Polymeric properties and metal extraction performance of poly (vinyl chloride)/Aliquat 336 polymer inclusion membanes and electrospun fibres

This thesis aimed to investigate the polymeric properties and the metal extraction performance of polyvinyl chloride (PVC) and Aliquat 336 polymer inclusion membranes (PIMs) and electrospun fibres. The PIMs and the electrospun fibres were prepared using PVC and Aliquat 336 as the base polymer and extractant, respectively. The results showed that PVC/Aliquat 336 PIMs were non-homogenous and phase separated at sub micrometre scale even though all PIMs were transparent and homogenous to the naked eye or upon microscopic examination by scanning electron microscopy. The surface morphology of PIMs showed smooth surface with no apparent pores for PIMs with less than 30 wt.% Aliquat 336. Above 30 wt.% Aliquat 336, the PIMs showed some wrinkles and it became obvious as the Aliquat 336 content reach 40 wt.% suggesting that it might contain two separate domains. The phase separation was confirmed by the DMA results where the glass transition (Tg) and the melting temperature (Tm) of separated PVC and Aliquat 336 rich phases was clearly identified. This two phases is assigned to the α transition and β transition respectively. But, the later transition was not detected by DSC due to small changes in heat capacity where it could only be used to determine the Tg of PIMs with low Aliquat 336 content. For the PIMs observed here, the Tg was independent of Aliquat 336. This result indicates that Aliquat 336 does not act as a plasticising reagent in PIMs even though it has successfully produced a transparent and flexible thin film. The phase separation nature of PVC/Aliquat 336 PIMs has important implication towards the metal ion extraction performance in which the metal ions extraction could only occur when the proportion of Aliquat 336 exceeded 30 wt.%. This Aliquat 336 content of 30 wt.% also coincide with the appearance of Aliquat 336 rich phase observed by DMA. In addition, results from impedance study showed that PIMs with less than 30 wt.% Aliquat 336 were far out from the ideal plot and were not suitable to be used as a solid state polymer-electrolyte for metal ions extraction. This is due to the high resistance and low conductivity of the PIMs film. However, the metal extraction rate can also be improved by increasing the extraction temperature which increases the diffusivities in Aliquat 336 phase. The impact of aging on PVC/Aliquat 336 PIMs was also investigated in this thesis work. The results showed that freshly prepared PIMs contain residual tetrahydrofuran (THF) which was used as solvent for membrane manufacture. Removal of some residual THF by membrane aging resulted in notable changes in the thermomechanical properties of the PIMs where the PIMs exhibited two thermal transitions over the same range temperature. Although there is a clear impact of aging on membrane properties, there is no significant impact on the extraction of Cd(II) by PVC/Aliquat 336 PIMs. The preparation of electrospun fibres from PVC and Aliquat 336 was also demonstrated in this study. A detailed thermomechanical characterisation revealed that key characteristics and properties of PVC/Aliquat 336 PIMs and electrospun fibres differ significantly. The PVC/Aliquat 336 electrospun fibres were homogenous at sub micrometre scale. The homogeneity of PVC/Aliquat 336 electrospun fibres was confirmed by a single transition that is an α transition observed using DMA. Furthermore, the Aliquat 336 in electrospun fibres could function as a plasticizer. This was confirmed by the appearance of a single Tg that decreased with the increasing of Aliquat 336 content. In terms of metal ion extraction, the extraction of Cd(II) increased with the increasing of Aliquat 336 content. There was a significant extraction even at low Aliquat 336 content (i.e., 6 wt.%). In contrast, the extraction of Cd(II) in PIMs needs to exceed the percolation threshold of 30 wt.% Aliquat content. Besides, results from extraction capacity showed that electrospun fibres have higher absorption capacity compared to PIMs which clarify why they have better extraction. On the other hand, it appears that the applied voltage might influence the formation of beads and fibres diameters of PVC/Aliquat 336 electrospun mats but the level of significance may varies with the polymer concentration and tip distance or in this case Aliquat 336 concentration