Abstract Polymer processing parameters may considerably affect final product characteristic as, if properly chosen, these parameters may lead to products with optimal properties. The aim of this work is to evaluate the rheological characteristics of poly(ethylene terephthalate) (PET) by torque rheometry, as well as to estimate its incipient degradation rate during processing in an internal laboratory mixer. In order to estimate the temperature coefficient of the viscosity (β), and the pseudoplasticity index (n) of PET, two sets of experiments need to be performed. In the first one, the polymer is processed at three different temperatures at a single rotor speed for 10 min, getting temperature coefficient of the viscosity equal to β = 0.053 °C-1. In the second set of experiments, the resin (PET) is processed at a single temperature at six different rotor speeds for the same time interval and the pseudoplasticity index was determined, n = 0.78. From the results obtained, it is possible to indicate the internal mixer as an equipment not only for mixing polymers or composites, but as a tool for determining important rheological variables for predicting degradative processes.
Abstract The rheological behavior of poly (butylene adipate-co-terephthalate) (PBAT) and its composites prepared with three different organoclays was investigated. Composites containing up to 7.5%, w/w organoclay, were prepared by two routes: (a) direct melt blending in an internal laboratory mixer with high intensity rotors and (b) concentrates (prepared in the internal mixer) with 50 %, by weight, of the organoclays diluted in a co-rotating twin screw extruder equipped with a high intensity mixing thread operating at a nominal speed of 480 rpm. The samples were characterized by both torque and parallel plate rheometry. Results indicate that nanodispersions in the clay layers were obtained during processing and that, like the pure matrix, at high shear rates, the organoclay compounds follow the power law, although with higher viscosity. It is believed that the interaction of the polymer with the organoclay is responsible for the increase in melt viscosity (observed by increases in torque and relaxation time) of the hybrid systems.
ABSTRACT The melt crystallization characteristics of a compound of coconut lignocellulosic fibers dispersed in poly(butylene adipate terephthalate) (PBAT), a fully biodegradable copolyester matrix, was studied by differential scanning calorimetry (DSC). PBAT/coconut fiber compounds with 10% and 20% filler content were prepared in a laboratory internal mixer; torque rheometry showed negligible degradation during processing. Nonisothermal melt crystallization of the matrix was thoroughly studied by DSC in 10% compounds at cooling rates between 2 and 32°C/min, and quantitative information was provided on crystallization temperatures and rates, as well as the crystallinity developed, which turned out to be higher than expected at the high cooling rates. Crystallization kinetic results were correlated using classical macrokinetic Pseudo-Avrami, Ozawa, and Mo models, in order to obtain quantitative analytical expressions appropriate for processing applications. Pseudo-Avrami and Mo models were found to represent well the experimental data. A detailed analysis of the model fitting is presented, in order to assess the expected uncertainties. Despite its failings at the onset and end of the crystallization process, Mo model is recommended as best overall empirical correlation of the experimental data for the intended purpose.
RESUMO Os parâmetros da cristalização a partir do fundido de um composto de fibras lignocelulósicas de côco dispersas em poli (butileno adipato tereftalato) (PBAT), uma matriz de copoliéster totalmente biodegradável, foi estudada por calorimetria exploratória diferencial (DSC). Os compostos de PBAT/fibra de côco com 10% e 20% de fibra foram preparados num misturador interno de laboratório; a reometria de torque mostrou degradação insignificante durante o processamento. A cristalização não-isotérmica a partir do fundido da matriz foi estudada por DSC em compostos com 10% de fibra com taxas de resfriamento entre 2 e 32°C/min, e informações quantitativas foram fornecidas em temperaturas e taxas de cristalização, bem como a cristalinidade desenvolvida, que apresentou valor maior do que o esperado nas altas taxas de resfriamento. Os resultados cinéticos da cristalização foram correlacionados usando modelos clássicos macrocinéticos: Pseudo-Avrami, Ozawa e Mo, para obter expressões analíticas quantitativas apropriadas para o processamento. Os modelos Pseudo-Avrami e Mo representaram bem os dados experimentais. Uma análise detalhada da modelagem é apresentada, a fim de avaliar as incertezas esperadas. Apesar de desvios observados no início e no final do processo de cristalização, o modelo Mo é recomendado como a melhor correlação empírica geral dos dados experimentais para o propósito pretendido.
Abstract Nonisothermal crystallization and melting of the biodegradable thermoplastics poly(3-hydroxybutyrate) (PHB), poly(butylene adipate-co-terephthalate) (PBAT), and a 1:1 PHB/PBAT blend were investigated by differential scanning calorimetry (DSC) over an extensive range of heating/cooling rates (2 to 64°C/min). The different phase transition behavior of the neat components was reflected in the mixture and suggest an immiscible blend. Pseudo-Avrami, Ozawa and Mo classical macrokinetic models were used to describe the evolution of the melt crystallization process. Results suggest that none of these models could be used to predict the experimental results of crystallization kinetics of the blend with sufficient precision for polymer processing applications. However, some methods may be of used for the neat resins over restricted ranges of cooling rate, temperature or conversion (e.g., Ozawa for PHB at low cooling rate, Mo for PBAT).
Abstract Compounds of poly(3-hydroxybutyrate) (PHB) and titanium dioxide (TiO2) with filler content between 1% and 10% were prepared in a laboratory internal mixer. The effect of heating and cooling rates on the crystallization and melting of PHB/TiO2 compounds was investigated by differential scanning calorimetry (DSC). Melt and cold crystallization rates rise with increasing cooling/heating rates. A higher cooling rate translates to a lower melt crystallization temperature, while a higher heating rate results in a higher cold crystallization temperature. TiO2 promotes melt crystallization of PHB, behaving as a nucleant agent. The total crystallinity developed after melt and cold crystallization decreases for low levels of TiO2, i.e. 2% per weight, and is almost independent of the heating/cooling rate. The melting temperatures and rates are minimally affected by both the heating rate and filler content. The results suggest that the desired PHB microstructure can be controlled by filler content and adjusted heating/cooling rate.
PHB has interesting features such as biodegradability, sustainability and durability. However, it has a high cost, in addition to being hard, brittle and thermally unstable during processing. Therefore, it was found convenient to study the crystallization of PHB/20% babassu compounds, with the intention of reducing the cost of the composite, in addition to seeking improvements in thermal properties. In this work, the parameters of melt crystallization were studied for PHB/20% babassu compounds driven at different cooling rates under a nitrogen flow. Subsequently, crystallization parameters were compared for different cooling rates. A kinetic analysis of data obtained for melt crystallization was performed. Among the models studied, Pseudo-Avrami showed the best correlation with experimental data, with discrepancy between +6% and -4%. The Mo model presented a discrepancy between +15% and -8%. A modified Mo model discrepancies are reduced to +3% and -4% within the range of validity of the model.
ABSTRACT PHB/TiO2 and PHB/ZnO compounds were prepared in a laboratory internal mixer. Crystallization was investigated by differential scanning calorimetry (DSC) with heating and cooling rates ranging from 5 to 30 °C/min. Fractured surface of selected samples was analysed by scanning electron microscopy (SEM). From the SEM images, it was observed that ZnO and TiO2 nanoparticles were properly dispersed in the PHB matrix. DSC studies revealed that the addition of TiO2 and ZnO changed the temperature and crystallization rate but did not affect the total crystallinity significantly. In general, TiO2 behaved as nucleating agent greatly influencing the PHB crystallization.
RESUMO Foram preparados compósitos PHB/TiO2 e PHB/ZnO num misturador interno de laboratório, a cristalização foi investigada por calorimetria exploratória diferencial (DSC), com taxas de aquecimento e resfriamento entre 5 e 30 °C/min e a superfície de fratura de seletas composições analisada por microscopia eletrônica de varredura (MEV). Através das imagens de MEV foi observado que as nanopartículas de ZnO e TiO2 estão bem dispersas na matriz de PHB. Por DSC, observou-se que a adição de TiO2 e ZnO modificou a temperatura e taxa de cristalização do PHB, sem afetar significativamente a cristalinidade total. Em geral, a adição da carga TiO2 promoveu alterações mais significativas na matriz de PHB, comportando-se como um agente nucleante.
The present work is concerned with the photodegradation and photostabilization of poly(3-hydroxybutyrate) (PHB) biopolymer. Two commercial grades of PHB were investigated, containing of 4.0% and 6.2% of hydroxyvalerate (HV) comonomer, named PHB1 and PHB2, respectively. Injection moulded specimens were exposed to ultraviolet radiation (UV-A) in the laboratory for periods of up to 12 weeks and then characterized by tensile testing, surface appearance, size exclusion chromatography (SEC), and scanning electron microscopy (SEM). The exposure to UV radiation caused great damaged on the surface color, reduction of molecular size and mechanical properties. The effects were more pronounced on PHB2, probably due a lighter surface color and less packed macromolecular structure which facilitates the transmission of light throughout the samples. Specimens of PHB1 were also injected with the addition of a UV absorber and antioxidant, resulting in a higher UV stability of PHB, as shown by a low reduction in molar mass and better mechanical properties.
ABSTRACT The addition of natural fiber is a biodegradable polymer matrix has been an alternative for composites having enhanced thermal and mechanical properties. Considering that the properties of the composite can be influenced by the processing conditions, type and concentration of the dispersed phase, this study aimed to obtain composites from a commercial blend made of Poly (butylene adipate co-terephthalate) - PBAT / Starch (EB), of biodegradable character, and rice husk (CA). Initially composites were prepared PBAT / starch containing 10, 20 and 30% (CA) using a dual extruder and internal mixer screw. Subsequently, there were certain mechanical and thermal properties of the systems obtained. The results of mechanical properties showed that the elastic modulus of the composite was affected by the type of employee processing the composites obtained in the extruder have a higher modulus than the composite obtained in the mixer: 92% higher in composites with 10% load and 38% higher in composites with 30% filler. The impact resistance decreased significantly and the tensile strength increased moderately with rice husk content, regardless of the type of processing used. The impact resistance of composites with 30% load is approximately 33% the impact resistance of the pure blend. In the tensile strength, there was a 25% increase in the composite with 30% filler. SEM analyzes indicated that the filler particles were adequately wetted by the matrix and the adhesion load / matrix was good. The evaluation of the results obtained with the DSC analysis indicated that the addition of CA in the extruded composite alter the crystallization temperature ranging from 75 ° C pure sample to 101ºC for samples with rice husk, as a result attributable to the nucleating effect caused by the greater this type of load dispersion processing.
RESUMO A adição de fibras naturais a uma matriz de polímero biodegradável tem sido uma alternativa para obter compósitos com melhores propriedades térmicas e mecânicas. Tendo em vista que as propriedades dos compósitos possam ser influenciadas pelas condições de processamento, tipo e concentração da fase dispersa, este trabalho teve como objetivo obter compósitos a partir de uma blenda comercial constituída de Poli (butileno adipato co-tereftalato) - PBAT/ Amido (EB), de caráter biodegradável, e casca de arroz (CA). Inicialmente foram preparados compósitos com PBAT/Amido contendo 10,20 e 30% de (CA) utilizando extrusora de dupla rosca e misturador interno. Posteriormente, foram determinadas propriedades mecânicas e térmicas dos sistemas obtidos. Os resultados das propriedades mecânicas mostraram que o módulo elástico dos compósitos foi afetado pelo tipo de processamento empregado, os compósitos obtidos em extrusora apresentam maior módulo que os compósitos obtidos no misturador: 92% maior em compósitos com 10% de carga, e 38% maior em compósitos com 30% de carga. A resistência ao impacto diminuiu significativamente e a resistência a tração aumentou moderadamente com o teor de casca de arroz, independente do tipo de processamento utilizado. A resistência ao impacto de compósitos com 30% de carga é aproximadamente 33% da resistência ao impacto da blenda pura. Já na resistência a tração, observou-se um aumento de 25% nos compósitos com 30% de carga. Análises de MEV indicam que as partículas de carga foram adequadamente molhadas pela matriz e que a adesão carga/matriz é boa. A avaliação dos resultados obtidos com as análises de DSC indicou que a adição de CA nos compósitos extrusados altera a temperatura de cristalização, variando de 75ºC da amostra pura, para 101ºC para as amostras com casca de arroz, resultado atribuível ao efeito nucleante causado pela maior dispersão da carga neste tipo de processamento.
<title>Abstract</title><p>We studied the crystallization and melting phenomena of poly (3- hydroxybutyrate) (PHB), a biodegradable and biocompatible semi-crystalline thermoplastic, obtained from renewable resources. Its high crystallinity motivated several studies on crystallization and melting behavior, and also on ways to increase the amorphous polymer fraction. The effect of heating and cooling rates on the crystallization and melting of commercial PHB was investigated by differential scanning calorimetry. Several rates, ranging from 2.5 to 20 °C min<sup>–1</sup>, were used to study the phase changes during heating/cooling/reheating cycles. The results showed that PHB partially crystallizes from the melt during the cooling cycle and partially cold crystallizes on reheating, and that the relative amount of polymer crystallizing in each stage strongly depends on the cooling rate. The melt and cold crystallization temperatures, as well as the rates of phase change, depend strongly on the cooling and heating rates.</p>
Environmental stress cracking (ESC) is one of the most important causes of polymer premature failure, occurring when a combination of mechanical load and an aggressive fluid is applied. The phenomenon is well know by polymer producers and product designers but its mechanisms are not very well understood. Although the ESC effects of many commercial polymers are well known, this type of failure in biopolymers were not studied yet. In the current work, the stress cracking behaviour of poly(3-hydroxybutyrate) (PHB) with 4,0 and 6,2% of hydroxyvalerate (HV) was investigated in injection-moulded bars under contact with sodium hydroxide (NaOH) solutions. The experiments were conducted using two different types of stress arrangements: (i) an ordinary tensile testing and (ii) a relaxation experiment. In both situations the injection-moulded bars were exposed to the NaOH solution and some testing conditions where varied, like the cross-head speed of the tensile test and the maximum load of the relaxation arrangement. The results showed that NaOH acted as a strong stress cracking agent for PHB, causing surface cracking and reducing significantly the mechanical properties. Catastrophic failure with an extensive surface damage was also observed by photographed and scanning electron microscopy (SEM) images. The magnitude of the effects increased with decreasing crosshead speed and increasing loading level.
Mechanical properties, morphology and nonisothermal crystallization of poly(3-hydroxybutyrate) (PHB) and blends of PHB and polystyrene (PS) were studied by tensile tests, scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). A two-phase structure composed by a PHB matrix and nearly spherical particles of PS was clearly noticed in SEM images. The presence of small amounts (0.5% to 3%) of amorphous PS affected the crystallinity of PHB, being more evident when high cooling rates were applied. The kinetics of nonisothermal crystallization was modeled according to Ozawa equation. The dependence of Ozawa parameters on temperature followed the same trend for PHB and PHB/PS blends; model parameters were found to be lower for the blends than for the neat PHB.
The flammabilities of nanocomposites made with three polypropylene grades (homo and copolymers) with 5 wt % of organoclay (Cloisite 20A), 5 or 15 wt % of maleated polypropylene as compatibilizer, and 0, 0.5 or 1 wt % of cis-13-docosenamide (Erucamide) as co-intercalant, were studied using the horizontal burning test UL94HB. Masterbatches prepared in an internal mixer were diluted in the polypropylene matrix using a corotating twin-screw extruder, with different screw configurations and operating at 240 or 480 rpm. Results indicate that the high burning rate of the composites was not affected by the processing conditions. For all formulations was observed a significant reduction in smoke release, lack of dripping and the formation of a char surface layer, that protected the core of the samples.
A inflamabilidade de nanocompósitos com três tipos de polipropileno (homo e copolímeros) contendo 5% de argila montmorilonita organofílica (Cloisite 20A), 5 e 15% de polipropileno enxertado com anidrido maleico como agente compatibilizante e 0, 0,5 e 1% de cis-13-docosenamida (Erucamida) como agente co-intercalante foi estudada através do teste de queima horizontal UL94HB. Concentrados foram preparados em misturador interno e diluídos com a matriz de polipropileno em extrusora de dupla rosca corrotacional com diferentes configurações de rosca e velocidades rotação de 240 e 480 rpm. Os resultados indicaram aumento da velocidade de queima dos compósitos quando comparados às das matrizes e que a velocidade de queima não foi afetada pelas condições de processamento. Em todos os casos, foi observado durante o ensaio uma redução da emissão de fumaça, ausência de gotejamento de material e a formação de uma camada carbonácea, levando à preservação da estrutura interna da amostra.
PP/organoclay/PP-g-MA/erucamide composites with 5% commercial organo-montmorillonite (Cloisite 20A), 5 and 15% maleated polypropylene as compatibilizer, and 0, 0.5 and 1% erucamide as a co-intercalating agent were prepared by melt intercalation. A masterbatch of compatibilizer and organoclay was compounded in an internal mixer and then diluted in the polypropylene matrix in a corotating twin-screw extruder. The compounds were characterized by x-ray diffraction, optical microscopy and mechanical properties. Results indicate that the organoclay acted as a reinforcer. Addition of the co-intercalating agent significantly increased the interlayer spacing of the clay, without notably affecting the mechanical behavior of the composites. Optical microscopy showed the dispersive effect of the screw profile used, which promoted the breaking of clay agglomerates.
Compósitos de PP/argila/PP-g-MA/erucamida contendo 5% (em peso) de argila montmorilonita organofílica (Cloisite 20A), 5 e 15% de PP-g-MA como agente compatibilizante e 0, 0,5% e 1% de cis-13-docosenamida (erucamida) como agente co-intercalante, foram preparados por intercalação no estado fundido. Concentrados de argila e compatibilizantes foram processados em misturador interno e em seguida diluídos com a matriz de polipropileno em extrusora de dupla rosca corrotacional. Os compósitos foram caracterizados através das propriedades mecânicas, difração de raios X e microscopia óptica. Os resultados indicaram o efeito reforçante da argila organofilizada. A presença de co-intercalante aumentou significativamente a distância interlamelar da argila em todos os compósitos, em geral, não afetando notavelmente o comportamento mecânico dos compósitos. Por microscopia óptica foi possível observar o efeito dispersivo do perfil de rosca utilizado, que promoveu a quebra dos aglomerados de argila.
Montmorillonite (MMT), natural (AN) and purified (AP) bentonite clays modified with alkyl ammonium (A), alkyl phosphonium (F) and a mixture of both (A and F) salts were incorporated (1% w/w) into PET by melt blending. The hybrids thus obtained were characterized by XRD, TG, DSC and TEM. Nanocomposites having intercalated ordered structures and intercalated disordered/exfoliated structures were obtained with the clays modified with the ammonium and the mixture of ammonium and phosphonium salts, respectively. A nanocomposite was not obtained with the addition of 1% w/w of an alkyl phosphonium modified clay into PET. The organoclays ANOA, APOF and MMTOF, when added to PET not only led to an increase in its thermal stability but also acted as heterogeneous nucleating agents, increasing its crystallization temperature. This result is industrially significant as the low crystallization rate of PET makes its use difficult in preparing injected goods. Besides, as the behaviour of the bentonite clays supplied by a local industry was similar to that of the imported montmorillonite, the use of this raw material of lower cost, modified with national technology, can be an attractive technology for injection molded PET applications, where cost is of utmost importance.
Argilas bentoníticas natural e purificada (AN e AP) e montmorilonita (MMT), modificadas organicamente com os sais alquil amônio (A), alquil fosfônio (F) e com uma mistura de ambos (A e F), foram incorporadas, em teor de 1% em massa, ao PET pelo processo de fusão. Os híbridos obtidos foram caracterizados por difratometria de raios X (DRX), termogravimetria (TG), calorimetria exploratória diferencial (DSC) e microscopia eletrônica de transmissão (MET). Nanocompósitos com morfologia intercalada ordenada e intercalada desordenada/esfoliada foram obtidos quando manufaturados com as argilas organofilizadas com sal amônio e com a mistura dos sais amônio e fosfônio. A incorporação das argilas organofilizadas com o sal fosfônio ao PET não resultou na formação de nanocompósitos. As argilas organofílicas ANOA, APOF e MMTOF, quando misturadas ao PET, provocaram aumento da sua estabilidade térmica, além de atuarem como agentes nucleantes heterogêneos para o referido polímero, aumentando sua temperatura de cristalização. Este resultado é significativo do ponto de vista industrial, pois a baixa velocidade de cristalização do PET dificulta seu uso na preparação de artefatos injetados. Além disso, como as argilas bentoníticas fornecidas por empresa local apresentaram comportamento semelhante ao da montmorilonita importada, o uso dessa matéria-prima de menor custo, modificada com tecnologia nacional, pode ser uma alternativa atraente para aplicações do PET moldado por injeção onde o custo é um fator primordial.