Question

Current Attempt in Progress The density and associated percent crystallinity for two polytetrafluoroethylene materials are as follows: plg/cm3) crystallinity (%) 2.111 61.4 2.280 77.2 (a) Compute the density of totally crystalline polytetrafluoroethylene. g/cm3 (b) Compute the density of totally amorphous polytetrafluoroethylene. Pa = g/cm3 (c) Determine the percent crystallinity of a specimen having a density of 2.28 g/cm % crystallinity =

Answer 1

% crystallinity can be calculated from density measuments as : % crystallinity = Pc(Ps-Pa). 100 Ps(Pc-Pa) where ps is the density of specimen Pa is the density of totally amorphous powder Pc is the density of perfectly crystalline polymer On rearranging above equation, % crystallinity _ PcPs-Pa) 100 Ps(Pc-Pa) % crystallinity= 100 C = Pc(Ps-Pa) Ps (Pc-Pa) Cps(pc - Pa) = Pc(Ps - Pa) Cpspc - Cpspa = Pcps - Pepa Cpspc - Pcps + PcPa - CosPa = 0 Pc(Cps - Ps) + Pepa - Cospa = 0 Now, we have 2 values for ps and C. Thus, we can write above 2 equations for these 2 values as: Pc(Cips, – Psz) + Pcpa - Cips, Pa = 0 --> (1) Pc(C2Psz - Ps) + Pepa - C2Ps Pa = 0 --> (2) Now, From the given data, Ps, = 2.111 gm/cm Ps, = 2.28 gm/cm3 _% crystallinity 100 - = 614 100 = 0.614 c. -% crystallinity2 100 = 77.2 = 0.772 100 Putting all data in equations (1) and (2),

Pc (0.614 * 2.111 – 2.111) + Popa - Pa* 0.614 * 2.111 = 0 Pc (0.772 * 2.28 - 2.28) + Pepa - Pa*0.772 * 2.28 = 0 Thus, Pc(-0.814846) + PcPa - 1.296154 Pa = 0 pc(-0.51984) + PcPa -1.76016Pa = 0 On solving above 2 equation, we get, Pc = 2.5778 g/cm3 (Density of totally crystalline) Pa = 1.6389 g/cm3 (Density of totally amorphous) (c) Density (ps) = 2.28 g/cm3 % crystallinity = Pe(Ps-Pa) Ps(Pc-Pa) 100 2.5778 (2.28-1.6389) 2.28 + (2.5778-1.6389) * 100 77.2 %