Researchers have tested layer-by-layer deposition (LbL) coating on PET film and on polyurethane foam (not specified), alternating cellulose nano-fibrils and clay. The cellulose nano-fibrils were extracted from pulp fibres, then cationised. These fibrils are expected to show good mechanical properties because of crystallinity. The clay was anionic vermiculite clay (of mineral origin) as nano-platelets. Alternate deposition (by simple dipping, rinsing, drying) of the two oppositely charged materials resulted in a nano-scale coating with high levels of structure and of clay platelet alinement. A twenty bilayer coating (total thickness c. 140 nm) showed low oxygen transmission (reducing 180 µm PET film transmission from 17.5 to 0.03*), high elasticity modulus and hardness. Two (or four) bilayers on polyurethane foam (4.4% weight of coating) reduced mass loss in a 10 second butane torch test from 100% to 31% (26%) and prevented melt-dripping. The authors conclude that this LbL technology, using renewable components, could potentially provide effective fire protection to a range of materials and applications.
* unit for oxygen transmission: cm3/cm/cm2-s Pa.1016
“Super Gas Barrier and Fire Resistance of Nanoplatelet/Nanofibril Multilayer Thin Films”, S. Qin, J. Grunlan et al., Adv. Mater. Interfaces 2019, 6, 1801424 http://dx.doi.org/10.1002/admi.201801424