Polymer-emulsion pre-coating of wood fibres for improving the dimensional stability of magnesium oxysulphate cement-bonded fibreboards

Magnesium oxysulphate cement-based wood fibreboard (MOSCWF) is a promising lightweight building material, but moisture-induced swelling of hygroscopic fibres limits its dimensional stability and mechanical performance. Here, wood fibres were pre-coated with polyacrylate (PA), silicone-acrylic (SA), or styrene-acrylic (StA) emulsions at 5–17 wt% before incorporation into MOSC. Density, 28 d bending performance, 24 h dimensional stability, XRD/FTIR characteristics, SEM–EDS morphology, and apparent contact angle were evaluated. Emulsion dosage did not significantly affect apparent density, while moderate dosages improved both dimensional and bending performance. Under the investigated conditions, the 11–14 wt% range provided a favourable balance between short-term dimensional stability and bending performance; for P4, MOR and MOE increased by 48.6% and 37.0%, whereas length and thickness swelling decreased by 57.8% and 51.3%, respectively. The principal MOSC structural features were retained, while pre-coating increased apparent contact angle and altered local fibre–matrix morphology. The mismatch between apparent-wettability and swelling rankings indicated that initial outer-surface wettability alone did not govern dimensional response. Overall, the results support an evidence-constrained interpretation involving coupled moisture-regulation and fibre–matrix interfacial effects and identify fibre pre-coating as a practical fibre-targeted strategy for improving the short-term dimensional stability and bending performance of mineral-bonded wood composites.