The atmospheric conditions and other facilities to rear silk filaments are good in Ethiopia. In Awassa, Awash Melkassa, and Kombolcha silk rearing is started with good progress. The quality of the cocoons produced in the country is not determined in relation to commercial silk produced in major silk producing countries. So far there was no information available about the basic properties of silk filaments produced. In this research paper, the different physical properties of the eri and mulberry cocoon and their filaments were evaluated. Eri cocoons have shell ratio of approximately 14%, average fiber fineness of 3 dtex, and average weight of 3.2–3.3 g, while mulberry cocoons have raw silk ratio of 13-14%, average fiber fineness of 2 dtex, and average weight of 1.5 g. Even though the method of rearing, handling, and harvesting of the cocoons is poor, the physical properties of the silk produced in Ethiopia fall within the limits of commercial silk produced in major silk producing countries.
Silk is very soft, lustrous, smooth, strong, and durable than any natural or artificial fiber. The industrial and commercial uses of silk contributed to the silkworm promotion all over the world especially in developing nations [
Ethiopia’s bimodal rainfall pattern, ambient temperature, and other agro-ecological factors provide a fertile ground for mulberry and caster seed cultivation and silkworm production [
According to sericulture training guide report (2005), considerable quantity of dried cocoons, over 3000 kg, was produced both by farmers and investors from which 95% was marketed to Addis. According to Sabahar yearly report, currently the silk production in Ethiopia has increased by almost 200% since 2014. Today, Sabahar, the pioneer of local silk, is the only company in the country which produces textiles made of Ethiopian silk for export. Silk products produced in Ethiopia are organic by nature as the plantation for rearing uses natural fertilizers [
The favorable conditions of silkworm rearing; rapidly expanding production of silk in the country and the need of organic materials in the world will surely increase the export potential and local utilization of silk. However, so far there are no postcocoon facilities and no information available about the basic properties of silk filaments produced [
Unless basic properties such as silk fineness, cocoon weight, shell ratio, cleanness, and uniformity are known, it will be impossible to market such silk or even to go ahead for further value addition through reeling and weaving. The success of this work largely depends on characterizing its silk cocoon in terms of fiber properties as well as laying a foundation for further processing such as reeling and twisting.
In this paper, the different physical properties of the eri and mulberry cocoon and their filament were evaluated. Even though the method of rearing, handling, and harvesting of the cocoons is poor, the physical properties of the silk produced in Ethiopia fall within the limits of commercial cocoons produced in major silk producing countries.
Samples of eri cocoons were collected from Bahir Dar, Awassa, and Awash Melkassa while samples of mulberry cocoons were collected from Awassa and Awash Melkassa. Longitudinal appearance, silk percentage, fiber fineness, moisture regain, cocoon weight, and quality of cocoons were analyzed using ASTM standard method.
Longitudinal appearance of the filaments was studied under projection microscope with magnification power of ×125 and ×250 with mounting media of liquid paraffin.
Two-pan cooking method was used for reeling by manipulating time and temperature within 45–98°C. Alkali gum removal method was used to degum the filaments. 5% sodium carbonate, 1 : 20 material to liquor ratio, 98°C temperature of cooking, and 2 hours of degumming were used during degumming.
Weight of cocoons, shell, and degummed filaments was measured using electronic weighing balance and appropriate proportions were calculated. Broken filaments were taken from outer layer; filaments were degummed and their linear density was measured on vibroscope (fineness testing machine) with appropriate loads of 200 mg–400 mg for eri silk, while for mulberry silk the filament of 25 m length was taken on the outer layer during reeling. Filaments were degummed and weighed. Linear density was calculated.
Moisture content of the fiber was analyzed by SDL Rapid Regain Tester and weighing balance. Ten samples, each weighing 10 gm, were prepared from each type and origin. The oven was heated until the temperature rose to 105°C. One sample was inserted in the oven and its weight was measured after 25 minutes. This was done repeatedly till the weight loss is less than 0.05%. This is taken as dried sample and moisture content was measured.
Sorting of quality cocoons was made by observation. During observation the quality of dirty/impurities, degree of whiteness, size of the cocoon, and hardness of the cocoon were taken into consideration. Those cocoons with defects and with fewer defects are differentiated.
When fiber is observed under microscope it is smooth in surface and profile, and sometimes nodes appear. The eri filament is more irregular than mulberry silk. Undegummed eri cocoons are grey, while mulberry silk varies from grey to yellow as shown in Figures
Cocoons: (a) mulberry and (b) eri.
Degummed silk filaments: (a) mulberry and (b) eri.
10 samples, each weighing nearly 200 grams, were prepared; pupa was separated from the cocoons and shell weight was measured for eri cocoons. Mulberry cocoons were degummed after reeling. Average weights of cocoon, shell, and raw silk were taken as shown in Tables
Shell percentage of eri cocoon.
Sample of eri silk | Cocoon weight (gm) | Shell weight (gm) | Shell percentage (%) |
---|---|---|---|
Awash Melkassa | 200.8 | 29.5 | 14.2 |
Bahir Dar | 200.2 | 26.8 | 13.4 |
Awassa | 201.0 | 27.7 | 13.7 |
Silk percentage of mulberry cocoons.
Sample of cocoon | Cocoon weight (gm) | Weight of filament (gm) | Raw silk percentage (%) |
---|---|---|---|
Awash Melkassa | 68.3 | 9.7 | 14.2% |
Awassa | 36.4 | 4.5 | 12.9% |
As can be seen from Tables
Raw silk ratio varies with breed of silk worms and care taken in rearing and mounting. It also varies with the age of cocoons. The trend observed by K. Subramanianan, N. Sakthivel, and S. M. H. Qadri shows that South Indian eri cocoons shell percentage ranges from 10 to 15% [
Broken filaments were taken from the outer layer of eri cocoons and linear density was measured on vibroscope after degumming. The filament of 25 m length was taken from outer layer of mulberry cocoons during reeling. Filaments were degummed and weighed. Linear density of the filaments was calculated. The distribution of linear density in dtex is shown in Figures
Fiber fineness distribution in dtex of eri silk from Bahir Daar, Awassa, and Awash Melkassa.
Fiber fineness distribution in dtex of mulberry silk from Awassa and Awash Melkassa (note: frequency: number of times it has occurred).
The fiber fineness distribution of eri and mulberry cocoons of all places is shown in smoothened curves in Figures
Silk worm varieties are many and the filaments they produce are also diverse in characteristics. Even in the same species, the filaments they produce vary because the environmental conditions and the host plant they could use are different. Fineness of silk fiber varies from 1 dtex to 5 dtex depending on type and place of fibers, while eri and mulberry silk takes fineness ranges of 1 dtex to 3 dtex [
Sample of cocoons was randomly selected for all types of cocoons. Individual cocoons of the samples selected were weighed on precision weighing balance in grams. The distribution of cocoon weight is given in Figures
Distribution of cocoon weight in grams for eri silk fiber from Bahir Dar, Awassa, and Awash Melkassa.
Distribution of cocoon weight in grams for mulberry silk fiber from Awassa and Awash Melkassa.
Figure
Cocoon weight of pure breed mulberry varies from 1.5 to 2 g. Eri silk produced in major silk producing countries varies from 2.5 to 3.5 [
Cocoons were degummed before moisture analysis. Ten samples of degummed fibers from each type and origin were prepared. Each sample was heated repeatedly in oven dryer till the weight loss is less than a difference of 0.05%. Average value of the regain percentage is given for each type of samples as shown in Table
Percent moisture regain of the various silk types.
Fiber type | Origin | Initial weight (g) | Average final constant weight (g) | % regain |
---|---|---|---|---|
Eri silk | Awassa | 10.00 | 9.05 | 10.50 |
Bahir Dar | 10.00 | 9.10 | 9.93 | |
Awash Melkassa | 10.00 | 9.15 | 9.79 | |
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Mulbery | Awasa | 10.00 | 9.30 | 8.50 |
Awash Melkassa | 10.00 | 9.25 | 9.10 |
The moisture regain at standard conditions of eri silk was approximately 10% while mulberry silk was approximately 9% [
Mulberry raw silk fiber has a moisture regain of 11%, which reduces to about 9% after degumming (at standard atmospheric conditions, 27°C and 65% RH). This is due to the removal of much hygroscopic sericin from the raw silk fiber during the degumming process. Eri silk fibers have about 10% moisture regain values [
200 gram of cocoon was randomly taken for all types of cocoons. Sorting by manual observation, good quality cocoon and poor quality cocoons were identified. Any defected cocoons, having difference in color, or being smaller in size were considered as poor cocoons. By measuring the sorted samples percentage values were obtained. This was made five times and average values of good and poor quality cocoons were calculated as shown in Table
Percentage of good quality cocoons for the various types of cocoons.
Fiber type | Origin | Good quality cocoons in % |
---|---|---|
Eri silk | Bahir Dar | 52 |
Awassa | 64 | |
Awash Melkassa | 60 | |
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Mulberry silk | Awassa | 68 |
Awash Melkassa | 65 |
As per the guidelines of sorting given, Table
The poor quality cocoons could be due to the weak method of rearing, handling, and harvesting of the cocoons in these harvesting areas. All the places use traditional houses for rearing and simple wooden/timber/frames with corn stalk ribs for rearing stages in uncontrolled conditions. They also do not follow a regular leaves feeding but rather provide leaves to worms irregularly. Feed efficiency affects quality of cocoons produced.
Even though the method of rearing, handling, and harvesting of the cocoons is poor, the quality of cocoons produced in Ethiopia is in the range of commercial silk produced in major silk producing countries. The shell percentage of eri cocoons is nearly 14% for all the places, while raw silk ratio of mulberry is bout 13-14%. The mean value of the fiber fineness for eri silk is 3.09 dtex from Bahir Dar, 2.91 dtex from Awassa, and 3.11 dtex from Awash Melkassa, while fineness for mulberry silk is 2.1 dtex from Awassa and 2.4 dtex from Awash Melkassa. The mean cocoon weight of eri silk is 3.23 g for Bahir Dar, 3.28 g for Awassa, and 3.22 g for Awash Melkassa cocoons while cocoon weight of mulberry silk is 1.55 g for Awassa and 1.52 g for Awash Melkassa cocoons. More than 60% of the cocoons observed are good. If proper rearing and handling of cocoons are used, it is possible to produce higher quality cocoons.
The authors declare that they have no conflicts of interest.