Читать книгу Poly(lactic acid) - Группа авторов - Страница 57

Troupe et al. [32] observed that the viscosity increased over time as did the titratable acidity when a 75 apparent wt% lactic acid sample was freshly prepared from 85 wt%. At room temperature, it took more the 20 days to reach equilibrium. Equilibration of solutions is critical to obtain reliable viscosity data, and equilibration is slow at 20°C. Suggested equilibration times are provided by Vu et al. [27]. Troupe et al. fitted their viscosity data with Equation 2.29 where each wt% was fitted separately. The individual fits represent the experiments within 5%. For practitioners, we provide a rapid way to interpolate the viscosity. We have regressed the coefficients A and B for the common log of viscosity η ,in cP, as a function of apparent wt% lactic acid as given in Equations 2.30 and 2.31. These correlations are compared with experimental data in Figures 2.9 and 2.10. The equations are within 10% except for the most concentrated measurement at 25°C where the error is 12%. For Equations 2.30 and 2.31, w is apparent wt% lactic acid (Figures 2.9 and 2.10).

FIGURE 2.8 Comparison of aqueous lactic acid density calculated using Equations 2.26–2.28 with experimental data of Troupe et al. as a function of apparent wt% and temperature.

(2.29)

(2.30)

(2.31)

FIGURE 2.9 Comparison of viscosity calculated using Equations 2.29–2.31 with experimental data of Troupe et al. as a function of temperature and apparent wt%.

FIGURE 2.10 Comparison of viscosity calculated using Equations 2.29–2.31 with experimental data of Troupe et al.