Deep Eutectic Solvent-Extracted Lignin as an Efficient Additive for Entirely Biobased Polylactic Acid Composites

Abstract

This work reports the fabrication and characterization of entirely biobased composites made with polylactic acid (PLA) and deep eutectic solvent (DES)-extracted lignin. White fir sawdust and corn stover were used as feedstocks to extract sawdust lignin (SDL) and corn stover lignin (CSL). Commercial alkali lignin (CAL) was also used as a baseline. PLA/lignin composites were fabricated using a twin-screw extrusion process followed by compression molding. Characterizations of the composites were conducted using scanning electron microscopy (SEM), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and tensile testing. Overall, the results revealed that PLA/DES lignin biocomposites significantly outperform their PLA/CAL counterparts. SEM results indicated the absence of microcracks in PLA/DES lignin morphologies and better lignin dispersion and smaller lignin agglomerates compared with PLA/CAL composites. The initial thermal degradation temperature of PLA slightly dropped by 8−27 °C with the addition of 5−15 wt % DES lignin, compared with a significant reduction of 89−124 °C when incorporating CAL. DSC analysis showed a maximum drop of about 5 and 15 °C in the melt temperature of PLA when DES lignin and CAL lignin, respectively, were added. Moreover, SDL increased the PLA's crystallinity several folds. The tensile strength and elongation at break of PLA/DES lignin composites were significantly greater than those of PLA/CAL composites, up to a maximum of 1 order of magnitude. The better performance of PLA/DES lignin biocomposites was associated with the high purity, ultrafine particle size, low heterogeneity, and low molecular weight of DES lignin. The results suggest DES lignin as a potential feedstock for entirely biobased high-performance materials.

Synthesis and Characterization of Poly(lactic acid) Composites with Organosolv Lignin

“…The composites also crystallize less, as the X c is smaller and decreases with an increased lignin content. The increase in T cc and the suppression of crystallinity are attributed to a reduced PLA chain mobility, caused by the interactions of the PLA with the lignin and its ability to absorb heat during heating, which prevents it from being absorbed by the PLA [ 21 , 26 , 27 , 28 , 29 ]. The small decrease in the T g was observed before [ 7 , 26 , 30 , 31 , 32 , 33 ] and it was attributed to the beneficial interactions between the lignin and the PLA, possibly by a plasticizing effect of a low molecular weight fraction of the lignin.…”

“…Furthermore, the reduction in the size of the particles after ball milling, with surfactants, seemed to positively affect the mechanical properties of the final materials [ 21 , 37 ]. On the other hand, the use of deep eutectic solvents exhibited a drop in the tensile features of the PLA [ 26 ]. Thus, the presented data is in accordance with the literature, showing the advantages of using low percentages of unmodified lignin and avoiding additional energy and time-consuming procedures.…”

Poly(Lactic Acid) Composites with Lignin and Nanolignin Synthesized by In Situ Reactive Processing

“…Even though many publications on PLA-lignin composites are available, most of them do not mention the particle size of lignin and disregard its effect on the obtained results. A few studies have demonstrated that size reduction of lignin from the microscale to sub-micron particles helps achieve better reactivity and compatibility with PLA due to the high specific surface area and better dispersion ability, which allows it to bond more effectively with the PLA matrix [ 5 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 ]. In all cases, the composites were prepared by either melt mixing or solution casting.…”

Eco-Friendly Polyurethane Reactive Hot-Melt Adhesive Derived from Poly(ε-caprolactone-co-lactic acid) Diols

“…Poly(lactic acid) (PLA) can be derived from green resources such as wheat, sugarcane, and corn through biofermentation. 19,20 It is currently one of the most desirable bio-based polymers due to its favorable mechanical performance, biocompatibility, biodegradability, and low production cost. 21,22 The market value of PLA is projected to reach approximately 1.82 billion U.S. dollars in 2028, approximately 3.5 times its market value in 2020.…”

“…Poly­(lactic acid) (PLA) can be derived from green resources such as wheat, sugarcane, and corn through biofermentation. , It is currently one of the most desirable bio-based polymers due to its favorable mechanical performance, biocompatibility, biodegradability, and low production cost. , The market value of PLA is projected to reach approximately 1.82 billion U.S. dollars in 2028, approximately 3.5 times its market value in 2020 . However, the limited toughness, slow crystallization rate, and poor heat resistance of PLA significantly restrict its application. − Similarly, PCL is broadly applied in packaging and biomedical fields due to its flexibility, processing properties, biocompatibility, and biodegradability. , …”