Andreja Kutnar

Soy-based adhesives for wood-bonding – a review

Abstract Over recent years, the interest in bio-adhesives, including soy-based adhesives, has increased rapidly. Among natural renewable resources suitable for industrial use, soy is a reasonable choice due to its high production volume and the small use of soy meal-based products for human food consumption. Soy flour can be an ideal raw material for the manufacturing of wood adhesives due to its low cost, high protein content and easy processing. There are also more concentrated forms of soy proteins, i.e. concentrates and isolates, which are also suitable raw materials for adhesive production except that their prices are higher. Extensive research has been carried out on improving the cohesive properties, especially water resistance, of soy-based adhesives. However, there is insufficient experimental data available for understanding the influences of modification methods on the structure of soy proteins and therefore for understanding the influences of structural changes on the adhesion. In this paper, some experimental techniques are proposed to be used for analysing soy-based adhesives to enable better understanding of those factors and improve future development. This review of soy-based adhesives is made with the focus on soy proteins’ chemical composition, soy protein product types (raw materials for adhesive production), modification methods for improving the adhesive properties of soy-based adhesives, and commercial soy-based adhesives.

Microstructure of viscoelastic thermal compressed (VTC) wood using computed microtomography

The paper describes for the first time the analysis of the structure of compressed wood using computed tomography. The anatomical structures of Douglas-fir and hybrid poplar before and after densification with the viscoelastic thermal compression (VTC) process were described by pore size distributions and mean pore sizes and compared. The compression of Douglas-fir mainly affected earlywood, while the compression of hybrid poplar mainly occurred in the vessels. In both wood species, the densification resulted in a significant decrease in the pore volumes. The porosity decreased to less than half of the original value for Douglas-fir earlywood and to approximately one-quarter for the vessels in hybrid poplar. The relevant mean pore sizes also decreased dramatically to about one-quarter compared to the original values. In contrast, latewood in Douglas-fir and libriform fibers in hybrid poplar are quite stable under compression. Douglas-fir latewood retained its original structure after compression and did not show any reduction in pore size. The results confirmed that the anatomical structure of VTC densified wood can be described by pore size distributions and mean pore sizes. However, in the case of broad or bimodal distributions, the mean pore sizes are of less significance.

Erratum to: The wettability and bonding performance of densified VTC beech (Fagus sylvatica L.) and Norway spruce (Picea abies (L.) Karst.) bonded with phenol–formaldehyde adhesive and liquefied wood

The influence of viscoelastic thermal compression (VTC) on surface wettability and bonding performance of wood was evaluated. Low quality beech (Fagus sylvatica L.) and Norway spruce (Picea abies (L.) Karst.) were densified with the VTC process to different degrees of densification. Control and densified strips were bonded with phenol–formaldehyde (PF) adhesive and liquefied wood (LW). Shear strength of bonded assemblies was determined after 1 week of conditioning at 20 °C and relative humidity of 65 %. Wettability was determined on the basis of the contact angle of water, PF adhesive, and LW using the Wilhelmy method. Results showed that densification of beech and spruce wood did not significantly affect the shear strength of specimens bonded with PF adhesive. In beech assemblies bonded with LW shear strength decreased significantly with increased density, whereas in bonded spruce specimens decrease of shear strength was not significant. It was found that degree of densification and bonding process used in the study were not appropriately chosen for spruce wood specimens, since major deformations after the bonding process occurred. Wettability changed significantly after densification. Contact angle of water and LW increased after densification, whereas contact angle of PF showed inverse trend and decreased after VTC process. Furthermore, the degree of densification had a minor effect on the wettability.

Wood and human stress in the built indoor environment: a review

Individuals spend most of their time indoors, and therefore indoor environments are important aspects of one’s life. Creating healthful indoor environments should be a priority for building designers, and evidence-based design decisions should be used to ensure the built environment provides healthful benefits to occupants. This review was conducted to examine the body of research studying wood use and human stress to determine the potential fit for wood in the restorative environmental design paradigm. Previous studies on psychophysiological responses to wood are reviewed, as are current methods for assessing stress in experimental settings. To date, studies examining the psychophysiological effects of wood use in interiors have revealed reduced autonomic stress responses when compared to rooms without and with less wood. Therefore, by increasing wood use in design paradigms seeking to bring the positive health benefits of nature into the built environment, like restorative environmental design, building designers may improve the well-being of building occupants. This review reveals further studies are needed to better understand the psychophysiological responses to wood, and suggests specific aspects of wood such as colour, quantity, and grain pattern should be examined and how stress and stress recovery should be analysed.

Compressed and moulded wood from processing to products

Abstract This paper presents the state of the art of different wood densification processes as one emerging process technology. The main principles for the processes are discussed, such as bulk and surface densification, bending, moulding of shells and tubes, as well as methods for reducing the shape memory effect of densified wood. The main challenges are in the field of scaling up to industrial applications. To provide a better understanding with this regard, some relevant scientific results are presented. Furthermore, the discussion considers the contribution of thermo-hydro and thermo-hydro-mechanical processes to a sustainable and low-carbon economy.

Assessment of Carbon Footprinting in the Wood Industry

The management of natural resources is a subject that often arises when sustainable development is considered. Wood is a renewable, biological raw material used in numerous applications and is therefore growing in importance for sustainable development efforts. This chapter presents the applicability of carbon footprinting in the wood industry by comparing the carbon footprint of 14 primary wood products: air-dried and kiln-dried softwood and hardwood sawn timber, hard fiberboard, glued laminated timber for indoor and outdoor use, medium-density fiber board, oriented strand board, particleboard for indoor and outdoor use, plywood for indoor and outdoor use, and wood pellets. Furthermore, the use of timber products for the purposes of carbon storage and the effect of allocation methods on carbon footprinting are discussed. Additionally, the European policy strategies and actions directly impacting the forest products industry are discussed in relation to primary wood products. Also, wood as a building material and its placement in green building programs are considered.

Comparison of the flexural behavior of natural and thermo-hydro-mechanically densified Moso bamboo

The flexural properties in the longitudinal direction for natural and thermo-hydro-mechanically densified Moso bamboo (Phyllostachys pubescens Mazel) culm wall material are measured. The modulus of elasticity (MOE) and modulus of rupture (MOR) increase with densification, but at the same density, the natural material is stiffer and stronger than the densified material. This observation is primarily attributed to bamboo’s heterogeneous structure and the role of the parenchyma in densification. The MOE and MOR of both the natural and densified bamboo appear linearly related to density. Simple models are developed to predict the flexural properties of natural bamboo. The structure of the densified bamboo is modelled, assuming no densification of bamboo fibers, and the flexural properties of densified bamboo are then predicted using this structure and the same cell wall properties of that of the natural material modelling. The results are then compared with those for two analogous structural bamboo products: Moso bamboo glulam and scrimber.

Influence of treatment temperature on wettability of Norway spruce thermally modified in vacuum

Wettability of Norway spruce modified by a new vacuum thermal modification procedure was studied. The mass loss caused by this process ranged from almost 0% when treated at 140 °C to 4.3% at 210 °C. Apparent contact angles of water, formamide, and diiodomethane were measured by the Wilhelmy plate method on the specimens taken from the centers of the thermally modified wood samples. For the treatment at the highest temperature, the contact angle of water was significantly higher when compared to untreated spruce (96.6° vs. 83.6°); lower treatment temperatures, however, did not result in a clear correlation between treatment temperature and contact angle. Formamide yielded lower contact angles for treated spruce compared to the untreated one, but without clear influence of the treatment temperature and diiodomethane always gave perfect wetting. Surface energy calculations according to the Owens, Wendt, Rabel, and Kaelble method revealed that the thermal modification process in vacuum increased the surface free energy and lowered the polarity of wood significantly only at the highest applied temperature (210 °C); the treatment had only limited effect at lower temperatures of modification. These results indicate that adequate wetting and adhesion can be achieved on the surfaces of Norway spruce thermally modified in vacuum.

Bonding of densified beech wood using adhesives based on thermally modified soy proteins

The bondability/glueability of aged and sanded thermo-hydro-mechanically (THM) densified beech wood (Fagus sylvatica L.) was tested and compared with undensified sanded beech wood as a control. THM and control specimens were bonded with five different soy protein isolate (SPI) based adhesives. Commercial SPI powder was thermally modified in the vacuum chamber at 50 or 100 °C and pH adjusted (to pH 10.0) dispersions in water prepared at 24, 50 or 90 °C. Wettability was determined with measuring the sessile drop contact angles of water. Effective penetrations (EPs) and tensile shear strengths of THM and control specimens were determined. THM and control wood had similar wettability. Although THM wood had lower moisture content than control wood, it absorbed the water more slowly than control wood. THM specimens showed lower EPs than control specimens when comparing individual adhesives due to increased density of THM wood. Adhesives prepared with SPI thermally modified at 50 °C showed statistically significantly lower tensile shear strength of bonded THM specimens than that of bonded control specimens. THM densification had no significant effect on the bonding strengths of adhesives prepared with non-modified SPI and SPI thermally modified at 100 °C.

Commercialization Potential of Viscoelastic Thermal Compressed Wood: Insights from the US Forest Products Industry

The increasing demand for forest products and restricted use of natural forests has resulted in a shortage of high-strength wood fiber. The area covered by plantation forests is steadily rising, bu...