Martina Meincken

The Effect of Wood Species on the Mechanical and Thermal Properties of Wood—LLDPE Composites

Different wood species can be expected to affect the properties of wood—polymer composites (WPCs) differently, as they have different chemical compositions. The chemical composition (cellulose, lignin, hot water, and ethanol/ cyclohexane extractive contents) of acacia, eucalyptus, pine, and oak and the morphological properties such as wood fiber length distribution were determined in order to investigate this effect. Composites of linear low-density polyethylene and 10 wt% of each of the wood species were prepared, using polyvinyl alcohol-co-ethylene as a compatibilizer. Significant differences were found between the wood species in terms of both chemical composition and wood fiber length distribution. These affected the properties of the WPCs in different ways. Use of acacia resulted in a WPC with superior mechanical properties and thermal stability compared with the other species, due to its higher cellulose and lignin contents and a favorable wood fiber length distribution; however, acacia composites also showed a higher water absorption rate due to the higher cellulose content. We also found that WPCs containing wood species with a high lignin and extractive content, such as acacia and oak, had a higher resistance to UV degradation.

Determination of the influence of the polymer structure and particle size on the film formation process of polymers by atomic force microscopy

Abstract The particle size and morphology of a synthetic polymer latex were shown to influence the film formation behavior. Theoretical models predict that small particles coalesce more easily than large colloids do. The influence of particle size and morphology of differently structured lattices on the film-formation process was investigated by atomic force microscopy (AFM). Sequences of AFM images were acquired over a certain temperature range or at room temperature as a function of time. From the resulting images the average particle diameter of the latex particles in the surface layer was determined as a function of the time or temperature. The resulting curves could be compared to observe differences in the film formation kinetics of the different lattices. These AFM studies confirmed that the film formation behavior is influenced by the particle size and particle morphology, but that the core/shell ratio of core–shell particles has no significant influence on the film formation kinetics.

Nanoscale characterization of wood photodegradation using atomic force microscopy

AbstractAtomic force microscopy (AFM) can image materials at the nanometer scale and obtain quantitative information on their surface energy, roughness and hardness (Morris et al. 1999). AFM has also been used to quantify changes in the surface properties of polymer films and coatings exposed to UV radiation or natural weathering, but it has not been used to assess the photodegradation of wood (Biggs et al. 2001). The advantage of using AFM to assess the photodegradation of polymers lies in its ability to reveal early changes in the material on a nanometer scale and elucidate mechanisms responsible for such degradation. This study examined if AFM could provide similar information and insights for wood exposed to solar radiation.

Using extractive-free wood as a reinforcement in wood-LLDPE composites

Hot water extractives, solvent extractives and both hot water and solvent extractives were eliminated from different wood species via Soxhlet extraction. Different wood–linear low density polyethylene (LLDPE) composites were prepared using 10% wood and 7% poly(ethylene-co-vinyl alcohol) as a compatibilizer. A comparison of the mechanical properties, water absorption behaviour and resistance to UV radiation between composites filled with unextracted wood and composites filled with the same species but without the above extractives were carried out. The results illustrated that there are several distinct benefits and drawbacks when using wood without extractives as a filler. Unextracted wood produced composites with better mechanical properties and resistance to UV radiation, while extracted wood led to composites with lower water absorption rates. Using wood without both hot water and solvent extractives as a filler caused the largest reduction in mechanical properties, UV resistance and water absorption rate, compared to composites made with wood where only one extractive component was removed.

Biomass from Wood in the Tropics

Bioenergy production from wood is one of the oldest forms of energy and it was for a long time considered a primitive energy source in many industrialised countries. However, it is currently experiencing an increase in attention worldwide. Considering its importance and history, it is astonishing that the widespread cognizance of wood as an important energy source in modern times is a recent phenomenon. It has been mainly driven by the pressure of diminishing fossil fuel resources in industrialised countries, as well as the wish to become more independent from nuclear power and its risks in some developed countries. In addition, amongst other renewable energy sources, bioenergy was identified as an alternative to fossil fuels, which could also help to prevent furthering an anthropogenic climate change by attempting to reduce greenhouse gas emissions. Currently, two different development routes are recognizable, which appear to go in opposite directions and result in competition for land resources in tropical countries. One route is driven by developing countries and the other by developed countries. Globally, wood is the most important source of renewable energy and is used to produce more energy than all other renewable energy sources combined (FAO 2012). According to, the global annual woodfuel consumption, which comprises fuelwood, charcoal and other wood based energy sources, sums up to 1.87 billion m3. Of this amount, 13 % are consumed in the tropical and sub-tropical regions of the Americas and Caribbean region, 30 % in Africa and 30 % in Asia and the Pacific region. In total, almost three quarters of the global woodfuel consumption occur in tropical countries.

Determination of the cellulose and lignin content on wood fibre surfaces of eucalypts as a function of genotype and site

We compared the chemical composition of wood fibres and fibre surfaces of several eucalypt species and hybrids originating from various growth sites in South Africa. The objective was to test for differences in chemical surface composition due to genetics or site with the ultimate aim to facilitate a tailor-made supply of wood for pulping that results in an optimal blend of fibres that can be pulped together with similar yields. This, however, requires a sound knowledge of the fibre properties. The surface functionality on the single fibre level is a key property, because it determines how good inter-fibre bonding will be when paper is formed, which depends amongst other fibre properties on the amount of free hydroxyl groups that are available and therefore on the cellulose content on the fibre surface. The cellulose and lignin content on the fibre surface were determined with chemical force microscopy, a variation of atomic force microscopy. Since the general bulk composition of the fibre and the surface composition might differ, both parameters were determined. We found significant differences in the cellulose and lignin content on fibre surfaces, with regard to genotype and site, respectively. In some, but not all, cases, the surface composition of wood fibres followed the bulk composition, and differences were generally more pronounced. Differences due to genotype were significant, especially with regard to the surface lignin content—but variation due to site was also distinctly recognisable. This variation in surface functionality could be the reason why some pulpwood blends result in a lower pulp yield and different quality.

Visualising and quantifying thermal degradation of wood by computed tomography

Wood samples from South African pine were subjected to thermal degradation of varying degrees, and their dimensional change as well as changes in cell wall density were determined with a micro CT scanner. It was possible to visualise and quantify those changes and also determine a temperature threshold above which the degradation seemed to be too severe to use this wood for any structural purposes. Below this threshold, however, wood properties changed little and the wood may still be of economic value.

Physical properties of burnt timber, with special focus on the drying performance

Burnt wood has been found to perform different from sound (green) wood when dried together, but also with regards to other physical and mechanical properties. In this study the drying performance of wood burnt to different degrees in recent plantation fires was investigated, and the physical, chemical and wood anatomical properties of these different wood types were determined. Different cell structure and chemical composition due to thermal degradation could be observed as well as different drying performance and variation in mechanical properties. An explanation for the deviant drying performance was attempted with the observed structural changes.ZusammenfassungEs wurde festgestellt, dass sich verbranntes Holz oft anders verhält als unbeschädigtes (frisches) Holz, wenn beide Holzarten zusammen getrocknet werden, aber auch in Hinsicht auf physikalische und mechanische Eigenschaften. In diesem Projekt wurde das Trocknungsverhalten von Holz mit unterschiedlich starkem Verbrennungsgrad untersucht und Unterschiede in physikalischen, chemischen und anatomischen Eigenschaften festgestellt. Ein Unterschied in der Zellstruktur und in der chemischen Zusammensetzung, hervorgerufen durch thermische Degradierung, konnte festgestellt werden; ebenso ein Unterschied im Trocknungsverhalten und eine Variation in den mechanischen Eigenschaften. Eine Erklärung für das unterschiedliche Trocknungsverhalten anhand der beobachteten strukturellen Änderungen wurde versucht.

The effect of surface fire on tree ring growth of Pinus radiata trees

Key messagePinus radiatatrees showed significantly reduced basal area increments and increased latewood/earlywood ratios, when their stem was charred by surface fires even if no needle damage occurred. An interaction of fire damage and precipitation on growth was observed.ContextHeat from forest fires is able to penetrate beyond the bark layer and damage or completely kill a tree’s cambium. Short-term growth reductions following surface fires have been reported for some species. However, most studies have in common that they describe a compound effect of stem and foliage damage.AimsThis study investigated the impact of surface fires on the radial growth of Pinus radiata, where only the stem of trees was charred, while no needle damage was recorded.MethodsTree ring measurements were performed on cores obtained at breast height. Analysis of variance and tests, based on annual basal area increment values were calculated to quantify pre- and post-fire growth differences of tree ring width and latewood/earlywood ratios.ResultsThe analysis revealed significant growth reductions following a surface fire on P. radiata in the year on which the fire occurred as well as in the following year. As a consequence of the fire, basal area increment and latewood/earlywood ratios were significantly reduced. An interaction of fire damage and precipitation on growth was observed.ConclusionThe obtained results show how fires without crown damage can affect growth and tree ring structure of P. radiata trees and indicate that stem char could be associated with a significant decrease in ring width and latewood/earlywood ratio.

Use of atomic force microscopy to detect wavelength dependent changes in wood veneers, and spin coated lignin and cellulose films exposed to solar radiation

Abstract We examined whether spin coated lignin and cellulose films could act as material models for wood exposed to solar radiation. Films and wood were exposed to sunlight under filters that transmitted different parts of solar radiation. Changes in surface roughness, hardness and polarity of the films were analysed with atomic force microscopy and compared with those occurring on wood. All properties changed after exposure and the magnitude depended on the wavelength and substrate. The roughness of wood and lignin films increased after exposure, whereas it decreased on cellulose. The surface hardness of all three substrates increased more after exposure to less energetic radiation. Lignin films became more hydrophilic, whereas polarity changes of wood and cellulose were wavelength dependent. We conclude that lignin and cellulose films can act as material models for wood exposed to solar radiation and discuss how they might be used to develop new photoprotective wood treatments.