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glucomannan (Ebringerova´ 2005). Total hemicellu- lose content was determined by adding together the xylan and glucomannan fractions. The hemicellulose content of cotton linters (which is negligible) was also used as the hemicellulose content of the jeans cotton, since it was expected that the presence of dye and other additives in the jeans cotton would give misleading results. This is a reasonable assumption as textile-grade cotton contains negligible hemicellu- lose (Prado and Spinace´ 2015).
tensile index in Nm/g. The tensile index of this MFC- mineral composite nanopaper is much weaker than pure MFC due to the mineral disrupting inter-fibril bonding. However, work with MFC made from this process by Phipps et al. (2017) has shown that the tensile indices of FiberLean MFC with or without a given fraction of mineral added are roughly propor- tional (i.e. breakage is mainly bonding-limited in both cases), so the conclusions are still believed to be applicable to pure MFC. Three nanopaper sheets were produced for each sample, each cut into five strips. The mean tensile index of these fifteen strips is reported as the sample tensile index here. Fibre content was verified to be on target by measuring the ash content after burning off the cellulose in a 450 C furnace for 2 h (these results are displayed in the T ensi l e Shee t Minera l Con t en t tab in the S uppl emen t ar y Ma t eria l ).
Lignin content
Acid-soluble and acid-insoluble lignin content of the pulps were measured by Lab t i u m O y according to a modified TAPPI standard T 222 om-88 test.
Fibre zero-span tensile testing
Fibre image analysis
Zero-span tensile tests were carried out on the initial fibre samples rather than the MFC. The TAPPI standard T 2 3 1 cm-07 (Technical Association of the Pulp and Paper Industry 2007) was followed, using 60 gsm mineral-free handsheets for each fibre species produced according to TAPPI standard T 205 s p -12 (Technical Association of the Pulp and Paper Industry 2012). Each handsheet was cut into five strips, which were clamped in a P ul mac zero-span tensile tester and strained until broken. As with conventional tensile testing, the force measured was converted to a zero-span tensile index. Four dry sheets were tested for each fibre species, and a mean average result is reported here.
A Va l me t FS5 fibre image analyser was used to measure geometric parameters of the original fibres before grinding, and the MFC particles after grinding. This equipment operates by pumping a sample suspension past a camera that takes thousands of images, and parameters such as length and width distributions are determined by a computer algorithm. Though designed for fibre measurement, this is sensitive enough to measure MFC particles with lengths around a hundred microns and above.
Hemicellulose content
Scanning electron microscopy
Hemicellulose measurements were subcontracted to Lab t i u mO y , who used the SC A N-CM 71:09 method (Scandinavian Pulp, Paper and Board Testing Com- mittee 2009). Fibre samples underwent sulphuric acid hydrolysis, and the resultant concentration of various monomer sugar residues were detected by chromatog- raphy. This included glucose, xylose, mannose, ara- binose, and galactose. To convert these sugar contents into xylan and glucomannan hemicellulose contents, it was assumed that the xylan content was the sum of all the xylose and arabinose, and the glucomannan content consisted of all the galactose, mannose, and 1 unit of glucose for every 4 units of mannose, since a ratio of 1:4 glucose to mannose is typical in softwood
A Jeo l 6700 Scanning Electron Microscope was used to image several MFC samples at 10,000 x magnifi- cation. Preparation involved filtering a dilute MFC sample through a 0.2 l m nucleopore membrane. The samples were sputter coated with platinum to form a conductive monolayer. Secondary electrons emitted from the sample during measurement were used to form the images.
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