Chemical and appearance changes of wood due to artificial weathering – Dose–response model

Abstract

The aim of this study was to assess a model for the surface degradation kinetics of natural wood exposed to artificial weathering. The photochemical and physical processes of weathering result in simultaneous changes of both the wood matrix composition (i.e. lignin content, cellulose crystallinity index, cellulose polymerization degree) and wood's appearance (i.e. colour, gloss, roughness). European larch, a popular cladding material, was used for experimental samples. Weathering was conducted in a QUV artificial weathering machine for 672 h according to the EN927-6 standard. The response of wood was assessed using multi-sensor measurements. Results revealed that changes in colour are evident already after 28 h of artificial weathering, with an increase in a à and b à , and a decrease in L Ã. That initial trend was reversed afterward, with the colour changing to grey. Due to the particular shape of the curves representing colour coordinates, it is difficult to use CIE L à a à b à parameters to model the weathering dose. However, the degradation curve established for selected near infrared bands was useful to build a dose-response model of wood surface degradation. In all cases, a clear trend of change in absorbance values that progressed along with the weathering dose was observed. These curves, unlike the CIE L à a à b à values, are monotonic, meaning that dose value corresponded with only one value of absorbance. Principal component analysis of the near infrared spectra allowed clustering of the spectra by different dose classes, with the main differentiation in the reference class and in the final class (maximum dose). It was found that the discrimination between spectra at diverse cumulative weathering doses was more evident for earlywood than for latewood. This confirms the hypothesis that degradation kinetics differ depending on the anatomical configuration of wood. This research is a first step for establishing dose-response model for natural weathering, where precise quantification of weathering parameters is more challenging.

Bioinspired Living Coating System in Service: Evaluation of the Wood Protected with Biofinish during One-Year Natural Weathering

“…Several studies are reporting a decrease in wood glossiness associated with exposure to natural weathering [18,20,60,61]. It was not directly confirmed by the present experimental results that are related to the relatively short period of the test as well as the initial surface configuration that was intended to be moderately rough.…”

“…The colour space coordinates defined by the International Commission on Illumination CIE L*a*b* and derived ∆E are frequently used to quantify colour alterations due to lignin degradation and chromophores generation [11][12][13][14]. Spectroscopic techniques such as Fourier Transform Infrared Spectroscopy (FTIR) [15,16], Fourier Transform Infrared Spectroscopy-Attenuated Total Reflectance (FTIR-ATR) [17], and/or Fourier Transform Near Infrared Spectroscopy (FT-NIR) [18][19][20] are often used to investigate changes in functional groups of wood chemical components. Other aspects frequently assessed while evaluating the weathering process of materials include the determination of the surface roughness [21,22], wettability [23,24], or glossiness [18,25,26].…”

Environmental effects of stratospheric ozone depletion, UV radiation, and interactions with climate change: UNEP Environmental Effects Assessment Panel, Update 2020

“…Wood exposed to solar UV radiation typically undergoes surface discolouration and degradation that reduces its adhesive strength for coatings [ 458 , 459 ]. A novel variant of the APP technology was shown to successfully reverse moderate effects of surface degradation due to exposure to UV radiation of Fagus sylvatica (beech wood) [ 460 ].…”

Bio-based Building Skin

“…Diverse weather factors may cause numerous alterations to the weathered material. Dose-response relationships should be used to explain the biomaterial façade degradation in relation to varying exposure conditions (Petrillo et al 2019). A procedure in developing a dose-response model typically includes the following steps.…”