Dr. Michael Y. Sun
濕端化學 Wet End Chemistry -1
2014/5/20
WL
Objectives w
To understand and review functions of wet-end chemical additives that affect machine runnability, productivity, and paper properties. 總觀濕端化學的藥品添加如何影響造紙機的運轉性、產量、和其他的紙張性質。
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To apply wet-end chemistry knowledge gained from this course on papermaking processes for productivity improvement and/or cost reduction. 應用濕端化學的知識來增加生產力和價格競爭
講座主題 :
Scope of the Course
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有什麼?
Lecture
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加什麼?
Q&A Case Stadies
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What's in the Wet-end?
什麼是濕端 ?
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為什麼?
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What's added to the Wet-end?
濕端添加了什麼?
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幹什麼?
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How do the chemical work?
化學藥品如何工作?
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What can you do to improve your Wet-end?
可以做什麼來改善濕端?
Water - H2O
Water - H2O
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Material in HeadBox : Water + Fiber
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Hardness
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Suspension Medium for stock and additives
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Acidity / Alkalinity
(AKD - Alkalinity)
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Liquid for Fiber Swelling and Interfiber Bonding
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Conductivity
mS/cm
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Solvent for Wet-end Polymers
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Higher temperature / Lower Viscosity / Better Table Drainage
lower the better !
> The amount of total dissolved ions in an aqueous sample
濕端化學 Wet End Chemistry -2
Dr. Michael Y. Sun
2014/5/20
WL
Wood Ingredient w
Lignin
30%
Ligin
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Extractives
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Phenolic groups of lignin byproducts can cause the wet-end system to be very anionic
3%
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Lower Retention
Cellulose
42%
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Lower sheet strength
Hemicellulose
25%
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Increased wet-end chemical consumption
Cellulose
Softwood vs Hardwood
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Major fiber Cell Wall stractural Material
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Long Linear Molecular Chain n > 10,000
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Tensile
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Smoothness
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Structure Unit : C6H12O6 smilar to starch
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Tear
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Formation
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Linkage Between Structure Units : b-o-4
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Web Strength
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Bulk
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A Mixture of Crystaline and Amorphous Regions
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Speed
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Cost
Hemicellulose
Softwood
Extractives
Hardwood
effect on wet-end chemistry
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Minor Componet of Fiber
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Trigycerides
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About 1-4% dry mass of wood
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Branched Chains ( n < 400 sugar units )
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Fatty Acid
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Mostly removed by chemical pulping process
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Various Structure Units in Wood Types
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Resin Acid
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Some are harmlessly in the wet-end
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Anionic Source ( Surface Charge )
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Othrs
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Major source of pitch/foam problems
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Amorphous ( non-crystalline )
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Self-sizing (in mechanical pulp)
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Contributes to Fiber Sweling in Water
濕端化學 Wet End Chemistry -3
Dr. Michael Y. Sun Wet-end additives
Alum : Chemistry & Application
PAC Poly-Aluminum Chloride
2014/5/20
WL
Aln(OH)mCl(3n-m)
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Alum / PAC
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Improve retention and drainage
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Starch
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Neutralize anionic trash
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PAC is more expensive than alum ( aluminum sulfate)
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Defoamer
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Assist rosin sizing
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PAC solutions are not as acidic as alum
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Wet/Dry Strength Additives
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PAC does not decrease pH of the furnish as much as
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Dye
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Fillers
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Size Agents
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Coagulant
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Retention Aid
an equivalent amount of alum w
PAC is more cationic than alum, and is more effective for changing charges in papermaking furnish
Function of Wet-end Starch w
PAC Benefits
Increase fiber contact areas over which adjacent fibers form hydrogen bonds (dry strength)
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Increase drainage rates especially in neutral papermaking
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Hold fillers tightly in the sheet (retention)
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Reduced barium sulfate scale problems (unbleached kraft mills)
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Help internal sheet sizing
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Improved efficiency of rosin sizing and charge changes Use starch with Caution
Cautions of using PAC
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Cationic starch does not function well if the wet-end system is very cationic or anionic
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May accelerate corrosion of standless steel (Chloride ions)
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May overcharge the wet-end system (over-cationization)
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Degradation will occur over storage time
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May not be cost-effective to improve drainage (white paper machiens)
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Bugs love starch! Monitoring pH of starch slurry is critical
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Cost more than alum
Dr. Michael Y. Sun
濕端化學 Wet End Chemistry -4
Wet Strength Additives - Applications
Wet Strength Additve Mechanism 1. Protection
2014/5/20
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Hydrogen bond vs Covalant Bond
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Carton and Corrugating Paper
- Bond Preservation
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Filter Paper
Resin "spot welds" fiber cross over points preventing fibers from disengaging
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Liquid Packaging Board
when the sheet is saturated with water
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Paper Bags
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Specialty Paper
Resin forms new bonds with cellulose fibers over and above the bonding
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Tissue Paper
developed by the "spod welds"
2. Reinforcement
Wet Strength Additives : Characteristics
- Bond Formation
Benefits of Dry Strength Additives
a)
Water solubility - water dispersable polyamide
1)
Increase tensile / bond / tear strength of paper
b)
Cationicity - azetidium groups
2)
Increase the degree of paper stiffness
c)
Polymeric - partially cross-linked polyamide
3)
Increase bulk ( through reduced stock refining ) and dimensional stability
d)
Reactive - azetidinium groups react with residual
4)
Allow use of weaker / recycled fibers
5)
Reduce alum requirments
6)
Serve as retention aid forrosin size and other fillers
7)
Assist in drainage efficiency and increase machine speed
8)
Save energy
amine and carboxyl groups.
Dry Strength Additives Polymers with MW of 100-500K/mole and charge density of 5-10%
Applications
1)
Cationic ( Polyacrylamide or C-PAM )
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Tissue / Towels grades
2)
Anionic ( Polyacrylamide or A-PAM, CMC )
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Printing and writing grades with weak / recycled fibers
3)
Amphoteric ( AM-PAM )
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Packaging and board grades
Dr. Michael Y. Sun
濕端化學 Wet End Chemistry -5
Sizig : Resistance to penetration of water / liquid
Dispersed Rosin size
Internal Treatment
2014/5/20
WL
Dispersed Rosin size Procedure
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Higher size efficiency
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Added to thick stock after alum
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Reduce Fiber wetability
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Lower alum requirement
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Headbox pH : 4.6-5.5
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Rosin size : Rosin soap / Dispersed Rosin
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Extended pH range (5-7)
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Alum to Size ration 1-2 : 1
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AKD / ASA size
>
More expensize (relatively)
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Total alum 10-15 #/MT
Surface Specialty TreatmentPaper w
Reduce Fiber wetability : Reactive Size
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Reduce Pore Radius :
Cellulose-Reactive Size ( Alkaline Size ) w
CMC / Starches / Copolymers
A cellulose- reactive size is a hydrophobic material that can achieve sizing by direct reaction with the cellulose without the use of alum.
Advantage of Alkaline Sizing over Rosin Sizing Rosin-Based Size Rosin Soap Sizes ( Salt of Free Aid ) Forms : Dry, Paste, Fluid Dispersed Rosin Size ( Free Acid )
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Lower production cost - substitute filer for fiber or TiO2
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Ability to size Calcium Carbonate-filled sheets
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Reduced alum-related deposits
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Reduced corrosion
Forms : Emulsion
AKD
Rosin Soap Size Procedure
vs
ASA
Easy to handle
Fast Reaction
Few Deposit problems
No Slippery problems
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Add to thick stock ( Blend Chest, Machine Chest, MC Pump )
Can size at higher filler levels
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Add after alum ( reverse sizing )
Slippery problems
Hydrolyzate deposits
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Headbox pH : 4.5 - 5.0
Only moderate
Complex in-mill emulsifications
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Alum to size ratio : 2-2.5 : 1
Reaction rate with cellulose
Total Alum : 15-20 #/MT
Dr. Michael Y. Sun
濕端化學 - 7 Good Habits -1
2014/5/20
WL
Variables Contributing to Machine Runnability
Broke Usage and Quality
Pulp Quality and Carryover
Deposits
Slime
Wet-end additives
Filler Usage and Types
Holes
Others
Good Habit #1 Control Headbox pH DO's :
Good Habit #2 Minimize Alum Usage DO's :
Use Acid or Caustic to control the pH
Watch Alum o Rosin Ration ( ~2 : 1 )
Always try to use closed-loop control system
Dilute Alum before Addition
Check and Change pH Probes Frequently
Add 3-7 #/MT trim Alum to help Drainage / Retention
Verify pH Data in the Lab Daily
Check Alum Pump Frequently
DONT's :
DONT's :
Use Alum to cntrol pH
Use Alum to Control pH
Use strong Acid or Caustic to control pH
No Control of Alum Usage
Use Carbonate (PGCGCC) containing Broke without Acidification
Use Alum to Control Charge
Benefits of Control Headbox pH
Benefits of Minimizing Alum Usage
Improved Sizing Efficiency
Less Alum-related Deposits
Less wet-end Deposits / Foaming Problems
Fewer Wet-end Chemistry Upsets
More Stable First Pass Retention
Better Drainage / Retention
Fewer Wet-end Breaks
Improved Machine Runnability
Dr. Michael Y. Sun
濕端化學 - 7 Good Habits -2
Good Habit #3 Stabilize 1st Tray Consistency
2014/5/20
Good Habit #4 Monitor Headbox Charge
DO's :
DO's :
Watch FPR, but control 1st try Consistency
Set a Target Rage for Headbox Charge
Adjust RA According to Grade Specification
Watch Incoming Stock streams for Charges
Ask your Boss to gte an Online-monitor system
Adjust Coagulant Usage to Stabilize Charge
Check Headbox Charge Once Per Shift
DONT's :
Adjust RA too quickly if there is a variation
DONT's :
Use FPR as a control Target
Use Alum to Change Charge
Benefits of Stabilize 1st Tray Consistency
Use RA to Change Charge
Use Starch to Change Charge
"Cruise Control" on Retention
Fewer Wet-end Breaks
Less Chemical Usage
More Stable Retention and Formation
More Production rate
Fewer Wet-end Breaks
Less Chemical Usage / Wet-end Deposits
More Stable Sizing Efficiency
Benefits of Monitor Headbox Charge
Good Habit #5 Control Sheet Ash Content DO's :
DONT's :
Set a Target Range for Each Grade
Monitor Ash FPR%, Headbox, and Tray Ash
Adjust Filler Addition Rate at MC
Watch For Broke type and Usage
Benefits of Control Sheet Ash Content
Adjust Broke Usage to Stabilize Sheet Ash
More stable Sheet Brightness / Opacity / Size Efficiency
Check Sheet Ash in the Lab every other spool
Less Basis Weight / Moisture variations
Adjust Ra to Change Ash Content ( Normally )
Stable Strength
WL
Dr. Michael Y. Sun
濕端化學 - 7 Good Habits -3
Good Habit #6 Regulate Stock Ratio DO's :
2014/5/20
WL
Good Habit #7 Keep Anionic Trash away from Wet-end DO's :
Set a Stock Ratio Target for Each Grade
Watch and Control you Broke type and Usage
Monitor Headbox Fiber Length for Each Grade
Ask pulp mill for Cleaner Pulp
Watch for MC Consistency and flow Variations
Use Less Defoamers and Dispersants
Ask your boss to get online-fiber length analyzer
Understand Neutralizing Charge Is Not Equal to Getting Less Anionic Trash
DONT's :
Rely on Consistency and flow meters
Assume Pulp mill Always Supply Correct Fibers
Assume All the Fibers Are the Same
Benefits of #6 Regulate Stock Ratio
DONT's :
Just Reply on Chemical Suppliers' Advice for your Wet-end
Benefits of #7 Keep Anionic Trash away from Wet-end
More stable Sheet Strength Properties
Cleaner Wet-End Systems
Improved Sheet Formation
Less Deposit Problems
More Stable Sizing Efficiency
Low Boil-Out Frequency
Fewer Wet-end Breaks