Characterization of physical and viscoelastic properties of polymer films for coating applications under different temperature of drying and storage

Preparation of Poly(acrylic acid-acrylamide/starch) Composite and Its Adsorption Properties for Mercury (II)

The poly(acrylic acid-acrylamide/starch) composite was synthesized by solution polymerization, aiming to adsorb mercury (II) in water. The resulted copolymer was characterized by particle size exclusion chromatography (SEC), Fourier transform infrared spectroscopy (FTIR), thermogravimetry (TG), scanning electron microscopy (SEM) and dynamic light scattering particle size analyzer (DLS). It turned out that starch was successfully incorporated with the macromolecular polymer matrix and played a key role for improving the performance of the composites. These characterization results showed that the graft copolymer exhibited narrow molecular weight distribution, rough but uniform morphology, good thermal stability and narrow particle size distribution. The graft copolymer was used to remove Hg(II) ions from aqueous solution. The effects of contact time, pH value, initial mercury (II) concentration and temperature on the adsorption capacity of Hg(II) ions were researched. It was found that after 120 min of interaction, poly(acrylic acid-acrylamide/starch) composite achieved the maximum adsorption capacity of 19.23 mg·g⁻¹ to Hg(II) ions with initial concentration of 15 mg·L⁻¹, pH of 5.5 at 45 °C. Compared with other studies with the same purpose, the composites synthesized in this study present high adsorption properties for Hg(II) ion in dilute solution. The adsorption kinetics of Hg(II) on the poly(acrylic acid-acrylamide/starch) composite fits well with the pseudo second order model.

Tribomechanical Comparison between PVA Hydrogels Obtained Using Different Processing Conditions and Human Cartilage

Designing materials for cartilage replacement raises several challenges due to the complexity of the natural tissue and its unique tribomechanical properties. Poly(vinyl alcohol) (PVA) hydrogels have been explored for such purpose since they are biocompatible, present high chemical stability, and their properties may be tailored through different strategies. In this work, the influence of preparation conditions of PVA hydrogels on its morphology, water absorption capacity, thermotropic behavior, mechanical properties, and tribological performance was evaluated and compared with those of human cartilage (HC). The hydrogels were obtained by cast-drying (CD) and freeze-thawing (FT), in various conditions. It was found that the method of preparation of the PVA hydrogels critically affects their microstructure and performance. CD gels presented a denser structure, absorbed less water, were stiffer, dissipated less energy, and withstood higher loads than FT gels. Moreover, they led to friction coefficients against stainless steel comparable with those of HC. Overall, CD hydrogels had a closer performance to natural HC, when compared to FT ones.

Determination of the Shear Modulus of Thin Polymer Films with a Quartz Crystal Microbalance: Application to UV-Curing

The photoinduced curing of a light-sensitive varnish was followed, based on a change of the film's shear modulus, G, as determined with a quartz crystal microbalance (QCM). The film thickness was in the range of a few hundred nanometers. Both the storage modulus, G', and the loss modulus, G″, were obtained. The analysis is based on a perturbation calculation. The equations differ from the more commonly used set of equations derived from the small-load approximation and the acoustic multilayer formalism (sometimes termed Voigt-model). The discussion revisits assumptions, accuracy, and limits of the technique. Critical to the analysis is a knowledge of the thickness of the electrode underneath the film.

Physicochemical and thermomechanical characterization of tara gum edible films: effect of polyols as plasticizers

The aim of this study was to evaluate tara gum as edible film material as well as the influence of polyols as plasticizers on the properties of the films. Thermomechanical, physicochemical and barrier properties were determined as a function of plasticizer type and concentration. Glycerol, sorbitol and PEG 400 were used in the range of 0.075-0.3g/tarag. Glycerol was the best plasticizer in terms of mechanical properties with the highest elongation (16-44%) and resistance (45-90 MPa). Sorbitol presented the best barrier properties with the lowest hydrophilicity and water vapour permeability (0.24-0.34 g mm m(-2)h(-1) kPa(-1)). Fourier transform infrared (FTIR) spectroscopy showed no significant effect on the structure of the polysaccharide. Dynamic mechanical analysis (DMA) revealed that incorporation of plasticizers increased the mobility of the polymer chains and reduced the glass transition and melting temperature by 30 and 100 °C respectively.

Comprehensive study of dynamic curing effect on tablet coating structure

The dissolution method is still widely used to determine curing end-points to ensure long-term stability of film coatings. Nevertheless, the process of curing has not yet been fully investigated. For the first time, joint techniques were used to elucidate the mechanisms of dynamic curing over time from ethylcellulose (Aquacoat)-based coated tablets. X-ray micro-computed tomography (XμCT), Near Infrared (NIR), and Raman spectroscopies as well as X-ray microdiffraction were employed as non-destructive techniques to perform direct measurements on tablets. All techniques indicated that after a dynamic curing period of 4h, reproducible drug release can be achieved and no changes in the microstructure of the coating were any longer detected. XμCT analysis highlighted the reduced internal porosity, while both NIR and Raman measurements showed that spectral information remained unaltered after further curing. X-ray microdiffraction revealed densification of the coating layer with a decrease in the overall coating thickness of about 10 μm as a result of curing. In addition, coating heterogeneity attributed to cetyl alcohol was observed from microscopic images and Raman analysis. This observation was confirmed by X-ray microdiffraction that showed that crystalline cetyl alcohol melted and spread over the coating surface with curing. Prior to curing, X-ray microdiffraction also revealed the existence of two coating zones differing in crystalline cetyl alcohol and sodium lauryl sulfate concentrations which could be explained by migration of these constituents within the coating layer. Therefore, the use of non-destructive techniques allowed new insights into tablet coating structures and provided precise determination of the curing end-point compared to traditional dissolution testing. This thorough study may open up new possibilities for process and formulation control.

Pharmaceutical applications of dynamic mechanical thermal analysis

The successful development of polymeric drug delivery and biomedical devices requires a comprehensive understanding of the viscoleastic properties of polymers as these have been shown to directly affect clinical efficacy. Dynamic mechanical thermal analysis (DMTA) is an accessible and versatile analytical technique in which an oscillating stress or strain is applied to a sample as a function of oscillatory frequency and temperature. Through cyclic application of a non-destructive stress or strain, a comprehensive understanding of the viscoelastic properties of polymers may be obtained. In this review, we provide a concise overview of the theory of DMTA and the basic instrumental/operating principles. Moreover, the application of DMTA for the characterization of solid pharmaceutical and biomedical systems has been discussed in detail. In particular we have described the potential of DMTA to measure and understand relaxation transitions and miscibility in binary and higher-order systems and describe the more recent applications of the technique for this purpose.

Dynamic mechanical thermal analysis of hypromellose 2910 free films

It is common practice to coat oral solid dosage forms with polymeric materials for controlled release purposes or for practical and aesthetic reasons. Good knowledge of thermo-mechanical film properties or their variation as a function of polymer grade, type and amount of additives or preparation method is of prime importance in developing solid dosage forms. This work focused on the dynamic mechanical thermal characteristics of free films of hypromellose 2910 (also known as HPMC), prepared using three grades of this polymer from two different manufacturers, in order to assess whether polymer chain length or origin affects the mechanical or thermo-mechanical properties of the final films. Hypromellose free films were obtained by casting their aqueous solutions prepared at a specific concentrations in order to obtain the same viscosity for each. The films were stored at room temperature until dried and then examined using a dynamic mechanical analyser. The results of the frequency scans showed no significant differences in the mechanical moduli E' and E″ of the different samples when analysed at room temperature; however, the grade of the polymer affected material transitions during the heating process. Glass transition temperature, apparent activation energy and fragility parameters depended on polymer chain length, while the material brand showed little impact on film performance.