Air drying scalable production of hydrophobic, mechanically stable, and thermally insulating lignocellulosic foam

Abstract

Demand for sustainable building thermal regulation is driving the development of low carbon-intensive, renewable, and safe-to-use materials to substitute the dominant synthetic polymers and inorganic mats. This study proposes a novel mild mechanical pretreatment strategy to fabricate high-performance, self-strengthening thermal insulation board in a low cost and scalable approach from chemi-thermomechanical pulp (CTMP), a type of high-yield wood pulp. CTMP fibers, after subject to a short period of disc milling, were found to gain abundant sub-fibrous structures at multiple scales. After foaming and air-drying, such micro-fibrillated fibers (MF-CTMP) formed robust, binder-free foam under capillary force with remarkedly stronger physical entanglement between fibers compared to that of pristine CTMP, achieving 3.7 folds Young’s modulus, 2.9 folds ultimate stress, and 1.9 folds toughness with respect to the latter. Palm wax coating further provided a sustainable hydrophobic protection for the foam (contact angle of ∼ 110°). The high porosity and structural tortuosity endowed the hydrophobic MF-CTMP foam with excellent thermal insulation property (thermal conductivity of 33.1 ± 2.3 mW/(m∙K)), demonstrating significantly better performance than a commercial glass fiber thermal insulator. Compared to other lignocellulosic boards prepared using freeze-drying or supercritical drying operations, the hydrophobic MF-CTMP foam represents a novel low cost, binder-free, and scalable technology for commercial sustainable thermal insulation applications.