PTFE Filament Testing

Polytetrafluoroethylene (PTFE) filament testing mainly conducts scientific testing and analysis on linear density and denier, breaking tenacity and elongation at break, thermal shrinkage, friction coefficient, chemical corrosion resistance, and appearance quality and defects, 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 and denier: Linear density is the most basic physical indicator of PTFE filaments, usually expressed in tex or denier. It directly affects the grammage, thickness and final use of the fabric. The test method usually refers to GB/T 14343 or ASTM D1907, and the calculation is made by measuring the dry weight of the filament of a specified length. The influence of the environmental temperature and humidity on the measured value needs to be considered in the results.

Breaking tenacity and elongation at break: This indicator evaluates the ability of the filament to resist tensile breakage, and is the key to measuring its mechanical properties. An electronic single yarn strength tester is used, in accordance with the GB/T 3916 or ISO 2062 standard, to clamp a specimen of a specified length and stretch it until breakage, recording the maximum breaking force and the corresponding elongation, and calculating the strength per unit linear density, expressed in cN/dtex.

Thermal shrinkage: PTFE filaments shrink under heating conditions, and this property is crucial for subsequent processing and the dimensional stability of the products. During testing, a specific pre-tension is applied to the filament, it is treated at a specified high temperature (such as 150 ℃ or 200 ℃) for a fixed time, and after cooling, the length change is measured and the thermal shrinkage percentage is calculated, usually referring to the enterprise standards or relevant industry test methods.

Friction coefficient: The filament surface is smooth and the friction coefficient is extremely low, which directly affects its textile processing performance (such as twisting and weaving) and the hand feel of the products. The capstan method or inclined plane method is mostly used for testing, measuring the dynamic and static friction coefficients between the filament and standard friction materials (such as ceramics and metals). The test needs to be carried out under constant temperature and humidity conditions to ensure data comparability.

Chemical corrosion resistance: Although PTFE itself is famous for its excellent chemical inertness, the filament products still need to verify their tolerance to specific extreme chemical media. In the test, the filament specimen is usually immersed in strong acids, strong bases or organic solvents for a certain time, and then its appearance change, weight change and strength retention rate are evaluated, to confirm its applicability in actual harsh environments.

Appearance quality and defects: Including observing surface defects such as the colour uniformity, fluff, stiff filaments, contamination and knots of the filament. The test is usually carried out under a standard light source cabinet, evaluated by visual inspection or with auxiliary magnifying equipment against reference photographs or standards. The appearance quality directly affects the quality and aesthetics of the subsequent fabric.

Testing Scope

Industrial filter materials: PTFE filament filter media used for high-temperature flue gas dust removal (such as in coal-fired power plants and cement plants). The testing focus is on the breaking strength retention rate at high temperatures, acid and alkali resistance, and the peel strength after lamination, ensuring its long-term service life and filtration efficiency under harsh working conditions.

High-performance protective clothing and sealing materials: Filaments applied in fire protection, chemical protection and high-end sealing fields. In addition to basic physical properties, the testing scope focuses more on dimensional stability at extreme temperatures, low friction coefficient, and penetration resistance tests for specific chemical reagents, ensuring the safety of personnel and equipment.

Medical textile materials: Filaments used for artificial blood vessels, sutures and protective fabrics. The testing requirements are extremely strict, and biocompatibility tests (such as cytotoxicity and sensitization), sterility verification and long-term strength decay evaluation after implantation need to be carried out, which must comply with the relevant requirements of the YY/T 0506 standard series or ISO 10993.

Aerospace and military fields: Used for special cables, parachutes and radomes. The testing scope includes the mechanical property changes in an ultra-wide temperature range (-196 ℃ to +260 ℃), vacuum outgassing characteristics, radiation resistance, and the dielectric constant and loss tangent at high frequencies.

Civil high-end textiles: Such as the base fabric of waterproof and breathable membranes for outdoor sportswear and high-performance sewing threads. Testing focuses on garment performance indicators such as washing fastness, ultraviolet aging resistance, moisture permeability and the peel strength after lamination with other materials.

Testing Methods

Tensile property test method: In accordance with standards such as GB/T 3916, a constant rate of extension (CRE) strength testing machine is used. The specimen length is usually 500 mm, and the stretching speed is set according to the material characteristics. Full conditioning needs to be carried out under standard atmospheric conditions before the test. The load-elongation curve is recorded, and a series of parameters such as breaking force, breaking tenacity, elongation at break and initial modulus are calculated.

Thermal property analysis (DSC/TGA) method: Differential scanning calorimetry is used to determine the melting temperature, crystallinity and thermal history of the filament; thermogravimetric analysis is used to evaluate its thermal decomposition temperature and thermal stability. Through programmed temperature control, the heat flow or mass change of the sample is monitored in an inert or oxidizing atmosphere, providing data support for the thermal processing and the upper application temperature limit of the material.

Microscopic observation method: An optical microscope or scanning electron microscope is used to observe the surface morphology, cross-section shape, diameter uniformity and possible internal defects (such as holes and impurities) of the filament. SEM can also carry out fracture morphology analysis to assist in judging the fracture mechanism.

Friction coefficient determination method: The capstan method is commonly used. The filament is wrapped around a friction roller at a certain wrap angle, one end is applied with a fixed tension, and the other end is connected to a force sensor. By measuring the tension change during the pulling process, the dynamic and static friction coefficients are calculated. During the test, the environmental temperature and humidity and the running speed of the filament need to be controlled.

Chemical stability test method: The immersion method is adopted. The filament specimen is placed in a chemical reagent of a specific concentration and temperature, immersed for a specified time, then taken out, cleaned with deionized water, dried, and then its mass change rate, diameter change and mechanical property retention rate are tested, comprehensively evaluating its corrosion resistance grade.

Density gradient column method: Used to precisely determine the density of PTFE filaments. A series of mixed liquid columns with a density gradient are configured, the filament specimen is put into them, left to rest at the equilibrium position, and its density value is determined through the calibration curve. Density is an important indirect indicator for identifying the material type and evaluating the crystallinity.

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 3916-2013, Textiles — Yarns from packages — Determination of single-end breaking force and elongation at break using constant rate of extension (CRE) tester

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

5. GB/T 1033.1-2008, Plastics — Methods for determining the density of non-cellular plastics — Part 1: Immersion method, liquid pycnometer method and titration method

6. GB/T 3140, Textiles — Test method for friction coefficient of yarns and filaments

International Standards:

1. ISO 2062, Textiles — Yarns from packages — Determination of single-end breaking force and elongation at break using constant rate of extension (CRE) tester

2. ASTM D1907, Standard test method for linear density of yarn (yarn number) 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

Electronic single yarn strength tester: The core mechanical property testing equipment, with high-precision force and elongation sensors. It needs to satisfy the CRE testing principle, the grips should effectively prevent the filament from slipping, and the software can automatically calculate and output various parameters such as the breaking tenacity, elongation at break, load at specified elongation and work, and comply with multiple standards such as GB, ISO and ASTM.

Yarn length measuring instrument and precision balance: Supporting equipment for linear density testing. The yarn length measuring instrument can wind a specified length of yarn (such as 100 m) at a constant low tension, and the precision balance (accuracy of at least 0.001 g) weighs its mass. Combining the two, the accurate linear density value is obtained by calculation, and the measurement process needs to be carried out in a constant temperature and humidity laboratory.

Thermal shrinkage tester: Usually composed of a heating oven, specimen holder, pre-tensioning device and length measuring ruler. The initial length of the specimen is marked under a specific pre-tension, and after heat treatment in the oven set to a specified temperature, it is cooled to room temperature and the final length is measured. The instrument can directly calculate and display the thermal shrinkage percentage.

Friction coefficient tester: An instrument specially used to measure the friction characteristics of materials such as fibres, filaments and films. It usually adopts a capstan-type or flat sliding-type design, is equipped with high-sensitivity sensors and a data acquisition system, can record the force change during the friction process in real time, and automatically calculate and report the dynamic and static friction coefficient curves and average values.

Thermal analyzer (DSC/TGA): The differential scanning calorimeter and thermogravimetric analyzer are key instruments for studying the thermal properties of PTFE filaments. DSC is used to analyze the melting and crystallization behavior, and TGA is used to evaluate the thermal stability and decomposition temperature. The instruments need to have precise temperature control and atmosphere switching functions, and data analysis is carried out by professional software.

Standard light source color assessment cabinet: An environmental device for evaluating the appearance colour and defects of the filament. It provides multiple standard light sources such as D65 and TL84, ensuring the accuracy and consistency of observing and comparing the filament colour, gloss and surface defects under different lighting conditions. It is an essential tool for appearance inspection.