Maria Mucha

Polymer composites based on gypsum matrix

The role of polymers as retarder additives is to prolong the workability connected with setting time of gypsum. Various cellulose derivatives, soluble in water in concentration up to 1,5% by weight were applied taking different water/binder ratio. The hydration process of calcium sulfate hemihydrate (gypsum binder) into dihydrate (gypsum plaster) was observed by setting and calorimetric techniques. Scanning electron microscopy confirmed that the gypsum microstructure was varied when polymers are used. The mechanical properties of gypsum plasters were studied by bending strength test and they are correlated with sample microstructure

Activation energy of copper-induced thermal degradation of chitosan acetate functional groups

Abstract Thin films of chitosan acetate (CSA)-copper (II) [Cu (II)] complex were prepared by mixing Cu (II) oxide (CuO) nanoparticles in acetic acid solution of chitosan and the casting method. The changes in chemical structure of modified chitosan were confirmed by UV-Vis spectroscopy. Fourier transform infrared (FTIR) spectroscopy was applied to monitor thermal degradation processes occurring in chitosan and its composites with Cu. The changes in concentration of chitosan functional groups were observed. On a base of the kinetic constants of group thermal degradation at various temperatures, the activation energies for various groups were calculated. It was found that the presence of Cu (II) ions accelerates the thermal degradation of chitosan acetate. The higher the Cu (II) content was in the CSA matrix, the lower was the activation energy.

Analysis of mesophase formation in side-chain liquid crystalline polycarbosilanes

This paper is concerned with an analysis of the thermodynamics and kinetics of mesophase formation by cooling from the isotropic state of side-chain liquid crystalline polycarbosilanes containing spacers in the range from 3 to 11 CH2-groups. The polymers are characterized by their thermotropic behaviour as far as temperature, enthalpy and entropy of the transitions are concerned. The kinetics was followed by optical and calorimetric methods. Longer spacer length leads to more perfect ordering in the mesophase, higher isotropization temperatures, and lower glass transition temperatures. The Avrami and Ozawa formalism to describe the transition kinetics to the mesophase from the isotropic state cannot be interpreted as the nucleation and growth mechanism known from crystallization.

Hydroxyethyl methyl cellulose as a modifier of gypsum properties

The study is focused on the influence of a water-soluble polymer (in weight fraction up to 1.5%), cellulose derivatives—hydroxyethyl 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.

CHITOSAN APPLIED FOR GYPSUM MODIFICATION

In order to improve the properties of gypsum materials, including workability, mechanical strength and ability to retain water, various admixtures (also polymers), known as plasticisers, have been applied. These polymers can be soluble in water, such as cellulose and starch ethers, or unsoluble applied in a form of dispersion up to 5% of weight fraction. The admixtures are added into initial water and mixed with hemihydrate calcium sulphate in a proper ratio. In the hydration process of the hemihydrate into dehydrate, a crystallisation process leading to gypsum setting occurs. In the present work, a chitosan sample of DD=85% in two forms was applied: dissolved in 1% acetic acid and as a water dispersion in the weight fraction up to 1% of the gypsum matrix. The water to gypsum ratios of 0.6 or 0.74 was applied. The influence of chitosan on the rate of setting and kinetics of crystallisation of gypsum was investigated and discussed. The morphological structure of the resulting gypsum sample was examined using SEM microscopy. In the presented results, chitosan in the form of a 1% dispersion was a setting retardant and it changed the morphological structure of gypsum. However, mechanical tests showed a decrease of bending strength. When chitosan was applied as a biomaterial, the chitosan content in the composite was equal to 10%, and thus a compressing strength increased. The presence of PVA (polyvinyl alcohol) in the gypsum matrix caused a small effect on gypsum setting in contrast to PVAc (polyvinyl acetate), which is a good admixture for both cement and gypsum [2,3].

CHITOSAN/POLY(VINYL ALCOHOL) HYDROGELS AS CONTROLLED DRUG DELIVERY SYSTEMS

In order to achieve hydrogel and drug release profiles, a comprehensive knowledge of the types, properties and syntheses of hydrogel polymer networks are needed. For this reason, a natural biopolymer hydrogel based on chitosan was described. Chitosan has many advantages, which meet the requirements necessary for the preparation of medical materials; for example, wound dressings. This article focused on the biomedical use of a chitosan hydrogel: chitosan– poly(vinyl alcohol) (PVA). The method of preparation of hydrogels containing a drug as an active wound dressing was described. To obtain a hydrogel dressing to be applied in patients with burns or difficult curative wounds, gentamicin (an aminoglycoside antibiotic) was used as a medicament. The effect of the PVA concentration in hydrogels on the release rate of the antibiotic was examined. For this, the crosslinking agent of the hydrogel, glutaraldehyde, was used. The release process of gentamicin was described by using an equation of first order kinetics.