Self-Healing UV-Curable Acrylate Coatings for Wood Finishing System, Part 2: Impact of Monomer Structure and Self-Healing Parameters on Self-Healing Efficiency

Chloé Paquet,Stephen Brown,Véronic Landry,Jolanta E Klemberg-Sapieha,Jean-François Morin

doi:10.3390/coatings11111328

Abstract

Wood is increasingly used in construction for the benefits it brings to occupants and for its ecological aspect. Indoor wood products are frequently subject to mechanical aggressions, their abrasion and scratch resistance thus need to be improved. The coating system ensures the wood surface protection, which is, for wood flooring, a multilayer acrylate UV-curable 100% solid system. To increase the service life of wood flooring, a new property is studied: self-healing. The objective of this study is to observe the impact of monomer structure on self-healing efficiency and the effect of self-healing parameters. A previous formulation was developed using hydrogen bond technology to generate the self-healing property. In this paper, the assessment of the formulation and the self-healing parameters’ impact on self-healing efficiency as well as the physicochemical properties are presented. The composition of the monomer part in the formulations was varied, and the effect on the conversion yield (measured by FT-IR), on the Tg and crosslinking density (measured by DMA) and on mechanical resistance (evaluated via hardness pendulum, indentation, and reverse impact) was analyzed. The self-healing efficiency of the coatings was determined by gloss and scratch depth measurements (under constant and progressive load). It was proven that monomers with three acrylate functions bring too much crosslinking, which inhibits the chain mobility necessary to observe self-healing. The presence of the AHPMA monomer in the formulation permits considerably increasing the crosslinking density (CLD) while keeping good self-healing efficiency. It was also observed that the self-healing behavior of the coatings is different according to the damage caused. Indeed, the self-healing results after abrasion and after scratch (under constant or progressive load) are different. In conclusion, it is possible to increase CLD while keeping self-healing behavior until a certain limit and with a linear monomer structure to avoid steric hindrance. Moreover, the selection of the best coatings (the one with the highest self-healing) depends on the damage.

Highlights

The reference formulation is the most efficient self-healing coating developed in the previous study [15], i.e., the HEMA–Ebecryl 4738 formulation
A variable quantity of PETA and AHPMA monomers were added to this formulation to improve the mechanical properties of the coatings and to study the impact of these monomers on self-healing efficiency
The Fourier Transformation Infrared Spectroscopy Measurements (FTIR) spectroscopy allows the calculation of acrylate groups conversion yield in the formulations following Equation (1)

Summary

Introduction

It has been proven that being in contact with the natural elements reduces stress, maintains the feeling of well-being, and increases productivity and performance. This phenomenon, called biophilia [1], was elaborated by the biologist Edward O. Many institutions consider the biophilia in construction projects [3] by increasing the use of wood as indoor material in walls, floors, or furniture. As wood use increases in construction, it is important to ensure wood resistance to mechanical and chemical aggressions. This permits the improvement of wood service life

Objectives

Methods

Results

Conclusion