Polyisobutene/polycyclohexyl methacrylate interpenetrating polymer networks

Interpenetrating polymer networks (IPNs) combining polyisobutene (PIB) and poly(cyclohexyl methacrylate) (PCHMA) networks were prepared using an in situ strategy. PIB networks were formed by alcohol-isocyanate addition between the hydroxyl end groups of telechelic dihydroxypolyisobutene and an isocyanate cross-linker, catalyzed by dibutyltindilaurate (DBTDL). PCHMA networks were obtained from free-radical copolymerization of cyclohexyl methacrylate (CHMA) with ethylene glycol bismethacrylate (EGDM) in the presence of dicyclohexyl peroxydicarbonate (DCPD) as the initiator. The network formations into the IPN architecture were followed by FTIR spectroscopy. In a large composition range, transparent IPNs exhibit two mechanical relaxation temperatures as determined by dynamic mechanical thermal analysis (DMTA), corresponding to those of a PIB enriched phase and of one interpenetrating phase containing the PCHMA network. This morphology was confirmed by IPN surface analysis by AFM. As expected, mechanical properties of PIB networks are improved by the presence of PCHMA network in such IPN architectures.     

Stress influence on the deformation mechanisms of tetragonal zirconia polycrystals

The influence of stress on deformation mechanisms of tetragonal zirconia polycrystals (TZP) has been studied by constant strain rate tests and creep tests. It has been shown that the deformation results from two mechanisms: (1) a low-stress mechanism where the strain rate is proportional to σ²/d (where d is grain size) and (2) a high-stress mechanism with strain rate proportional to σ/d³. These results are discussed, taking into consideration the possible role of the vitreous phase on the diffusion mechanisms.     

Challenges to surface water quality in mid‐sized African cities: conclusions from Awetu‐Kito Rivers in Jimma,south‐west Ethiopia

Rapid urbanization and industrialization, uncontrolled population growth, indiscriminate waste discharge and poor infrastructure are problems that African cities are facing. This paper describes an exemplary case study from Jimma, south‐west Ethiopia. A cross‐sectional study was conducted along the Awetu‐Kito drainage system in Jimma town to assess the level of pollution from urban dwellers and related activities. The study indicates that the Environmental Protection Agency (EPA) norms for biochemical oxygen demand (BOD), dissolved oxygen (DO) and orthophosphates are not met downstream of the major industrial and institutional activities. Small‐scale industries, Jimma University and residential areas contributed 50, 15 and 23% pollution load on the river, respectively. It can be concluded that the pollution effect in Jimma town is mainly as a result of the growing (uncontrolled) industrial activities and not to discharge of household wastewater. Given the same trends of urbanization and population growth, similar development (socio‐economic) indicators and similar climatic conditions, the key findings for Jimma are transferable to other mid‐sized African cities.