Cheila G. Mothé

Properties of polyurethane elastomers and composites by thermal analysis

Abstract Polyurethane elastomers based on castor oil or polybutadiene liquid hidroxyl (PBLH), as well as polyurethane composites reinforced with coir or sisal fibers at different proportions: 5, 10 and 20% w/w were prepared. The thermal behavior of the samples was analyzed by thermogravimetry (TG/DTG). TG/DTG curves showed two decomposition stages, except samples from castor oil with three decomposition stages (Tonset 257°C). The PU from PBLH presented a principal degradation at around 400°C, but with 15% weight loss at 250°C and the composites exhibited first decomposition stage at around 290°C. MDSC thermal profiles for PBLH PU presented one transition, occurring at the glass transition temperature ( T g ) 73.8°C, two transitions in castor oil PU T g : −1.6 and 62.7°C, and three transitions for composites from sisal T g : −52.9°C, 66.7 and 122°C. These transitions suggest soft and hard segments.

Thermal behavior of gum arabic in comparison with cashew gum

Abstract Thermal behavior of gum arabic and cashew gum, the exudate polysaccharides from Acacia and Anacardium occidentale L., containing different gum/water concentrations: 100/0, 80/20, 60/40, 50/50, 40/60, 20/80 and 5/95% w/w, were studied by differential scanning calorimetry (DSC) and thermogravimetry (TG). DSC thermal profiles for gum arabic with low water content (0–40%) showed an endothermic event at about 90°C (Tonset) and with increasing water content (50–80%) multiple melting endotherms and associated enthalpies were observed. Similar behavior was found in the DSC curves of cashew gum with Tonset of about 97°C. TG curves show two decomposition stages, the major decomposition occurred at 252°C (Tonset) to arabic and cashew gums pure.

Caracterização térmica e mecânica de compósitos de poliuretano com fibras de Curauá

This work is aimed at investigating the thermal properties, the mechanism of thermal degradation and the reaction mechanisms of polyurethane composites with different proportions of curaua fiber (5, 10 and 15%w/w). The samples were characterized by thermal analysis techniques such as: TG, DTG, DTA and DSC and mechanical properties (tensile strength, elongation at break and Youngs modulus). Polyurethane composites were degraded in two stages and showed three temperatures of glass transition, since the material exhibits flexible and rigid segments. The addition of curaua fiber into PU composites yields an increase in the Youngs modulus and a decrease in the elongation at break.

Thermal Decomposition Kinetics of Polyurethane-composites with Bagasse of Sugar Cane

Polyurethane composites with bagasse of sugar cane (BSC) at different proportions: 5, 10 and 20 mass/mass% were prepared by melt mixing method. The thermal behavior of these composites were studied by thermogravimetry (TG/DTG). The influence of fiber concentration on the kinetic parameters of the composites was studied and a better interaction was suggested between PU/BSC with 5mass/mass% of fiber. Scanning electron microscopy was carried out to investigate surface morphology.

Kinetic study of heavy crude oils by thermal analysis

The present work investigates the thermal behavior and kinetic of four types of petroleum samples: a medium crude oil—P1, one heavy oil—P2, and two extra heavy oils—P3 and P4 by TG, DTG, and DSC methods. Thus, this study may contribute to the characterization of petroleum with different °API values.

Síntese e caracterização do copolímero poli (ácido lático-b-glicol etilênico)

Two series of tri-block copolymers, poly(lactic acid-b-ethylene glycol) (PLA-PEG-PLA), were synthesized from l,l-lactide using stannous di-octoate as initiator and di-hydroxy terminated poly(ethylene glycol) (PEG) (Mn= 600 or 4000) as co-initiator. The chemical linkage between the PEG segment and the PLA segments was confirmed by Fourier transform infrared spectroscopy (FTIR), by proton magnetic resonance spectroscopy (1H-NMR) and thermal analyses. The polymerization degree of PLA segments in copolymers, DPPLA, was estimated from 1H-NMR spectra and has shown a dependence on the PEG molar mass and the relative l,l-lactide feed concentration. The physical aspect of copolymers changed according to the hydrophilic and hydrophobic segments lengths. The solubility tests revealed the amphiphilic nature of copolymers. Longer PLA segments in copolymers still presented crystallinity while the crystallization of the PEG segments was suppressed.

Thermal investigation of heavy crude oil by simultaneous TG–DSC–FTIR and EDXRF

Present study investigates thermal behavior of two heavy crude oils with different °API values by simultaneous thermogravimetry–differential scanning calorimetry–fourier transform infrared spectroscopy (TG–DSC–FTIR), and an evaluation of the chemical element levels present in the oils’ ashes was done by energy dispersive X-ray fluorescence spectrometry. TG and DSC curves were obtained for two samples in nitrogen atmosphere. Among all inorganic components evaluated, the highest concentration in the two oils was SO3. Thus this study may contribute to a better understanding of the thermal behavior of heavy crude oils and their composition.

Macrocospic and physiochemical characterization of a sugarless and gluten-free cake enriched with fibers made from pumpkin seed (Cucurbita maxima, L.) flour and cornstarch.

O interesse do consumidor por produtos com reducao calorica e crescente e seu desenvolvimento um desafio tecnologico. O produto bolo vem adquirindo crescente importância de consumo e a demanda por produtos dieteticos vem estimulando a utilizacao de edulcorantes e a otimizacao de produtos panificados. O consumo de fibra alimentar associa-se a prevencao de doencas cronicas, e a semente da abobora (Cucurbita maxima, L.), rica em fibra alimentar, pode ser utilizada como fonte, em produtos alimenticios. Uma dieta isenta de gluten nao constitui pratica facil, sendo raros os produtos panificados deste tipo. O objetivo deste trabalho e caracterizar de forma fisico-quimica bolos elaborados com Farinhas Mistas (FM) a base de Farinha de Semente de Abobora (FSA). Os bolos foram elaborados com FM nas proporcoes 30:70 (B30) e 40:60 (B40) a partir de FSA e Amido de Milho (AM), nesta ordem. Os resultados mostraram ausencia de gluten e pH proximo a neutralidade. As analises quimicas de B30 e B40 mostraram aumento no teor de cinzas, lipidios, proteinas e fibra alimentar insoluvel e, por outro lado, diminuicao no teor de carboidratos e calorias. A composicao quimica do B40 apresentou os melhores parâmetros fisicos, e a composicao quimica mostrou maior teor de lipidios e fibra alimentar e menor de calorias.

Study of recycling and biodegradability of ethylene-co-vinyl acetate reject by thermal analysis

A process for the recycling of ethylene-co-vinyl acetate (EVA) waste has been investigated. Biodegradable blends have been prepared by the addition of polysaccharides to EVA and blend films obtained. These films were analysed by thermogravimetric analysis (TG and DTG), differential scanning calorimetry (DSC) and scanning eletronic microscopy (SEM). The results are discussed in terms of thermal stability and biodegradability.

Core Shell Silica-Silicon Hybrid Nanoparticles: Synthesis and Characterization

Silica-silicon hybrid nanoparticles completely soluble in hydrocarbon were prepared by copolymerization of tetraethoxysilane (TEOS) and alkylethoxysilanes like methyltriethoxysilane (MTEOS), dimethyldiethoxysilane (DMDEOS) and dimethoxydiphenylsilane (DMODPS) by using the sol-gel process catalyzed by ammonium hydroxide in ethanol and methanol. Control of surface chemical structure and solubility was achieved by introducing trimethylchlorosilane (TMCS) as polymerization terminator. Nanoparticles with diameter in the range of 10 to 52 nm were obtained. The structure and thermal stability of the nanoparticles were highly dependent on the reaction condition. Higher conversion of hydrocarbon soluble silica-silicon nanoparticles were attained using water:Si molar ratio close to 9. The hexane soluble nanoparticles present hydroxyl and methyl groups on the surface. Wide angle X-ray diffraction and Si solid state NMR show evidences that these silica-silicon hybrids presents a core-shell structure with a core constituted by SiO2 and a shell formed by methyl or phenyl siloxane. The material can be applied to prepare different types of silica-silicon hybrid membranes.