Aerogels from mannans

Transcription

1 Aerogels from mannans Maija Tenkanen Abdul Ghafar Suvi Alakalhunmaa Kirsti Parikka Kirsi Mikkonen Department of Food and Environmental Sciences Faculty of Agriculture and Forestry University of Helsinki, Finland November 4, 2015, Lund, Sweden

2 Outline q Introduction to aerogels q Aerogels from guar galactomannan q Aerogels from spruce galactoglucomannan q Conclusions

3 Aerogels lightest materials Aerogels are highly porous and lightweight materials prepared by removing liquid from a gel. Figs: Kangas 2012, stardust.jpl.nasa.gov

4 Polysaccharide hydrogels q Different polysaccharides may show physical q nanofibrillated cellulose q starch q β-glucan q chitosan q agar or chemical hydrogel formation. q alginate, pectin (di- or trivalent cations) q others (organic crosslinking agents) q Hydrogel formation can be confirmed by rheology.

5 Polysaccharide aerogels Prepared from a hydrogel by replacing the liquid phase by air. Aerogels Gel formation Drying o Supercritical CO 2 drying o Freeze-drying Aerogel Up to 99% air Biodegradable 5 Illustrations: Jung et al. Sci Rep, 2012, DOI: /srep00849

6 Polysaccharide aerogels q From renewable materials. q Biodegradable and non-toxic. q High mechanical stiffness and large surface area of the aerogels can be utilized, e.g., in sorption of desired components on the aerogel surface. q Possible applications are in thermal insulators, drug release, cell growth media, active packaging etc. Mikkonen, K.S. et al. Trends Food Sci. Technol. 2013, 34, 124.

7 Aerogels from guar galactomannan

8 Galactose oxidase qan extracellular copper-containing enzyme produced by Fusarium sp. belongs to CAZy AA5_2 quses molecular oxygen as the electron acceptor and produces hydrogen peroxide (two electron transfer). qsubstrates are D-galactose as well as D-galactosecontaining oligo- and polymers, terminal D-galactose. qacts selectively on the primary C-6 hydroxyl resulting in aldehyde: D-galactose => D-galacto-hexodialdose. qused in biosensors and in diagnostics. 8

9 Oxidative and reductive halfreactions of galactose oxidase 9

10 Oxidized guar galactomannan hydrogel formation Native GM (1%) Oxidized GMox (1%) Viscoelastic moduli (Pa) Viscoelastic moduli (Pa) Parikka et al., J. Agric. Food Chem.2010,58, Ghafar et al. European Polym. J

11 Oxidized guar galactomannan hydrogel formation After enzymatic oxidation Angular frequency (rad/s) Parikka, K. et al. Food Hydrocolloids

12 Formation of hemiacetal crosslinks between polymers after oxidation

13 Preparation of aerogels from GMox hydrogels Guar gum galactomannan 1% solution Enzymatic Oxidation Hydrogel Aerogel Aerogel Density GM ± g/cm 3 Freeze-drying Molding Mikkonen et al. RSC Advances 2014.

14 Morphology of GMox aerogels by Focused Ion Beam Scanning Electron Microscopy (FIB-SEM) Conventional freezing Ice-crystal template = oriented Unidirectional freezing = ice crystal templating Mikkonen et al. RSC Advances Ghafar et al. European Polym. J Ice crystals growing starting from the bottom of the sample. CO 2 -ice & EtOH bath 14

15 Water uptake of GMox aerogels Time (h) Weight (g) Water uptake (g) Water uptake ( aerogel weight) ± ± ± ± ± ± ± GMox aerogels did not dissolve in water during 24 hours. Mikkonen et al. RSC Advances 2014.

16 Nanofibrillated cellulose in aerogels

17 Guar galactomannan NFC hydrogel Native GM (1%) Native GM (1%) with NFC (25%) Viscoelastic moduli (Pa) Viscoelastic moduli (Pa) Ghafar et al. European Polym. J

18 Enzymatically oxidized guar galactomannan NFC hydrogel 0 % NFC 5 % NFC 15 % NFC 25 % NFC Ghafar et al. European Polym. J

19 Reinforcement of GMox hydro- and aerogels by nanofibrillated cellulose (NFC) Hydrogels Aerogels conventionally frozed Ghafar et al. European Polym. J

20 Aerogels from spruce galactoglucomannans Mannose:Glucose:Galactose 4:1:0.5 Acetylated => water soluble Molar mass kda => low viscose solutions

21 Spruce galactoglucomannans (GGM) qsoftwoods contain 15-20% O-acetylgalactoglucomannans (GGM) qabout 5-10% of GGM is dissolved in mechanical pulping of spruce wood qthis corresponds to about 5000 tons/year in an average mechanical pulp mill qggm can be recovered in good yield from thermomechanical pulping process water (Willför et al. 2003)

22 GGM-based aerogels CNF 16 44% AZC 0 23% GGM Mechanical properties Alakalhunmaa et al., submitted Moisturerelated properties Morphology

23 Effect of crosslinking with AZC Share of CNF: 30% Alakalhunmaa et al., submitted

24 Effect of CNF reinforcement AZC content 12.5% Alakalhunmaa et al., submitted

25 Water uptake of GGM-based aerogels AZC content: 12.5% Share of CNF Water uptake (g water/g aerogel) ± ± ± 1.8 CNF increased ability to hold water. Share of CNF: 30% AZC content (%) Water uptake (g water/g aerogel) 0 Disintegration 2 Disintegration ± ± 1.5 AZC required to maintain the structure Maatalo us-

26 Sponge capacity

27 Conclusions q Enzymatic oxidation is a new non-toxic way to prepare bio-based aerogels from galactose containing large polysaccharides as guar GM. q Enzymatic oxidation technology enables addition of reinforcements (such as NFC) or active compounds to aerogels prior gel formation. q Water insoluble and adsorbing mannan-based aerogels were prepared. q Spruce GGM reinforced with NFC and crosslinked with AZC resulted in relatively stiff aerogels with repeatable sponge capacity. q These aerogels could be exploited in, e.g., food packaging applications (active packaging, encapsulation, adsorbents).

28 Acknowledgements Funding The Academy of Finland Magnus Ehrnrooth Foundation (Abdul Ghafar) Galactose oxidase preparation: Dr. Sybe Hartmans GGM: Stefan Willför, Åbo Akademi NFC: Prof. Monika Österberg, Aalto University, Finland Prof. Lars Berglund, Assoc. Prof. Qi Zhou, KTH, Stockholm, Sweden DMA-RH analysis: Dr Lennart Salmén, Innventia, Sweden FIB-SEM images: Dr. Marko Vehkamäki, University of Helsinki 28