hot water by filtration and hot water in Soxhlet apparatus, respectively: Dinizia excelsa (33%, 63%, 81% and 99%) and Dipteryx odorata (25%, 47%, 68% and 92%). The results of X- Rays Diffraction (XRD) suggest that: 1) the Portlandite phase precipitates on the cellulose during cement hydration; 2) the hemicelluloses delay the hydration of the cement, but the delay effect depends on the amount of hemicelluloses that react in the alkaline medium; 3) The higher Syringyl / Guaicyl (S/G) lignin ratio of Dinizia excelsa renders it more susceptible to degradation in alkaline medium, exposing cellulose micro - fibrils and allowing the Portlandite precipitation on them. In addition, lignin does not retard the hydration of Tricalcium aluminate (C3A), retarding the Tricalcium silicate (C3S) particles preferentially. 4) The polar extractives are efficient retarders and can be classified in two groups: initial and late retarders. 5) The ashes of the species studied did not cause delay or inhibitory effect during hydration. 6) Hot water treatment in Soxhlet apparatus showed better results for both species and can be used to improve the compatibility of cement-wood composites. The experimental results suggest that wood with higher content of hot water-soluble removable extractives, higher S / G ratio and low quantity of inhibitory hemicelluloses, such as Dinizia excelsa, should be used for cement - wood composites, due to the greater compatibility with the cement chemicals