01 Oct Microfibrillated Cellulose in Barrier Coating Applications
The Use of Microfibrillated Cellulose in Barrier Coating Applications
Jonathan Phipps
Principal Scientist
FiberLean Technologies Ltd.
Introduction
- Microfibrillated cellulose (MFC) is well established as an additive in graphic papers
- Increased wet web, tensile and Z direction strength
- Increased filler content
- Improved smoothness, formation and filler retention
- Reduced porosity
- Packaging grades present new challenges
- Bending stiffness and delamination resistance
- Water-intensive printing methods (flexography and ink-jet)
- Replacement of plastics / laminates
- Waterbased barrier coatings
FiberLean process for Microfibrillated Cellulose manufacture
Impact of Microfibrillated Cellulose on Graphical paper physical properties
 Tensile |
 Burst |
 Roughness |
 Permeability |
| Lab study : Messmer recirculating hand sheets (12 sheets) 70% Eucalyptus, 30% NBSK, 550 CSF, Intracarb 60 filler | |
- In current applications, microfibrillated cellulose (MFC) is added as a filler.
- It is possible to increase filler content by 10% or more and suffer no strength loss.
- Wet web strength is also increased – typically by more than dry strength.
- MFC increases fibre bonding and fills voids in sheet – rapid decrease in permeability.
Impact of Microfibrillated Cellulose on coating holdout
- Reduction in permeability and pore size improves holdout of coating components on surface
- Benefits in graphical papers
- Reduced Coatweight
- Improved Gloss
- Improved printing properties
- Benefits for barrier coatings
- Reduced Coatweight
- Reduced permeability (improved barrier)
- Elimination of precoat
 No MFC |
 2% MFC |
 No MFC |
 2% MFC |
| Pilotmachine basepaper, Helicoater (short dwell) 500 m min-1: 80 gsm base 70% Eucalyptus, 30% NBSK, 450 CSF, 20% GCC filler. 10gsm coating of Kaolin/GCC 10pph latex | |
Coating MFC at the wet end
- Microfibrillated cellulose holds too much water for conventional coating…
- …but it can be applied at the wet end near the wet line
- Dewatering is achievable with existing elements – vacuum boxes, presses and dryers
- MFC immobilises rapidly and keeps coating on surface
Properties of wet-end coated sheets
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| Porosity and smoothness – 50% MFC/50% GCC* coatings | Brightness – all coatings |
Pilot coated papers: 100 gsm base (100% Unbleached long fibre Kraft) . Coatings of 50/50 MFC/GCC and 20/80 MFC/GCC Speed ~25 m min-1
Microfibrillated Cellulose as a precoat for barrier applications – lab studies
Microfibrillated Cellulose coatings as barrier substrates
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Surfaces of lab coated papers
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Barrier properties of lab coated papers
Pilot 50:50 Microfibrillated Cellulose-mineral coated papers
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Pilot coated papers: 72 gsm base (Bleached Kraft 80/20 hardwood/softwood) . Coating of 50% MFC/50% CaCO3 Speed ~25 m min-1
Pilot coated papers – calculated barrier coating permeability vs. MFC layer Coat Weight
Coating Microfibrillated Cellulose at high speed
Many Challenges!
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8.5% solids, 20% MFC/80% GCC coating – 500 m/min
Viscosity vs. Shear Rate
- Permeability & Drainage
- Coating strength vs. solids
- Coating Elongation
Rheology of Microfibrillated Cellulose suspensions
Viscosity and consolidation
20% MFC/80% GCC suspensions – viscosity vs. shear rate |
Typical Elastic modulus vs. strain – oscillation 1Hz
Elastic modulus (LVE region) vs. solids content |
Permeability and drainage of Microfibrillated Cellulose suspensions
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Permeability of 20% MFC/80% GCC filtercake as function of initial solids
Calculated time to drain 30gsm of 20% MFC/80% GCC coating as a function of initial solids
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Visualisation of high speed coating
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Conclusions
- Microfribrillated Cellulose (MFC) is well established as a wet end additive
- Increased strength and/or filler content
- Reduced porosity
- Improved coating holdout
- Wet end coating of MFC for barrier applications is very promising
- Smooth, non-porous surface for further coating
- Excellent oil and grease resistance
- High speed applications are developing quickly