Industrial Crops & Products 117 (2018) 159–168
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Assessment system to characterise and compare different hemp varieties based on a developed lab-scaled decortication system
T
Shaoliang Wanga, Hans-Jörg Gusoviusb, Carsten Lührb, Salvatore Musioc, Birgit Uhrlauba, ⁎ Stefano Amaduccic, Jörg Müssiga, The Biological Materials Group, Biomimetics, HSB – Hochschule Bremen, City University of Applied Sciences Bremen, Neustadtswall 30, D-28199, Bremen, Germany Leibniz Institute for Agricultural Engineering and Bioeconomy Potsdam-Bornim (ATB), Max-Eyth-Allee 100, 14469 Potsdam, Germany c Department of Sustainable Crop Production, Università Cattolica del Sacro Cuore, Via Emilia Parmense, 84, 29122 Piacenza, Italy a
b
A R T I C LE I N FO
A B S T R A C T
Keywords: Hemp Natural fibre Decortication Assessment system Fibre quality
With superior quality, hemp fibres are being more and more widely used for a large number of traditional and innovative industrial applications. The quality of the final products is strongly influenced and determined by the quality of the fibres, which in turn is subjected to agronomic factors, such as genotypes (hemp accessions), growing conditions, harvesting and processing. To improve hemp productivity and raw material quality for enduser requirements and advance scientific understanding of gene-to-trait relationships in this crop, characterisation and comparison of hemp samples of different varieties are important research tasks, which are normally carried out on small samples and require accurate and reproducible measurements. Decortication, the mechanical processing of stems to separate bast fibres from shives, plays a very central role in the whole natural fibre production chain. In the frame of the MultiHemp project (http://multihemp.eu/) a partially automated labscaled decortication process was designed and developed. The energy consumption during decortication was investigated to characterise and compare different hemp varieties. In order to calibrate the breaking unit a method was developed, and the process stability was analysed. Furthermore a new characterisation value, a socalled κ-number was introduced and a model of an assessment system was established for a more objective and reproducible evaluation of hemp varieties. Finally the assessment system was tested on three hemp varieties (Fédora 17, Futura 75 and Tygra) cultivated in the frame of a large Multihemp trial.
1. Introduction Nowdays natural fibres, such as flax, ramie, kenaf and hemp, are being more and more widely used as they are biodegradable, environmentally friendly, economically feasible and naturally occuring (Piotrowski and Carus, 2010). Considered as one of the oldest crops known to man, hemp is sustainable, high yielding, it has advantageous environmental and agronomical characteristics, it can promote carbon sequestration and it requires less water and agrochemicals than other fibre crops (Amaducci and Gusovius, 2010; Amaducci et al., 2008a; Carus et al., 2013). Hemp fibre has been used as reinforcement in composite materials (Holbery and Houston, 2006; Müssig et al., 2005), for example, to produce car interior panels and insulation products, and to form hemp concrete together with or without the woody core (hereafter referred to as shives) in the bio-building sector (de Bruijn et al., 2009; Li et al., 2006). The quality of these end use products depends on the quality characteristics of the hemp fibre (Müssig et al.,
⁎
2005). Thus, the suitability of hemp fibre as polymer reinforcement depends on various fibre features such as fibre surface characteristics and its fineness, that influence the interfacial bonding strength between the fibres and the matrix, and fibre tensile strength (Graupner et al., 2014). Fibre quality is influenced by a variety of factors, such as agrotechnique, growing conditions, and harvesting (Müssig and Amaducci, 2018; Müssig and Martens, 2003; Amaducci et al., 2005; Amaducci et al., 2008b; Höppner and Menge-Hartmann, 2007). Dislocations, known as damages to the fibre cell wall structure, are found in unprocessed fibres (Hänninen et al., 2012; Thygesen and Asgharipour, 2008), and particularly are formed when hemp is processed mechanically (Hänninen et al., 2012; Hernandez-Estrada et al., 2016). To enhance the suitability of hemp fibre for industrial applications, various biological, chemical and physical treatments on the fibre have been developed (Baker et al., 2010). For the mechanical treatment, decortication plays a very central role in the whole natural fibre production
Corresponding author. E-mail address:
[email protected] (J. Müssig).
https://doi.org/10.1016/j.indcrop.2018.02.083 Received 1 September 2017; Received in revised form 21 February 2018; Accepted 28 February 2018 Available online 22 March 2018 0926-6690/ © 2018 Elsevier B.V. All rights reserved.
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Table 1 Selected 14 varieties from the field experiment in Rovigo, Italy.
Fig. 1. Integrated quality concept within the MultiHemp project from small test plots through lab-scaled decortication, separation and fibre quality assessment until the final variety selection process for optimised hemp breeding activities. The first important step in the quality concept is the realisation of a semi-automated separation system. In particular, starting with the decortication as a core element.
Field code
Variety
Sex
Origin
AGM-702 AGM-704 AGM-703 AGM-705 CRA-411 FNPC-251 FNPC-252 FNPC-253 FNPC-254 FNPC-255 IWNRZ-901 IWNRZ-902 IWNRZ-903 VDS-303
Tiborszallasi Kc Dora Tisza Monoica C.S. Férimon Fédrora 17 Félina 32 Epsilon 68 Futura 75 Bialobrzeskie Beniko Tygra Markant
dioecious dioecious dioecious monoecious & dioecious dioecious monoecious monoecious monoecious monoecious monoecious monoecious monoecious monoecious monoecious
Hungary Hungary Hungary Hungary Italy France France France France France Poland Poland Poland Netherlands
demonstration of the features of our assessment system. Samples chosen for the evaluation of the decortication system came from the field experiment in Rovigo, at the Research Centre for Industrial Crops (CRA), Italy (45°N, 11°E). The weather data of Rovigo for the cultivation time in 2013 were as follows: GDD = 1831; Mean temperature = 20.1 °C; Mean relative humidity = 69%; amount of rainfall = 185 mm; Tmin = 6.6 °C and Tmax = 35.8 °C. 14 varieties were selected for the evaluation of the lab-scaled decortication system (Table 1). Sowing (18–19 of April 2013) and harvesting (15–17 of July 2013) were carried out at the same time for all the tested varieties. Considering that the selected varieties have contrasting phenology and flower at different times, harvesting was carried out at different phenological stages for the 14 varieties (Fig. 2). At harvest stems from each variety were cut at ground level and subsequently the lower stem portion, of 1 m length, was prepared for further processing. We are aware that a significant variation of tensile properties of hemp fibre bundles selected from the top, middle and bottom part of the stem exist (Liu et al., 2015) but within the MultiHemp project we focused on the bottom meter of the stem because traditional flax processing equipment like scutching and hackling machines (Müssig and Haag, 2014), that are not able to process stems longer than 1 m, are used for the production and processing of longitudinal hemp (Amaducci and Gusovius, 2010). Using the bottom meter only, might have created some variability among varieties, especially between short ones, for which the whole stem was only 1 m (in this case the whole stem was used as a specimen for the decortication process) and tall ones, whose stems length exceeded 2 m (in this case only the basal part was used). This variability, which might lead to biased conclusions when comparing genotypes having different height or phenology, was useful in this work in order to develop and test a decortication methodology that is able to assess hemp samples (for decortability, energy consumption etc.) independently of their phenotype. A new indicator was introduced in order to take this situation into account and to evaluate what effects possibly results from a conical versus a cylindrical shaped stem (stem shape factor; see Eq. (5)). Half of the harvested stems were dried in open air protected by a roof in order to prevent retting. The other proportion of the harvested stems was dried and warm water retted for 3 days at an average temperature of 23 °C according to a protocol published by Van den Oever et al. (2003). After water retting the stems were dried in open air and decorticated with the decortication system (lab-scaled breaking unit).
chain (Amaducci and Gusovius, 2010; Müssig et al., 2010) (Fig. 1). In the decortication process the shives are broken and mechanically separated from the fibre bundles (Amaducci and Gusovius, 2010; Baker et al., 2010; Gratton and Chen, 2004; Hobson et al., 2001). Research on the effect of decortication is necessary to highlight the complex nature of hemp fibre characteristics (Keller et al., 2001). An effective quality analysis system would also support the selection of improved genotypes (Salentijn et al., 2015) and the optimisation of agrotechnique (Amaducci et al., 2015) leading to optimal fibre production for specific end uses. Decortication of small samples containing only few stems (Beckmann, 1998; Keller, 2001) obtained from experimental field trials cannot be carried out on industrial processing plants. In the frame of the MultiHemp project (Fuentes et al., 2017; Multihemp, 2017; Tang et al., 2016) a lab-scaled decortication process was developed to process and analyse a large number of samples and to obtain accurate and reproducible measurements. A great challenge of the Multihemp project was the processing of a very large number of hemp accessions from multiple locations and contrasting agrotechniques (Fig. 1). Hemp samples obtained during field trials had a very large variation in stem diameter. This is an important property of hemp samples that affects directly mechanisation of harvesting and that seems to influence indirectly other properties, for example fibre content and stem density (ratio between mass and volume of a stem). To evaluate and compare the decortication related properties of stems obtained from different hemp accessions having different diameters, it is necessary to minimise or eliminate the possible influence that stem diameter has on the stem and fibre characteristics. Besides the development of a lab-scaled decortication process, another aim of this work was to build a criterion to assess stem and fibre quality characteristics from stems having contrasting diameters. 2. Material and methods 2.1. Samples In order to develop and test our lab scale decortication process, a set of stem samples encompassing a large variability of traits (i.e. different genotypes, phenology, stem diameter) was needed. For this, hemp stem samples were selected from a field experiment carried out during the MultiHemp project. Analysis of fibre properties on the full set of varieties examined in the frame of MultiHemp is outside the scope of this paper and will be undertaken in future publications. In this work reference to quality traits of a subset of varieties is provided only as a
2.2. Development of the lab-scaled breaking unit During decortication the woody core is mechanically broken and removed from the fibre bundles. These broken removed pieces are named shives. Fig. 3 shows the developed lab-scaled breaking unit 160
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Fig. 2. Phenology of the female plants of 14 varieties cultivated in the field experiment of Rovigo, Italy.
(Worthmann Maschinenbau GmbH, Barßel-Harkebrügge, Germany) with four pairs of profiled rollers. The most important prerequisite for a proper working decortication device is the design of the breaker rollers as well as the selection of the materials used to manufacture them. Fig. 3 shows the installed bottom and top breaking rollers of the decortication device. These are arranged in two opposite orientated rows of 4 rollers, with counter rotating, helical geared, involute profiles. Based on exsiting experiences and experiments, the upper row was equipped with rollers made of polytetrafluoroethylene (PTFE), the lower row with rollers made of steel (42CrMo4). The rollers of both rows are driven by a chain drive with an infinitely variable DC motor. In order to guarantee an effective and reproducible decortication process the breaker was adjusted considering the following steps:
• •
• • •
rollers are perpendicular to their counterparts. The two red rubber buffers located between the transparent PMMA plate and the machine frame are to be set to the same height to ensure that both sides are adjusted in the same way. In the frame of this work the height was 15 mm Each of the upper roller suspensions is equipped with a spring in order to control the pressure to the lower one of the pair. In order to minimise the spring pressure and to prevent damage of the fibres the screws of the socket head was adjusted to a depth of 0 mm (Fig. 3). Setting a value of 50 Hz at the frequency converter which corresponds to a transportation speed of the specimens of 9 m min−1.
2.3. Process and measurement automation
Installation of the rollers from the coarse toothing at the intake side to the fine toothing at the outlet. Adjustment of the horizontal distance between the lower rollers measured from one axis centre to the next to 65 mm, and four upper
Within the MultiHemp project a huge number of samples from different varieties, consisting of 10 stems each, were decorticated with the developed breaking unit. Our approach for a lab-scaled decortication process is based on the method developed for flax by Heyland et al. Fig. 3. Lab-scaled decorticator (breaker) as part of the complete breaking system (frequency converter, calliper and scale) equipped with the automated data acquisition and analysis system. Graphical user interface (GUI) of the function block for the automated decortication process to monitor and control the devices, to fetch, plot and stream the measured data into the corresponding database for the subsequent analysis.
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Fig. 4. (A) Mass change along the decortication process after 6 passages (1–6) and the manual shive removal (7); 0: hemp stem before decortication; (B) Motor power waveform measured during a decortication process (6 passages) of a hemp stem, recorded with the process monitoring and controlling program with the automated peak value recognition.
decortication process, while all data were measured and recorded. At least 10 stems were selected to obtain the amount of fibre bundles required for subsequent characterisations, such as measurement of fineness, length, dislocations (Hernandez-Estrada et al., 2016) or mechanical properties (Fuentes et al., 2017). Hemp specimens from different varieties or even within the same variety had a large variability in stem diameter. To take into account the effect of stem diameter on decorticability the diameter of the stems was measured, prior to decortication, at three positions: at the middle of the stem and 10 cm from both ends. For the first passage through the breaker, the stem was fed into the breaker from its top part (the thinner end) while the bottom part went through the breaker first in all following passages, to facilitate shives removal. After each passage through the decorticator the stem/bast specimen was taken off the machine by gripping it on one side. Loose shives were removed from the bast by a slight movement of the hand before the bast is again fed into the breaker for the next passage. Loosened shives were removed without picking or peeling them off in order to prevented their aggregation in the following decortication step. Finally, the mass of the decorticated specimen was determined and recorded. Each specimen was passed through the decortication device for six times, after the sixth passage the remaining shives were removed manually from the bast and the shives-free bast was weighed (Fig. 4A). For the measurement of the mass the scale Kern 440–35 M, D = 0.01 g (Kern & Sohn GmbH, Balingen, Germany) was used. Bast or fibres bundles thereof can wrap (partly or completely) around the rollers during the decortication process. These should be removed from the rollers and discarded from the sequential processes and analyses, because the wrapping can lead to extra damages of the specimen. The same approach was chosen when a stem or the bast has lost its structure and parts of the sample fell in-between the rollers. At the end of the process, all stem parts (bast and shives) from each sample were separately stored in airtight plastic bags, such as Rotilabo 180 mm × 250 mm (Carl Roth GmbH & Co.KG, Karlsruhe, Germany).
(1995). Scheer-Triebel et al. (2000) used 10 stems for a lab-scaled decortication to evaluate the fibre content and fibre properties for flax and linseed stems. While Keller et al. (2001) used 15 hemp stems for a lab-scaled decortication process, von Francken-Welz and Leon (2003) used 100 g of dried hemp stems for decortication to get reliable data. Based on the literature review and our own experience the amount of 10 stems was considered sufficient to estimate the difference between the different hemp accessions and to get enough fibre bundles for further analysis. In order to enhance the work efficiency, an automated system for data acquisition and analyses (Fig. 3), was developed and connected to the breaking unit. The system consists of a calliper for measuring the stem diameter, a scale for weighing the mass of the stems and a frequency converter to record the energy consumption of the decortication process. The measuring devices are connected to a laptop where a data management system developed within the MultiHemp project is installed. During the decortication process a measuring centre (Fig. 3), as part of the data management system, monitors and controls the devices, collects and streams automatically the measured data into the corresponding database. The measuring centre can also carry out simple statistical calculations inline while the stem is processed. An advantage of this function is that large deviations and errors can be recognized immediately during the decortication process, and corresponding corrective actions can be undertaken. This applies in particular if measured values for stem diameter, losses vary in an abnormal or destruction of specimen takes place, which can be compensated, for example, by decortication of additional stems. 2.4. Requirements for the preparation of hemp stem samples After collecting and drying, the hemp stems were cut to one meter and were stored at 20 ± 3 °C and a relative humidity of 60 ± 5%, which was monitored by a measuring instrument and reported regularly. One stem of each hemp variety was cut into 5 cm long pieces, to measure the moisture content of specimens gravimetrically with the torrefaction method. This was carried out at 105 °C for 6 h according the procedure recommended by the National Renewable Energy Laboratory (Sluiter et al., 2008).
2.6. Process analysis and sample characterisation Based on the measurements undertaken during the decortication process, hemp samples of different varieties were characterised and the decortication process was analysed on the basis of the following characteristic values. 1) Bast content after decortication BCD is calculated from the initial mass m0 of the non-decorticated stem and the mass m7 of the decorticated and cleaned bast (after 6 passages and an additional cleaning step; see Fig. 4A). It is important to collect all fibrous parts as precise as possible as well those fallen in between the rollers and down
2.5. Standardisation of the decortication process From each sample we randomly selected 10 stems, that we considered as the minimum number of stems to capture the variability of the sample while maintaining the time of analysis within a reasonable time consumption. Each selected stem went through all steps of the 162
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locations or post harvesting processings, such as non-retted or water retted samples. The investigation of the energy consumption during decortication enables us to better understand the process and to define a criterion to judge the processability of different hemp samples. An evaluation concept was developed within this work. From the acquired motor power signals, the consumed energy to break the hemp stem was calculated as the area under the impulses (light grey areas in Fig. 4B). The idle motor power, about 0.027 kW, was removed by calculation. Using the numerical computing environment MATLAB (MathWorks, Inc., Natick, USA) a routine was developed to automatically recognize the impulses together with their peak values. Because the motor power at the idle state ranged between 0.026 kW and 0.029 kW, the idle motor power was calculated between the white dots (see Fig. 4B) for each peak to calculate the exact breaking energy. For comparing the hemp samples of different varieties or locations based on the energy used during decortication, a new defined characteristic value the so called “energy efficiency” (Eq. (7)) was introduced, which represents the energy consumption to produce a given amount (e.g. 1 g) of shive-free bast. Low εm values indicate a high processability.
in the drawer.
m BCD = 7 ⋅100 m0
in %
(1)
2) Decortication efficiency is calculated as: Initial decortication efficiencyηDec_1 describes the efficiency of the initial stage of the decortication process on the handled stem, thus influences of e.g. variety, agronomy or harvest/post-harvest measures on the processability/decorticability. It is calculated by using the following equation:
ηDec_1 =
m 0 − m2 ⋅100 m 0 − m7
in %
(2)
where m0 is the mass of the non-decorticated hemp stem, m2 is the mass after two passages and m7 the cleaned bast mass after six passages and the final manual removal of all remaining shives. Ultimate decortication efficiency ηDec _2 is calculated by Eq. (3), and represents the overall decortication efficiency (decorticability):
ηDec_2 =
m 0 − m6 ⋅100 m 0 − m7
in %
(3)
whereby m6 is the mass after six passages without subsequent cleaning. If shives could not be removed mechanically any more, for example, after the 5th passage (m6≈ m5), ηDec_2 represents the maximum decortication efficiency that the mechanical process can achieve. Furthermore, this characteristic value enables the comparison of different types and/or configurations of breakers used for decortications. Besides the three characteristic values mentioned before, additional properties were defined within this work: 3) Shives content after decortication χ describes the ratio of the manually removed shives to the total sample mass m6 (bast + shives) after the sixth passage (Eq. (4)). This characteristic value is coherent with the ultimate decortication efficiency.
χ=
m6 − m 7 ⋅100 m6
in %
6
Σ Ei
εm =
D1 D3
4⋅m 0 π⋅Dmean⋅Dmean⋅L
(7)
3.1. Analysis of the decortication process stability An essential feature of the decortication process, developed to compare and assess stem samples, is the stability with which it measures relevant properties (i.e. bast fibre content or decortication efficiency). To test the process stability identical samples are normally needed. Hemp stems are very variable, differing in shape, size and mass; it is therefore not possible to verify the process stability of the developed breaking unit using real hemp stems. A number of trials with different sample types and materials (thermoplastic elastomer tubes and wires, elastomer tubes and wires as well as folded sheets of paper) were carried out. Ropes made of polyamide (PA) and sisal, available in hardware stores, proved to be well suited to represent homogeneous specimens. Experimental series were carried out with two different ropes, a PA rope of 5 mm in diameter having a linear density of 16.24 g/ m, and a sisal rope of 6 mm in diameter having a linear density of 18.00 g/m (both BAHAG AG, Mannheim, Germany). To simulate hemp stems, the ropes were cut into one meter specimens, and each one was passed through the breaker for 15 or 25 times. This high number of passages was required to control the possible influence of temperature induced by friction. Fig. 5B shows a time curve of the motor power for a PA rope specimen processed in the breaker unit. Breaking energy consumption was calculated and recorded with a routine developed in MATLAB (see M&M section). Rope specimens normally do not lose mass during the decortication process and, as expected, the relative impulses have almost the same signal duration and height at every passage. Because the used rope samples are more flexible than hemp stems, the tested rope could not pass through the rollers straight and smoothly at the first passages. In order to guarantee reliable test results and to avoid the influence of the “run-in behaviour” of a new rope, the first passage of PA-samples and the first 6 passages of sisal-samples were not taken into account when analysing the process stability. The higher amount of passages for the sisal rope was chosen because we evaluated a longer run-in behaviour for sisal ropes than for PA ropes. Fig. 5A shows the energy consumption of the test series, where each measurement point indicates the energy consumption of six passages. Because the samples are not 100% identical (small variation in rope mass and diameter
(4)
(5)
in g/m3
in kW/g
3. Results and discussion
5) Stem density is calculated by Eq. (6):
ρ=
m7
whereby Ei is the energy consumption of each passage.
4) Stem shape factor is the ratio of the measured diameter at the top (D1) and bottom (D3) of the hemp stem.
KD13 =
i=1
(6)
whereby Dmean = (D1 + D3)/2 and L is the stem length (within this work L = 1 m). 2.7. Breaking energy and processability of hemp samples To monitor and record continuously the motor power during the decortication process, the breaker was equipped with a Danfoss frequency converter FC51 (digi table GmbH Wittenberg, Germany). The passage of the stem through the breaker results in an electrical impulse on the motor power signals. Considering that for each sample the hemp stems were cut into one meter pieces, these impulses on the motor power signals should theoretically have a constant duration. In practice, however, the transformation from the stem to the decorticated bast could reduce the length of the specimen (linear shape of the stem versus curved shape of the decorticated bast), and the corresponding impulses gets shorter and smaller (Fig. 4B) as well. The reduction of the dimension of the peaks is related to a reduction of the volume and the shive content of the tested specimen which results in a bending of the specimen and curved shape of the decorticated bast. We defined the energy consumption during the decortication process as an indicator of the decorticability of different hemp varieties, 163
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Fig. 5. (A) Chronological sequence of the energy efficiency passing polyamide (PA) and sisal ropes (1 m rope length) through the breaker; (B) Waveform of motor power output of the passing process using a polyamide rope of 1 m length; passage 1, identified by the grey coloured ellipse was not introduced in the comparison (explanation is given in the text); the signal used for the evaluation are marked by the grey dashed line boxes.
stem diameter, a fitting curve was added. The grey dashed fitting curve represents the average level of the BCD over a stem diameter range from 3 to 10 mm for the hemp variety Fédora 17 (Fig. 7). The range of stem diameters was divided into several classes with a class width of 1 mm; the corresponding boxplot of each class is presented in Fig. 7. The influence of stem diameter on BCD is obvious, with bast fibre content decreasing when stem diameter increases. This relation creates a bias when hemp varieties having different stem diameter are compared. In order to minimise or eliminate the influence of stem diameter, an evaluation concept was developed, and is described as follows. The black fitting curve in Fig. 7 represents the average level of the relation between BCD and stem diameter, along the whole diameter range of the 14 varieties. This can be used to characterise the relative behaviour of one variety compared to the others, independently of stem diamater, using only one characteristic value. As an example the hemp variety FNPC 252 B1, whose measured BCD values lies under the fitting curve, has a lower than average bast fibre content. To compare and rank varieties based on their BCD, a factor κ is introduced (Eq. (8)). This κ-number of a stem of the given variety is defined as the ratio of the BCD of the stem to the average BCD value, that lies on the fitting curve at the same stem diameter level. Stem related values lying above the fitting curve have a higher than average bast content, and their calculated κ-numbers are larger than 1. With the introduction of the κnumber the influence of the stem diameter can be reduced or eliminated. For all stems of one hemp variety, for example FNPC 252 B1, a group of κ-values is acquired and can be presented as a box plot (right side of Fig. 7), in which each value represents one stem. Fig. 8 shows the κ-values for BCD of the 14 varieties considering three different blocks. The overall judgement of the sample can be given by the geometric mean of these ratios.
along the rope length), particularly for the sisal samples, the ratio of the energy consumed through the decortication to the sample mass was used instead of the energy alone. As shown in Table 2, the test assessed the stability of the decortication process within a large range (εm: 0.02–0.04 kW/g), which includes the range of values measured for stems processed within the MultiHemp project. The deviations were mainly related to stochastic events (e.g. the formation of loops) of the passing sequences. Due to their inhomogeneity, results from sisal specimens had larger scattering than PA ropes. No trends of steady increase or decrease in power values were recorded during the test series, for this it was considered that the influence of the warming of the motor or rollers during long measuring periods could be neglected. The tests proved that the ropes are suitable to examine the process stability of the breaker, ropes of different materials (for example: PA and sisal) and diameters are easily available and can be used to calibrate the breaker systematically. 3.2. Development of an evaluation method for sample comparisions Within the MultiHemp project 100 hemp accesions cultivated at three locations (Italy, France and Netherlands), with three replications (blocks B1, B2 and B3) for each location, were processed and subsequently analysed for all the properties described in Sections 2.5 and 2.6 (Eqs. (1)–(7)). As an example of the range of variation of stem features encountered in this large experiment, Fig. 6 shows the stem diameter of 14 selected varieties of water retted samples obtained from the trial carried out in Italy (see Table 1 and Fig. 2). We observed a high variation in stem diameter among varieties or even among different replications of the same variety. Considering that stem diameter is manly affected by plant density (Tang et al., 2017; Amaducci et al., 2002), and unwanted difference in plant density, when comparing different varieties, might indirectly affect relevant stem traits (i.e. BCD as shown in Fig. 7), a method to minimise or eliminate the influence of stem diameter will be proposed as follows. The correlation between BCD and stem diameter for the 14 seleced varieties is shown in Fig. 7. To describe the relation between BCD and
n
K=
Mean in kW/g
Standard deviation in kW/g
PA passage 2–7 PA passage 8–13 Sisal passage 7–12 Sisal passage 13–18
0.0225 0.0221 0.0397 0.0373
0.00096 0.00078 0.00210 0.00179
Π ki =
i=1
n
k1⋅k2⋅⋅⋅⋅kn
(8)
The overall judgement κ = 0.82 for the BCD of Fédora 17 (FNPC 252 B1) provides a bast fibre content under the average level of the 14 varieties. This assessment is also consistent with the observation from Fig. 7, in which almost all measurements for the variety Fédora 17 (FNPC 252 B1), along the whole range of stem diameters, lie under the fitting curve of the 14 varieties. This leads to the conclusion that every stem of the sample has a relatively low bast fibre content in comparison with the other 13 varieties. The same procedure was used to compare varieties on the basis of other properities. As an example, the results of the initial decortication efficiency, stem density, stem shape factor and energy consumption of the
Table 2 Testing results εm with PA and sisal rope samples (mean and standard deviation). Tests
n
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Fig. 6. Box plots of the stem diameter of 14 hemp varieties of the water retted samples from Italy, here Dmean = (D1 + D3)/2; grey dots are illustrating the diameter of each measured stem. Fig. 7. Analysis of the bast content after decortication (BCD) for hemp variety Fédora 17–FNPC-252 (B1). Left: grey dots are illustrating each measured BCD value from the 14 selected varieties; the grey dotted line represents the trend line of all BCD values in the plot; the black dots represent the BCD values of variety Fédora 17 while the black solid line shows the trend line for the BCD values of Fédora 17. Right: box plot of the κ-number and the geometric mean of κ for the BCD of variety Fédora 17.
Fig. 8. Box plots of the k-numbers for the bast content after decortication (BCD) of the 14 varieties (B1, B2, B3) of the water retted samples from Italy (UCSC WP2); grey dots are illustrating the k-numbers for the BCD of each measured stem.
Fédora 17 is characterised by a low bast fibre content (κ = 0.82; Fig. 7), a high stem density (κ = 1.13; Fig. 10A) and a high initial decortication efficiency (κ = 1.15; Fig. 9) compared to the other 13 hemp varieties (Fig. 8). The applicability and the advantages of the developed evaluation concept using the κ-values will be demonstrated by comparing different hemp varieties. As an example, the κ-numbers of bast content after decortication, initial decortication efficiency, stem shape factor, stem density
decortication relative to the variety FNPC-252 (B1) are presented in Figs. 9 and 10. The influence of stem diameter on bast content after decortication, on initial decortication efficiency (Fig. 9), on stem density (Fig. 10A) and on stem shape factor (Fig. 10B) is evident. Energy efficiency of variety FNPC-252 is the only characteristic value that was not affected by stem diameter in our study (Fig. 10C). Using the new introduced κ-values the processing behaviour and the properties of variety Fédora 17 (FNPC-252 B1) can be described as follows. Variety 165
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Fig. 9. Analysis of the initial decortication efficiency for hemp variety Fédora 17 (FNPC-252 (B1)), Left: grey dots are illustrating each measured “initial decortication efficiency” value from the 14 selected varieties; the grey dotted line represents the trend line of all “initial decortication efficiency” values in the plot; the black dots represent the “initial decortication efficiency” values of variety Fédora 17 while the black solid line shows the trend line for the “initial decortication efficiency” values of Fédora 17. Right: box plot of the κ-number and the geometric mean of κ for the “initial decortication efficiency” of variety Fédora 17.
Fig. 10. (A) Stem density, (B) stem shape factor and (C) energy efficiency for hemp variety Fédora 17 (FNPC-252 (B1)), Left: grey dots are illustrating each measured values from the 14 selected varieties; the grey dotted line represents the trend line of all values in the plot; the black dots represent the values of variety Fédora 17 while the black solid line shows the trend line for the values of Fédora 17. Right: box plot of the κnumber and the geometric mean of κ for each characteristic value of variety Fédora 17.
Fig. 11. Overall assessment by κ-numbers of three hemp varieties: Fédora 17 (FNPC-252), Futura 75 (FNPC-255) and Tygra (IWNRZ-903) (three blocks: B1, B2 and B3); ηDec_1 = initial decortication efficiency; ρ = stem density; χD13 = stem shape factor; BCD = Bast content after decortication; εm = energy efficiency to produce a given amount of shive free fibre.
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consumption of the decortication process, (iv) shives content after decortication, (v) stem shape factor and (vi) stem density, and a method to reduce or eliminate the effect of stem diameter on stem quality. Comparing hemp varieties for quality charateristics is hampered when stem diameter are not homogenous among varieties due to variable plant density at harvest. In fact, stem diameter is relevant to numerous quality properties of hemp and to the decortication process. In order to reduce the influence of stem diameter on quality parameters a κ-factor was introduced and an assessment system was established, based on the great number of hemp samples analysed within the MultiHemp project. The energy consumed during decortication of hemp stems is an effective indicator of the processablity of different hemp varieties. As a part of our quality management system, the decortication process and the measurement were partially automated. Profound analyses and investigations can be initiated and untertaken, which will enable us to better understand different hemp varieties and to optimise the decortication process. With the assessment method introduced within this work, differences of the hemp varieties relative to their decortication behaviours can be identified without, or with a reduced, influence of the stem diameter. The purpose of this paper was to provide a powerful and time effective methodology to assess decortication efficiency in hemp. We were able to show the functionality of the system and the feasibility of the evaluation concept, comparing, as an example, three different hemp varieties, using the decortication system in combination with the developed evaluation concept, including the so-called κ-values. We have acquired a powerful tool to further analyse hemp from large variety trials, like that carried out in the MultiHemp project − one of the largest accessions trial programs for hemp.
Table 3 Comparison of the shive content (in%) after decortication process of three hemp varieties: Fédora 17 (FNPC-252), Futura 75 (FNPC-255) and Tygra (IWNRZ-903) (three blocks: B1, B2 and B3). Block
FNPC-252
FNPC-255
IWNRZ-903
B1 B2 B3 Mean Standard deviation
14.2 14.1 14.7 14.3 0.26
9.9 12.2 9.3 10.5 1.25
19.7 16.8 19.7 18.7 1.37
and energy efficiency, were used to compare the three varieties Fédora 17 (FNPC-252), Futura 75 (FNPC-255) and Tygra (IWNRZ-903) replicated in three blocks in Italy. To get more detailed agronomic information about the mentioned varieties the authors refer to the publications of Amaducci et al. (2008a,b), Westerhuis et al. (2009) and Tang et al. (2016). The overall assessment is shown in Fig. 11, and the sum of the κ-numbers is calculated using the values obtained in each block, which is illustrated by three different colours. Comparing Fédora 17 (FNPC-252) with Futura 75 (FNPC-255) it is apparent that the latter has a higher bast fibre content (BCD) than the former (κ = 2.57 and κ = 2.97, respectively), and Futura 75 (FNPC-255) consumes less energy during the decortication process than Fédora 17 (FNPC-252) (κ = 2.90 and κ = 3.21, respectively; Fig. 11). Furthermore, FNPC-255 has a high processability (initial decortication efficiency is high and shives are easier to remove during decortication than in FNPC-252 – see Table 3 for comparison). Based on this evaluation of the mentioned characteristic values, the overall quality is higher in FNPC-255 than in FNPC-252. Moreover, differences between specimens of both varieties regarding stem density (κ = 3.28 for Fédora 17 (FNPC-252) and κ = 2.84 for Futura 75 (FNPC-255)) and stem shape factor (κ = 3.18 for Fédora 17 (FNPC-252) and κ = 2.90 for Futura 75 (FNPC-255)) can also be found. This information could be linked to the phenology of the two varieties and is described as follows. In fact all varieties were harvested on the same date and as a result early varieties, that had reached flowering and had ceased stem growth sooner than late varieties, had shorter stems, more conical in shape compared to the long and more cylindrical stems of late varieties. In contrast to stem specimens of both FNPC varieties, those of IWNRZ-903 as a late variety had the highest bast fibre content, but consumed more energy than FNPC-255, which is nearly on the same level as FNPC-252. IWNRZ-903 stems showed a low initial decortication efficiency (κ = 2.47; see Fig. 11) and more shives were still attached to the fibre bundles after decortication (Table 3). These results and observations are also quite consistent independently of the blocks B1, B2 and B3 analysed (Fig. 11). Based on the knowledge and observations obtained by this evaluation concept using the new introduced κ-values, more intense analysis and investigations can be carried out. The realised concept allows us to get deeper insights into the decortication process and to analyse and characterise different hemp varieties by using the proposed characteristic values (Eqs. (1)–(7)). For example, the initial decortication efficiency is a characteristic value of the process. This value is influenced by the variety and agronomic factors and is related to the shives content after the decortication, which normally is considered as a characteristic value of the stem material. Comparing the characteristic values stem shape factor and energy consumption (Fig. 11), stems of more cylindrical shape consumed a little more energy than conical stems.
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