Lignocellulosic materials for production of cement composites: valorization of the alkali treated soybean pod and Eucalyptus wood particles to obtain higher value-added products

Abstract

Brazil, as a predominantly agricultural country is the second largest world producer of soybean. Consequently, these plantations are responsible for high production of agricultural wastes. For reusing the large volume of one type of this material generated, the soybean pods, one type of waste generated by this crop, could be applied as a raw material for production of higher value-added products. Good examples of value-added product are those applied in the field of construction. The building construction is an intensive activity and it requires a great variety of materials. A great ideal in this field would be the obtainment of a material that relates good mechanical strength and reuse of wastes. In this context, the aim of this study was to produce cement composites with soybean pods associated with eucalyptus wood, both treated with alkaline solution and evaluate their physical properties and mechanical strength. The wood and the wastes particles were submitted to alkaline treatment in NaOH solution (5%) during 48 h in order to removing chemical compounds that could harm the cement solidification. For the composites production, the soybean pods addition was performed in proportions of 0, 25, 50, 75 and 100% and mixed with the complementary percentage of Eucalyptus grandis wood particles until achieve the amount of 100% of lignocellulosic material which constitutes the composite. The lignocellulosic materials were evaluated by basic density and chemical composition. The physical properties of water absorption (WA) (2 and 24 h) and thickness swelling (TS) (2 and 24 h) and the mechanical properties modulus of elasticity (MOE), modulus of rupture (MOR), compression strength and janka hardness of the cement composites were evaluated. Scanning electron microscopy (SEM) images showed the occurrence of cavities in the composites produced with higher proportions of soybean pods. All the properties were analyzed by ANOVA and in case of significance, the regression equation was adjusted to correlate the property with the percentage of soybean waste added. It was noted an increase of WA 24 h in the samples with high insertion of soybean pods. The TS was not affected by the different compositions of the composites. The mechanical properties decreased with the increase of soybean pod in the cement composites. However, the cement composites could be produced with up to 48% of soybean pods associated to eucalyptus wood and applied, for example, as partition walls or thermal and acoustic insulation walls.