In this study, ammonium polyphosphate (APP) and aluminum hydroxide (ALH) with different mass contents were used as fire retardants (FRs) on plant-based natural flax fabric-reinforced polymer (FFRP) composites. Thermogravimetric analysis (TGA), limited oxygen index (LOI), and the Underwriters Laboratories (UL)-94 horizontal and vertical tests were carried out for evaluating the effectiveness of these FR treatments. Flat-coupon tensile test was performed to evaluate the effects of FR treatment on the mechanical properties of the FFRP composites. For both fire retardants, the results showed that the temperature of the thermal decomposition and the LOI values of the composites increased as the FR content increases. Under the UL-94 vertical test, the FFRP composites with 20% and 30% APP (i.e., by mass content of epoxy polymer matrix) were self-extinguished within 30 and 10 s following the removal of the flame without any burning drops, respectively. However, the mechanical tensile tests showed that the APP treated FFRP composites reduced their elastic modulus and strength up to 24% and 18%, respectively. Scanning electronic microscopic (SEM) for morphology examination showed an effective coating of the flax fibres with the FRs, which improved the flame retardancy of the treated composites.

No abstract

Citric acid together with sorbitol (SorCA) have been used to modify wood and improve its properties, such as dimensional stability and biological durability, which partly result from its swelling and sorption behavior. However, the underlying mechanism of water interaction with SorCA-treated wood is very complex and not fully understood. Previous research confirmed cell wall bulking and suggested cross-linking, however the extent of their contribution to moisture-induced changes has not been researched. This study investigated the effect of SorCA treatment on sorption properties of wood in the hygroscopic range (0–95% RH). Scots pine sapwood (Pinus sylvestris L.) was chemically modified with an aqueous SorCA solution at different treatment levels and measured by dynamic vapor sorption (DVS). The observed permanent increase in oven-dry dimensions did not result in a decreased swelling compared to untreated specimens. It was ascribed to the excessive expansion of cell wall matrix caused by a degradation of cell wall constituents by the acidic impregnation solution. However, a reduction in moisture content in comparison to untreated reference was detected. Present findings suggest that the SorCA polyester structure is altered after impregnation inside the wood and affects its sorption behavior by covalent bonding and, presumably, cross-linking with wood polymer constituents.

No abstract

Recent studies showed treatments with sorbitol and citric acid (SorCA) to significantly improve the dimensional stability and biological durability of wood. The industrialization of this process requires a quality control (QC) method to determine if the fixated chemicals are homogenously distributed within the piece of wood, which is essential for uniform material performance. Therefore, the objective of this work was to evaluate the use of common electromagnetic radiation-based methods to determine the degree of modification in SorCA-treated wood. Both Fourier transform infrared (FTIR) spectroscopy and near-infrared (NIR) spectroscopy have been used to create rough calibrations for the weight percent gain (WPG) prediction models. The FTIR measurements resulted in a high linear correlation between the band area ratio (BAR) and the WPG (R2 = 0.93). Additionally, a partial least square (PLS) regression of NIR spectroscopic data resulted in a model with a high prediction power (R2 = 0.83). Furthermore, X-ray density profiling emerged as a simple alternative for the QC by showing a gradient of modification chemicals inside the sample and differences in chemical uptake between earlywood and latewood. Overall, it can be concluded that the results from FTIR, NIR and X-ray densitometry can serve as indicators of impregnation chemical distribution in SorCA-modified wood.