Polyamide-based composite membranes: Part 1. Preparation and characterization

The miscibility, crystallinity and morphology of membranes from polyamides/poly(vinylalcohol) (PAs/PVA) blend materials were studied at various weight fractions and various crystallization temperatures. The blend systems of PA6/PVA, PA66/PVA, PA69/PVA and PA610/PVA can be written as: AxB1−n/AyC1−y, where A, B and C are the hydrocarbon chain, amide and methyl hydroxide segments, respectively, and x and y are the molar fractions of the corresponding segments in the repeating units of the polymers. The experimental approaches utilized differential scanning calorimetry, Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy. The Flory-Huggins interaction parameter X12 and the segmental interaction parameters X′AB, X′AC and X′BC were calculated following a developed Ellis approach. The equilibrium melting temperatures of polyamides in the blends were obtained using Hoffman-Weeks plots, and the interaction parameters were calculated using the Nishi-Wang equation, which is based on the Flory-Huggins theory. The values of the Flory-Huggins interaction parameters X12 were negative, and the values of the segmental interaction parameters X′AB and X′AC were positive, whereas the X′BC value was negative. FTIR was used to study the hydrogen bonding that enhances the miscibility of the blends. Significant upward shifts of vNH were observed with increasing the volume fraction of the second polymer (Ф2). The negative values of the interaction parameters and the shifts in the NH frequency reflect the miscibility of the blend systems. The solubility parameters of the polymeric materials can be employed to choose polymeric materials for the RO membranes. Both high-pressure mercury porosity and scanning electron microscopy results are presented.