24 Jun Benefits of microfibrillated cellulose in Paperboard
Jonathan Phipps
Robyn Hill
PRESENTED BY:
Jonathan Phipps
Principal Scientist
FiberLean Technologies Ltd.
Benefits of microfibrillated cellulose in Paperboard
Introduction
- Microfibrillated cellulose (MFC) is well established as an additive in graphic papers
- Increased filler content
- Increased wet web, tensile and Z direction strength
- Reduced porosity
- Packaging grades present new challenges
- Complex, multi-layered structures
- Laboratory evaluation methods
- Delamination resistance
- Bending stiffness
Impact of MFC on Graphical paper physical properties

Lab study Mesmer recirculating hand sheets (12 sheets) 70% Eucalyptus, 30% NBSK, 550 CSF Intracarb 60 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
- Increasing fibre bonding and filler content decreases bulk
Overcoming bulk loss with filler increase
- Full scale trial, copy paper machine
- Microfibrillated cellulose has a positive effect on formation, retention, porosity and smoothness
- Calender loading can be reduced to restore bulk and stiffness
- Large filler increase still possible
Bending Stiffness and Elastic properties
- Bending a sheet of material stretches its outer surface and compresses its inner surface
- Resistance to bending is therefore directly related to the elastic modulus of the material
- Modulus (E) = Force / (x-section area x strain)
- For paper, x-section area depends on pressing and calendering, so instead we define tensile stiffness index (TSI): –
TSI = Force/ (width x gsm x strain)
![]() Stiffness calculated from tensile properties agrees well with experimental values |
![]() Calculated stiffness typically shows less variability than measured values, because grammage variations are eliminated |
For a single layer, Bending stiffness = (E x t3 ) /12 = (TSI x gsm x t2) /12
Stiffness is very sensitive to thickness
Corrugated grades – White Top Liner
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White-top liner board |
- White Top Liner is a 2-layer sheet
- Typically a filler-containing bleached short fibre pulp layer is laminated on top of an unbleached long fibre Kraft layer
- The white layer hides the brown layer and provides a surface for printing
- Minimum grammage is used to achieve optical coverage
- Maximum possible filler content for opacity
- Final corrugated stiffness is high from the I-beam effect of the fluting
- Liner bulk/bending stiffness are not required
- Liner needs high tensile stiffness index from white and brown layers, but it is often not a specification
- Main specifications are brightness, burst strength, Short-span compression strength, surface/Z-direction strength & delamination resistance
- Filler loading is limited by its effect on Z-direction and burst strength (wet web strength is not important)
- Specifications could be obtained with a range of grammages, but grades are still typically defined by basis weight
Use of microfibrillated cellulose for filler increase and top layer weight reduction
- Pilot papermachine trial, 100% Eucalyptus 500 CSF, GCC filler, 70gsm
- Brightness calculation based on 80% ISO target on 25% ISO base
- Replacing top layer weight with unbleached Kraft base maintains burst and reduces costs
White Top Liner full scale example
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Microfibrillated cellulose in Paperboard: Folding Boxboard (FBB)
- Folding boxboard is a multilayer product
- Typically FBB middle layers are made from bulky but weak TMP, outer layers from chemical pulp
- The outer layers hide the middle layers and also contribute strongly to bending stiffness
- Bulk of middle layer separates the outer layers to enhance the ‘I-beam’ effect
- Outer layers require high tensile stiffness to resist stretching and enhance overall stiffness
- Outer layers may contain filler but loading may be limited by effect on stiffness
- Z-direction strength and resistance to delamination are critical
- Stiffness of complex structures can in principle be calculated
- Elastic modulus and thickness of each layer required
- Contributions of each layer are calculated and added together: –
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Microfibrillated cellulose in Paperboard: Making 3-layer handsheets
- Top/bottom layer weight and thickness from trimmed excess
- Total weight and thickness from 3-ply sheet
- Middle weight and thickness from difference
Measured vs. calculated stiffness for 3-ply sheets
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Effects of mfc in Folding Boxboard outer layers
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Microfibrillated cellulose in Paperboard:
Adjusting the outer layer weights
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180 gsm total Brightness 70 ISO Stiffness 9.5mN m |
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180 gsm total Brightness 75 ISO Stiffness 9.5 mN m |
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180 gsm total Brightness 70 ISO Stiffness 12.0 mN m |
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180 gsm total Brightness 75 ISO Stiffness 12.0 mN m |
Folding boxboard full scale example
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Microfibrillated cellulose in Paperboard:
Conclusions
Single layer products
- MFC allows bulk and stiffness to be maintained with large increases in filler content
- Improved smoothness and formation
- Reduced calender load
White Top Liner
- MFC allows large filler increases in the white layer
- Increased delamination resistance
- Increased burst strength
- Reduced white layer / increased brown layer grammage
Folding Boxboard
- MFC in outer layers can enable improved stiffness and brightness specifications
- Increased delamination resistance and tensile stiffness
- Increased filler content
- Reduced outer-ply / increased mid-ply grammage