Expansion of Polystyrene Using Water as the Blowing Agent

The expansion of polystyrene using water as the blowing agent has been investigated. Hydrophilic particles are dispersed in styrene before the suspension polymerization. During this polymerization the necessary amount of water is absorbed and/or adsorbed by these additives. The different additives used in this work are ordinary corn starch and high-amylose starch, zeolite A and Y, and SiO2. Factors that influence the density and the morphology of the expanded product are the type of additive, the additive and water content, the polymerization conditions, and the expansion procedure. High frequency electric field heating and hot air have been used for the expansion. The lowest density is obtained with high frequency electric field heating.

Structural and rheological properties of methacrylamide modified gelatin hydrogels

Dynamic shear oscillation measurements at small strain were used to characterize the viscoelastic properties and related differences in the molecular structure of hydrogels based on gelatin methacrylamide. Gelatin was derivatized with methacrylamide side groups and was subsequently cross-linked by radical polymerization via photoinitiation. The light treatment of methacrylamide gelatin solutions resulted in the production of hydrogel films with high storage modulus (G'). Mechanical spectra and thermal scanning rheology of the obtained hydrogels are described. The temperature scan of the network below and above melting point of gelatin allowed us to identify the respective contributions of chemical and physical cross-linkage to the hydrogel elastic modulus. The results indicate that the rheological properties of the gelatin-based hydrogels can be controlled by the degree of substitution, polymer concentration, initiator concentration, and UV irradiation conditions.

Comparison of the enthalpy state of vesicles of different size by their interaction with alpha-lactalbumin

The characteristics of small unilamellar, large unilamellar and large multilamellar vesicles of dimyristoylphosphatidylcholine and their interaction with alpha-lactalbumin are compared at pH 4. (1) By differential scanning calorimetry and from steady-state fluorescence anisotropy data of the lipophilic probe 1,6-diphenyl-1,3,5-hexatriene it is shown that the transition characteristics of the phospholipids in the large unilamellar vesicles resemble more those of the multilamellar vesicles than of the small unilamellar vesicles. (2) The size and composition of the lipid-protein complex formed with alpha-lactalbumin around the transition temperature of the lipid are independent of the vesicle type used. Fluorescence anisotropy data indicate that in this complex the motions of the lipid molecules are strongly restricted in the presence of alpha-lactalbumin. (3) The previous data and a comparison of the enthalpy changes, delta H, of the interaction of the three vesicle types with alpha-lactalbumin allow us to derive that the enthalpy state of the small unilamellar vesicles just below 24 degrees C is about 24 kJ/mol lipid higher than the enthalpy state of both large vesicle types at the same temperature. The abrupt transition from endothermic to exothermic delta H values around 24 degrees C for large vesicles approximates the transition enthalpy of the pure phospholipid.