a Preparation of functional polyHIPE polymers for agro-process and bio-process applications

Abstract

Porous polymers containing specific functional groups are attracting scientific interest due to their diverse applications. Polymerized high internal phase emulsions, or polyHIPEs are porous polymers which can be moulded into beads, membranes, films or monoliths. The characteristics of polyHIPEs are their low density, internal pore architecture and interconnectivity along with their high porosity which make them extensively applicable in separation processes, medicine and tissue engineering, agriculture and catalyst supports. However, the major drawback in exploiting the full potential of these polymers is that most of the techniques carried out for functionalization concentrate on their external surfaces. This thesis describes the development of functionalized polyHIPEs as catalyst supports and agricultural soil additive. Firstly, this work highlights the preparation, sulphonation and characterization of polyHIPE polymers. Sulphonation via microwave irradiation enhances the polyHIPE morphology whilst increasing the specific surface area. PolyHIPEs produced with low surface area (ca. 9 m2/g) were successfully enhanced to 110 m2/g without compromising their mechanical stability. Subsequently, these sulphonated polyHIPEs exhibited hydrophilic behaviour capable of absorbing up to 1700 times their own weight of water. These polyHIPEs also demonstrated good ion exchange capacity of 3.4 meq/g. They were further tested for catalytic biofilm growth with Shewanella Oneidensis MR-1 and the hierarchical structure of the pores and interconnects facilitated the transport into the material. These sulphonated polyHIPEs with high ion exchange capacity, hydrophilicity and thermal stability suggest potential application as a catalyst support. In addition, surface area with good bio-compatibility also suggests agricultural application. Secondly, to further increase the specific surface area hypercrosslinked polyHIPEs were synthesized and functionalized. PolyHIPEs were prepared using a novel approach of depositing the metal catalyst at the synthesis stage. The incorporation of the catalyst precursor before polymerization into a monolithic ii support was demonstrated for the first time. This method enables homogenous distribution of the catalyst throughout the open cellular structure imparting catalytic functionalization. We showed catalyst size can be controlled and BET surface area up to 911 m2/g can be achieved by varying the homogenization time. These catalytic hypercrosslinked polymers with accessible porosity and transport pores can remove diffusional barriers for the reactants and products. However, addition of porogens and hypercrosslinking reduces the mechanical and thermal properties of the polyHIPEs. Hypercrosslinked sulphonated polyHIPEs were more robust than those prepared with porogens. Finally, the sulphonated polyHIPEs were investigated for their water absorption capacity in sandy loam and clay loam soils. Addition of small quantities of these polyHIPEs improved the hydrological properties in both the soils. Incorporation of 1% of SPHPA10 polyHIPEs had significant effect on soil water retention characteristics in sandy loam soils, resulting in 3 fold increase in moisture content at field capacity as compared to the control. The most intensive impact in readily available water capacity (RAWC) was seen in 0.5% polyHIPE treatment in both sandy loam and clay loam soils which showed increased retention capacity of 68.9% and 52.8% respectively. The experiments suggest that application of lower levels of SPHPA10 polyHIPEs (0.25-0.5%) may be recommended in both type of soils.