Starch for surface sizing
Topics
Enzyme conversion for surface sizing application
Batch process
Continuous process
Critical control points
Important starch parameters
Stability in storage
Troubleshooting
Paper properties
Starch in Papermaking
Cellulose
Fillers
Starch
Additives Coating
Wet End Spray Surface
Starch Starch
Improve Surface
Improve Printing Improve Optical,
Paper Formation Strength
Improve Surface Printing and
Retention Improve Ply Bond
Process Strength Functional
Dry Strength Improve Internal
Fill voids Properties
Bond
Oxidized
Starch and Latex
Cationic Unmodified Starch Enzyme Converted
Starch Mixtures with
Amphoteric Polymers Other Modified
Fillers
Specialty
Typical Uptake 0.3 2% 1-4% 2-6% 0.5 2.0%
Surface sizing starch
Paper makers use native starch which is converted in-situ for the surface sizing
application using alpha amylase enzymes
The viscosity develops during the cooking and the enzymes assist in reducing the final
cooked starch viscosity
Batch Enzyme Conversion
Agitator Fill Reactor with 1st Water
Starch
Water
Add 0.05% Calcium Carbonate on Starch
CaCO3 Enzyme
Add Starch
Add 2nd Water to Wash Dome and sides
Reactor Heat to 55C
Add Enzyme
Steam
Heat to 80C and hold for 15 minutes
Heat to 110C and hold 10 minutes
Continuous Enzyme Conversion
1ST Jet Cooker
3 Minutes
80-82C Retention
Starch Silo Steam
MASS
FLOW
METER
Enzyme
Reactor
~20 Minutes 80C
Water
Retention
Slurry To Storage
Make-up 130-135C Tank
2ND
JET
Enzyme
Critical Control points
Make up: affects starch solids
Enzyme dosage: affects the final viscosity
Mass flow meters: Controls retention time in the convertor
Jet 1 temperature: affects the enzyme activity starch gelling
Jet 2 temperature: denatures the enzymes stop breakdown of viscosity in
the storage tank
Variables are interdependent to produce quality starch
Starch important parameters
Viscosity
Starch solids (make down and dilution)
Enzyme dosage
Cooking (temperatures)
Temperature (storage and measurement)
Shear rate pump speeds and mixing
Setback
Factors Affecting Storage Stability
pH 7 7.5 to prevent RAPS
Temperature (avoid 65C to 90C for long time)
Gentle agitation required
Cleanliness of storage tank any existing crystals will grow
bigger and contaminate new starch
Factors Affecting Day Tank Viscosity
Temperature
Solids content
Fibre return from paper
Sludge formation
Setback
Troubleshooting the size press
Variable hold out High hold out
Wet-end sizing efficiency* Low cobb
Retention of size on the Low sheet density
paper Low starch solids
Variation in filler and fines Low starch viscosity
surface area High paper moisture into
Surfactants size press
*Tests for sizing efficiency and fines and filler content:
Percent active sizing agent
Test pre-size press cobb
White water consistency
Headbox or machine chest furnish ash
Headbox or machine chest furnish fines
Starch Solids/Viscosity
Paper Property Relationship
Property Low Viscosity High Viscosity
High Solids Low Solids
(more penetration) (stays on surface)
Surface Strength Good Better
Internal Strength Better Good
Porosity Decrease Decrease
Ink Hold Out Good Better
Opacity Slight loss Least Loss
Stiffness Increase Most Increase
CONTACT DETAILS
FOR MORE INFORMATION PLEASE CONTACT
NKULI KHANYEZA
TECHNICAL SERVICES MANAGER
011 458 5000
nkuli.khanyeza@tongaat .com
