While most of the influences on the mechanical properties of particleboard appear to have been investigated, there is a lack of knowledge about the influence of particle size or particle dimensions due to the absence of a suitable particle measuring technique. The introduction of laser-based 3D scanning technology makes it possible to automatically determine the dimensions, surface area, and volume of particles. In this study, the influence of particle size on the mechanical properties of particleboards was investigated. To isolate potentially overlapping influences, single-layer particleboards with a uniform density profile were produced and analyzed. The amount of adhesive specific to the surface of the (fine) face layer particles and (coarse) core layer particles was adjusted utilizing 3D scanning of the surface areas to ensure comparability despite changes in particle size. It was found that with increasing particle size, the modulus of rupture (MOR) and modulus of elasticity (MOE) increase, while the internal bond strength (IB) decreases. It is considered whether these effects result from a particle-size-dependent orientation of the particles in the board. Furthermore, it is shown that all the aforementioned properties increase with increasing surface-specific adhesive amounts. Examples are provided to demonstrate how such fundamental relationships can be utilized to enhance the particleboard production process.

Particleboard properties result from a variety of material and process-related parameters. While many of them have been extensively investigated, there is a notable lack of knowledge regarding the influence of the particle geometry. This is due to a longstanding lack of suitable measurement technologies and, in the investigation, unintentional overlapping of other interference factors. In the present study, the influence of particle size and surface-specific adhesive amount (SSAA) on the formation of particleboard properties was investigated. Laser-based 3D scanning technology was used to determine the dimensions and the specific particle surface area of particles of different sieve fractions, from which different types of boards were produced. This approach allowed the SSAA to either be maintained at a constant level for boards made from different sieve fractions (influence of particle size) or to be specifically adjusted for boards made from a single fraction (influence of SSAA). To further isolate the influence of particle size and SSAA from the interfering influences of an uneven distribution of particles of different size, adhesive and density, the boards were produced with a single-layer structure and a homogenous density profile. As particle size increased, a statistically significant reduction (all statistical tests were carried out at a significance level of α = 0.05) in modulus of rupture (MOR), modulus of elasticity (MOE) and internal bond strength (IB) was observed, accompanied by an also statistically significant increase in thickness swelling (TS) and water absorption (WA). As the SSAA increased, the MOR, MOE and IB showed a corresponding statistically significant rise, while TS and WA significantly decreased. This knowledge of basic coherences (since significant interference factors were excluded) provides the basis for targeted process optimization in the production of particleboards.

This study reports on the use of poly(lactic acid) (PLA) as a renewable thermoplastic adhesive for laminated panels using birch, spruce, and pine veneers. Consolidated panels were prepared from veneer and PLA foils by hot-pressing from 140 to 180 °C to achieve minimum bondline temperatures. Evaluation of panel properties revealed that the PLA-bonded panels met minimum tensile strength and internal bond strength performance criteria. However, the adhesion interface which developed within individual bondlines varied with distinctions between hardwood and softwood species and PLA grades. Birch samples developed greater bondline strength with a higher pressing temperature using semi-crystalline PLA, whereas higher temperatures produced a poorer performance with the use of amorphous PLA. Panels formed with spruce or pine veneers had lower bondline performance and were also similarly distinguished by their pressing temperature and PLA grade. Furthermore, the potential for PLA-bonded laminated panels was demonstrated by cold water soak testing. Samples exhibiting relatively greater bondline adhesion had wet tensile strength values comparable to those tested in dry state. Our study outcomes suggest the potential for PLA bonding of veneers and panel overlays with the added benefits of being renewable and a no added formaldehyde system.

Wood and its processing into particles are, combined, the largest cost factor in the production of particleboard, followed by the cost of adhesive. Thus, reducing their cost is a goal of process optimization. This study investigated whether possible savings could be identified and quantified by determining the particle surface using automated three-dimensional laser-scanning technology (3D Particleview, Fagus-Grecon). The focus was on saving adhesive by sieving out adhesive-consuming fines. It was shown that, currently, with the actual prices for wood (89 €/t), particle preparation (37 €/t), and adhesive (570 €/t), the resulting additional costs for particles are overcompensated by the savings for adhesive with high adhesive content (e.g., 19%). The assumption of uniform distribution of adhesive on the total surface of all particles was checked for correctness using digital reflected light microscopy (VHX-5000, Keyence). Since urea-formaldehyde (UF) adhesive commonly used in particleboard production can only be detected with increased effort, phenol-formaldehyde (PF) adhesive was applied for the tests. Ultraviolet microspectrophotometry (UMSP) was used to rule out excessive penetration of the adhesive into the wooden tissue of the particles. The examination of the distribution of the adhesive over the surface showed that smaller particle sizes tended to be more heavily coated with adhesive. This means that the calculated savings still underestimate the real-life potential or that potential savings exist even with lower adhesive prices or higher prices for wood.

Fluorescence microscopy was applied to understand adhesion interfaces developed within laminated composite sandwiches formed between poly(lactic acid) (PLA) and wood veneers. Composites formed with maple veneer had greater tensile bond strength when manufactured at 200 °C (10.4 N/mm²) compared to formation at 140 °C (8.7 N/mm²), while significantly lower bond strength was achieved using spruce veneers, at 5.2 and 3.5 N/mm², respectively. Qualitative and quantitative confocal microscopy assessments revealed differing bondline thicknesses and PLA ingress within the wood ultrastructure. Forming maple veneer composites at 200 °C promoted greater PLA mobility away from the bondline to reinforce the wood–PLA interface and deliver associated greater composite bond strength. The addition of 25% wood fibre to PLA led to fibre alignment and overlap within bondlines contributing to relatively thicker, heterogeneous bondlines. Study outcomes show that the composite processing temperature impacts the adhesion interface and composite performance and will have broad application over veneer overlays, laminates and wood plastic composites (WPCs) using wood, particles or fibres with PLA.

Deep understanding of the structural composition and growth of biological specimens is becoming increasingly important for the development of bio-based and sustainable material systems. Full-field nano-computed tomography is particularly suitable for this purpose as it allows for non-destructive 3D imaging at high spatial resolution. However, most biological samples are functionalized by water and respond sensitively to any changes in climate conditions, specifically relative humidity, by adjusting their material moisture content. To date, only a limited number of tomography instruments offer an in situ climate control option to users. These, however, are limited either by the range of relative humidity states, the long times required to change the climate state, or obstruction or attenuation of the beam. Here, the first fully automatized climate cell for in situ full-field nanotomography is presented. It has been designed, built and integrated at the nanotomography station at the P05 imaging beamline, operated by Hereon at the DESY storage ring PETRA III, Germany. The highly flexible and windowless design allows the humidity dependent swelling and shrinking of lignified plant cell walls to be studied in situ , using phase contrast nanotomography. The concept of this climate chamber can easily be integrated into other setups. It operates in the relative humidity range of 0–90% and can be controlled in a temperature range of 10–50°C. Climate conditions can be adjusted at any time, remotely from the control hutch by using a humidity generator. Results show that the developed setup maintains a stable climate during the entire duration of a tomographic scan at different humidities and does not obstruct the sample or hinder the imaging conditions. During the tomographic investigation the sample remains stable in the flow of the air stream and shows typical cell wall swelling and shrinking behaviour depending on the equilibrium moisture content. This new climate cell is now available to all users of the P05 nanotomography instrument for conditioning samples, serving a wide range of scientific applications.