Properties of fiber cement reinforced with cellulose pulp modified by plasma treatment with sulfur hexafluoride (SF6)

Cellulose pulps in cementitious matrix have been investigated because of their high tensile strength, which improves the mechanical properties of the composites. Nonetheless, the material's hydrophilic nature could impair cement and potentially diminish the durability of the compound. In this work, to improve physical-mechanical performance of fiber cement produced with cellulose, the surface of the cellulose pulp was modified by sulfur hexafluoride (SF6) plasma treatment at different conditions (0.1, 0.3, 0.5 and 0.7 Torr). Fiber cement composite was subsequently produced from treated pulps. Theoretical calculations suggested that cellulose interacts with SF6 molecules through adsorption. The cellulose pulps were evaluated using spectroscopy, diffractometry and water affinity techniques. The physical and mechanical properties of the composites produced were evaluated before and after accelerated ageing cycles. The surface modification of cellulose pulp by SF6 plasma treatment was viable and suitable. FTIR and Raman spectroscopy showed the presence of specific bands related to C-Fx bonds. An exchange of behavior of the cellulose pulp occurred, transitioning from hydrophilic to hydrophobic. After 192 hours of analysis, moisture absorption was reduced by 15.28%, 13.99%, 8.30%, and 14.05% for the 0.1SF6, 0.3SF6, 0.5SF6, and 0.7SF6 treatments, respectively. Only the 0.1SF6 treatment yielded satisfactory results for all mechanical properties assessed, including rupture modulus (MOR), elasticity modulus (MOE), limit of proportionality (LOP), and toughness, when compared to untreated cellulose pulp. The positive results were particularly evident following accelerated ageing cycles, as the properties were either maintained (MOR, LOP) or improved (MOE, toughness). Therefore, this treatment is recommended for the intended application. Graphical abstract: (Figure presented.)