AFM Study of the Effect of AFM Study of the Effect of Recycling on - - PowerPoint PPT Presentation

AFM Study of the Effect of AFM Study of the Effect of Recycling on Fiber Surface Recycling on Fiber Surface Properties Properties

Adam Brancato Adam Brancato1

1,

, Frances L. Walsh, Ron Sabo &

Frances L. Walsh, Ron Sabo & Sujit Banerjee Sujit Banerjee Institute of Paper Science & Technology Institute of Paper Science & Technology Georgia Tech Georgia Tech

1 Ph.D. Candidate

Objective & Overview Objective & Overview

• How does recycling affect the

How does recycling affect the nanoscale nanoscale properties of fiber? properties of fiber?

• Fiber Preparation Methodology

Fiber Preparation Methodology

• Bulk Fiber Results

Bulk Fiber Results

• Atomic Force Microscopy Results

Atomic Force Microscopy Results

• Conclusions

Conclusions

Hornification Hornification

• Irreversible changes to fiber

Irreversible changes to fiber

• Affects final paper properties (lowers tensile strength

Affects final paper properties (lowers tensile strength and water retention) and water retention)

• Effects continue with progressive recycling (cycles of

Effects continue with progressive recycling (cycles of drying and rewetting) of fibers drying and rewetting) of fibers

Surface Wrinkling Surface Wrinkling

• The contact angle of water on fiber increases upon

The contact angle of water on fiber increases upon recycling recycling

• Suggests that the fiber becomes more hydrophobic

Suggests that the fiber becomes more hydrophobic

• Both chemistry and surface roughness affect contact angle

Both chemistry and surface roughness affect contact angle

• Fiber surface is known to

Fiber surface is known to “ “wrinkle wrinkle” ” upon recycling upon recycling

• Increase in contact angle not caused by chemical change, but

Increase in contact angle not caused by chemical change, but due to roughness due to roughness

Experimentation Experimentation

• Materials

Materials

• TMP

TMP – – Augusta Newsprint Augusta Newsprint

• Bleached Softwood Kraft Pulp

Bleached Softwood Kraft Pulp – – Stora Stora Enso, Enso, Wisconsin Rapids Wisconsin Rapids

• Use AFM as a

Use AFM as a nanoscale nanoscale tack tester to characterize tack tester to characterize changes in fiber surface properties caused by changes in fiber surface properties caused by recycling recycling

• Handsheets at 3 levels of refining & 4 levels of

Handsheets at 3 levels of refining & 4 levels of recycling (AFM measurements made in air) recycling (AFM measurements made in air)

• Single fiber analysis (AFM measurements made in air &

Single fiber analysis (AFM measurements made in air & water) water)

Recycling & Refining Recycling & Refining

• Refining (Valley Beater)

Refining (Valley Beater)

• No beating, 675 ml CSF

No beating, 675 ml CSF

• Medium beating, 400 ml CSF

Medium beating, 400 ml CSF

• High beating 250 ml CSF

High beating 250 ml CSF

• Recycling

Recycling

• Never

Never-

• dried pulp disintegrated and made into handsheets

dried pulp disintegrated and made into handsheets

• Handsheets were air

Handsheets were air-

• dried/repulped three times to give

dried/repulped three times to give virgin, x1, x2 and x3 recycled sheets. virgin, x1, x2 and x3 recycled sheets.

Tensile Strength Tensile Strength

• Unrefined bleached kraft handsheets

Unrefined bleached kraft handsheets

• Shows expected strength loss due to recycling

Shows expected strength loss due to recycling

Number of Recycles Tensile Strength (kN/m) % Decrease in TS from Unrecycled 2.13 1 1.91 10.4 2 1.79 15.9 3 1.73 18.8

Water Retention Value Water Retention Value

TMP Bleached Kraft

1.1 1.15 1.2 1.25 1.3 1.35 1.4 1.45 Unrecycled 1 Recycle 2 Recycles WRV (g/g) 1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 Unrecycled 1 Recycle 2 Recycles 3 Recycles WRV (g/g) No Refining Medium Refining High Refining

Atomic Force Microscopy Atomic Force Microscopy

• Analyzes sample on extremely small scale

Analyzes sample on extremely small scale

• Measures force of adhesion between probe and sample

Measures force of adhesion between probe and sample surface surface

• Because images are rough, AFM used to measure

Because images are rough, AFM used to measure nanoscale nanoscale tack not as an imaging tool tack not as an imaging tool

• Force measurements dependent on several factors

Force measurements dependent on several factors

• Contact area

Contact area

• Tip and surface chemistry

Tip and surface chemistry

• Presence of water (for hydrophilic surfaces)

Presence of water (for hydrophilic surfaces)

Atomic Force Microscopy Atomic Force Microscopy

Sample AFM force curve in contact mode Sample AFM force curve in contact mode

AFM Force Measurements AFM Force Measurements

TMP Handsheets TMP Handsheets

10 15 20 25 30 35 40 45 Unrecycled 1 Recycle 2 Recycles Surface Adhesion (nN)

AFM Force Measurements AFM Force Measurements

Bleached Softwood Kraft Pulp Handsheets

20 40 60 80 100 120 140 0x 1x 2x 3x Times Recycled Surface Adhesion (nN) Unrefined Low Refining High Refining

– Adhesion force increases by over 300%

Single Fiber AFM Analysis Single Fiber AFM Analysis

1 2 3

• no. of recycles

20 40 60 80 surface adhesion (nN) 20 40 60 80 air water air water TMP kraft

• Single fiber analysis in air

Single fiber analysis in air matches the results seen for matches the results seen for handsheet samples handsheet samples

• Slightly lower increase in

Slightly lower increase in surface adhesion, possibly due surface adhesion, possibly due to restraining of fiber to restraining of fiber

• Testing in water indicated

Testing in water indicated lower surface adhesion than lower surface adhesion than in air in air

• Lack of capillary forces in water

Lack of capillary forces in water

• Swelling of fiber

Swelling of fiber

AFM Results AFM Results

• AFM analysis of surface is at odds with currently

AFM analysis of surface is at odds with currently accepted effects of recycling accepted effects of recycling

• Bulk fiber tests indicate fiber is more hydrophobic and

Bulk fiber tests indicate fiber is more hydrophobic and absorbs less water absorbs less water

• Surface appears to be more hydrophilic, with the measured

Surface appears to be more hydrophilic, with the measured adhesion force doubling after one recycle adhesion force doubling after one recycle

• AFM force depends on surface chemistry and contact area

AFM force depends on surface chemistry and contact area – – surface chemistry cannot change by 300% surface chemistry cannot change by 300%

• The increase in force must derive from a change in contact

The increase in force must derive from a change in contact area, possibly due to fiber shrinkage and collapse area, possibly due to fiber shrinkage and collapse

Surface Collapse Surface Collapse

• Hypothesis: surface does not become more

Hypothesis: surface does not become more hydrophilic, but the bonding sites are drawn hydrophilic, but the bonding sites are drawn closer together with recycling closer together with recycling

• Surface drawing closed inhibits water penetration

Surface drawing closed inhibits water penetration – – decreasing WRV and increasing contact angle decreasing WRV and increasing contact angle

• Proximity of bonding sites inhibits formation of

Proximity of bonding sites inhibits formation of interfiber bonds interfiber bonds

Changes in fiber water content Changes in fiber water content

• WRV measures both bound and pore water

WRV measures both bound and pore water

• A new technique

A new technique1

1 showed that the water bound as a monolayer

showed that the water bound as a monolayer to fiber did not change significantly upon recycling. to fiber did not change significantly upon recycling.

• The decrease in WRV must derive from a reduction in pore

The decrease in WRV must derive from a reduction in pore water & not from monolayer water & not from monolayer-

• bound water.

bound water.

Monolayer water (relative) (g/g)

0.05 0.1 0.15 0.2 0.25 0.3 Unrecycled 1x Recycle 2x Recycle 3x Recycle

1 Holzforschung, 2007, 16, 115

Surface Packing Changes Surface Packing Changes

AFM Profiles of a Newsprint Mill AFM Profiles of a Newsprint Mill

• The surface adhesion of

The surface adhesion of virgin fiber is > 12nN. virgin fiber is > 12nN.

• Lower values must reflect

Lower values must reflect hydrophobic contaminants. hydrophobic contaminants.

• There can be high day

There can be high day-

• to

to-

• day

day variability of surface variability of surface hydrophobicity hydrophobicity. .

• Can potentially be used for

Can potentially be used for after after-

• the

the-

• fact analysis of

fact analysis of problems. problems.

20 40 60 80 100 surface adhesion (nN) 20 40 20 40 frequency 40 80 20 40 June 22 June 28 June 29 July 3

Conclusions Conclusions

• Collapse of pores during recycling compacts the

Collapse of pores during recycling compacts the surface, which increases the bonding sites contacted surface, which increases the bonding sites contacted by the AFM probe tip and leads to higher surface by the AFM probe tip and leads to higher surface adhesion values. adhesion values.

• The AFM responds to changes in the packing density

The AFM responds to changes in the packing density

• f the surface, not to changes in surface chemistry.
• f the surface, not to changes in surface chemistry.
• Highlights day

Highlights day-

• to

to-

• day variability in newsprint and

day variability in newsprint and potentially identifies regions of contamination. potentially identifies regions of contamination.