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Lignin has enormous potential for use as a raw material in the polymer industry. However, lignin has not been utilized as a raw material despite its many advantages because of its brittleness and difficulty of processing. Chemical modification of lignin is an important area of lignin research. In this study, two types of alkyl-chain-based modification agents were used. In the case of the polymeric materials blend, polymers are blended well so that the polymer solubility parameter (SP) values are close to each other. This is similar to the well-mixed combination of water and alcohol. If the SP value is very different, phase separation occurs, as in the relationship between water and oil. The two alkyl chain derivatives block the hydroxyl groups of lignin and replace them with glycoside. Moreover, they can alter the SP value of the modified lignin to make it similar to that of a synthetic polymer to enable blending. Cellulose is compatible with hemicellulose, which is coupled to lignin by ether, glycoside, and ester bonds in plant fibers. To mimic this structure, in this study, lignin was combined with an alkyl chain with a similar SP value and was used as a matrix polymer to form glycoside bonds. This relationship between lignin and the alkyl chain is similar to that between the cellulose and lignin-carbohydrate-complex (LCC). PLA-modified lignin (PLAL) and tetrahydrofuran-modified lignin (THFL) exhibited remarkable changes in the presence of an alcohol functional group. The results of 1H-NMR analysis confirm those obtained by FT-IR analysis. The results of the DSC analyses indicate that lignin and modified lignin exhibit different thermal properties. The results of the thermal and mechanical analyses of the modified lignin/PLA blends demonstrate that the characteristics of the alkyl chains used to modify lignin were well reflected in the final blends. Alkyl-chain-modified lignin that mimics LCC was observed to enhance the compatibility between the matrix polymers used in this study and modified lignin.

Polyurethanes are polymers with urethane linkages in their backbone. It is prepared by polyaddition polymerization between isocyanates and polyols, which produce different chemical, physical, and mechanical properties depending on their types and characteristics. Previous reports of polyurethane foams prepared by using PEG polyol indicated prominent features in the elasticity and recovery of the foams. However, it is necessary to improve the mechanical strength of these materials. In this study, polyurethane foams were prepared using a PLA/PEG polyol mixture and 1,6-hexamethylene diisocyanate. PLA polyol was synthesized by the direct condensation polymerization of lactic acid. The polyurethane foams were characterized using FE-SEM analysis, FT-IR spectroscopy, water absorbency measurement, and mechanical property measurement. In FE-SEM analysis, it was shown that the PLA content of polyol mixture significantly affected the porous structure. FT-IR spectra confirmed that urethane linkages formed between the PLA/PEG polyols and the isocyanates. The water absorbency decreased due to the hydrophobicity of PLA. With respect to the mechanical properties, the breaking stress and the Young’s modulus increased with increasing PLA content. When the PLA content of polyols was 60 and 70 percent, the breaking strain was significantly higher than those of other polyurethane foams.

Softwood kraft lignin (SKL)-based water-blown flexible polyurethane foams were prepared using SKL as a crosslinking agent and a hard segment polyol. Polyethylene glycol (PEG) as a soft segment diol and 2,4-toluene diisocyanate (TDI) were used. While increasing hard segment content caused the increase in crosslink density in foams, the foams became more and more viscous with increasing hard segment content due to the distinctive phase heterogeneity in foams. In this case, the contributiveness of the filler-like behaviors of separated hard segments always overtook the crosslinking effects derived from SKL in terms of overall viscoelasticity, thus the resultant viscometric properties such as tanδ max and hysteresis loss increased as hard segment content increased. Furthermore, increasing M n,PEG caused the severer microphase separation and intensified the filler effects in foams, thus the foams became more viscous with increasing M n,PEG. The 25 % and 65 % CFD values and Young’s moduli of foams increased with increasing hard segment content due to the increase in crosslink density for foams, and the properties also increased with increasing foam density. Most of foams showed the support factors in the range of 2–3, which are suitable values for cushioning use. Even though the microscopic deformation behaviors in foams are irrelevant to foam density, the cyclic compressive tests showed that the higher foam density possess the better shape recovery performances.

Thermoplastic polyurethanes were prepared using 90 % acetylated softwood kraft lignin, polyethylene glycol and 4,4-methylene diphenyl diisocyanate. Due to the glass transitions of the compatible soft and hard segment mixtures, the polyurethanes exhibited the first glass transitions at −40 to 10 °C, and the transition temperatures increased with increasing hard segment content. Due to the glass transitions of the microphase separated hard domains, the second glass transitions occurred at 150 °C. The viscous responses during the second transitions decreased as the separated hard domains-induced chemical and physical crosslinks increased. The Young’s modulus and tensile strength increased with increasing hard segment content, whereas the breaking strain decreased. The phase morphology changed from an isolated hard domain structure to an interconnected one as the physical crosslinks increased, which caused drastic changes in the increasing or decreasing tendency of the tensile strength or breaking strain. Because of the phase morphology, the polyurethanes exhibited viscoplasticity or viscoelasticity.