Abstract
In this work we have analyzed the pine and spruce softwood lignin fraction recovered from a novel pressurized hot water extraction pilot process. The lignin structure was characterized using multiple NMR techniques and the thermal properties were analyzed using thermal gravimetric analysis. Acetylated and selectively methylated derivatives were prepared, and their structure and properties were analyzed and compared to the unmodified lignin. The lignin had relatively high molar weight and low PDI values and even less polydisperse fractions could be obtained by fractionation based on solubility in i-PrOH. Condensation, especially at the 5-position, was detected in this sulphur-free technical lignin, which had been enriched with carbon compared to the milled wood lignin (MWL) sample of the same wood chips. An increase in phenolic and carboxylic groups was also detected, which makes the lignin accessible to chemical modification. The lignin was determined to be thermally stable up to (273–302 °C) based on its Tdst 95% value. Due to the thermal stability, low polydispersity, and possibility to tailor its chemical properties by modification of its hydroxyl groups, possible application areas for the lignin could be in polymeric blends, composites or in resins.
Highlights
As there is an uncertainty surrounding fossil-based raw materials, new alternative sources need to be explored for fuel and platform chemicals
In this article we have studied the softwood lignin fraction obtained from a novel pressurized hot as poly lactic acid (PLA) at elevated temperatures [26]
In this article we have studied the softwood lignin fraction obtained from a novel pressurized are isolated by extraction from wood chips with hot water at oxygen-starved hot water extraction (PHWE) biorefinery process [27,28]
Summary
As there is an uncertainty surrounding fossil-based raw materials, new alternative sources need to be explored for fuel and platform chemicals. Lignin is the most abundant aromatic biopolymer and could potentially be such an alternative source. The structure of lignin, in its native form, consists of phenylpropanoic units bonded together mainly by alkyl-aryl ether bonds that are formed by radical coupling reactions of the corresponding monolignols [1]. The native lignin in biomass differs greatly in properties, both physical and chemical, compared to lignin isolated through biomass processing. These types of isolated lignins, Molecules 2019, 24, 335; doi:10.3390/molecules24020335 www.mdpi.com/journal/molecules
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