Grafting of Fatty Acids on Polyvinyl Alcohol: Effects on Surface Energy and Adhesion Strength of Acrylic Pressure Sensitive Adhesives

Eva Germek,Markus Schmid,Martina Lindner

doi:10.3389/fmats.2019.00335

Abstract

Chemical grafting with fatty acid chlorides is known to reduce the surface tension of polymer substrates. The aim of this study was to evaluate the effect of different grafting parameters on functional properties such as the surface tension of grafted substrates and adhesion of acrylic pressure sensitive adhesives (PSA) on those substrates in dependence of storage time. There-fore, two substrates, paper and polyethylene terephthalate (PET), were coated with polyvinyl alcohol (PVOH). The PVOH showed similar degrees of hydrolysis but different molecular weights. Fatty acid chlorides (palmitoyl chloride, stearoyl chloride) were grafted on pure PET, pure paper, PVOH coated paper, and PVOH coated PET. On these samples, roughness was measured and peel strength and surface energy were determined over storage time. Peel strength was observed to increase with roughness. The chain length of fatty acid chlorides and storage time did not majorly influence peel strength.

Highlights

The chemical grafting method used here is based on the esterification of fatty acid chlorides with hydroxyl groups under gaseous conditions
Surface energy was measured on polyethylene terephthalate (PET)/fatty acid chlorides (FA) and G/FA over storage time (Figure 4 and Supplementary Tables 1, 2)
For each substrate (S) there are six different variations differing in coating (C) type and fatty acid chloride (FA)

Summary

Introduction

The chemical grafting method used here is based on the esterification of fatty acid chlorides with hydroxyl groups under gaseous conditions. During the esterification of the carbonyl group of a fatty acid chloride with the hydroxyl group, hydrogen chloride is formed (Stinga, 2008). Chemical grafting is one method to achieve hydrophobic surfaces and a low surface energy (Stinga, 2008). Grafting of fatty acids might be a suitable treatment for paper and PET to be used as release liners for PSAs. low surface energy alone does not guarantee perfect release performance. Other important factors influencing adhesion and peel strength (which were not further evaluated in this study) are fluidity, strength and exact chemical composition of the release agent as well as roughness, modulus and flexibility of the substrate, peel velocity, and peel geometry (Newby et al, 1995; Zhang Newby and Chaudhury, 1997; Gordon et al, 1998; Hose, 2007; Mohammed et al, 2016)

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Conclusion