Hasell - analytical techniques and copolymers/blends Flashcards
what is thermal analysis?
the study of the relationship between a sample property and its temperature as the sample is heated or cooled in a controlled manner
What techniques can’t you use for insoluble materials?
1) solution NMR, FTIR, and UV-Vis
2) chromatography (GPC, HPLC)
3) Mass spec
What techniques can you use for insoluble materials?
1) solid state NMR (longer & lower resolution)
2) diffraction (if crystalline)
3) solid state FTIR, UV-Vis, Raman
4) Thermal analysis (TGA, DSC)
5) Mechanical analysis
what is TGA
- a mass sample in a controlled atmosphere is recorded continuously as a function of temp (or time) as the temp of the sample is increased
- a plot of mass % as a function of time or temp
what is DSC
- the differences in heat (energy or power) flow into a sample and a reference blank pan are measured as a function of temp while the two are subjected to a controlled temperature program (heat, cool…)
- a plot of heat flow as a function of temp, often repeated cycles
Describe TGA procedure
1) sensitive analytical balance with range of ~2mg to 100mg
2) sample holder in the furnace, temp of upto 1500C, by resistance wire heating or IR lamps
3) purge gas system prevents oxidation (N2, Ar, He), gas flows in the direction over the sample pan last to not contaminate the reference pan
4) Temperature control screen
5) autosampler, allows queuing of samples
Why is Pt used in TGA
withstand high temp and is inert
Describe a general N2 TGA trace
1) vaporisation of low molecular weight material right at the start (high residual mass %) e.g. trace solvent, unreacted monomer, plasticiser, water from atmosphere
2) decomposition of polymer at the point where there is a sudden decrease (vertical down) in mass % = breakdown of polymer backbone
3) at the end when plateau, if not 0% residual mass % then must be a thermally stable residue e.g. inorganic fillers, highly crosslinked char (graphene - would require O2 to burn)
Describe a difference you might see in a TGA trace when O2 has been used instead of inert gas?
any residue at the end will be ash and not char
When is time on the x axis for a TGA?
when hold periods are used, temp is then shown as a separate signal
How do high vs low performance polymers perform in TGA?
low performance polymers tend to decompose at lower temperatures, high performance at higher
Applications of TGA?
1) material characterisation through analysis of characteristic decomposition patterns
2) studies of degradation mechanisms and reaction kinetics
3) determination of organic content in a sample (crosslinked char)
4) determination of inorganic content (ash) in a sample for predicting material structures or chemical analysis
Describe DSC procedure
1) temperature controlled heating chamber
2) chiller unit to control cooling rate
3) electronic control unit
4) heat flux plate for sample pan and reference pan to measure heat flow (Al pans) 1-20mg sample
5) autosampler
6) gas flow (N2)
What does the temperature of the pan mean for DSC?
a slightly cooler sample pan = the sample is absorbing heat
a slightly higher sample pan = the sample is giving out heat
Describe a typical DSC trace?
- temperature on the x axis, vs heat flow (y)
- ## remember EXO UP OR ENDO UP
