For almost 5 decades METTLER TOLEDO has provided instrumental solutions for the automatic determination of the thermal values melting point, dropping and softening point. The melting point and Dropping Point Excellence line, METTLER TOLEDO’s latest release of compact instruments for thermal characterization, support the complete analytical. Dropping point is generally used for greases, and indicates heat resistance of a grease up to a temperature. At this point, greases tends to start dropping down a vertical surface. The softening point of a bituminous material can be defined as the temperature at which this bituminous material further softens after its arbitrary softness point is reached. There are various methods that are helpful in determining the softening point of a bituminous material. They are as follows: Vicat method as per ASTM D1525 or ISO 306.

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The softening point is the temperature at which a material softens beyond some arbitrary softness.^[1] It can be determined, for example, by the Vicat method (ASTM-D1525 or ISO 306), Heat Deflection Test (ASTM-D648) or a ring and ball method (ISO 4625 or ASTM E28-67/E28-99 or ASTM D36 or ASTM D6493 - 11). A ring and ball apparatus can also be used for the determination of softening point of bituminous materials.^[2]

References[edit]

^Petrie, Edward (2006). Handbook of Adhesives and Sealants. McGraw-Hill. p. 146. ISBN0-07-147916-3.
^'Softening Point / Ring & Ball Apparatus'. http://cooper.co.uk. Cooper Research Technology Ltd. Retrieved 16 July 2015.External link in |website= (help)

Retrieved from 'https://en.wikipedia.org/w/index.php?title=Softening_point&oldid=671712729'

Key Difference – Glass Transition Temperature vs Melting Temperature

Investigation of thermal properties of elastomers is essential to decide their final application and manufacturing process parameters. The thermal properties of elastomers can be examined using different test parameters such as transition temperatures, useful temperature range, heat capacity, thermal conductivity, temperature dependence of mechanical properties and coefficient of linear thermal expansion. There are two types of temperature parameters that come under transition temperatures namely, glass transition temperature (T_g) and melting temperature (T_m). In polymer industry, these temperatures are used for the identification of materials and their quality parameters. The transition temperature of polymers can be assessed very accurately by using advanced instruments like dynamic mechanical analyzer (DMA) and differential scanning calorimeter (DSC). At glass transition temperature, a reversible change in phase from viscous to glassy or vice versa occurs in the amorphous regions of the polymer due to a change in temperature, whereas at melting temperature, the crystalline or semi-crystalline regions of a polymer change to a solid amorphous phase. This is the key difference between glass transition temperature and melting temperature.

1. Overview and Key Difference
2. What is Glass Transition Temperature
3. What is Melting Temperature
4. Side by Side Comparison – Glass Transition Temperature vs Melting Temperature in Tabular Form
5. Summary

What is Glass Transition Temperature?

Melting Point Science

The glass transition temperature is the temperature at which a viscous or rubbery state of an amorphous or semi-crystalline polymer changes to a brittle, glassy state. This is a reversible transition. Below glass transition temperatures, polymers are hard and rigid like glass. Above glass transition temperature, polymers show viscous or rubbery properties with less rigidity. Glass transition is a second order reaction as there is a change in the derivatives. The changes in polymer above and below occur due to the molecular motion due to energy changes. This temperature is greatly influenced by the structure of the molecules. Moreover, it also depends on the frequency of cyclic deformation, the effect of compounding ingredients such as plasticizers, fillers, etc., and rate of change of temperature.

As per experimental observations, it is found that in a symmetrical polymer, glass transition temperature is half of its melting temperature, while in an unsymmetrical polymer, glass transition temperature is 2/3 of its melting value (in degrees of Kelvin). However, these relationships are not universal and have deviations in many polymers. Glass transition is important to determine the working range of polymer, evaluating flexibility and nature of the response to mechanical stress.

What is Melting Temperature?

Melting is another important parameter of thermal transitions in polymers. Usually, melting temperature is the temperature at which a phase transition occurs; for example, solid to liquid or liquid to vapor.

However, as far as polymers as concerned, the melting temperature is a temperature at which a transition from a crystalline or semi-crystalline phase to a solid amorphous phase takes place. Melting is a first order endothermic reaction. The enthalpy of melting of the polymer can be used to calculate the degree of crystallinity, given that the melting enthalpy of 100% of the same polymer is known. Knowing the melting temperature is also very important as it gives an idea about the working range of a polymer.

What is the Difference Between Glass Transition Temperature and Melting Temperature?

Difference Between Softening Point And Melting Point

Glass Transition Temperature vs Melting Temperature
Glass transition temperature is the temperature at which a viscous or rubbery state of an amorphous or semi-crystalline polymer changes to a brittle, glassy state.	Glass transition temperature is the temperature at which a viscous or rubbery state of an amorphous or semi-crystalline polymer changes to a brittle, glassy state.
Order of Reaction
Glass transition is a second order reaction.	Melting is a first order reaction.
Above T_g or T_m
Amorphous regions become rubbery, less rigid and not brittle	Crystalline regions transform into solid amorphous regions.
Below T_g or T_m
Amorphous regions become glassy, rigid and brittle.	Stable crystalline regions
Relationship (as per experimental observations)
Tg =1/2 Tm (for symmetrical polymers)	Tg =2/3 Tm (for unsymmetrical polymers)

Summary – Glass Transition Temperature vs Melting Temperature

Both glass transition and melting temperatures are very important thermal transition properties of polymers. Above glass transition temperature, polymers have rubbery properties, whereas, below this temperature, they have glass properties. Glass transition occurs in amorphous polymers. Melting is the change of phase from crystalline to solid amorphous. Melting temperature is important to calculate the degree of crystallinity. Both temperatures values are extremely useful to determine the quality and working range of polymers.

Download PDF Version of Glass Transition Temperature vs Melting Temperature

You can download PDF version of this article and use it for offline purposes as per citation note. Please download PDF version here Difference Between Glass Transition Temperature and Melting Temperature

Reference:

1. Adams, Robert D., et al. Structural adhesive joints in engineering. Chapman & Hall, 1997.
2. Gowariker, V. R., Viswanathan, N. V., & Sreedhar, J. Polymer science. New Age International

See also[edit]

Softening Point Vs Melting Point