Oil Flax Straw Processing and Utilization 1

The ﬂax ( Linum usitatissimum ) is widely used as a source of linen 8 oil and ﬁber. As a rule, the ﬂax varieties serve to produce either seeds (oil), or 9 stem ﬁbers, as the “ﬁber” varieties bring the low amount of seeds, while the “oil” 10 varieties have poor ﬁbers that cannot be used in textile. The straw of the oil ﬂax has 11 not been applied in industry and has to be burned or degrade naturally in the ﬁeld. 12 However, it contains a low degree of polymerization cellulose, which can be used at 13 least for varnish production. The main challenge in the industrial application of the 14 oil ﬂax cellulose is the necessity of separating the cellulose ﬁbers and shive enriched 15 in lignin. On the other hand, the low cost of the ﬁnal products restricts the set of 16 available tools. Here we describe a machine designed for oil ﬂax straw stripping 17 and several ways of further conversion of the obtained tow into microcrystalline 18 or ﬂuﬀ-like cellulose. The supposed processes run at the temperatures below the 19 water boiling point and at the atmospheric pressure and could be held in the 20 plastic reactors. 21

1 Introduction 23 Flax (Linum usitatissimum) is an annual herbaceous plant cultivated for fiber (so-24 called "fiber" flax) or oil (so-called "seed" or "oil" flax) production. The linen oil 25 The work was completed as a part of the state assignment (theme number AAAA-A20-120013190076-0) S. Nikolsky  despite the excellent purity of the fiber obtained. Therefore, cutting the cost of 70 the oil flax fiber separation seems to be of crucial importance.

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The modern literature on the oil flax cellulose utilization passing over the 72 opportunity of flax papermaking, while such a possibility was discussed in the 73 middle of 20-th century (Dillman, 1943). The main problem of papermaking from 74 Oil Flax Straw Processing and Utilization 3 oil flax is the same as in the textile industry, i.e., too short fibers. However, using 75 the calcium hydroxide (milk of lime process) for raw delignification instead of more 76 common today kraft and sulfite processes allows producing the fiber of sufficient 77 for papermaking length (Schafer and Curran, 1938). We feel that this possibility 78 undeservedly put behind. Another method of high-quality oil flax fiber production 79 was shive precipitation by centrifugation of a diluted (solvent-to-pulp ratio ∼ 80 100) pulp suspension of the pulp retted in the caustic soda solution within 24-81 72 hours (Wells, 1949). Despite the excellent purity of the final fiber, the described 82 approach seems to be too expansive for commercial use.

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In this work, we present the very simple approach to the separation of oil flax 84 straw fiber from the shive, based on usage of the soft-bristles stripping drums able 85 of processing of the dry straw directly in the field. Our approach does not require 86 the preliminary retting and cutting stages, the stems could be processed as they 87 are, which significantly decreases the time of processing and cost. Besides that, we 88 have found several properties of the short-fiber oil flax cellulose that provides for 89 its effective utilization. The fraction of alpha-cellulose was determined as the proportion of cellulose in-93 soluble in 17.5 % NaOH (Richter, 1929). The molecular weight and the degree of  125 By now, the straw does not utilized and degrades naturally in the field.

126
The mechanical treatment of the oil flax straw was a one-stage process in a 127 novel machine (Fig. 1). Neither preliminary cutting nor retting was required; the 128 straw was processed immediately after the seeds collecting. shive content of about 15 % (Fig. 3B), which is a rather good result (Anthony,135 2005). Reducing the processing stages allowed decreasing the power consumption 136 down to 6.5 kW per 500 kg of the initial straw per hour. The obtained tow was 137 rather long-fiber and had a tendency to clump, so after the stripping, the tow was 138 cut into the 5-10 cm pieces.

139
The mechanical processing was followed by a two stage chemical treatment of 140 the obtained oil flax tow. The first stage was a delignification in 5 % solution of 141 NaOH or NaHCO 3 at 95 • C for 120 minutes (solvent-to-pulp ratio 50). Here and 142 hereafter, the former cellulose will be refereed to as "alkali cellulose", while the 143 latter -as "bicarbonate cellulose" The process was held in a plastic tank instead of The bleached oil flax cellulose delignified in Na 2 CO 3 (on the left) and NaOH (on the right). The insets represent the optical microscope images (x10) of the corresponding cellulose materials.

Paper production 152
The bicarbonate oil flax cellulose was not used for the laboratory paper samples 153 production due to significant share of very long (several centimeters) fibers. The 154 bleached alkali flax cellulose (sample weight 16 ± 0.5 g) was retted in distilled 155 water (500 ml room temperature) for 24 hours. The retted pulp was diluted to 156 1100 ± 20 ml with the distilled water (cellulose concentration 1.5 %) and disinte-157 grated with an impeller (3000 rmp) for 10 min to homogenize the raw additionally.

227
Despite the resistance to the bleaching procedure, the residual lignin content in 228 the final (bleached) bicarbonate cellulose was pretty low (0.5 %). and ∼ 105 µm (Fig. 4). Considering the low cost of the initial raw, using the oil 298 flax for MCC production could also be considered a potentially merchantable way 299 of its straw utilization.