Poster

P2.2 – Phase morphology of plasticized lignin investigated using CP-relaxation ssNMR

Åke Henrik-Klemens

Chalmers

Co-author(s):
Åke Henrik-Klemens, Chalmers university of technology
Anette Larsson, Chalmers university of technology

One major obstacle to lignin material processing and application is its heterogeneity. Lignins are molecularly heterogeneous, both along the chain and between chains. This heterogeneity stems from both the biosynthesis of lignin (relatively uncontrolled radical coupling) and by cleaving and coupling reactions taking place during processing. Based on this molecular diversity, it appears likely that lignins would form morphologically heterogeneous materials. That is, materials with nanodomains of varying composition, as found for some synthetic copolymers and polymer blends. One potential indication of this heterogeneity is that DMA studies of lignin often find very broad glass transition (~100 °C), possibly stemming from varying local glass transition temperatures. In our previous work, we have found that plasticization of both native isolated lignin and a kraft lignin reduced the width of the glass transition, which suggests that a morphologically more homogeneous material was formed. In this study, the dispersal of plasticizer and its effect on lignin morphology was studied using CP-relaxation solid-state NMR. In spin diffusion relaxation, components with similar relaxation times are likely to have similar dynamics and physical proximity. Thus, by studying the relaxation within the rotating frame (1HT1ρ), which has relatively fast relaxation times, information can be gained on the phase composition of both lignin and plasticizers in the low nanometer range. The relaxation of lignin prior to plasticization exhibited biexponential decay, indicating a heterogeneous chemical environment (i.e. there are nanometer-sized domains with different relaxation behavior). Upon plasticization, the biexponentially remained, but the difference in relaxation time between the two domains decreased, suggesting the formation of a system with less spatial difference in molecular dynamics. Thus, it would appear that, in addition to being a resource-efficient method for reducing the glass transition temperature, plasticization also serves as a means to homogenize some properties of lignin.

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