LOW PRESSURE PLASMA COATINGS FOR FOOD PACKAGING O. Kylian, J.Hanuš, O.Polonskyi, A. Choukourov, A. Shelemin, A. Kuzminova, D. Slavínká, L. Hanyková, H. Biederman Charles University in Prague Faculty of Mathematics and Physics
Motivation Deposition of a-c:h and SiOx thin barrier films Deposition of nanocomposites Conclusions
Materials traditionally used for food packaging Glass Paper Metal Polymers Cheap, transparent but heavy and brittle Light weight, recyclable, but always coated, laminated with other materials Higher cost, opaque but impossibility to use in microwave ovens Low cost, light weight, transparent but worse barrier properties Purpose! Improve and enhance properties of polymers for food packaging
Polymers Low cost, light weight, transparent but worse barrier properties Purpose! Improve and enhance properties of polymers for food packaging Plasma treatment surface activation improved printability enhanced sealability etc. Deposition of thin films metals metal oxides plasma polymers nanocomposites Example on Poster of A. Choukourov et al.
1. Deposition of SiOxCyHz coatings 2. Deposition of a-c:h coatings Gas mixture: HMDSO/O 2 (1:0-1:60) Pressure: 4 Pa Power: 40 W Gas mixture: Ar/hexan (9:1) Working pressure: 2 Pa RF power: to 90 W DC negative self-bias: to -500V
P [Torr] Summary of results presented at COST meeting in Prague 2013 1,0x10-3 8,0x10-4 6,0x10-4 4,0x10-4 2,0x10-4 a-c:h(12nm, -400V) a-c:h(30nm, -400V) a-c:h(60nm, -400V) a-c:h(120nm, -400V) a-c:h(6nm, -400V) PET 0,0 0 500 1000 1500 2000 2500 3000 3500 Time (sec) Water vapor permeability of PET foil coated by a-c:h films High barrier properties were observed for a-c:h films. Barrier properties strongly depend on the thickness of the coatings. There exists an optimal thickness around 10-20 nm. Decrease of barrier properties for thicker coatings is most likely due to formation cracks due to different mechanical properties of polymeric foils and a-c:h film. Disadvantage: low surface energy = low wettability of a-c:h
HMDSO Deposition rate 35 nm/min HMDSO/O 2 1:60 Deposition rate7 nm/min 110 o 11 o Roughness of thin films was in all cases below 1 nm
Pressure [Torr] Changes in chemical composition lead to different barrier properties of deposited films 1.4x10-3 1.2x10-3 phmdso 50 nm Higher barrier properties were observed for SiO2-like than for SiOxCyHz films. 1.0x10-3 8.0x10-4 6.0x10-4 4.0x10-4 9nm PET 19nm 90 nm 33 nm Barrier properties strongly depend on the thickness of the coatings. There exists an optimal thickness around 30 nm. 2.0x10-4 0.0 0 200 400 600 800 1000 1200 1400 Time [s] Water vapor permeability of PET foil coated by SiO2-like and SiOxCyHz films Decrease of barrier properties for thicker coatings is most likely due to formation cracks due to different mechanical properties of PET and SiOx film.
Permeability coefficient 10-13 *cm 3 *cm*cm -2 *sec -1 *Pa -1 Mismatch of mechanical properties may be overcome by deposition of layered structures combining soft plasma polymer and SiO x layers. This was experimentally confirmed. 14 12 13,3 PET 10 8 phmdso 7,1 6 4 2 0 SiOx 0,8 phmdso SiOx phmdso 0,45 phmdso SiO x phmdso Substrate Permeability coefficients of PET foil coated by SiO 2 -like, SiOxCyHz and multilayered thin films
Both a-c:h and SiOx thin films deposited on polymeric foils may significantly decrease permeability of gases through coated foils. Barrier properties of SiOx films may be improved when combined with soft plasma polymers in multilayer structures. In order to add some functionality, these multilayer structures may be combined with metallic nanoclusters. Three different methods were tested.
Deposition of sandwich structure Sequential deposition of plasma polymer and metallic nanoparticles DC Step A Step B DC DC Deposition of polymer or SiOx Deposition of metal
At certain deposition conditions metal nanoclusters may be formed on a surface. This may be used for the deposition of SiO x /metal nanocomposites. Ag nanoclusters on SiO x. Deposition time of Ag 15s, magnetron current 40 ma and pressure 3 Pa Increasing amount of silver
Permeability coefficient 10-13 *cm 3 *cm*cm -2 *sec -1 *Pa -1 Permeability coefficient 10-13 cm 3 *cm*cm -2 s -1 *Pa -1 14 13,3 14 12 10 8 6 4 2 0 PET phmdso 7,1 SiOx 0,8 phmdso SiOx phmdso 0,45 phmdso SiO x phmdso Substrate 12 10 8 6 4 2 0 HMDSO or SiOx Ag SiOx HMDSO Substrate Top layer SiO x Top layer phmdso 5" Ag 10" Ag 5" Ag 10" Ag Presence of Ag nanoclusters has no significant effect on permeability of coatings and they remain comparable to the coatings without Ag nanoclusters. We can adjust independently barrier properties and properties of functional layer.
Absorbance Absorbance 1.0 0.8 0.6 0.4 0.2 As deposited Autoclave UV sterilization Deposited coatings may be sterilized by UV radiation. Autoclaving (but also high temperatures) lead to alterations of properties of prepared coatings 0.0 300 400 500 600 700 800 900 Wavelenght [nm UV/Vis spectra of films before and after sterilization. 1.0 0.8 As deposited 1 day in H 2 O Slight changes were observed after immersion of samples to water. These changes indicate release of silver from the coatings. 0.6 0.4 0.2 0.0 300 400 500 600 700 800 900 Wavelenght [nm] UV/Vis spectra of films before and after immersion to water for 1 day..
Inhibition zone For nanocomposites SiOx/Ag/SiOx was observed mild antibacterial effect. Sample In other words it is possible to produce barrier coatings with antibacterial character. 0.6-0.8 mm 5 mm Tested bacteria: E.Colli
Deposition of sandwich structure using gas aggregation sources Sequential deposition of plasma polymer and metallic nanoparticles Step A Step B DC DC Gas inlet Gas inlet
Transmittance Transmittance Transmittance 0,6 0,4 0,2 Ag nanoparticles in C:H matrix 300 400 500 600 700 800 Ag Ag 0,6 0,4 0,2 Cu nanoparticles in C:H matrix 300 400 500 600 700 800 Cu Cu 0,6 0,4 0,2 Ag and Cu nanoparticles in C:H matrix 300 400 500 600 700 800 Wavelength [nm] It is possible to combine more kinds of nanoclusters. Cu Ag
Simultaneous deposition Substrate DC Gas inlet Plasma Cu nanocluster source RF electrode This method allows production of a-c:h/cu nanocomposites. More details at poster J.Hanus etal.
Plasma based methods are highly suitable for deposition of passive barrier thin films on polymers. Plasma based methods enable fabrication of nanocomposite materials. Multilayered coatings provide good barrier properties and additional functionality (e.g. antibacterial character of the coatings) In addition: Plasma based modification of polymers is fully vacuum-based processe It is easily scalable It allows in-line deposition There is limited use of toxic substances environmentally friendly Processes are relatively fast and cheap
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