A FTIR study of interfacial interactions between ethylene copolymers and hydrated aluminium surfaces

Abstract

Interfacial interactions to hydrated aluminium were examined for poly(ethylene-covinylacetate) EVA, poly(ethylene-co-butylacrylate) EBA, and poly(ethylene-co-acrylic acid) EAA. By means of IR reflection-absorption spectroscopy, the interactions between the effective functional groups were analysed at the polymer/aluminium interface. Thin copolymer films were prepared by solution casting onto aluminium, which had been hydrated by immersion in boiling water. The spectra representing the interface material revealed a strong hydrogen bond interaction between hydroxyl groups on the hydrated aluminium surface and the carbonyl oxygen in the ester group in EVA and EBA. The absorbance mode of the hydrogen bonded carbonyl was displaced to lower wavenumbers and appeared 34 cm-1 and 38 cm-1 below the 'free' carbonyl for EVA and EBA, respectively, which indicates that the hydrogen bond is very strong. For the C-O stretching mode in the ester group, a displacement of 36 cm 1 in the opposite direction was observed, also an effect due to the hydrogen bond to the carbonyl. Furthermore, it was found that the absorptivity for the hydrogen bonded carbonyl was much higher than for the 'free', and for that reason a relative absorptivity ratio between them was determined. For EAA cast onto hydrated aluminium surfaces, the absorbance mode of the carbonyl disappeared, but new peaks arose at lower wavenumbers indicative of a carboxylate. This was explained to be due to a reaction between carboxylic acid groups and aluminium hydroxyl groups on the hydrated surface.

Adhesion between LDPE and hydrated aluminium in extrusion-coated laminates

“…This has also been suggested by other authors to be the adhesion mechanism for LDPE laminated to porous surfaces [16], and also in the case of hydrated aluminium [17][18][19]. We have also shown that the hydroxyl groups developed on the hydrated surface can form strong hydrogen bonds to carbonyls in ethylene copolymers containing ester groups, as in butyl acrylate and vinyl acetate [11]. At higher temperatures, it was shown that this bond induced a catalysed hydrolysis due to the evaporation of physically adsorbed water [14].…”

“…This was suggested to be due to interaction with the electron-accepting aluminium in the oxide. In a similar study but with hydrated aluminium, a strong interfacial interaction was found which displaced the absorbance of the carbonyl in EBA by 37 cm-' from the bulk [11]. The large displacement in this case was explained to be due to hydrogen bonding.…”

“…During the hydration of aluminium in boiling water, the chemical composition on the surface changes from an aluminium oxide to an aluminium oxyhydroxide according to the reaction The hydration of aluminium under these conditions is known to produce an adherent and porous pseudoboehmite film, which contains physically adsorbed water. The reaction between aluminium and boiling water can be followed by means of IR spectroscopy [11]. Before the reaction starts with evolution of hydrogen gas on the surface, an induction period is observed.…”

“…At higher temperatures, it was shown that this bond induced a catalysed hydrolysis due to the evaporation of physically adsorbed water [14]. For ethylene copolymers with acrylic acid, carboxylate coupling was found to form at the interface with hydrated aluminium [ 11 ]. The bonds formed between different polar groups and hydrated aluminium are stronger than those formed with an ordinary oxidized aluminium surface, leading to improved adhesion.…”

Interaction of Ester Functional Groups with Aluminum Oxide Surfaces Studied Using Infrared Reflection Absorption Spectroscopy

“…The surface treatment leads to changes in the oxide chemistry and composition, which will have a direct influence on the subsequent bonding behavior with the organic functional groups. 6,7 Stralin et al, for example, found that the ester groups of an EVA polymer showed a stronger bonding to a pseudoboehmite aluminum oxyhydroxide than to a dehydroxylated aluminum oxide. 7 Because of the widespread use of polymer-coated aluminum, knowledge of the nature of the ester-oxide bond is important.…”