How to calculate Lycra percentage in Elastic Core Spun Yarn

Md. Bashar Uddin 
Lecturer, Department of Yarn Engineering, Bangladesh University of Textiles 

Core Spinning: Core spinning is a process by which fibres are twisted around an existing yarn, either filament or staple spun yarn, to produce a sheath-core structure in which the already formed yarn is the core. The production of Core-spun yarns are done successfully by most of the spinning system with or without any additional attachments.

Lycra calculation | Texpedi.com

Core spun yarn: Core-spun yarns are two-component structure with Core and sheath. Generally continuous filament yarn is used as core and the staple fibres are used as sheath covering. The core-spun yarns are used to enhance functional properties of the fabrics such as strength, durability and stretch comfort.

Incorporating core part within the resultant yarn structure makes the yarn cheaper, stronger and qualified. Besides, sheath fibers conserve the traditional appearance, handle and comfort properties. It is exemplified as using cotton covered elastic (spandex/lycra) core-spun yarn is a good example to enable free movements and at the same time provide higher fabric comfort with cotton in the yarn structure.
Core spun yarn production in ring frame with additional attachments
Core spun yarn production in ring frame with additional attachments

Elastane/Spandex/Lycra: Lycra is a product of DuPont for spandex fiber. It is a polyether-polyurea copolymer that was invented in 1958 by chemist Joseph Shivers at DuPont's Benger Laboratory in Waynesboro, Virginia. Lycra® is a trademark and Brand name of DuPont Company. Spandex is synonyms of elastane fiber. Spandex or elastane specify properties of fiber (rubber like stretchable) those are used in skin tight clothes such as swimsuits, jeans, sports wears etc. There are other companies who also manufacture spandex fibers. So, there is no technical difference in between Lycra and Spandex. Both Lycra and Spandex are same. Spandex is the generic name of a fiber and Lycra is spandex product of DuPont company.

Elastic core spun yarn: Elastic core-spun yarn which is used as weft yarn for textile fabrics (e.g. denim) gained great importance in the last decade due to the fact that stretch and recovery, comfort fits and flexibility properties. Elastic (spandex/lycra) percentage plays an important role on physical, dimensional, and mechanical properties of the final products. Fabric properties will vary based on what percentages of elastane (spandex) are used in the yarn. So, it is very important to study on the calculation procedure of lycra percentage in core spun yarn.

Example: We want to produce a 50 Ne elastic core spun yarn where lycra is used as core and cotton is used as sheath material. Linear density of lycra is 70 Denier and lycra tension draft is 3.25. Now, find out the lycra% & cotton% in resultant elastic core spun yarn?


Structure of an elastic core spun yarn
Structure of an elastic core spun yarn

Solution: 
>>Cotton Covered Lycra Yarn (Elastic Core Spun Yarn), Resultant Yarn (N)= 50 Ne = 5314.9÷50= 106.298 D. 
>Input Lycra filament= 70 D. 
>Lycra tension draft= 3.25 

We know, Draft= Input Count (Den)/Output Count (Den) 
>Lycra count in output (Resultant Yarn), N1= Input lycra filament count÷Lycra tension draft. 
>N1= 70÷3.25= 21.538 D. 
>> Lycra count in output (Resultant Yarn), N1= 21.538 D.

Again, we know, N= N1 + N2 (Direct System) 
>>106.298= 21.538+N2 
>>N2= 106.298-21.538= 84.760 D. 
>>Cotton yarn count in output (Resultant Yarn), N2= 84.760 D. 
>>Lycra% in Resultant Yarn (Core Spun Yarn) = [21.538/(21.538+84.760)]×100%= 20.26% 
>>Cotton% in Resultant Yarn (Core Spun Yarn) = [84.760/(21.538+84.760)]×100%= 79.74%

Or, 
Cotton Covered Lycra Yarn (Elastic Core Spun Yarn), Resultant Yarn (N)= 50 Ne. 
Input Lycra filament= 70 D = (5314.9÷70) = 75.927 Ne. 
>Lycra tension draft= 3.25 

We know, Draft= Output Count (Ne)/Input Count (Ne) 
>Lycra count in output (Resultant Yarn), N1= Lycra tension draft × Input lycra filament count. 
>N1= (3.25×75.927) Ne = 246.763 Ne= (5314.9÷246.763) = 21.538 D. 

Again, we know, 1/N = 1/N1 + 1/N2 (Indirect System) 
>> (1/50) = (1/246.763) + (1/N2) 
>>Cotton yarn count in output (Resultant Yarn), N2= 62.705 Ne.= (5314.9÷62.705)= 84.760 D. 
>>Lycra% in Resultant Yarn (Core Spun Yarn)=[21.538/(21.538+84.760)]×100%= 20.26% 
>>Cotton% in Resultant Yarn (Core Spun Yarn)= [84.760/(21.538+84.760)]×100%= 79.74%. 

Shortcut Method:
1. Lycra%= [(Lycra denier/lycra draft)/Resultant yarn denier] × 100%
2. Lycra%= [(Lycra denier/lycra draft)/5314.9/Resultant yarn Ne] × 100%
3. Lycra%= [(yarn count (Ne) × lycra denier)/(5314.9 × lycra draft)] × 100℅.


References: 
1.https://www.fibre2fashion.com/industry-article/1764/production-and-properties-of-core-spun-yarns 
2. Balasubramaniam, Properties of core spun yarns-Journal of Textile Institute T534-61-1970 
3.https://www.onlineclothingstudy.com/2013/06/what-is-difference-between-lycra-and.html?m=1 

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