What Standard Governs Acrylic Fiber Testing in China?
Acrylic fiber testing in China is anchored in GB/T 16602-2008 Acrylic Staple and Tow, the product standard for acrylic staple fiber and tow used in textile spinning. The standard classifies product into three quality grades — 优等品 (premium), 一等品 (first grade), 合格品 (qualified) — and sets the threshold tables for the mechanical, dimensional, and processing properties a production batch must meet for each grade. The test methods it invokes are consolidated in the synthetic-fiber method-standard family (GB/T 14335, GB/T 14337, GB/T 6504, GB/T 14336).
Two further standards are mandatory overlays. GB/T 20389-2006 Determination of Acrylonitrile Residues in Acrylic Fibre measures the residual acrylonitrile monomer — a controlled residual because acrylonitrile is a suspected human carcinogen (IARC Group 2B), and the residual monomer can migrate from the fiber during dyeing and wear. GB 18401-2010 General Safety Technical Code for Textile Products applies if the fiber is sold as a finished textile article (formaldehyde, pH, colorfastness, odour, aromatic amines).
The international product-method references are ISO 11567 (fiber identification), ISO 5079 (single-fiber tensile), and ASTM D3218 (staple fiber properties). The US FTC labelling rule defines the fibre category (≥ 85 % acrylonitrile = "acrylic"; 35–85 % = "modacrylic") but does not itself set mechanical thresholds. Knowing which framework applies up front decides both the test panel and the regulatory exposure — a fiber destined for the EU market is tested for residual acrylonitrile and against REACH/Oeko-Tex limits, while a domestic batch release is tested against the GB/T 16602 grade table.
What Are the Mechanical Property Requirements?
The mechanical block of GB/T 16602-2008 is organised by quality grade and by nominal linear density (dtex) band. The four mechanical indicators that drive pass/fail:
Linear density and linear density deviation (线密度及线密度偏差率): the fiber's fineness in decitex (g per 10 000 m), and how tightly the measured value clusters around the nominal. Measured per GB/T 14335 (gravimetric method). Typical acrylic staple is 1.67–6.67 dtex; the deviation-rate ceiling is tight (typically a few percent) because a fiber out of spec drifts the yarn count, which propagates into fabric weight and dye uptake.
Breaking tenacity and breaking tenacity CV (断裂强度及变异系数): the fiber's tensile strength, expressed in centinewton per decitex (cN/dtex) or gram-force per denier (g/d), and the coefficient of variation across the test specimen set. Measured per GB/T 14337 on a single-fiber tensile tester (CRD — constant rate of deformation). Typical acrylic tenacity ranges from 2.0 to 3.6 g/d; the CV ceiling is the quality discriminator — a batch at the mean tenacity but with high CV will spin unevenly and produce yarn-strength variability that shows up in fabric. Premium grade carries the tightest CV.
Breaking elongation and elongation CV (断裂伸长率及变异系数): the strain at fiber fracture. Acrylic fibers extend 25–45 % before breaking, depending on the draw ratio applied during spinning. The elongation and tenacity are trade-linked — a higher-drawn fiber has higher tenacity and lower elongation. A batch tested at high tenacity but abnormally low elongation is brittle, typically from over-drawing, and will fibrillate and break in carding.
Loop (knot) strength (勾接强度): the fiber's strength when tested in a looped configuration rather than straight — the test that best predicts performance in knitting and in fabrics subject to snagging. A fiber with good straight tenacity but poor loop strength will snap at the inter-fiber crossover points in a knit, producing runs and holes.
The grade table sets pass/fail thresholds for each of these by grade. A report that gives the mean values without the CV (the variability term) is incomplete — in textile fiber QC, the CV is often the controlling parameter, because uniformity is what the spinner pays for.
What Are the Processing and Dimensional Properties?
The processing block of GB/T 16602 covers the properties that determine how the fiber runs on the spinner's equipment, not how strong the final yarn is.
Oil content (含油率): the spin finish — the surface treatment applied during fiber manufacturing to control static, friction, and cohesion. Measured per GB/T 6504 (extraction method or neutral-soap wash). Oil content that is too low produces static buildup and cylinder lapping on the card; too high produces roller slipping and drafting instability. The window is narrow, and a fiber tested within the oil window spins cleanly while one outside it does not, regardless of mechanical properties.
Crimp and crimp stability (卷曲): the fiber's waviness, which controls how the fibers pack in a yarn and how the yarn bulk develops. Crimp number (crimps per cm), crimp ratio, and crimp stability are measured. A fiber with low crimp produces flat, lifeless yarn; one with unstable crimp loses its bulk in downstream wet processing.
Staple length and overlength fiber (长度及倍长纤维): measured per GB/T 14336. The staple length controls the spinning system the fiber is suited to (cotton-system vs wool-system). Overlength fibers (倍长) — fibers significantly longer than the nominal cut length — are a defect, because they wrap around the drafting rollers and cause yarn breaks and drafting waves. Premium grade carries a tight overlength ceiling.
Defects (疵点): fused fibers, entanglements, slubs, and other manufacturing defects. Counted per unit mass. A high defect count indicates a spinning-process or cutter problem upstream and predicts drafting-room breaks at the yarn mill.
Moisture regain (回潮率): the moisture content of the fiber at delivery. Acrylic has a low moisture regain (typically 1.0–2.5 %) by chemistry — much lower than cotton or wool. The moisture regain affects the fiber's weight at sale (textile fibers are traded by weight) and its behavior in processing.
How Is Residual Acrylonitrile Monomer Tested?
Residual acrylonitrile monomer (残余丙烯腈单体) is the controlled residual that distinguishes acrylic fiber testing from generic synthetic-fiber testing. Acrylonitrile, the monomer from which acrylic fiber is polymerised, is a suspected human carcinogen (IARC Group 2B), and the residual unreacted monomer can migrate out of the fiber during dyeing, finishing, and wear. The test, per GB/T 20389-2006 Determination of Acrylonitrile Residues in Acrylic Fibre, extracts the fiber with a defined solvent and quantifies the acrylonitrile by gas chromatography.
The regulatory ceiling depends on the destination market and the product category. For skin-contact textiles sold in the EU, the residual acrylonitrile limit under REACH Annex XVII is ≤ 1.0 mg/kg (1 ppm) for fibers used in articles intended to come into contact with skin; for Oeko-Tex Standard 100 Product Class I (infants and toddlers), the limit is tighter. A fiber batch with residual acrylonitrile above the ceiling cannot be placed on the EU market for skin-contact use regardless of its mechanical properties.
The diagnostic logic: a high residual acrylonitrile reading indicates incomplete polymerisation or inadequate washing during fiber manufacture. It is not a property the spinner can fix downstream — it is set at the polymerisation and washing stages of fiber production. A fiber that fails residual acrylonitrile but passes mechanical grade is a manufacturing-process problem, not a quality-tuning problem.
How Are Acrylic and Modacrylic Fibers Distinguished?
The FTC labelling rule defines two fiber categories by acrylonitrile content: acrylic at ≥ 85 % acrylonitrile units, modacrylic at 35–85 %. The distinction is regulatory and commercial — modacrylic is used in flame-retardant applications (it self-extinguishes, while acrylic burns), and the two fibers carry different labelling, different dyeing behavior, and different regulatory limits.
The laboratory identification stack:
Burn test (screening): acrylic shrinks rapidly when the flame approaches, burns with sputtering and black smoke, has a chemical odor, and leaves a yellow-brown, hard, irregularly-shaped residue that continues to burn after the flame is removed. Modacrylic, by contrast, self-extinguishes — it shrinks from the flame and does not sustain combustion. The burn test separates acrylic from modacrylic, but cannot quantify the blend if both are present.
FTIR (confirmatory): the infrared spectrum identifies the polyacrylonitrile backbone. The cyano (-C≡N) absorption at ~2240 cm⁻¹ is diagnostic. FTIR distinguishes acrylic/modacrylic from other fiber types (cotton, polyester, nylon) but does not cleanly separate acrylic from modacrylic when the comonomer content is moderate.
Solubility test (definitive): per the JIS-recommended method, the fiber is immersed in N,N-dimethylformamide (DMF) — both acrylic and modacrylic dissolve, but at different rates. A refined method using DMF/ethanol (90:10) discriminates acrylic from modacrylic more cleanly than pure DMF, because the ethanol modulates the dissolution kinetics enough to separate the two categories by time-to-dissolution. This is the method cited in forensic fiber discrimination, where distinguishing acrylic from modacrylic in a single transferred fiber is the entire question.
Quantitative blend analysis (GB/T 2910): for a fiber claimed as "100 % acrylic" that may contain modacrylic, polyester, or cotton as adulterants, the chemical dissolution method per GB/T 2910 selectively dissolves one component and weighs the residue. Acrylic and modacrylic are difficult to separate chemically (both are polyacrylonitrile-based) — the dissolution + gravimetric method works for acrylic-vs-non-acrylic blends, but for acrylic-vs-modacrylic the spectroscopic method is more reliable.
How Does Safety Performance Apply Under GB 18401?
If the acrylic fiber is sold as a finished textile article (a yarn, a fabric, a garment), it must additionally clear GB 18401-2010, the mandatory safety baseline. The relevant parameters for acrylic:
Formaldehyde: acrylic itself does not use formaldehyde-based finishes in manufacture, but dyeing auxiliaries and finishing resins can introduce formaldehyde residues. Category B (skin contact) ceiling is ≤ 75 mg/kg; Category A (infants) ≤ 20 mg/kg.
pH: acrylic is dyed with cationic dyes under acidic conditions, and the residual pH on the fiber must fall within the Category B band (4.0–8.5). A fiber with residual acidity from dyeing fails pH.
Colorfastness: acrylic dyed with cationic dyes can have colorfastness issues — particularly to rubbing (cationic dye can rub off onto adjacent fibers) and to perspiration. The GB 18401 colorfastness floors are ≥ 3 grade for most parameters in Category B.
Odor: no off-odour. A residual solvent smell (DMF, DMAc) from incomplete washing is a fail and is also a marker of high residual acrylonitrile — the two residuals are correlated.
A complete compliance report for acrylic fiber destined for the consumer market combines the GB/T 16602 product-grade block (mechanical, dimensional, processing) with the GB/T 20389 residual-acrylonitrile test and the GB 18401 safety block. A report covering only one of these is incomplete — a fiber can pass product grade and fail safety, or pass safety and fail the residual-monomer ceiling, and each failure blocks a different market.
Our Testing Capabilities
Beijing ZKGX Research provides acrylic fiber testing against the GB/T 16602-2008 product standard, the GB/T 20389-2006 residual-acrylonitrile method, and the GB 18401-2010 safety framework.
Mechanical properties (GB/T 16602 / GB/T 14337):
- Linear density and deviation (GB/T 14335)
- Breaking tenacity and CV, breaking elongation and CV
- Loop (knot) strength
- Grade determination: premium / first grade / qualified
Processing and dimensional:
- Oil content (GB/T 6504)
- Crimp (number, ratio, stability)
- Staple length and overlength fiber (GB/T 14336)
- Defect count, moisture regain
Residual monomer and chemical:
- Residual acrylonitrile by GC (GB/T 20389-2006)
- Solvent residue (DMF, DMAc)
Safety (GB 18401-2010):
- Formaldehyde, pH, colorfastness (rubbing, perspiration, water), odour
- Decomposable carcinogenic aromatic amines (azo dyes)
Fiber identification and blend:
- Burn test, FTIR, DMF/ethanol solubility (acrylic vs modacrylic)
- Quantitative blend analysis per GB/T 2910
If you need a GB/T 16602 acrylic fiber batch-release report, a GB/T 20389 residual acrylonitrile certificate for EU/REACH compliance, an acrylic-vs-modacrylic identification, or a GB 18401 safety compliance test for a finished acrylic textile — contact our laboratory with the fiber type (staple / tow / filament), intended market, and applicable standard, and we will scope the test plan.
FAQ
What is the difference between acrylic and modacrylic fiber, and why does it matter for testing?
The acrylonitrile content. Acrylic is ≥ 85 % acrylonitrile; modacrylic is 35–85 %, with the balance typically a halogenated flame-retardant comonomer. The two have different burning behavior (modacrylic self-extinguishes, acrylic burns), different dyeing behavior, and different regulatory limits. The lab distinguishes them by FTIR (the cyano absorption is common to both) followed by solubility testing in DMF/ethanol, and the label claim on the finished article must match the identified category.
Why is residual acrylonitrile measured separately from the general GB 18401 safety test?
Because acrylonitrile is a fiber-specific residual — it is the monomer from which the fiber is polymerised, and it is a suspected human carcinogen (IARC 2B). The general GB 18401 test covers formaldehyde, pH, colorfastness, and azo dyes, but does not cover residual monomers. GB/T 20389 is the dedicated method for acrylonitrile residue in acrylic fiber, and the REACH ceiling for skin-contact articles is ≤ 1.0 mg/kg. A fiber can pass GB 18401 and still fail the residual-acrylonitrile ceiling.
What does the linear density deviation rate tell the spinner?
How uniform the fiber fineness is across the production batch. A tight deviation rate means the fiber will spin into uniform yarn count; a wide deviation rate means the yarn will have thick and thin sections, which produces fabric weight variation and dye-uptake variation. In textile QC, the deviation rate and the tenacity CV together are often more important than the mean values, because uniformity is what produces a consistent downstream product.
Can a fiber pass mechanical grade and still be unsuitable for spinning?
Yes — if the oil content (含油率) is out of spec, or the crimp is unstable, or the overlength-fiber count is high. These are processing properties, not mechanical properties. A fiber with excellent tenacity but no spin finish will static-lap on the carding cylinder and never make it to yarn. A fiber with unstable crimp will lose its bulk in dyeing and produce a flat fabric. This is why the GB/T 16602 grade table includes the processing block, not just the mechanical block.
How accurate is the burn test for identifying acrylic fiber?
As a screening tool, useful. Acrylic shrinks rapidly from the flame, burns with sputtering black smoke and a chemical odor, and leaves a yellow-brown hard irregular residue. This distinguishes it from cotton (clean flame, papery smell, gray crushable ash), wool (slow burn, hair smell, crushable ash), and polyester/nylon (melt to a hard bead). But the burn test cannot separate acrylic from modacrylic cleanly, cannot quantify a blend, and is affected by fiber finishes. For a defensible identification — especially in a dispute or a labelling-claim case — the FTIR + solubility method is required.