Understanding the thermal and dielectric response of organosolv and modified kraft lignin as a carbon fibre precursor

Culebras, Mario ORCID: 0000-0001-9244-9347, Sanchis, Maria J. ORCID: 0000-0002-3528-3966, Beaucamp, Anne, Carsí, Marta, Kandola, Baljinder K. ORCID: 0000-0002-3621-3724, Horrocks, Richard ORCID: 0000-0003-1431-058X, Panzetti, Gianmarco, Birkinshaw, Colin and Collins, Maurice N. ORCID: 0000-0003-2536-4508 (2018) Understanding the thermal and dielectric response of organosolv and modified kraft lignin as a carbon fibre precursor. Green Chemistry, 20 (19). pp. 4461-4472. ISSN 1463-9270

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Official URL: https://pubs.rsc.org/en/journals/journalissues/gc#...

Abstract

Understanding the thermal behaviour of lignin is crucial in order to realise its valorisation as an engineering polymer. Two hardwood lignins, organosolv (OSL) and chemically modified kraft lignin (ML) have been chosen to represent important classes of renewable and abundant raw material. The relationship between ionic mobility and viscosity in OSL and ML have been studied. The rheological results have been interpreted in terms of the competitive processes of thermal plasticisation and stiffening through crosslinking. Results show that with OSL crosslinking proceeds relatively rapidly, and this is consistent with its more reactive structure. Higher molecular weight (Mw) influenced the melt stability as cross-linking kinetics were reduced and this was attributed to the reduction of chain ends available for cross-linking reactions. Scanning calorimetry has shown that both materials are glassy and pass through the glass transition between 100 °C and 115 °C, with the higher molecular weight modified material having the slightly higher Tg. Both lignins show pronounced maxima in the Gramm-Schmidt plots for methane or methanol around 400°C. However, a significant difference between the materials is observed with the detection of a strong carbonyl peak in the evolution products of the ML, this is attributed to scission of the hydroxypropyl substituent present in the ML structure. The differences in the degradation processes are further reflected in the dielectric properties of the partially degraded materials where loss maxima occur at different temperatures, and show different degrees of frequency dependence. An important observation is the difference in conductivity, where higher values for OSL are attributed to cross-linking between adjacent benzene rings, whereas with the ML lower conductivity is associated with intrinsically less conductive intermolecular linkages. These results demonstrate that the thermal decomposition of the two lignins, follow significantly different paths at the molecular level. With the more reactive OSL it appears to be the case that there is a greater tendency to form direct ring to ring crosslinks and this is very significant for the properties of the intended end product.

Item Type: Article
Uncontrolled Keywords: Pollution, Environmental Chemistry
Subjects: T Technology > TP Chemical technology
Divisions: University of Bolton Research Centres > Institute for Materials Research and Innovation
SWORD Depositor: JISC Publications Router
Depositing User: JISC Publications Router
Date Deposited: 31 Jan 2019 14:21
Last Modified: 18 Feb 2019 18:22
Identification Number: 10.1039/c8gc01577e
Funders: Funder: Horizon 2020 Framework Programme; FundRef: 10.13039/100010661; Grant(s): 720707, Funder: Ministerio de Economía y Competitividad; FundRef: 10.13039/501100003329; Grant(s): MAT2015-63955-R
URI: http://ubir.bolton.ac.uk/id/eprint/1993

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