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. 2021 Jun 2;11(1):11647.
doi: 10.1038/s41598-021-91115-4.

Chemical and physical interactions of regenerated cellulose yarns and isocyanate-based matrix systems

Bernhard Ungerer  1 , Ulrich Müller  2 , Antje Potthast  3 , Enrique Herrero Acero  4 , Stefan Veigel  2
Affiliations

Chemical and physical interactions of regenerated cellulose yarns and isocyanate-based matrix systems

Bernhard Ungerer et al. Sci Rep. .

Abstract

In the development of structural composites based on regenerated cellulose filaments, the physical and chemical interactions at the fibre-matrix interphase need to be fully understood. In the present study, continuous yarns and filaments of viscose (rayon) were treated with either polymeric diphenylmethane diisocyanate (pMDI) or a pMDI-based hardener for polyurethane resins. The effect of isocyanate treatment on mechanical yarn properties was evaluated in tensile tests. A significant decrease in tensile modulus, tensile force and elongation at break was found for treated samples. As revealed by size exclusion chromatography, isocyanate treatment resulted in a significantly reduced molecular weight of cellulose, presumably owing to hydrolytic cleavage caused by hydrochloric acid occurring as an impurity in pMDI. Yarn twist, fibre moisture content and, most significantly, the chemical composition of the isocyanate matrix were identified as critical process parameters strongly affecting the extent of reduction in mechanical performance. To cope with the problem of degradative reactions an additional step using calcium carbonate to trap hydrogen ions is proposed.

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Conflict of interest statement

The authors declare no competing interests.

Figures

Figure 1
Figure 1
(a) 2440dtex twisted yarn iso (left) and ref (right) taken from fabric, (b) 2440dtex untwisted iso without avivage, iso with avivage, ref without avivage, ref with avivage (left to right), (c) schematic (!) of twisted, treated yarn (d) schematic (!) of untwisted treated yarn. Image c and d were drawn in SOLIDWORKS® 2019 SP3.0. Software available at https://www.solidworks.com/.
Figure 2
Figure 2
Tensile tests on 2440 dtex yarns; representative load-strain curves and maximum tensile load for untwisted (a, c) and twisted (b, d) samples, respectively. Immersion time is given in parenthesis (d).
Figure 3
Figure 3
Characteristic fracture pattern of 2440dtex twisted yarn; untreated (a), isocyanate hardener (b) and pMDI (c) treated.
Figure 4
Figure 4
Ratio of tensile force at break of treated yarns and their untreated references over the average amount of isocyanate substance for each batch.
Figure 5
Figure 5
Maximum tensile load and elongation at break of twisted (white) and untwisted (grey) viscose yarns treated with isocyanate hardener (iso) and pMDI, respectively.
Figure 6
Figure 6
Tensile modulus of twisted and untwisted 2440 dtex samples of untreated (ref) and isocyanate-treated (iso, pMDI) yarns; isocyanate batch with 15 days treatment was additionally indicated (iso 4).
Figure 7
Figure 7
Tensile properties of single viscose filaments without further treatment (fil-ref) and treated with isocyanate hardener for 10 s (fil-iso 1) and 3 days (fil-iso 2), respectively.
Figure 8
Figure 8
Digital microscope scan of an untreated viscose filament (a) and a filament subjected to 3 days immersion in isocyanate hardener (b), observation method: PO (polarization), objective lens: DSX10-XLOB20X, zoom: ×2.5, total magnification: ×700.
Figure 9
Figure 9
Tensile properties of twisted (tw) and untwisted (un-tw) yarns with and without (n.a.) avivage, respectively, conditioned at 20 °C, 65% RH or kiln dried at 103 °C prior to impregnation with isocyanate hardener.
Figure 10
Figure 10
IR spectra of untreated (black line) and pMDI-hardener treated and NMP purified (grey line) yarns.
Figure 11
Figure 11
molar mass distribution of 2440 dtex yarns without treatment (black and red line) and with pMDI-hardener treatment followed by purification with NMP (green and blue line).
See this image and copyright information in PMC

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