HMDSO plasma treatment of cellulose fibers influences water resistance and mechanical performance of extruded fiber cement composites

The performance of cellulose-reinforced fiber-cement composites can be affected by moisture uptake, dimensional instability, and progressive fiber mineralization under aging conditions. In this study, bleached cellulose fibers were modified by plasma-enhanced chemical vapor deposition (PECVD) using hexamethyldisiloxane (HMDSO) as an organosilicon precursor, and the effects of the modified fibers on extruded fiber cement composites were investigated. Plasma treatments were performed using HMDSO concentrations ranging from 2.3 to 70.0% in the gas mixture and were designated ORG-T02, ORG-T30, ORG-T50, and ORG-T70 according to the nominal HMDSO concentration. The modified fibers were characterized by Fourier-transform infrared spectroscopy, scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy, X-ray diffraction, water contact angle, and moisture absorption measurements. Quantum Theory of Atoms in Molecules analysis was used as a supporting approach to investigate possible interactions between HMDSO-derived species and cellulose hydroxyl groups. Plasma treatment changed the surface chemistry and moisture response of the fibers while preserving their fibrous morphology and crystalline structure. ORG-T30 reduced fiber moisture absorption by 12.20% after 192 h compared with untreated cellulose. The corresponding extruded fiber cement composites were designated F02-ORG, F30-ORG, F50-ORG, and F70-ORG according to the plasma treatment applied to the reinforcing cellulose. After 20 accelerated aging cycles, F02-ORG, F30-ORG, and F50-ORG showed modulus of rupture values 22.54%, 38.01%, and 6.62% higher, respectively, than the composite reinforced with untreated fibers, whereas F70-ORG showed a 9.19% lower value. These results show that maximum hydrophobicity did not correspond to the best composite response and that intermediate HMDSO treatment conditions produced the most favorable mechanical performance under the accelerated aging protocol used in this study. HMDSO-based PECVD therefore provides a solvent-free and tunable route for modifying cellulose surface properties and influencing the aging response of extruded fiber-cement composites.