Polyme Analysis 2010 Part 6 pps

Thermal AnalysisüThermal analysis TA is frequently used to describe analytical experimental techniques which investigate the behaviour of a sample as a function of temperature.. TA refer

Thermal Analysis

üThermal analysis (TA) is frequently used to describe analytical experimental

techniques which investigate the behaviour of a sample as a function of temperature

TA refers to conventional TA techniques such as:

+Differential thermal analysis (DTA) +Differential scanning calorimetry (DSC) +Dynamic mechanical analysis (DMA) +Thermogravimetry (TG/TGA)

Representative TA curves

The advantages of TA over other analytical methods can be summarized as follows:

(i) the sample can be studied over a wide temperature range using various temperature programmes

(ii) almost any physical form of sample (solid, liquid or gel) can be accommodated using

a variety of sample vessels or attachments

(iii) a small amount of sample (0.1 µg-10 mg) is required

(iv) the atmosphere in the vicinity of the sample can be standardized

(v) the time required to complete an experiment ranges from several minutes to several hours

(vi) TA instruments are reasonably priced

Thermal Analysis

üAs the sample goes through the programmed temperature change, there is no

temperature difference until the sample undergoes an exothermic or endothermic chemical reaction or change of physical state

üThe thermal event (a temperature difference between the sample and the

reference (∆T)) will be recorded→∆T versus time or temperature plot

üMeasure the differential temperature between a sample and a reference pan

→ to determine the temperature of the transitions

Test procedures:

Differential thermal analysis (DTA)

Schematic of a DTA apparatus

Differential thermal analysis (DTA)

A DTA curve

The subscripts represent: s-sample, r-reference, i-initial,f-final.

Tr

Tg = Glass Transition Temperature = The temperature (°C) at which an amorphous

polymer or an amorphous part of a crystalline polymer goes from a hard, brittle state to

a soft, rubbery state

Tm = melting point = The temperature (°C) at which a crystalline polymer melts.

∆Hm = the amount of energy in (joules/gram) a sample absorbs while melting.

Tc = crystallization point = is the temperature at which a polymer crystallizes upon

heating

∆Hc = the amount of energy (joules/gram) a sample releases while crystallizing.

The data can be used to identify materials, differentiate homopolymers from

copolymers or to characterize materials for their thermal performance

Differential Scanning Calorimeter(DSC)

Scope: DSC measures:

üA sample of 10 to 20 mg in an aluminum

sample pan is placed into the differential

scanning calorimeter.

üThe sample is heated at a controlled

rate (usually 10°/min)

üa plot of heat flow versus temperature

is produced.

üThe resulting thermogram is then

analyzed.

Test Procedure:

Dsc3.wmv

DSC