Behavior of Adhesive Materials in Screening Devices for ...

Behavior of Adhesive Materials

in Screening Devices for Paper

Recycling

Bradley E. Lucas

Co-chairs: R. A. Venditti and H. Jameel

Committee: S. A. Khan and M. A. Hubbe

December 10, 2003

Outline

Background

Research Objective

Results and Discussion

PSA Particle Screening

PSA Particle Breakage

PSA Particle Extrusion

Overall Conclusions

Future Research

Stickies in Paper Recycling

Wastepaper generally contains contaminants that must be removed during recycling

One type of contaminant is adhesive material from stamps, labels, and envelopes

Upon repulping of the wastepaper, the adhesive material is broken down into particles called stickies

One adhesive label can generate about 4000 stickies particles during repulping

Stickies Impact on

Paper Recycling

Stickies deposit on the paper machine

equipment and appear as dirt in the final

product

Stickies cost the paper industry almost $700

million per year due to downgrading of the

product, mill downtime, and waste disposal*

*Friberg, T., Progress in Paper Recycling, 6(1):70-72, 1996.

Pressure Sensitive Adhesives

Pressure sensitive adhesive base polymers consist of acrylic or rubber-based polymers

Glass transition temperature is below room temperature and depends on the adhesive formulation

Young’s modulus and shear strength are low and depend on the adhesive formulation and the system temperature

Pressure Screening

Pressure screening is

considered to be the most

effective way to remove

adhesive contaminants from

pulp

Typical removal efficiencies

of adhesive contaminants

range from 50 to 80% for

commercial pressure screens

Percentage of Adhesive Material

Removed by Each Operation

Sutherland, N.R., and Donermeyer, D., 2000 Tappi Recycling Symposium, pp. 433-470, 2000.

0

20

40

60

80

100

Primary Screen Secondary

Screen

Forward

Cleaners (2)

Through-flow

Cleaners (2)

Flotation Washing

Recycling Operations

Rem

ov

al

Per

cen

tag

e, %

33202

33204

33210

33216

Screening Equipment Parameters

Rotor shape

Rotor speed

Shape of openings

Holes

Slots

Size of openings

Degree of surface contour

Screen Operating Parameters

Feed consistency

Reject rate

Pressure difference

Slot velocity

Temperature

Particle Behavior in Screens

Mechanisms for particle removal

Positive size separation

Particle alignment with the rotor

Proposed mechanisms for particle passage

Particle alignment with the slot

Particle bending

Particle extrusion

Bliss, T., and Ostoja-Starzewski, M., 1997 Tappi Korea Recycling Symposium, pp. 1-17, 1997.

Shear Stress in a Pressure Screen

Pressure screens are second only to the fan pump in shear stress for the wet end of the paper machine

High shear forces can occur due to movement of the foil over the pulp mat formed on the face of the screen plate

Shear and tensile forces occur as material passes through the screen openings

Particle Breakage

Breakage of PSA particles depends on the:

Shear/tensile strength of the PSA

Shear/tensile forces in the device

If the forces in the device are greater than

the strength of the PSA material, then the

PSA material will break

Research on Screening of Stickies

Studies of the effects of operating parameters and

equipment on removal efficiency by: Consistency, slot velocity, and slot width [Vitori, Pulp and Paper

Canada, 1993]

Reject rate, rotor speed, and slot velocity [Heise, Tappi Journal,

1992]

Consistency, reject rate, rotor speed, slot velocity, and slot width

[Seifert, et. al., 5th Research Forum on Recycling, 1999]

Consistency, rotor speed, slot velocity, and slot width [Saint Amand

and Perrin, Tappi 1998 Pulping Conference, 1998]

Results from Previous Research

Removal efficiency increased to a maximum at an optimum consistency

Removal efficiency increased as the:

Reject rate increased

Rotor speed, slot velocity, or slot width decreased

Weaknesses in the studies were:

Undefined materials

Relationships between efficiency and operating conditions were defined but not explained

Little insight provided on the mechanism of passage

Research Objective

To understand how the operating

conditions and adhesive formulation

affect the passage of pressure sensitive

adhesive particles in industrial and

laboratory screens

Outline

Background

Research Objective





Overall Conclusions

Future Research


Do pressure sensitive adhesive particles

behave differently in industrial pressure

screens than in laboratory screens?

Approach: Study the removal of pressure

sensitive adhesive particles by an industrial

pressure screen and laboratory screens

Pilot Plant Layout

Rejects

Flow

Meter

Pump

Industrial

Screen

Feed

Stock

Tank

Second

Stock

Tank

Accepts

Shower

Screening Parameters:

1% Consistency, 50oC,

0.006 in. wide slots,

Mass Reject Ratios of

4.5%, 12%, 15%, and 25%

Experimental Procedure

Valley Flat Screen

0.006 in. slots

25oC, 45oCPulmac

MasterScreen

0.006 in. slots

25oC

Accepts

Accepts

Rejects

Rejects

Pilot Plant

Pulper

Samples

Detection of Stickies

Handsheet

Morplas Blue - Heptane Dye Solution

Dyed

Handsheet

for Image

Analysis

Cleanliness Efficiency of

Industrial and Laboratory Screens

0

20

40

60

80

100In

du

stri

al,

RR

=4

.5%

Ind

ust

rial,

RR

=1

2%

Ind

ust

rial,

RR

=1

5%

Ind

ust

rial,

RR

=2

5%

Pu

lmac,

25

C

Vall

ey

,

25

C

Vall

ey

,

45

C

Screening Devices

Cle

an

lin

ess

Eff

icie

ncy

, %


Do pressure sensitive adhesive particles behave differently in industrial pressure screens than in laboratory screens?

Yes, pressure sensitive adhesive particles behave differently in industrial pressure screens (40-70% efficiency) than in laboratory screens (99% efficiency).

Outline

Background

Research Objective





Overall Conclusions

Future Research


Do PSA particles breakdown in the industrial pressure screen?

Approach: Analyze the PSA particles before and after the industrial pressure screen

Pressure Sensitive Adhesive

Particle Size Distribution

10

100

1,000

10,000

<0.50 0.50-

1.00

1.00-

1.50

1.50-

2.00

2.00-

2.50

2.50-

3.00

>3.00

Particle Size Ranges, mm2

Nu

mb

er o

f P

arti

cle

s in

1 m

2

Feed

Comb. Accepts + Rejects

Screen Removal Efficiency

Versus Particle Size

-1500

-1300

-1100

-900

-700

-500

-300

-100

100

<0.50 0.50-

1.00

1.00-

1.50

1.50-

2.00

2.00-

2.50

2.50-

3.00

>3.00

Particle Size Ranges, mm2

Reje

ct

Eff

icie

ncy,

%

RR=4.5%

RR=10%

RR=15%

RR=25%


Do PSA particles breakdown in the

industrial pressure screen?

Yes, it has been confirmed that PSA

particles do breakdown in the industrial

pressure screen.


Which operating parameters in an industrial pressure screen have the most significant effect on the breakage of PSA particles?

Approach: Conduct a statistical analysis experiment using a high intensity laboratory mixer to treat pulp containing PSA particles


Pilot Plant Pulper

10% K, 45oC, 20 min

80 OD lbs.

Copy Paper with

Adhesive Labels

(1% by wt.)

Samples

Quantum

High Shear Mixer

3 Liters

(vary parameters)

Handsheets

Dyeing

Image Analysis

Operating Parameters

Full Factorial Design Experiment with a

Center Point

Variable Low Value Center Point High Value

Pulp Consistency,% 3 7.5 12

Mixing Time, seconds 30 165 300

Initial Temperature, oC 20 35 50

Rotor Speed, rpm 600 1500 2400

0

300

600

900

1200

1500

1800

2100

CO

NS

TIM

E

TE

MP

RO

TO

R

CO

NS

TIM

E

CO

NS

TE

MP

CO

NS

RO

TO

R

TIM

ET

EM

P

TIM

ER

OT

OR

TE

MP

RO

TO

R

CO

TIT

E

CO

TIR

O

CO

TE

RO

TIT

ER

O

CO

TIT

ER

O

Variable

|Eff

ect|

2 Limit

Pareto Analysis: Number of PSA Particles

Versus Operating Variables


Which operating parameters in an industrial pressure screen have the most significant effect on the breakage of PSA particles?

The operating parameters of consistency, time, and temperature have the most significant effect on the breakage of PSA particles.


Do the mechanical properties of PSA formulations affect the breakage of PSA particles?

Approach: Analyze the average particle size

in the laboratory pulper for PSA films with

different formulations

Preparation of PSA Materials

Two base polymers from Union Carbide

9165 LT: 92% butyl acrylate (BA)

9175: 50% butyl acrylate and 50% 2-ethylhexyl acrylate (BA-EA)

Two rosin-based tackifier resins from Akzo Nobel

775A (Tack A)

Snowtack 780G (Tack G)

Prepare adhesive films for each base polymer with 0 or 40% of tackifier resin for each combination

Compare with acrylic (AC) and SIS commercial PSA films

Physical Properties of PSA Films

0.696.00.86-28AC

0.31206.4-16BA-EA:G

1.4443.1-27SIS

0.221.50.67-23BA-EA:A

0.305619-49BA-EA

0.51183.5-12BA:G

0.383.00.78-20BA:A

0.84252.9-37BA

Modulus,

MPa

Yield

Stress, kPa

Yield

Strain, %

Tg, oC

Polyethylene: 8-35 MPa Yield Stress and 100-600 MPa Modulus


450H Pulper

12% K, 45oC,

415 rpm, 30 min

450 OD g of paper

6 adhesive labels

Handsheets

Dyeing

Image Analysis

Average Particle Size After

Pulping for Eight Formulations

0

0.5

1

1.5

2

2.5

BA BA:A BA:G BA-

EA

BA-

EA:A

BA-

EA:G

AC SIS

Adhesive Formulation

Aver

age

Par

ticl

e S

ize,

mm

2

10 minutes

30 minutes

Cumulative Particle Size

Distributions After Pulping

0

20

40

60

80

100

<0.5 0.5-1.0 1.0-1.5 1.5-2.0 2.0-2.5 2.5-3.0 >3.0

Particle Size, mm2

Cu

mu

lati

ve

Par

ticl

e D

istr

ibu

tio

n,

%

BA BA:A

BA:G BA-EA

BA-EA:A BA-EA:G

AC SIS

Equation for Particle Size

Compared average particle size after pulping to the physical properties of the PSA formulations

Particle Size = -0.43 + 0.34*Yield Strain -0.10*Yield Stress + 3.22*Modulus R2 = 0.86

F = 8.15

Glass transition temperature and contact angle did not correlate with particle size after pulping

Calculated Versus Actual Average

Particle Size

0.0

0.5

1.0

1.5

2.0

0.0 0.5 1.0 1.5 2.0

Actual Particle Size, mm2

Cal

cula

ted

Par

ticl

e S

ize,

mm

2


Do the mechanical properties of PSA formulations affect the breakage of PSA particles?

Yes, changes in the mechanical properties due to PSA formulation differences correlate with the breakage of PSA particles.

Outline

Background

Research Objective





Overall Conclusions

Future Research


How do the pressure difference across the

slot and operating temperature affect

particle passage through a slot?

Approach: Measure the pressure difference

at which PSA particles pass through the slot

of a pressurized single slot device at

different temperatures


450H Pulper

12% K, 45oC,

415 rpm, 60 min

450 OD g of paper

10 adhesive labels

Single Slot Device

0.18 mm wide slot

Single Slot Device Procedure

Remove a PSA particle from pulp

Measure the dimensions of the PSA particle under a microscope

Place the PSA particle on the slot

Add 1000 mL of deionized water

Slowly open the vacuum line valve to increase the pressure difference across the slot

If the particle passes through the slot, record the vacuum pressure at which the particle passes through the slot

Top View

Side View

PIV

a

c

u

u

m

Commonly Observed

Particle Passage Process

Increasing Pressure Difference

indicates

Cumulative Particle Passage

Versus Pressure Difference

0

20

40

60

80

100

0 20 40 60 80

Pressure Difference, kPa

Cu

mu

lati

ve

Par

ticl

e P

assa

ge,

%

5C

20C

50C

Typical Pressure Differences in an

Industrial Pressure Screen*

*Bliss, T., and Ostoja-Starzewski, M., 1997 Tappi Korea Recycling Symposium, pp. 1-17, 1997.


How do the pressure difference across the

slot and operating temperature affect particle

passage through a slot?

Increasing the pressure difference across

the slot or the operating temperature

increases particle passage through a slot.


How do the dimensions of PSA particles

affect their passage through a slot?

Approach: Measure the length, width, and

thickness of the particles before analyzing

their passage through the single slot device

Dimensions of the Particles

WidthLength

Thickness

Length >> Width > Thickness

Area = Length x Width

Top Views of Typical Shapes of

Analyzed Particles

Particle Passage Versus

Particle Length

Maximum Pressure Difference of 75 kPa

0

20

40

60

80

100

<1.00 1.00-1.50 1.50-2.00 2.00-2.50 2.50-3.00 >3.00

Particle Length, mm

Part

icle

Pass

age,

%


Average Particle Width


0

20

40

60

80

100

<0.30 0.30-0.40 0.40-0.50 >0.50

Average Particle Width, mm

Part

icle

Pass

ag

e, %

Note that the slot width is 0.18 mm


Average Particle Thickness


0

20

40

60

80

100

<0.20 0.20-0.30 0.30-0.40 0.40-0.50 >0.50

Average Particle Thickness, mm

Part

icle

s P

ass

age, %

Note that the slot width is 0.18 mm


Calculated Particle Area


0

20

40

60

80

100

<0.50 0.50-1.00 1.00-1.50 >1.50

Average Particle Area, mm2

Part

icle

Pass

ag

e, %


How do the dimensions of PSA particles

affect their passage through a slot?

Increasing the dimensions of width,

thickness, or area decreases the passage of

PSA particles through a slot.


Do the mechanical properties of the PSA formulations affect the passage of PSA particles through a slot?

Approach: Analyze particle passage in the

single slot device for PSA films with

different formulations


450H Pulper

12% K, 45oC,

415 rpm, 30 min

450 OD g of paper

6 adhesive labels

Single Slot Device

0.18 mm wide slot

Particle Passage Versus Yield

Stress for Eight Formulations

0

20

40

60

80

100

0 10 20 30 40 50 60

Yield Stress, kPa

Par

ticl

e P

assa

ge,

%

Equation for Particle Passage

Compared the particle passage to the physical properties and particle dimensions of the eight different PSA formulations

Particle Passage = 99.52 - 2.54*Yield Stress + 1.74*Yield Stress*Average Particle Area -50.18*Average Particle Area

R2 = 0.90

F = 21.41

Yield strain, modulus, glass transition temperature, contact angle, particle length, particle width, particle thickness, and particle volume did not correlate with particle passage

Calculated (Yield Stress and Area)

Versus Actual Particle Passage

0

20

40

60

80

100

0 20 40 60 80 100

Actual Particle Passage, %

Cal

cula

ted

Par

ticl

e P

assa

ge,

%

Particle Passage Versus Particle Area for

Eight Different Formulations

0

20

40

60

80

100

0.0 1.0 2.0 3.0 4.0

Calculated Particle Area, mm2

Cum

ulat

ive

Par

ticl

e P

assa

ge, % BA BA:A

BA:G BA-EA

BA-EA:A BA-EA:G

AC SIS


Do the mechanical properties of the PSA

formulations affect the passage of PSA

particles through a slot?

The mechanical property of yield stress in

combination with the average particle

area affects particle passage.


Can a simple model for extrusion predict

particle passage?

Approach: Develop a model for passage

using energy balance, mass balance, and

deformation equations and compare the

model to data

Model for Particle Passage

Through the Single Slot Device

0

1

3

2

101 zzgPP atm

103222

3zz

gPPP gaugeatm

gaugeatm PPP 33

atmPP 0

P is the pressure and z is the height at point 0, 1, 2, or 3

Measurable variables: P3gauge, Patm, z0, and z1

Particle Deformation

AFF Y221

PartYSlotPart WWPWP 221

F2

F1

A is the cross-sectional area of the particle perpendicular to the forces

Y is the yield stress of the material

A, Y F = PA and A = LW

Model for Particle Passage

Through the Single Slot Device

Slot

Part

atmYatmgaugeW

WzzgPzz

gPP 10103 2

23

2

0

1

3

2

P3gauge is the gauge pressure required in the vacuum line for passage

Model Prediction

If the calculated P3gauge for a particle is:

Less than the minimum pressure that can be

obtained by the device (-73 kPa gauge), the

particle should not pass through the slot

Between the minimum pressure that can be

obtained by the device (-73 kPa gauge) and

atmospheric pressure (0 kPa gauge), the particle

should pass through the slot

Model Predictions Versus

Observed Behavior

Of the 60 particles predicted to be blocked,

58 were actually blocked (97% predicted

correctly)

Of the 164 particles predicted to pass, 77

actually passed (47% predicted correctly)

Observation

Less than 50% predictability for particle passage may be due to adhesion between the particle and the slot surface

Adhesion may have prevented particle passage and was not taken into account in the model

Adhesion needs to be incorporated into the model for particle passage


Can a simple model for extrusion predict

particle passage?

There is some agreement between the

data and the model. Inclusion of adhesive

forces may improve the utility of this

model.

Overall Conclusions

PSA particles broke down in industrial

pressure screens and not in laboratory

screens, resulting in lower removal

efficiencies for industrial pressure screens

than in laboratory screens

Overall Conclusions (cont.)

Consistency, time, and operating

temperature significantly affected the

breakage of PSA particles in a high shear

device

Yield strain, yield stress, and modulus,

which depended on the adhesive

formulation, were significant for particle

size after pulping

Overall Conclusions (cont.)

Particle passage through a single slot device increased by increasing the pressure difference across the slot or the operating temperature

Yield stress and average particle area, which

depended on the adhesive formulation, were

significant for particle passage through the

slot of a pressurized single slot device

Suggestions for Future Research

Develop a dynamic system for the analysis of particle passage through a slot

Further investigate the effects of adhesive formulation on adhesive properties and particle passage by considering other PSA materials

Develop new screening techniques that reduce the breakage and extrusion of PSA particles

Improve the theoretical model for particle passage by investigating the effects of adhesive forces on passage

Acknowledgements

Agglomeration Consortium

Ecosynthetix

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