| Abstract | The potential utilization of lignin, as a natural-based material, in unsaturated polyester (UPE) has been investigated. Kraft (Indulin AT) and sulfite lignin (ArboSO1) samples from forestry biomass and their consistencies in UPE were evaluated by qualitative and quantitative methods. The tensile and impact properties of the cured UPE with and without lignins, as well as fracture surfaces, were also studied. The result indicated that the ash content is quite high for lignosulfonate ArboSO1. NMR spectra show significant differences almost in the entire spectral region for the two lignins. The aliphatic hydroxyl groups were found more uniform in Indulin AT than in ArboSO1. Indulin AT seems to have more pronounced condensed units than ArboSO1. The guaiacyl units in Indulin AT were found to be more uniform and of higher magnitude than in ArboSO1, similarly to free phenolic units. However, the terminal carboxylic content in ArboSO1 was found to be higher than in Indulin AT. The investigation by SEM showed that the particles of the two lignins are porous and have different sizes, mostly less than 100 µm. The addition of different concentrations of lignins increased the viscosity of UPE; however, the viscosity was still suitable for processing at the lignin loading levels. The results also indicated that the lignin types and loadings did influence the tensile properties, but not the impact property of the UPE. The modulus of UPE decreased almost linearly with the loading of ArboSO1 for both UPEs. On the other hand, the modulus of UPE leveled up for Indulin AT only at 10 and 20 wt% loading. The positive effect of adding 10 wt% of both lignin samples on the tensile strength of UPE was demonstrated. The presence of lignin affected the fracture surface of the UPE systems, regardless of the lignin type and consistency. This novel approach could reduce costs and environmental impact of manufacturing UPE products, while improving their quality. |
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