Tracking Hydroplasticization by DSC: Movement of Water Domains Bound to Poly(Meth)Acrylates during Latex Film Formation.

Sebastian M Dron,Maria Paulis

doi:10.3390/polym12112500

Abstract

The film formation step of latexes constitutes one of the challenges of these environmentally friendly waterborne polymers, as the high glass transition (TG) polymers needed to produce hard films to be used as coatings will not produce coherent films at low temperature. This issue has been dealt by the use of temporary plasticizers added with the objective to reduce the TG of the polymers during film formation, while being released to the atmosphere afterwards. The main problem of these temporary plasticizers is their volatile organic nature, which is not recommended for the environment. Therefore, different strategies have been proposed to overcome their massive use. One of them is the use of hydroplasticization, as water, abundant in latexes, can effectively act as plasticizer for certain types of polymers. In this work, the effect of three different grafted hydroplasticizers has been checked in a (meth)acrylate copolymer, concluding that itaconic acid showed the best performance as seen by its low minimum film-formation temperature, just slightly modified water resistance and better mechanical properties of the films containing itaconic acid. Furthermore, film formation monitoring has been carried out by Differential Scanning Calorimety (DSC), showing that itaconic acid is able to retain more strongly the water molecules during the water losing process, improving its hydroplasticization capacity.

Highlights

The new developments and increased use of waterborne paints can be traced back to a growing environmental awareness and development of strict environmental regulations
The main reason for the lower properties of waterborne coatings comes from the process of film formation and from the connection between the minimum film-formation temperature (MFFT) and the glass transition temperature (TG ) of the binder polymer
For all latexes used during this work butyl acrylate (BA) and methyl methacrylate (MMA) were used as basic co-monomers

Summary

Introduction

The new developments and increased use of waterborne paints can be traced back to a growing environmental awareness and development of strict environmental regulations. The growth of the waterborne coating market is driven by architectural applications, an area which does not have as high requirements for durability and strength as industrial applications. The main reason for this imbalance is that waterborne paints still do not reach the properties of hardness, block and print resistance, the ability to withstand freeze-thaw cycles and dirt pick up resistance combined with a low film-formation temperature, as solventborne paints do. The main reason for the lower properties of waterborne coatings comes from the process of film formation and from the connection between the minimum film-formation temperature (MFFT) and the glass transition temperature (TG ) of the binder polymer. For coating applications, the formation of a hard and scratch-resistant coherent film is essential, which needs a polymer with a high TG. This is known as the “film-formation dilemma” and Polymers 2020, 12, 2500; doi:10.3390/polym12112500 www.mdpi.com/journal/polymers

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