Solvent-free bulk polymerization of lignin-polycaprolactone (PCL) copolymer and its thermoplastic characteristics

Abstract

The pristine lignin molecules contain multiple reactive hydroxyl [OH] groups, some of which undergo limited polymerization depending on their configuration (aromatic or aliphatic) or conformation. The key issue in lignin-polymerization is to quantify the number of hydroxyl groups in the pristine molecules for subsequent activation to specific lignin-polymer chain lengths or degree of grafting. In this study, using ε-caprolactone (CL) as a reactive solvent, we successfully polymerized CL on the [OH] sites in the kraft lignin macromonomers (LM, Mw = 1,520 g mol−1), which resulted in a thermoplastic lignin-polycaprolactone (PCL) grafted copolymer. We found that the average number of [OH] groups in the LM was 15.3 groups mol−1, and further detected 40–71% of the [OH] groups in the CL bulk polymerization. The degree of polymerization of PCL grown on each [OH] site ranged between 7 and 26 depending on the reaction conditions ([CL]/[OH] and reaction-time) corresponding to 4,780 and 32,600 g mol−1 of PCL chains per a LM. The thermoplastic characteristics of the synthesized lignin-PCL copolymers were established by the melt viscosity exhibiting a shear-thinning behavior, e.g., 921 Pa.s at 180 °C. The thermal stability was remarkable providing a Tid (2% of weight loss) of 230 °C of the copolymers, compared with 69 °C for the pristine lignin.

Biobased superhydrophobic coating enabled by nanoparticle assembly

“…12,13 More importantly, the understanding of molecular structures and interactions within biobased polymers is very limited, as these polymers oen possess complicated architectures and vary from different parent sources. [14][15][16][17][18] The fundamental study and systematic comparison of nanoparticle assembly structures within different biopolymers are needed to provide insight on the interactions and assembly mechanism.…”

Self-assembly in biobased nanocomposites for multifunctionality and improved performance

“…Lignin, a side product of cellulose forms cross-linked phenolic structures, which can be both aromatic or aliphatic. 104 Chitosan, a biopolymer found in marine exoskeletons, is composed of randomly mixed b- (1,4) linked N-acetylglucosamine and glucosamine units. 105 The chain morphology can vary dramatically with temperature and pH, allowing rod, globule, and coil conformations.…”

Structural and Thermal Studies of Fluorescein and Rhodamin6G Grafted Diblock Copolymers

“…Initiators like pullulan [11], heparin [12], chitin [13], Ag-kaolinite [14] and palygorskite were used for the preparation of PCL [15]. Park et al [16] investigated the ROP of CL using lignin as an initiator. Similarly,aminoacids [17], Fe 3 O 4 nanoparticles [18], n-butanol [19], L-proline [20] and cellulose [21] were employed as an initiator for the ROP of CL [22].…”