Glass transition temperature and crystalline melting point

GLASS TRANSITION TEMPERATURES AND CRYSTALLINE MELTING POINTS OF CIS- AND trans- DIENE POLYMERS... 

The performance of an extruder is determined as much by the characteristics of the feedstock as it is by the machine. Feedstock properties that affect the extrusion process inciude buik properties, meit flow properties, and thermal properties. Important buik flow properties are the buik density, compressibility, particle size, particle shape, external and internal coefficient of friction, and agglomeration tendency. Important melt flow properties are the shear and eiongational viscosity as a function of strain rate and temperature. The commonly used melt indexer provides only limited information on the meit viscosity. Important thermal properties include the specific heat, the glass transition temperature, the crystalline melting point, the latent heat of fusion, the thermal conductivity, the density, the degradation temperature, and the induction time as a function of temperature. 

E is also independent of chain stiffness and chain interactions, these factors play a role in the height of the glass-rubber transition temperature and the melting point. A stiffer chain, therefore, does not result in a stiffer polymer except, sometimes, in an indirect way, namely when stiff chains enable the formation of high orientation, such as in liquid-crystalline polymers (see 4.6). 

During the thermoforming process (see Fig. 12), the sheet is heated above the glass transition temperature and below the melting point of the crystalline phase [35]. Afterwards, the hot sheet is formed into a chilled mold using vacuum, pressure and/or mechanical force. After a cooling step, the thermoformed containers are punched out and ejected. The skeleton (30-70% of the total volume) is recycled in the same application (Fig. 12). 

For semi-crystalline polymers with melting points of more than 100 °C above the glass transition temperature and for amorphous polymers far above the glass transition temperature Tg (at around T = Tg + 190°C), the shift factors obtained from time-temperature superposition can be plotted in the form of an Arrhenius plot for thermally activated processes ... 

DSC finds many applications in characterizing materials. Quantitative applications include the determination of heals of fusion and the extent of crystallization for crystalline materials. Glass transition temperatures and melting points arc useful for qualitative classification of materials, although thermal methods cannot be used alone for identification. Melting points are also very useful in establishing the purity of various preparations. Hence, Ihcrmal methods are often used in quality control applications. 

It often occurs that it is desirable to modify the properties of a homopolymer to achieve certain application-specific characteristics that are perhaps not possible by solely manipulating the polymer molecular weight or by chemical modification of the final producf. Perhaps one is interested in achieving properties that are intermediate to two homopolymers. Properties of interest could include crystallinity, flexibility, tensile strength, melting point, glass-transition temperature, and many others. 

These authors have used the technique of lamellar decoration [76] which enables detailed assessment of cheu-acteristic mesophase defects and texture on a much finer scale than previously possible with conventional electron-microscopy preparations. The defects and texture existing in the polymer melt state are first retained by thermal quenching of the polymer fluid to room temperature. The glassy LCP film is then annealed above its glass transition, but below the melting point. Crystalline lamellae grow perpendicular to the local chain axis and effectively decorate the molecular director... 

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