Docstoc

Lignosulfonat som ytaktivt mne

Document Sample
Lignosulfonat som ytaktivt mne Powered By Docstoc
					Lignosulfonat som ytaktivt
          ämne

  Krister Holmberg, Chalmers

    Föreläsning FPIRC Augusti 2008
Schematic illustration of a surfactant
A good surfactant has a strong tendency to go to interfaces
(surfaces), where it should pack densely.

A good surfactant should have low solubility in the bulk phases.
Some surfactants – and some surface active macromolecules –
are only soluble at the interface, i.e., in the presence of both bulk
phases.

Typical values of surface and interfacial tensions:
air – water                                        72-73 mN/m
air – aqueous surfactant solution                  28-32 mN/m
hydrocarbon – water                                20-40 mN/m
hydrocarbon – aqueous surfactant solution           1-10 mN/m
At a certain surfactant concentration micelles start to form. This
concentration is called the critical micelle concentration (CMC).
Many physical-chemical properties change at the CMC
 In solution:                      The physical-chemical properties of a
                                   solution at the CMC:

                                                           Osmotic pressure


                                                    Surface tension Turbidity




                                              CMC
                               0                    0,01          0,02

 At the air/water interface:                 Concentration (mol/cm3)
 air


 water
                    Surfactants are used …

•   as dispersants
•   as emulsifiers
•   as foaming agents
•   as wetting agents
•   to make microemulsions
•   as anti-corrosion agents
•   for impregnation
•   to solubilize drugs, dyes, etc
•   for soil removal
•   as hydrophobizing agents
•   as lubricants
•   etc
Polymers can be surface active
          Amphiphilic polymers are used…

•   as dispersants
•   as stabilizer of emulsions
•   as stabilizer of foams
•   to control the rheology of a solution
•   as antiredeposition agents
•   etc
                         General
• Small amphiphiles, surfactants, are needed in the dynamic
  processes, such as
  - foaming
  - wetting
  - emulsification

• Larger amphiphiles, surface active polymers, are good at
  stabilizing dispersed systems

• The two are often used together. (Nature often uses a
  combination of a polar lipid and a surface active
  macromolecule to make stable emulsions and foams.)
The structure of lignin (according to Adler)
Is lignin surface active?
Surface activity of lignins from black liquors

                                              Lignin Derivatives
                         70
 Surface Tension, mN/m



                              Typical Surfactant
                                                          UNICAL
                         60


                         50                  INDULIN C



                         40

                                                          ¿CMC?
                         30
                                     CMC
                                                             ¿CMC ?
                         20
                          0,0001   0,001   0,01     0,1      1     10   100

                                           Concentration, w%
                          But …

• the pH-sensitivity is a big problem
• only the dissociated form of Kraft lignin can be regarded
  to be surface active
• the pKa of guaiacol is around 10
Formation of lignosulfonates in the sulfite
            pulping process




                 Carbocation
      Lignin                    Lignosulfonate
                 intermediate
Lignosulfonate
The lignosulfonate obtained from the sulfite
            process is not pure

                                                   Softwood Hardwood

           Spent sulfite liquor   Lignosulfonate       58 %     55 %
             Lignosulfonate
              intermediate
                                  Hexoses              20 %      7%
                                  Pentoses              8%      20 %
                                  Organic acids         6%      10 %
                                  Ash                   8%       8%


   Difference in:
                                              Softwood and hardwood
   - chemical composition
                                              lignosulfonate can be processed to
   - molecular weight
                                              have the same performance
   - degree of sulphonation
       Lignosulfonates are mainly used as
                  dispersants
• Plasticizer in making concrete

        Amount
                                             Adsorbed
                                             on cement
              In solution




                                        Molecular
                                        weight
• Grinding agent in cement production
• Drilling mud additive
  - removes the cuttings
  - lubricates and cools the bit
• Dispersant for dyes

• Dispersant for carbon black

• Dispersant for pesticides

• Dispersant for ceramics
             A dispersing agent must…

• anchor to the solid particle

• repel the particle from other dispersant-covered particles
There are two mechanisms for stabilization of
                dispersions

 1. Electrostatic stabilization
2. Steric stabilization
  A lignosulfonate can be regarded as a poly-
electrolyte, providing electrostatic stabilization
                     100.00
                                                    50 vol% alumina, 0.50% CP
                                                    55 vol% alumina, 0.35% LS
                            10.00                   55 vol% alumina, 0.25% PAA
         Viscosity (Pa s)




                                                                                   Uncharged comb polymer
                             1.00
                                                                                   Lignosulfonate
                                                                                   Poly(acrylic acid)

                             0.10




                             0.01
                                    0.1   1.0           10.0       100.0         1000.0
                                                Shear rate (s-1)


QCM measurements showed that while the comb copolymer gave a thick
layer (6.4 nm), the lignosulfonate and the poly(acrylic acid) formed thin
layers at the surface (0.6 and 0.5 nm, respectively).

				
DOCUMENT INFO
Shared By:
Categories:
Stats:
views:23
posted:4/28/2011
language:Swedish
pages:24