The susceptibility of surface-modified wood, surface-modified acetylated wood and acetylated wood to mold and blue stain fungi was investigated. The surface modifications were based on fluorinated and non-fluorinated silicone nanofilaments for increased hydrophobicity. Results showed an increased mold resistance of the surface-modified superhydrophobic wood with mold appearing later or with less intensity on the modified surfaces than on the untreated wood in accelerated mold chamber tests due to the increased water resistance of the samples. All acetylated wood samples exhibited good mold resistance as the available water in acetylated wood was reduced. The surface modifications on acetylated wood had a slightly negative effect on mold resistance due to side effects from the modification. The surface-modified wood showed high blue stain fungi coverage, whereas almost no blue stain fungi were observed on the acetylated wood and surface-modified acetylated wood. The surface-modified superhydrophobic wood showed high mold coverage after conditioning in a high-humidity environment or after exposure to UV irradiation. Meanwhile, the acetylated wood and surface-modified superhydrophobic acetylated wood showed a small amount of mold coverage in these conditions. © 2023 The Authors

Durability tests of wood materials related to constructions in Björnlandet National Park

The aim of the present study, primarily initiated by the Swedish Environmental Agency, is to study the durability of different wood materials related to and used in constructions in Björnlandet National Park in northern Sweden (63°97´N, 18°05´E), completed during 2014 and 2015. Of particular interest is to determine the durability properties in a scientific way of local materials used, such as mountain-grown Norway spruce and locally grown Scots pine and larch. The effect on the performance of charring and superficial wood-tar treatment is also studied.

The study consists of a laboratory test according to ENV 807, a field trial according to EN 252 and a service trial on-site in the national park, including constructions such as load-bearing piles, ramps, foot-bridges and platforms. Results from the tests according to ENV 807 and EN 252 as well as the initial inspection of the constructions and components of different materials are presented in this report.

During the initial inspection of the constructions on site, then in use for 1-2 years, no decay was found besides a small initial attack on one single pile of larch.

The accelerated tests in laboratory and field have provided interesting information on the durability properties of the different materials and the ranking between them from a durability point of view which can be concluded as follows:

• The local materials show moderate durability with marginal differences between the materials, with the exception of the spruce materials which show lower durability, comparable to the durability of pine sapwood.

• Heartwood of locally grown pine and larch show basically equal durability properties.

• Slow-grown wood will not enhance the durability properties.

• Superficial treatment with wood-tar contributes so far to a somewhat increased durability. However, the primary positive effect is most certainly owing to the smell and appearance of wood treated with wood-tar, which in certain environments contributes to a positive perception. Charring does not add any value from a durability point of view.

It is important that the results of the laboratory and field tests are interpreted with some care and common sense. The relatively extensive decay achieved with all materials but the preservative-treated wood does not necessarily mean that the constructions will be subject to early decay. With respect to the geographical location of Björnlandet National Park in the inland of northern Sweden, where the decay hazard in general is moderate, the local materials can thus be expected to have a reasonably long service.

However, results from the tests indicate that efforts to select local materials/use "traditional" treatments most certainly will not result in longer service life than can be achieved with corresponding materials commercially available.

Finally, it is pointed out that:

• Avoiding moisture traps by correct design of components and constructions is vital for the service life when "traditional" local materials and treatments are used.

• Preservative treatment will in general give critical wooden constructions a longer service life. The use of untreated wood involves more uncertainty with expected service life. Regular inspections and maintenance are therefore particularly important for constructions critical to personal safety (e.g. foot bridges, ramps) or infrastructure (e.g. bridges).

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Urgent future objectives to complete are the inspections of the field trial until remaining stakes have been exposed for five years, and to follow up the service trial in Björnlandet National Park with inspections in 4-5 years, i.e. in 2022 or 2023 in order to confirm or reassess the preliminary conclusions.

The properties of the fibre/matrix interface contribute to stiffness, strength and fracture behaviour of fibre-reinforced composites. In cellulosic composites, the limited affinity between the hydrophilic fibres and the hydrophobic thermoplastic matrix remains a challenge, and the reinforcing capability of the fibres is hence not fully utilized. A direct characterisation of the stress transfer ability through pull-out tests on single fibres is extremely cumbersome due to the small dimension of the wood fibres. Here a novel approach is proposed: the length distribution of the fibres sticking out of the matrix at the fracture surface is approximated using X-ray microtomography and is used as an estimate of the adhesion between the fibres and the matrix. When a crack grows in the material, the fibres will either break or be pulled-out of the matrix depending on their adhesion to the matrix: good adhesion between the fibres and the matrix should result in more fibre breakage and less pull-out of the fibres than poor adhesion. The effect of acetylation on the adhesion between the wood fibres and the PLA matrix was evaluated at different moisture contents using the proposed method. By using an acetylation treatment of the fibres it was possible to improve the strength of the composite samples soaked in the water by more than 30%.

We have developed a method based on isothermal calorimetry to monitor the colonization of wood materials by decay fungi. The heat produced is a direct and continuous measure of the activity (respiration) of the fungus. This pre-study shows that wood materials treated in different ways give results that reflect the known ranking of the materials regarding resistance to decay. In addition to this, the 40 days measurements show several phases and periods of oscillating respiration. As the calorimeter continuously monitors the colonization and degradation process, this method provides more information than classical/standardized decay tests in which typically only the final mass loss is determined.

The chapter deals with different aspects on the use and performance of bio-based building materials in constructions and buildings.

Testing different materials exposed in jetties at Öresund - Progress report No. 3

This report contains results of the fourth inspection on the performance of different decking materials – preservative-treated wood, modified wood, natural durable wood, recycled plastics and wood-plastic composites (WPCs), available on the market and exposed in two jetties near the Øresund Bridge, south of central Malmö in Sweden. The objective of the test is to gather information relatively quickly on material performance with respect to appearance, durability and function of the tested materials.

The test has, in spite of the relatively short exposure time, provided useful information on the properties of the different materials and their suitability for outdoor end-use situations exposed to wet conditions and attacks by wood-destroying organisms, but also withrespect to mechanical and aesthetic aspects.

All wood materials have become greyish in short time, whereas the colour of the recycled plastics and composites still remains roughly the same as the original after exposure during four summers.

All materials but the re-cycled plastics and composites have been more or less attacked by discolouring fungi and algae. No decay has been observed with the exception of minorincipient decay around screws in roble and Western Red Cedar.

The mechanical properties vary considerably between the materials. Oak, robinia, bangkirai, azobé and Thermowood® have all shown tendencies of formation of cracks andsplinters, which may cause injuries in bare feet

Denna rapport innehåller resultat från den fjärde besiktningen av olika trä-, plast- och kompositmaterial exponerade i två bryggor vid Sibbarps badplats vid Öresund strax norrom Øresundsbron. Tanken med att exponera materialen i denna miljö är att relativt snabbt får besked om vilka material som ser ut att klara sig bäst och uppfylla Malmö Stadsgatukontors krav på utseende, hållbarhet och funktion i en utsatt miljö.

Försöket har, trots att det pågått under en förhållandevis kort tid, givit värdefull information om olika materials egenskaper och lämplighet för användning utomhus i utsatta miljöer med hänsyn till fuktpåverkan och angrepp av biologiska skadegörare menäven med hänsyn till mekaniska och utseendemässiga aspekter.

Samtliga trämaterial har snabbt blivit gråa, medan plast- och kompositmaterialen ännuefter fyra somrars exponering i stort sett har kvar sin ursprungsfärg.

Samtliga material utom plast och kompositer har i varierande grad angripits av missfärgandesvamp samt alger. Inga rötskador har observerats med undantag från små begynnande angrepp runt skruvskallar i två av trämaterialen.

De mekaniska egenskaperna har visat sig skilja en hel del mellan materialen. Sprickbildning och uppfläkning av virkesytan, särskilt på kantsidor, kan i värsta fallorsaka skador på framför allt bara fötter.

A superamphiphobic coating on a biobased material shows extreme liquid repellency with static contact angles (CA) greater than 150° and roll-off angles less than 10° against water, ethylene glycol, diiodomethane and olive oil, and a CA for hexadecane greater than 130°. The coating consisting of titania nanoparticles deposited by liquid flame spray (LFS) and hydrophobized using plasma-polymerized perfluorohexane was applied to a birch hardwood. Scanning electron microscopy (SEM) imaging after sample preparation by UV laser ablation of coated areas revealed that capped structures were formed and this, together with the geometrically homogeneous wood structure, fulfilled the criteria for overhang structures to occur. The coating showed high hydrophobic durability by still being non-wetted after 500 000 water drop impacts, and this is discussed in relation to geometrical factors and wetting forces. The coating was semi-transparent with no significant coloration. A self-cleaning effect was demonstrated with both water and oil droplets. A self-cleanable, durable and highly transparent superamphiphobic coating based on a capped overhang structure has a great potential for commercial feasibility in a variety of applications, here exemplified for a biobased material.

COST Action FP 1303 “Performance of bio-based building materials” successfully started in October 2013 and an ambitious program was set up for the four year programme. COST Actions provide an excellent opportunity for collaborative research, e.g. in the frame of Round Robin tests.

The idea of this respective test was to distribute a fairly simple test set up to as many places in Europe as possible in order to collect performance data reflecting the range of climatic exposure conditions. Furthermore we wanted to consider performance in its manifold meaning, i.e. optical, aesthetical, moisture and functional performance and durability. In contrast to traditional Round Robin tests aiming on comparative evaluation and validation of results from different test laboratories, this initiative aims on collecting performance data under climatically different exposure conditions. Therefore it was required to provide weather data from the respective test sites to allow establishing relationships between climate conditions and the following measured, which shall be evaluated regularly: decay, discolouration, development of mould and other staining fungi, corrosion, formation of cracks and moisture performance (if data logging device is included). Further details about the test and the first outcomes are presented in this paper.