Generation of O₂-Permeation Barrier during the Gamma-Irradiation of Polyethylene/Ethylene-Vinyl Alcohol/Polyethylene Multilayer Film

Abstract

Polymers such as polyethylene (PE) and ethylene vinyl alcohol (EVOH) are primary constituents of multilayer films used in the food and biopharmaceutical packaging. In order to explore the film behavior after gamma-sterilization, several tests are performed (tensile tests, differential scanning calorimetry (DSC), oxygen transmission rate (OTR) and water vapor transmission rate (WVTR). The investigation of the PE/EVOH/PE multilayer film is done at several gamma-irradiation doses up to 270 kGy. For irradiation dose up to 50 kGy, mechanical properties are not altered. Whatever the irradiation dose, water barrier in PE/ EVOH/PE multilayer film is not altered whereas the oxygen barrier property is increased by 300%. This enhancement is shown not to occur due to reorientation, closer chain packaging and restriction of chain mobility of polymer chains in the amorphous phase of the different polymers. This enhancement rather comes from a change of the chemical environment of the EVOH layer.

Effect of gamma irradiation on the oxygen barrier properties in ethyl‐vinyl acetate/ethylene‐vinyl alcohol/ethyl‐vinyl acetate multilayer film

“…The gamma irradiation in the 30-270 kGy range does not influence the robustness of the EVA film compared to the nonsterile film (i.e., 0 kGy film). Regarding previous results obtained with another multilayer film PE/EVOH/PE, [15] toughness was higher for both modes at non irradiated dose whereas they decreased until 40 mJ.mm −3 at 270 kGy.…”

“…The gamma irradiation processing, and the different measurement methodologies of the tensile strength features (UTS, elongation, toughness), the thermal properties by DSC, the OTR and the WVTR are described in a previous article. [15] For more details see SI. Figure 2 displays the stress-strain curve obtained either in the machine direction (MD) or in the transversal direction (TD) of the EVA/EVOH/EVA multilayer film.…”

“…The stress-strain curve shows that the EVA film is a soft material according to ISO527-3. [15,21] The mechanical properties are specified hereby by the tensile strength, the elongation at break and the toughness. Results for all lots are similar and are provided in SI.…”

“…Either EVA/EVOH/EVA or PE/EVOH/PE multilayer films become less flexible when they are gamma irradiated. [15]…”

“…Recently, for PE/EVOH/PE multilayer film, we reported an increase in its O 2 barrier property upon gamma irradiation, keeping unchanged the water barrier property as well as the mechanical properties. [15] This result is ascribed to the generation of persistent alkyl radicals in the EVOH layer. These radicals play the role of O 2 scavengers.…”