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

Abstract

Poly(lactic acid) (PLA) composites with 0.5 wt% lignin or nanolignin were prepared with two different techniques: a) conventional melt-mixing and b) in situ Ring Opening Polymerization (ROP) by reactive processing. The ROP process was monitored by measuring the torque. The composites were synthesized rapidly using reactive processing that took under 20 min. When the catalyst amount was doubled, the reaction time was reduced to under 15 min. The dispersion, thermal transitions, mechanical properties, antioxidant activity, and optical properties of the resulting PLA-based composites were evaluated with SEM, DSC, nanoindentation, DPPH assay, and DRS spectroscopy. All reactive processing-prepared composites were characterized by means of SEM, GPC, and NMR to assess their morphology, molecular weight, and free lactide content. The benefits of the size reduction of lignin and the use of in situ ROP by reactive processing were demonstrated, as the reactive processing-produced nanolignin-containing composites had superior crystallization, mechanical, and antioxidant properties. These improvements were attributed to the participation of nanolignin in the ROP of lactide as a macroinitiator, resulting in PLA-grafted nanolignin particles that improved its dispersion.

Structure–property relationships in renewable composites of poly(lactic acid) reinforced by low amounts of micro- and nano-kraft-lignin

“…Two series of relatively new PLA–kraft lignin (kL) composites recently prepared by our groups 49 are studied here. Each series of polymer composites consists of neat linear PLA and two composites of PLA filled with 0.5 wt% micro-kL and nano-kL.…”

“…42 Among others, the addition of lignin in polymers, including PLA, facilitates antioxidation and antibacterial performance. 46–49…”

“…Despite the vast amount of published works on PLA and related systems, not many of them deal with totally biobased PNCs; moreover, quite a few focus on PLA–lignin PNCs. 49–52 Thus, there is still room for such basic research studies. In this basic-research study, we present an investigation of the structure–properties relationship of the addition of kraft Lignin, in particular, in the micro-(as received) and nano-metric form, at the small loading of 0.5 wt% in PLA.…”

Lignins as Promising Renewable Biopolymers and Bioactive Compounds for High-Performance Materials

“…Reactive processing produced nanolignin-containing composites with superior crystallization, mechanical, and antioxidant properties. LNPs act as a macroinitiator in the ROP of lactide, resulting in PLA-grafted nanolignin particles, improved dispersion and the formation of interfacial covalent bonds facilitated by LNPs [201] Lignin-based nano-micelles using the "grafting-from" method pH-sensitive, biocompatible, suitable for oral drug delivery [202] Nanolignin/chitin nanofibrils and complexes loaded with active molecules, such as vitamin E, sodium ascorbyl phosphate, lutein, nicotinamide, and glycyrrhetinic acid Spray-drying method; nanostructured chitin; Functional agents in skin regeneration and antimicrobial, anti-inflammatory, and antioxidant activities; cytocompatibility in skin regeneration.…”

Structure and Properties of Polylactide Composites with TiO2–Lignin Hybrid Fillers

“…Various studies have explored the potential of PLA and lignin composites. Makri et al [8] demonstrated that reactive in situ processing can significantly enhance the properties of these composites, particularly when using nanolignin. Arjhan et al [9] found that the addition of lignin can reduce the tensile strength of PLA/lignin films, but also increase their elongation.…”