## 5 Challenges and Opportunities with Alternative Feedstocks for L-MMCF
Alternative sources of cellulose also promote whole plant utilisation, which supports a circular economy as well as the overall bioeconomy. Industrial hemp is a fast-growing plant, averaging 7 cm to 10 cm per day in the vegetative growth phase (July to August in Canada) [140]. It can produce 250 times the biomass of cotton and 600 times the biomass of flax on the same land mass [141]. It also requires less water, fertilisers, herbicides, and pesticides than other agricultural crops, and the large tap root decreases soil erosion. This leads to improvements in soil health (i.e., removal of contaminants, topsoil enhancement, improve soil oxygenation) [142]. In Canada, there are 87 approved cultivars of industrial hemp that are grown primarily for seed or nutraceutical end uses, with the intention of dual-purpose utilisation of the stalk [143; 144]. Unfortunately, nutraceuticalal blast fibre is too young and seed bast fibre is too old and coarse for traditional bast textile manufacturing [7]. However, as demonstrated in Table 2, there is the opportunity to utilise both hemp bast and hurd towards L-MMCF production. As discussed throughout this paper, there are challenges with the utilisation of industrial hemp as a L-MMCF feedstock, with one of the concerns being metal content. Due to the fast growth, hemp plants accumulate heavy metals present in the soil [78; 140]. These metals can react with peroxide in a TCF bleaching sequence to decrease the DP of the cellulose pulp; additionally, they can react with NMMO during the L-MMCF process, resulting in catalytic, exothermic reactions [15; 79; 100]. This is addressed through the chelation process, which has been shown to effectively remove metallic ions from pulp and the use of either ECF or TCF in the bleaching sequence [79; 106]. There are also challenges relating to the harvesting and processing of hemp. Hemp stalks are unique as they can be exposed to various conditions prior to processing (i.e., method of retting), which can change the composition of cellulose, lignin, and extractives, [132; 145]. This can affect the prehydrolysis and Kraft pulping parameters. A characterisation of the feedstock prior to prehydrolysis is needed to provide a baseline for determining optimal processing conditions. Ultimately, it generates knowledge into what growing conditions (e.g., rainfall, temperature, soil type, days of growth) affect the most these feedstock characteristics. Hemp stalks also require proper separation (i.e., separation of bast from hurd), which is typically performed via decortication or scutching and hackling to produce fibre tow [146; 147; 55; 148]. New mechanical separation techniques are being developed which may offer more precise separation. Additionally, these techniques can lead to more consistent feedstock to the L-MMCF process, requiring less processing. As an example, finely milled and screened fibre, which can be produced via the sequence illustrated in Figure 9, may significantly reduce the time and temperature to produce a high alpha-cellulose pulp ideal for L-MMCF. There may also be potential for continuous production of pulp, which would decrease energy consumption and reduce the overall capital footprint towards commercialisation. For high alpha-cellulose, bast fibre is desired, so any hurd contamination needs to be completely removed. Alternatively, depending on end use, having controlled addition of hurd to reduce the overall alpha-cellulose content and DP may be desired. Figure 9: Hemp straw processing towards pulp for L-MMCF manufacturing. Currently, the Canadian textile industry mostly depends on imports for textile fibre for yarn spinning [149]. This is a unique opportunity for the Canadian textile industry not only to establish L-MMCF manufacturing, but also use hemp as a feedstock towards L-MMCF manufacturing. The Canadian Cannabis Act of 2018 allows for whole plant utilisation, which L-MMCF would support.