Novel polymer nanomaterials for food packaging based on modified cellulose nanofibres

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International CST Workshop, Espoo, Finland, September 15-16, 2011 Novel polymer nanomaterials for food packaging based on modified cellulose nanofibres Per Stenstad a, Kristin Syverud

1 International CST Workshop, Espoo, Finland, September 15-16, 2011 Novel polymer nanomaterials for food packaging based on modified cellulose nanofibres Per Stenstad a, Kristin Syverud b, Martin Andresen c & Ruth Schmid a a SINTEF, Trondheim, Norway b PFI, Trondheim, Norway c current address: Borregaard, Sarpsborg, Norway Corresponding author: per.m.stenstad@sintef.no

production Chemical modifications of MFC MFC films and

2 utline of the presentation Introduction Nanocomposites as food packaging materials Microfibrillated cellulose (MFC) production Chemical modifications of MFC MFC films and surface layers Antimicrobial MFC materials Summary Nano fibrillar cellulose

SINTEF is the largest independent research

the natural science and technology, environment,

countries Annual sales of 350 mill euro customers

3 SINTEF is the largest independent research organisation in Scandinavia Leading expertise in the natural science and technology, environment, health and social science 2,100 employees from 67 countries Annual sales of 350 mill euro customers in 60 countries A non-commercial research foundation with subsidiaries

4 Paper and Fibre Institute - PFI

5 Close collaboration is the basis for innovation and high scientific quality Industrial relevance Industrial involvement Scientific methods

Nanocomposites as food packaging materials Nanosized additives in polymers or coatings New properties Improved performance Active and intelligent packaging solutions Changed properties: Mechanical

6 Nanocomposites as food packaging materials Nanosized additives in polymers or coatings New properties Improved performance Active and intelligent packaging solutions Changed properties: Mechanical properties, e.g. strength ptical properties Transparency UV-barrier Barrier properties Antimicrobial properties Types of additives: Nano clay Carbon nanotubes Nano calcium carbonate Titanium dioxide Nano fibrillar cellulose Composite film (epoxy polymer) with amine derivatised MFC 10 nm..... HR-TEM of MFC in composite film

7 Examples of polymer nano composites on the market Product Polymer Nano additive Function Imperm (ColorMatrix Corp.) Durethan KU LanXess GmbH) Aegis X (Honeywell) Nylon 6 Nylon 6 Nylon 6 Nano clay (Nanocor) Nano clay (Nanocor) Nano clay (Nanocor) Gas barrier ( 2 og C 2 ) in multilayer soda bottles Film and paper coatings for medium barrier applications Combined nano composite barrier and 2 scavenger in one system for beer bottles

Motivation: Nano fibrillar cellulose Produced in nature Renewable Environmentally friendly and biodegradable Applications Reinforcement in nano composites Coatings

8 Motivation: Nano fibrillar cellulose Produced in nature Renewable Environmentally friendly and biodegradable Applications Reinforcement in nano composites Coatings Improved strength Innovative and sustainable barrier concepts Stabilizer for emulsions Carriers of specific components (e.g. antimicrobial properties) Filters, membranes

9 From wood to sugar monomers Cellulose micro fibrils (MFC) A. Wood structure B. Macro fibrils C. Bundle of micro fibrils D. Nano-sized micro fibril cellulose chains 1-50 nm thick Length of several µm E. Bundle of cellulose molecules (thread like aggregates) F. Cellulose molecule G. β-d-anhydroglucopyranose units bound together by β-(1 4)- glycosidic linkages

10 Production of micro fibrillated cellulose To main strategies: Hydrolysis with strong acid and high shear mechanical treatment Manufacturing by homogenization Sheet-dried fully bleached spruce sulphite cellulose (Borregaard VHV-S) The α-cellulose content was 93.5% To avoid plugging during homogenizing, the fibres were cut to reduce the fibre length (average fibre length of approximately 1 mm) For final disintegration to MFC the fibres were diluted to 2% consistency and subjected to ten passes through a Gaulin M12 homogenizer, with a pressure drop of 600 bar at each pass. AFM phase contrast image of MFC prepared by homogenization

11 TEM images of isolated micro fibrils prepared by homogenization 25 nm 25 nm 12,5 nm

12 Chemical modifications of MFC MFC is suitable for chemical modifications: Large surface area Large number of hydroxyl groups available for functionalization Why modify MFC? New composite materials Environmentally friendly and biodegradable Increased strength Increased barrier properties Introduction of reactive hydroxyl groups Compatibility with matrix or film material Introduction of hydrophobic groups Varied degree of substitution Varied chain length Use of MFC as cross-linker Introduction of vinyl groups Introduction of reactive groups like amine, anhydride, epoxy, etc.

13 Chemical modifications of MFC (2) Introduction of new functionality Antimicrobial activity xygen scavengers Antioxidants Sorption agents Specific binding proteins Drug delivery Emulsion stabilization

14 Hydrophobic MFC by silylation Introduction of isopropyl dimethylchlorosilane Study of the degree of substitution CH 3 CH 3 Cell H + Cl Si i-c 3 H 7 Cell Si i-c 3 H 7 + HCl CH 3 CH 3 The oxygen peak decreases with increased substitution The silicon peak increases with increased substitution XPS spectra of silylated MFC

15 TEM images of silylated MFC Silylated MFC 4 equivalents silane per glucose unit Silylated MFC 6 equivalents silane per glucose unit At high concentration of isopropyl dimethylchlorosilane, the microfibrils seem to disintegrate

Contact angle measurements on silylated MFC surfaces 160 140 Water Contact Angle ( º ) 120 100 80 60 40 20 Water droplet on hydrophobized MFC surface (DSS 0.

16 Contact angle measurements on silylated MFC surfaces Water Contact Angle ( º ) Water droplet on hydrophobized MFC surface (DSS 0.9; contact angle 145º) 0 0 0,2 0,4 0,6 0,8 1 1,2 1,4 DSS DSS = degree of surface substitution (number of silyl groups per glucose unit), calculated from the surface Si mass concentration derived from the areas of the Si 2p peaks in the XPS spectra

17 Reactive MFC for further functionalization or cross-linking Introduction of glycidyl methacrylate by cerium grafting CH 2 H H H + Ce 4+ CH 2 H H H Ce 4+ CH 2 H. H CH2H. H + CH 3 CH 2 C C CH 2 CH CH 2 CH 2H H CH 3 [ CH 2 C ] n C CH 2 CH CH 2 %T FTIR spectrum Ref MFC MFC + PGMA 4000, ,0 cm-1 Peak at 1722: C=: Shows that poly-gma is introduced

18 GMA grafting: Regulation of chain length Hi Res C 1s components from XPS analysis GMA added C1 C2 C3 C4 [µmol/mg] C-C C- C= -C= 1,9 2,7 75,9 19,7 1,7 7,6 5,2 74,4 18,3 2, ,5 66,0 14,3 5, ,2 40,2 5,6 9, CH2H H Atomic concentration GMA added [µmole/mg MFC] C1 C2 C3 C4 CH 3 [ CH 2 C ] n C CH 2 CH CH 2

19 Reactive MFC for further functionalization or cross-linking Diisocyanate functionalization with Hexamethylene-diisocyanate H H + CN NC C N NC NC H C N NC + C N NC C CN N H %T FTIR spectrum Ref MFC diisocyanate CN 4000, ,0 cm-1 Peak at 2265: Free isocyanate groups (N=C=) at the surface

20 Reactive MFC for further functionalization or cross-linking Maleic anhydride on MFC H + C CH CH C - %T FTIR spectrum Ref MFC Maleic anhydrid 4000, ,0 cm-1 Peak at 1722 (C= groups) demonstrates that maleic groups are introduced Peak at 1636 shows that the sample contains vinyl groups The vinyl groups may be a starting point for polymerization reactions e.g. introduction of poly(styrene-co-maleic anhydride)

21 MFC films and surface layers on base paper 3 types of MFC films were prepared: Films of MFC without orientation Films of oriented MFC Layers of MFC on substrate base paper MFC films with high strength properties (tensile index Nm/g) much higher than of paper ( Nm/g) Improved strength properties of paper by application of thin layers of MFC MFC films with thicknesses of µm fulfil the requirements for oxygen transmission rate in modified atmosphere packaging and are comparable to the best synthetic polymers Syverud, K. &Stenius, P., Cellulose (2009) 16:75-85: : Strength and barrier properties of MFC films

MFC films barrier properties 100000 10000 Air perm.

22 MFC films barrier properties Air perm. (nm/pa s) MFC basis w eight (g/m 2 ) Air permeability as a function of film thickness Syverud, K. &Stenius, P., Cellulose (2009) 16:75-85: : Strength and barrier properties of MFC films

23 MFC films barrier properties *Litteratur values Very good barrier properties were obtained. Recommended oxygen permeability for modified atmosphere packaging is below ml/m² day Syverud, K. &Stenius, P., Cellulose (2009) 16:75-85: : Strength and barrier properties of MFC films

24 Antimicrobial surfaces Traditionally, antimicrobial materials are prepared by incorporating a leachable antimicrobial into a polymer matrix The antimicrobial is gradually released and kills the microorganism by diffusing into the cell Several disadvantages with this approach: toxic substance is released into the environment antimicrobial activity of the material only temporary decreasing level of the released compound provides perfect conditions for development of bacteria resistance. Ideal strategy would be to covalently immobilize the antimicrobial compound onto the material surface

25 ctadecyldimethyl-(3-trimethoxysilyl-propyl)-ammonium chloride (DDMAC) and its antimicrobial activity Me Si Cl - + Me Me DDMAC C 18 H 37 N Quaternary ammonium compound with alkoxy silane anchor Used as antimicrobial coating in the textile industry Can be covalently linked to the MFC surface

26 Antimicrobial MFC materials by covalent attachment of DDMAC Me C 18 H 37 + N Si Me Me H 2 H Si H H C 18 H 37 + N + H H C 18 H 37 + N Si Si H H C 18 H 37 + N Monomer Dimer C 18 H 37 MFC C 18 H 37 N H Si H H H + N H Si Si H H H H C 18 H 37 + N H Heat - 3H 2 C 18 H 37 + N H Si H C 18 H 37 + N H Si Si H C 18 H 37 + N MFC surface

Antimicrobial activity of films of DDMAC-modified MFC The antibacterial activity of films prepared from DDMAC modified MFC was tested

bacteria deposited on the modified film surface were killed When performing an agar diffusion test, no inhibition zone was observed

The films kill only on contact Unmodified MFC MFC soaked in DDMAC DDMAC immobilized on MFC M. Andresen, P. Stenstad, T. Møretrø, S.

27 Antimicrobial activity of films of DDMAC-modified MFC The antibacterial activity of films prepared from DDMAC modified MFC was tested against Staphylococcus aureus (Gram (+) bacteria) and Escherichia coli (Gram (-) bacteria) After 24 h essentially 100% of the bacteria deposited on the modified film surface were killed When performing an agar diffusion test, no inhibition zone was observed around the film, confirming that there is no diffusion of the antimicrobial into the surroundings. The films kill only on contact Unmodified MFC MFC soaked in DDMAC DDMAC immobilized on MFC M. Andresen, P. Stenstad, T. Møretrø, S. Langsrud, K. Syverud, L-S. Johansson & P. Stenius, Biomacromolecules 8, (2007), Nonleaching Antimicrobial Films Prepared from Surface- Modified Microfibrillated Cellulose.

28 Summary MFC films and coatings have high tensile strength and air barrier properties Many different chemical surface modifications could be demonstrated: Hydrophobic MFC by silanisation Functional MFC for cross-linking, introduction of functional groups, compatibility with matrix materials Antimicrobial properties Antimicrobial films from DDMAC-modified MFC could be prepared: Permanent antibacterial effect No surviving bacteria after 24 h Non-leaching Possible applications: films or composite additive in packaging, biomedical coatings (e.g. wound healing), antibacterial separation filters, etc. Microfibrillated cellulose has a high potential as nanocomposite additive in food packaging, introducing totally new material properties, e.g. a combination of high strength, low air barrier and antimicrobial activity

29 Acknowledgement Per Stenstad, Kristin Syverud, PFI Martin Andresen, currently Borregaard, former PhD student at NTNU Financial support from The NANMAT research program of the Norwegian Research Council Södra Cell, Borregaard, Akzo Nobel and Domsjö Fabriker

Surface modification of Microfibrillated Cellulose films by Gas-Phase Esterification: Improvement of Barrier Properties.

Surface modification of Microfibrillated Cellulose films by Gas-Phase Esterification: Improvement of Barrier Properties. G. Rodionova*, M. Lenes**, Ø. Eriksen**, B. H. Hoff*, Ø. W. Gregersen* * Norwegian