Felix Riehle1,2,3, Daniel Hoenders1,2,3, Jiaqi Guo1,2,3, Alexander Eckert4, Shinsuke Ifuku5, Andreas Walther1,2,3,6. 1. Institute for Macromolecular Chemistry , Stefan-Meier-Strasse 31, University of Freiburg , 79104 Freiburg , Germany. 2. Freiburg Materials Research Center , Stefan-Meier-Strasse 21, University of Freiburg , 79104 Freiburg , Germany. 3. Freiburg Center for Interactive Materials and Bioinspired Technologies , Georges-Köhler-Allee 105, University of Freiburg , 79110 Freiburg , Germany. 4. DWI - Leibniz-Institute for Interactive Materials , Forckenbeckstr. 50 , 52056 Aachen , Germany. 5. Graduate School of Engineering , Tottori University , 101-4 Koyama-cho Minami , Tottori , 680-8502 , Japan. 6. Freiburg Institute for Advanced Studies , University of Freiburg , 79104 Freiburg , Germany.
Abstract
Sustainable polysaccharide nanofibrils formed from chitin or cellulose are emerging biobased nanomaterials for advanced materials requiring high mechanical performance, barrier properties, for bioactive materials, or other functionalities. Here, we demonstrate a single-step, waterborne approach to prepare additive-free flame-retardant and self-extinguishing, mechanical high-performance nanopapers based purely on surface-deacetylated chitin nanofibrils (ChNFs). We show that the flammability can be critically reduced by exchanging the counterions, e.g. to the phosphate type, using the respective acid providing electrostatic stabilization in the preparation of the ChNFs. This exchange renders beneficial elemental combinations of high contents of N/P (nitrogen/phosphorus) in the final nanopapers, known to provide outstanding performance in halogen- and heavy metal-free flame-retardant materials. Full fire barrier nanopapers can even be obtained by hybridizing the ChNF with nanoclay. Comprehensive fire retardancy tests, including vertical and horizontal flame tests and microscale cone combustion calorimetry, as well as fire breakthrough tests elucidate excellent flame-retardant properties and high structural integrity when being burned. The intrinsic elemental composition of chitin, containing nitrogen, and the simple modification of the counterions to include phosphorus provides key advantages over related, but flammable nanocellulose materials that often require significant chemical modifications and additives to become fire-retardant. By activating a global food waste, this study presents a critical advance for bioinspired, green, and mechanical high-performance materials with extraordinary flame-retardant and fire barrier properties based on sustainable feedstock, using benign water-based room temperature processing, and by avoiding heavy metals and halogen atoms in their composition.
Sustainable n class="Chemical">polysaccharide nanofibrils formed from n class="Chemical">chitin or cellulose are emerging biobased nanomaterials for advanced materials requiring high mechanical performance, barrier properties, for bioactive materials, or other functionalities. Here, we demonstrate a single-step, waterborne approach to prepare additive-free flame-retardant and self-extinguishing, mechanical high-performance nanopapers based purely on surface-deacetylated chitin nanofibrils (ChNFs). We show that the flammability can be critically reduced by exchanging the counterions, e.g. to the phosphate type, using the respective acid providing electrostatic stabilization in the preparation of the ChNFs. This exchange renders beneficial elemental combinations of high contents of N/P (nitrogen/phosphorus) in the final nanopapers, known to provide outstanding performance in halogen- and heavy metal-free flame-retardant materials. Full fire barrier nanopapers can even be obtained by hybridizing the ChNF with nanoclay. Comprehensive fire retardancy tests, including vertical and horizontal flame tests and microscale cone combustion calorimetry, as well as fire breakthrough tests elucidate excellent flame-retardant properties and high structural integrity when being burned. The intrinsic elemental composition of chitin, containing nitrogen, and the simple modification of the counterions to include phosphorus provides key advantages over related, but flammable nanocellulose materials that often require significant chemical modifications and additives to become fire-retardant. By activating a global food waste, this study presents a critical advance for bioinspired, green, and mechanical high-performance materials with extraordinary flame-retardant and fire barrier properties based on sustainable feedstock, using benign water-based room temperature processing, and by avoiding heavy metals and halogen atoms in their composition.
Authors: Wan M F B W Nawawi; Mitchell Jones; Richard J Murphy; Koon-Yang Lee; Eero Kontturi; Alexander Bismarck Journal: Biomacromolecules Date: 2019-10-23 Impact factor: 6.988