Specific heat glass transition

Differential scanning calorimetry (DSC) The method to measure the heat flow to a sample as a function of temperature. It is used to measure, for example, specific heats, glass transition temperatures, melting points, melting profiles, degree of crystallinity, degree of cure, and purity. 

List the dry product properties, such as powder size distribution, particle shape, bulk density, specific heat, glass transition temperature, hygroscopicity, powder flammability. 

As mentioned above, van Krevelen (1990) presents semi-empirical, group-contribution methods and data for each group in a polymer repeating unit. Data are provided to estimate a host of polymer properties, including the density, specific heat, glass-transition temperature, water absorption, and refractive index. For a specific property, these are in one of two forms ... 

Injection molding binders have been characterized for thermal conductivity, specific heat, glass transition temperature and pressure-volume-temperature (p-v-t) correlation. These properties have also been used for the FEM (finite element method) analysis of the injection molding process. DSC and Gel Permeation Chromatography techniques were also utilized to characterize the virgin binder and the molding compound for Q.C purposes. 

Thermal Properties. Thermal properties include heat-deflection temperature (HDT), specific heat, continuous use temperature, thermal conductivity, coefficient of thermal expansion, and flammability ratings. Heat-deflection temperature is a measure of the minimum temperature that results in a specified deformation of a plastic beam under loads of 1.82 or 0.46 N/mm (264 or 67 psi, respectively). Eor an unreinforced plastic, this is typically ca 20°C below the glass-transition temperature, T, at which the molecular mobility is altered. Sometimes confused with HDT is the UL Thermal Index, which Underwriters Laboratories estabflshed as a safe continuous operation temperature for apparatus made of plastics (37). Typically, UL temperature indexes are significantly lower than HDTs. Specific heat and thermal conductivity relate to insulating properties. The coefficient of thermal expansion is an important component of mold shrinkage and must be considered when designing composite stmctures. 

Glass transition Transition region or state in which an amorphous polymer changed from (or to) a viscous or rubbery condition to (or from) a hard and relatively brittle one. Transition occurs over a narrow temperature region similar to solidification of a liquid to a glassy state. This transformation causes hardness, brittleness, thermal expansibility, specific heat, and other properties to change dramatically. 

Material >ensity (kg/m ) Specific heat (kJ/kg K) Thermal conductivity (W/m/K) Coeff. of therm exp (/Am/m/ C) Thermal dififusivity (m /s) X 10" Glass transition Temp, TgCO Max. operating, Temp (°C)... 

These techniques help in providing the following information specific heat, enthalpy changes, heat of transformation, crystallinity, melting behavior, evaporation, sublimation, glass transition, thermal decomposition, depolymerization, thermal stability, content analysis, chemical reactions/polymerization linear expansion, coefficient, and Young s modulus, etc. 

The experimental data show that the magnitude of the heat capacity (or similarly of the specific heat) under adiabatic conditions decreases regularly with the increase of filler content. This phenomenon was explained by the fact that the macromolecules, appertaining to the mesophase layers, are totally or partly excluded to participate in the cooperative process, taking place in the glass-transition zone, due to their interactions with the surfaces of the solid inclusions. 

Fig. 5. Typical DSC-traces for the specific-heat jumps at the glass transition regions of iron-epoxy particulates, or E-glass fiber-epoxy composites and the mode of evaluation of ACp s...

Fig. 14. The variation of the specific heat jumps at glass-transition temperatures of elacc-epoxy composites, versus the fiber volume content, uf. The values for the factor X and the mesophase, (uj and matrix, (nm) volume fractions, versus uf, as derived from the values of the respective AC, s are also plotted...

By using Lipatov s theory, interrelating the abrupt jumps in the specific heat of composites at their respective glass transition temperatures with the values of the extents of these boundary layers, the thickness of the mesophase was accurately calculated. 

The transition between crystalline and amorphous polymers is characterized by the so-called glass transition temperature, Tg. This important quantity is defined as the temperature above which the polymer chains have acquired sufficient thermal energy for rotational or torsional oscillations to occur about the majority of bonds in the chain. Below 7"g, the polymer chain has a more or less fixed conformation. On heating through the temperature Tg, there is an abrupt change of the coefficient of thermal expansion (or), compressibility, specific heat, diffusion coefficient, solubility of gases, refractive index, and many other properties including the chemical reactivity. 

A sample of the polymer to be studied and an inert reference material are heated and cooled in an inert environment (nitrogen) according to a defined schedule of temperatures (scanning or isothermal). The heat-flow measurements allow the determination of the temperature profile of the polymer, including melting, crystallization and glass transition temperatures, heat (enthalpy) of fusion and crystallization. DSC can also evaluate thermal stability, heat capacity, specific heat, crosslinking and reaction kinetics. 

The glass-transition temperatures and the corresponding specific heats were measured three times for each sample in order to enable the calculation of the standard deviations, which were in the range of 3% or lower. Apparently, the kind of substituent greatly influences the Tg values, and rigid substituents (phenyl or methyl) or flexible substituents (ethyl or nonyl) cause an increase or decrease in corresponding Tg values, respectively. The measured Tg values are plotted in Fig. 19. 

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