Volatility of additives from polymers. Concentration dependence and crystallinity effects

The evaporation of 2-hydroxy-4-methoxybenzophenone (HMB) from polypropylene was studied by an isothermal method at different concentrations of HMB ranging from 0.3 to 1.2 wt %. The evaporation of the additive was correlated according to first-order kinetics. and rate constants of evaporation were calculated. A linear dependence of the rate constants of volatility on the initial concentration of the additive in the polymer was observed. This result suggests that in the given system, volatility is governed by evaporation from the polymer surface. Volatility of HMB from polypropylene depends on the degree of crystallinity of polypropylene. Samples with different degrees of crystallinity were prepared by quenching of the polymer blends and subsequent annealing at 423K. Isothermal measurements at 383 and 423K yielded higher rate constants for annealed samples than for quenched samples. The rate constant of evaporation at 383K was 20% higher for the annealed sample, whereas at 423K it was 27.5% higher. These results are interpreted on the basis of the concentration changes occurring during annealing. © 1993 John Wiley & Sons, Inc.