Linen Fiber Testing

Bast fibre testing mainly conducts scientific testing and analysis on key performance indicators, objectively assessing the product quality grade and issuing a detailed test report, providing a basis for manufacturers' quality control and downstream users' product acceptance.

Core Testing Items

Length and length distribution: The bast fibre length is the key indicator for evaluating its spin ability and the final yarn quality. The test usually adopts a roller-type length analyzer or a capacitive length tester, measuring the weighted average length, staple length and short fibre content (such as the content below 30 mm) of the fibre. This data directly affects the drafting efficiency, broken end rate and evenness of the spun yarn in the spinning process.

Fineness: The fineness determines the softness, cohesion and the final product style of the bast fibre. The cut-middles weighing method or the airflow method is usually adopted for testing, expressed in metric count (Nm) or linear density (dtex). The fineness range of bast fibres such as flax and hemp is usually between 2.5 and 6.0 dtex. The finer the fineness, the softer the fibre and the better the spin ability.

Breaking strength and elongation: Reflects the ability of the bast fibre to withstand external forces during processing and use. A single fibre strength tester or bundle fibre strength tester is used to test its breaking force (cN), breaking tenacity (cN/dtex) and elongation at break (%) under standard temperature and humidity conditions. High strength and low elongation are the typical characteristics of bast fibres, and their strength directly affects the durability of the fabric.

Moisture regain and moisture content: Bast fibres have good hygroscopicity, and their moisture state directly affects the weight settlement, processing performance and static control. In accordance with standards such as GB/T 9995, the oven-drying method or a resistance moisture meter is used to determine the moisture content of the bast fibre under specified conditions. In commercial transactions, the official regain is usually used for weight conversion.

Impurity content and residual gum content: Refers to the content of non-fibrous substances (such as pectin, lignin, epidermis and dust) in the bast fibre. The separation and weighing are carried out by chemical analysis methods (such as the alkali boiling method for determining the residual gum) or an impurity analysis machine. This indicator is related to the difficulty and loss of the subsequent degumming and carding processes, as well as the cleanliness and hand feel of the final product.

Colour and appearance: The hue, brightness, saturation and uniformity of the bast fibre are evaluated by visual inspection or colorimeters (such as Datacolor and X-Rite). The appearance inspection includes checking the colour consistency, spots, mildew, entangled filaments and hard strips of the bast fibre, and is an intuitive basis for evaluating the raw material grade and suitability.

Main Testing Scope

Raw bast (raw stalk and dry stalk): A preliminary inspection of the harvested bast plant stalks is carried out, including the stalk height, diameter, maturity, pest and disease conditions and a preliminary estimation of the bark content, used for raw material purchase grading and estimating the bast yield rate.

Scutched bast (degummed bast): Refers to the bundle-shaped long fibres obtained after preliminary processing such as retting (degumming) and scutching. This is the main trading and testing form in the bast fibre spinning industry, with the most comprehensive test items, directly determining the spinning value and cost.

Bast slivers and bast yarns: For the sliver after the carding process, its evenness, weight deviation per unit length and impurity content are tested; for the spun bast yarn, its linear density, twist, single yarn strength, evenness CV value and hairiness are tested, to control the quality of the semi-finished products and finished yarns.

Bast fabrics and products: For the final products, such as bast cloth, bast clothing and home textiles, the items including the fabric density, breaking strength, tearing strength, abrasion resistance, shrinkage and colour fastness are tested, to ensure that they comply with the product standards and use requirements.

Special and modified bast fibres: Special tests are carried out for bast materials that have undergone fine treatment, chemical modification, blending with other fibres or have specific functions (such as antibacterial and flame retardancy), evaluating their modification effect and functional durability.

Import and export trade arbitration inspection: In accordance with the international trade contract or letter of credit terms, a third-party notary inspection institution (such as SGS and BV) inspects the weight, quality and specification of the bast fibre and issues a certificate, as the basis for settlement and claims.

Common Testing Methods and Standards

Physical property test methods: In accordance with the GB/T, ISO and ASTM standard series. For example, the length test refers to GB/T 18147 (ramie) or ISO 2370 (flax); the strength test refers to GB/T 5882 (ramie breaking strength) or ASTM D3822; the fineness test refers to GB/T 5888 (ramie fibre count). These methods focus on the mechanical and geometric morphology indicators of the fibre.

Chemical analysis test methods: Used to determine the chemical composition and residual gum of the fibre. For example, the pectin content is determined by the carbazole colorimetric method or the m-hydroxybiphenyl method; the lignin content adopts the sulfuric acid method; the residual gum rate (the sum of fat and wax, water-soluble substances, pectin, hemicellulose, etc.) is systematically analyzed in accordance with the GB/T 5889 "Ramie chemical composition quantitative analysis method" standard series.

Microscopic observation method: A biological microscope or scanning electron microscope (SEM) is used to observe the longitudinal morphology (the transverse joint and vertical streak characteristics), cross-section shape (polygonal and kidney-shaped) and surface attachments and damage conditions of the bast fibre, for fibre type identification and quality analysis.

Near-infrared spectroscopy analysis method (NIRS): A rapid, non-destructive modern testing technology. By establishing calibration models between indicators such as the composition (such as cellulose and lignin content) and strength of the bast fibre and the near-infrared spectrum, the rapid prediction of multiple indicators of large-batch samples can be realized in a short time.

Hand feel, visual inspection and grading inspection method: Still widely used at the raw material purchase and production sites. Relying on experience, inspectors quickly grade the bast bundles by observing the colour, gloss, hand feel, length uniformity, impurity content and defects, and comparing with physical reference samples, such as the numbering grading of flax.

Ecological and safety item test methods: For export or high-end products, in accordance with Oeko-Tex Standard 100 and the REACH regulation, the content of hazardous substances such as banned azo dyes, formaldehyde, heavy metals (Pb and Cd) and pesticide residues in bast fibres and their products is tested.

Testing Instruments and Equipment

Fibre length tester: Such as the Almeter or the Seydel length tester, which automatically measures and statistically analyzes the length distribution curve, staple length, short fibre content and other data of the fibre through capacitive or photoelectric scanning. It has high efficiency and objective results.

Single fibre / bundle fibre strength tester: Such as the electronic strength testers of brands like Instron and Textechno, equipped with dedicated grips suitable for fibres, which can precisely determine the stress-strain curve of a single bast fibre or a bundle of bast fibres, obtaining parameters such as the breaking force, elongation and initial modulus.

Fibre fineness analyzer: Including the traditional cut-middles cutting device, precision balance and projection microscope (for the cut-middles weighing method), as well as the fast and convenient air-compression fineness analyzer (airflow meter), the latter indirectly calculating the average fineness through the resistance of the fibre plug to the air flow.

Standard constant temperature and humidity laboratory: All physical property tests must be carried out under standard atmospheric conditions (such as a temperature of 20±2 ℃ and a relative humidity of 65±4%), to ensure the accuracy and comparability of the test results. This environment is jointly maintained by a constant temperature and humidity air conditioning system, humidifiers and dehumidifiers.

Impurity analysis machine and oven: The impurity analysis machine separates the impurities and fibres in the bast sample through mechanical combing and beating and airflow separation, and weighs them to calculate the impurity content. The forced-air oven is the standard equipment for determining the moisture regain, calculating the moisture content by drying to constant weight.

Chemical analysis laboratory equipment: Including Soxhlet extractors (for fat and wax extraction), analytical balances, constant temperature water baths, ultraviolet-visible spectrophotometers (for colorimetric analysis) and muffle furnaces (for ash content determination), used to complete the systematic quantitative analysis of the chemical composition.

Electron microscope and near-infrared spectrometer: A scanning electron microscope (SEM) is used to observe the ultra-fine structure of the fibre; a near-infrared spectrometer (such as FOSS NIRS) combined with professional software and models realizes the rapid, online or offline non-destructive testing of multiple quality parameters of the bast fibre, and is the development direction of intelligent testing.

Testing Standards

Domestic Standards:

1. GB/T 18147.1-2000, Test method for ramie fibre — Part 1: Determination of length

2. GB/T 18147.2-2000, Test method for ramie fibre — Part 2: Determination of fineness

3. GB/T 18147.3-2000, Test method for ramie fibre — Part 3: Determination of breaking strength and elongation at break

4. GB/T 5882-2012, Test method for the breaking strength of ramie fibre

5. GB/T 5888-2010, Test method for the fineness of ramie fibre

6. GB/T 5889-2010, Quantitative analysis method of ramie chemical composition

International Standards:

1. ISO 2370, Textiles — Determination of fineness of flax fibres by permeametric methods

2. ASTM D3822, Standard test method for tensile properties of single textile fibers

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.