A Review on the Thermal Characterisation of Natural and Hybrid Fiber Composites.

The thermal stability of natural fiber composites is a relevant aspect to be considered since the processing temperature plays a critical role in the manufacturing process of composites. At higher temperatures, the natural fiber components (cellulose, hemicellulose, and lignin) start to degrade and their major properties (mechanical and thermal) change. Different methods are used in the literature to determine the thermal properties of natural fiber composites as well as to help to understand and determine their suitability for a certain applications (e.g., Thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and differential mechanical thermal analysis (DMA)). Weight loss percentage, the degradation temperature, glass transition temperature (Tg), and viscoelastic properties (storage modulus, loss modulus, and the damping factor) are the most common thermal properties determined by these methods. This paper provides an overview of the recent advances made regarding the thermal properties of natural and hybrid fiber composites in thermoset and thermoplastic polymeric matrices. First, the main factors that affect the thermal properties of natural and hybrid fiber composites (fiber and matrix type, the presence of fillers, fiber content and orientation, the treatment of the fibers, and manufacturing process) are briefly presented. Further, the methods used to determine the thermal properties of natural and hybrid composites are discussed. It is concluded that thermal analysis can provide useful information for the development of new materials and the optimization of the selection process of these materials for new applications. It is crucial to ensure that the natural fibers used in the composites can withstand the heat required during the fabrication process and retain their characteristics in service.

Thermo-kinetics of Forest Waste Using Model-Free Methods / Termocinética de residuos de bosque usando los métodos de modelo libre / Termocinética de resíduos de bosque usando métodos de modelo livre

Abstract Thermal behaviour of pine needles (Pinus Roxburghii) is examined through a thermogravimetry technique. The dried samples of pine needles undergo the non-isothermal decomposition at temperature range of 308-1173 K. The heating rates used for experimental purposes are: 5 ◦ C min-1, 10 ◦ C min-1 and 15 ◦ C min-1. Kinetic parameters of thermal decomposition reactions of pine needles are obtained through the model-free schemes. The estimated values of activation energy and frequency factor derived from Kissinger method are 132.77 kJ mol-1 and 13.15 x 107 min-1, respectively. Furthermore, the averaged values of the same kinetics parameters retrieved from the isoconversional methods are 82.38 kJ mol-1 and 74.833 kJ mol-1, 25.42 x 1013 min-1 and 13.449 x 1010 min-1, respectively. Instead of the Flynn-Wall- Ozawa (FWO) and Kissinger- Akahira- Sunrose (KAS) schemes, the kinetic parameters derived from the Kissinger method are relatively promising for the thermal decomposition process, since the kinetic parameters are highly affected by intermediate stages and overlapping of the concurrent reaction occurred during pyrolysis.

Resumen Se examina el comportamiento térmico de las agujas de pino (Pinus roxburghii) a través de la técnica de termogravimetría. Las muestras secas de las agujas de pino se someten a una descomposición no isotérmica en un rango de temperatura de 308-1173 K. Las tasas de calentamiento usadas para los propósitos experimentales son: 5 °C min-1, 10 °C min-1 y 15 °C min-1. Los parámetros cinéticos de las reacciones de descomposición térmica de las agujas de pino se obtuvieron a través de esquemas de modelo libre. Los valores estimados de la energía de activación y el factor de frecuencia derivado del método Kissinger son: 132.77 kJ mol-1 y 13.15 x 107 min-1, respectivamente. Por otra parte, los valores promediados de los mismos parámetros cinéticos recuperados por los métodos isoconversionales son 82.38 kJ mol-1 y 74.833 kJ mol-1, 25.42 x 1013 min-1 y 13.449 x 1010 min-1, respectivamente. A diferencia de los esquemas Flynn-Wall-Ozawa (FWO) y Kissinger-Akahira-Sunrose (KAS), los parámetros cinéticos derivados del método Kissinger son relativamente promisorios para los procesos de descomposición térmica, ya que estos parámetros se afectan grandemente por los estados intermedios y la superposición de la reacción concurrente que ocurre durante la pirólisis.

Resumo O comportamento térmico de agulhas de pinheiro (Pinus roxburghii) foi examinado por meio da técnica de gravimetria. As amostras secas das agulhas de pinheiro se submeteram a uma decomposição não-isotérmica em uma faixa de temperatura de 308-1173 K. As taxas de aquecimento usadas para propósitos experimentais foram: 5 °C min-1, 10 °C min-1 e 15 °C min-1. Os parâmetros cinéticos das reações de decomposição térmica das agulhas de pinheiro se obtiveram por meio de esquemas de modelo livre. Os valores estimados da energia de ativação e o fator de frequência derivado do método Kissinger são: 132.77 kJ mol-1 e 13.15 x 107 min-1, respectivamente. Adicionalmente, os valores médios dos mesmos parâmetros cinéticos recuperados pelos métodos isoconversionais são 82.38 kJ mol-1 e 74.833 kJ mol-1, 25.42 x 1013 min-1 y 13.449 x 1010 min-1, respectivamente. Diferentemente dos esquemas Flynn-Wall-Ozawa (FWO) e Kissinger-Akahira-Sunrose (KAS), os parâmetros cine'ticos derivados do método Kissinger são relativamente promissórios para os processos de decomposição térmica, já que estes parâmetros são altamente afetados pelos estados intermediários e sobreposição da reação concorrente que ocorre durante a pirólise.

Solid-State Characterization of Spironolactone 1/3 Hydrate.

Spironolactone (SPR) is a poorly water-soluble drug widely used for the treatment of various diseases. The objective of this study was to carry out the preparation and solid-state characterization of SPR 1/3 hydrate. The solid form was generated by an unreported recrystallization process in acetone and characterized for the first time by a combination of X-ray powder diffraction (XRD), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), Fourier-transform infrared spectroscopy (FTIR), equilibrium solubility, and an accelerated stability study. XRD, DSC, and TGA studies revealed that SPR 1/3 hydrated converts completely to form II after heating to 180°C. Solubility studies at 37°C showed that SPR 1/3 hydrate was statistically less soluble than SPR form II in all tested media and that SPR form II partially converts to SPR 1/3 hydrate in aqueous media. Accelerated stability studies demonstrated that both forms were physically and chemically stable up to 6 months (40°C/75% RH). We concluded that contamination of SPR 1/3 hydrate in SPR raw materials is undesirable. Taking this into account we recommend its polymorphic monitoring either in active pharmaceutical ingredients or commercial tablets by solid-state identification/quantification methods (XRD, DSC, TGA, and FTIR). Of these, XRD proved to be the most conclusive and accurate.

Compatibility study of paracetamol, chlorpheniramine maleate and phenylephrine hydrochloride in physical mixtures.

Paracetamol (PAR), phenylephrine hydrochloride (PHE) and chlorpheniramine maleate (CPM) are commonly used in clinical practice as antipyretic and analgesic drugs to ameliorate pain and fever in cold and flu conditions. The present work describes the use of thermal analysis for the characterization of the physicochemical compatibility between drugs and excipients during the development of solid dosage forms. Thermogravimetric analysis (TGA) and Differential Scanning Calorimetry (DSC) were used to study the thermal stability of the drug and of the physical mixture (drug/excipients) in solid binary mixtures (1:1). DSC thermograms demonstrated reproducible melting event of the prepared physical mixture. Starch, mannitol, lactose and magnesium stearate influence thermal parameters. Information recorded from the derivative thermogravimetric (DTG) and TGA curves demonstrated the decomposition of drugs in well-defined thermal events, translating the suitability of these techniques for the characterization of the drug/excipients interactions.