AFM Study of the Effect of AFM Study of the Effect of Recycling on Fiber Surface Recycling on Fiber Surface Properties Properties Adam Brancato 1 , Frances L. Walsh, Ron Sabo & Frances L. Walsh, Ron Sabo & Adam Brancato 1 , 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 Tensile Strength % Decrease in TS Recycles (kN/m) from Unrecycled 0 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 1.45 2.6 No Refining 2.4 1.4 Medium Refining 2.2 1.35 High Refining 2 WRV (g/g) WRV (g/g) 1.3 1.8 1.25 1.6 1.2 1.4 1.15 1.2 1 1.1 Unrecycled 1 Recycle 2 Recycles 3 Recycles Unrecycled 1 Recycle 2 Recycles
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 tack not as an imaging tool tack not as an imaging tool nanoscale � 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 45 40 Surface Adhesion (nN) 35 30 25 20 15 10 Unrecycled 1 Recycle 2 Recycles
AFM Force Measurements AFM Force Measurements Bleached Softwood Kraft Pulp Handsheets Unrefined Low Refining 140 High Refining 120 Surface Adhesion (nN) 100 80 60 40 20 0 0x 1x 2x 3x Times Recycled – Adhesion force increases by over 300%
Single Fiber AFM Analysis Single Fiber AFM Analysis 80 � Single fiber analysis in air Single fiber analysis in air � TMP air 60 matches the results seen for matches the results seen for surface adhesion (nN) handsheet samples 40 handsheet samples water 20 � Slightly lower increase in Slightly lower increase in � surface adhesion, possibly due surface adhesion, possibly due 0 to restraining of fiber to restraining of fiber air 80 kraft � Testing in water indicated Testing in water indicated � 60 lower surface adhesion than lower surface adhesion than 40 water in air in air 20 � Lack of capillary forces in water Lack of capillary forces in water � 0 � Swelling of fiber Swelling of fiber 0 1 2 3 � no. of recycles
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 Monolayer water (relative) (g/g) 0.3 0.25 0.2 0.15 0.1 0.05 0 Unrecycled 1x Recycle 2x Recycle 3x Recycle � WRV measures both bound and pore water WRV measures both bound and pore water � 1 showed that the water bound as a monolayer � A new technique A new technique 1 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- -bound water. bound water. water & not from monolayer 1 Holzforschung , 2007 , 16, 115
Surface Packing Changes Surface Packing Changes
AFM Profiles of a Newsprint Mill AFM Profiles of a Newsprint Mill 40 June 22 � The surface adhesion of The surface adhesion of � 20 virgin fiber is > 12nN. virgin fiber is > 12nN. 0 � Lower values must reflect Lower values must reflect 80 � June 28 hydrophobic contaminants. hydrophobic contaminants. 40 frequency � There can be high day There can be high day- -to to- -day day 0 � 40 variability of surface variability of surface June 29 20 hydrophobicity. hydrophobicity . 0 � Can potentially be used for Can potentially be used for 40 � July 3 after- -the the- -fact analysis of fact analysis of after 20 problems. problems. 0 0 20 40 60 80 100 surface adhesion (nN)
Recommend
More recommend
