Bridging Adhesion and Barrier Properties with Functional

180 Pages·2007·49.8 MB·English

Bridging Adhesion and Barrier Properties with Functional
Dispersions

Towards Waterborne Anti-Corrosion Coatings

Willem Jan Soer
Bridging Adhesion and Barrier Properties with Functional Dispersions: Towards
Waterborne Anti-Corrosion Coatings/ by Willem Jan Soer
Eindhoven: Technische Universiteit Eindhoven, 2007

Proefschrift. – ISBN 978-90-386-1197-6

Printed by PrintPartners Ipskamp, Enschede, 2007
Cover design by Willem Jan Soer

© 2007, Willem Jan Soer

The research described in this thesis was financially supported by innovation-oriented
research program (IOP) on surface technology (IOT03001), sponsored by the Dutch
Ministry of Economic Affairs.

A catalogue record is available from the Eindhoven University of Technology Library
(http://w3.tue.nl/en/services/library).
Bridging Adhesion and Barrier Properties with Functional Dispersions

Towards Waterborne Anti-Corrosion Coatings

PROEFSCHRIFT

ter verkrijging van de graad van doctor aan de
Technische Universiteit Eindhoven, op gezag van de
Rector Magnificus, prof.dr.ir. C.J. van Duijn, voor een
commissie aangewezen door het College voor
Promoties in het openbaar te verdedigen
op dinsdag 22 januari 2008 om 16.00 uur

door

Willem Jan Soer

geboren te Staphorst
Dit proefschrift is goedgekeurd door de promotoren:

prof.dr. R.A.T.M. van Benthem
en
prof.dr. C.E. Koning

Copromotor:
dr. W. Ming
CHAPTER 1. INTRODUCTION 1
1.1 Introduction 2
1.2 Anti-corrosion coatings 2
1.3 Requirements for anti-corrosion coatings 3
1.4 Latexes and dispersions 6
1.5 “One stone, multiple birds“ strategy 8
1.6 Objectives and thesis outline 8
1.7 References 10
CHAPTER 2. SYNTHESIS AND MODIFICATION OF MALEIC ANHYDRIDE
CONTAINING COPOLYMERS 15
2.1 Introduction 16
2.2 Experimental 20
2.3 Results and discussion 25
2.3.1 Free radical copolymerization with maleic anhydride and α-olefins 25
2.3.2 RAFT-mediated polymerization 27
2.3.3 Imidization of PSMA copolymers 38
2.4 Conclusions 44
2.5 References 44
CHAPTER 3. SURFACTANT-FREE ARTIFICIAL LATEXES FROM MALEIC
ANHYDRIDE CONTAINING COPOLYMERS 49
3.1 Introduction 50
3.2 Experimental 51
3.3 Results and discussion 52
3.3.1. Used polymers 52
3.3.2. Preparation of artificial latexes 53
3.3.3 Latexes obtained from other polymers 60
3.4 Conclusions 63
3.5 References 63
CHAPTER 4. CROSSLINKING AND FILM FORMATION OF SURFACTANT-
FREE LATEXES 65
4.1 Introduction 66
4.2 Experimental 69
4.3 Results and Discussion 72
4.3.1 Properties of the latexes in the presence of crosslinker 72
4.3.2 pH stability of the latexes in the presence of crosslinker 75
4.3.3 Interaction between crosslinker and latexes 78
4.3.4 Model studies on crosslink chemistry 81
4.3.5 Crosslinking kinetics 86
4.3.6 Fate of the amic acid moieties originating from ammonolysis 91
4.3.7 Film formation 92
4.4 Conclusions 101
4.5 References 102
CHAPTER 5. MECHANICAL AND ANTI-CORROSIVE PROPERTIES OF
LATEX-BASED COATINGS 105
5.1 Introduction 106
5.2 Experimental 110
5.3 Results and discussion 115
5.3.1 Coating properties 116
5.3.2 Adhesion 121
5.3.3 Barrier properties 125
5.3.4 Immersion tests 141
5.4 Conclusions 156
5.5 References 157
CHAPTER 6. EPILOGUE 159
SUMMARY 163
SAMENVATTING 165
CURRICULUM VITAE 169
DANKWOORD 171
Chapter 1. Introduction

Abstract
In the introduction of this thesis the strategy to obtain anti-corrosion coatings from
water-borne systems will be explained. A short introduction to coatings will be given,
followed by a more detailed look at the properties of typical anti-corrosion coatings,
such as barrier properties and adhesion. The approach of using water-borne latexes to
obtain homogeneous films with a combination of different properties, referred to as
“one stone, multiple birds” approach, will be explained. Finally, an overview of the
contents of the thesis will be given.
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Chapter 1
1.1 Introduction
Coatings play a crucial role in the applicability and the lifetime of a large group of
products in modern society. They are used for both esthetic and protective purposes,
and can be evaluated by a large variety of properties, such as color, gloss, durability
and mechanical properties. Protective coatings prolong the lifetime of a wide variety
of products, such as wood and metal objects, by creating a barrier between the actual
product and its surroundings. By doing so, the product does not suffer from
degradation as it would while being in direct contact with the environment. Wood is
painted to prevent rotting, while metals are coated to prevent corrosion (or “rust”) of
the metal. Coatings can be roughly divided in four groups; organic, inorganic,
conversion and metallic coatings 1. In this thesis, the focus will be on organic
coatings.
Almost all commercial organic coatings consist of a large number of different
“ingredients”, each of which serves a specific purpose. Polymers form the matrix of
the final coating, while other compounds can be added to obtain the desired
processing or final product properties. To obtain an appealing color pigments are
added, improved scratch resistance can be obtained by adding small silica, clay or
titanium dioxide particles, and good chemical properties are obtained by crosslinking
the polymers providing a dense network. Furthermore, additives are frequently used
to improve film formation, viscosity and formulation stability among other properties
2. Every coating is a balanced system consisting of different ingredients, leading to the
specified desired properties.
The main goal of this thesis is to prepare a polymer matrix that can protect metallic
substrates against corrosion by combining as many of the desired properties as
possible in one polymer system. Furthermore, to obtain an environmentally friendly
system, this coating will be applied from a water-borne system. The obtained coating
will be studied as a possible candidate for use in anti-corrosion coatings.

1.2 Anti-corrosion coatings
Corrosion is a process of a metal reacting with oxygen or water, leading to the
formation of metal oxides 1. One of the most commonly observed examples of
corrosion is rust on iron substrates. This oxidation of iron leads to the formation of a
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Introduction
porous iron oxide layer. Due to the porosity of the layer, the corrosion products (such
as Fe2+-ions) can be freely transported from the substrate to its surroundings. This
leads to a progressive corrosion of the metal object which finally leads to decreased
mechanical properties and therewith failure of the object. Other compounds, such as
pure aluminum, form a closed oxide layer, which forms a barrier against the transport
of water and oxygen, and therewith preventing it from corrosion.
A proper coating applied on the substrates prevents the corrosion reactions to take
place, and therewith increases the lifetime of the product. The use of magnesium,
which is one third lighter than aluminum, in weight saving applications such as
automotive, aerospace and electronic industries is severely limited by the lack of
corrosion resistance. Therefore, a large number of different techniques to protect the
metal from corrosion has been studied in recent years 3, 4. A wide variety of protective
coatings, such as those consisting of ceramics 5, 6, (rare earth7-9)-metals 10-14,
phosphates15, ionic liquids16-18, diamond like carbon19, silanes 20, 21 or anodic
pretreated magnesium 22 have been reported. Most of these techniques suffer from
drawbacks like environmental issues, inhomogeneities, high costs or poor mechanical
properties of the final coating 3.
The use of organic (or polymeric) coatings reduces these drawbacks significantly.
Most organic anti-corrosion coatings that are currently used are applied from systems
with a high content of volatile organic compounds (VOCs)23. Due to stringent
regulations concerning environmental impact and human safety, the use of VOCs in
coating formulations is strictly limited by law 24. Therefore, since the late 1980’s,
water-borne anti-corrosion coatings were developed. Water-borne coatings that are
used for this purpose usually rely on the addition of anti-corrosive compounds, such
as zinc-phosphates 25-27 or iron oxides28 or anticorrosive surfactants29. The aim of this
work is to develop a coating that protects metallic substrates without the use of any of
these compounds. To meet the requirements for anti-corrosion coatings, multiple
aspects should be considered.
1.3 Requirements for anti-corrosion coatings
Anti-corrosion properties can be obtained by applying a coating with good barrier
properties to the substrate that needs to be protected. Coatings with good barrier
properties should reduce the transport of water as well as ions that facilitate corrosion,
such as Cl-, through the polymer matrix 30-33. To prevent the transport of water
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Chapter 1
through the coating, and therewith ions, a sufficiently densely crosslinked polymer
should be applied 33, 34. The polarity of the polymers also plays a role in the barrier
properties of coatings against water transport35. With increasing polarity, the barrier
properties towards liquid water generally decrease 34. Therefore, an anti-corrosion
coating is preferably hydrophobic after it has been applied. Besides, water transport at
the interface layer between polymer and substrate should be prevented as well, since
this will enhance corrosion processes that occur underneath the coating (or filiform
corrosion). This process starts in most cases at the edges of the coated substrates, as
well as at defects in the coating 36, 37. This will cause the coating to delaminate from
the substrate, which in turn enhances the corrosion processes 38, 39.
Apart from excellent barrier properties, also good chemical and mechanical
properties should be obtained. The chemical properties should prevent the coating
from dissolving in organic solvents. A good chemical resistance can be obtained by
forming a highly crosslinked network. The mechanical properties should prevent the
coating from failure after impact. The coating should be both hard and flexible,
resulting in high toughness. If the coating is very hard, but not flexible, damage can
occur easily upon impact. If the coatings are soft and flexible, the coating is also
destroyed easily, for instance by scratching.
As a third requirement, a good adhesion of the coating to the substrate is essential to
increase the (filiform) corrosion resistance 31, 36, 37. In most cases metallic substrates,
such as aluminum or magnesium alloys, contain a lot of oxides and hydroxide groups
on the surface (Figure 1.1), due to pretreatments or reactions with oxygen or water
from the air. These metal hydroxides or oxides allow for good interaction with
functional groups in polymers. Chemical bonds of the coating to the substrate can be
obtained by choosing materials that have strong interaction or undergo reaction with
the metal oxides that are present on the surface of metals 40-43. Carboxylic acids and
amines are known to give strong ionic bonds with aluminum oxide, while other
functional groups such as alcohols give weaker interactions by dipole interactions 44.
These weak bonds are easily destroyed when water accumulates at the interface 45. To
optimize the interactions between coating and substrate, the substrates need to be
thoroughly cleaned from oil or lubricants before a coating is applied. Furthermore, an
appropriate surface pretreatment can increase the number of metal oxides, and
therewith provide stronger bonding between the coating and the substrate 37, 46, 47.

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