Polyaniline/Biopolymer Composites for Moisture Detection and Their Electromechanical Properties
Date
2022-07-15
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
ORCID
0000-0003-1726-1170
Type
Thesis
Degree Level
Doctoral
Abstract
Nowadays, atmospheric air pollution is among the most vital problems of humankind. This issue has inspired the development of sensing materials, which are capable of detecting harmful gases. The detection of water vapour (humidity) in atmospheric air is variable, where the ability to monitor the relative humidity (RH; %) is important for diverse applications.
The overall purpose of this research is fabrication of a humidity sensing material. The design approach involved the formation and application of composite materials. Electrically conductive polymer (polyaniline – PANI), hydrophilic biopolymer (chitosan – CHT) and a hygroscopic film-making polymer (polyvinyl alcohol – PVA) were used to prepare hybrid composite films with variable composition. Ternary polymer composites were prepared via a two-step procedure: 1) in situ polymerization of PANI onto CHT and 2) physical blending of the PANI/CHT binary composite with PVA. The resulting ternary composites were characterized using spectroscopy and other complementary physical methods. The overall tendency showed that samples with higher CHT content possessed higher dye adsorption, greater dynamic modulus, and lower conductivity.
To fabricate a proper humidity sensing material, the nature of chemical interactions between PANI and CHT was investigated. Three types of binary composites were prepared according to three synthetic routes: (1) in situ polymerization of aniline with CHT (Type 1); (2) molecular association of PANI and CHT (Type 2); and (3) physical mixing of dry powders (Type 3). The composites were studied by several spectroscopic methods in conjunction with water swelling tests and equilibrium dye adsorption. As a result, in situ polymerized samples featured covalent PANI-CHT bonding. Molecularly associated composites indicated the primary role of hydrogen bonding compared to physical blends. Dye adsorption revealed the uniqueness of Type 1 composites, whereas noncovalent interactions occur for Type 2 and 3 composites.
To compare sensing performance of CHT-based composites with other (bio)polymers, cellulose-based (CMP) and carbon-nanofiber-based (CNF) composites were prepared. It was noted that, although PANI/CMP/PVA and PANI/CNF/PVA freestanding films exhibited better conductivity (compared to that of PANI/CHT/PVA), their mechanical performance expressed lower tensile strengths. That allows to conclude that CHT-based ternary films represent the optimal composition for a prospective cost-effective, environmentally friendly and sustainable humidity sensor material.
Description
Keywords
Polyaniline, chitosan, humidity sensor, binary/ternary composites, structure-function, tensile testing, conductivity, characterization
Citation
Degree
Doctor of Philosophy (Ph.D.)
Department
Chemistry
Program
Chemistry