PRA’s 13th Wood Coatings Congress

This work originated from the evidence that wooden products, during their use, may come into contact with liquid substances and fluid preparations (e.g. hand-creams) for prolonged or repeated periods of time, potentially resulting in progressive variations in the hardness of the coating films applied on their surfaces. Consequently, they become more prone to defects caused by reduction in adhesion and by the effects of mechanical actions, such as cleaning operations, carried out on their surfaces. After many experiments, meetings and discussions the Italian”wood coatings” standardization group has produced a reliable test method that would allow coating manufacturers to develop the most suitable formulations to address this critical issue. Currently (2024), this method is being published as an “experimental standard” to allow the market to acquire the necessary experience both to further improve the test procedure and to optimistically define minimum requirements for coated wooden surfaces in the coming years.

This study examines the surface properties of various biosourced materials from Cameroon to predict their compatibility with polymer resins. By-products like coconut shells, canarium schweinfurthii fruit cores, and raffia vinifera fruit cores were analyzed. Fourier Transform Infrared Spectroscopy (FTIR) with an Attenuated Total Reflection (ATR) device assessed the chemical composition of the materials’ surfaces. Contact angle measurements determined the wettability properties, aiding in calculating surface energy—a crucial factor for predicting polymer resin wetting. The study suggests correlations between surface energy values and chemical composition, aiding in identifying the most suitable biosourced material for polymer impregnation. Co-authors: Narcisse Defo, Rodrigue Nicodeme Tagne Sikame, Ebenezer Njeugna.

Outlook on the various possibilities of using natural and functional fillers in wood coatings. UV curing systems for glossy and matt topcoats, water-based and eximer-curing formulations will be presented. A summary of the newest results in optical and mechanical characteristics as well as cost reduction potential against common used matting agents is also included. Producing environmentally friendly and long-lasting wood coatings for a world that lasts longer.

Before a tree becomes sawn timber, it was encased in bark. The bark’s function is to protect the wood of the living tree, which makes it a natural candidate in the search for bio-based and sustainable components for a protective wood coating. As part of the project SuperBark, we explore the potential of pine and spruce bark derived polyphenol rich nanocelluloses as a component for heavy duty plywood coatings, e.g. in the transportation industry. Combined with wood substrate hardening techniques based on in-situ mineralization, these >95% bio-based coating systems have the potential to fulfill the demanding industry requirements, especially regarding scratch and abrasion resistance as well as surface hardness.

Various matting agents used are discussed in order to compare their impact on the gloss reduction efficiency of 2K WB wood varnishes based on PU dispersion, including matting fillers (e.g. nepheline syenite, talc, silica) as well as additives such as waxes. The impact on gloss reduction at both 60° and 85° angles for the best efficiency of obtaining various gloss levels and their classification are presented, as well as the impact on other parameters of varnishes and coatings, such as storage stability (setting), image clarity, hardness, mar resistance and stain resistance. The importance of properly prepared filler suspensions used to matt coatings as well as their impact on the parameters of liquid varnishes and coatings were discussed. The presented tests were performed in accordance with ASTM test methods, and their results can serve as a guide for formulators looking for appropriate matting agents.

Influence of multiphase latex particles morphology on anti-blocking properties, mechanical strength and elasticity of varnishes and trim paints films was studied. The general focus was put on correlation between coating elasticity and blocking resistance to obtain cracking resistant wood coating. Different types of multiphase binders were tested in varnishes and trim paints for exterior application. Elongation at break, anti-blocking on wood and Lenet’s panels were measured. Additionally adhesion for old alkyds and stain resistance were measured to check coatings quality. Coatings were checked also visually by coating surface observation after weather conditions exposure (QUV chamber).
Composition of multiphase binder polymers influence wood coatings performance with low MTTF and high hardness providing a sufficient balance between blocking resistance and elasticity to ensure long service life and resistance to weather conditions. The study present results of dedicated tests and experiments with reference to polymer morphology and its influence on wood coatings properties.

The objective of this paper is to present new exterior wood coatings made of bio-based polyacrylates from terpenoids, a subcategory of terpenes. Terpenoid-based acrylates are bio-based monomers as they can be synthesized from terpenoids, by-products of the pulp and paper industry. The synthesis and purification of acrylates based on terpenoids on a laboratory scale were carried out. Free radical co-polymerization of biobased menthyl and tetrahydrogeranyl acrylate has been achieved in miniemulsion stabilized by natural in-situ generated surfactant. A range of acrylate copolymers based on menthyl and tetrahydrogeranyl acrylates was synthesized and characterized. Different bio-based latexes with tuneable thermomechanical properties have been produced as binders for exterior wood coatings. The performance of these bio-based coatings has been assessed before and after artificial weathering. This paper shows some results such as Persoz hardness, tensile tests, gloss variation, liquid water permeability, mould resistance.

EPS® – Engineered Polymer Solutions has developed biobased acrylic copolymers with low and High MFFT suited for high-performance furniture and exterior wood finishes, applied as sealer and topcoat, without losing performance in comparison to conventional 100% fossil-based products. The calculated biobased content is up to 20 %, and development is ongoing to increase the biobased content further. Evaluated properties are in-can clarity, solvent compatibility, levelling, transparency, hardness development, gloss, adhesion (dry and wet), chemical and mechanical resistances and anti-blocking properties – helping to ensure durability and minimization of damage to coated objects when stacked. These biobased copolymers will bring improved environmental sustainability and regulatory compliance with no additional cost of utilization.

Sustainability is a prominent concern in the wood coatings sector, with IKEA’s clear sustainability strategy setting a model for better carbon implementation which leads to greater utilization of bio-based or recycled materials. The adoption of sustainable resins is therefore crucial, but concerns about their performance remain. Our team developed a new generation of “better carbon” acrylic resins with increased bio-based or recycled content. These resins serve as direct substitutes for some of our best-selling resins, already widely established in the wood coating market. Coatings formulated with these resins were compared to those with original resins to objectively evaluate their performance. Additionally, we conducted a carbon footprint assessment, comparing results with standard resin counterparts. Our findings indicate that the developed environmentally friendly resins not only reduce environmental impact but also maintain the high-performance standards of the coatings, which are in line with the requirements of most demanding customers.

Radiation curing is well known for its fast curing and energy-efficiency. Driven by higher sustainability targets, the industry is actively working on further improvements. Allnex, a global leader in coating resins, and pioneer in UV, developed a new range of biobased resins for industrial wood sealers and topcoats. These resins are commercially available with C14 and/or mass balance certificate. In this presentation we are demonstrating their use and performance for LED cured industrial wood applications. We’ll cover challenges related to surface curing, and in-depth curing.

Wood as building material is of high interest due to its sustainable origin. In addition, a warm and homelike atmosphere is created if the natural appearance of wood is visible and not hidden by paints or plasters. However, fire-retardant agents often confer opacity or even non-transparency to coating films. When flame-retardant coatings are used, these are often intumescent coatings. This involves the use of ingredients that can lead to unsightly chalking under humid conditions and ultimately to a loss of fire protection performance. The use of transparent wood coatings offers the advantage that the wood or wood-based materials remain visible. In this study, flame retardant agents with different mode of actions are compared and evaluated regarding transparency and flame retardancy. In addition, coating performance is determined after applying wet room conditions. A high content of renewable raw materials was used for both the binders and the flame retardants.

Radiation curing technology is gaining more momentum in industrial wood coatings, being a high performance environmentally friendly solution with superior productivity and energy efficiency. This presentation introduces a cutting-edge new UV-curable polyurethane dispersion that enables the conversion of standard air-curing waterborne systems into radiation-curing solutions. This new product not only enhances performance and productivity of standard air-drying systems, but also serves as a potent booster of waterborne UV-curable systems.

Wood changes its moisture content (MC) dependent on the ambient climate. This material property to absorb and desorb moisture and thereby to moderate the indoor variations in relative humidity, RH, is referred to as moisture buffer capacity, MBC. The MBC has been shown to be utilized for improving indoor climate and saving energy. The challenge of fully utilizing wood’s MBC is that wood products are usually coated for improving their aesthetics and technical properties; these coatings may significantly reduce the MBC. We will present results on the water vapor permeability (cup test) and hygroscopicity (dynamic vapor sorption) of different interior coatings, including FR-paints and -varnishes. Based on hygrothermal energy simulations, we discuss the influence of the coatings on utilizing wood products for the passive regulation of indoor air relative humidity.

To simulate and investigate cracking of coatings on wood surfaces, a zero-span tensile test for coated wood surfaces was developed. On the one hand, this test was carried out on a tensile testing machine. On the other hand, in-situ tensile tests were carried out inside a SEM where cracking of the coating was observed on cross-sections of coated wood samples. Inside the SEM crack formation was observed in-situ and recorded. Mechanical characterization included stress relaxation tests of free coating films to create material models for coatings for FE simulation. This was done with waterborne coating formulations including 12 different acrylic binder polymers. The results showed that there is no detachment on the crack flanks, but the material flows in from the surrounding volume. Microcracks occurred around the opening simulated wood crack which were used to estimate the area of influence of the viscoelastic material.