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

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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

Aerogels from guar galactomannan

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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.

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Oxidative and reductive half-reactions of galactose oxidase

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

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Angular frequency (rad/s)

Parikka, K. et al. Food Hydrocolloids 2012.

After enzymatic oxidation

Oxidized guar galactomannan– hydrogel formation

Formation of hemiacetal crosslinksbetween polymers after oxidation

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

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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.

Nanofibrillated cellulose in aerogels

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

Share of CNF: 30%

Effect of crosslinkingwith AZC

Alakalhunmaa et al., submitted

AZC content 12.5%

Effect of CNFreinforcement

Alakalhunmaa et al., submitted

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

Sponge capacity

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).

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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