Artificial Weathering Resistance Test Methods for Building Performance Assessment of Profiles Made of Natural Fibre-Reinforced Polymer Composites

A growing popularity of profiles made of natural fibre-reinforced polymer composites in civil engineering encourages determining test methods relevant for building performance assessment. Weathering resistance is among the key aspects that condition the durability of building structures. The paper includes a comparative analysis of two artificial weathering resistance test methods. Polyvinyl chloride and wood flour composite profiles were tested. They were subjected to UV and spraying (X-exposure) and UV, spraying and wetting by condensation (F-exposure), both at different exposure times. The influence of the applied weathering procedures on the composite’s microstructure and its mechanical characteristics were analysed. No changes in the microstructure of brittle fractures were observed. However, surface morphology changes were revealed, noticeably greater following X-exposure than F-exposure. F-exposure exerted significant influence on the mechanical properties of brushed profile, including, but not limited to, flexural modulus. Whereas X-exposure exerted more influence on the mechanical properties of non-brushed profile.

Effect of Artificial Ageing on Adhesive Bonds from Heat Treated Spruce

The influence of artificial ageing on bonded heat-treated spruce lamellas was investigated. Heat-treated spruce lamellas with different degrees of thermal modification were bonded with PVAc and MUF and then exposed to 500 artificial weathering cycles, combined with rain, UV and IR radiation. The colour change of the exposed surface, weight change, delamination of the bonded joints and adhesive bond strength were measured. Artificial weathering caused cracking and delamination of the bonded joints and reduced the bond strength of both adhesives. The results show that delamination was higher for PVAc adhesive than MUF, but increased for both adhesives with the temperature of heat treatment of wood. The shear strength of bonds on the exposed side of the samples after the artificial weathering was lower than the average strength of the whole sample.

A durable coating to prevent stress corrosion effects on the surface strength of annealed glass

The durability of an innovative polymeric coating recently developed by the authors to prevent stress corrosion in annealed glass is herein examined. The coating, having functional graded properties through the thickness, is optimised to provide a very good adhesion with glass and an excellent hydrophobic behavior on the side exposed to the environment, thus creating a good barrier to humidity, which is the triggering agent for stress corrosion. Three scenarios are analysed in terms of ageing: (i) cyclic loading, accomplished by subjecting coated samples to repetitive loading; (ii) natural weathering, performed by exposing coated samples to atmospheric agents; (iii) artificial weathering, carried out by exposing coated specimens to fluorescent UV lamps, heat and water. The durability of the coating is assessed indirectly, on the base of its residual effectiveness in preventing stress corrosion, by comparing the bending strength, obtained with the coaxial double ring test, of aged coated glass specimens with that of un-coated and freshly coated specimens. The obtained results prove that the proposed formulation is almost insensitive to cyclic loading, maintains a very good performance in case of natural weathering, whereas is slightly more sensitive to artificial weathering.

The Effect of Artificial Weathering on Surface Properties of Thermally Modified Oriental Beech Wood

The study aimed to determine some surface parameters such as surface roughness and color changes of thermally modified Oriental beech (Fagus orientalis L.) wood samples after 750 hours of artificial weathering. The results of the study showed that artificial weathering led to an increase in surface roughness of Oriental beech wood. Thermal modification interval of 210 °C - 230 °C gave a smoother surface than unmodified samples after artificial weathering. Artificial weathering caused darker, reddish, and yellowish tone of unmodified and thermally modified Oriental beech wood. According to the study fi ndings, surface properties of thermally modified Oriental beech wood were better than those of unmodified Oriental beech.

Durability of Flame-Retarded, Co-Extruded Profiles Based on High-Density Polyethylene and Wheat Straw Residues

At present, little information is available in the scientific literature related to the durability (weathering resistance) of fire-retarded wood and natural fiber-reinforced thermoplastics. In this work, thermoplastic profiles for façade applications based on high-density polyethylene, wheat straw particles, and fire-retardants were extruded and their reaction-to-fire performance before and after artificial weathering evaluated. Profile geometries were either solid or hollow-core profiles, and fire-retardants (FR) were added either in the co-extruded layer or in the bulk. Various FR for inclusion in the co-extruded layer were screened based on UL-94 tests. For profile extrusion, two types of FR were chosen: a coated intumescent combination based on ammonium polyphosphate (APP) and an APP coated with melamine and without formaldehyde. Before weathering, the peak heat release rate (pHRR) and the total heat release (THR), which were determined using cone calorimeter measurements, were reduced by up to 64% and 67% due to the FR. However, even before weathering, pHRR of the profiles was relatively high, with best (lowest) values between 230 and 250 kW/m2 under the test conditions. After 28 days of artificial weathering, changes in reaction-to-fire performance and color were evaluated. Use of the APP in the co-extruded layer worsened color change compared to the formulation without APP but the pHRR was not significantly changed. The influence of weathering on the fire behavior was small compared to the difference between fire-retarded and non-fire-retarded materials. Results from the cone calorimeter were analyzed with regard to ETAG 028, which provides requirements related to the durability of fire performance of building products. In many formulations, increase in THR was less than 20% compared to before weathering, which would place some of the profiles in class C or better (EN 13501-1). However, due to the high pHRR, at best, class D was obtained under the conditions of this study. In addition to cone calorimeter measurements, results from the single flame source test, limiting oxygen index determination and thermogravimetric analysis, are shown and discussed. Strength properties, water uptake and swelling of the profiles, thermal conductivity, and energy dispersive X-ray data are also presented.

Cellular-level chemical changes in Japanese beech (Fagus crenata Blume) during artificial weathering

Since wood chemical components can be depolymerized and modified by weathering, a better understanding of the mechanisms governing these processes in needed to develop effective protection methods for wood surfaces. Unfortunately, very little has been reported about the micro-scale chemical changes in wood, particularly hardwood, during weathering. The purpose of the present work is to determine the degradation behavior of Japanese beech (Fagus crenata Blume) under artificial weathering at the cellular-level. Herein, the structural and micro-distributional changes in wood components during weathering were investigated using micro-Raman spectral and chemical mapping analyses. The Raman spectra showed that weathering facilitated lignin degradation and modification. The degradation behavior of lignin differed depending on the type of wood tissue. The rate of lignin reduction followed a descending order: vessel element > axial parenchyma cell > wood fiber. Raman mapping determined that cellular-level lignin reduction on the surface layers differed for wood species. Although lignin degradation of cedar tracheids proceeded from both the surface and the cell lumen, the lignin in beech fibers degraded according to the depth.

Influence of compounding conditions, treatment of wood particles with fire-retardants and artificial weathering on properties of wood-polymer composites for façade applications

Various fire-retardants (FR) for the pre-treatment of wood flour, for example, ammonium polyphosphate and different formulations based on phosphorus- and nitrogen-compounds, as well as for application during compounding were tested for their effectiveness in injection-molded and extruded composites based on high-density polyethylene and polypropylene. Small-scale tests for flammability of polymeric materials and for determination of the limiting oxygen index were used to characterize the composite materials. Differences pertaining to the applied compounding conditions, i.e., underwater granulation versus air granulation, were determined. The amount of phosphorus leached from FR during underwater granulation was analyzed. Artificial weathering trials were performed and reaction-to-fire performance and color changes of FR-composites were evaluated. Tensile strength properties of the composites and results for cold water immersion tests are also reported. An optimized formulation based on pre-treated wood flour was developed and extruded into façade profiles for the single burning item test according to DIN EN 13823. The test showed that classification C-s3, d0 according to DIN EN 13501-1 can be achieved if pre-treated wood flour is used. The use of untreated wood flour leads to a lower classification (D-s2, d0). Fire performance of extruded façade profiles can be improved by the use of pre-treated wood flour and enables new applications in the building sector.