A note on artificial weathering of spruce (Picea abies) with a carbonised layer

Abstract

Wood in outdoor applications undergoes various degradation processes such as biological degradation as well as weathering. However, since carbon black is a very effective photostabilizer, it is hypothesised that wood surfaces can be protected from weathering by a layer of carbon (charcoal). Norway spruce (Picea abies) samples were pyrolised to create carbonised layers of varying thickness and exposed to artificial weathering for eight weeks.To investigate surface changes due to weathering, colour measurements and ATR FTIR measurements were made. The results show that carbonised surfaces protect wood from weathering but they also undergo chemical changes. Thus, the thickness of carbonised layers influences the weathering protection of wood.

Effect of Weathering on Surface Functional Groups of Charred Norway Spruce Cladding Panels

“…Therefore, lignin is photodegraded also on the charred surface. Similar changes were reported also by Kamke and Pfriem [24] in short-term artificial weathering of charred spruce surfaces. The magnitude still needs to be assessed with more detailed comparisons of different surfaces, since thickness of char layer is speculated to be crucial [24].…”

Review of Wood Modification and Wood Functionalization Technologies

“…Relevant surface properties therefore include wear resistance, dimensional stability, and surface wettability. Because char is rather inert both chemically and biologically, it is presumed that the overall performance is determined by the thickness of the carbonized layer [211,214,229]. In general, char is porous and friable, and therefore is not very resistant to mechanical wear caused by handling, installation, use, and abrasion from rain and wind.…”

“…Candelier et al [205] concluded that under vacuum the degradation was slower than under nitrogen: a vacuum removes all volatile products, restricting secondary reactions, while a nitrogen atmosphere increases the lignin and carbon content of the residue. Kampe and Pfriem [229] published a short note on flame charred spruce, describing an experimental device utilizing gas flame under a flow of nitrogen to avoid ignition. Char depths were not reported, but other results seem comparable to published studies.…”

Natural weathering of soft- and hardwoods modified by contact and flame charring methods

“…The composition of the char depends on the used method, but to simplify, the further the thermolysis proceeds, the more inert the surface will be. Kampe and Pfriem (2018) and Kymäläinen et al (2020) have published results on natural weathering of Norway spruce charred with experimental devices-one with gas flames and one utilizing a continuous contact heating method. Both reported rather good weatherability when assessed visually but noted changes in the modified lignin component that indicates photodegradation.…”