Re-Examining the Oxygen Barrier of Nylon 6 Films. I. Role of Moisture and Processing Induced Variables

Abstract

A common misconception over the years has been that the oxygen transmission rate (OTR) of nylon 6 increases as the relative humidity (RH) increases from 0 to 100%. Recent OTR measurements, however, have revealed that the OTR of nylon 6 exhibits a minimum at about 35% RH, i.e., maximum barrier. The improvement factor [OTRO%RH/OTR35%RH] depends on the type of nylon 6 film, e.g., 1.7X for cast film (AlliedSignal's Capran' film) and 2.7X for biaxially oriented film (AlliedSignal's Capran Emblem" film). In fact, there is no deterioration of OTR up to 65-80% RH, i.e., OTRO%RH OTR65%RH for cast films and OTRORH = OTR80%RH for biaxially oriented nylon 6 films. Prompted by this unexpected development, the role of morphological parameters in controlling the OTR of nylon 6, has been revisited. Infrared (IR) spectra reveal structural changes that can partly relate to the OTR vs% RH dependence. A neural network based approach has been used to model the OTR vs% RH curves in the 15-45% crystallinity range and make projections at low crystallinities (e.g., 0-15%) where direct OTR measurements would have been unreliable. Having known the effect of crystallinity on a quantitative basis, we have been able to demonstrate that the contribution of orientation (i.e., after correcting for induced crystallinity) to the OTR of nylon 6, is insignificant. Under otherwise similar physicochemical structural environment, processing history (i.e., shockcool) appears to have about 40% negative impact on the OTR of nylon 6. The highlight of this manuscript is that it quantifies the impact of moisture andprocessing related parameters on the OTR of nylon 6.