Water transport phenomena in `green and `petrochemical polymers. Differences and similarities

The paper is devoted to the description of specific differences of water transport between petroleum-based (`petroʹ polymers) and environmentally friendly polymers (`greenʹ polymers). The differences in water transport mechanisms are presented for poly-R-(3-hydroxybutyrate) and its blends with low density polyethylene (68¯100 wt%) on the chemical and crystalline levels. The water diffusion coefficients and permeabilities were obtained using vacuum quartz spring microbalance techniques and permeability cells at 25°C. Spectral characteristics were obtained with FTIR procedure (IFS-48 Brucker IR spectrometer). ESR spectra for Tempol spin probe (sensitive to polar sites in polymer) are presented using Radiopan spectrometer within the temperature range of 20¯75°C. As a result of polymer manufacture process, the accumulation of hydrophilic embedded groups is observed in petropolymers (PELD, PP, synthetic rubbers, etc.) which results in the water sorption increase and the effective diffusivity decrease. The immobilization of water both on polar polymeric groups and on impurities leads to an essential decrease in water molecule mobility. Due to their soft natural origin, this situation is less typical for green polymers. The effect of hydrophilic groups on water permeability was demonstrated for PHB/LDPE blends. Narrow MW distribution, stereo regularity and rigid order of polymeric fragments make for a more perfect crystalline structure as compared with petro polymers. The crystalline structure perfection leads to the decrease of water diffusivities as was shown for PHB. ESR data elucidate the relationship between the isotropic/textured PHB crystalline structure and spin probe rotating mobility. The study of the transport features in petro and green polymers is the necessary stage of investigation of such basic processes as physical aging at high humidity and corrosive stability of polymer membranes. The results may promote the design of novel environmentally friendly membranes for desalination and separation processes.