No abstract

The dinuclear indium catalyst [(NNO)InCl] 2 (μ-OEt)(μ-Cl), previously reported to be highly active for the living ring-opening polymerization of cyclic esters lactide (LA) and β-butyrolactone (BBL), was used to generate a series of triblock copolymers of poly(lactic acid) (PLA) and poly(hydroxybutyrate) (PHB). Copolymers PLLA−PDLLA−PLLA and PLLA−PDLLA−PDLA, synthesized via sequential monomer addition, showed low molecular weight distributions and excellent correlation between the calculated and experiment molecular weights. Significantly, triblock copolymers of the type PLA−PHB−PLA were also synthesized for the first time through a sequential addition technique. Analysis of polymers after each addition of monomer showed that although only 85% conversion was achieved after addition of BBL, the remaining chain ends were active and addition of more lactide yielded a triblock. Rheological studies of PLLA−PHB−PDLA indicated solid like behavior even well above the temperature at which stereocomplex formation was observed. These elastomeric triblocks exhibited elongations at break 5−10 times greater than those of corresponding PLLA−PDLLA−PLDA triblocks.

The conversion of lignocellulosic biomass into bioethanol or biochemical products requires a crucial pretreatment process to breakdown the recalcitrant lignin structure. This research focuses on the isolation and characterization of a lignin-degrading bacterial strain from a decaying oil palm empty fruit bunch (OPEFB). The isolated strain, identified as Streptomyces sp. S6, grew in a minimal medium with Kraft lignin (KL) as the sole carbon source. Several known ligninolytic enzyme assays were performed, and lignin peroxidase (LiP), laccase (Lac), dye-decolorizing peroxidase (DyP) and aryl-alcohol oxidase (AAO) activities were detected. A 55.3% reduction in the molecular weight (Mw) of KL was observed after 7 days of incubation with Streptomyces sp. S6 based on gel-permeation chromatography (GPC). Gas chromatography-mass spectrometry (GC-MS) also successfully highlighted the production of lignin-derived aromatic compounds, such as 3-methyl-butanoic acid, guaiacol derivatives, and 4,6-dimethyl-dodecane, after treatment of KL with strain S6. Finally, draft genome analysis of Streptomyces sp. S6 also revealed the presence of strong lignin degradation machinery and identified various candidate genes responsible for lignin depolymerization, as well as for the mineralization of the lower molecular weight compounds, confirming the lignin degradation capability of the bacterial strain.