1 Polymer characterisation_density - Copy (1) (1).pdf

PHCO3309 – Pharmaceutical Materials Science Density Professor Walkiria Schlindwein De Montfort University 1 Pharmaceutical Polymer Characterisation After studying this topic, you should understand: the nature and importance of the physical/ chemical/ mechanical properties of polymer solids, liquids,...

PHCO3309 – Pharmaceutical Materials Science Density Professor Walkiria Schlindwein De Montfort University 1 Pharmaceutical Polymer Characterisation After studying this topic, you should understand: the nature and importance of the physical/ chemical/ mechanical properties of polymer solids, liquids, solutions with respect to pharmaceutical applications the general principles of density, surface tension dissolution and solubility of polymers the use of spectroscopic techniques such as FTIR for the characterisation of polymers the viscoelastic behaviour of polymeric materials Density Density (“true density”) is the relation of mass and volume. r= ! " [ # $! ! 𝑜𝑟 %# !! ] Density is normally defined/given at a specified temperature, either 20 or 25 0C and atmospheric pressure, but: - increase in temperature expands volume and therefore reduces density. As polymers are essentially organic derivatives they will have a coefficient of temperature expansion considerably greater than metal. Density -an increase in pressure reduces volume and therefore increases density. But the pressure/volume coefficients of solid/liquid monomers and polymers is small and will not significantly affect monomer/polymer densities for a range of 1-10 bar. -But at the high pressures of injection moulding and related processes, ~1000 bar,the reduction in volume due to the high applied pressure will increase density. Gas Pycnometry https://www.3p-instruments.com/measurement-methods/density-tapping-volumetry/ Polymer density measurement Watch this low density region e.g. Organic solvents: If you mix them slowly and in a controlled manner you can create a gradient Standards with known densities Yellow = high density Blue = low density high density region Density Column 1 2 3 Height [cm] Polymer sample 4 Density [g/cm3] Densities of Common Polymers Polymer Density/ g cm-3 0.91 0.93 0.96 1.10 1.20 1.40 2.20 Polypropylene Linear low density polyethylene High density polyethylene Polystyrene Polycarbonate Un-plasticised PVC Polytetrafluoroethylene Polypropylene Density range = 0.855 g/cm3 (amorphous) 0.946 g/cm3 (crystalline) Poly(tetrafluoroethylene) - PTFE Density = 2.20 g/cm3