Polypropylene Fiber Inspection

Polypropylene fibre inspection mainly conducts scientific testing and analysis on fibre linear density testing, breaking strength and elongation at break testing, melt flow index determination, heat shrinkage testing, colour fastness testing and anti-aging performance testing, 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 linear density testing: The fibre linear density is the core indicator for measuring the thickness degree of the polypropylene fibre, usually expressed in decitex (dtex) or denier. The purpose of testing this parameter is to evaluate the uniformity of the fibre, and it directly affects the grammage, handle and physical properties of the final fabric. For the polypropylene of different uses, such as spunbond nonwovens and filaments, the required linear density ranges differ significantly.

Breaking strength and elongation at break testing: This item is the key to evaluating the mechanical properties of the polypropylene material. A tensile testing machine is used to apply a tensile force to the specimen under standard conditions until fracture, recording its maximum force value (breaking strength) and the elongation percentage at fracture (elongation at break). These data are directly related to the durability and reliability of the polypropylene products, such as geotextiles, ropes and packaging materials, in actual use.

Melt flow index determination: The melt flow index (MFI) is an important parameter for measuring the fluidity of the polypropylene resin in the molten state, reflecting the average molecular weight and molecular weight distribution of the polymer. Under a specific temperature and load, the mass of the melt passing through a standard die within 10 minutes is determined. This indicator is crucial for the setting of the processing processes such as spinning and extrusion, and directly affects the spinnability of the fibre and the uniformity of the final product.

Heat shrinkage testing: Polypropylene is a thermoplastic fibre and will shrink when heated. In the heat shrinkage testing, the fibre or fabric is usually placed in a specific temperature (such as boiling water or hot air) for a certain time, and the percentage of the length change before and after the treatment is measured. This item is of great significance for evaluating the stability of the finishing process, the dimensional stability of the finished product, and the performance in some high-temperature application environments.

Colour fastness testing: For the coloured polypropylene products, the stability of their colour under the action of various external factors needs to be evaluated. The conventional testing items include the colour fastness to rubbing, colour fastness to washing, colour fastness to perspiration and colour fastness to light. By simulating the actual use conditions through the standardized test methods, the degree of colour change and the staining situation are rated, which is an important link in the quality certification of textile products.

Anti-aging performance testing: The molecular chains of polypropylene are sensitive to ultraviolet light and thermal oxidation, and are prone to degradation. In the anti-aging performance testing, the artificial accelerated aging tests are usually adopted, such as xenon lamp aging, ultraviolet aging or hot air aging, evaluating the strength retention rate, colour change and micro-structural change of the sample after the aging treatment, to predict its service life in harsh environments such as outdoors.

Testing Scope

Polypropylene staple fibres: The testing scope covers the various polypropylene staple fibres used for spinning, nonwovens and filling materials. The key tests are the linear density deviation rate, length deviation rate, breaking strength, defect content, crimping performance and oil content, to ensure their processability and product consistency in the subsequent blending or pure spinning processes.

Polypropylene filaments and textured yarns: Including the polypropylene multifilaments, monofilaments and stretch yarns used for weaving, knitting and high-strength ropes. In addition to the basic physical properties, their twist, interlace degree, boiling water shrinkage and elastic recovery rate also need to be tested, with special attention paid to their evenness (CV value), which has a direct influence on the appearance and handle of the fabric.

Polypropylene nonwovens: Covering the polypropylene nonwovens produced by the processes such as spunbond, meltblown, needle punching and thermal bonding, widely used in the fields of medical, hygiene, geotechnical and filtration. The testing items include the mass per unit area, thickness, longitudinal and transverse breaking strength and elongation, bursting strength, air permeability, water permeability and specific functional properties (such as filtration efficiency).

Polypropylene woven and knitted fabrics: Including the various apparel, decorative and industrial fabrics woven with the pure or blended polypropylene yarns. The testing scope involves the physical properties (such as breaking strength, tearing strength and abrasion resistance), dimensional stability (washing shrinkage and heat shrinkage), appearance retention and wearing performance of the fabric.

Polypropylene industrial products: Specifically referring to the high-strength or functional products such as ropes, cables, geotextiles, tarpaulins, filter bags and packaging straps. The testing includes not only the performance of the material itself, but also focuses on the key application performance of the finished products, such as the equivalent opening size and vertical permeability coefficient of the geotextile, the minimum breaking force of the rope, and the weathering aging performance of the various products.

Polypropylene masterbatches and chips: The polypropylene resin chips used for producing the fibres and the masterbatches added with colour powders and functional additives (such as anti-aging agents and flame retardants) are tested. The key items include the melt flow index, ash content, isotacticity, yellowness index, volatile content, and the active ingredient analysis and dispersion uniformity evaluation of the additives.

Testing Methods

GB/T 14335-2008 "Testing method for linear density of man-made fibres — Staple fibres": This method specifies the standard procedure for determining the linear density of the man-made staple fibres by the middle-section weighing method. Specifically, a sufficient number of fibres are randomly drawn from the sample, the middle section of the specified length is cut, conditioned under standard temperature and humidity conditions and weighed, and the average linear density and coefficient of variation are obtained through calculation. It is the basic method for evaluating the fineness uniformity of the fibre.

GB/T 14344-2008 "Testing method for tensile properties of man-made filament yarns": This standard is applicable to determining the breaking strength, elongation at break and initial modulus of the polypropylene filament yarns. A constant-rate-of-extension strength tester is used, and the testing is carried out under the specified clamping length, tensile speed and pretension. The result takes the average value of multiple measurements, and the coefficients of variation of the breaking strength and elongation at break are required to be reported.

GB/T 3682-2018 "Plastics — Determination of the melt mass-flow rate (MFR) and melt volume-flow rate (MVR) of thermoplastics": This is the melt flow index determination method adopted by the national standard. The polypropylene chips or pellets are added to the barrel heated to 230 ℃, under the standard load of 2.16 kg, the melt is extruded and the samples cut at the specified time intervals are weighed, calculating the melt mass-flow rate. It is the core test for controlling the processing performance of the raw materials.

GB/T 6505-2017 "Testing method for heat shrinkage of man-made filament yarns": This method usually adopts the boiling water shrinkage method. The initial length of the filament specimen under the specified pretension is marked, then it is placed in boiling water for a specific time, taken out and cooled, and its length is measured under the same tension, calculating the heat shrinkage. This method simulates the dimensional change of the fibre when subjected to damp-heat treatment in the post-processing or use.

GB/T 3920-2024 "Textiles — Tests for colour fastness — Colour fastness to rubbing": This method is the basis of the colour fastness series testing. The standard white cotton rubbing cloths in the dry and wet states are used to rub back and forth on the surface of the dyed specimen for a certain number of times with the specified pressure and stroke, and then the staining grade of the rubbing cloth is rated with the grey scales, thereby judging the fixation degree of the dye on the polypropylene fabric and the rubbing fastness grade.

GB/T 16422.2-2014 "Plastics — Methods of exposure to laboratory light sources — Part 2: Xenon-arc lamps": This is the commonly used accelerated aging test method for evaluating the anti-aging performance of polypropylene. The specimen is placed in a controllable xenon arc lamp test chamber, simulating and intensifying the climatic factors such as sunlight, temperature and humidity, and its mechanical properties and colour changes are regularly detected, thereby quickly comparing the weather resistance of the products of different formulations or processes.

Testing Standards

Domestic Standards:

1. GB/T 14335-2008, Testing method for linear density of man-made fibres — Staple fibres

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

3. GB/T 6505-2017, Testing method for heat shrinkage of man-made filament yarns

4. GB/T 3682-2018, Plastics — Determination of the melt mass-flow rate (MFR) and melt volume-flow rate (MVR) of thermoplastics

5. GB/T 16422.2-2014, Plastics — Methods of exposure to laboratory light sources — Part 2: Xenon-arc lamps

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

International Standards:

1. ISO 105, Textiles — Tests for colour fastness

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

3. ISO 1133, Plastics — Determination of the melt mass-flow rate (MFR) and melt volume-flow rate (MVR) of thermoplastics

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 determine the breaking strength and elongation of a single polypropylene fibre. The instrument has a high-precision force sensor and displacement measurement system, can set multiple test modes, and provides a detailed stress-strain curve. It is the key equipment for studying the intrinsic mechanical properties of the fibre and for research and development.

Melt flow rate instrument: Specially used to execute the GB/T 3682 standard and determine the melt flow index of the polypropylene chips or masterbatches. The core components of the instrument are the heated barrel with precise temperature control, the standard die and the piston rod that can be loaded with weights. Through the automatic cutting and weighing system, the efficient and accurate MFR/MVR value measurement can be realized.

Fully automatic yarn comprehensive tester: This equipment integrates multiple functions and can carry out the automated testing of the linear density, twist, strength and elongation of the polypropylene filaments and yarns. Through the advanced sensing technology and software control, the test efficiency and result consistency are greatly improved, and the human errors are reduced. It is suitable for the testing of batch samples.

Xenon lamp weathering test chamber: An accelerated aging equipment simulating the environmental conditions such as full-spectrum sunlight, rain and condensation. By precisely controlling the irradiance, black panel temperature, chamber temperature and humidity cycles, the aging effect of months or even years outdoors can be reproduced in a short time. It is an indispensable instrument for evaluating the light resistance and weather resistance of the polypropylene material.

Standard light source colour matching cabinet: The key auxiliary equipment for the colour fastness rating and colour comparison. It provides multiple standard light sources such as D65, TL84, CWF and UV, ensuring that the observers can objectively and accurately rate the colour difference grades of the tested specimens after the rubbing and washing tests with the grey scales or staining scales under unified and stable lighting conditions.

Scanning electron microscope: Used for the micro observation and analysis of the polypropylene fibres, fractures, cross-sections and the surface morphology after aging. The SEM can provide high-resolution surface images, helping to analyse the morphological structure, defect causes, additive dispersion and the micro mechanism of the aging degradation of the fibre. It is an important tool for the in-depth study of the relationship between the material performance and structure.