## 4 L-MMCF Manufacturing Process
### Chelation and Bleaching  
\(N\)-methylmorpholine-n-oxide (NMMO) is the solvent commercially utilised in the dissolution of PHK pulp for the production of L-MMCF. It is the main organic cyclic polar solvent (i.e., cyclic amine oxide), and is capable of high cellulose dissolution without extensively damaging the alpha-cellulose content on a commercial scale [20; 21]. It is also deemed more environmentally-friendly than the viscose process [7]. While there is extensive research in the use of alternative solvents, such as LiCl/DMAC, ionic solvents, and deep eutectic solvents, these alternatives are not yet commercially available [1; 97; 98; 99]. With the use of NMMO, there is the unfortunate risk of a runaway or exothermic reaction during the dissolution process if metal ions are present [15; 100; 101]. Catalytic decomposition is seen with all transition metals with multiple oxidation states, but is most frequent with manganese (Mn), iron (Fe), and copper (Cu) [15; 101; 102]. Due to their potential presence in raw feedstock, the monitoring of all metals present in the pulp is required throughout each processing step. [PERSON] and [PERSON] stated that \"the presence of reagents capable of inducing the autocatalytic degradation of NMMO, even if present only in substoichiometric, catalytic amounts, must be strictly avoided under these conditions. This refers to alkylating agents, such as alkyl halides, alkyl sulfates or diazoalkanes, acylating agents, such as acyl halides or anhydrides, and redox-active transition metal salts\" (p. 5987) [100]. Furthermore, they recommend using cautionary statements when referencing the use of NMMO in experimental settings. [PERSON] et al. [15] provide an extensive understanding of the potential for exothermic runaway reactions when both Fe and Cu are present in the L-MMCF dope. As the temperature increases, the concentration of Fe and Cu required for exothermic reaction onset decreases from 60 ppm (138 \({}^{\circ}\)C) to 10 ppm (149 \({}^{\circ}\)C) and from 300 ppm (130 \({}^{\circ}\)C) to 30 ppm (157 \({}^{\circ}\)C), respectively. This indicates the importance of maintaining a temperature consistently below 120 \({}^{\circ}\)C during the dissolution, dope preparation, and spinning processes. Additionally, [PERSON] et al. [15] describe how metal ions can affect the stability of NMMO when heated to 150 \({}^{\circ}\)C, further providing reasons to keep metal ion concentration low and processing temperatures below 120 \({}^{\circ}\)C.  
Inorganic materials, including metals, can be present in cellulosic pulps for numerous reasons [39; 103]. Plants and trees draw various inorganics from the soil as they grow, and these inorganics get stored within the cell structure [104; 105]. Industrial hemp is a very fast-growing plant, and due to this fast growth, it is capable of soil remediation [51]. This plant readily takes up inorganic materials, which depending on the end use, need to be removed during various processing stages. Soil parameters and proximity to certain industrial processes (i.e., mining) can also increase the quantity of inorganic compounds within the plant structure [78]. Additional inorganic compounds can also contaminate the pulp during processing steps. An example would be exposure to rusty equipment, which would increase the Fe content of the cellulosic pulp [79]. Additionally, the presence of metal ions during bleaching can lead to a change in the oxidation state (i.e., reactive oxygen species formation due to metal catalysed oxidation) [79];this can lead to the cellulose hydroxy groups forming into carbonyl structures, resulting in chain cleavage. Metal ions may react with the bleach or peroxides to form free oxy radicals, degrading the cellulose and lowering the DP of the pulp [79]. Heavy metal contaminants are removed during the chelation stage of the manufacturing process [79; 106]. It involves adding a chelating agent to the pulp [79; 106; 107; 108].