Microencapsulated di-ammonium hydrogen phosphate (DAHP) with a polyurethane shell: characterization and its properties in wood

This work deals with the microencapsulation of di-ammonium hydrogen phosphate (DAHP) in polyurethane using an interfacial polymerization method. The produced microcapsules were characterized by Fourier transform infrared spectroscopy (FTIR), particle size analysis, and scanning electron microscopy (SEM). The fire resistance, flexural (bending) strength, and leaching properties of the impregnated wood were determined and SEM, thermogravimetric analysis (TGA), and FTIR examinations were carried out. Results indicated that as the temperature was increased, weight loss was increased in the DAHP samples, while weight loss occurred in two stages with the microencapsulated DAHP (MCDAHP) samples. The average particle size of the produced microcapsules using PEG400 was measured as 40 µm. According to FTIR results, phosphorus peaks were observed in the MCDAHP samples. Although the DAHP-impregnated samples showed lower thermal stability compared to the control, the samples impregnated with MCDAHP behaved similarly to the control. According to the leaching test results, the fixation of MCDAHP in the wood had increased. According to the limiting oxygen index (LOI) results, fire resistance of the MCDAHP sample was found to be higher than in the DAHP sample. No significant change in mechanical properties was observed in the samples impregnated with DAHP or MCDAHP. The SEM results showed that the microcapsules had covered the entire surface of the wood. According to the FTIR results, the wood samples impregnated with DAHP and MCDAHP reflected the properties of the DAHP and MCDAHP.