aerogels from mannans - lth · conclusions qenzymatic oxidation is a new non-toxic way to prepare...
TRANSCRIPT
Aerogels from mannansMaija TenkanenAbdul GhafarSuvi AlakalhunmaaKirsti ParikkaKirsi Mikkonen
Department of Food and Environmental SciencesFaculty of Agriculture and ForestryUniversity of Helsinki, FinlandNovember 4, 2015, Lund, Sweden
Outline
q Introduction to aerogels
q Aerogels from guar galactomannan
q Aerogels from spruce galactoglucomannan
q Conclusions
Figs: Kangas 2012, www.extremetech.com, stardust.jpl.nasa.gov
Aerogels – lightest materials
Aerogels are highly porous and lightweight materialsprepared by removing liquid from a gel.
q Different polysaccharides may show physicalq nanofibrillated celluloseq starchq β-glucanq chitosanq 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.
Polysaccharide hydrogels
5
Prepared from a hydrogel by replacing theliquid phase by air.
Aerogels
Gel formation
Drying
Aerogel
Illustrations: Jung et al. Sci Rep, 2012, DOI:10.1038/srep00849
o Supercritical CO2 dryingo Freeze-drying
Biodegradable
Polysaccharide aerogels
Up to 99% air
q From renewable materials.
q Biodegradable and non-toxic.
q High mechanical stiffness and large surface area ofthe aerogels can be utilized, e.g., in sorption of desiredcomponents on the aerogel surface.
q Possible applications are in thermal insulators, drugrelease, cell growth media, active packaging etc.
Mikkonen, K.S. et al. Trends FoodSci. Technol. 2013, 34, 124.
Polysaccharide aerogels
8
Galactoseoxidase
qAn extracellular copper-containing enzyme produced byFusarium sp. – belongs to CAZy AA5_2
qUses molecular oxygen as the electron acceptor andproduces hydrogen peroxide (two electron transfer).
qSubstrates are D-galactose as well as D-galactose-containing oligo- and polymers, terminal D-galactose.
qActs selectively on the primary C-6 hydroxyl resulting inaldehyde: D-galactose => D-galacto-hexodialdose.
qUsed in biosensors and in diagnostics.
Native GM (1%) Oxidized GMox (1%)
Vis
coel
astic
mod
uli(
Pa)
Vis
coel
astic
mod
uli(
Pa)
Ghafar et al. European Polym. J. 2015.
Oxidized guar galactomannan– hydrogel formation
Parikka et al., J. Agric. Food Chem.2010,58,262–271
11
Angular frequency (rad/s)
Parikka, K. et al. Food Hydrocolloids 2012.
After enzymatic oxidation
Oxidized guar galactomannan– hydrogel formation
MoldingFreeze-dryingAerogel
EnzymaticOxidation
Guar gum galactomannan1% solution
Preparation of aerogels from GMoxhydrogels
Mikkonen et al. RSC Advances 2014.
Aerogel DensityGM 0.016 ± 0.0002 g/cm3
Hydrogel
14
Morphology of GMox aerogels byFocused Ion Beam Scanning ElectronMicroscopy (FIB-SEM)
Conventional freezing Ice-crystal template = oriented
Unidirectional freezing =ice crystal templating
Ice crystals growing startingfrom the bottom of the sample.
CO2-ice & EtOH bath
Mikkonen et al. RSC Advances 2014.Ghafar et al. European Polym. J. 2015.
Water uptake of GMox aerogels
Mikkonen et al. RSC Advances 2014.
Time (h) Weight (g) Water uptake (g) Water uptake(× aerogel
weight)0 0.06 ± 0.006 0 01 2.5 ± 0.4 2.4 ± 0.4 402 2.7 ± 0.2 2.6 ± 0.2 44
24 2.6 ± 0.5 2.5 ± 0.5 42
GMox aerogels did not dissolve inwater during 24 hours.
Native GM (1%) Native GM (1%)with NFC (25%)
Ghafar et al. European Polym. J. 2015.
Guar galactomannan – NFC hydrogelV
isco
elas
ticm
odul
i(Pa
)
Vis
coel
astic
mod
uli(
Pa)
0 % NFC 5 % NFC
15 % NFC 25 % NFC
Enzymatically oxidized guargalactomannan – NFC hydrogel
Ghafar et al. European Polym. J. 2015.
Reinforcement of GMox hydro- and aerogelsby nanofibrillated cellulose (NFC)
Ghafar et al. European Polym. J. 2015.
Hydrogels Aerogels
conventionallyfrozed
Aerogels from spruce
galactoglucomannans
Mannose:Glucose:Galactose 4:1:0.5
Acetylated => water soluble
Molar mass 30-60 kDa => low viscose solutions
Spruce galactoglucomannans (GGM)
qSoftwoods contain 15-20% O-acetyl-galactoglucomannans (GGM)
qAbout 5-10% of GGM is dissolved inmechanical pulping of spruce wood
qThis corresponds to about 5000 tons/yearin an average mechanical pulp mill
qGGM can be recovered in good yield fromthermomechanical pulping process water(Willför et al. 2003)
CNF16–44%
AZC0–23%
Mechanicalproperties
Moisture-related
propertiesMorphology
GGM-based aerogels
Alakalhunmaa et al., submitted
GGM
5.11.201525 Maatalous-
Share ofCNF
Water uptake(g water/g aerogel)
16 29.8 ± 0.830 34.1 ± 1.844 37.3 ± 1.8
AZCcontent
(%)
Water uptake(g water/g aerogel)
0 Disintegration2 Disintegration
12.5 34.1 ± 1.823 33.1 ± 1.5
AZC content: 12.5%
CNF increased ability tohold water.
Share of CNF: 30%
AZC required to maintainthe structure.
Water uptake of GGM-based aerogels
Conclusions
q Enzymatic oxidation is a new non-toxic way to preparebio-based aerogels from galactose containing largepolysaccharides as guar GM.
q Enzymatic oxidation technology enables addition ofreinforcements (such as NFC) or active compounds toaerogels prior gel formation.
q Water insoluble and adsorbing mannan-based aerogelswere prepared.
q Spruce GGM reinforced with NFC and crosslinked withAZC resulted in relatively stiff aerogels with repeatablesponge capacity.
q These aerogels could be exploited in, e.g., food packagingapplications (active packaging, encapsulation, adsorbents).
28
Acknowledgements
n FundingnThe Academy of FinlandnMagnus Ehrnrooth Foundation (Abdul Ghafar)
n Galactose oxidase preparation: Dr. Sybe Hartmans
n GGM: Stefan Willför, Åbo Akademi
n NFC:nProf. Monika Österberg, Aalto University, FinlandnProf. Lars Berglund, Assoc. Prof. Qi Zhou, KTH, Stockholm, Sweden
n DMA-RH analysis: Dr Lennart Salmén, Innventia, Swedenn FIB-SEM images: Dr. Marko Vehkamäki, University of Helsinki