## 4 L-MMCF Manufacturing Process
### Pulping Process  
There are numerous methods available for processing cellulose pulps; however, the two primary pulping methods for the manufacturing of L-MMCF are prehydrolysis Kraft(PHK) pulp and acid sulphite (AS) pulp. Both processes produce dissolving pulps, with PHK more commercially available than AS pulping due to issues with environmental sustainability (i.e., chemical recovery) in AS pulping [82]. AS pulps have a higher yield (45-55%) than PHK pulps (40-50%) [38]; however, the fibre strength of PHK pulps is higher [19]. This directly relates to DP, where AS pulps have a lower DP than PHK, which is an important parameter for L-MMCF manufacturing. Additionally, PHK pulps typically have a higher alpha cellulose content when compared to AS pulps [62]. The prehydrolysis stage in PHK pulps is imperative for the removal of hemicellulose and partial removal of lignin prior to the pulping process [18; 62; 71]. This section and the rest of the paper focuses on PHK pulp preparation since it is readily available, utilises chemical recovery, has a higher fibre strength lending towards a higher DP, and has a higher alpha cellulose content when compared to AS pulp. Table 3 outlines the characteristics of PHK pulps ideal for L-MMCF. Intrinsic viscosity measurements provides the cellulose DP, which translates to dope viscosity and, ultimately, strength of the resulting L-MMCF (i.e., an indication of the effect of cellulose content on the overall viscosity of the solution) [83]. Alkali solubility expressed as S10 and S18 represents the amount of cellulose that dissolves in 10% NaOH (hemicellulose and degraded alpha-cellulose) and 18% NaOH (hemicellulose), respectively [62; 84]. These numbers indicate the suitability of the cellulose feedstock towards dissolution in the L-MMCF process. They can also provide guidance towards pulping parameters, as higher S10 and S18 numbers indicate a higher amount of degraded cellulose. Viscosity and DP are also provided in Table 3. Having a low DP will result in weak L-MMCF, whereas dissolving pulp with a high DP will not be spinnable in the L-MMCF process. The ideal viscosity and DP for L-MMCF manufacturing are 4-6 dL/g and 550-650, respectively [17; 18; 65; 75]. These can be affected greatly by pulping parameters. Post pulping, hemp best fibre has a DP of 500-650 and an intrinsic viscosity of 3.7-4.5 dL/g; hemp hurd has a DP of 624-632, indicating the suitability of industrial hemp for L-MMCF manufacturing [26; 75]. Initially, both viscosity and DP need to be determined independently; however, once the relationship between these two parameters is established, DP can be estimated via the following equation using cuen viscometry [85]: DP = 190 [\(\eta\)], where \(\eta\) is the intrinsic viscosity (dL/g). This equation can be utilised until the relationship between intrinsic viscosity and DP has been established. This characterisation will lead to a new constant to replace the constant 190, or possibly a new mathematical relationship altogether. Additionally, DP can be calculated based on Molar Mass (M): M = 2.15 \(\times\) 10\({}^{4}\) [\(\eta\)] and \begin{table}
\begin{tabular}{c c c} \hline \hline
**Properties** & **Specification** & **References** \\ \hline Feedstock Fibre/Chip Length (mm) & 10–30 & [38] \\ \(\Omega\)Custom & 550–650 & [7; 65; 75] \\ \(\alpha\)-cellulose (\%) & \(>\)90–95 & [16; 17; 18; 37; 75] \\ Hemicellulose (\%) & 1–6 & [17; 18; 37] \\ Pulp Yield (\%) & 40–55 & [38] \\ Intrinsic Viscosity (dL/g) & 4–6 & [17; 18] \\ Ash (\%) & \textless{}0.1 & [16; 24] \\ Lignin (\%) & Trace (\textless{}0.05) & [17; 18; 37] \\ Kappa & \textless{}1–5 & [17; 25; 75] \\ S10 (\%) & \textless{}10 & [17; 62; 84] \\ S18 (\%) & \textless{}5 & [17; 62; 84] \\  & Fe, Cu: \textless{}10 & \\  & Mn, Cr, Ni: \textless{}20 & \\ Metal (mg/kg) [75] & Na: \textless{}500 & [24; 25; 75] \\  & K, Ca, Mg: \textless{}100 & \\ \hline \hline \end{tabular}
\end{table} 
Table 3: PHK pulp properties for L-MMCF.