Synthesis of poly(N-isopropylacrylamide-co-acrylic acid) model compounds for filtration experiments

 

Theoretical development within solid/liquid separation in colloidal systems is largely based on inorganic, low charged and incompressible particles. These do not reflect the properties in biosolid/organic systems. There is therefore a need for a development of colloidal and particles which mimic these biosolid/organic systems and thereby make a basis for further theoretical development with respect to filtration.

 

Poly(N-isopropylacrylamide-co-acrylic acid) microgels are synthesized by free-radical surfactant free emulsion polymerization as an organic model system for biosolids. The model system is investigated by titration, differential scanning calorimetry (DSC) and capillary rheometry. The titration experiments indicates that the polymerization is a block copolymerization and the DSC result show that the blocks of poly(N-isopropylacrylamide) are not randomly distributed in the microgels. Capillary rheometry indicates that the blocks of poly(acrylic acid) are placed on the surface of the microgels. The combination of these three results reveal that the microgels have a core mainly consisting of poly(N-isopropylacrylamide) and a diffuse/cloudy surface consisting mainly of poly(acrylic acid).

 

The core/shell structure of the microgels is a good model for Danish sewage sludge which consists of a core of microcolonies and a shell of extracellular polymer substance (EPS). EPS  combined with microcolonies is a highly charged (0.5-2 mmol/g) material. This property is modeled by the microgels by using varying concentrations of acrylic acid as co-monomer. The microgels have a charge density between 0.2 and 0.9 mmol/g.

 

Preliminary filtration experiments show that filtration properties of the microgel model system significantly differs from the properties for inorganic colloidals such as titaniumdioxid.