Abstract
Cellulose can be dissolved with another biopolymer in a protic ionic liquid and spun into a bicomponent hybrid cellulose fiber using the Ioncell® technology. Inside the hybrid fibers, the biopolymers are mixed at the nanoscale, and the second biopolymer provides the produced hybrid fiber new functional properties that can be fine-tuned by controlling its share in the fiber. In the present work, we present a fast and quantitative thermoanalytical method for the compositional analysis of man-made hybrid cellulose fibers by using thermogravimetric analysis (TGA) in combination with chemometrics. First, we incorporated 0–46 wt.% of lignin or chitosan in the hybrid fibers. Then, we analyzed their thermal decomposition behavior in a TGA device following a simple, one-hour thermal treatment protocol. With an analogy to spectroscopy, we show that the derivative thermogram can be used as a predictor in a multivariate regression model for determining the share of lignin or chitosan in the cellulose hybrid fibers. The method generated cross validation errors in the range 1.5–2.1 wt.% for lignin and chitosan. In addition, we discuss how the multivariate regression outperforms more common modeling methods such as those based on thermogram deconvolution or on linear superposition of reference thermograms. Moreover, we highlight the versatility of this thermoanalytical method—which could be applied to a wide range of composite materials, provided that their components can be thermally resolved—and illustrate it with an additional example on the measurement of polyester content in cellulose and polyester fiber blends. The method could predict the polyester content in the cellulose-polyester fiber blends with a cross validation error of 1.94 wt.% in the range of 0–100 wt.%. Finally, we give a list of recommendations on good experimental and modeling practices for the readers who want to extend the application of this thermoanalytical method to other composite materials.
Highlights
Ionic liquids (IL) can dissolve a wide range of biopolymers, including cellulose (Hermanutz et al 2019), hemicelluloses, lignin (Pu et al 2007), chitin and chitosan (Shamshina 2019), or natural composite matrices like wood (Ma et al 2018a, b)
The Enocell cellulose pulp, which was the main component of the hybrid fibers was composed of 91.7% cellulose, 7.7% hemicelluloses, and 0.6% lignin
The thermogravimetric analysis (TGA) and the derivative signals (DTG) curves of the cellulose-lignin samples are shown in Fig. 2
Summary
Ionic liquids (IL) can dissolve a wide range of biopolymers, including cellulose (Hermanutz et al 2019), hemicelluloses, lignin (Pu et al 2007), chitin and chitosan (Shamshina 2019), or natural composite matrices like wood (Ma et al 2018a, b). Using the IoncellÒ technology (Sixta et al 2015), we are able to dissolve mixtures of biopolymers in a protic ionic liquid and spin the solution into hybrid fibers. 2020; Le et al 2020; Trogen et al 2021), cellulose-chitosan (Zahra et al 2020), cellulose-chitin (Ota et al 2020) or cellulose-betulin (Makarov et al 2018) have found applications in textiles (Ma et al 2015) or as precursors for biobased carbon fibers (Byrne et al 2016). The macromolecular composition of the spun fibers can change in comparison to the initial biopolymers share used during the dissolution stage. Loss of biopolymers can occur during the dope filtration stage because of incomplete dissolution, or during the spinning operation due to diffusion and leaching of the biopolymers in the spin bath (Ma et al 2015) (Mikkilaet al. 2020)
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