Abstract
This paper reports a novel procedure to fabricate multilayer composite biofilms based on halloysite nanotubes (HNTs) and sustainable polymers. Among the biopolymers, the non-ionic (hydroxypropyl cellulose) and cationic (chitosan) molecules were selected. The nanocomposites were prepared by the sequential casting of ethanol solutions of hydroxypropyl cellulose and aqueous dispersions of chitosan/HNTs. The composition of the bio-nanocomposites was systematically changed in order to investigate the effect of the hydroxypropyl cellulose/HNTs ratio on the thermal properties of the films, which were investigated by differential scanning calorimetry (DSC) and thermogravimetry (TG). DSC studies were conducted in the static air (oxidative atmosphere), while TG measurements were carried out under nitrogen flow (inert atmosphere). The analysis of DSC data provided the enthalpy and the temperature for the oxidative degradation of the bio-nanocomposites. These results were helpful to estimate the efficacy of the well-compacted middle layer of HNTs as a flame retardant. TG experiments were performed at a variable heating rate and the collected data were analyzed by the Friedman’s method (non-isothermal thermogravimetric approach) with the aim of studying the kinetics of the hydroxypropyl cellulose degradation in the multilayer nanocomposites. This work represents an advanced contribution for designing novel sustainable nanocomposites with excellent thermal behavior as a consequence of their peculiar multilayer structure.
Highlights
This paper reports a novel procedure to fabricate multilayer composite biofilms based on halloysite nanotubes (HNTs) and sustainable polymers
The nanocomposites were prepared by the sequential casting of ethanol solutions of hydroxypropyl cellulose and aqueous dispersions of chitosan/HNTs
The composition of the bio-nanocomposites was systematically changed in order to investigate the effect of the hydroxypropyl cellulose/HNTs ratio on the thermal properties of the films, which were investigated by differential scanning calorimetry (DSC) and thermogravimetry (TG)
Summary
Halloysite is an emerging nanofiller for the fabrication of smart nanocomposites with specific functionalities useful for several technological purposes, such as anti-corrosion coatings [1,2,3], food packaging [4,5,6], remediation [7,8,9,10,11], catalysis [12,13,14,15], tissue engineering [16,17,18], preservation of art-works [19,20,21], and antimicrobial protection [22,23]. In the pH 2–8, the cavity possesses a positive net charge, whereas the shell is negatively charged [29] This peculiarity allows for a selective modification of the halloysite surfaces by means of ionic molecules that can be exploited to control its colloidal stability and rheological properties as requested for the numerous applications on tubular nanoparticles [30,31,32,33]. The addition of halloysite nanotubes (HNTs) within anionic polymers represents an efficient strategy to enhance the thermal stability of the biomaterials because the polymeric chains are entrapped within the HNTs lumen [4,34] This effect was detected for pectin/HNTs [4,35] and alginate/HNTs nanocomposites [34]. This study provides a contribution to the fabrication of bio-nanocomposites with a controlled structure that can be exploited for engineering and biological applications
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