Gas permeability and selectivity of cellulose nanocrystals films (layers) deposited by spin coating

Cellulose nanocrystals (CNC) were extracted from a cellulose residue using two different acid hydrolysis procedures. CNC extracted with sulfuric acid (CNC(S)) showed higher surface charge (339 μmol/g) compared with crystals extracted with hydrochloric acid (CNC(HCl)). Spin-coated films with two different configurations were prepared; the first with alternate layers of poly(allylamine hydrochloride) (PAHCl) and CNC, and the second with a single layer of PAHCl coated with multilayers of CNC. Film characteristics such as roughness, thickness, contact angle, orientation, gas permeability and gas selectivity were studied. Optical microscopy showed more homogeneous films of CNC(S) compared to CNC(HCl). The surface charge of the crystals impacted the films' hydrophobicity, being highest for 25 alternate layers of PAHCl and CNC(HCl). The gas permeability coefficient was different for each film, depending primarily on the surface charge of the crystals and secondly on the film configuration. The films made with CNC(HCl) displayed gas barriers with nitrogen and oxygen, and gas selectivity with some gas combinations. CNC(S) films did not show gas selectivity. These results indicate that CNC with low surface charge can be further developed for gas separation and barrier applications.