Thermal Analysis

Question 1

What is Thermal analysis?

Answer 1

It is a broad term that encompasses all the analytical tests that measure physicochemical properties as a function of time, temperature and atmosphere.

It provides information of structure and quality of food materials and products.

Question 2

What is the necessary temperature range for food thermal analysis?

Answer 2

Around -40C to 400C, this accounts for freezing (storage) and Cooking (deep frying).

Question 3

What are the three structure types a food material can have?

Answer 3

Crystalline, Amorphous and Semi-Crystalline

Question 4

What is a glass transition temperature?

Answer 4

It is when you convert a amorphous or semi-crystalline material into a more crystalline form

Question 5

What is a melting temperature?

Answer 5

It is when a crystalline or semi-crystalline material converts into a more amorphous structure.

Question 6

What are some applications for Thermal analysis?

Answer 6

Quality Assurance, Product development. Research into new materials, formulations and processes.

Question 7

Why is it important that we analyse our products with thermal analysis?

Answer 7

Because the End-use properties (Functionality) of a material at a specific temperature are dependent on the materials structure at said temperature.

Question 8

What is the primary use of thermal analysis and why is it important?

Answer 8

the primary use is to determine structure by measuring physical properties. It is important because if we understand structure and physical properties we can develop and provide desired end use properties.

Question 9

What are the two most common thermal analysis techniques?

Answer 9

Thermogravimetric (TGA) and Differential scanning calorimetry (DSC).

Question 10

How does TGA work?

Answer 10

This is used to determine the quantitative presence of water and associated water, it also identifies the temperature of molecular decomposition (Chemical change). This method weighs the material whilst increasing the heat to analyse the relationship between the two

Question 11

What does DSC measure?

Answer 11

DSC measures the sum of all heat flows in a material. Differential scanning calorimetry determines the structure of a material and transition temperatures at which the structure changes significantly.

Question 12

Under what two circumstances can a transition in structure be recorded?

Answer 12

The sample could absorb the energy in a ‘endothermic’ reaction. Or it could expel energy in a ‘exothermic’ reaction.

Question 13

How is a DSC test done?

Answer 13

Samples (mg) are hermetically sealed in a small metalpan along side a reference sample. the samples are then either heated or cooled in order the measure the change in mobility (thermal induced)

Question 14

What heating rate is used?

Answer 14

A single heating rate is selected for the test in celsius per minute. the higher the heating rate the higher the sensitivity, whereas the lower the rate the higher the resolution.

Question 15

What can DSC tell you?

Answer 15

Glass transition temp of a amorphous structure
melting temp of a crystalline structure
percent crystalinity of a semicrystalline material
crystialization of an amorphous material
denaturation of proteins
Gelatinization of starch

Question 16

How would a endothermic or exothermic material appear on a DSC graph?

Answer 16

An endothermic material would absorb heat and go more towards an amorphous state, on a graph this would show as a decrease of heatflow (a dip in the graph). an exothermic material would expel heat and it would show as an increase of heat flow.

Question 17

If an amorphous structure is below a glass transition temperature what characteristics does it have? what about above?

Answer 17

It has a glassy characteristic, being rigid, high viscosity and low molecular mobility. If the material is above glass transition temp then it becomes rubbery, viscous liquid with an increase in free volume and mobility.

Question 18

What effect does moisture content have on glass transition?

Answer 18

Moisture content changes the range of glass transition temperature significantly. a glassy amorphous potato chip becomes more rubbery when its moisture content increases - the glass transition is lowered (becomes stale).

Question 19

What is the biggest difference between amorphous and crystalline food structures.

Answer 19

Amorphous structures are unordered, highly energetic and chaotic, where as crystalline structures are order, low energy, low mobility and stable

Question 20

What happens if a crystalline material melting point is greater then the temperature required to turn it into a gas?

Answer 20

It would vaporise before melting.

Question 21

If you dont have a melting temperature, what type of structure do you have?

Answer 21

An amorphous structure

Question 22

If you have a melting temperature what type of structure do you have?

Answer 22

a crystalline or semi crystalline structure.

Question 23

What can cause a loss of a crystalline structure?

Answer 23

Dissolving into a solution
Dehydration of a hydrated structure
Chemical interactions
Decomposition

Question 24

If the heating rate is increased in a dsc what can you expect?

Answer 24

The endothermic peak will jump to a higher peak.

Question 25

What is a semicrystalline structure?

Answer 25

It is a structure that contains both amorphous and crystalline structures.

Question 26

What can be noted on a DSC of a semicrystalline structure?

Answer 26

It might show polymorphs with various glass transtition points and melting points.
By analysing the melting points above and below 22*C room temperature you can determine the ratio of liquid to solid in your product.