Surface modification of ethylene-co-acrylic acid copolymer films: Addition of amide groups by covalently bonded amino acid intermediates

Abstract

Amide groups were anchored covalently on the surface of ethylene-co-acrylic acid (EAA) copolymer film by surface grafting of amino acid intermediates. The process consisted of four steps: conversion of carboxylic acid groups on the EAA surface to acid chloride groups, amino acid attachment, conversion of amino acid carboxyl groups to acid chloride groups, and amidation. All steps were carried out at room temperature. ATR-FTIR spectroscopy was used to characterize the film after each step and to measure the kinetics of amino acid attachment. Three amino acids were studied: 12-aminododecanoic acid (12-ADDA), 5-aminophthalic acid (5-APA), and L-aspartic acid (AA). The longer-chain 12-ADDA compound was selected for its chemical similarity to migratory gatty amides that are commonly used to alter the frictional behavior of polyolefin films. The 5-APA and AA compounds were selected because each has two carboxylic acid groups that can be converted to amide groups. After amidation, the modified EAA films were characterized by static water contact angle measurements and scanning probe microscopy. Results showed that the 12-ADDA reacted to the surface much faster than the 5-APA or AA. Several steps of aggressive rinsing confirmed that the 12-aminododecanamide was chemically anchored onto the EAA surface. As a result, both hydrophilicity and surface roughness were increased. © 2004 Wiley Periodicals, Inc.