Investigation of the water absorption in polyamide and wood plastic composite by terahertz time-domain spectroscopy

Non-destructive evaluation by terahertz spectroscopy for penetration of acid solutions into epoxy resin

“…The slopes of n at 0.4 and 0.6 THz and those of κ at 0.4 and 0.6 THz are also the same, respectively. This behavior is in a good agreement with the complex refractive index spectrum of polyamide (PA) immersed in water reported by Jördens et al [18] even though PA absorbs more water than EP and saturates at about 10 mass%.…”

“…Although the THz spectra of the ñ of bulk water are already known [18,23,24,34], as mentioned in section 1, it is challenging to separate experimentally the contributions from bound and free water in materials [18,20]. In our study, some water molecules in the specimen can be bound to the amine and hydroxyl groups in the resin.…”

“…The main advantages of THz-TDS for NDT studies are the high penetration of THz electromagnetic waves into polymers [13][14][15][16][17][18], high sensitivity to the inter/intra molecular vibrations (especially for water) [18][19][20][21][22][23][24][25][26], and ability to estimate the materials dielectric properties without direct contact [27][28][29]. The THz spectra of various thermoplastics [13][14][15] and thermosets [16,17] measured by THz-TDS were reported.…”

“…Note that water molecules in material can also exist as both 'free' and 'bound' water and it is difficult to separate experimentally the contributions from bound and free water to the THz spectra [20]. In certain cases, the assumption that only bound water exists in a material makes it possible to measure its content [18,20]. For example, the amounts of water in polyamide and wood plastic composites were estimated with THz-TDS by measuring the complex refractive index as a function of water content [18].…”

“…In certain cases, the assumption that only bound water exists in a material makes it possible to measure its content [18,20]. For example, the amounts of water in polyamide and wood plastic composites were estimated with THz-TDS by measuring the complex refractive index as a function of water content [18]. In the case of wood materials in humid environment, the real and imaginary parts of the complex dielectric function of the samples strongly correlated with density and moisture content [21].…”