Abstract
This paper reports the usage of cellulose nanofibers (CNFs) as a continuous nanoporous matrix and nanoclay (NC) as additive to fabricate hybrid films. CNF/Cloisite Na+ nanoclay composite films containing 10–50 wt % of NC were prepared for the study. The effects of NC incorporation and its content on mechanical, wettability and thermal degradation properties were investigated. The results showed that the film had a multilayer structure with gradually deposited CNT-NC hybrid on the filter paper Pure CNF films had higher moduli compared with those from the composite films, as the incorporation of NC decreased hydrogen bonding and networking ability of CNFs, especially at the high NC loading levels. The composite films demonstrated self-extinguishing ability when being exposed to the open flame. Composites with over 35 wt % NC did not burn because of the formation of a protective barrier containing ordered NC platelets. The addition of montmorillonite NC led to increased surface water contact angle, showing enhanced hydrophobicity of the material. During the film’s thermal pyrolysis, the first process occurred between 100 and 200 °C, resulting mainly from the evaporation of absorbed water; the second, between 280 and 350 °C, indicated thermal decomposition of cellulose; and the slow third stage happened from the 350 to 600 °C, representing carbonization. The results demonstrate that the apparent activation energies for all the CNF/NC composites were higher than the pure CNF film. CNF/NC films fabricated in this process are a promising barrier material for packaging applications.
Highlights
Combining inorganic and organic polymer components is a convenient way to fabricate composite materials, which have improved mechanical and barrier characteristics [1]
The resulting composite films demonstrated a multilayer structure (Figure 2b) with the wave-like layers positioned parallel to each other. We believe that such morphology was very likely predetermined by the flocculation process, which took place during film making [4]
The NC platelets attached to cellulose nanofibers (CNFs) only at the edge of NC platelets by electrostatic interactions because NC has negatively charged surface but positively charged edges, which attract negatively charged CNFs [14]
Summary
Combining inorganic and organic polymer components is a convenient way to fabricate composite materials, which have improved mechanical and barrier characteristics [1]. Such materials include hybrid systems containing layered clay minerals [2]. Hybrid materials containing organic polymers and layered NCs are flexible and easy to fabricate and process, and offer fire retardancy and excellent wettability properties without compromising their mechanical integrity [4,5,6,7]. A combination of cellulose nanofibers (CNFs) and NCs with a nacre structure was successfully demonstrated by [9] in a layered composite with unique properties. Coats–Redfern [12] and Flynn–Wall–Ozawa methods [13]) were employed to evaluate the apparent activation energies among various materials
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