Preparation and property assessment of eco-friendly composite based on polyvinyl alcohol and lignin extracted from biomass
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- 3.4. The UV-shielding performance of the composite film
- TNU Journal of Science and Technology 226(06): 3 - 9 http://jst.tnu.edu.vn 8 Email: jst@tnu.edu.vn Figure 4.
| Figure 3. Mechanical properties PVA/lignin composites
Moreover, the elongation at break of the composite reached the maximum value of 171.3%, an increase of 32.5% compared with the PVA film. It could be seen that the lignin molecules are compactly linked with PVA molecules by hydrogen bonds. Therefore, under tensile force, lignin molecules stretched together with the PVA molecule, increasing the elongation of the composite. However, with higher lignin content, a part of lignin molecules clumped and acted as a poorly dispersed filler, reducing the ductility of the film, leading to a decrease in the elongation at break of the composite. The maximum tensile strength and elongation at break of the composite were 62 MPa and 171.3% respectively with the lignin content at 25 wt%. As a result, PVA/lignin composite with 25 wt% lignin content had good mechanical properties and lignin acted as the filler strengthening the mechanical property for the film. 3.4. The UV-shielding performance of the composite film According to the previous article, lignin is capable of absorbing UV radiation [11]. Therefore, lignin was added to PVA in order to improve the ultraviolet-shielding property of the PVA composite films, enabling this composite to be applied for a wide range of applications [12]. The UV-vis absorbency of PVA and the composite was revealed through the UV-vis spectra (Figure 4). The wavelength range was from 300 to 1100 nm. TNU Journal of Science and Technology 226(06): 3 - 9 http://jst.tnu.edu.vn 8 Email: jst@tnu.edu.vn Figure 4. UV spectra of the samples In particular, the UV spectrum less than 380 nm, and the visible light region from 380 to 500 nm were completely absorbed by the composite samples containing 5 wt% lignin. Whereas, the PVA sample without the addition of lignin allowed the majority of ultraviolet light to transmit, revealing that the PVA membrane had no UV-shielding property. As shown in Figure 4, when the lignin content increased, the light transmittance of the PVA/lignin composite decreases significantly. The transmittance of light from 500 to 600 nm decreased to zero at the sample containing 15 wt% lignin, compared to 5 wt% lignin sample which transmitted about less than 20%. At 700 nm visible light, the transmittance of the samples with more than 15 wt% lignin reached from 15% to 20%, which was referred to shielding ability of 80%, an improvement of 63% compared to PVA film (17%). In the infrared region (more than 1000 nm), the composites with 5 wt% and 15wt% lignin had a negligible decrease in transmittance compared to the PVA film. However, the light absorbency of the 45 wt% lignin sample was significantly improved. At 1100 nm, the transmittance of this film (PL5) was only about 35%, compared to 85% transmittance of PVA film (PL0). It could be seen that the addition of lignin into the PVA matrix had significantly improved the light absorbency of the composite film, especially UV radiation. The more the lignin content added, the better the light absorbency reached. The composite with 45 wt% lignin gained the best light absorbency amongst the samples. Besides, all the samples containing lignin with the content from 15 wt% to 45 wt% could absorb a broad spectrum of UV light in the range of 300–400 nm. Therefore, the PVA/lignin composite containing 25 wt% lignin had both prominent properties including high mechanical property and good UV-shielding performance. tải về 0.53 Mb. Chia sẻ với bạn bè của bạn:
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