Flame Retardant Eco-Friendly Foams Derived from Partially Hydrolyzed Collagen, Ammonium Polyphosphate and Miscanthus Fibers

There is growing interest in the development of sustainable thermal insulating materials from renewable resources, a strategy which can stand as an alternative to conventional petroleum-based insulating materials. In this study, bio-based porous insulating materials derived from partially hydrolyzed collagen (rabbit-skin) and containing ammonium polyphosphate (APP) as flame retardant and miscanthus fibers as reinforcement are prepared. Four freeze-dried formulations were prepared: pure partially hydrolyzed collagen (COL), partially hydrolyzed collagen with APP (COL-APP), partially hydrolyzed collagen with miscanthus particles (COL-M) and a ternary formulation that included both additives (Col-APP-M). The density, porosity, thermal conductivity, specific heat capacity, compressive mechanical properties and fire behavior were evaluated. The neat collagen foam had the lowest density (122 kg·m−3), highest porosity (91%), and lowest thermal conductivity (0.045 W·m−1·K−1). The addition of APP and/or miscanthus increased density and showed limited change in thermal conductivity, which remains comparable with insulating materials (0.0445–0.0510 W·m−1·K−1). Specific heat capacities of partially hydrolyzed collagen foams were also relatively high (1319–1390 J·kg−1·K−1) as compared to some other typical insulating materials. Mechanical experiments demonstrated that APP had considerably improved the compression stiffness and strength through the physical crosslinking and densification effects in the partially hydrolyzed collagen network. Analysis of fire behavior with both Pyrolysis Combustion Flow Calorimetry (PCFC) and cone calorimetry further indicated that the addition of APP yielded improved flame retardancy with a very low heat release. These results showed that partially hydrolyzed collagen-based foams reinforced by APP and lignocellulosic particles are sustainable thermal insulation materials with desired thermal performances, improved mechanical stability, and enhanced flame retardancy.