Holger Militz

University of Göttingen | GAUG · Department of Wood Biology and Wood Products

The study investigated the production process and properties of a new wood-based material called Bioblocks. This sustainable composite is made from medium-density-fibreboard (MDF) residues, citric acid and either sorbitol or hexanediol. The process involves mixing in-water diluted chemicals with the MDF residues and curing the mixture in a laborato...

Scots pine (Pinus sylvestris L.) sapwood of 200 × 20 × 80 mm3 (L×R×T) was treated with both cell wall filling and lumen filling chemical agents (low-molecular phenol-formaldehyde, bio-oil, N-methylol/N-methyl compounds, sorbitol-citric acid, polysiloxane), which were fixed inside the wooden structure during heat-curing processes. The present study...

Utilizing furfurylated veneers to improve the quality of plywood has not been extensively studied before. This study investigated the characteristics of plywood made from furfurylated rubberwood (Hevea brasiliensis) veneers at various modification levels. Rubberwood veneers were first impregnated with furfuryl alcohol (FA) at different concentratio...

Wood modification has been explored in various ways to enhance dimensional stability and reduce flammability, with a focus on environmentally friendly treatments to meet market demands. This study aimed to investigate the efficacy of new, potential fire-retardant materials. Specifically, the study examined the combination of tripotassium citrate (T...

The wood modification by impregnation with phenol-formaldehyde (PF) resin results in an increased dimensional stability, a reduced water absorption and an improved durability (Fleckenstein 2018). The disadvantage of PF resins is that phenol is produced from non-renewable resources (Schmidt 2005). For this reason, there have been many efforts in the...

In this study, the tensile and bending strength of birch and beech lamellas finger jointed with conventional (Standard) and newly developed finger-joint profiles (New) are presented. Polyurethane (PUR), Melamine-Urea-Formaldehyde (MUF) and Phenol-Resorcinol-Formaldehyde (PRF) adhesive systems were used to bond the finger joints. The objective of th...

Acetylation is a breakthrough in wood modification and has been established on industrial scale. However, concerns have been raised regarding the stability of acetylated wood under elevated temperatures, particularly during post hot-pressing processes to manufacture products such as laminated veneer lumber (LVL). At around 150 °C, the added acetyl...

Wood modification processes based on citric acid in combination with various copolymers have gained in importance in recent years. These processes also include modification with citric acid (CA) and sorbitol, a sugar alcohol, which is currently in the industrial realisation phase in Germany (SorCA) and Norway (CIOL). The modification of wood with s...

The combination of different wood-modification technologies to obtain improved performance is increasingly receiving attention in research. In this study, Scots pine (Pinus sylvestris) sapwood was impregnated with furfuryl alcohol (FFA) in pure aqueous 20, 40, and 60% solution strength without adding any catalyst. In a second step, the FFA was poly...

The combination of different wood modification technologies to obtain improved performance is increasingly receiving attention in research. In this study, Scots Pine (Pinus sylvestris) sapwood was impregnated with furfuryl alcohol (FFA) in pure aqueous 20, 40 and 60% solution strength without adding any catalyst. In a second step, the FFA was polym...

Currently, approvals for structural adhesive systems are largely limited to softwood bonding. With increasing interest in hardwood utilization for structural timber products, it is pertinent to identify suitable adhesive systems for approval and standardization of bonded hardwood-based materials. This study focused on evaluating the suitability and...

Hardwood utilization as alternative to declining softwood for structural timber products continues to attract global interest at exploiting the material potentials of hardwood for manufacturing engineered wood products. Recent attempts at refocusing utilization of eucalyptus wood have led to significant progress, mostly face-bonding of Eucalyptus g...

The impregnation modification of wood with phenol-formaldehyde (PF) resins increases the woods dimensional stability and resistance against fungal decay. However, to decrease the usage of non-renewable resources, the substitution of phenol has been a topic of scientific interest. Lignin is a currently underutilized resource with a chemical structur...

Natural wood has been widely used for construction and building purposes. However, wood is susceptible to wood-destroying organisms moisture-induced dimensional changes and fire. Although chemical wood modification technologies with thermosetting resins like phenol-formaldehyde (PF) may compensate durability and swelling issues, the latter may not...

Thermal modification of wood is an environmentally friendly method to improve wood durability, mainly against microorganisms. By employing a process similar to the ThermoWood®, various Gmelina arborea (gamhar) wood specimens were thermally modified at 180 °C, 200 °C, and 220 °C for 3 hours. The effects of the thermal modification process on the res...

Synergizing coating and wood modification is a promising concept to develop wood products that have multi-qualities that include excellent dimensional stability, durability, and weathering resistance. However, the nature of the modified substrate is a critical parameter for coating adhesion. Chemical modification of wood impacts the physicochemical...

Phenol-formaldehyde (PF) resins can be impregnated and cured in situ to improve the woods dimensional stability and decay resistance. In search of renewable alternatives, the substitution of phenol by lignin cleavage products (LCP) has been discussed. However, the different chemical nature may affect the performance of the resin against fungal deca...

This study focused on the thermal modification of Gmelina arborea Roxb. wood following processes using the open reactor and low-pressure closed reactor systems. The aim is to determine the optimum treatment conditions suitable for gmelina wood due to its poor drying characteristics using the low-pressure closed reactor thermal modification. Subsequ...

Acetylation of wood with acetic anhydride reduces the wood–moisture interaction, improves the dimensional stability and resistance against biodegradation. However, the adhesive bonding is affected by the modification, which is crucial to manufacture engineered wood products, such as laminated veneer lumber (LVL). In this study we report the bonding...

Phenol-formaldehyde resins can be used for wood modification through an impregnation process and subsequent curing within the wood cell wall. Phenol is gained from non-renewable resources, and its substitution by renewable chemicals has been a research goal. A promising example for renewable phenol substituents are lignin-derived organic chemicals....

The modification by impregnation of veneers for the production of plywood with phenol–formaldehyde resins is a well-known method to improve the dimensional stability and fungal resistance. Because phenol is obtained from non-renewable resources, finding substitutes has been a topic of research. Due to similarities in chemical structure and availabi...

Wood modification with thermosetting resins results in improved dimensional stability and durability. However, the treatment does not enhance fire resistance. To address this, Scots pine sapwood (Pinus sylvestris L.) was impregnated with thermosetting resins such as 1,3-dimethylol-4,5-dihydroxyethyleneurea, phenol-formaldehyde resin and melamine-fo...

This study aimed to investigate the relationship between moisture dynamics of sorbitol and citric acid (SorCA) modified wood and its biological durability. Specifically, the research aimed to determine the chemical loading needed for effective protection against wood-destroying basidiomycetes, while also improving the understanding of the moisture...

Because of the different properties and advantages of wood and inorganic materials, the combination of both can bear an improved product. There are many ways how these two material classes can be combined, one of them being the in-situ synthesis of minerals inside of the wood. The synthesis of calcium carbonate (CaCO3) in wood (for example through...

Recent research activities focus to manufacture laminated veneer lumber (LVL) from of acetylated beech (Fagus sylvatica L.) veneers. The LVL production requires a hot-bonding (150°C) step. However, it is not known yet whether hot-bonding may cleave esterified acetyl groups and by that affect the material performance (de-acetylation). Acetic acid, a...

Beech is an important tree species in Europe. This study aimed to elucidate the influence of four molecular weights of phenol formaldehyde (PF) resin (266, 286, 387, and 410 g/mol) on the sorption behavior of unmodified and modified beech wood samples using a dynamic vapor sorption (DVS) apparatus. The variations in the environmental relative humid...

The present study aimed to evaluate the effect of citric acid on the properties of solid pine wood, which were submitted to thermomechanical treatment. A preliminary test was performed in a previous study to evaluate the influence of different temperatures of pressing and concentrations of citric acid on the physical properties of wood. After choos...

The present study aimed to evaluate the effect of the citric acid on the properties of solid pine wood, which were submitted to thermomechanical treatment. A preliminary test was performed in a previous study to evaluate the influence of different temperatures of pressing and concentrations of citric acid over the physical properties of wood. After...

Experiments on finger-jointing acetylated beech (Fagus sylvatica L.) laminated veneer lumber (LVL) have been made. The specimens were examined on its wet tensile shear strength (TSS) using three adhesives, including phenol resorcinol formaldehyde (PRF), one-component polyurethane (PUR) (without primer), and melamine urea formaldehyde (MUF). Contact...

Wood modification by impregnation and curing inside of the cell wall using phenol–formaldehyde resins (PF resins) is a well-known and commercialized method to improve, amongst others, the dimensional stability and the durability of wood. However, phenol is mainly obtained from non-renewable resources, and the substitution of phenol by renewable res...

The level of protection achieved by any wood treatment process is dependent on achieving a sufficient uptake and penetration of the treatment chemicals. This phenomenon is also applicable when considering chemical modification of any wood species. The desired changes in physical, mechanical or durability enhancement of treated species can only be a...

Wettability and surface free energy (SFE) are crucial parameters for evaluating the adhesion thermodynamics of solid surfaces. Hence, this study investigated the effects of copper azole (CA) and disodium octaborate tetrahydrate (DOT) preservative impregnations on Eucalyptus grandis wood wettability and SFE. Wettability was determined in terms of co...

Alternatives to preservative impregnation are emphasized in Germany and other European countries. Even though these treatments significantly improve wood's resistance to decay, they often do not have a beneficial impact on the dimensional stability. One alternative product, which may be used in ground contact for items like poles and railway sleepe...

Non-durable softwood and hardwood species were treated with the water-soluble cyclic N-methylol compounds 1,3-dimethylol-4,5-dihydroxyethyleneurea (DMDHEU) and methylated DMDHEU. One half of the modified specimens were coated with a waterborne acrylic coating system prior a natural weathering for 5.5 years according to EN 927-3 (2020). By frequent...

The overall aim of this study was to investigate the durability of acetylated beech (Fagus sylvatica L.) laminated veneer lumber (LVL) against wood-destroying basidiomycetes. The secondary objective was to test whether the specimen size affects the mass loss and durability assessment of wood-material under test. The durability test was based on the...

Wood is a commonly used material in construction. However, its application is limited due to its flammability. Modification of wood with phenol-formaldehyde resin (PF) can improve many of its inherent properties, but does not upgrade its fire resistance. To address this issue, Scots pine (Pinus sylvestris L.) sapwood was impregnated with a low mole...

This chapter presents the technology of chemical and thermal wood modification. It describes fundamental principles as well as practical aspects of wood modification. In addition to thermal modifications, various types of chemical modifications are presented with respect to the chemicals applied and resulting properties of the modified wood. This d...

The effects of pressurized hot water extraction (HWE) treatment on the mould resistance of wood have not been extensively investigated yet. The activity of the mould fungi is dependent on the availability of nutrients. Therefore, the soluble degradation products produced during HWE treatment could affect the wood’s susceptibility to mould growth. S...

Wood modification using phenol-formaldehyde resins (PF resins) is a well-known and commercialized method to improve, amongst others, the dimensional stability and the durability of wood. However, phenol is mainly obtained from non-renewable resources, and the substitution of phenol by renewable resources has been a topic of research interest for ye...

In this study, a specimen geometry for testing finger joints was developed using finite element simulation and proofed by experimental testing. Six different wood species and three adhesives were used for finger-jointing specimens. With the test specimen geometry, the bonding strength of the finger joints was determined without the usual self-locki...

Knowledge about the resistance of wood–polymer composites (WPCs) to biological attack is of high importance for purpose-oriented use in outdoor applications. To gain this knowledge, uniform test methods are essential. EN 15534-1 (2018) provides a general framework, including the recommendation of applying a pre-weathering procedure before the biolo...

Plantation-grown juvenile wood species are extensively used as raw materials in the Chinese wood industry. The weathering performances of the wood are crucial for outdoor application. Two of the most important plantation-grown juvenile woods, poplar (Populus × euramericana cv. ‘74/76ʼ) and Chinese fir (Cunninghamia lanceolata Hook), were sliced int...

The success of any wood treatment process and the measure of protection conferred on treated wood are determined by the uptake and penetration of the treatment chemicals, in addition to the efficacy of the chemicals used for the treatment. Hence, the level of treatability of wood species should be pre-determined prior to the wood treatment to ensur...

Chemical and thermo-chemical modification processes were applied to European beech wood to make it applicable for interior applications which place high demands on aesthetics, hygrothermal and water resistance performance. In particular, the use of modified wood in kitchen tools was foreseen. Impregnation modification with a 20% DMDHEU solution, th...

The objective of this study was to determine the effects of four phenol–formaldehyde (PF) resin treatments with different molecular weights at four different concentrations (5, 10, 15, and 20%) in treated beech wood. The mechanical properties of untreated and treated beech wood were evaluated. After impregnation with PF resin, all modified beech wo...

Scots pine sapwood (Pinus sylvestris L.) was modified with an aqueous solution of sorbitol and citric acid (SorCA) and a commercial phosphorus-based fire-retardant (FR). The aim of this study was to assess whether the fire behavior can be improved when the SorCA solution is supplemented by an FR and if this effect is resistant to leaching. The fire...

In this study, it was tested whether density and moisture content have an influence on the self-locking of finger-jointed wood. To quantify self-locking, shear tensile tests were carried out on adhesive-free finger joints. To proof the influence of density, six wood species, three of them softwoods and three hardwoods were tested. In addition, the...

In this study, rotary-cut poplar veneers were impregnated with sorbitol and citric acid (SorCA) in a vacuum-pressure process. Three different treatments (untreated reference, middle and high concentration) were chosen. The impregnated veneers were air-dried and pre-dried at 60 °C before pressing the boards. As is typical with phenol-formaldehyde (P...

The use of acetic anhydride to acetylate wood enhances its dimensional stability and durability. In this study, rotary-cut beech veneers were acetylated in an industrial process. Thereafter, eight-layered laminated veneer lumber (LVL) was bonded at 150°C using a phenol-formaldehyde (PF) resin at pressures of 1, 3, and 6 MPa. Leaching, set-recovery,...

Due to the steadily increasing availability of hardwoods, hardwoods will gain economic and scientific interest today and in the future. Fast-growing hardwood species, such as poplar, may become an additional wood source for the wood-based industry. However, in outdoor applications, hardwood species show low durability against biological degradation...

In-depth knowledge of the interaction effects of wood and preservative chemicals on surface adhesion characteristics is crucial for developing pathways to improve the adhesive bonding of treated woods. Therefore, this study investigated fundamental changes in the surface adhesion-related chemical characteristics of E. grandis sapwood and heartwood...

In recent years, a wood treatment system based on sorbitol and citric acid (SorCA) has emerged as a promising alternative to already commercialized modification processes of European-grown wood species. The improvement of dimensional stability and biological durability have been reported. However, the mode of action behind the changes in wood struc...

This study demonstrates acetylation with acetic anhydride, one of the few industrial wood modification techniques on the market, to increase the dimensional stability and durability of laminated veneer lumber (LVL) made from beech wood (Fagus sylvatica L.). After being acetylated, veneers were hot-bonded to LVL using phenol-formaldehyde resin (PF)...

On this poster an overview of vacuum low-temperature microwave-assisted pyrolysis products of pine kraft lignin, examples for potential applications of the products as described in literature, as well as the ongoing or planned research on new valorizations with our involvement are presented.

Pressurized hot water extraction (HWE) treatment has the benefit of simultaneous extraction of hemicellulose-based carbohydrates and modification of the solid phase, but it does not drastically improve wood durability. However, removing hemicelluloses from the wood by HWE treatment creates water-filled spaces in the cell walls which could be filled...

Main conclusion TEM and AFM imaging reveal radial orientations and whorl-like arrangements of cellulose microfibrils near the S1/S2 interface. These are explained by wrinkling during lamellar cell growth. Abstract In the most widely accepted model of the ultrastructure of wood cell walls, the cellulose microfibrils are arranged in helical patterns...

Cleavage by microwave-assisted pyrolysis is a way to obtain higher-value organic chemicals from technical lignins. In this report, pine kraft lignin (PKL), spruce and beech organosolv lignin (SOSL and BOSL), and calcium lignosulfonates from spruce wood (LS) were pyrolyzed at temperatures between 30 and 280 °C using vacuum low-temperature, microwave...

Acetylation with acetic anhydride is well known to improve the dimensional stability and durability of wood. Veneer is appealing for acetylation because of its thin thickness, which supports a complete and even impregnation of difficult-to-treat wood species, such as beech (Fagus sylvatica L.). Unlike resin-based veneer impregnation, acetylated ven...

Most European-grown wood species are susceptible to biological degradation, specifically, they suffer from a poor resistance against wood-destroying fungi. Therefore, prior to outdoor exposure, wood has to be treated either by applying a protective coating on its surface or by full-volume impregnation with antifungal chemicals. However, due to envi...

The purpose of this review is to put previous research findings on acetylated wood and the fabrication of veneer-based products in a common context. The first research on wood acetylation was already conducted in the 1920s using wood meal, whereas relevant research on veneer acetylation was published nearly two decades later, during the 1940s. In t...

In this study, the surface parameters wettability, roughness, and adhesive penetration, which are important for wood bonding, were investigated and evaluated utilizing non-destructive methods after different mechanical processing. For this purpose, beech and birch finger joints were prepared with different cutting combinations (three cutters with di...

Die chemische Modifizierung von Holz durch das Imprägnieren und Aushärten von Kunstharzen verbessert die Dimensionsstabilität sowie die Resistenz gegen biologischen und witterungsbedingten Abbau behandelter Hölzer. Eine Möglichkeit hierzu ist die Imprägnierung mit Phenol-Formaldehyd (PF)-Harz, jedoch wird Phenol aus nicht-erneuerbaren Ressourcen ge...

The changes of regulations issued by legislative bodies of the European Union have limited the use of wood preservatives. Therefore, the chemical wood modification market in Europe has been constantly expanding. One of the novel wood modification methods, based on entirely bio-delivered chemicals sorbitol and citric acid (SorCA) is seen as a possib...

Chemical wood modification offers a non-biocidal alternative to protect wood against decay fungi and wood-destroying organisms, while simultaneously improving its various properties, such as hardness and UV-resistance. In the last years, wood treatment system based on sorbitol and citric acid (SorCA) has emerged as a promising alternative to alread...

In the last years, wood modification with carboxylic acids and their anhydrides has become a subject of intense studies. Among various investigated chemicals, sorbitol and citric acid (SorCA) have gained a particular attention. Both chemicals are derived from renewable resources, do not cause a threat to the environment and, being soluble in water,...

The prospect of manufacturing durable structural laminated wood with copper and boron-based preservative-impregnated Eucalyptus grandis wood was previously investigated but revealed adhesive-bond performance below standard requirements. In this study, bonding process factors, viz. mechanical pretreatment (surface planing) and bonding pressure in co...

Improving the properties of laminated veneer lumber (LVL) through wood modification expands its usage as building material, especially for outdoor applications. The outdoor performance of LVL products needs to be tested against different biotic agents, and methods are needed for testing and evaluating their effect on the structural integrity of LVL...

For nearly 200 years wooden railway sleepers are impregnated with creosote. After initially using vacuum pressure processes for impregnation, empty-cell processes have been developed quickly and are used until today. Because of political developments and its alarming properties against human health and environment the use of creosote is already res...