Stimuli-Responsive Cellulose Nanocrystals based Materials

• Autor(a) principal: Almeida, Ana Rita Gonçalves Lobato de
• Data de Publicação: 2020
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10362/104027
• topic: Cellulose nanocrystals; azobenzene; reversible photoisomerization; stimuli-responsive materials; Domínio/Área Científica::Engenharia e Tecnologia::Engenharia dos Materiais

The continued demand for the sustainable products has emerged due to the environmental awareness, prompting the development of the new polymeric materials whose properties change when subjected to the external stimuli; these are called the “intelligent” polymers or the stimuli-responsive polymers. The cellulose nanocrystals (CNCs) have a high versatility of the physical, chemical and biological properties, making them excellent candidates for the production of the sustainable products that respond to stimuli. Thus, the main objective of this project involved the production and the characterisation of a stimuli-responsive composite material based on the CNCs functionalised with a chromophore and coated with a conductive polymer, polypyrrole (PPy). The CNCs suspensions were produced from the cellulose microcrystals derived from the cotton, by the process of the acid hydrolysis. A new product has emerged, Azo-CNCs, from its functionalisation with azobenzene (Azo) derivative. The materials were characterised by the techniques of ATR-FTIR, EA, CP/MAS 13C NMR, UV-Vis spectroscopy, AFM and TGA/DSC, and the wettability was determined. The CNCs with an average nanoparticle length of 166 ± 55 nm gave rise to Azo-CNCs with 219 ± 62 nm. This new product presents reversible photoisomerisation, when suspended in THF, with full isomerization after 5 minutes of UV irradiation. It showed a hydrophobic behaviour (water contact angle 96.3) in film form, but after irradiation with UV light, it became hydrophilic (water contact angle of 65). It was still sensitive to low pH with a photochromic response. The CNCs were also coated with polypyrrole using the in situ chemical polymerization of pyrrole. The influence of poly(N-vinylpyrrolidone) (PVP) as a surface modifier was additionally studied and, since the CNCs became less hydrophilic, the deposition of PPy onto their surface was promoted, increasing its conductivity. The composite systems containing Azo-CNCs and PPy-CNCs will lead to the use of the CNCs in advanced and promising applications, complementing their versatility and renewability