Heat-induced changes in cellulose nanocrystal/amino-aldehyde biocomposite systems
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Heat‑induced changes in cellulose nanocrystal/amino‑aldehyde biocomposite systems Sebestyén Nagy1 · Erika Fekete1,2 · János Móczó1,2 · Krisztina Koczka3 · Emília Csiszár1 Received: 24 March 2020 / Accepted: 12 August 2020 © The Author(s) 2020
Abstract Cellulose nanocrystals (CNCs) were extracted from natural cellulosic fibres such as bleached cotton and flax with a controlled multi-step sulphuric acid hydrolysis. From the aqueous suspensions of CNCs, the biocomposite films were prepared by casting and evaporation, with an amino-aldehyde (AA) compound in a wide concentration range from 0 to 30%. The AA compound (dimethylol dihydroxy ethylene urea) was considered both as a cross-linker of the CNC and as a matrix polymer for the CNC-reinforced composite system. Two series of films were prepared using different polyols such as sorbitol and glycerol as plasticizers to improve tractability. Heat treatment of the films was performed at elevated temperatures ranging from 140 to 200 °C for 10 min. Results clearly proved that besides temperature, the factors affecting the response of CNCbased nanocomposites to heat treatment were the source of cellulose, the type of plasticizer and the amount of cross-linking agent. Films based on flax–CNC and plasticized with glycerol showed a higher increase in yellowness and a more significant decrease in haze than those derived from cotton–CNC and plasticized with sorbitol, respectively. The cross-linking agent (AA) had a moderating effect on the heat-induced changes of properties. Furthermore, thermal gravimetric analysis (TG) of films revealed that thermal stability of the CNC films improved considerably when AA was added and cross-linking occurred. The increase in Tmax was more significant for the flax–CNC films (from about 230 to 290 °C) than for the cotton–CNC ones (from about 250 to 280 °C). Keywords Cellulose nanocrystals · Nanocomposites · Thermal degradation · Discolouration · Plasticizers · Cross-linking
Introduction Today’s complex composites industry requires sustainable and value-added products that are environmentally efficient. Among the various composite materials, natural fibre-reinforced polymer composites have found great interest. Cellulose is the most important natural polymer, which
* Emília Csiszár [email protected] 1
Laboratory of Plastics and Rubber Technology, Department of Physical Chemistry and Materials Science, Budapest University of Technology and Economics, Műegyetem rkp. 3, Budapest 1111, Hungary
2
Institute of Materials and Environmental Chemistry, Research Centre for Natural Sciences, Magyar tudósok körútja 2, Budapest 1117, Hungary
3
Department of Biotechnology, University of Natural Resources and Life Sciences, Muthgasse 18, Vienna 1190, Austria
is available in a large quantity and represents a renewable resource for different industrial applications. Recently, cellulosic nanomaterials have received much attention in an effort to improve their production, as well as the application especially in green composites including packag
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