Effect of ball milling on lignin polyesterification with ε-caprolactone

Abstract

Industrially produced lignins are by-products of the pulp and paper industry and depending on the source and pulping technology they have deviating functional groups, solubility behavior and reactivity. In the present paper, kraft lignin was pretreated by mechanical milling and polyesterified with ε-caprolactone to create hydroxyl groups that are more easily available for further reactions. The products obtained were analysed by size exclusion chromatography (SEC), differential scanning calorimetry (DSC) and functional group determination. The analytical data are presented as a function of reaction time, crosslinking reactions and the amount of ε-caprolactone input.

Bio-based polyurethane prepared from Kraft lignin and modified castor oil

“…The type of pulping process determines the type of lignin industrially available because it unavoidably modifies the lignin structure from that in the original feedstock. To increase the potential applications of lignin in polymeric materials, some chemical modifications have been developed [11,12], but these add stages to the process and/or raise their costs considerably. Therefore, the direct use of industrial lignin is the most favorable option because it is a relatively cheap raw material.…”

Enhanced Catalytic Depolymerization of a Kraft Lignin by a Mechanochemical Approach

“…For example, ball milling of kraft lignin before the reaction was found to increase the rate of polyesterification with ε-caprolactone. This was attributed to a higher surface area of the lignin as a result of a reduction of the lignin particle size by the pretreatment procedure . Here, we explore the use of ball milling, a grinding process widely employed in the industry, to increase the extent of depolymerization and, thus, the amounts of low-molecular-weight chemicals for the solvent-free catalytic hydrotreatment of kraft lignin.…”

“…The slight decrease of C, H, and S contents upon milling could be due to some oxidation that was previously observed during milling. , The weight-average molecular weight of milled lignin is only slightly lowered (about 5%), and the molecular weight distributions are about similar (Figure S7 of the Supporting Information). The 2D-HSQC NMR of the samples showed a condensed guaiacyl aromatic structure with some stilbenes and the expected low amounts of β–O–4, β–5, and β–β linkages (Figure S8 of the Supporting Information). , Some very minor resonances from, for example, enol ethers disappeared after ball milling, possibly as a result of some repolymerization or degradation induced by intensive ball milling. , Overall, differences in integration data of the signals in the linkage region are minimal (Table ), indicating that the ball milling under the prevailing conditions did not significantly alter the lignin chemical structure.…”

“…This phenomenon was also reported in the literature when kraft lignin was milled with glass balls. 15 Ball milling also resulted in major changes in the specific surface area and pore volume of the samples (Table S4 of the Supporting Information). The unmilled kraft lignin has a very low surface area (1.0 m 2 /g) and limited pore volume (0.004 cm 3 /g), while these numbers are significantly higher for milled samples (surface areas of 3.4−3.5 m 2 /g and pore volumes in the range of 0.015−0.026 cm 3 /g).…”

“…The PSD for each sample was determined, showing a drastic reduction in the average particle size upon ball milling (63 μm for unmilled to 7.2 μm for 10 min milling and 4.9 μm for 60 min milling; see panels g, h, and i of Figure ). This phenomenon was also reported in the literature when kraft lignin was milled with glass balls …”