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Because of their biocompatibility and total biodegradability, poly(3-hydroxybutyrate) (PHB) and starch have attracted attention as promising raw materials for manufacture of single-use plastic items and biomaterials. PHB/ maize starch blends with starch contents in the range of 0 -50 wt % were processed in an internal mixer, and their compression-molded films were characterized by tensile tests, X-ray diffraction, thermogravimetric analysis, wettability measurements, and scanning electron microscopy. Water and glycerol were used as plasticizers. The results indicated that the thermal degradation behavior of the blends were similar to that of pure PHB films. All the blends showed heterogeneous morphology, wherein starch granules were dispersed in continuous PHB-rich matrix. Despite the decrease in elongation at break and tensile strength, starch incorporation of up to 30 wt % into PHB matrix resulted in materials as hard as pure PHB films, but exhibiting less crystallinity and more hydrophilic character, which might lead to a higher biodegradation rate.

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Reactions of pentacyanonitrosylferrate(2-), ((NC),FeN02", nitroprusside) with hydroxylamine and azide were examined.With azide at pH 6, N2 and N,0 are produced according to the equation (NC)sFeN*Q2' + *NNN" + H20 = (NC)S-FeH203" + N2 + *NN*0. The rate law for the first step, the formation of a nitrosyl-azide adduct, I, is assumed to be d[I] /df = fcla[(NC)sFeN02'] [N3~], with ki& = 0.2 AT1 sec"1 at pH 6, T= 23°. This adduct decomposes to give (NC)S-FeH203" (Xmax 455 nm, e 460 M~l cm"1), N2, and N20; and the rate law is assumed to be -d[I]/df = Ar^fl]; k^i s approximately 0.2 sec"1 at pH 6, 7= 23°. The complex (NC)sFeH203' dimerizes to (NC)10Fe,6" (Xmax 395 nm, e 940M"1 cm"1). In excess azide the dimer reacts to form (NC)sFeN34~(Xmax 440 nm, e 1400 M'1 cm"1); the rate law is d[(NC)5-FeN34"]/df = fc2[(NC)10Fe26"][N3"], with kt = 1.0 (±0.1) X 102 M"1 sec"1 at pH 6, 7=23°. £°for the couple (NC)S-FeN33" + e" = (NC)sFeN34" is-0.3 (±0.1) V and (NC)5FeN34" is oxidized by 02 according to the equation d[(NC)s-FeN33']/dí = fc3[(NC)5FeN34"][02], with k3 = 3.0 (±0.7) X 102 M~' sec"1 at pH 6,7=23°. Hydroxylamine reacts with (NC)jFeNO2" according to the equation (NC)5FeN02" + *NH2 *OH + OH" = (NC)sFeH203" + N*N*0 + H20. An intermediate, 3 (Xmax 445 nm, e 700 M'1 cm"1), is formed, the rate law being d[J]/df = k4a[(NC)5FeN02"][NH20H][0H"], with &4a = 4.5 X 10s M~2 sec"1 at 25°a nd£a = 9.5 ± 1.0 kcal/mol. The possibility exists that J is (NC)5FeN203". Subsequent reactions occurred which were not quantitatively examined. It is apparent from these studies that the stability of pentacyanoferrate(II) complexes toward oxygen oxidation is strongly dependent on the rr-accepting ability of the sixth ligand.

ABSTRACT:The gelatinization and extrusion processes of corn starch were studied. Differential scanning calorimetry was used to determine the gelatinization temperature as a function of the water content. Plasticized corn starch was processed in single-and twin-screw extruders to produce thermoplastic materials. The mechanical properties of the films obtained in the twin-screw extruder with the addition of different quantities of water were evaluated. Dynamic mechanical analysis applied to thermoplastic starch samples obtained with 33% (w/w) total plasticizers showed two transitions, attributed to the presence of two phases in the starch-glycerol-water system.

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