Hydrophilic Edible Films: Modified Procedure for Water Vapor Permeability and Explanation of Thickness Effects

TLDR

The study modifies the ASTM E96 method to determine water vapor permeability of hydrophilic edible films. The authors introduced a correction method that accounts for the water‑vapor partial‑pressure gradient in the stagnant air layer of the test cup, requiring accurate relative‑humidity control and a constant air speed of 152 m/min. Without the correction, errors reached 35 %; applying the guidelines clarified that relative humidity, not film thickness, drives the observed thickness effects on WVP.

Abstract

ABSTRACT The ASTM E96 Standard Method for determining water vapor permeability (WVP) was modified for hydrophilic edible films. Accurate measurement of relative humidity conditions and maintenance of 152 m/min air speeds were essential outside the test cups. The WVP Correction Method was developed to account for the water vapor partial pressure gradient in stagnant air layer of the test cup. Errors were as high as 35% without this correction. Applying these guidelines explained commonly observed thickness effects on WVP values of hydrophilic films. Relative humidity was the cause of observed thickness effects.