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Abstract

This research studies the solubility properties of certain regenerated cellulose fibers in commonly-used acidic reagents, including formic acid/zinc chloride. A dissolution method for qualitative identification of Tencel A100 (lyocell) fiber in the presence of various other regenerated cellulose fibers was established. This qualitative method was simple, rapid, and had high sensitivity.

Keywords

Formic Acid Lyocell Modal Qualitative Analysis Rayon Regenerated Cellulose Fiber Tencel Viscose Zinc Chloride

Introduction

In recent years, the development and use of regenerated cellulose fibers has gained greater attention. One essential way of identifying textiles is fiber composition, which is mandatory for meeting many international import/export technical regulations. Due to large differences in perceived comfort for fabrics made from various regenerated cellulose fibers, and significant variance in the price of raw materials, there is an urgent need to develop qualitative and quantitative analysis techniques for the detection of blended products containing regenerated cellulose fibers.

There are no qualitative or quantitative dissolution analysis test methods and standards for regenerated cellulose fibers, not only in the GB/T 2910,^1,2 GB/T 2911,³ SN/T 3315,^4,5 and FZ/T 01057^6,7 methods, but also in AATCC Test Method (TM) 20A⁸ and ASTM D629.⁹ There is a considerable amount of literature on qualitative and quantitative analysis of regenerated cellulose fibers and cotton^10–18 or other fibers,^19–22 such as rayon made from bamboo and cotton,¹²lyocell and cotton,^11,14–17 viscose or modal and cotton,^10,11,17,18lyocell and fax,¹⁹ rayon made from bamboo and Shengma fiber (regenerated cellulose fiber made from jute and ambary),²⁰ and regenerated cellulose fiber and spandex.^21,22There were also some studies among the regenerated cellulose fibers,^23–25 such as lyocell, Modal,^23,24 Tencel A100, and Tencel G100 fibers.²⁵ The methods used in these studies were mainly dissolution,^10–19,22 diameter,²⁴ spectrophotometric,²⁵and infrared spectroscopy^21,26–28 methods. There were also studies reviewing various properties of regenerated cellulose fibers, including the effects of different treatments.^29,30

The chemical characteristics of regenerated cellulose fibers are very similar, which is due to the structure of celluloses, which are polymers of beta-D-glucose. The degree of polymerization (n) of several common cellulose fibers are different. For instance, cotton fiber n values are generally 2000, lyocell and modal are ∼900, and viscose fiber is 250 to 500.¹ In acidic solvents, dissolution of cellulose fibers occurs when the large molecular chains of cellulose are shortened by breaking 1,4-glycosidic bonds, followed by degradation. During this process, the resulting n values become smaller until dissolution occurs.¹² Use of formic acid/zinc chloride to distinguish between regenerated cellulose fibers and cotton fiber relies on the large difference in n values between them based on acidic solvent solubility. Differences in the degree of polymerization between A100 fiber and other regenerated cellulose fibers may be exploited in practical work.

Therefore, it is important that qualitative and quantitative analytical methods with high efficiency, simple operation, and high sensitivity be established for these regenerated cellulose fibers. In this study, our lab developed a qualitative identification method for A100 fiber and certain other regenerated cellulose fibers by choosing a suitable acidic solvent and operating under appropriate experimental conditions. Use of this method will also help to improve the identification of these fibers in textile products and prevent commercial fraud. In a related study, a quantitative method has also been developed based on the same technology.³¹

Experimental

Materials

Tencel A100, Tencel LF, Tencel G100, and Modal fibers were produced by Lenzing Co. Rayon made from bamboo (Hebei Jigao Chemical Fiber Co. Ltd.) and viscose fiber (standard material from the Shanghai Textile Institute of Technical Supervision, and separated into fibers before use) were also tested.

All proper safety precautions, including wearing safety glasses and protective clothing, must be taken when working with these reagents. Hydrochloric acid (36–38%, Beijing Chemical Works), formic acid/zinc chloride reagent (20 g of anhydrous zinc chloride (mass fraction > 98%, Tianjin Zhiyuan Chemical Reagent Co. Ltd.) and 68 g of anhydrous formic acid (Tianjin Zhiyuan Chemical Reagent Co. Ltd.), with water added to give a final weight of 100 g). Sulfu-ric acid (60%, Beijing Chemical Works) was prepared by slow addition of 343 mL of concentrated sulfuric acid (p = 1.84 g/mL) into ∼368 mL water, to reach a density of p = 1.4988 g/mL (20 °C) or p = 1.4948 g/mL (25 °C). 1/2 hydrochloric acid (1:1 (v/v) hydrochloric acid and water), and 1/4 hydrochloric acid (1:3 (v/v) hydrochloric acid and water) were prepared.

A thermostatic oscillator (SHA-BA, Jintan City Union Instrument Research Institute), a 100-mesh stainless steel screen, and an electronic analytical balance (AE160, Mettler) were used.

Procedures

The original regenerated cellulosic fibers given above and their mixtures were used in this work to simplify analysis. Fiber quantities were determined as the quantity after moisture regain, and the fiber samples in all evaluations (before and after testing) were weighed the same day to ensure consistency of moisture regain.

Qualitative Analysis

The fiber sample (0.5 g) was quickly added to the formic acid/ zinc chloride solution (50 mL) in an Erlenmeyer flask with a grinding plug, and placed in a water bath with the temperature preheated to and kept at 70 °C. The treatment time was 20 min, the samples oscillated at a frequency of 100 rpm, and a bath ratio of 1:100 was used. The reactant was poured onto the 100-mesh stainless steel screen, and the remaining insoluble matter was identified as A100 fiber by microscopic analysis.

Dissolution Characteristics and Differences of Recycled Cellulose Fibers

The insoluble material was washed with water, dried by heating in an oven, and then weighed after moisture regain.

Results and Discussion

Commonly-Used Acidic Reagents

The goal of a qualitative method is to be as simple, quick, and reliable as possible. Acids are commonly used reagents for regenerated cellulose fiber analysis. In this study, the various test regenerated cellulose fibers did not dissolve in formic acid, therefore, the reagents in Table I were used.

Table I

Solubility of Regenerated Cellulose Fibers in Commonly-Used Acid Reagents

Reagents/Conditions	Fibers Tested
Reagents/Conditions	A100	LF	G100	Viscose	Modal	Rayon from Bamboo
HCl (70 °C)	dissolved quickly	dissolved quickly	dissolved quickly	dissolved quickly	dissolved quickly	dissolved quickly
HCl, oscillation (RT, 30 min)	dissolved	dissolved	dissolved	dissolved	dissolved	dissolved
60% Sulfuric acid, oscillation (RT, 30 min)	dissolved	dissolved	dissolved	dissolved	dissolved	dissolved
1/2 HCl, oscillation (40 °C, 3.5 h)	—	—	—	—	—	—
1/4 HCl, oscillation (70 °C, 2 h)	—	—	—	—	—	—
Formic acid/zinc chloride, oscillation (70 °C, 20 min)	much residue	dissolved	dissolved	dissolved	dissolved	dissolved
Formic acid/zinc chloride, oscillation (40 °C, 2.5 h)	much residue	much residue	little residue	dissolved	dissolved	dissolved

Hydrochloric acid (70 °C) caused all fibers to quickly (and violently; see precautions in experimental section) dissolve. Hydrochloric acid (room temperature (RT), 30 min) and 60% sulfuric acid (RT, 30 min) gave similar results. Formic acid/zinc chloride solution is commonly used in regenerated cellulose fiber composition analysis. The solubility of the regenerated cellulose fibers tested in formic acid/zinc chloride solution under different experimental conditions were different, thus this solution was chosen for further study.

Formic Acid/Zinc Chloride System

Experiments were carried out to study the solubility and dissolution process of the regenerated cellulose fibers being tested in formic acid/zinc chloride at different temperatures. The results are given in Table II. These data were obtained from 40 °C to 70 °C over 20–150 min.

Table II

Solubility of Regenerated Cellulose Fibers in Formic Acid/Zinc Chloride System

Conditions	Fibers Tested
Conditions	A100	LF	G100	Viscose	Modal	Rayon from Bamboo
70 °C, 20 min	residue (0.210 g/0.505 g) ^a	dissolved	dissolved	dissolved	dissolved	dissolved
65 °C, 40 min	residue (0.202 g/0.505 g)	dissolved	dissolved	dissolved	dissolved	dissolved
60 °C, 50 min	residue (0.336 g/0.507 g)	dissolved	dissolved	dissolved	dissolved	dissolved
55 °C, 2.0 h	residue (0.249 g/0.505 g)	dissolved	dissolved	dissolved	dissolved	dissolved
55 °C, 1.5 h	residue (0.350 g/0.508 g)	dissolved	dissolved	dissolved	dissolved	dissolved
55 °C, 1.0 h	residue (0.403 g/0.502 g)	little residue(0.008 g/0.501 g)	dissolved	dissolved	dissolved	dissolved
50 °C, 2.0 h	residue (0.410 g/0.507 g)	dissolved	dissolved	dissolved	dissolved	dissolved
50 °C, 1.5 h	residue (0.435 g/ 0.505 g)	dissolved (little residue)	dissolved	dissolved	dissolved	dissolved
50 °C, 1.0 h	residue (0.458 g/0.504 g)	residue (0.202 g/0.501 g)	little residue (0.009 g/0.505 g)	dissolved	dissolved	dissolved
45 °C, 2.0 h	residue (0.461 g/0.503 g)	residue (0.245 g/0.503 g)	dissolved (little residue）	dissolved	dissolved	dissolved
45 °C, 1.5 h	residue (0.476 g/0.505 g)	residue (0.335 g/0.506 g)	little residue (0.014 g/0.502 g)	dissolved	dissolved	dissolved
45 °C, 1.0 h	residue (0.473 g/0.501 g)	residue (0.384 g/0.505 g)	residue (0.257 g/0.504 g)	dissolved (little residue）	dissolved	dissolved
40 °C, 2.5 h	residue (0.491 g/0.505 g)	residue (0.377 g/0.501 g)	little residue (0.017 g/0.505 g)	dissolved	dissolved	dissolved
40 °C, 2.0 h	residue (0.496 g/0.504 g)	residue (0.398 g/0.505 g)	some residue (0.131 g/0.506 g)	dissolved	dissolved	dissolved
40 °C, 1.5 h	residue (0.504 g/0.507 g)	residue (0.428 g/0.508 g)	residue (0.310 g/0.508 g)	little residue (hard to collect)	dissolved	dissolved
40 °C, 1.0 h	residue (0.499 g/0.501 g)	residue (0.465 g/0.505 g)	residue (0.357 g/0.503 g)	little residue (0.039 g/0.505 g)	little residue (hard to collect)	little residue (hard to collect)

(*/*) Residual fiber amount after reaction/initial fiber amount

The solubility of the various regenerated cellulose fibers tested, when reacted with formic acid/zinc chloride, (from least soluble to most) was as follows: A100 < LF < G100 < viscose < Modal and rayon made from bamboo.

Temperature was an important factor in the dissolution of the regenerated cellulose fibers tested in formic acid/ zinc chloride. Besides the A100 fiber, the other regenerated cellulose fibers tested only needed 20 min to completely dissolve at 70 °C, and 2 h at 50 °C. Loss of residual A100 fiber increased with increased temperature.

The data in Table II show the dissolution of the regenerated cellulose fibers tested under various experimental conditions. Tests over time (1.0, 1.5, 2.0, and 2.5 h) at 40 °C showed the G100 fiber was more soluble after 1.5 h, and was almost completely dissolved at 2.5 h. The G100 fiber was more soluble after 1 h at 45 °C, and was almost completely dissolved at 1.5 h.

Method Establishment

To decrease analysis time, qualitative analysis conditions for regenerated cellulose fiber analysis were refined around a temperature of 70 °C (Table III).

Table III

Analytical Conditions for Qualitative Analysis of Regenerated Cellulose Fibers using Formic Acid/Zinc Chloride System

Conditions	Fibers Tested
Conditions	A100	LF	G100	Viscose	Modal	Rayon from Bamboo
65 °C, 20 min	residue	residue	dissolved	dissolved	dissolved	dissolved
70 °C, 30 min	almost dissolved (little residue)	dissolved	dissolved	dissolved	dissolved	dissolved
70 °C, 20 min	residue	dissolved	dissolved	dissolved	dissolved	dissolved
70 °C, 15 min	residue	almost dissolved (little residue)	dissolved	dissolved	dissolved	dissolved
75 °C, 20 min	almost dissolved (little residue)	dissolved	dissolved	dissolved	dissolved	dissolved

Method Specificity

This experiment, using pure and mixed fiber samples under the previously determined test conditions, is given in Table IV. Tests 1 and 2 demonstrate that the insoluble matter was only A100 fiber. Tests 3–7 show the results for the five other fibers in the presence of 50% A100 fiber—residue was observed in all five cases. These results indicate that the method could distinguish A100 fiber from the other regenerated cellulose fibers tested.

Table IV

Presence of Residue after Dissolution Testing of Various Regenerated Cellulose Fiber Mixtures

Test No.	Fibers and Mixtures Tested (%)						Results^a
Test No.	A100	LF	G100	Viscose	Modal	Rayon from Bamboo	Results^a
1	100	—	—	—	—	—	Y
2	—	20	20	20	20	20	N
3	50	50	—	—	—	—	Y
4	50	—	50	—	—	—	Y
5	50	—	—	50	—	—	Y
6	50	—	—	—	50	—	Y
7	50	—	—	—	—	50	Y

Y-residue after experiment, N-no residue after experiment

Experiments were carried out at 65 °C (20 min), 70 °C (15, 20, and 30 min), and 75 °C (20 min) as shown in Table III. The A100 fiber almost completely dissolved at 70 °C (30 min) and 75 °C (20 min). LF fiber could not be completely dissolved at 65 °C (20 min) or 70 °C (15 min). Thus, 70 °C (20 min) in formic acid/zinc chloride was suitable for qualitative analysis of A100 fiber versus the other regenerated cellulose fibers tested. While increasing the reaction temperature could shorten the reaction time, loss of residual A100 fiber would increase with increasing temperature, which would affect the detection limit.

Method Robustness

An orthogonal experiment was designed for investigating method robustness, including three factors (solution temperature, dissolution time, and oscillation frequency) (Table V). The results show that the conditions, including solution temperature of 70 °C, dissolution time of 20 min, and oscillation frequency of 100 rpm, were reproducible. The detection limit for A100 fiber content was greater than or equal to 1%, the detection range is the content of A100 fiber from 1% to 100%. In addition, different batches of reagents and different experimental personnel were also investigated, with the same results achieved.

Table V

Robustness of Qualitative Analysis Method for Regenerated Cellulose Fibers

Conditions		Experiment No.
Conditions		1	2	3	4	5	6	7	8	9
Dissolution temperature (°C)		69	69	69	70	70	70	71	71	71
Dissolution time (min)		19	20	21	19	20	21	19	20	21
Oscillation frequency (rpm)		90	100	110	100	110	90	110	90	100
Results	A100 fiber after experiment^a	Y	Y	Y	Y	Y	Y	Y	Y	Y
	other fibers after experiment^a	N	N	N	N	N	N	N	N	N
	detection limit of A100 fiber (%)	1	1	1	1	1	1	1	1	1

Y-residue, N-dissolved (noresidue)

Method Verification

Internal and external laboratory verification of the method was carried out. Eight laboratories, all of which are CNAS (China National Accreditation Service for Conformity Assessment) accredited fiber composition analysis item laboratories, were invited for the method verification and validation. One independent lab gave results of method robustness and sample verification and validation, and seven other coordinated laboratories gave sample verification and validation results. These results were consistent with results from our laboratory. The results indicated good reliability and general applicability of this method from different laboratories.

Conclusion

In this work, we studied the solubility of various regenerated cellulose fibers in commonly-used acidic reagents using the dissolution method, and established a qualitative method for detecting the presence of Tencel A100 fiber alone and in the presence of the other regenerated cellulose fibers tested. This method was simple, rapid, and highly sensitive. The dissolution characteristics of the regenerated cellulose fibers tested in formic acid/zinc chloride solution, including similarities and differences, were summarized. This study provided a solid foundation for the next step in establishing qualitative and quantitative analysis dissolution methods among other regenerated cellulose fibers.

References

GB/T 2910.1-2009, General Administration of Quality Supervision, Inspection, and Quarantine of the P. R. C., http://www.chinesestandard.net/PDF-English-Translation/GBT2910.1-2009.html (accessed December 2016).

GB/T 2910.5-2009, General Administration of Quality Supervision, Inspection, and Quarantine of the P. R. C., http://www.chinesestandard.net/PDF-English-Translation/GBT2910.5-2009.html (accessed December 2016).

GB/T 2911-1997, General Administration of Quality Supervision, Inspection, and Quarantine of the P. R. C., http://www.codeofchina.com/standard/GBT2911-1997.html, (accessed December 2016).

SN/T 3315.1-2012, General Administration of Quality Supervision, Inspection, and Quarantine of the P. R. C.

SN/T 3315.3-2012, General Administration of Quality Supervision, Inspection, and Quarantine of the P. R. C., http://www.worldstdindex.com/soft4/3345957.htm (accessed December 2016).

FZ/T 01057.1-2007, General Administration of Quality Supervision, Inspection, and Quarantine of the P. R. C.

FZ/T 01057.4-2007, General Administration of Quality Supervision, Inspection, and Quarantine of the P. R. C.

AATCC Test Method 20A-2014, AATCC Technical Manual; AATCC: Research Triangle Park, NC, USA, 2016, Vol. 91, pp 80–88.

ASTM D629-15, ASTM International, West Conshohocken, PA, USA, 2015, www.astm.org.

10.

Liu

China Fiber Inspection 2012, 12, 55–57.

11.

Zhai

C.L.

; Dong

J.W.

; Hu

H.H.

; Zhu

M.Y.

Shanghai Textile Science & Technology 2012, 40 (4), 10–12.

12.

Chen

B.X.

; Liu

Q.D.

; Zhang

J.M.

; Sun

B.S.

; Liu

; Cheng

H.Y.

Journal of Inspection and Quarantine 2010, 20 (2), 33–37.

13.

Zheng

S.M.

; Li

Knitting Industries 2014, 2, 69–71.

14.

Chen

Shanghai Wool & Jute Journal 2013, 1, 21–24.

15.

Zhou

Progress in Textile Science & Technology 2014, 1, 54–55.

16.

Tang

L.C.

; Li

Y.H.

; Liu

C.M.

; Wang

C.Y.

; Zhu

N.C.

Shanghai Textile Science & Technology 2011, 39 (2), 47–48, 51.

17.

Huang

Y. L.

Journal of Shazhou Professional Institute of Technology 2012, 15 (9), 31–34.

18.

P.L.

; Yang

; Yuan

X.H.

Advanced Textile Technology 2014, 6, 43–47.

19.

H.S.

; Xu

; Zhang

X. L

; Zheng

Y.J.

; Lan

L.L.

Dyeing and Finishing 2009, 17, 40–42.

20.

S.B.

; Zhang

R.J.

Progress in Textile Science & Technology 2010, 3, 70–73.

21.

Pang

Y.L.

; Han

; Su

Y.X.

; Tian

C.X.

; Zhong

Y.C.

; Chen

Journal of Wuhan Textile University 2014, 27 (6), 6–10.

22.

Cheng

H.Y.

; Liu

; Li

J.H.

China Fiber Inspection 2009, 5, 59–61.

23.

Liang

Z.W.

; He

M.R.

China Fiber Inspection 2011, 7, 50–51.

24.

Liang

X.Y.

; Cao

C.F.

China Fiber Inspection 2014, 4, 79–81.

25.

Wang

C.Y.

; Tang

L.C.

; Chu

N.Q.

; Li

Y.H.

; Shen

Y.L.

; Liu

C.M.

Journal of Ningbo Polytechnic 2010, 14 (5), 94–97.

26.

Carrillo

; Colom

; Suñol

J.J.

; Saurina

European Polymer Journal 2004, 40 (9), 2229–2234.

27.

; Yu

; Tesso

; Dowell

; Wang

Applied Energy 2013, 104 (2), 801–809.

28.

Qian

W.J.

; Jin

M.J.

; Zhu

J.J.

Advanced Textile Technology 2011, 2011 (4), 37–39.

29.

Goswami

; Blackburn

R.S.

; El-Dessouky

H. M.

European Polymer Journal 2009, 45 (2), 455–465.

30.

Heinsoo

; Kogerman

; Kirret

; Čoupek

; Vilkova

Journal of Analytical & Applied Pyrolysis 1980, 2 (2), 131–139.

31.

Liu

; Gao

; Zhang

; Zhao

AATCC Journal of Research 2017, 4 (2), 15–19.

Qualitative Analysis of Tencel A100 Fiber and Selected Regenerated Cellulose Fibers

Abstract

Keywords

Introduction

Experimental

Materials

Procedures

Qualitative Analysis

Dissolution Characteristics and Differences of Recycled Cellulose Fibers

Results and Discussion

Commonly-Used Acidic Reagents

Formic Acid/Zinc Chloride System

Method Establishment

Method Specificity

Method Robustness

Method Verification

Conclusion

References