Cellulose (2020) 27:6149–6162
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Table 1 Fibre species used in this study
Softwoods
Hardwoods
Non-woods
Nordic pine
Birch #1
Cotton (linters)
Jeans
Black spruce
Birch #2
Radiata pine
Eucalyptus
Abaca
Southern pine
Acacia
Sisal
Douglas Fir
Mixed South Asian Hardwood
Kenaf
Enzyme-treated Nordic Pine
Mixed European Hardwood
Giant Reed ( A r u ndo Donax )
Tissue Dust
Dissolving Pulp*
Bagasse (sugar cane) Miscanthus Sorghum Flax
* Dissolving Pulp is a Nordic pine/spruce blend (Domsjo¨ Fabriker AB—Domsjo¨ Cellulose Plus) that was subjected to the sulphite bleaching process, rather than the kraft (sulphate) process which all other softwoods and hardwoods listed underwent Waste short fibres collected from the dust extraction system of a tissue mill Cotton fibres from recycled jeans, following disintegration into individual fibres and formation into a pulp board
S w ee p s tab in the S uppl emen t ar y Ma t eria l . Conse- quently, a single energy input was chosen which was applied to all fibre species listed in Table 1 to produce MFC.
was removed by a vacuum filter, forming a cake. To avoid choking of the grinder due to entanglement of very long fibres, the flax fibres were cut with a guillotine into fragments around 3 mm in length.
Nanopaper sheet preparation
MFC production by stirred media detritor grinding
The MFC-mineral composite product was collected as an aqueous slurry. The solids content was measured by weighing a sample before and after oven drying. The mineral content was determined from the change in weight of an oven-dried sample after burning off the cellulose in a 450 C furnace for 2 h. Using this information, sufficient IC60 calcium carbonate min- eral was added to the sample to dilute the MFC content to 20 wt% on a dry mass basis. These samples were used to form a nanopaper sheet in a vacuum sheet former and dried using a Ra p id-Ko¨ t hen dryer, target- ing a weight of 220 gsm. These sheets were condi- tioned in a controlled environment at 23 C and 50% relative humidity overnight prior to tensile testing.
MFC was produced from these fibres using a lab-scale version of the FiberLean production process. This involves a grinder that uses the motion of media beads to disintegrate the fibres. The presence of micron-scale mineral particles greatly improves the efficiency of this process, so the fibre charge was complemented with an equal amount (on a dry mass basis) of IC60 (60 wt% \ 2 l m) ground calcium carbonate mineral ( Imer y s ). Sufficient water was also added to form a slurry with the target fibre solids content. The precise operating conditions, including the energy input, are proprietary. When a grind was completed, the slurry was separated from the media with a vibrating screen, or by a washing method when particles were too coarse for the screen. Previous experience with this process has shown that almost all fibre sources reach a peak tensile strength at around the same energy, and an unpub- lished investigation with seven of the fibre species in listed in Table 1 has confirmed this. The relationships between energy input and MFC tensile strength for these seven fibre species are displayed in the Energ y
Nanopaper tensile testing
The nanopaper samples were weighed and cut into strips 15 mm wide. These strips were clamped in a T es t ome t ric M 3 50 tensile tester and strained at a constant rate until failure. The force applied at break was divided by the strip width and gsm to obtain the
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