Structure of the polymer:
Prepared under heterogeneous conditions by reaction of vinylsulfonate and insoluble cellulose (Michael Addition). The properties of the polymer can be varried in wide range by changing the conditions during the reaction.
- mean molecular weight 132,600 g/mol
- weigthed molecular weigth 765,900 g/mol
- degree of substitution of 0.42.
- solid white sodium salt
- viscosity (aqueous solution of 2 % SEC, 20 °C): 1860 mPa·s
- delivered with a moisture of 4.6 %
- biodegradable
- long-term storage under dry conditions is possible
- derivative of the world´s most important renewable resource: cellulose
SEC can be easily produced in large technical scale in constant quality.
For practical use the mechanical stability of the capsules is of great interest.
Mechanical stability here should be defined as the maximum force a capsule can
stand without bursting.
Mechanically stable capsules with bursting forces up to 7 N were obtained by using
more than 2 % (w/w) SEC and more than 4 % (w/w) PDADMAC.
In the case of Chitosan a maximum stability of 4.4 N is obtained at 3.5 % (w/w) SEC
and 8 % (w/w) chitosan.
Figure: picture of a cross section of the membrane (REM exposure)
Hollow beads with good mechanical stability on basis of polyelectrolyte-polyelectrolyte-complexes (symplexes) could be formed with SEC as a polyanion. Preparation of hollow beads on basis of Sulfoethylcellulose (SEC) and Polydiallyldimethylammoniumchloride (PDADMAC) or Chitosan was done with very good results.
Capsules are prepared by dripping an aqueous solution of the anionic SEC into
a stirred aqueous solution of a polycation like
Polydiallyldimethylammoniumchloride (PDADMAC) or
Chitosan (Poly-[ß-(1,4)-2-amino-2-desoxy-D-gluco-pyranose]).
Hollow beads can be made at room temperature by dripping an aqueous mixture
of the polyanion SEC and the cells, enzymes, etc. into a stirred precipitation bath
with the polycation. The membrane is formed in a fast reaction between the polyanion
and the polycation on the surface of the droplet (polyelectrolyte-polyelectrolyte-complex).
The core of the capsule containing the bioactive material remains in liquid state.
SEC capsules and hollow beads were tested for encapsulation of the fungus Hirsutella rhossiliensis for biological pest control of nematodes. The encapsulation did no harm to the fungus.
Hollow beads of 0.15 to 5 mm can be prepared by dripping techniques. Beside this fibres or irregular forms can be made by means of extrusion.
(no entry yet)
Applications
Hollow beads on basis of the polyelectrolyte Sulfoethylcellulose (SEC) for
encapsulation of a nematophagous fungus for use in biocontrol.
Another possible application is the microencapsulation of bioactive materials like cells, bacteria, enzymes, etc. under moderate conditions for use in biotechnology or environmental technology.
Probably SEC is even allowed for food application.
Rose, T., Neumann, B., Thielking, H., Koch, W. and Vorlop, K.-D. (2000).
Hollow beads of Sulfoethylcellulose (SEC) on basis of polyelectrolyte complexes.
Chemical Engineering & Technology (in press)
Thomas Rose, Klaus-D. Vorlop
Institute of Technology
Federal Agricultural Research Centre (FAL)
Bundesallee 50, D - 38116 Braunschweig, Germany
Phone: + 49 531 - 596 511
Fax : + 49 531 - 596 363
e-mail: tec@fal.de