The study is focused on the influence of a water-soluble polymer (in weight fraction up to 1.5%), cellulose derivativeshydroxyethyl methyl cellulose, on gypsum properties. Gypsum setting involves two processes: gypsum hydration/crystallization and probably formation of a polymer film in material pores. The processes are studied by various methods such as setting time and mechanical measurements, scanning electron microscopy and differential scanning calorimetry. The additive acts as a retarder (an increase in setting time), and it modifies the morphology of calcium sulfate dihydrate crystals, leading to the change in mechanical properties-an increase in bending stress. The mechanism of gypsum crystal growth during hemihydrate hydration is predicted to be a nucleation control process (the Avrami equation is applied). The value of nucleation rate constant decreases with an increasing additive content.
The poly(lactic acid), PLA, mixed with nanosilver in solution easily forms nanocomposite in solid state (after solvent evaporation), which was proved by UV-Vis spectroscopy. This work focuses on photodegradation occurring in PLA films doped with nanosilver. The changes in chemical structure of photodegraded PLA has been determined using FTIR spectroscopy. Differential scanning calorimetry of UV-irradiated PLA samples provided information on polymer glass transition and crystallization/melting processes. It was found that PLA alone is more sensitive to photodegradation than PLA/silver nanocomposites. The mechanism of nanocomposite photodegradation and effect of nanosilver was discussed.
Pastes based on gypsum (calcium sulphate hemihydrate) and two chosen water-soluble polymer admixtures, i.e. hydroxyethylmethyl cellulose (HEMC) and poly(vinyl acetate) (PVAC) were prepared. The impacts of the polymers on gypsum setting, as well as thermal and mechanical properties were studied. Heat effect and the rate of setting depending on water to gypsum ratio and the presence of admixtures were measured. The results have shown a strong effect of the polymer admixture (1%) on the prolongation of gypsum setting time. The presence of polymer molecules in water solution hinders the crystallization process of gypsum dihydrate. HEMC and PVAC have also a significant influence on gypsum mechanical properties especially at low water content. Kinetics of the setting process of gypsum hemihydrate is discussed.
The paper presents various structural forms of chitosan for medical applications. These are films and microgranules for transdermal and oral application of active substances and porous scaffolds constituting support for the regenerating cells in bone tissue engineering. Tested porous systems were obtained by lyophilization or electrolytic method. Methods of sample preparation and the morphology analyses were presented. The influence of water on properties of transdermal systems and changes in release kinetics of active substances for microgranules and films under modification of their structures, were carried out.
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