Chapter 9. Detergency of Surfactants

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Chapter 9. Detergency of Surfactants

• 2006.6.6.

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1. Introduction

• Cleaning process is a very complex process
• No surfactants by self can clean a surface
• Detergency (????) this term, when applied to a
  surfactants, means the special property it has of
  enhancing the cleaning power of a liquid.
• Detergency a combination of effects involving
  adsorption at interface, alteration of
  interfacial tension, solubilization,
  emulsification, and the formation and dissipation
  of surface charges
• Detergency involving mechanical action,
  biochemical action, and fabric softening.
  

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2. Mechanisms of the cleaning process

• Three elements in cleaning process
• The substrate (the surface that is to be cleaned)
• Hard surface glass , metals, and etc
• Soft surface fabric , fiber
• The soil (the material that is to be removed from
  the substrate in the cleaning process)
• Liquid soils oil or fat
• Solid soils black carbon, dust, and etc
• (3) The bath or cleaning solution.

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• 2. Force between substrates and soils
• Mechanical force soft porous substrates,
  particle diameter r of the particles ?, then
  force?,
• r lt 100nm, then difficult to wash off
• (2) Electrostatic force surface potentail
• ?wool/water - 48mV
• ?cotton/water - 38mV
• ?silk/water - 1mV
• cation bridge (????) - polyvalency ions

Soil---

- - - - - - - - - - - - - - - -
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• 2. Force between substrates and soils
• Mechanical force soft porous substrates,
  particle diameter r of the particles ?, then
  force?,
• r lt 100nm, then difficult to wash off
• (2) Electrostatic force surface potentail
• ?wool/water - 48mV
• ?cotton/water - 38mV
• ?silk/water - 1mV
• cation bridge (????) - polyvalency ions
• Electrostatic force gt Mechanical force

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• (3) Chemical force polar soils proteins , fats
  , oxides etc
• Hydrogen bond and electrovalent bond
• (4) Van Der Waals force interactions between
  polar polar or polar non-polar or non-polar
  non-polar
• Two cleaning process
• removal of the soil from the substrates
• suspension of the soil in the bath and
  prevention of its redeposition (???)
• 3. Removal of the soil from the substrates
• It not cover the removal of soil by
  mechanical work, or chemical reagents (e.g.
  bleaches, reducing agents) or enzymes

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• Removal of liquid soil roll-back or roll-up
• Young equation
• ?SO ?SB- ?BO Cos ?
• Cos ? (?SB- ?SO)/?BO
• ?SO ?, Cos ??, ??, then roll-up
• ?SB ?, Cos ??, ??, then spreading

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• (b) Roll-up force R
• Initial state R (?SO-?SB) ?BOCos? ,
• ?? lt 0, ? lt 90 ,Cos? gt
  0
• ? R ?? ?BO Cos ? 0 ,
  force balance
• If surfactants is added and only adsorbed on
  interface S/B and O/B, then ?SB ?, ?OB ?, then
  ?? gt 0, ? lt 90, ?BOCos? gt 0, R gt 0, force
  imbalance, roll-up and ??,
• ? gt 90, ?? gt 0, ?BOCos? lt 0, R 0, anew force
  balance

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• (c) Three kinds of roll-up
• Complete removal
• Spontaneously roll-up
• (????) ? 180
• e.g. anionics only S/B,O/B
• By mechanism work
• (????)90lt ? lt180
• e.g.nonionics S/B,O/B,S/O
• Incomplete removal
• ?SO lt ?SB , Cos ? gt 0
• ? lt 90

Complete removal of oil droplets from substrate
Rupture and incomplete removal of large oil
droplets from substrate
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• (2) Removal of solid soil
• Mechanism
• Liquefiable (???) soil roll-up
• Particulate soil
• Wetting of the substrate and the soil particles
  by the bath
• Spreading coefficient
• particles SB/P?PV- ?PB-
  ?BV gt 0
• substrates SB/S?SV- ?SB-
  ?BV gt 0
• Additive pressure gap capillary (?????)
• ?P ?LVCos?/R
• Adhesion of solid soil
• WSP ?SB ?PB- ?SP gt 0

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• (B) Potential curve
• DLVO theory VVAVR
• A state adsorbed state
• B state transition state
• C state separating state
• Esoil removal - energy barrier
• of soil removal
• Ere-soiling- energy barrier
• of re-soiling

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• 4. Suspension(????) of the soil in the bath and
  prevention of re-deposition (?????)
• Solid particulate soil formation of electrical
  and steric barrier
• Liquid oily soil
• Solubilization C gt CMC
• Ionic surfactants C lt CMC (only adsorption)
• Nonionic surfactants C gt CMC (adsorption and
  solubilization)
• (b) Macro-emulsification

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• 5. Dry cleaning hydrocarbon or chlorinated
  hydrocarbon
• Thickness of electrical double layer is very thin
  (very low dielectric constant) low electrical
  barrier
• Surfactants are probably adsorbed with polar head
  oriented toward the substrate and soil high
  steric barrier

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3. Detergents

• Composition of detergents
• Surfactants enhancing the cleaning power
• builders increasing the efficiency and
  effectiveness of surfactants as detergents and
  supplement their beneficial effects on soil
  removal (????)
• Other auxiliary agent
  

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• 2. The relation of the chemical structure of the
  surfactant to its detergency
• Effect of soil and substrate hydrophilic head
  oriented toward the bath or substrates
• Oily soil
• hydrophobic substrates (e.g. polyester, nylon)
  POE
• hydrophilic substrates (e.g. cotton, wool)
  negative charge at neutral or alkaline pH
  anionics gt nonionics (partly hydrogen bond) gt
  cationics
• (b) Particulate soil anionics gt nonionics gt
  cationics

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• (2) Effect of the hydrophobic group of the
  surfactants extent and orientation of
  adsorption (efficiency of adsorption)
  solubility in bath.
• R?, surface activity? R??, solubility?
• e.g. carboxylate the optimum Rn
• Used temperature 38?C R12 R14 55 ?C R16
• Counter ion valence number ?, Rn?
• Hardness of water ?, Rn?
• (b) Straight gt branching chains

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• (3) Effect of the hydrophilic group of the
  surfactant
• Anionics
• Nonionics
• Zwitterionic surfactants
• 3. Builders chelation (??), buffering (??),
  dispersion (??)
• Sodium tripolyphosphate (Na5P3O10 STPP)
• Chelation power of Ca-
• Water 102 CaCO3 mg/g
• STPP 468 CaCO3 mg/g
• Polyacrylate (PAA) 466 CaCO3 mg/g

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• (b) Alkaline buffering power pH adjusting
• Water neutralizing 0.15 ml 0.1M NaOH aq.
• STPP neutralizing 5.20 ml 0.1M NaOH aq.
• PAA neutralizing 4.60 ml 0.1M NaOH aq.
• (c) Dispersing power dispersion of particles
• Water dispersing 8.0 ppm Mn
• STPP dispersing 13.0 ppm Mn
• PAA dispersing 11.0 ppm Mn
• Disadvantage pollute environment
• (2) Zeolite molecular sieve (4A??????)
• NaOAl2O3 nSiO2H2O
• A type Al2O3 SiO2(mole) 1.3 - 2.4

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• Mechanism
• Ion exchange power of Caexchange 300mg
  CaCO3/g
• Coprecipitation with soil (??????)
• Safety (??)
• (b) Disadvantage
• Low rate of exchange
• No dispersibility
• (3) Other builders
• Polyacrylate
• Polymaleate (????)

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• 4. Other auxiliary agents
• Bleacher (???) peroxide , sodium perborate
  (????), sodium percarbonate(????), etc
• Fluorescent bleachng agent (???) adsorption
  300-400nm ultraviolet radiation
• radiation 400-500nm visible light
• (3) Enzyme protease (???), amylase(???), lipase
  (???), cellulase (????)
• (4) Finishing agents - antistatic agents (????),
  anti-bacterial agents (???), softening agents
  (???)

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• 5. Standard washing powder
• Surfactants 15
• Builder (STPP) 17
• Sodium silicate(???) 10
• Sodium carbonate(???) 3
• Sodium sulfate(???) 18
• CMC 1