In Situ Observation of Chemical Reactions at Buried Solid/Solid Interfaces in Coextruded Multilayer Polymer Films

Abstract

The characterization of chemical reactions at the buried interface is critical to understand interfacial molecular interactions and improve interfacial properties like adhesion. Interface-sensitive sum frequency generation (SFG) vibrational spectroscopy can probe the buried interface in situ nondestructively. While SFG has been used to study many model polymer interfaces, it has never been applied to study multilayer polymer films produced on commercial coextrusion lines.Here, we apply SFG to elucidate the molecular details of chemical reactions at the buried interface in multilayer cast films consisting of maleic anhydride (MAH)-modified Tie layers promoting the adhesion between polyamide and polyethylene. We demonstrated the utility of SFG to identify the reaction products from the interfacial reaction between MAH and polyamide with varying MAH concentrations and to monitor changes of the interfacial molecular orientation. The developed approach is generally applicable to probe chemical reactions and molecular interactions at buried interfaces in multilayer polymer films.

Quantifying Chemical Reactions and Interfacial Properties at Buried Polymer/Polymer Interfaces

“…Our SFG spectrometer has been described in detail in a previous publication. 4 Briefly, the custom-designed SFG system is based on a Spectra Physics Ti:sapphire laser producing 5 mJ pulses, at 1 kHz, centered at 800 nm. Of that source, 2 mJ is used to pump a Light Conversion (Vilnius, Lithuania) optical parametric amplifier (OPA).…”

“…Recently, we have used SFG to study the interfacial MAH chemistry using MAH- g -PE at the polymer/tie interface in several systems including nylon/tie and EVOH/tie model systems, as well as coextruded multilayer polymer films containing a nylon/tie buried interface. ,,, The primary mechanisms for the interfacial reaction of MAH with both nylon and EVOH were elucidated with model systems (spin-coated nylon or EVOH film in contact with MAH- g -PE pellets), using SFG to observe the formation of the imide or ester/acid product peak, as well as the other structural changes to the interface during the reaction. ,, We also observed similar reaction products at the interface in coextruded multilayer polymer films, demonstrating the utility of SFG for studying these more complex commercially relevant systems . Since these model systems were conducted on tie layers with excess MAH, this study describes quantitative analytical research performed on model systems with a range of MAH concentrations.…”

“…8−10 Typically, the MAH-modified polyolefin tie layer is miscible with the adjacent polyolefin layer and can form covalent bonds via reaction of MAH with a functional group on the barrier layer such as nylon or EVOH, forming a strong linkage between the two polymers. [4][5][6]11,12 While MAH-modified polymers have been studied for decades, and many commercial products exist, only recently have we begun to characterize the molecular details of the buried interfacial chemistry responsible for the improved adhesion. 8,9,11−15 Understanding the chemistry at the tie/polymer interface is critical to design more cost-effective, reliable, and high-quality packaging.…”

“…11,12,15 We also observed similar reaction products at the interface in coextruded multilayer polymer films, demonstrating the utility of SFG for studying these more complex commercially relevant systems. 4 Since these model systems were conducted on tie layers with excess MAH, this study describes quantitative analytical research performed on model systems with a range of MAH concentrations. We utilize SFG to quantitatively study the MAH concentration-dependent reaction at the polymer/tie interfaces in both EVOH and nylon model systems, elucidating crucial details of the reaction as a function of different MAH concentrations.…”

Silane Effects on Adhesion Enhancement of 2K Polyurethane Adhesives

“…Sum frequency generation vibrational spectroscopy (SFG) is an advanced and unique technique to study surfaces and buried interfaces in situ nondestructively. − SFG is second-order nonlinear optical spectroscopy. According to its selection rule, SFG signals can only be detected from materials without inversion symmetry (under the electric dipole approximation). ,,,− ,− Therefore, most cases the SFG signal can only be generated from surfaces/interfaces (with no inversion symmetry), not from the bulk media (which usually are centrosymmetric).…”