Using the colour code presented earlier, subjective assessment of the 26 fibre samples was undertaken by four CSIR researchers and the results are presented in Figure 74 and Appendix 3 Table 3.
Figure 74. Photographs of retted fibre bundles placed according to their respective colour grades, as subjectively assessed [Colour Grade: 1 = very under-retted; 2 = slightly under-retted; 3 = well retted; 4 = slightly over-retted; 5 = very over- retted].
174 | P a g e The percentage of samples in each colour grade is tabulated below.
Retting Degree (Colour Grade) Very under- retted [1] Slightly under-retted [2] Well retted [3] Slightly over- retted [4] Very over- retted [5] Percentage of samples 30.8 34.6 19.2 7.7 7.7
Figure 75 compares photographs of local inadequately retted combed fibre samples (the first 4 photos of fibre samples on the left), with those of well-prepared fibre samples received from the Institute of Natural Fibres (INF) in Poland (3 photos of hackled and carded fibre samples on the right).
Figure 75. A comparison of inadequately retted local hemp (four photos on the left) with well retted hemp (three photos on the right).
A = Manually extracted; B = 1 x pass through machine; C = 2 x Pass through machine; D = 3 x pass through machine ; E = hackled fibres; F = carded fibres and G = 2 x (carded fibres)
Discussion
Based upon the colour grade results (Figures 74 & 75) the following conclusions may be drawn:
The colour grade chart can be used as a guide to decide on the most appropriate time to stop the retting process.
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A retting period of between 2 to 4 weeks, depending on the prevailing climatic conditions, generally produced well retted straw.
The colour rating chart can only be used as a screening tool by growers, traders and buyers to ascertain the quality and thus the price of hemp on the fields. It does not, however, replace the use of some methods and mobile testing systems to evaluate retting degree particularly suitable for rural use, and
Appropriate experience and technical skills, relating to the primary growing and processing of hemp fibre crops are essential for the production of fibres with the specific quality requirements for various industrial applications.
Fibre Microscopy
Figure 76 shows SEM micrographs of the cross- and longitudinal sections of locally grown hemp.
Figure 76. Examples of SEM micrographs of cross - and - longitudinal sections of locally grown hemp
176 | P a g e Discussion
The SEM micrograph on the left of Figure 76 shows the cross-section of hemp fibre bundles with a thin cell wall, while the longitudinal one on the right shows cracks visible along the length of the fibre, as indicated by the arrows.
Analysis of the SEM micrograph in Figure 76 leads to the following observations:
Inherent natural defects, such as cracks, occur along the length of the fibre, and
these cracks represent weak spots which will affect the fibre bundle physical properties and thus limit their use in industrial applications.
3.2.4.2 Chemical Properties and Composition
The results of the chemical analysis (Cellulose, Hemicellulose, Moisture Regain, Ash, Aqueous Extract, Petroleum Ether Extract and Lignin) and of the elemental analysis of the fibres are given in Tables 27 and 28, respectively.
Table 27. Chemical composition of fibres after retting.
Cultivar Locality Cellulose & Hemicellulose (%) Moisture Regain (%) Ash (%) Aqueous Extract (%) Pet.Ether Extract (waxes) (%) Lignin (%) Novosadska Dohne 68.1 & 10.1 9.3 3.0 4.9 0.37 4.4 Novosadska Qamata 70.4 & 13.0 9.4 3.1 3.1 0.15 10.8 Futura Libode 72.0 & 14.1 9.1 2.1 3.6 0.22 4.9 Felina Libode 73.1 & 12.5 9.8 2.8 3.6 0.23 4.5 French Low Grade France 72.8 & 12.0 9.0 3.3 3.1 0.37 5.5
177 | P a g e Discussion
From the chemical composition results given in Table 27, it can be concluded that:
The hemp fibres from different localities had cellulose content ranging from 68.1 to 73.1 %, hemicellulose content from 10.1 to 14.1%, moisture regain from 9.0 to 9.8 %, ash content from 2.1 to 3.3 %, aqueous extract levels from 3.1 to 4.9, petroleum ether extract levels from 0 to 0.37 % and lignin content from 4.4 to 10.8 %, with the Qamata site showing an unusually high lignin content of 10.8 %,
The chemical composition of the locally grown fibres closely matched that published in the literature (see Table 21) and those of the French low grade reference hemp sample (Table 27). It can, therefore, be concluded that the chemical composition of the locally grown hemp falls within the ranges published for hemp grown overseas.
The moisture content values were slightly higher than the published values. According to Harris and Mauersberger [166,167], the moisture content of hemp fibres is approximately 8.8 % with the moisture regain varying from 8 to 8.9 %, while here it ranged from 9.0 to 9.8%.
The values for ash content (2.1 to 3.3%) were higher than those cited in the literature, namely from 0.82 to 1.5% [168]. According to Sadov et al [169], this discrepancy could be due to the quality and maturity of the hemp, since studies on cotton fibres have shown that immature cotton fibres have a higher ash content than more mature ones [169].
Three of the four samples, namely Novosadska grown at Qamata, and Futura-77 and Felina-34, grown at Libode, had aqueous extract levels similar to those cited by Mathews and Mauersberger [170], namely 3.48%, the exception being Novosadska cultivar grown at Dohne, that had a higher aqueous extract level of 4.9%.
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Table 28. Elemental composition (%) of hemp fibre samples
Elements
Cultivar and Planting Site
Novosadska Novosadska Novosadska Futura Felina French Low Grade Hemp
Dohne Mtiza Qamata Libode Libode France
Ash (%) 3.0 4.7 3.1 2.1 2.8 3.3 Sodium 0.0 0.45 0.0 0.0 0.0 0.0 Magnesium 1.4 1.7 1.8 1.1 2.3 0.48 Aluminium 0.2 0.2 0.4 0.1 0.0 0.0 Silicon 1.9 1.9 1.5 2.0 1.3 0.6 Phosphorous 0.4 0.3 1.0 0.4 0.5 0.8 Sulphur 3.3 3.9 3.4 2.1 2.3 5.1 Calcium 3.9 2.2 4.1 2.4 0.0 5.3 Potassium 1.5 4.4 2.9 0.9 2.4 4.5 Titanium 0.0 0.0 0.0 0.1 1.3 0.0 Manganese 0.0 0.0 0.0 0.3 0.2 0.0 Chromium 0.0 0.1 0.0 0.0 0.0 0.0 Iron 0.3 0.4 0.5 0.3 0.4 0.0 Discussion
The main elements found in plant fibres are minerals, such as, Calcium (Ca), Potassium (K), Phosphorus (P) and Magnesium (Mg) [168], the actual mineral content depending on various agronomic factors, including the composition of the soil. Silicon (Si) is the second most abundant element in the earth‘s crust, after oxygen, and thus large quantities of silicon are present in most soils and are thought to play a role in plant stiffening [171, 172].
From the elemental composition results of the fibres given in Table 28, the following conclusion may be drawn:
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The five main elements present in the ash of the various hemp samples were Calcium, Sulphur, Potassium, Silicon and Magnesium, confirming what has been reported in the literature [168].
The elemental content levels of the locally grown hemp were similar to those found in the French sample for the five most prevalent elements, the exception being Silicon, which was higher than that of the imported French hemp fibre.
According to the results of the locally grown cultivars and those of the imported French hemp sample as well as those published in the literature, it is reasonable to conclude that the elemental composition of the plant fibres, such as hemp, depends on both agronomic factors, notably the composition of the soil on which the cultivars are grown.
Main overall conclusions:
The following represent the main overall conclusions drawn from this part of the study:
Planting site, retting period and lighting conditions did not affect the fibre yield of the different cultivars in a consistent manner. The low levels of fibre yield achieved could negatively impact the economic viability of the primary fibre production industry.
Inconsistencies in the experimental results of the fibre properties, such as linear density and bundle strength, can most probably be attributed to the local lack of technical expertise on hemp crop production.
The retting period of between 2 to 4 weeks, depending on the prevailing climatic conditions, produced well retted straw, and appeared to be optimum.
Microscopic studies on the fibre revealed inherent natural defects, such as cracks, occurring in some spots along the fibre which could affect the fibre physical properties and which could limit their use in industrial applications.
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It can be concluded that the chemical composition of the locally grown fibres matched those published for hemp producing countries.
The elemental composition of the locally grown hemp matched those published for hemp from traditional hemp producing countries, being dependent on agronomic factors, particularly the composition of the soil.
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PART II: THE PERFORMANCE OF EUROPEAN FLAX CULTIVARS