Véronic Landry

Nanocrystalline Cellulose: Morphological, Physical, and Mechanical Properties

Morphological, physical, thermal, and mechanical properties of nanocrystalline cellulose (NCC) were determined. Moisture content as well as oil absorption were also studied. The NCC was obtained from sulfuric acid hydrolysis of wood pulp. Transmission electron microscopy showed that NCC has a diameter of 10 nm and a length of 150 nm. Fourier transform–Raman spectroscopy and x-ray diffraction experiments both showed that NCC has a very high degree of crystallinity. Using an Abbe refractometer, the average refractive index of the NCC in different solvents was determined to be 1.499. Hardness and elastic modulus of the homogeneous, translucent NCC films were determined by nanoindentation technique. Oil absorption and moisture content were related to the particle size.

Mechanical properties of UV-waterborne varnishes reinforced by cellulose nanocrystals

There are many instances in the literature of nanocellulose-thermoplastic composites, but there are few studies on coatings reinforced by cellulose nanocrystals (CNCs). The overall objective of this research was to develop organic nanoparticles-reinforced UV-water-based coatings for wood applications and to study the effect, mainly on wear properties, of the final composite coatings. CNC was mixed in the varnishes to improve the mechanical properties of the coatings. One of the key aspects in the technology of nanocomposites remains the dispersion of the nanoparticles within the matrix as well as its affinity with the matrix. To quantify the dispersion, efficient methods of characterization are needed in order to reveal the nanosized particles. In this article, a novel characterization method based on atomic force microscopy was employed to characterize such nanocomposite coatings, by measuring surface nanoroughness, which is clearly correlated with quality of dispersion and mechanical properties. CNC was modified by either alkyl quaternary ammonium bromides or acryloyl chloride. The mechanical properties (abrasion and scratch resistances, hardness and adhesion) were analyzed and compared to the reference varnish without nanoparticles. The modified CNC addition in UV-water-based coatings results in an approximately 30–40% increase in wear resistance (abrasion and scratch), without any loss of appearance.

Nanocrystalline Cellulose as Effect Pigment in Clear Coatings for Wood

Nanocrystalline cellulose (CNC) is a renewable material with high potential in many applications. Due to its unique self-assembly and optical properties, CNC tends to behave as an iridescent pigment. The aim of this research was to explore the potential of CNC as an effect pigment in wood coatings. CNC-based coatings were developed from an aqueous CNC solution, a UV-curable water-based clear coating formulation, several colorants, and specialized additives. In this paper, the morphology of the resulting CNC films was investigated through circular dichroism and optical microscopy under polarized light. The effect of the CNC surface charge changes was monitored through zeta potential measurements. Color changes, or travel, and flop index were used to assess the iridescent effect of the coatings containing CNC. The experimental wood coatings contained CNC showed that the enhancement of the iridescent effect depends on the distribution and alignment of the CNC rod-like particles in order to generate the right pitch in the helical structure and their interaction with the polymer matrix as well with the additives. In conclusion, CNC could be successfully used as effect pigment in finishing systems, which can enhance the attractiveness and bring out the special grain of various types of wood.

Surface Preparation of Wood for Application of Waterborne Coatings

Abstract Year after year, water-based coatings gain market share due to new regulations on volatile organic compound emissions and voluntary certification programs. Work still has to be done on wood surface preparation, however, for water-based finishes to become truly reliable. In this research, water-based and solvent-based coatings were applied to edge-glued panels of yellow birch (Betula alleghaniensis Brit.). Sandpaper grits from 150 to 280 were used to prepare wood surfaces prior to coating application. A first series of specimens was prepared with a wiping stain and a second series with a spray stain. Contact angle measurements showed that surface preparation—more precisely the sandpaper grit—strongly affects water wettability and hence coating adhesion. Adhesion was found to change with the contact angle of the water. It was found that using a 150-grit sandpaper leads to unfilled wood cavities, high contact angles, and poor coating adhesion. At the opposite end of the range, using a 180-grit sandp...

Transparent UV-cured clay/UV-based nanocomposite coatings on wood substrates: surface roughness and effect of relative humidity on optical properties

The esthetic durability of coatings on wood surfaces of components constituting wood furniture used in bathrooms is generally affected by high humidity. In this study, surfaces of yellow birch wood (Betula alleghaniensis Britton) were protected with three different types of transparent UV-cured multilayer coatings (MCs), namely MC1, MC2, and MC3. Each MC consisted of three layers: primer, sealer, and topcoat. MC1, MC2, and MC3 contained, respectively, 0, 1, and 3 wt% of nanoclay (NC) in the topcoat, while no nanoparticle was added in the primer and sealer. The surface roughness of coated wood surfaces was measured before accelerated aging and optical properties (color and gloss) were investigated before, during, and after accelerated aging. Statistical results have shown that: (1) all coated wood samples have a similar surface roughness and (2) NC in the topcoat does not have a significant effect on initial color, whereas its effect on initial gloss is significant. There is a significant effect on relative humidity (RH) on color changes, but not between the different types of MCs. With respect to gloss, a lowering of gloss retention with the increase in aging time and RH has been observed for all coatings on wood surfaces. Significant differences appear only at high RH between: MC1 vs MC3 and MC2 vs MC3.

Metal Oxide Sol-Gels (, AlO(OH), and ) to Improve the Mechanical Performance of Wood Substrates

Wood is a renewable material widely used in many applications due to its unique properties and distinctive look. However, as wood is organically constituted, it is slowly destroyed by the long-term impact of oxygen, UV radiations, water, and biological attacks (Mahltig et al., 2008). Therefore, protective treatments are necessary to improve the mechanical, thermal, and chemical properties of wood. In order to improve the mechanical properties of sugar maple (Acer saccharum Marsh.), as this species is widely used in the wood products industry, samples of sugar maple were impregnated with sols of metal oxides (AlO(OH), SiO2, and ZrO2). The weight gain and two different techniques of microscopy were used to evaluate the efficiency of the impregnation in the wood samples. The mechanical properties were evaluated using hardness test, scratch test, and impact test. It was shown that the maple samples impregnated with ZrO2 led to the greatest improvement of the mechanical properties.

Determination of In Situ Esterification Parameters of Citric Acid-Glycerol Based Polymers for Wood Impregnation

The development of wood treatments is of increasing industrial importance. A novel technique for improving the properties of lodgepole pine and white pine through modification of the microstructure is described. The present investigation is devoted to the synthesis and determination of in situ parameters of citric acid and glycerol based polymers for wood impregnation. This solvent free approach is environmentally friendly and achieved through an esterification condensation reaction under acidic conditions. Crude glycerol and citric acid reactants were cross-linked via a curing process at 160 °C creating a polymer with only water as the byproduct. The ester bonds and crosslinking levels were controlled using different catalysts and citric acid contents and related to the reaction time and temperature. The nature of bonding within the polymers and at the wood cell walls was determined by FT-IR analysis. The thermal properties such as glass transition temperature (Tg) were studied using TGA/DSC and the effect of citric acid content and catalyst type determined. Dimensional stability of impregnated wood samples improved above 50% for each sample with HCl and p-TSA catalysts compared to control samples. FTIR spectra were studied to show the presence of the ester linkages of the polymer in situ at the wood cell walls. Bonding between the polymer and wood macromolecules were observed by scanning electron microscopy and interpreted as evidence of chemical bonds at the wood cells. When prepared using a catalyst, the polymer was intimately incorporated into wood structure significantly improving the substrate dimensional stability. Enhanced stability makes this approach of particular interest for exterior wood products especially as a green renewable option for the wood industry.

Synthesis and incorporation of poly(methyl methacrylate) microspheres with UV stabilizers in wood clear coating binder

The durability of clear coatings is an important problem in the coatings industry. This problem can be partly solved with the addition of UV absorbers (UVAs) in the coating formulation. UVAs can absorb part of the UV radiation and convert it into harmless heat. Organic UVAs are prone to photodegradation and can migrate in the binder of a coating formulation. In this study, commercial UVAs have been encapsulated in poly(methyl methacrylate) microspheres using the internal phase separation method. Microspheres have been incorporated into a clear acrylic binder. The acrylic was then applied on wood panels and was placed into an artificial UV chamber. Efficiency of coatings after aging as well as chemical and physical properties were monitored using a colorimeter, FTIR spectroscopy and transmission electron microscopy. This study presents a comparison between the efficiency of free and encapsulated Tinuvin 1130 and 292 commercial absorbers. Results have shown that the coating efficiency is slightly improved when using the encapsulated products.

Wear resistance of nanocomposite coatings

There are several instances in the literature of nanocellulose–thermoplastic composites, but there are few studies on coatings reinforced by cellulose nanocrystals. One of the key aspects in the technology of nanocomposites remains the dispersion of the nanoparticles within the matrix. To quantify the dispersion, efficient methods of characterization are needed. In this chapter a new characterization method based on atomic force microscopy is applied to characterize such nanocomposite coatings. The overall objective of the research is to develop nanoparticles-reinforced UV–water-based coatings for wood applications, and to study the effect mainly on wear properties of the final composite coatings. Cellulose nanocrystals (CNC) was mixed to the coating formulation to improve the mechanical properties of the coatings. The coating formulations were sprayed on sugar maple boards, which were then placed in an oven to evaporate the water to finally be UV-cured. The dispersion analysis was done by atomic force microscopy by measuring roughness. Elemental analysis was done to measure the amount of TiO2 white pigment in paint aggregates. CNC addition in coatings results in a ca. 20–30% increase in wear resistance, without loss of appearance. When the reinforced varnish was applied to an opaque paint layer, rather than the wood, the same reinforcement took place.

Surface engineering of wood substrates to impart barrier properties: a photochemical approach

In this study, sugar maple and white pine, two species of wood commonly used in indoor and outdoor applications, were treated by photo-initiated chemical vapor deposition to impart barrier properties. After treatment, wood wettability decreased significantly, as evidenced by water contact angle measurements (from 50° to 113° for sugar maple and 87° to 172° for white pine). Further, beyond being able to repel water, the coating shows the ability to breathe, evidenced by standardized vapor sorption tests. However, accelerated weathering via ASTM G155 testing determined that the treatment could not protect the wood from photo-degradation, or retain its properties post-weathering. This treatment could therefore be best suited for wood pre-treatment in combination with other coatings.