Fiber Flax Testing

Flax fibre testing mainly conducts scientific testing and analysis on fibre fineness, breaking force and elongation at break, length and length distribution, moisture regain and moisture content, impurity and shive content, and colour and appearance quality, 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 fineness: Fibre fineness is one of the core indicators for measuring the quality of flax fibre, usually expressed by linear density (tex or dtex) or metric count (Nm). Fineness directly affects the evenness, strength of the yarn and the hand feel and style of the final fabric. During testing, a sufficient number of single fibres need to be randomly drawn from a representative sample and measured under standard atmospheric conditions, and the average value is calculated to evaluate its spinning value.

Breaking force and elongation at break: This indicator is directly related to the durability of flax yarn and fabric. A constant rate of extension (CRE) strength testing machine is used, the fibre specimen is clamped according to the standard, stretched at a constant speed until breakage, and the maximum breaking force (unit: cN or N) and the elongation at break are recorded. Flax fibre usually has the characteristics of high strength and low elongation.

Length and length distribution: Fibre length is the key to determining spin ability and yarn quality. It is usually tested by the hand sorting method or instruments such as the fibre fineness and length analyzer and Almeter, analyzing parameters such as the staple length, mean length and short fibre content of the fibre. The uniformity of the length distribution is crucial for reducing broken ends and unevenness of the sliver during spinning.

Moisture regain and moisture content: Flax fibre has strong moisture absorption, and its moisture state directly affects the weight settlement and subsequent processing performance. The moisture regain test usually adopts the oven-drying method, drying the specimen in an oven at a specified temperature (such as 105±2 ℃) to constant weight, and calculating according to the mass difference before and after drying. This is an important basis for trade and process design.

Impurity and shive content: This test is used to evaluate the cleanliness of flax fibre, including the content of non-fibrous impurities (such as shives, dust and stalk fragments). Through manual sorting or impurity analysis machines, the impurities in the specimen are separated and weighed, and their percentage of the original weight of the specimen is calculated. A high impurity content will increase the difficulty and loss of spinning.

Colour and appearance quality: The colour, gloss, uniformity of the fibre and whether there are defects such as disease spots, mildew and rust spots are evaluated by visual inspection or colour measuring instruments. The colour is usually divided into silver white, light yellow, grey brown and so on. The appearance quality directly affects the aesthetics and grade classification of the final product.

Residual gum content (content of pectin and other substances): After the degumming process, flax fibre still retains some non-cellulosic substances such as pectin and hemicellulose. The residual gum content test mostly adopts the chemical dissolution method (such as the sulfuric acid method or sodium hydroxide solution treatment), and is calculated by measuring the mass loss of the specimen before and after treatment. A moderate residual gum is beneficial to spinning, while too high affects the fibre separation and hand feel.

Testing Scope

Scutched flax (long fibre): Refers to the bundle-shaped long fibre obtained after preliminary processing such as retting and scutching, and is the main raw material of flax spinning. Its testing focuses on comprehensive indicators such as fibre length, strength, fineness, impurity content and colour, and is used to classify the raw material grade and guide the fibre blending process.

Tow (short fibre): The shorter fibres produced during the scutching process, usually less than 20 cm in length. The testing focus is on the short fibre content, impurity content, fibre strength and spin ability evaluation. These indicators determine its use value in the cotton spinning or blending systems.

Dressed flax (long fibre after hackling): The long fibre obtained after the scutched flax is combed by the hackling machine, removing the short fibres and further parallelizing and straightening the long fibres. The testing items are more refined, including the separation degree, uniformity, strength and residual shive content of the fibre, and are the key raw material inspection for producing high-count and fine linen yarn.

Sliver and combing waste: The sliver is a continuous strand made by doubling and drawing of the dressed flax, and its evenness, weight deviation per metre and fibre structure are tested. The combing waste is the short fibre dropped in the combing process, and its length distribution, impurity content and recyclability need to be tested.

Imported and domestic flax raw materials: The testing scope covers flax raw materials from different production areas such as Europe (such as France and Belgium), Eastern Europe and mainland China. According to the trade contract or relevant standards, the fibres from different origins need to be compared, verified and quality certified in terms of fineness, strength, colour and other characteristics.

Work in progress at different processing stages: Testing runs through the whole process from raw material to yarn, including the pretreated fibre, the sliver of the drawing process, the roving and the untwisted spun yarn. The purpose of work-in-progress testing is to monitor the process stability and timely discover and adjust quality problems.

Testing Methods

Physical property test methods: Mainly in accordance with the GB/T, ISO and ASTM standard series. For example, the fibre length adopts the hand sorting method (GB/T 18147.2) or the instrumental method; the strength and elongation adopt the single fibre method (GB/T 18147.6) or the bundle fibre method; the fineness adopts the cut-middles weighing method (GB/T 18147.3) or the airflow method. All tests need to be carried out under standard temperature and humidity conditions (such as 20±2 ℃ and 65±4% RH).

Chemical composition analysis methods: Used to determine the content of cellulose, hemicellulose, lignin, pectin, wax and so on. Common methods include: using the sulfuric acid method to determine α-cellulose; using the chlorine number method or Coomassie brilliant blue method to determine the residual gum (pectin) content; and evaluating the inorganic impurities by ash content determination. These methods require laboratory equipment such as analytical balances, ovens, muffle furnaces and burettes.

Appearance quality inspection methods: Usually carried out under a standard light source cabinet or north-facing natural light, by experienced inspectors comparing with physical reference samples for sensory inspection. The colour, gloss, defects and the type and degree of impurities are graded and evaluated. The instrumental colour measurement method (such as using a spectrophotometric colorimeter) can provide more objective colorimetric data.

Moisture content (moisture regain) test methods: The standard method is the oven-drying method (GB/T 9995), drying the specimen to constant weight for calculation. For rapid inspection, a resistance-type or capacitance-type moisture regain meter can be used for non-destructive testing, but it needs to be regularly calibrated with the oven-drying method.

Impurity content test methods: Mainly including the manual hand sorting method and the mechanical method. The manual method sorts out the impurities in accordance with the standard (such as GB/T 18147.4) and calculates them by weighing. The mechanical method uses an impurity analysis machine to separate the fibre and impurities through airflow and mechanical sieving, which is more efficient and suitable for large-batch inspection.

Fibre length instrumental analysis method: Photoelectric scanning equipment such as the fibre fineness and length analyzer or the Almeter is used. By scanning the fibre beard, the cumulative length distribution curve of the fibre is obtained, thereby quickly obtaining a series of data such as the staple length, mean length, uniformity index and short fibre content.

Testing Standards

Domestic Standards:

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

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

3. GB/T 3921-2008, Textiles — Tests for colour fastness — Colour fastness to washing with soap or soap and soda

4. GB/T 3922-2013, Textiles — Tests for colour fastness — Colour fastness to perspiration

International Standards:

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

2. 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

Electronic single fibre strength tester: Used to precisely measure the breaking force and elongation at break of a single flax fibre. The instrument adopts a high-precision sensor and microcomputer control system, can automatically complete clamping, stretching, data acquisition and processing, and output statistical results such as the maximum value, average value and standard deviation. It is the core equipment for evaluating the mechanical properties of the fibre.

Fibre length fineness and length analyzer / Almeter: A rapid analysis instrument for fibre length based on the photoelectric principle. By preparing a fibre beard and scanning it, according to the relationship between the light transmission or capacitance change and the fibre length, the length-frequency distribution diagram is automatically drawn, and various length indicators are calculated, greatly improving the testing efficiency and consistency.

Standard constant temperature and humidity laboratory: Not a single piece of equipment, but a whole environment composed of an air conditioning system, humidifiers, dehumidifiers and precision temperature and humidity monitoring instruments. It ensures that the laboratory environment is maintained under the standard atmospheric conditions of a temperature of 20±2 ℃ and a relative humidity of 65±4%, which is the premise for the comparability of all fibre physical property test results.

Oven and electronic balance: The oven is used for the drying step in the tests of fibre moisture regain, moisture content and some chemical components, and requires precise and uniform temperature control. The electronic balance needs to have high sensitivity (usually 0.01 mg or 0.1 mg), and is used in all weighing-related testing links, such as fineness weighing, impurity weighing and sample preparation.

Fibre fineness airflow meter or projection microscope: The airflow method (such as the Micronaire) indirectly represents the fibre fineness by measuring the resistance of a constant flow of air passing through a fibre plug of a certain mass. It is fast but gives an indirect value. The projection microscope combined with a micrometer can directly observe and measure the fibre diameter or width. The result is more intuitive and accurate, but it takes longer.

Impurity analysis machine and standard light source cabinet: The impurity analysis machine effectively separates the fibre and impurities (shives, dust and so on) through mechanical combing, beating and air suction, and collects and weighs them separately. The standard light source cabinet provides standard lighting sources such as D65, eliminating the interference of ambient light on the colour and appearance inspection, and ensuring the objectivity and fairness of the evaluation results.

Chemical analysis supporting equipment: Including Soxhlet extractors (for extracting wax), muffle furnaces (for determining ash content), water baths, titration devices, spectrophotometers and various glassware. These devices jointly support the quantitative analysis of various chemical components in flax fibre, to evaluate its degumming degree and chemical properties.