ABSTRACT
Glass transition theory is an important theory in polymer science, which is used to characterize the physical properties. It refers to the transition of amorphous polymer from the glassy state to the rubber state due to heating or the transition from rubber state to glassy state due to cooling. In this paper, the glassy state and glass transition of food and the similar relationship between the composition of Chinese medicine extract powder and food ingredients were described; the determination method for glass transition temperature (Tg) of Chinese medicine extract powder was established and its main influencing factors were analyzed. Meanwhile, the problems in drying process, granulation process and Chinese medicine extract powder and solid preparation storage were analyzed and investigated based on Tg, and then the control strategy was put forward to provide guidance for the research and production of Chinese medicine solid preparation.
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The purpose of this study was to compare the effect of different DE values of malto-dextrin on Schisandrae Chinensis Fructus spray-dried powder. The glass transition temperature (Tg) of the spray-dried powder, powder properties and microscopic morphology were determined, and then the moisture absorption isotherms and the glass transition temperature were used to predict its storage stability. The study showed that after adding malto-dextrin, the powder rate was increased; moisture content was decreased; Tg was increased; mobility got better; produced spherical microstructure; and Tg was increased with the decrease of DE value. The water activity-equilibrium moisture content (aw-EMC) relationship in GAB models showed, the moisture absorption of powder was increased with the rising of DE value; and the equilibrium moisture content-glass transition temperature (EMC-Tg) relationship in Gordon-Taylor models showed that, Tg was decreased with the increase of moisture content. As a result, the storage critical condition of the spray-dried powder was improved, and along with the decrease of DE value, the critical water activity and the critical water content were increased. Therefore, the smaller the DE value, the greater the stability of the spray-dried powder.
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10.3969/j.issn.2095-4344.2013.25.017
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INTRODUCCIÓN: para la obtención en forma de polvo de los extractos y jugos de origen vegetal se emplea el secado por aspersión, porque es un método que preserva los componentes naturales presentes en estos productos. La presencia de compuestos como los azúcares impiden que estos puedan ser secados por aspersión sin que se adhieran a las superficies internas del equipo, lo que trae como consecuencia el bajo rendimiento en la recuperación del producto. El uso de aditivos inertes como el almidón soluble, celulosa o maltodextrina, favorece la recuperación del producto, elevando la temperatura de transición vítrea. OBJETIVOS: aplicar herramientas para el diseño del proceso de secado por aspersión de extractos de plantas. MÉTODOS: se determinaron las temperaturas de transición vítrea de diferentes extractos por calorimetría de barrido diferencial. Se calcularon las temperaturas de apelmazamiento y los índices individuales de secado. RESULTADOS: se determinó, que el uso de aditivos en el proceso de secado por aspersión de extractos de plantas permite obtener extractos en polvo en aquellos casos que no es posible secarlos solos. La metodología empleada, puede ser aplicada a distintos extractos. CONCLUSIONES: se demostró la factibilidad de la metodología propuesta como herramienta para definir la concentración de coadyuvante del secado y las temperaturas de secado
INTRODUCTION: to obtain extracts and juices of vegetal origin as powders, it is necessary to use the spray drying because this method preserves the natural compounds present in these products. Compounds like sugars prevent them from being spray dried without sticking to the inner surfaces of the dryer, all of which results in poor product recovery. The use of inert additives as soluble starch, cellulose or maltodextrin, favors the product recovery by increasing the glass transition temperature. OBJECTIVES: to use design tools for plant extract spray drying process. METHODS: the glass transition temperature was estimated for different extracts by differential scanning calorimetry. Sticking temperature as well as individual drying indexes were calculated. RESULTS: it was demonstrated that the use of additives in plant extract spray drying processes allows obtaining powdered extracts when it is not possible to dry the extract alone. This methodology can be applied to various extracts. CONCLUSIONS: the feasibility of the submitted methodology as a tool for defining adjuvant concentration and drying temperatures was shown
Subject(s)
Plant Extracts , Powders , Transition TemperatureABSTRACT
The Eucalyptus grandis logs temperatures were determined and correlated with the board's cracks during steaming. Thermocouples were inserted in the logs center, registering their temperatures during steaming at 90"C. The logs were sawed and the board's cracks measured. It was concluded that: (1) the logistic S-shaped curve explains the logs temperature variation; (2) the logs with diameter of 20 to <25, 25 to <30 and 30 to <35 cm presented, respectively, 84.2"C, 73.1"C and 45.8"C in the steaming; and (3) the cracks lengths significantly decreased in logs that reached the glass transition temperature.
As temperaturas em toras de Eucalyptus grandis, durante a vaporização, foram determinadas e correlacionadas com as rachaduras das tábuas. Nos centros das toras foram inseridos termopares e registradas suas temperaturas durante a vaporização à 90"C. As toras foram desdobradas e as rachaduras das tábuas mensuradas. Concluiu-se que: (1) o modelo estatístico sigmoidal logístico explica a variação da temperatura nas toras; (2) as toras com 20 a <25, 25 a <30 e 30 a <35 cm de diâmetro apresentaram, respectivamente, 84,2"C, 73,1"C e 45,8"C ao final da vaporização; e (3) as rachaduras foramsignificativamente menores nas toras que atingiram a temperatura de transição vítrea.
Subject(s)
Eucalyptus , Transition Temperature , Wood , Glass , Models, Theoretical , VolatilizationABSTRACT
OBJECTIVE: This study evaluated the glass transition temperature (Tg) and degree of conversion (DC) of a light-cured (Fill Magic) versus a chemically cured (Concise) orthodontic composite. MATERIAL AND METHODS: Anelastic relaxation spectroscopy was used for the first time to determine the Tg of a dental composite, while the DC was evaluated by infrared spectroscopy. The light-cured composite specimens were irradiated with a commercial LED light-curing unit using different exposure times (40, 90 and 120 s). RESULTS: Fill Magic presented lower Tg than Concise (35-84ºC versus 135ºC), but reached a higher DC. CONCLUSIONS: The results of this study suggest that Fill Magic has lower Tg than Concise due to its higher organic phase content, and that when this light-cured composite is used to bond orthodontic brackets, a minimum energy density of 7.8 J/cm² is necessary to reach adequate conversion level and obtain satisfactory adhesion.
Subject(s)
Humans , Composite Resins/chemistry , Glass/chemistry , Orthodontic Brackets , Resin Cements/chemistry , Transition Temperature , Bisphenol A-Glycidyl Methacrylate/chemistry , Composite Resins/radiation effects , Curing Lights, Dental/classification , Elastic Modulus , Energy Transfer , Friction , Glass/radiation effects , Hot Temperature , Light , Materials Testing , Polymers/chemistry , Resin Cements/radiation effects , Spectroscopy, Fourier Transform Infrared , Spectrum Analysis , Time FactorsABSTRACT
La reacción de polimerización del ácido láctico por el mecanismo de policondensación por fusión directa es de gran importancia cuando se desean obtener polímeros de bajo peso molecular, principalmente para aplicaciones médicas, debido a la facilidad del proceso y el bajo costo. Un ejemplo de esto es la elaboración de dispositivos para la liberación controlada de medicamentos. En este trabajo se estudiaron las diferentes etapas que involucra la policondensación (oligomerización y polimerización) para obtener PAL. La etapa de oligomerización se estudió en un estrecho intervalo de temperatura, 100-150 °C, donde el modelo cinético que describe la reacción es una ley de potencias de orden tres con Ea y factor preexponencial de 22,7 kcal/mol °K y 3,28x10-7 L²/mol²h respectivamente. Para la etapa de polimerización se estudiaron la influencia de la temperatura, el porcentaje de catalizador (SnCl2 2H2O) y el tiempo de reacción tomando como variable de respuesta la temperatur a de transición vítrea.
The polymerization reaction of d,1-lactic acid through polycondensation by direct melting is very important when low molecular weight polymers are desired, mainly for biomedical uses due to the easiness and low cost of process. And example of this is the manufacture of controlled delivery devices for drugs. In this work the steps involved on the polycondensation (oligomerization and polymerization) to obtain PLA were studied. The oligomerization was studied in a narrow range of temperatures 100-150°C where the kinetics model that describes the reaction is a kinetic law of powers of third order, with Ea and preexponential factor at 298.15K being 22,7 kcal/molK and 3.28x10-7 L²/mol²h respectively. For the polymerization step was studied the influence of temperature, the catalyst ratio (SnCL2.2H2O) and the time of reaction at the glassy transition temperature.
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Objective To study the stability of glucosamine sulfate prepared by spray drying. Methods The microcapsules of glucosamine sulfate were produced by spray drying,and the effects of different adjuvants on the indices of the microcapsules,such as the yield,fluidity,glass transition temperature and store stability were compared. Results and conclusion The yield,fluidity,glass transition temperature and stability of glucosamine sulfate could be greatly improved by adding 0.5%,1.0%,2.0%,3.0% and 5.0% cyclodextrin,gelatin and copvidone.