Question

Amorphous polyvinyl chloride is expected to have a density of 1.38 g/cm3. Calculate the percentage crystallization in PVC that has a density of 1.45g/cm3. (Hint: Find the density of completely crystallized PVC from its lattice parameters, assuming four repeat units per unit cell.)

Answer 1

repeat units / unit cell n = 4 units

Molecular weight of vinyl chloride (C2H3Cl) A = 62.45 g/mol

Avogadro number NA = 6.023 x 10^23 units/mol

Volume V = 10.40 x 10^-8 cm x 5.3 x 10^-8 cm x 5.1 x 10^-8 cm

= 2.81 x 10^-22 cm3

density of completely crystallized PVC

= (n x A) / (V x NA)

= (4 x 62.45) / (2.81 x 10^-22 x 6.023 x 10^23)

d1 = 1.476 g/cm3

Density of Amorphous polyvinyl chloride

d2 = 1.38 g/cm3

Density of PVC

d3 = 1.45 g/cm3

% crystallization

= [(d1) x (d3 - d2) x 100] / [(d3) x (d1 - d2)]

= [(1.476) x (1.45 - 1.38) x 100] / [(1.45) x (1.476 - 1.38)]

= 10.332 / 0.1392

= 74.22 %