Diffusion of Model Contaminants in High‐Density Polyethylene

Abstract

Four liquid solvents – 1,1,1‐trichloroethane, toluene, chlorobenzene and octane – are used as model contaminants in sorption experiments in polyethylene in order to study their diffusion behavior between 40 and 70 °C and assess the plausibility of utilizing recycled plastics as safe functional barriers in food packaging applications. A hybrid model that combines molecular and free volume theory elements is used to interpret the collected experimental data. This helps in evaluating microstructural characteristics pertaining to the penetrant‐polymer systems tested, correlating these characteristics with the molecular properties of the solvent, and has an eventual role in predicting sorption and diffusivity in similar untested systems.magnified image

Estimation of Self‐Diffusion Coefficients of Small Penetrants in Semicrystalline Polymers Using Single‐Sided NMR

“…The reported results are in good agreement with previous investigations and the general concept that an increase in the crystallinity decreases the solvent mobility in the amorphous polymer phases and increase the tortuosity (Figure 3b) 2–9. The observed correlation shows that the tortuosity is sensitive to the morphological changes.…”

“…The crystalline phase in semicrystalline polymers is considered to be impermeable to the liquids and they can penetrate only the amorphous phase 3, 4. The crystalline phase hinders the solvent diffusion and extends the diffusion path.…”

“…Among the various techniques capable of determining diffusion coefficients D , gravimetry2–4 and pulsed gradient nuclear magnetic resonance (NMR) techniques5–9 are the ones used most frequently. With gravimetry, D is estimated indirectly with the help of Fick's law by analyzing the weight changes due to liquid ingress until full saturation or due to liquid evaporation starting with a fully saturated sample 2–4.…”

“…Among the various techniques capable of determining diffusion coefficients D , gravimetry2–4 and pulsed gradient nuclear magnetic resonance (NMR) techniques5–9 are the ones used most frequently. With gravimetry, D is estimated indirectly with the help of Fick's law by analyzing the weight changes due to liquid ingress until full saturation or due to liquid evaporation starting with a fully saturated sample 2–4. The main drawbacks of this method are as follows: (1) the method can be applied only for well‐defined geometries and fails for samples with complicated geometries and for powders; (2) it can assess only global information even for samples with intrinsic heterogeneities; and (3) the measurement is quite demanding as the ingress/evaporation has to be monitored throughout the entire process.…”

“…The main drawbacks of this method are as follows: (1) the method can be applied only for well‐defined geometries and fails for samples with complicated geometries and for powders; (2) it can assess only global information even for samples with intrinsic heterogeneities; and (3) the measurement is quite demanding as the ingress/evaporation has to be monitored throughout the entire process. Despite these disadvantages, gravimetry was successfully used to estimate the diffusion coefficients of various liquids in different semicrystalline polymers, and the results were used to test theoretical models of solvent diffusion 2–4…”