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Wood-based materials are generally prone to colonization by mould fungi and other discoloring microorganisms, but their resistance to fungal discoloration varies. Different standardized test methods for determining the susceptibility to mould fungi have been used to evaluate various wood-based materials, but the obtained results suggest that mould resistance depends on the method applied. Therefore, this study aimed at a comparative evaluation of two commonly used methods for determining the mould resistance of wood-based materials, i.e. the chamber method according to BS 3900—Part G6 and the malt agar plate method according to ISO 16869. Solid wood, wood fiber insulation boards and wood polymer composites were inoculated, incubated for different time intervals, and assessed with regard to superficial mould growth. Mould growth ratings obtained with the two methods did not correlate well, neither within one type of material nor across different materials, which can be attributed to higher moisture contents and additional nutrients available for the specimens in the agar plate test compared to those in the chamber test. It was concluded, that the experimental set up could have an overriding effect on the results of mould resistance tests.

The structural integrity of wood–polymer composites (WPC) has not been fully investigated, which can be attributed to a lack of applicable test procedures. In this study, wood–polypropylene composites were assessed by High-Energy Multiple Impact (HEMI) testing. The acquired composites were based on wood particles from various sources and different wood fibre contents, respectively. With respect to wood fibre content, a clear relationship between resistance to impact milling (RIM) and unnotched impact bending strength (acU) was obtained. The lower the fibre content of the WPC the more structural integrity was retained. In return, various wood sources had no effect on acU, but a major impact on RIM values. RIM is suggested to be predominantly affected by structural features, such as fibre/particle content and characteristics, particle agglomerations, and spatial void distribution.

Thermomechanical wood fibers, as usually used for medium density fiberboard or cardboard production, feature promising characteristics, like a high aspect ratio, for the utilization in thermoplasti...

In most countries, fibreboards are not recovered after utilization but burned for energy production. This study aims at recovering fibres from industrial fibreboards and reusing them as reinforcement elements in wood polymer composites (WPC). Recovered fibre (RF) material was generated by the thermo-hydrolytic disintegration of medium and high density fibreboards bonded with urea-formaldehyde resin. Various formulations of RF and polypropylene were used with or without the addition of the coupling agent to manufacture WPC using a co-rotating extruder. Test specimens were produced via injection moulding whereby those containing ‘virgin’ fibres served as a reference with respect to mechanical and physical properties. WPC formulations containing RF and ‘virgin’ fibres exhibited similar results, but composites containing RF exhibited improved mechanical and water-related properties, especially without coupling agent. The study indicates that recovered fibres are suitable to produce WPC with very simil...

Softwoods can be nailed with high density solid wood like Santos Rosewood (Machaerium scleroxylon) or nails made of densified laminated beech wood composite by hammering or shooting, for example with air nail guns, without pre-drilling. Shooting with about 30 m/s causes friction between nail surface and softwood matrix, heating up the interface to temperatures high enough to soften lignin. Re-condensation of softened lignin causes wood welding which doubles pull out strength in comparison to wood nails fixed without wood welding. Changes in lignin UV-absorption within the single cell wall layer and deformation of main anatomical features of spruce wood tissue are characterized by scanning UV microspectrophotometry (UMSP) whereas structural deformations of spruce wood tissue are revealed by X-ray micro-computed tomography (µ-CT).

Kiri trees are fast-growing species, which are increasingly cultivated on plantations in Europe. This study assesses the application of kiri wood (Paulownia tomentosa) for the production of particleboards. Single-layer particleboards (PBs) were produced from kiri particles (KPs), industrial particles (IPs) and various mixtures of both materials with target densities of 350, 500 and 650 kg m−3, respectively. The composition of the PBs was 100% KPs, 66% KPs, 33% KPs and 0% KPs (100% IPs). PBs based on 100% IPs exhibited the lowest mechanical strength properties, which increased with increasing proportions of KPs within the same density range. The swelling properties of the boards were similar within one density range. The formaldehyde contents of PBs made of KPs were higher compared to PBs based on IPs, but all values were below the threshold value given in EN 13986 (Wood-based panels for use in construction—characteristics, evaluation of conformity and marking, German version. European Committee for Standardisation, Brussels, Belgium, 2004). X-ray micro-computed tomography (XµCT) revealed differences in the structure and compression of the PBs based on KPs and IPs resulting in smaller and more evenly distributed voids between the particles in PBs based on KPs. This study shows that kiri wood is a promising raw material for the PB industry, both alone and in mixtures with other particles.

In this study, we investigated injection molded wood-polypropylene composites based on various wood sources and their decay resistance against white rot (Trametes versicolor) and brown rot (Coniophora puteana) in a laboratory test according to EN 15534-1:2014. The manufactured composites consisted of poplar (Populus spp.), willow (Salix spp.), European beech (Fagus sylvatica L.), Norway spruce (Picea abies (L.) H. Karst.), and a commercial wood source (Arbocel&reg, C100), respectively. All formulations were compounded on a co-rotating twin screw extruder and subsequently injection molded to wood&ndash, PP specimens with a wood content of 60% or 70% by weight. It was found that the test procedure had a significant effect on the mechanical properties. Loss in mechanical properties was primarily caused by moisture and less by fungal decay. Moisture caused a loss in the modulus of rupture and modulus of elasticity of 34 to 45% and 29 to 73%, respectively. Mean mass and wood mass losses were up to a maximum of 3.7% and 5.3%, respectively. The high resistance against fungal decay was generally attributed to the encapsulation of wood by the polymer matrix caused by sample preparation, and enhanced by reduced moisture uptake during the preconditioning procedure. Notable differences with respect to the wood particle source and decay fungi were also observed. Structural characterization confirmed the decay pattern of the fungi such as void cavities close the surface and the deposition of calcium oxalates.

Polypropylene wood flour composites made from short-rotation coppice (SRC) and low valued beech wood (Fagus sylvatica) were investigated with respect to their suitability for use in the production of wood–polymer composites (WPC). An industrial wood source consisting of spruce wood flour (Picea abies) was used as reference material. All composites were compounded on a co-rotating twin screw extruder containing either 60 or 70 wt% wood flour. Consolidation was done by profile extrusion. Mechanical and physical properties of the composites were investigated. The wood sources were characterized concerning their particle length and shape by the use of a dynamic optical particle analysis system. X-ray microtomography (µ-CT) was used to study the dispersion of wood particles and the internal composite structure. However, all composites based on alternative wood sources showed an equivalent performance regarding mechanical properties compared to the composite reference. Composites containing beech wood flour showed notably reduced water absorption rates, whereas the composites based on SRC wood flour revealed significantly reduced moisture content compared to reference composites. A different particle length distribution was depicted between the industrial wood source and three other investigated wood sources. Moreover, all wood flour sources were characterized by a mean aspect ratio up to 3:1. The X-ray microtomography illustrated morphological differences between composites. Based on the X-ray images, an alignment along the melt flow and a decent encapsulation by polypropylene were shown.

X-ray micro-computed tomography (XμCT) allows a non-destructive and three-dimensional (3D) study of otherwise complex and opaque wood tissues. In wood research, XμCT datasets are highly useful for the qualitative and quantitative examination of wood structures. In this study, XμCT was introduced and tested for examining X-ray dense silica particles in the Australian turpentine wood (Syncarpia glomulifera). It was possible to three-dimensionally visualize and numerically quantify silica particles. Numerical analysis was performed to scrutinize the size and content of silica particles. In comparative studies of silica size through scanning electron microscopy and silica content through thermo-gravimetric analysis after acid digestion of ash, our findings pointed out that XμCT is indeed a powerful tool for examining silica particles in wood; because XμCT enables a simultaneous visualization and quantification of the silica particles in 3D without being destructive. Despite these benefits, comparative examination through scanning electron microscopy and energy-dispersive X-ray spectroscopy is necessary to verify silica particles in tomographic images. XμCT technology might further aid in probing the biological and ecological function of silica in silica-bearing wood species.

In this study, various wood material sources were used for the manufacture of wood-polymer composites (WPC). The materials were categorised as virgin wood particles (VWP), reprocessed WPC particles (RWP) and recycled thermoset composite particles (RCP) and derived from two virgin wood sources, three-layer particleboards, medium-density fibreboards (MDF) boards, or two different wood/polypropylene composites. All produced wood-polypropylene compounds contained 60% wood material and were manufactured using a co-rotating extruder. Malleated polypropylene was used as a coupling agent. Specimens were injection moulded and subsequently tested for their physico-mechanical properties. To characterize particles before and after processing, dynamic image analysis (DIA) measurement were performed. Additionally, X-ray micro-computed tomography (X&micro, CT) was used to characterize the internal structure of the composites and to verify the obtained particle&rsquo, s characteristics. It was found that length and aspect ratio of particles were remarkably different before and after processing (loss in length of 15&ndash, 70% and aspect ratio of 10&ndash, 40%). Moreover, there were notably differences between the particle sources (RCP retained the highest length and aspect ratio values, followed by VWP and RWP). The results suggest that increased aspect ratios can indeed significantly improve mechanical properties (up to 300% increase in impact bending strength and 75% increase in tensile strength, comparing WPC based either on virgin spruce or MDF material). This phenomenon is suggested to be partially superimposed by improved dispersion of particles, which is expected due to lower variance and increased mechanical properties of RWP composites. However, no notable alterations were observed for composite density. Reprocessed WPC and, particularly, RCP material have proved to be an appealing raw material substitute for the manufacturing of wood&ndash, polymer composites.

The distinctive length and morphology characteristics of thermomechanical produced wood fibers make it a promising candidate for the utilization in polymer composites. However, due to the low bulk density of these fibers, the feeding into the compounding process (i.e., extruders) is quite challenging. In this study, a novel simultaneous defibration and compounding process are conducted in order to solve the feed-in problem of thermomechanical fibers. A disc-refiner was used to defibrate wood chips to fibers and compound the fibers with neat polymer granulates in one process step. After the process, the material showed typically thermomechanical fibers with chopped polymer particles which were inseparably attached to the fiber. The observed mechanical properties of the composites were slightly lower than some literature values. With field emission scanning electron microscopy and X-ray microtomography analysis, voids and a polymer enriched surface were found influencing the composites performance. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45859.