Is glass transition endothermic or exothermic?

Is glass transition endothermic or exothermic?

Glass transition is an endothermic reaction which shows it self as a S- Shape transition on the DSC plot with a positive slope inflection point should be taken as Tg glass transition point where the second variations of Cp becomes zero.

How do you determine the miscibility of a polymer?

Miscibility of two polymers can be judged by mechanical properties, morphological behavior and glass transition temperature. Glass transition temperature can be measured by various methods includes Dilatometry, DSC or DTA, Spectroscopy, diffraction, rheological, dielectric methods.

What is glass transition temperature of polymers?

The value of Tg depends heavily on the mobility of the polymer chain, and for most synthetic polymers lies between 170°K and 500°K (-103°C and 227°C). Pure crystalline polymers do not have a glass transition temperature because the glass transition temperature is only applicable to amorphous polymers.

How do you calculate glass transition temperature from DSC?

by Differential Scanning Calorimetry (DSC) In DSC measurements, the glass transition can be observed by a step in the baseline of the measurement curve (Fig. 1). It is characterized by its onset, midpoint, inflection and endset temperature. The step height corresponds to Δcp and is given in J/(g⋅K).

Why do polymers undergo glass transition?

The polymer does undergo an increase in its heat capacity when it undergoes the glass transition. Because the glass transition involves change in heat capacity, but it doesn’t involve a latent heat, this transition is called a second order transition.

What is DSC in polymer?

Differential scanning calorimetry (DSC) is a technique used to investigate the response of polymers to heating. DSC can be used to study the melting of a crystalline polymer or the glass transition. The DSC set-up is composed of a measurement chamber and a computer.

What is miscible polymer blend?

Miscible or homogeneous polymer blends: These mixtures are often made from polymers with similar chemical structures, resulting in a polymer blend with a single-phase structure. One glass transition temperature is observed.

How do you determine miscibility?

The most common determination of miscibility is by visual evaluation. If two substances form a layer, they are clearly immiscible. More precise methods of determination include chromatographic analysis such as spectroscopy as well as viscometry, osmetry, and calorimetry.

What is the difference between glass transition and melting temperature?

The main difference between glass transition temperature and melting temperature is that glass transition temperature describes the transition of a glass state into a rubbery state whereas melting temperature describes the transition of a solid phase into a liquid phase.

What is HDT plastic?

The Heat Deflection Temperature (HDT), or Heat Distortion Temperature, is a measure of a polymer’s resistance to alteration under a given load at an elevated temperature. It is also known as the ‘deflection temperature under load’ (DTUL) or ‘heat deflection temperature under load (HDTUL)’.

Do crystalline polymers have glass transition temperature?

When an amorphous polymer is heated, the temperature at which the polymer structure turns “viscous liquid or rubbery” is called the Glass Transition Temperature, Tg. Crystalline polymers exhibit a Tm (melt temperature) and typically a Tg since there is usually an amorphous portion as well (“semi”-crystalline).