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 (洗涤作用) – 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 < 100nm, then difficult to wash off (2) Electrostatic force – surface potentail wool/water= - 48mV cotton/water= - 38mV silk/water= - 1mV cation bridge (阳离子桥) - polyvalency ions Soil--- ++ - - - - - - - - - - - - - - - -

5. Soil--- ++++ - - - - - - - - - - - - - - - 2. Force between substrates and soils • Mechanical force – soft & porous substrates, particle diameter r of the particles , then force, r < 100nm, then difficult to wash off (2) Electrostatic force – surface potentail wool/water= - 48mV cotton/water= - 38mV silk/water= - 1mV cation bridge (阳离子桥) - polyvalency ions Electrostatic force > 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 (再沉淀) 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 ,  < 0,  < 90° ,Cos > 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  > 0,  < 90°, BOCos > 0, R > 0, force imbalance, roll-up and , •  > 90°,  > 0, BOCos < 0, R = 0, anew force balance

9. (c) Three kinds of roll-up • Complete removal • Spontaneously roll-up (自动卷离)  = 180° e.g. anionics: only S/B,O/B • By mechanism work (作功卷离)90°<  <180° e.g.nonionics: S/B,O/B,S/O • Incomplete removal SO < SB , Cos  > 0  < 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 (可液化) soil – roll-up • Particulate soil • Wetting of the substrate and the soil particles by the bath • Spreading coefficient particles SB/P=PV- PB- BV > 0 substrates SB/S=SV- SB- BV > 0 • Additive pressure – gap capillary (间隙毛细管) P = LVCos/R • Adhesion of solid soil WSP= SB+ PB- SP > 0

11. (B) Potential curve DLVO theory V=VA+VR 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(悬浮作用) of the soil in the bath and prevention of re-deposition (预防再沉积) • Solid particulate soil: formation of electrical and steric barrier • Liquid oily soil • Solubilization – C > CMC • Ionic surfactants C < CMC (only adsorption) • Nonionic surfactants C > 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 (协助去污) • 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 > nonionics (partly hydrogen bond) > cationics (b) Particulate soil – anionics > nonionics > 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 > branching chains

17. (3) Effect of the hydrophilic group of the surfactant • Anionics • Nonionics • Zwitterionic surfactants 3. Builders – chelation (螯合), buffering (缓冲), dispersion (分散) • 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型沸石分子筛) – NaOAl2O3 nSiO2H2O A type : Al2O3: SiO2(mole) = 1.3 - 2.4

19. Mechanism • Ion exchange – power of Ca++exchange 300mg CaCO3/g • Coprecipitation with soil (与污垢共沉淀) • Safety (安全) (b) Disadvantage • Low rate of exchange • No dispersibility (3) Other builders • Polyacrylate • Polymaleate (聚马来酸)

20. 4. Other auxiliary agents • Bleacher (漂白剂) – peroxide , sodium perborate (过硼酸钠), sodium percarbonate(过碳酸钠), etc • Fluorescent bleachng agent (荧光剂) – adsorption 300-400nm ultraviolet radiation radiation 400-500nm visible light (3) Enzyme – protease (蛋白酶), amylase(淀粉酶), lipase (脂肪酶), cellulase (纤维素酶) (4) Finishing agents - antistatic agents (抗静电剂), anti-bacterial agents (抗菌剂), softening agents (柔软剂)

21. 5. Standard washing powder Surfactants 15% Builder (STPP) 17% Sodium silicate(硅酸钠) 10% Sodium carbonate(碳酸钠) 3% Sodium sulfate(硫酸钠) 18% CMC 1%