Miscibility and morphology of chiral semicrystalline poly-(R)-(3-hydroxybutyrate)/chitosan and poly-(R)-(3-hydroxybutyrate-co-3-hydroxyvalerate)/chitosan blends studied with DSC, 1H T1 and T1ρ CRAMPS

The phase structure of poly-(R)-(3-hydroxybutyrate) (PHB)/chitosan and poly-(R)-(3-hydroxybutyrateco-3-hydroxyvalerate) (P(HB-co-HV))/chitosan blends were studied with H-1 CRAMPS (combined rotation and multiple pulse spectroscopy). H-1 T-1 was measured with a modified BR24 sequence that yielded an intensity decay to zero mode rather than the traditional inversion-recovery mode. H-1 T-1p was measured with a 40-kHz spin-lock pulse inserted between the initial 90degrees pulse and the BR24 pulse train. The chemical shift scale is referenced to the methyl group of PHB as 1.27 ppm relative to tetramethylsilane (TMS) based on 1H liquid NMR of PHB. Single exponential T-1 decay is observed for the beta-hydrogen of PHB or P(HB-co-HV) at 5.4 ppm and for the chitosan at 3.7 ppm. T-1 values of the blends are either faster than or intermediate to those of the plain polymers. The T-1rho decay of beta-hydrogen is bi-exponential. The slow T-1rho decay component is interpreted as the crystalline phase of PHB or P(HB-co-HV). The degree of crystallinity decreases with increasing wt % of chitosan in the blend. The fast T-1rho, of P-hydrogen and the T-1rho of chitosan in the blends either follow the same trend as or faster than the weight-averaged values based on the T-1rho, of the plain polymers. Together with the observation by differential scanning calorimeter (DSC) of a melting point depression and one effective glass transition temperature in the blends, the experimental evidence strongly suggests that chitosan is miscible with either PHB or P(HB-co-HV) at all compositions. (C) 2002 Wiley Periodicals, Inc.