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Chapter 9. Detergency of Surfactants

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Chapter 9. Detergency of Surfactants 2006.6.6. 1. Introduction Cleaning process is a very complex process; No surfactants by self can clean a surface; Detergency ... – PowerPoint PPT presentation

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Title: Chapter 9. Detergency of Surfactants


1
Chapter 9. Detergency of Surfactants
  • 2006.6.6.

2
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.

3
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.

4
  • 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---

- - - - - - - - - - - - - - - -
5
  • 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

6
  • (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

7
  • 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

8
  • (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

9
  • (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
10
  • (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

11
  • (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

12
  • 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

13
  • 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

14
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

15
  • 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

16
  • (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

17
  • (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

18
  • (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

19
  • 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 (????)

20
  • 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
    (???)

21
  • 5. Standard washing powder
  • Surfactants 15
  • Builder (STPP) 17
  • Sodium silicate(???) 10
  • Sodium carbonate(???) 3
  • Sodium sulfate(???) 18
  • CMC 1
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