Regenerated Fiber Testing

Regenerated fibre inspection mainly conducts scientific testing and analysis on fibre qualitative and quantitative analysis, physical and mechanical property testing, fibre morphology and structural parameter determination, chemical property and component analysis, moisture absorption and dyeing property testing, and hazardous substance limit testing, objectively assessing the product quality grade and issuing a detailed test report, providing a basis for manufacturers' quality control and downstream users' product acceptance.

Testing Items

Fibre qualitative and quantitative analysis: This is the core item of the regenerated fibre inspection, aiming to accurately identify the fibre type of the sample and determine its content percentage. The qualitative analysis judges whether the fibre is a specific regenerated cellulose fibre such as viscose, lyocell, modal and cupro, or a chemically regenerated fibre such as the recycled polyester and recycled nylon, through the means such as the microscope observation, combustion method and dissolution method.

Physical and mechanical property testing: This testing item evaluates the mechanical characteristics of the regenerated fibres, mainly including the strength (breaking strength and elongation at break) and initial modulus. The wet-state strength and wet modulus of the regenerated fibres are the important evaluation indicators, especially for the regenerated cellulose fibres, and the wet-state property changes directly affect the durability of the final fabric.

Fibre morphology and structural parameter determination: The basic parameters such as the longitudinal morphology, cross-section shape, length and fineness (linear density, unit: dtex) of the regenerated fibres are measured with the instruments such as the optical microscope and scanning electron microscope. The cross-section morphology (such as the serrated shape of the viscose and the circular shape of the lyocell) is an important qualitative basis.

Chemical property and component analysis: Analyses the chemical composition and characteristics of the regenerated fibres, including the degree of polymerization, residual sulphur content (particularly important for the viscose fibres), ash content, oil agent content, pH value and aqueous extract. These indicators directly affect the spinnability, dyeing performance and the environmental safety of the final product.

Moisture absorption and dyeing property testing: Determines the standard moisture regain, water retention rate and other moisture absorption properties of the regenerated fibres, which are related to the wearing comfort of the fabric. At the same time, their adsorption property to the different types of dyes, dye uptake rate and colour fastness are evaluated, which is the key to judging their applicability in the dyeing and finishing processing.

Hazardous substance limit testing: In accordance with the relevant ecological textile standards, the hazardous substances that may remain in the regenerated fibres are detected, such as the heavy metals (lead, cadmium and mercury), formaldehyde, extractable heavy metals, prohibited azo dyes and short-chain chlorinated paraffins, ensuring that the products meet the environmental protection and safety regulatory requirements.

Testing Scope

Native regenerated fibres: Mainly testing the fibres regenerated by the chemical dissolution of the natural polymers as the raw materials, including the viscose fibres (ordinary viscose and high wet modulus viscose), lyocell fibres, modal fibres and cupro fibres. The testing focus is on identifying the types, distinguishing them from cotton, and evaluating their unique wet-state properties.

Chemically regenerated fibres (recycled synthetic fibres): The testing scope covers the fibres made from the waste polyester bottles and waste textiles as the raw materials through the chemical depolymerization-repolymerization or physical melt spinning, such as the recycled polyester fibres (rPET) and recycled polyamide fibres. The testing needs to verify the authenticity of their recycling sources and evaluate the performance differences from the traditional virgin fibres.

Regenerated protein fibres and special regenerated fibres: Including the regenerated protein fibres made from the natural proteins such as milk and soybean as the raw materials. In addition, there are the bio-based regenerated fibres such as the seaweed fibres and chitin fibres. The testing needs to pay attention to their protein content, biodegradability and functional indicators.

Regenerated fibre yarns and fabrics: The testing objects extend to the yarns spun from the regenerated fibres (pure spun or blended) and the fabrics woven or knitted from them. In addition to the fibre composition analysis, the wearing properties such as the twist, evenness and strength of the yarns, and the grammage, colour fastness and pilling of the fabrics also need to be comprehensively evaluated.

Industrial regenerated fibre products: The testing scope includes the regenerated fibres used in the industrial textiles such as the nonwovens, filter media and composite reinforcement substrates. The testing items focus on the functional indicators for meeting the specific uses, such as the filtration efficiency, strength, chemical resistance and flame retardancy.

Import and export trade and market supervision: In the commodity trade, customs clearance and market quality supervision spot checks, the conformity verification is carried out on the textile and garment products claimed to contain the regenerated fibres, cracking down on the commercial fraud of the false or wrong fibre composition labelling, and maintaining the market order and the rights and interests of the consumers.

Testing Methods

Microscope observation method: This is the most basic and intuitive method for the fibre qualitative identification. A biological microscope is used to observe the longitudinal morphological characteristics of the fibre (such as the longitudinal striations of the viscose), and a Hardy microtome is used to make the cross-section samples to observe their cross-section shapes (such as the circular cross-section of the lyocell), and the type identification is carried out by comparison with the standard photos or atlases.

Chemical dissolution method: The qualitative and quantitative analysis is carried out according to the difference in the dissolution characteristics of the different fibres in the different chemical reagents. For example, the 59.5% sulfuric acid solution can dissolve the regenerated cellulose fibres such as the viscose and lyocell, but does not dissolve the cotton and polyester, and is the key means for the quantitative analysis of the blended products, which needs to strictly follow the ISO 1833 or GB/T 2910 standard series.

Infrared spectroscopy analysis method: A Fourier transform infrared spectrometer (FTIR) is used to obtain the molecular vibration spectrum of the fibre, and through the comparison with the standard spectrum library, the regenerated fibre is quickly and non-destructively qualitatively identified. This method is particularly suitable for distinguishing the fibres with similar chemical structures, such as the viscose and lyocell.

Combustion method and thermal analysis method: The combustion method carries out the preliminary identification by observing the state, odour and ash characteristics of the fibre when approaching the flame, in the flame and after leaving the flame. The thermal analysis methods (such as the differential scanning calorimetry DSC and thermogravimetric analysis TGA) obtain the information such as the melting point and decomposition temperature of the fibre by analysing the thermal effects and weight changes under the programmed temperature control, assisting the qualitative identification and evaluating the thermal stability.

Standard physical property test methods: Executed in accordance with the standards such as the ISO, GB and ASTM. For example, the fibre strength and elongation testing follows GB/T 14337 "Testing method for tensile properties of man-made fibres — Staple fibres", determined with a constant-rate-of-extension strength tester (CRE) under the standard temperature and humidity conditions, and the results are significantly influenced by the pre-treatment and clamping methods.

Liquid/gas chromatography-mass spectrometry method: Mainly used to detect the trace hazardous chemical residues in the regenerated fibres, such as the prohibited azo dyes and alkylphenol ethoxylates. This method has high sensitivity and good selectivity, and is the core technology for verifying whether the products meet the high-level environmental protection standards such as the Oeko-Tex Standard 100 and REACH regulation.

Testing Standards

Domestic Standards:

1. GB/T 2910, Textiles — Quantitative chemical analysis

2. GB/T 14337, Testing method for tensile properties of man-made fibres — Staple fibres

3. GB 18401-2010, National general safety technical code for textile products

4. GB/T 3920-2024, Textiles — Tests for colour fastness — Colour fastness to rubbing

International Standards:

1. ISO 1833, Textiles — Quantitative chemical analysis

2. ISO 13934-1, Textiles — Tensile properties of fabrics — Part 1: Determination of maximum force and elongation at maximum force using the strip method

3. ISO 105, Textiles — Tests for colour fastness

Note: The applicable standard can be selected according to the product use and customer trade requirements; standards agreed in the contract take precedence over general standards.

Testing Instruments and Equipment

Optical microscope and electron microscope: The biological microscope is equipped with a polarizing device and micro-projection instrument, used to observe the fibre morphology; the scanning electron microscope (SEM) can provide higher-resolution surface morphology and cross-section images, and is a powerful tool for the in-depth study of the fibre micro-structure and the identification of the ultra-fine or profiled regenerated fibres.

Conventional equipment of the chemical analysis laboratory: Including the constant temperature water bath, analytical balance, Soxhlet extractor, drying oven and muffle furnace. These equipment are used to complete the pre-treatment and the basic operations such as the weighing and constant weight for the chemical testing items such as the dissolution method quantitative analysis, oil agent content determination and ash testing.

Spectroscopy and chromatography analysis instruments: The Fourier transform infrared spectrometer (FTIR) is used for the rapid qualitative identification; the high-performance liquid chromatograph (HPLC) and gas chromatography-mass spectrometer (GC-MS) are used for the precise determination of the hazardous substances; and the inductively coupled plasma mass spectrometer (ICP-MS) is used to detect the trace heavy metal elements, ensuring the detection accuracy reaching the ppb level.

Fibre physical property testers: The constant-rate-of-extension single-fibre strength tester (CRE) is used to test the strength and elongation of a single fibre; the fibre length/fineness analyser (such as the AFIS and Almeter) can quickly and automatically measure the length and fineness distribution of a large number of fibres; and the fibre friction coefficient tester is used to evaluate the spinnability.

Thermal analysis and rheological property testing equipment: The differential scanning calorimeter (DSC) is used to determine the glass transition temperature, melting temperature and crystallinity of the fibre; the thermogravimetric analyser (TGA) is used to analyse the thermal decomposition behaviour; and the capillary rheometer is used to study the rheological characteristics of the regenerated polymer materials in the molten state.

Dedicated ecological safety testing equipment: Including the UV-visible spectrophotometer and the matching extraction device for detecting the formaldehyde content; the washing fastness testing machine, rubbing fastness tester and light fastness tester for testing the colour fastness; and the pH value testing related equipment for simulating the human perspiration environment.