ISO/DIS 21235

ISO/TC 38/SC 23

Secretariat: SAC

Date: 2025-12-12

Textiles — Determination of pure cashmere content in raw cashmere — Near infrared spectrometry

DIS stage

© ISO 2025

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Contents

Foreword iv

Introduction v

1 Scope 1

2 Normative references 1

3 Terms and definitions 1

4 Principle ^[3][4] 1

5 Apparatus reagents 2

6 Sample preparation 2

6.1 Sampling from raw cashmere lot 2

6.2 Preparation of scoured cashmere sample 2

6.3 Test specimen preparation 3

7 Preparation of NIR spectrometer 4

7.1 Installation requirements 4

7.2 Calibration and validation 4

7.3 Start up 4

8 Test procedure 4

8.1 Reference spectrum collection 4

8.2 Absorbance spectrum collection 4

8.3 Pure cashmere content of the scoured cashmere sample 5

8.4 Calculation and expression of pure cashmere content of raw cashmere 5

9 Precision 5

10 Test report 5

Annex A (informative) Calibration and validation 7

Annex B (informative) Method of determining reference values 10

Annex C (informative) Precision 12

Bibliography 14

Foreword

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Introduction

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Textiles — Determination of pure cashmere content in raw cashmere — Near infrared spectrometry

This document specifies a test method for determining pure cashmere content of raw cashmere by means of near infrared spectrometer.

This document is applicable to testing of pure cashmere content of raw cashmere by different collection methods, it is also applicable to scoured cashmere.

The following documents are referred to in the text in such a way that some or all of their content constitutes requirements of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.

ISO 3074, Wool — Determination of dichloromethane-soluble matter in combed sliver

ISO 6741-1, Textiles — Fibres and yarns — Determination of commercial mass of consignments — Part 1: Mass determination and calculations

For the purposes of this document, the following terms and definitions apply.

ISO and IEC maintain terminological databases for use in standardization at the following addresses:

• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp

raw cashmere

unprocessed hair/cashmere fibre taken from double-layered cashmere goats that are predominated by undercoat fine down fibre with trace amounts of natural impurities

scoured cashmere

cashmere met specific quality requirements after scouring process

pure cashmere content

percentage of cashmere down in the lot sample on weight basis reported at IWTO DRAFT TM-45 17% regain and 1,5% ISO 5162 residual grease content

Near infrared spectrum (NIRS) is one of substance’s attributes which can reflect its composition information at molecular level. A calibration equation relating the NIR absorbance to the pure cashmere content in raw cashmere is established through multivariate regression techniques (employing linear or nonlinear models as appropriate). The pure cashmere content of an unknown raw cashmere sample is thereby predicted by applying its acquired NIR spectrum to this calibrated equation.

Near infrared spectrometer, with a wavelength range of approximately 1000 nm to 2500 nm (or a wave number range of approximately 10000 cm^-1 to 4000 cm^-1), a wavelength accuracy of 0,1 cm^-1@7181,68 cm^-1, a spectral resolution of 2 or 4 cm^-1, and an intensity accuracy of 0,1 T%.

Multivariate software, with the following basic functions: establishing and editing calibration and validation sample sets. The main data preprocessing methods are first derivative and centering, but are not limited to Vector Normalization, Savitzky–Golay smoothing, Savitzky–Golay derivation, Standard Normal Variate (SNV), Multiplicative Scatter Correction (MSC), Extended Multiplicative Scatter Correction (EMSC), Partial Least Squares (PLS), Orthogonal Signal Correction (OSC), and External Parameter Orthogonalisation (EPO), etc., which are related to the selected multivariate calibration methods. Using multivariate analysis methods to correlate the spectra with pure cashmere content, establishing and validating the multivariate calibration model, and then according to the calibration model, using the spectrum of the sample to be tested to predict its pure cashmere content based on the model.

A rotary cup, accessory with a minimum capacity of 10 g cashmere.

Balance, with a minimum scale value of 0,01 g.

Scouring equipment, a scouring bowl with effective capacity of 10 L or more, or that can meet the testing requirements, equipped with double-layer copper screen bed (100 mesh/25 mm) and proper draining system.

Centrifuge, synthetic fibre bag for dehydration use.

Drying oven.

Non-ion type detergent.

Lens wiping paper, cleaning fabric, etc.

Sampling proportion and quantity

Take from each of the bales if the lot size is equal to or less than 20. Take 30% of the increased amount to that of more than 20 bales in a lot. For those unpacked cashmere, count 50 kg as one bale. Less than a bale is counted as one bale. Total sampling mass shall not be less than 2 kg.

Preparation of lot sample

Unpack the bale and draw samples randomly from the middle and another random part of the sampling bale deeper than 15 cm or more from bale surface. Total sample quantity shall not be less than 2 kg. Lot sample shall be put into sealed container immediately after sampling and weigh within 4 h, record as m_a.

Open the lot sample container to blend the sample homogeneously by hand tearing or machine, foreign matters, dirt and dust scattered outside were discarded, collecting all cashmere fibres and weigh together, record as m_b.

Calculate K value according to Formula (1), round off to 4 decimal places. K value shall be sealed and kept together with lot sample.

(1)

where

K is the factor;

m_b is the mass of sample after opening, in gram(g);

m_a is the mass of sample prior to opening, in gram(g).

Draw 3 laboratory samples from the lot sample, the mass for each laboratory sample is 150 g × K [determined by Formula (1)], accurate to 0,1 g. The 3 laboratory samples are scoured under the conditions given in Table 1.

Table 1 — Conditions of scour process

Put each of the three laboratory samples into synthetic fibre bag to dehydrate with hydro-extractor, drying to absolute dry weight according to ISO 6741-1 after hydro-extraction, record as m_i.

Calculate scoured cashmere content according to Formula (2) as follows. Take the mean value of the results from the 3 laboratory samples as the result of scoured cashmere content.

(2)

where

Y_i is the scoured cashmere content of each of laboratory samples (i=1,2,3), %;

m_i is the oven-dry mass of each of the scoured sample(i=1,2,3), in gram (g);

R_s is the conventional moisture regain of scoured cashmere, %, R_s=15;

150 is the mass of fibre equivalent to raw cashmere sample drawn from the opened and mixed samples, in gram (g).

Take the average of the results as the scoured cashmere content of the raw cashmere, record as Y.

Put all the scoured and dried laboratory samples on the test stand, rapidly and fully mix them, to obtain scoured cashmere sample. Then the scoured cashmere sample is divided into two equal parts by bisection method, of which one part serves as laboratory sample, and the other as reserved sample.

Tear and mix the laboratory sample evenly. After guard hair and cashmere in the sample are fully mixed in an even state, 10 test specimens are prepared by multi-point method, with the mass of each test specimen being about 10 g.

Before spectral collection, the specimen shall be dried at 105°C for 20 minutes. However, this method is not exclusive, and alternatives include using spectral preprocessing to eliminate moisture interference.

The spectrometer shall be installed in a clean, no vibration environment with a room temperature and humidity not greater than 40%. The equipment shall be equipped with an uninterruptible power supply.

Calibration involves the comparison with a reference and adjustment processes to the instrument.

Calibration samples shall encompass as wide a range of variation as is feasible. It is important to have a sufficient number of representative samples, such as cashmere from different breeds of goats.

No specific procedure can be given for calibration, because a number of different calibration systems can be applied with NIR instruments. Calibration methods can be seen in Annex A or, with reference to manufacturer’s manual. The calibration model for pure cashmere content can also be developed referring to ISO 12099.

Calibration data set shall then be extended to widen the sample population over a period of time, to allow the calibration to develop in line with any changing characteristics of the source material or treatment processes. Unless the software utilised by the instrument allows 'outlier' spectra to be identified during measurements.

The instrument shall be validated against samples that have not been used in calibration prior to use, especially if there has been a long period of time between uses. If the instrument is frequently used, periodic calibration can be performed. The validation shall be monitored by testing at least 10 subsamples for which results have been obtained by the reference methods, and the laboratory shall retain up-to-date records for quality control checks.

The set of samples shall be carefully analysed following the reference methods, see Annex B.

Turn on the instrument and preheat it for approximately 30 minutes. Set the number of co-adds per spectrum to no less than 32. Load the calibration model for pure cashmere content in raw cashmere. Clean the inner and outer surfaces of the quartz glass window of the rotating sample cup with lens cleaning paper.

Before absorbance spectrum collection of a specimen, a single beam spectrum as the reference spectrum is collected by a standard diffuse reflection plate according to the set spectral acquisition parameters. Only one reference spectrum is needed for the collection of the three spectra.

Tear and mix specimen evenly just before testing.

Before absorbance spectrum collection, the empty rotary sample cup shall be cleaned with lens wiping paper to ensure that both the inner and outer surfaces of the cup window glass are clean.

Fill the rotating sample cup completely with the test specimen, cover it with the equipped screw-and-spring lid to reduce the rebound of cashmere, and place it on the rotating accessory of the spectrometer. Then the absorbance spectrum of the test specimen is collected according to the set spectral acquisition parameters.

Repeat step 8.2.3 two additional times using the same test specimen. A total of three absorbance spectra are obtained for the specimen. If the standard deviation of the absorbance intensity of the spectra is less than or equals to 0.005 A at any wavelength, the average of the three spectra is used as the absorbance spectrum of the specimen. Otherwise, the spectrum acquisition is to be repeated.

The pure cashmere content of the test specimen is calculated using its absorbance spectrum in accordance with the calibration model.

For each lot sample, at least 6 specimens are tested according to 8.3.1. When the range of their results is not more than 3%, take the average of the readings as the pure cashmere content of the scoured cashmere, record as P_m.

If the range of their readings exceeds 3%, the reading with the largest deviation is deleted as a suspect reading. If the range of the remaining readings is less than or equal to 3%, the suspect reading is discarded as an outlier and take the average of the remaining readings as the result of the scoured cashmere. If the range of the remaining readings still exceeds 3%, retain all the readings and test 4 additional test specimen, take average of the total readings as the result of the scoured cashmere.

Calculate pure cashmere content according to Formula (3):

(3)

where

P is the pure cashmere content, %;

P_m is the pure cashmere content of scoured cashmere, %;

Y is the scoured cashmere content, %.

The 95% Confidence Interval information are given in Annex C.

The test report shall include at least the following information:

1. nature of the sample (e.g. raw cashmere);
2. identifier and size of the test lot (e.g. Lot number and number of bales);
3. the pure cashmere content as a percentage rounded to the nearest 0,1%;
4. quality labelling code of each lot of raw cashmere;
5. test apparatus and its model number, acquisition parameters, model details(e.g. preprocessing chain, Confidence interval );
6. temperature and humidity of test condition;
7. any deviation from the specified procedure;
8. test date(s);
9. test operator(s).
10. 
    (informative)
    
    Calibration and validation
    1. Establishing of calibration set

Collect a batch of raw cashmere samples as a calibration set, which should cover the samples to be tested in terms of the composition range and origin. The number of different samples in any one percentage interval of pure cashmere content shall not be less than 7. Wash the samples refer to the scouring method in Annex B. Collect the near-infrared absorption spectra of the scoured cashmere samples using the provisions of Clause 7 and Clause 8 of this document. After collection of the spectra of the scoured cashmere samples, test their pure cashmere content as the reference values refer to Annex B as soon as possible.

The calibration sample set is composed of the near-infrared absorbance spectra and reference value data of the scoured cashmere samples of the calibration set (completed through multivariate analysis software).

• 1. Establishing of validation set

Collect several raw cashmere samples independent of the calibration set as the validation set, which should cover the samples to be tested in terms of the composition range and origin. Take one sample from every 5 percentages interval of pure cashmere content in the calibration set. Wash the samples refer to the scouring method in Annex B. Collect the near-infrared absorption spectra of the scoured cashmere samples using the provisions of Clause 7 and Clause 8 of this document. After collection of the spectra of the scoured cashmere samples, test their pure cashmere content as the reference values refer to Annex B.

The validation sample set is composed of near-infrared spectra and reference value data of the scoured cashmere samples of the validation set.

• 1. Pretreating spectra

Before building model, first-order derivative, second-order derivative, and multiplicative scattering correction can be used alone or in combination to process the spectrum and reduce the impact of spectral baseline drift on performance of calibration model. The band selection method can be used to eliminate the influence of moisture change on the spectrum; The spectral bands involved in building model can be selected based on the correlation coefficient curve between the pretreated spectra and the pure cashmere contents. The pre-treatment methods is not limited to the methods mentioned above. (completed through multivariate analysis software)

• 1. Establishing of calibration model
     1. Quantitative Model

Adopt one multivariate analysis method (Partial Least Squares, Support Vector Machine, etc. but not limited to the above methods) to correlate the spectral matrix composed of pretreated spectra of the calibration set with its corresponding vector of pure cashmere content. Use the Leave-One-Out Cross-Validation method for internal cross-validation to establish a quantitative model for predicting pure cashmere content based on spectra.

During the modeling process, use the correlation coefficient method (but not limited to other methods such as the loading weight method or Variable Importance in Projection (VIP) method) for spectral interval selection. Use the Correlation Coefficient of Calibration (RC), Correlation Coefficient of Prediction (RP), Root Mean Square Error of Prediction (RMSEP), Root Mean Square Error of Cross-Validation (RMSECV) and Residual Prediction Deviation (PRD) as the model performance evaluation parameters, and calculate RC, RP, RMSEP, RMSECV and PRD respectively according to the following Formula (A.1), Formula (A.2), Formula (A.3), Formula (A.4) and Formula (A.5).

After internal cross-validation, remove outliers and iteratively reconstruct and evaluate the model until the performance standard is met — that is, the absolute deviation between the results of this method and the manual method is maintained within 3%.

(A.1)

(A.2)

(A.3)

(A.4)

(A.5)

where

y _i,reference is the reference value of the ⅰth sample;

y_i,predicted is the predicted value of the ⅰth sample in the cross-validation process of the calibration set;

n is the number of samples in the calibration set;

R_c, R_p is the correlation coefficient for calibration and validation, respectively;

is the average of all the reference values of the calibration set, the validation set, respectively;

RMSECV is root mean square error of cross validation for calibration;

RMSEP is root mean square error of prediction;

RPD is residual prediction deviation;

SD_reference is the standard deviation of the sample reference value.

• • 1. Setting model Boundary

Perform principal component analysis on the spectral matrix composed of the pretreated spectra of the calibration set, establish a multidimensional principal component spectral space, calculate the Mahalanobis distance between each calibration sample and the multidimensional principal component spectral space, and set a Mahalanobis distance threshold as the boundary of the calibration model. If the Mahalanobis distance of the sample is greater than the threshold, the sample is an outlier and the model is not applicable to it. The method for setting model boundary is not limited to the Mahalanobis distance method mentioned above, as long as it is verified. Q-residuals (DModX), Euclidean/JM distance, leverage, and robust Mahalanobis can be as optional outlier detection method.

• • 1. Building calibration Model

Combine the quantitative model with the model boundary to build a pure cashmere content calibration model. Perform the same spectral preprocessing and principal component analysis on the spectrum to be tested as the model used, and calculate its Mahalanobis distance. If the Mahalanobis distance is less than or equal to the boundary threshold, apply a quantitative model to test its pure cashmere content by using spectrum, otherwise, it is an outlier.

• 1. Validating model

Based on the calibration model, use the validation set spectra to predict their pure cashmere content (completed through multivariate analysis software). And calculate the deviation between the predicted value and the reference value. If the absolute value of the deviation is less than or equal to the reproducibility limit of the manual method, the model validation is passed, otherwise, the model is not qualified.

1. 
   (informative)
   
   Method of determining reference values
   1. Instruments and reagents
      1. Scouring equipment

Scouring bowl with effective capacity of 10 L or more, or that can meet the testing requirements, equipped with double-layer copper screen bed (100 mesh/25 mm) and proper draining system.

• • 1. Non-ion type detergent
    2. Centrifuge

Synthetic fibre bag for dehydration use.

• • 1. Drying oven
    2. Scale

Gradient 1 g, 0,1 g, 0,01 g, 0,0001 g.

• • 1. tweezers
  1. Sample preparation
     1. Collect samples
        1. Collect raw cashmere samples from different breeds and origins. The pure cashmere content of the samples shall be distributed in a certain range (about 30% to 80%), the weight of the sample shall not be less than 30 g.
        2. Collect scoured cashmere samples are also allowed, the weight of the sample shall not be less than 20 g, and grease content shall no more than 1,5%.
     2. Scouring raw cashmere
        1. Take raw cashmere test specimens to carry out scouring test, scouring process conditions reference Table 1.
        2. Hydro-extraction: Put scoured sample into synthetic fibre bag to dehydrate with hydro-extractor, then drying the sample in drying oven after hydro-extraction.
     3. Divide sample and drying
        1. Divide the sample into two portions using the bisection method. One portion is used as test specimen, the other retains as a spare sample.
        2. Drying test specimens to absolute dry weight in accordance with ISO 6741-1, record as m_d, accurate to 0,01 g.
  2. Pure cashmere content testing
     1. Pick out the guard hair and foreign matter with tweezers from the test specimens, which fibre diameter ≥25 µm belongs to guard hair. Dry the pure cashmere to an absolute dry weight in accordance with ISO 6741-1, which fibre diameter≤25 µm, record as m_p, accurate to 0,001 g.
     2. Calculate pure cashmere content according to Formula (B.1) or Formula (B.2).

(B.1)

where

P is the pure cashmere content, %;

m_p is the oven-dry mass of the pure cashmere, in gram (g);

m_d is the oven-dry mass of the test specimen for pure cashmere content, in gram (g).

• • 1. If the grease content of the sample exceeds 1,5%, the grease content test shall be in accordance with ISO 3074.

(B.2)

where

J_e is the tested grease content, %;

J_p is the conventional grease content for dehaired cashmere, %, J_p=1,5.

NOTE The determination of reference values is only used for model calibration and validation, therefore the washing rate of the raw wool is not considered.

1. 
   (informative)
   
   Precision
   1. 95% Confidence Interval

The 95% Confidence Interval for cashmere sample can be calculated according to Formula (C.1) and Formula (C.2), or by referring to IWTO-0 (APPENDIX B) or IWTO DRAFT TM-45.

(C.1)

(C.2)

where

δ is, %;

x_i is the pure cashmere content of the ith sample;

μ is the mean pure cashmere content of samples, %;

n is the sample number, %.

• 1. Example of the One-Way Analysis of Variance Calculations

Calculation of the Variances and the 95% Confidence Limit for a single sample in Table C.1. The summary of analysis of variance in Table C.2.

Table C.1 — Summary of laboratory testing result

Table C.2 — Summary of Analysis of Variance

δ² within laboratory =0,416%.

δ² between laboratory =(MSB-MSW)/3=(6,234-0,416)/3=1,939%.

95% Confidence Limit= ±1,96×(0,416+1,939)^1/2= ±3,008%.

Bibliography

[1] IWTO DRAFT TM-45 :1999, Determination of Cashmere Down Yield for Core Samples of Cashmere Fibre

[2] ISO 5162:2023, Textiles — Quality labelling specification for dehaired cashmere

[3] Rapid drying-free determination of pure cashmere content in scoured cashmere using a novel method of NIR spectroscopy combined with moisture elimination and spectral reconstruction strategy

[4] Development of fast detection instrument for cashmere net rate by near infrared spectroscopy

[5] ISO 12099:2017, Animal feeding stuffs, cereals and milled cereal products — Guidelines for the application of near infrared spectrometry

[6] IWTO-0 (APPENDIX B):2020, Presentation of Supporting Technical Data