Mass Transfer Considerations in Hygiene Products

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  1. Mass Transfer Considerations in Hygiene Products Carol Blaney, Ph.D. Blaney Consulting 2. OUTLINE <ul><li>Business perspective – infant diapers…
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  • 1. Mass Transfer Considerations in Hygiene Products Carol Blaney, Ph.D. Blaney Consulting
  • 2. OUTLINE <ul><li>Business perspective – infant diapers </li></ul><ul><li>Problem – customer complaint </li></ul><ul><li>Background – brief overview of garment function </li></ul><ul><li>Strategy – mass transfer considerations </li></ul><ul><li>Execution – modeling and experimental </li></ul><ul><li>Conclusions - problem solved </li></ul>
  • 3. 1. Business perspective <ul><li>$26 billion dollar global industry </li></ul><ul><li>Fiercely competitive </li></ul><ul><li>Growing (Asia-Pacific) </li></ul>
  • 4. 1. Business Perspective <ul><li>New technology: </li></ul><ul><ul><li>New polymers </li></ul></ul><ul><ul><li>New fillers </li></ul></ul><ul><ul><li>New processes </li></ul></ul><ul><li>Innovations/Improvements Ultra high permeability never before possible </li></ul>
  • 5. 2. Problem – customer complaint <ul><li>Positive: skin health (dryer skin) </li></ul><ul><li>Negative: customer says ‘it leaks’ </li></ul><ul><li>(but it wasn’t actually leaking) </li></ul>
  • 6. 3. Background – overview of garment function <ul><li>Goal: ‘dry’ skin </li></ul><ul><li>Testing has consistently shown: </li></ul><ul><ul><li>Hydrated skin is abraded more easily, more susceptible to infection </li></ul></ul><ul><ul><li>Skin hydration is beneficially reduced by </li></ul></ul><ul><ul><ul><li>(a) use of SAP, and </li></ul></ul></ul><ul><ul><ul><li>(b) by reducing barriers to water vapor transfer out of diaper. </li></ul></ul></ul>
  • 7. 3. Background – overview of garment function
  • 8. 3. Background – overview of garment function <ul><li>Before Insult (all layers) </li></ul><ul><li>Insult (coversheet) </li></ul><ul><li>Transfer fluid away from skin (transfer layers) </li></ul><ul><li>Retain fluid away from skin (pulp, superabsorbent) </li></ul><ul><li>Continue removing moisture out of garment </li></ul>
  • 9. 4. Strategy <ul><li>Initial Goal: lower skin hydration </li></ul><ul><li>New Goal: Solve perception of ‘leakage’ </li></ul><ul><ul><li>Lab tests show no holes big enough to cause a real ‘leak’ of liquid urine </li></ul></ul>
  • 10. Young-Laplace Equation
  • 11. Visualizing criteria for leakage across a microporous film: <ul><li>Simple model: </li></ul>
  • 14. Maximum pore size allowed
  • 22. Why does diaper seem to be leaking? <ul><li>What do you feel when you feel wetness? </li></ul><ul><ul><li>What is it about water that feels wet? </li></ul></ul><ul><ul><li>Warm water doesn’t feel as wet as cold water. </li></ul></ul><ul><ul><li>Hypothesis: ‘wet’ means hand is losing heat . </li></ul></ul><ul><ul><li>Outercover feels ‘cold’, not ‘wet’. </li></ul></ul><ul><ul><li>Cause: Evaporative cooling </li></ul></ul>
  • 23. Remedy? <ul><li>Remedy #1. Lessen evaporative cooling </li></ul><ul><ul><li>Problem: raises humidity inside diaper </li></ul></ul><ul><ul><li>Raises skin hydration, compromises baby’s skin health </li></ul></ul>
  • 24. Another Remedy? <ul><li>Remedy #2. Lessen the human perception of evaporative cooling by reducing heat transfer from hand to diaper (while keeping evaporation levels high) </li></ul><ul><ul><li>How? Lower heat transfer coefficient of the outercover </li></ul></ul><ul><ul><li> add a layer of air. </li></ul></ul>
  • 25. New goal <ul><li>Minimize heat transfer into diaper outercover </li></ul><ul><li>AND </li></ul><ul><li>Maximize moisture transfer out of diaper </li></ul><ul><ul><li>this includes </li></ul></ul><ul><ul><li>maximizing water evaporation </li></ul></ul><ul><ul><li>and hence </li></ul></ul><ul><ul><li>maximizing evaporative cooling </li></ul></ul>
  • 27. New question: <ul><li>But will the extra layer of ‘heat insulation’ (air) add to the diffusional resistance of moisture vapor leaving the diaper? </li></ul><ul><li>Quickest way to answer this: Model </li></ul>
  • 28. 4. Strategy - Modeling <ul><li>Modeling is fastest way to see relative effects of various layers on overall moisture transfer </li></ul><ul><li>Use it to intelligently select the most effective fabric prototypes </li></ul><ul><li>AND </li></ul><ul><li>Test these fabrics in a product to see if it eliminates customer complaints. </li></ul>
  • 29. End of Section 4 (Strategy) <ul><li>We now have a clear strategy based on our hypothesis that ‘leakage’ perception is due to heat loss from hand : </li></ul><ul><ul><li>Use a Spacer layer (air) </li></ul></ul><ul><ul><li>To Reduce heat transfer </li></ul></ul><ul><ul><li>Hopefully it won’t appreciably reduce moisture flux </li></ul></ul>
  • 30. Section 5: Execution <ul><li>Modeling </li></ul><ul><li>Experimental </li></ul>
  • 33. Modeling <ul><li>Steady state, ordinary diffusion of water vapor through air (~ideal gas): </li></ul><ul><li> J = - D  (C) </li></ul>
  • 34. Microporous Films <ul><li>Fickian Diffusion in one direction </li></ul><ul><li>J A = - D AB dc A /dZ = - D AB (P/RT) dY A /dZ </li></ul><ul><li>  </li></ul><ul><li>Ideal gas mixture of components A and B at constant T, P </li></ul>
  • 35. Microporous Films <ul><li>N A = (1 – Y A ) -1 [ - D P/(RT) dY A /dZ ] </li></ul><ul><li>  </li></ul><ul><li>Where </li></ul><ul><li>  </li></ul><ul><li>D = [ __ 1__ + _ 1 _ ] -1 </li></ul><ul><li>D F  ) D K </li></ul><ul><li>  </li></ul>
  • 36. Boundary conditions for integration <ul><li>At Z=0, Y A =Y A1 </li></ul><ul><li>At Z=Z 0 , Y A =Y A2 </li></ul>
  • 37. Result for single layer: <ul><li>MVTR = N A = </li></ul><ul><li>D P/(Z 0 RT) ln [(1-Y A2 )/(1-Y A1 )] </li></ul>
  • 38. Add boundary layer: <ul><li>MVTR = NA = </li></ul><ul><li>ln [(1-Y A3 )/(1-Y A1 )] _ </li></ul><ul><li>Z 0 RT + h 0 RT </li></ul><ul><li>D F  ) P D F P </li></ul>
  • 46. Moisture flux (g/m 2 /day)
  • 47. Experimental <ul><li>Recruited and trained a sensory panel to perceive ‘dry’ vs ‘wet’ when they touched the diapers. </li></ul><ul><li>Set up laboratory: </li></ul><ul><ul><li>A dozen torsos that mimic real diaper use </li></ul></ul><ul><ul><ul><li>Realistic urine insults </li></ul></ul></ul><ul><ul><ul><li>Heated skin surface, correct anatomy </li></ul></ul></ul><ul><ul><ul><li>Humidity sensors </li></ul></ul></ul><ul><ul><ul><li>Mass balance every hour </li></ul></ul></ul>
  • 48. Experimental Results
  • 49. Experimental Results <ul><li>Perception of ‘dry’ correlated with lowered heat transfer coefficient of the outercover composite (hypothesis was correct) </li></ul>
  • 50. Experimental Results <ul><li>Perception of ‘dry’ correlated with lowered heat transfer coefficient of the outercover composite (hypothesis was correct) </li></ul><ul><li>Lower humidity levels inside diaper correlated with higher MVTR values (of outercover composite) </li></ul>
  • 51. Experimental Results <ul><li>Perception of ‘dry’ correlated with lowered heat transfer coefficient of the outercover composite (hypothesis was correct) </li></ul><ul><li>Lower humidity levels inside diaper correlated with higher MVTR values (of outercover composite) </li></ul><ul><li>Modeling correlated with experimental results, confirming our understanding. </li></ul>
  • 52. Summary <ul><li>A thin, open nonwoven ‘spacer’ layer was selected for commercialization: </li></ul><ul><ul><li>Lowered thermal conductivity to address ‘complaints’ </li></ul></ul><ul><ul><li>Didn’t lower MVTR too much </li></ul></ul><ul><ul><li>strong </li></ul></ul><ul><ul><li>cost effective </li></ul></ul><ul><ul><li>machine capacity available </li></ul></ul><ul><li>Patent protection obtained </li></ul><ul><li>(Patents: 6,673,980; 6,663,611; 6,660,086; 6,583,331; 6,177,607) </li></ul>
  • 53. 6. Conclusion <ul><li>Mission Accomplished </li></ul><ul><li>Company remained a leader in diapers, able to advertise skin health benefits </li></ul><ul><li>Without customer complaints </li></ul>
  • 54. Credits (Blaney) <ul><li>Solved riddle of ‘leakage perception’ </li></ul><ul><li>Proposed strategy </li></ul><ul><li>Applied model to gain clarity </li></ul><ul><li>Set up lab (with electrician) </li></ul><ul><li>Established testing protocol </li></ul><ul><li>Wrote up patent draft with preliminary claims </li></ul>
  • 55. My technical team <ul><ul><li>Recruited and trained an in-house sensory panel </li></ul></ul><ul><ul><li>Constructed ‘diaper’ products </li></ul></ul><ul><ul><li>Arranged material property testing </li></ul></ul><ul><ul><li>Ran lab tests </li></ul></ul><ul><ul><li>Collected data </li></ul></ul>
  • 56. Commercialization Team <ul><ul><li>Assessed material availability and cost </li></ul></ul><ul><ul><li>Ran trials to produced materials for testing </li></ul></ul><ul><ul><li>Commercialized the ‘winner’ </li></ul></ul>
  • 57. Model/Programming <ul><li>Sigma Software in Roswell, GA </li></ul><ul><li>Theory for Model </li></ul><ul><ul><li>Mass Transfer – Chemical Engineering Series </li></ul></ul><ul><ul><li>Sherwood, Pigford, Wilke McGraw Hill © 1975 </li></ul></ul>
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