Aramid Filament Testing

Aramid filament testing mainly conducts scientific testing and analysis on linear density, breaking tenacity and elongation at break, initial modulus, thermal shrinkage, oil content and moisture content, and twist and evenness, 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

Linear density: Linear density is the core indicator for measuring the fineness of aramid filaments, usually expressed in tex or denier. The test result directly affects the subsequent textile processing technology and the specification of the final product. During testing, under standard atmospheric conditions, a filament sample of a specified length is cut off, weighed with a precision balance and calculated. This indicator is the basis for evaluating the evenness and batch consistency of the filament.

Breaking tenacity and elongation at break: Breaking tenacity is the key property of aramid filaments as a high-strength material, referring to the maximum tensile force that the filament can withstand before tensile breakage, in cN/dtex. The elongation at break characterizes its toughness. The test is usually carried out on a universal material testing machine, stretching the specimen at a standard speed until breakage, recording the maximum force and elongation during the process, and calculating the final results.

Initial modulus: The initial modulus reflects the deformation resistance, i.e., the stiffness, of the aramid filament in the initial stage of loading. The higher the value, the less easily the material deforms at low strain, which is crucial for applications requiring high dimensional stability (such as ballistic protection and composite materials). This data is obtained by analyzing the slope of the initial section of the tensile curve.

Thermal shrinkage: Aramid filaments shrink after being heated, and the thermal shrinkage test is an important means to evaluate their heat-resistant dimensional stability. Usually, the filament is treated at a specific temperature (such as 177 ℃ and 250 ℃) under tension conditions for a specified time, and the length change rate before and after treatment is measured. This indicator has a direct impact on the subsequent heat setting process and the product performance in high-temperature environments.

Oil content and moisture content: The oil content refers to the content of textile spin finish coated on the filament surface, which affects the cohesion, smoothness and antistatic property of the filament. The moisture content is related to the weight and storage stability of the filament. The tests mostly adopt the extraction method (such as using a Soxhlet extractor to determine the oil content) or the oven-drying loss method, ensuring that they are within a reasonable range required by the process.

Twist and evenness: For twisted aramid filaments, the testing of the twist (number of turns per metre) is crucial, as it affects the cohesion, strength and final fabric style of the filament. The evenness test uses a capacitive or photoelectric evenness tester to evaluate the variation of the linear density of the filament in the length direction, which is an important basis for judging its internal quality.

Testing Scope

Para-aramid filaments (such as aramid 1414): Mainly tests its extreme tensile strength, high modulus, excellent thermal stability and chemical corrosion resistance. It is mainly applied in high-strength cables, ballistic protection, high-performance composite materials and other fields, and the testing standards and requirements are usually the most stringent.

Meta-aramid filaments (such as aramid 1313): The testing focus is on excellent high-temperature resistance, flame retardancy, thermal shrinkage and long-term thermal aging resistance. It is widely used in high-temperature filter materials, firefighter clothing and flame-retardant fabrics, and its electrical insulation performance is also one of the key test items.

Products of different specifications and deniers: Testing needs to cover filaments of various specifications from fine denier to coarse denier. Fine denier filaments focus more on strength, evenness and hairiness; coarse denier filaments focus on the absolute breaking force, structural uniformity and wettability with resin.

Colored aramid filaments: In addition to conventional physical and mechanical properties, testing of color fastness (light fastness, rubbing fastness and perspiration fastness) needs to be added, as well as the evaluation of the possible influence of dyes or pigments on their intrinsic strength and thermal properties.

Filaments with sizing or coating treatment: For aramid filaments used in composite materials, the content and distribution uniformity of the surface treatment agent, as well as the interfacial shear strength between the treated filament and the resin matrix, need to be tested. This is the key to determining the interlayer performance of composite materials.

Filaments from different production processes: Covering aramid filaments produced by different processes such as dry spinning and wet spinning. Different processes may lead to differences in the microstructure of the filament (such as the crystalline orientation degree), thus affecting its performance spectrum, and the test items need to be targeted.

Testing Methods

Mechanical property test (referring to GB/T 14344 and ASTM D7269, etc.): Carried out under standard temperature and humidity conditions using a constant rate of extension (CRE) strength tester. The effective length of the specimen is usually 500 mm, and the test is carried out at a specified gauge length and stretching speed, directly obtaining the breaking force and elongation at break, and calculating derived data such as breaking tenacity and initial modulus.

Linear density test (referring to GB/T 4743 and ISO 2060, etc.): The skein method is adopted. After conditioning in standard atmosphere, a skein of a certain length (such as 100 m) is wound, weighed with a balance with an accuracy of 0.001 g, and the linear density value (tex or denier) is calculated according to the relationship between the length and mass.

Thermal property analysis (referring to ASTM D696 and D3418): A thermomechanical analyzer (TMA) is used to determine the thermal shrinkage and coefficient of thermal expansion; differential scanning calorimetry (DSC) is used to determine the glass transition temperature (Tg), melting temperature (Tm, if any) and thermal decomposition temperature; thermogravimetric analysis (TGA) is used to evaluate its thermal weight loss behavior and heat-resistant oxidation stability.

Oil content and moisture content test: The oil content is usually determined by the solvent (such as ether and methanol) extraction method, using a Soxhlet extractor to completely extract the spin finish in the filament, and calculated from the mass difference before and after extraction. The moisture content adopts the oven-drying method, drying the specimen at 105±2 ℃ to constant weight and calculating the mass loss rate.

Microscopic morphology and structure analysis: A scanning electron microscope (SEM) is used to observe the surface morphology, cross-section structure and defects of the filament; wide-angle X-ray diffraction (WAXD) is used to analyze its crystallinity, grain size and molecular chain orientation; infrared spectroscopy (FTIR) is used to confirm the chemical structure and surface modification.

Environmental resistance test: Including UV aging resistance tests (xenon lamp or UV lamp accelerated aging), acid, alkali and salt solution corrosion resistance tests, and high-temperature damp heat aging tests. By comparing the retention rate of mechanical properties before and after aging, its long-term service reliability is evaluated.

Testing Standards

Domestic Standards:

1. GB/T 14344-2008, Testing method for tensile properties of man-made filament yarns

2. GB/T 14343-2008, Testing method for linear density of man-made filament yarns

3. GB/T 6505-2017, Testing method for thermal shrinkage of man-made filaments

4. GB/T 6504-2017, Testing method for oil content of man-made fibres

5. GB/T 6503-2017, Testing method for moisture regain of man-made fibres

6. GB/T 14345-2008, Testing method for twist of man-made filament yarns

International Standards:

1. ASTM D7269, Standard test methods for tensile testing of aramid yarns

2. ISO 2060, Textiles — Yarn from packages — Determination of linear density (mass per unit length) by the skein method

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

Universal material testing machine: The core equipment for tensile property testing, which needs to be equipped with special pneumatic or mechanical grips suitable for fibres to prevent the specimen from slipping or being damaged by the grips. The equipment should have a high-precision force sensor (accuracy better than ±0.5%) and a displacement measurement system, and have functions such as automatic calculation of strength and modulus.

Yarn and filament length measuring instrument and precision balance: The length measuring instrument (such as the wrap reel) is used to precisely wind a specified length of yarn, and its circumference accuracy needs to be regularly calibrated. The analytical balance used in conjunction should have an accuracy of 0.001 g or higher. The combination of the two is the basis for accurately determining the linear density.

Thermal analysis instrument set: Including a thermomechanical analyzer (TMA), differential scanning calorimeter (DSC) and thermogravimetric analyzer (TGA). These devices can provide key data such as the dimensional change, thermal transition temperature and thermal stability of aramid filaments during heating, which is crucial for evaluating their heat resistance grade.

Soxhlet extraction device and constant temperature oven: The Soxhlet extractor is used for the oil content determination, and needs to be combined with a water bath heating device and a solvent recovery system. The forced-air drying oven is used for the moisture content determination and specimen conditioning, and requires uniform and stable temperature control with a small fluctuation range.

Twist tester and evenness tester: The twist tester is used to determine the filament twist by the direct counting method or the untwist-retwist method. The capacitive evenness tester can continuously monitor the coefficient of variation (CV value) of the filament sliver unevenness and draw a spectrogram, which is used to analyze the source of periodic defects of the filament.

Environmental test chamber and aging equipment: Including programmable constant temperature and humidity chambers, UV aging test chambers and xenon lamp aging test chambers. They are used to simulate the performance changes of the filament under different service environments (temperature, humidity and light), and evaluate its durability and service life.