Delonix regia galactomannan hydrolysates: Rheological behavior and physicochemical characterization.

The galactomannan extracted from Delonix regia (DRGM) seeds was hydrolyzed at different enzyme dosages and reaction times. A linear relation between inverse Molecular weight (Mn) and hydrolysis time was obtained, and the Mn reduction was controlled from 4.86 × 105 to 1.95 × 105 Da. The hydrolysis does not affect galactomannan structure as observed by FT-IR and DRX, maintaining an amorphous structure with only a slight increase in galactose:mannose relationship as observed by 1H NMR. A rheological behavior shift was observed below Mn = 4.15 × 105 Da when viscoelastic behavior changes from a weak gel to a macromolecular solution in a 3% (w/v) galactomannan hydrolysate. Shear viscosity of 3% (w/v) galactomannan dispersion in water follows closely a power law equation where the consistency index decreased, and the flow behavior index increased with increasing hydrolysis degree. These results indicate the conditions for obtaining specific viscoelastic properties of DRGM dispersions for specific applications by a careful control of the enzymatic hydrolysis process.

Synthesis and characterization of new polyimides from diphenylpyrene dianhydride and ortho methyl substituted diamines.

Three new polyimides were synthesized via one-step polycondensation from 3,8-diphenylpyrene-1,2,6,7-tetracarboxylic dianhydride (DPPD) with two diamines with ortho methyl substitution (MBDAM and HFI) and one diamine without ortho substituents (BAPHF). The effect of diamine structure in DPPD based polyimides' physical, thermal, mechanical and gas transport properties has been studied. The polyimide structure was confirmed by FTIR and 1H NMR. All polymers show high thermal stability with decomposition temperatures above 493 °C, and glass transition temperatures above 336 °C. Changes in packing density of polyimide membranes were assessed by wide angle X-ray diffraction and correlated to fractional free volume FFV. Polyimides based on rigid DPPD dianhydride exhibited an improved gas permeability and selectivity when ortho methyl substituents are present in the diamine used for polyimide synthesis. DPPD-MBDAM polyimide showed the best gas productivity values with 565 barrer CO2 permeability and a selectivity of 16 for CO2/CH4.

Synthesis of HMDI-based segmented polyurethanes and their use in the manufacture of elastomeric composites for cardiovascular applications.

For short-term cardiovascular application, segmented polyurethanes (SPUs) based on 4,4-methylenebis(cyclohexyl isocyanate) (HMDI), polytetramethylenglycol (PTMG) and 1,4-butanediol (BD) were synthesized and characterized by spectroscopy (FT-IR, (1)H-NMR) and thermal (TGA, DMA, DSC) and mechanical techniques. The segmented nature of the SPUs was not easily established by spectroscopic means; however, TGA allowed the quantification of the rigid segments content by the significant mass loss between 348 and 356 degrees C. The alpha transition was detected by DMA and related to the T(g) of the soft segments at -50 degrees C, while DSC showed the presence of an endothermic transition above 80 degrees C attributed to the melting of rigid segments. Two types of composites were prepared using the synthesized SPUs and Lycra (either T162B or T162C). The first one consisted of a two layers casting laminated while the second one was a classic unidirectional fibre-reinforced material. Laminate composites prepared with SPU containing 23.9% and 33.9% of rigid segments and Lycra T162C exhibited a higher tensile modulus but lower tensile strength than composites prepared with Tecoflex SG-80A (39.7% of rigid segments). The energy of adhesion between layers on these composites ranged from 475 to 2150 J. Fibre-reinforced SPUs exhibited higher moduli than the two layer laminated composites with increasing amounts of rigid segments in the matrix and by increasing Lycra T162C content (up to 10%). This behaviour was explained by SEM, which showed a good fibre-matrix bonding.