Cotton fibre terms

By all means, the raw material is very important for good quality yarn. The following cotton fibre definitions are very important

1.  Length
2. Uniformity
3. Short fibres
4. Strength
5. Elongation
6. Fineness
7. Maturity
8. Colour and colour grade
9. Also, trash

Fibre length

The first and most important cotton fibre definition is length. So, the length of fibre is measured in different ways. Hence, normally called staple length.

Span length 2.5% (SL 2.5%)

(by ICC Mode)

Basically, the length of longer 2.5% fibre extended from the fibrous strand. The optical sensor of the fibro graph scans the randomly arranged stand of fibre until 2.5% of the fibres are counted and given as S.L 2.5%. Also, the greater the value better spinnability, yarn evenness, strength, lustre and hairiness.

Sapin length 50% similarly measured the length of longest 50% fibres is termed as span length 50%

Span length 2.5%
Under 20.5mm(3/16”)	Short
20.5mm(3/16”)  to 25.4mm(1”)	Medium
1  1/32”(26.2mm) to 1  3/32”(27.8mm)	Medium long
1  1/8” (28.6mm)to 1  5/16”(33.3 mm)	Long

 Upper half mean length (UHML)

(HVI mode)

UHML is the average length of the upper half of the longest fibres when measured on a weight basis i.e. average length of the longest fibres.

i.e. Mean length (ML)

HVI mode

Mean length is the average length of all fibres in the test specimen basically based on weight length data

• A span length of 2.5% is the basis of the drafting roller setting. it is a reference to the shortest distance between roller nips so that a few fibres are broken at this length. Normally S.L 2.5% is the setting distance but some technicians tend to set the roller gauge as (10+SL2.5%) mm as the best value.
• Also, a span length of 50% is a more valuable parameter for determining spinning performance and yarn quality.
• Altogether, a span length of 67% is considered the average length of the fibre and a greater value shows a strong increase in yarn.

Relationship between span length of 2.5% and UHML

Since the span length is measured in ICC mode and UHML is measured in fibre length in USDA HVI mode. Generally, both are measures of the longest fibre length in cotton.

Normally UHML is 0.040~0.080″ higher than the span length of 2.5%

Relationship between span length 50% and mean length ML

The mean length of a fibre measured in USDA HVI mode is 0.4~0.5″ higher than 50%span length. Since the calculation of both methods ICC and HVI (USDA) is different entirely, there is no way to convert any length result between them.

So, to properly understand  see the fibro graph and two different theories of length calculation

Uperhalf mean length (UQL)

(by AFIS)

 

Basically, 2.5% fibres measured by AFIS individualizer is termed as UQL.

Thus length calculation per ICC mode

i.e. ICC =international cotton calibration

Also, 100% is considered zero

i.e. length calculation in USDA mode

i.e. USDA = United States Department of Agriculture

(Called also HVI mode)

HVI spectrum standards

Upper half mean length

Less than 0.99″	Short
0.99~1.10″	Medium
1.11~1.26″	Long
Above 1.26″	Extra long

Uniformity index

Less than 77	Very low
77~80	Low
81~84	Medium
85~87	High
above78	Very high

Short fibre index

Less than 6	Very Low
6~9	Low
10~13	Medium
14~17	High
18~above	Very High

Strength GPT gram/tex

Less than 21	Very weak
22~24	Weak
25~27	Medium
28~30	Strong
31 ~above	Very strong

Following here are other cotton fibre definitions,

Uniformity

It is measured variation of length i.e. how much uniform distribution of fibre lengths, in fibrogram.

Uniformity ratio (UR%)

Basically, the uniformity ratio between span length is 50% and span length 2.5% expressed as a percentage. So, a higher value indicates there are lesser short fibres and more regularity in length. As a result, the better the value better is spinnability.

i.e.    U.R%= S.L 2.5%/S.L 50%x100

Uniformity Index (UNF) UI

Basically, it is the ratio of mean length to UHML and is a measure of fibre uniformity in the sample expressed as a percentage. Thus UNF is expressed as

i.e. UI= M.L/UHML x 100

i.e. ratio of the average length of all fibres to the average length of the longest fibres. Altogether, lesser value makes processing more to lower the quality of the product.

Relationship between UR% and UI

Generally, there is no confirmed relationship between the two parameters. So,

i.e. UI= 1.80 x U.R%  or    UI  = 1.70x U.R%

Short fibres

Those fibres which are shorter than half of the fibre length are called short fibres

Short fibre index (SFI)

By ICC mode, By HVI mode

SFI is a value that is calculated using a sophisticated algorithm. Also, the fibro gram is mathematically converted to a length distribution curve. Thus SFI is an indication of the number of fibres (%) that are less than 0.5″ or 12.7mm in length. So it correlates very well with AFIS SFC(w).

Short fibre content (SFC)

By AFIS

SFC is the percentage of fibres less than 0.5 inches by weight. Generally, AFIS measure SFC(w) and SFC(n).

In most spinning cases short fibres percentage by weight is considered but SFC by number is also important because it is believed that the number of short fibres is more important than weight.

Floating fibre percentage (FF)

As can be seen, those fibres which are not in control of drafting rollers are considered floating fibres. Thus, these fibres tend to deteriorate drafting.  At this point, resulting in thick & thin places. Also, as low the percentage it better will be drafting and spinnability.

The floating fibres percentage can be calculated as 

Hence, FF %age ={S.L2.5%/(S.L50%-0.075)²-1}X 100

Similarly in HVI mode and AFIS.

Floating fibre index

Hence, FFI=(UHML/ML-1)X 100

Also, FFI =(UQL/ML-1)X 100

Strength

Pressley is the fibre bundle strength expressed in thousand ponds/inch² while GPT is the breaking tenacity of fibres in grams per tex. Furthermore, good fibre strength results in better yarn strength.

A 1/8″ clamp is generally used to measure strength when a 1/8″ clamping distance is used fibre break at weak points and with a 0″ clamp they break with more force thus 1/8″ clamp gives correct results.

If you are using HVI then it will automatically give you a GPT value.

With stelometer ICC mode.

Hence, gram/tex=breaking load in kg/mass in milligram x 14.9

Also, Presslay= Break load in kg/mass in milligrams x 64.368

Also, P.I=breaking load in ponds/ milligrams.

Hence, exactly gram/tex= P. I  X 6.8

Strength ponds/ inch2 x1000(PSI)
75~80	low
81~85	Average
86~90	High
91 and above	Very high

Elongation percentage

The extent to which fibres bundle elongate before breaking. Lesser value results in poor strength and more value results in imperfections, so optimum value is required.

Fineness and maturity

Micronair is the measure of fibre’s linear density i.e. weight per unit length of fibres. (Also called microgram per inch). It is also expressed as milli-tex.

Basically, the degree of secondary wall development of cotton fibre has termed the maturity of cotton. Hence, a cotton fibre with 50~80% secondary wall developed is considered as mature, 30~40% immature and below 25% dead cotton. Thus the ratio between mature and dead cotton is called the maturity ratio. Thus technically

Fibre with more than 0.5 circularity/ fibre with 0.25 circularity

Also, the maturity and fineness of cotton are very important for yarn spinnability, the strength of the fabric and dying. Fibres with lesser micronair value are usually unripened with lesser maturity and result in poor strength, more hairy yarn, neps formation poor quality yarn, Also immature fibre cause varying yarn dyeability and white spots

Similarly, course fibres are not suitable for the fine count due to the lesser number of fibres in the yarn cross-section. Also, the normally good range is 4.0~4.8 mice and 0.9 ~0.95 maturity

Immature fibre content   ( IFC percentage)

Fibre with less maturity is very bad for yarn quality. thus fibre with 0.25  circularity is called immature fibre and %age is termed IFC %. The value of IFC should also be as low as possible.

i.e. IFC< 5.0%

Neps count per gram

Basically, immature fibre results in the formation of entangled knots of fibres termed nep. Hence, the number of these entangled knots per gram of fibre sample is called nep count/gram i-e lesser neps better will be imperfections.

Elongation

Less than 5.0	very low
5.0~5.9	low
6.0~6.7	medium
6.8~7.6	high
7.7~above	very high

Micronair

Less than 3.0	Very fine
3.0~3.6	Fine
3.7~4.7	Medium
4.8~5.4	Course
5.5~above	Very Course

Maturity index

Less than 0.75	Very immature
0.75~0.85	Immature
0.86~0.95	Mature
Above 0.95	Very mature

Neps/gram

Less than 100	Very low
101~200	Low
201~300	Medium
301~450	High
Above 450	Very high

Above all spinning cotton fibre definitions, need to understand before running fibre.

Trash

It is measured  as the amount of non-lint materials in cotton, such as leaf and bark from the cotton plant

Instruments used for classing/grading cotton

HVI

High volume instrument measures (HVI) trash or non-lint content by using cameras, made by Uster technologies. The increasing number of fibre measurement trends is provided to a set of instruments that can be analysed on the computer and can print results. HVI measure the most important fibre classing/grading properties that are high throughput results in spinning mills.

The trash is measured by using a video camera while micro-nair is measured by using air flow through the sample and the remaining parameter is measured by fibrograph. The system is capable of measuring 180 samples per hour.

The following characteristics can be measured by using an HVI instrument.

HVI Spectrum measurement
i	Spinning consistency index	SCI
ii	Micro-naire	Mic
iii	Maturity index	Mat
iv	Upper half mean length	Len
v	Uniformity index	Unf
vi	Short fibre index	SFI
vii	Strength	Str
viii	Elongation	Elg
ix	Moisture	Moist
x	Reflectance	Rd
xi	Yellowness	+b
xii	Colour grade	CG
xiii	Trash count	Tr Cnt
xiv	Trash area	Tr Area
xv	Trash grade	Tr Grade
xvi	Fluorescence	UV
xvii	Neps	Nep

 

AFIS

An advanced fibre information system is used to measure special neps in cotton. There are modules one are measuring the number of neps and the second one is used to measure the length and fibre diameter. This device work on aero-mechanical principles.

The following characteristic of fibre can be tested by using this instrument.

AFIS measurement
i	Fibre length	L(w) & its CV%
ii	Upper quartile length	UQL(w)
iii	Length(by number)	L(n) & its CV%
iv	Short fibre content	SFC(n)
v	Short fibre content	SFC(w) <0.5%
vi	Fibre length 2.5%	UQL 2.5%
vii	Fibre length 5%	UQL 5%
viii	Fine mtex	F mtex
ix	Immature fibre content	IFC%
x	Maturity ratio	Mat ratio
xi	Neps (diameter)	Nep(um)
xii	Neps (number)	Ct/gram
xiii	Seed coat neps(diameter)	SCN(um)
xiv	Total neps	Cnt/gram
xv	Nep mean size	Mean size
xvi	Dust	Dust Cnt/gram
xvii	Trash	Trash Cnt/gram
xviii	VMF%	VMF%