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

The paper is devoted to the description of specific differences of water tr ansport between petroleum-based ('petro' polymers) and environmentally frie ndly polymers ('green' polymers). The differences in water transport mechan isms are presented for poly-R-(3-hydroxybutyrate) and its blends with low d ensity polyethylene (68-100 Wt%) on the chemical and crystalline levels. Th e water diffusion coefficients and permeabilities were obtained using vacuu m quartz spring microbalance techniques and permeability cells at 25 degree s C. Spectral characteristics were obtained with FTIR procedure (IFS-48 Bru cker IR spectrometer). ESR spectra for Tempol spin probe (sensitive to pola r sites in polymer) are presented using Radiopan spectrometer within the te mperature range of 20-75 degrees C. As a result of polymer manufacture proc ess, the accumulation of hydrophilic embedded groups is observed in petropo lymers (PELD, PP, synthetic rubbers, etc.) which results in the water sorpt ion increase and the effective diffusivity decrease. The immobilization of water both on polar polymeric groups and on impurities leads to an essentia l decrease in water molecule mobility. Due to their soft natural origin, th is situation is less typical for green polymers. The effect of hydrophilic groups on water permeability was demonstrated for PHB/LDPE blends. Narrow M W distribution, stereo regularity and rigid order of polymeric fragments ma ke for a more perfect crystalline structure as compared with petro polymers . The crystalline structure perfection leads to the decrease of water diffu sivities as was shown for PHB. ESR data elucidate the relationship between the isotropic/textured PHB crystalline structure and spin probe rotating mo bility. The study of the transport features in petro and green polymers is the necessary stage of investigation of such basic processes as physical ag ing at high humidity and corrosive stability of polymer membranes. The resu lts may promote the design of novel environmentally friendly membranes for desalination and separation processes.