GB fiber content determination is the quantitative analysis of textile fiber composition performed in accordance with Chinese national standards, principally the GB/T 2910 series of quantitative chemical analysis methods. Accurate fiber content data are essential for fiber content labeling under GB/T 29862, for conformity assessment, and for quality control throughout the textile supply chain. This article explains the standards framework, applicable sample types, testing items, analytical methods, and frequently asked questions related to fiber content determination under GB standards.
Technical Overview
Fiber content determination establishes the mass percentage of each fibrous component in a textile product, such as the ratio of cotton to polyester in a blended shirt or the proportion of cashmere in a wool sweater. Under the Chinese national standards (GB) system, this analysis is governed by a coherent set of quantitative chemical analysis methods that are technically aligned with the ISO 1833 series, ensuring that results are consistent and mutually recognized in international trade.
Standards Framework
- GB/T 2910.1, Quantitative chemical analysis of textiles, Part 1: General principles of testing, which specifies sampling, pretreatment, drying, weighing, and calculation rules, corresponding to ISO 1833-1.
- GB/T 2910.2, which defines dissolution schemes for ternary fiber mixtures, corresponding to ISO 1833-2.
- GB/T 2910.3 through GB/T 2910.101, which provide fiber-pair-specific reagents, dissolution conditions, and correction factors, for example sulfuric acid for cellulose and polyester, formic acid for polyamide blends, and sodium hypochlorite for protein fiber blends.
- GB/T 16988, the projection microscope method for quantifying mixtures of specialty animal fibers and wool.
- GB/T 14593, the scanning electron microscopy method for quantitative analysis of cashmere and wool mixtures.
- GB/T 29862, which governs the designation and labeling of fiber content on textile products.
- GB/T 9994, which provides the conventional moisture regain values used to convert dry mass percentages into conventional commercial percentages.
Principle of Determination
The core principle of quantitative chemical analysis is selective dissolution. A pre-weighed, oven-dried specimen is treated with a specified chemical reagent that completely dissolves one fiber component while leaving the other component essentially unaffected. The insoluble residue is filtered, rinsed, dried to constant mass, and weighed. From the mass balance, together with standardized correction factors that compensate for minor mass loss or gain of the undissolved fiber, the percentage of each component is calculated. For fiber pairs that cannot be separated chemically, such as cashmere and wool, physical methods based on microscopic morphology are applied instead.
Expression of Results
Results are expressed in two forms: the net dry mass percentage, based on oven-dry masses, and the conventional mass percentage, obtained by applying the conventional moisture regain values from GB/T 9994 to each component. Labeling under GB/T 29862 is based on the conventional percentages, rounded to integer values in most cases, with permitted tolerances depending on the nominal content declared.
Testing Samples
Fibers, Yarns, and Slivers
Raw fiber lots, tops, slivers, and yarn packages can be tested directly. Yarn specimens are cut into short lengths to ensure uniform reagent penetration, and multiple packages from the same lot are combined to form a representative laboratory sample.
Fabrics
Woven, knitted, and nonwoven fabrics are sampled so that all yarn systems, such as warp and weft, are included in their correct proportions. Patterned fabrics are sampled across complete pattern repeats, and decorative or structural elements that are not part of the fiber content claim, such as labels and interlinings, are excluded before analysis.
Garments and Made-Up Products
For apparel and home textile products, specimens are taken from the main body of each labeled component. When a garment contains several fabrics with different fiber content, each component is sampled and analyzed separately, because each must be declared on the label.
Special Materials
Coated, laminated, heavily finished, or dyed materials require thorough pretreatment to remove non-fibrous matter before weighing. Products containing elastane, metal threads, or other special components are analyzed using dedicated dissolution sequences appropriate to the fiber combination.
Testing Items
Typical testing items under the GB fiber content determination framework include:
- Qualitative fiber identification to confirm which fibers are present in the sample.
- Quantitative analysis of binary fiber mixtures, such as cotton and polyester, viscose and cotton, wool and nylon, or silk and wool.
- Quantitative analysis of ternary and multi-component blends under GB/T 2910.2.
- Determination of cashmere, wool, and other specialty animal fiber ratios by microscopy-based methods.
- Determination of elastane content in stretch fabrics and core-spun yarn products.
- Fiber content labeling compliance assessment against GB/T 29862.
Testing Methods
Sample Preparation and Pretreatment
Non-fibrous matter, including oils, sizes, finishes, and certain dyes, is removed using appropriate pretreatment such as extraction with light petroleum and washing, as specified in GB/T 2910.1. The specimen is then pre-dried, conditioned, and weighed on an analytical balance with a precision of 0.1 mg. Specimens are dried at 105 ± 3 °C to constant mass, typically reached when successive weighings differ by less than 0.1 percent. At least two parallel specimens are analyzed, and duplicate results must agree within approximately one percentage point.
Qualitative Fiber Identification
Before quantification, the fiber types present are identified using a combination of light microscopy of longitudinal and cross-sectional morphology, burning behavior, solubility in selected reagents, and, where needed, infrared spectroscopy. Qualitative identification is critical because it determines which quantitative dissolution method and which correction factors apply.
Quantitative Chemical Analysis by Selective Dissolution
Depending on the fiber pair, a specified reagent is applied under controlled temperature and time conditions. Common examples include 75 percent sulfuric acid to dissolve cellulose in cellulose and polyester blends, 80 percent formic acid to dissolve polyamide in polyamide blends, sodium hypochlorite to dissolve protein fibers such as silk or wool, dimethylformamide to dissolve acrylic fibers, and boiling xylene to dissolve polypropylene. After dissolution, the residue is filtered through a sintered-glass crucible, rinsed neutral, dried, and weighed. International analogues include ISO 1833, ASTM D629, and JIS L 1030, which follow comparable principles.
Manual Separation Method
When the components of a textile can be physically separated, for example when different yarns are interwoven or when a fabric is constructed from yarns of distinctly different fibers, the manual separation method permitted under the general principles of GB/T 2910.1 is preferred. The separated fibers are individually dried and weighed, which avoids chemical correction factors entirely and typically yields lower analytical uncertainty.
Microscopic Projection and Scanning Electron Microscopy
For animal fiber mixtures that are chemically indistinguishable, GB/T 16988 uses projection microscopy: fibers are counted and their diameters measured, and the mass fraction is computed from the diameter distribution. GB/T 14593 uses scanning electron microscopy to distinguish cashmere from wool based on cuticle scale height, providing higher discrimination for fine animal fiber blends.
Calculation of Results
Net dry mass percentages are calculated from the dry masses of the dissolved and undissolved components, applying the standard correction factor d to correct for reagent-induced mass change of the insoluble fiber. For ternary mixtures, one of the four dissolution schemes in GB/T 2910.2 is selected based on fiber chemistry. Conventional mass percentages are then derived using moisture regain values from GB/T 9994, and the final result is compared with the labeled nominal content and the tolerances set in GB/T 29862, for example a permitted deviation of plus or minus five percentage points for fiber contents declared at ten percent or above, with tighter limits for lower declared values.
Applications
GB fiber content determination supports multiple stages of the textile product lifecycle:
- Regulatory compliance for products sold in China, where fiber content labeling is a mandatory element of product information.
- Import and export verification, since GB methods are harmonized with ISO 1833 and results are widely accepted alongside ASTM D629 and EN ISO 1833 data.
- Incoming material inspection and production quality control at spinning, weaving, knitting, and dyeing and finishing mills.
- New product development, including blend optimization and cost engineering of multi-component fabrics.
- Supplier audits, purchase contract verification, and resolution of commercial disputes by accredited third-party laboratories.
- Support for customs classification and e-commerce platform compliance documentation.
FAQ
What is the relationship between GB/T 2910 and ISO 1833?
The GB/T 2910 series is technically aligned with the ISO 1833 series. GB/T 2910.1 corresponds to ISO 1833-1, and the fiber-pair-specific parts adopt the same reagents, dissolution conditions, and correction factors, so results obtained by the two systems are generally comparable.
How much sample is required for testing?
A laboratory sample of at least a few grams is usually requested so that at least two parallel specimens of approximately one gram each can be prepared. For garments with multiple labeled components, each component must be sampled separately.
What is the correction factor d in chemical analysis?
The correction factor d compensates for the small mass loss or mass gain that the undissolved fiber experiences during treatment with the dissolving reagent. It is standardized for each fiber pair and reagent in the relevant part of GB/T 2910 and is applied when calculating the dry mass percentages.
Why are results reported on both a dry basis and a conventional basis?
The net dry mass basis eliminates moisture and provides an exact chemical proportion, while the conventional basis applies the standardized moisture regain of each fiber from GB/T 9994 to reflect the fiber mass in its normal commercial state. Fiber content labels under GB/T 29862 are based on conventional percentages.
How are cashmere and wool blends quantified?
Because cashmere and wool are chemically identical, their ratio is determined by microscopy. The projection microscope method counts fibers and measures diameters, while the scanning electron microscope method distinguishes them by scale structure, which is particularly useful for disputed or high-value cashmere claims.
Can all fiber blends be tested by chemical dissolution?
Most common blends can be analyzed chemically using the appropriate part of GB/T 2910. Blends of chemically similar fibers, such as different cellulosics in some cases or different animal fibers, require manual separation or microscopy-based methods instead, and complex multi-component products may need a combination of techniques.