Maria Isabel Felisberti

Mechanical behaviour and biocompatibility of poly(1-vinyl-2-pyrrolidinone)–gelatin IPN hydrogels

IPN hydrogels based on poly(1-vinyl-2-pyrrolidinone) and gelatin were obtained by casting of aqueous solution using potassium persulphate and glutaraldehyde as respective crosslinking agents. Studies of swelling and mechanical behaviour showed that the samples of different composition can incorporate high content of water and still exhibit high compression strength. The composition has influence at the global crosslinking density what affects the mechanical performance. In vitro biocompatibility and hemocompatibility were also investigated. The materials do not interfere on the cellular functions and neither induce platelet adhesion. From this preliminary evaluation, it is possible to conclude that these hydrogels have potential for applications in the biomedical field.

Poly(vinyl alcohol) and poly(vinyl pyrrolidone) blends : miscibility, microheterogeneity and free volume change

Abstract Blends of crystallizable poly(vinyl alcohol) (PVA) with poly(vinyl pyrrolidone) (PVP) were studied by differential scanning calorimetry (d.s.c.). PVA with different degrees of hydrolysis (88 and 99 wt%) and PVP with different molecular weights (10 000 and 360 000 g mol−1) were used. The blends exhibited a single glass transition, as determined by d.s.c., suggesting the miscibility of the system over the whole composition range studied. The enthalpy of fusion (ΔHf), as well as the glass transition temperature (Tg), heat capacity (ΔCp) and glass transition width (Δw), were also determined by d.s.c. These parameters changed with the degree of hydrolysis of PVA, PVP molecular weight and blend composition. The behaviour of ΔCp vs blend composition was complex for the different pairs of blends, suggesting strong interaction between PVA and PVP. From the analysis of Δw dependence on blend composition we concluded that blends containing PVP of 10 000 g mol−1 exhibit a larger number of relaxations than blends containing high molecular weight PVP, indicating that the density of interactions is larger in the former.

Unsaturated polyester resins: influence of the styrene concentration on the miscibility and mechanical properties

Styrene is frequently used as comonomer for unsaturated polyester (UP) resins. Variations in the styrene content in the polyester affect the resulting properties. Dynamic mechanical tests show the phase separation in the cured resin with an increase of styrene concentration. The dependence of the glass transition temperature of the UP resin on the styrene content is complex and reflects a balance of elastic forces of the network and the immiscibility of polystyrene and UP. The thermal stability and the mechanical properties are governed by the phase behaviour of the mixture and therefore can be controlled by the styrene content.

Miscibility, crystallinity and morphological behavior of binary blends of poly(ethylene oxide) and poly(methyl vinyl ether–maleic acid)

DSC and optical microscopy were used to determine the miscibility and crystallinity of blends of poly(ethylene oxide) (PEO) with poly(methyl vinyl ether–co–maleic acid) (PMVE–MAc). Single Tg was observed for all blends, indicating miscibility. The dependence of Tg on the weight per cent of PEO presents a negative deviation from linearity at high PEO content, associated to a greater blend free volume, mobility and flexibility than in pure PEO. A progressive decrease in the degree of crystallinity and in the size of the PEO spherullites as the PMVE–MAc is added is observed. FTIR provided evidence of specific interaction between the polymers.

Comportamento dinâmico-mecânico e relaxações em polímeros e blendas poliméricas

Dynamic mechanical analysis (DMA) is widely used in materials characterization. In this work, we briefly introduce the main concepts related to this technique such as, linear and non-linear viscoelasticity, relaxation time, response of material when it is submitted to a sinusoidal or other periodic stress. Moreover, the main applications of this technique in polymers and polymer blends are also presented. The discussion includes: phase behavior, crystallization; spectrum of relaxation as a function of frequency or temperature; correlation between the material damping and its acoustic and mechanical properties.

Thermal, mechanical and electrochemical behaviour of poly(vinyl chloride)/ polypyrrole blends (PVC/PPy)

Abstract The conductivity, thermal, mechanical and electrochemical properties of poly(vinyl chloride)/polypyrrole blends are described in this paper. These blends were prepared by oxidative chemical polymerization of pyrrole, in the vapour phase, in PVC films impregnated with FeCl3. They were characterized by attenuated total reflectance FT i.r. spectra, differential scanning calorimetry and dynamic-mechanical analysis. Infrared reflectance spectra suggested that the polymerization occurs preferentially on the matrix surface producing sandwich-type structures. The mechanical, thermal and conducting behaviour showed a dependence on (1) initial concentration of FeCl3 in the matrix and (2) exposition time to pyrrole vapour. By cyclic voltammetry we observe that blends synthesized by oxidative chemical polymerization show electrochemical properties similar to blends prepared by electrochemical methods. Their conductivity varies from 10−4 to 10−1 S cm−1. Dynamic-mechanical analysis results suggest a certain degree of miscibility among the polymeric components of the blend.

Blends of polyaniline with nitrilic rubber

Nitrilic rubbers containing 29 or 45% of acrylonitrile were blended with polyaniline doped with different acids (chloridric, dodecylbenzenesulfonic, tetrapropylbenzenesulfonic, and p-toluenesulfonic acids). The blends were prepared by mechanical mixing in a roll-mill and vulcanized in a hot press. The volumetric conductivities and mechanical properties were evaluated. The results show that the polyaniline concentration strongly affects the behavior of the blends. Increasing the polyaniline content from 50 to 100 phr induces an increase in the electric conductivity from 10−10 to 10−8 S cm−1; however, the blends become harder and more brittle than the crude rubber. Addition of polyaniline lowered the crosslinking degree, but produced a reinforcing effect in the elastomer.

Ação de colorantes na degradação e estabilização de polímeros

Dyes and pigments are additives used in polymers to improve mainly the aesthetic properties of the material. However, the incorporation of these additives can directly affect polymer stability. The colorants can drastically decrease the lifetime and the performance of the material or can act as a stabilizer, improving significantly the stability of the polymer against degradation. Interaction between colorants and polymers is the cause of the stability changes. Some mechanisms are proposed to explain the action of colorants on polymers. However it is difficult to foresee this action without experiments. This work reviews the main mechanisms involved in the degradation and stabilization of polymers containing colorants.

BLENDAS DE PHB E SEUS COPOLÍMEROS: MISCIBILIDADE E COMPATIBILIDADE

Poly(hydroxybutyrate) and its copolymers are linear polyesters behaving as conventional thermoplastic materials. However, they are totally biodegradable and produced by a wide variety of bacteria from renewable sources. Some properties and high production cost are still preventing future applications. In an attempt to improve the properties and to reduce cost blending PHB with others polymeric materials is one of the most efficient method. In this paper, miscibility, compatibility, morphological and mechanical aspects of PHB blends will be reviewed. An extensive revision over twenty last years was realized about works of blends based on PHB and its copolymers.

Blendas de PHB e seus copolímeros: miscibilidade e compatibilidade

Poly(hydroxybutyrate) and its copolymers are linear polyesters behaving as conventional thermoplastic materials. However, they are totally biodegradable and produced by a wide variety of bacteria from renewable sources. Some properties and high production cost are still preventing future applications. In an attempt to improve the properties and to reduce cost blending PHB with others polymeric materials is one of the most efficient method. In this paper, miscibility, compatibility, morphological and mechanical aspects of PHB blends will be reviewed. An extensive revision over twenty last years was realized about works of blends based on PHB and its copolymers.