Recyclable nanocomposite foams of Poly(vinyl alcohol), clay and cellulose nanofibrils – Mechanical properties and flame retardancy

Abstract

Foam-like clay-nanocellulose hybrids are of great interest as load-bearing structural foams with excellent fire retardancy, due to unique effects from clay on thermal cellulose degradation. For the first time, the fire retardancy of clay-nanocellulose foams are studied in detail, in particular the effect of a third polymer phase, poly(vinyl alcohol). The composition with optimum mechanical properties and fire retardancy is identified and analyzed. Foams are prepared by freeze-drying and the compositions are varied systematically. Thermogravimetric analysis is performed on foam degradation. Mechanical properties from compression tests and fire retardancy data from cone calorimetry are reported, together with cellular structures from SEM and relative density estimates for the foams. Self-extinguishing foams are obtained with superior flame retardancy to commercial polymer foams. Addition of poly(vinyl alcohol) is beneficial for mechanical properties of clay-nanocellulose foams, but impedes the fire retardancy by reducing clay-cellulose synergies and cellulose charring during degradation.