Abstract Segmented polyurethanes based on poly(l-lactide)diol - PLLA, poly(ethylene-glycol) - PEG, poly(trimethylene-carbonate)diol - PTMC and hexamethylene diisocyanate were synthesized by a two-step polyaddition. Polyurethanes with variable compositions and molar mass were semi-crystalline and presented PLLA or PLLA + PEG crystalline phases and a heterogeneous amorphous phase. Sequential crystallization of PLLA and PEG resulted in a confined PEG crystallization into the PLLA crystalline phase. The random distribution of the segments in the polymer chains and the partial miscibility of the segments in the amorphous phase strongly influenced the morphology of the crystalline phase, and the kinetics of the crystallization. Morphology changed from not well-defined spherulites with Maltese cross to ring banded spherulites and axialites as the PLLA mass fraction decreased. PLLA nucleation and crystal growth rates varied with crystallization temperature similarly to homopolymers, presenting a bell-shaped curve, and the temperature for the maximum growth rate dependent on the polyurethanes composition.

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.

Compostos orgânicos e inorgânicos, tais como óxidos, sais de metais, compostos policíclicos e azo, são freqüentemente usados como colorantes para polímeros. O pigmento vanadato de bismuto vem sendo usado como uma alternativa a pigmentos baseados em cádmio. Corantes baseados na antraquinona pertencem a classe de colorantes policíclicos amplamente usados em polímeros. Além de suas características como colorantes, o vanadato de bismuto e colorantes a base de antraquinona apresentam atividade fotocatalítica ou propriedades fotoquímicas que podem influenciar o mecanismo e a cinética de fotodegradação do polímero que o contem. Neste trabalho estudou-se a influencia do pigmento vanadato de bismuto e de um corante a base de antraquinona sobre a fotodegradação do policarbonato. Para tanto, amostras de policarbonato contendo os colorantes foram submetidas a envelhecimento fotoquímico de acordo com as recomendações da ASTM G53. Os resultados indicaram que o vanadato de bismuto acelera a fotodegradação do policarbonato, causando uma acentuada perda nas propriedades mecânicas e aumento na concentração de hidroperóxido durante o envelhecimento. As características relacionadas a cor do pigmento também foram alteradas. O comportamento do policarbonato contendo o vanadato de bismuto frente a fotodegradação é atribuído a possíveis reações envolvendo o polímero e o pigmento promovidas pela radiação UV. Por outro lado, a presença de um corante a base de antraquinona aparentemente estabilizou o policarbonato frente à fotodegradação através de um mecanismo de desativação de estados excitados no policarbonato.

Both inorganic and organic compounds, such as oxides or salts of metals and polycyclic and azo compounds, are frequently used as colorants in polymeric systems. Bismuth vanadate pigment has been used as an environmentally friendly alternative for cadmium containing pigments and anthraquinone dyes represent a polycyclic colorant class of wide use in polymers. Besides their coloring properties, both bismuth vanadate and anthraquinone present photocatalytic activity or photochemical properties that can influence the mechanism and the kinetics of the photodegradation of the polymer into which they are incorporated. In this paper the influence of bismuth vanadate pigment and anthraquinone dye on the photodegradation of polycarbonate was evaluated. For this purpose, samples of polycarbonate containing the colorants were submitted to photochemical aging following the recommendations of ASTM G53. Bismuth vanadate accelerates the photodegradation of polycarbonate, causing a faster drop in the mechanical properties and an increase in the hydroperoxide concentration during the aging process. The coloring ability of the pigment is also affected. The photodegradation behavior of polycarbonate in presence of bismuth vanadate may be caused by a possible direct chemical reaction between pigment and polymer, promoted by UV radiation. On the other hand, the presence of anthraquinone dye seems to stabilize the polycarbonate against photodegradation through a deactivation mechanism of the excited state.

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.

Poly(3-hydroxybutyrate) (PHB) is a thermoplastic polyester with a great potential owing to its biodegradability, bioreabsorbation and biological synthesis from a renewable source. Despite these characteristics, the applications of this polymer are very restricted due to its poor mechanical properties and thermal instability at temperatures above its melting point (around 175°C). Among the possibilities of improvement of these materials, the development of blends is a relatively fast and inexpensive option. Poly(epsilon-caprolactone) (PCL) is a semi-crystalline polymer that may be used as a biomaterial. It presents good mechanical properties, a low melting point (around 55 °C), and could be a good option to develop PHB blends, maintaining the biodegradability and bioreabsorption properties. The objective of the present work was to obtain blends of PHB and PCL by melting mixture in an internal mixer. The compositions varied from 0 to 30 wt% of PCL. DSC, DMA, and SEM were used to characterize the blends. The blends were found to be imiscible with no indication of interaction either the amorphous or crystalline state. The morphology shows PHB as the matrix and PCL as the dispersed phase.

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.

Este trabalho tem como objetivo avaliar a degradação térmica e fotooxidativa do terpolímero poli (acrilonitrila-butadieno-estireno), ABS, utilizado em componentes internos de automóveis. Corpos de prova de ABS moldados por injeção foram submetidos ao envelhecimento térmico, segundo a norma ASTM D794, e ao envelhecimento fotooxidativo segundo as normas ASTM G24 e G53. As amostras envelhecidas foram submetidas às análises dinâmico-mecânica, e microscópicas por microscopia de força atômica no modo não contato. Os resultados mostraram que as transições, tanto da fase vítrea quanto da fase elastomérica na superfície do ABS, são afetadas pela degradação. As áreas dos picos das curvas de módulo de perda em função da temperatura relativos às transições vítreas do ABS foram correlacionadas ao alongamento na ruptura, em função do tempo e tipo de envelhecimento. As propriedades mecânicas são influenciadas de forma mais acentuada pela extensão da degradação da matriz. O método de envelhecimento ASTM G24 mostrou-se mais agressivo que o G53, seja para a fase BR ou para a fase SAN. As imagens microscópicas mostraram que os diferentes envelhecimentos provocaram diferentes variações na rugosidade das superfícies. Amostras fotooxidadas, com perda de alongamento maior que 50%, foram reprocessadas e mostraram uma recuperação superior a 90% nessa propriedade.

The aim of this work is the evaluation of thermal and photo-oxidative degradation of the terpolymer acrylonitrile-butadiene-styrene, ABS, used in internal automotive components. Injection molded specimens were aged by ASTM D794, ASTM G24 and ASTM G53 standards. The aged test specimens were studied by means of dynamic mechanical analysis and non-contact atomic force microscopy. The results revealed that the transitions of the glass and rubber phases were affected by the degradation. The area under linear loss modulus-temperature curves was related to tensile properties in function of the aging time and standard test method. The degradation of the matrix had a higher influence on the mechanical properties. Both, PB and SAN phases, were more affected when the ASTM G24 standard test method was used. Microscopy images showed that the different ageing methods cause different changes on the surface roughess. The results showed that an ABS that had lost 50 % of rupture elongation has this property almost regenerated (90 %) after being reprocessed.

A degradação do ABS foi avaliada após envelhecimento térmico (ASTM D794) e fotooxidativo (ASTM G53 e G24). Essas condições foram escolhidas na tentativa de simular as condições a que esse polímero é submetido durante seu ciclo de vida como componente automobilístico. As mudanças ocorridas no ABS envelhecido pelos três métodos, em diferentes tempos, foram caracterizadas por ensaios mecânicos de tração e impacto, pelo índice de fluidez, pelo índice de carbonilas (FT-IR), pelo índice de amarelecimento e por fotografias ampliadas das fraturas de impacto. Os resultados mostraram que cada técnica utilizada fornece uma resposta característica em função do método de envelhecimento utilizado. A aplicação de técnicas de análise multivariada aos resultados permitiu uma visualização da degradação do material em função das técnicas de envelhecimento.

The ABS degradation was investigated after thermal- (80°C) and photo-oxidative ageing (ASTM G53 and G24). These conditions were selected to simulate a car interior and the ABS lifetime weatherability. ABS changes were characterised by mechanical properties, melt flow index, carbonyl index (FT-IR), yellowing index and macro-photography of impact fracture. The results showed that each technique gives a characteristically answer for the ageing method. The multivariate analysis provided the degradation view as a function of the ageing method.