Maximizing van der Waals Force in Papermaking

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Maximizing van der Waals Force in Papermaking

• John G.Penniman

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Introduction

• Van der Waals powerful intermolecular force
  increases exponentially, inversely with distance.
  In papermaking, as we shall show, it can enable
  significantly higher sheet ash without impairment
  of strength.

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Topics of Discussion

• Van der Waals force is enhanced by taking two key
  wet end chemistry actions
• Eliminating the repulsive electrostatic charge on
  the stock surfaces, and
• Using the chemicals most appropriate for this
  purpose

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The BEST Chemicals

• Should include an anionic microparticle
• And a cationic starch
• Because that combination provides the best
  balance of high retention coupled with excellent
  formation

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The BEST Chemicals

• Should also include a cationic scavenger that
  is cost-effective in maximizing drainage in the
  presence of anionic trash
• The superiority of polyDADMAC over polyamine, for
  example, is typically represented by a drainage
  increase of about 40 in a dirty system, vs 0
  for polyamine

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The BEST Chemicals

• Should include a gum, such as cationic guar.
  This class of chemicals has a high affinity for
  cellulose and a synergistic effect on the
  microparticulate process.
• Example in a system high in coated broke and
  PCC, replacing 0.5 of a total 10 cationic
  starch with cationic guar increases drainage from
  108 to 192, sizing from 129 to 203 HST seconds,
  sheet ash from 27 to 32 and Scott Bond from 42
  to 53/in2

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The BEST Chemicals

• Should EXCLUDE, as far as possible, a
  conventional retention aid for two reasons
• It limits the effort to minimize intermolecular
  distance, and
• It impairs formation, with corollary degradation
  of physical properties

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Eliminating the REPULSIVE
negative charge

• A cationic scavenger is added until drainage is
  at maximum
• The following graph shows that both process and
  physical property parameters are at maximum in
  the range 1 to 6 mV zeta potential
• HST sizing is especially sensitive

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On-Machine Correlation of HST Sizing
Zeta Potential

• In the graph, zeta potential is measured on-line,
  and
• AKD sizing is measured on each reel of alkaline
  coating base stock, using the Hercules Sizing
  Test (HST) expressed in seconds
• The Correlation Coefficient is 0.72

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Charge-neutralization Influence onvan der Waals
Force

• In the lab study, Ash Comparison, Series II vs
  Series III, PCC loading is incrementally
  increased to 30
• In the optimized Series II, ash increases from 6
  to 14

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Van der Waals Force
..continued

• In the work previously discussed, Scott Bond
  Comparison, Series II vs Series III, at the 14
  ash level, Scott Bond is maintained at 58/in2,
  exactly the same as the uncontrolled system at 4
  ash
• The 10 increase in sheet ash without loss of
  strength may be attributed to van der Waals
  force.

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Van der Waals Force
..continued

• On the paper machine, productivity can be easily
  enhanced and optimized at the higher ash level
• Under computer control, feed rates of both
  cationic scavenger and smectite are increased,
  and adjusted in parallel, to maintain the optimum
  zeta potential

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Van der Waals Force
CONCLUSIONSSelect the BEST
chemicalsEliminate the REPULSIONBalance feed
rates
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MAXIMIZINGVan der Waals Force
ENABLESMaximum feedstock
cost-efficiency at optimum quality and
productivity