Effect of hydrothermal treatment on the gelatinisation properties of potato starch as measured by differential scanning calorimetry

Gelatinisation temperatures as a function of moisture content were determined for potato starch. The native starch was then hydrothermally treated at a temperature 3% (Kelvin degrees) below the gelatinisation peak temperature and at moisture levels varying from 20 to 67% (by weight). Gelatinisation temperatures, temperature ranges and enthalpy values were affected for all treated samples. However, two sample populations could be distinguished: those samples treated under limited moisture conditions and other samples treated in the presence of extragranular moisture. A two-step hydrothermal treatment further increased the gelatinisation temperature, but the effect of the second step was small in comparison to that of the first.We thank the Belgian Nationaal Fonds voor Wetenschappelijk Onderzoek for research positions as aspirant (H. Jacobs) and post-doctoraal onderzoeker (R. C. Eerlingen).     

The effect of water content on the ultimate properties of rubbery nanocomposite gels

An investigation was conducted into the effects of water content (R) on the ultimate tensile properties of nanocomposite hydrogels (NC gels) based on poly(N‐isopropylacrylamide)/clay networks. Rubbery NC gels with low clay contents (<NC10) exhibited unique changes in their stress–strain curves, depending on the R. At high R, where PNIPA chains are fully hydrated, NC gels retained their rubbery tensile properties, whereas they changed to exhibit plastic‐like deformations with decreasing R. Consequently, for a series of NC gels with different R, a failure envelope was obtained by connecting the rupture points in the stress–strain curves. Here, the counterclockwise movement was observed as either the R decreased or the strain rate increased. This seemed to be analogous to that of a conventional elastomer (e.g., SBR), although the mechanisms are different in the two cases. From the R and C_clay dependences of the ultimate properties, three critical values of R were defined, where R showed a maximum strain at break, a steep increase in initial modulus, and onset of brittle fracture. Compared with NC gels, OR gels (chemically crosslinked hydrogels) showed similar but very small changes in their stress–strain curves on altering R, whereas LR (viscous PNIPA solution) showed a monotonic decrease (increase) in ε_b (E_i) with decreasing R. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2328–2340, 2009     

Synthesis,characterization, effect of architecture on crystallization,and spherulitic growth of poly(L‐lactide)‐b‐poly(ethylene oxide) copolymers with different branch arms

Well‐defined poly(L ‐lactide)‐b‐poly(ethylene oxide) (PLLA‐b‐PEO) copolymers with different branch arms were synthesized via the controlled ring‐opening polymerization of L ‐lactide followed by a coupling reaction with carboxyl‐terminated poly(ethylene oxide) (PEO); these copolymers included both star‐shaped copolymers having four arms (4sPLLA‐b‐PEO) and six arms (6sPLLA‐b‐PEO) and linear analogues having one arm (LPLLA‐b‐PEO) and two arms (2LPLLA‐b‐PEO). The maximal melting point, cold‐crystallization temperature, and degree of crystallinity (X_c) of the poly(L ‐lactide) (PLLA) block within PLLA‐b‐PEO decreased as the branch arm number increased, whereas X_c of the PEO block within the copolymers inversely increased. This was mainly attributed to the relatively decreasing arm length ratio of PLLA to PEO, which resulted in various PLLA crystallization effects restricting the PEO block. These results indicated that both the PLLA and PEO blocks within the block copolymers mutually influenced each other, and the crystallization of both the PLLA and PEO blocks within the PLLA‐b‐PEO copolymers could be adjusted through both the branch arm number and the arm length of each block. Moreover, the spherulitic growth rate (G) decreased as the branch arm number increased: G_{6sPLLA‐b‐PEO} < G_{4sPLLA‐b‐PEO} < G_{2LPLLA‐b‐PEO} < G_{LPLLA‐b‐PEO}. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2034–2044, 2006     

The effect of zinc(II) on the growth of <Emphasis Type="Italic">E . coli</Emphasis> studied by microcalorimetry

By using an LKB2277 Bioactivity Monitor, stop-flow mode, the power-time curves of E . coli at 37°C effected by zinc(II) were determined. Some parameters, such as growth rate constants k, inhibitory ratio I, the maximum heat production rate P _max heat output Q and the time in the maximum heat production t _max were obtained. According these parameters, we found that a low concentration of zinc(II) had a promoting action on the growth of E. coli, but a high concentration of zinc(II) had an inhibitory action. The toxicity of zinc(II) can also be expressed as half inhibitory concentration IC ₅₀ of zinc(II), i.e., 50% effective in this inhibition. The value of IC ₅₀ of zinc(II) on E. coliis 28.09 µg mL^-1. The assay is quantitative, inexpensive and versatile.