Probing Molecular Behavior of Carbonyl Groups at Buried Nylon/Polyolefin Interfaces in Situ

Abstract

Nylon and maleic anhydride (MAH)-grafted polyolefin-based thin co-extruded multilayer films are widely used in packaging applications encountered in daily life. The molecular structure of the nylon/MAH-grafted polyolefin buried interface and molecular bonding between these two chemically dissimilar layers are thought to play an important role in achieving packaging structures with good adhesion. Here, the molecular bonds present at a nylon/maleic anhydride (MAH)grafted polyethylene buried interface were systematically examined in situ for the first time using sum frequency generation (SFG) vibrational spectroscopy. The carbonyl stretching frequency region of the SFG spectra of a nylon/MAH-grafted polyethylene buried interface showed the presence of hydrolyzed MAH groups grafted to the polyethylene chain and very low levels of unreacted MAH enriched at the buried interface. The ability of SFG to detect these molecular species at the buried interface yields important understanding of the interfacial molecular structure and provides the basis for subsequent in situ studies of the bonding reaction between the grafted MAH and nylon directly at the interface. This understanding may guide the design of multilayer films with improved properties such as enhanced adhesion between polymer layers. The approach used in this study is general and is applicable to study the molecular characteristics of other buried interfaces of significance, such as buried interfaces involving polymers in solar cells, polymer semiconductors, and batteries. Nylon impact modification is another area of interest where the interaction between the MAH-grafted elastomer and the continuous phase of nylon is important.

Observing a Chemical Reaction at a Buried Solid/Solid Interface in Situ

“…The nylon carbonyl groups seem to lie more toward the plane of the interface at the buried nylon/EO interface than that at the nylon-air surface. Quantitative investigations of the carbonyl bond orientations at the nylon surface and at the buried nylon/ EO interface have been reported elsewhere 64 using the existing methodology for data analysis. 65 The SFG signals detected from the buried interface between nylon and MAHgEO (Figure 3C) reveal a new band at 1725 cm −1 , which is assigned to imide groups and carboxylic acid present in the interfacial reaction product from MAH as shown in scheme 3.…”

“…More details about this peak assignment were reported in a recent publication. 64 In this study, the entire reaction process (reactant consumption and product formation) was directly monitored at the buried nylon/MAHgEO interface at the molecular level and in situ using SFG. Kinetics of Buried Interface Reaction.…”

“…The open circles and solid lines are experimental data and fitting curves, respectively. Adapted with permission from ref . Copyright 2020 American Chemical Society.…”

“…The nylon carbonyl groups seem to lie more toward the plane of the interface at the buried nylon/EO interface than that at the nylon-air surface. Quantitative investigations of the carbonyl bond orientations at the nylon surface and at the buried nylon/EO interface have been reported elsewhere using the existing methodology for data analysis …”

“…This result further corroborates that the peak at 1725 cm –1 arises from the interfacial reaction products. More details about this peak assignment were reported in a recent publication . In this study, the entire reaction process (reactant consumption and product formation) was directly monitored at the buried nylon/MAHgEO interface at the molecular level and in situ using SFG.…”