What Is Carbon Black?
Carbon black testing is a group of experiments in which the proportion of carbon black in the polymer is determined by pyrolysis (ISO 6964 / ASTM D1603) and its distribution is graded by microscopy (ISO 18553).
Purpose of Carbon Black
The aim is to verify that carbon black is present in polyolefin products to be used outdoors at a rate that provides UV protection and is distributed homogeneously.
Which Products Is Carbon Black Applied To?
- Polyethylene pipe and inserts
- Jeomembranlar
- Cable sheaths
- Outdoor polyolefin products
In Which Sectors Is Carbon Black Used?
Standards Related to Carbon Black
- ISO 6964
- ASTM D1603
- ISO 18553
- ASTM D5596 (distribution)
Carbon Black Conditions
- Content measurement
- Weighing of carbon black remaining after pyrolysis in inert atmosphere
- Distribution
- Grading of lump size and frequency by microscopy in thin section
- Hedef oran
- Pipe standards typically require a range of 2–2.5% by mass
- Specimen
- Taken from representative locations of the product
Equipment for Carbon Black
- Pyrolysis furnace and inert gas system
- Analytical balance
- Microtome or hot press (for thin section)
- Light microscopy and image analysis
Sample Requirements for Carbon Black
- The sample must be taken from a representative location of the product
- Pyrolysis should be carried out in an inert atmosphere
- Thin and uniform cross-section is required for distribution
- The number of specimens is defined in the standard
Duration of Carbon Black
Typically 3–5 days.
Carbon Black Procedure
- 1The sample is taken from representative locations.
- 2Pyrolysis is applied in an inert atmosphere.
- 3The remaining carbon black is weighed and the ratio is calculated.
- 4Thin section is prepared.
- 5The distribution is graded under the microscope.
- 6The results are compared to the product standard.
Carbon Black Acceptance Criteria
Acceptance criteria are given in the product standard; The content ratio range and degree of dispersion are limited individually.
Evaluation of Results
If the correct proportion of carbon black is poorly dispersed, UV protection will not be sufficient and lumps will create stress concentration. Therefore, content and distribution should be evaluated together. If pyrolysis is carried out in an oxygen environment, the result will be low.
Carbon Black Report
- Applied standards
- Sampling locations
- Pyrolysis conditions
- Carbon black ratio
- Degree of dispersion and microimages
Accreditation
EUROLAB holds internationally recognised accreditation obtained from accreditation bodies party to the IAF and ILAC multilateral recognition arrangements, under ISO/IEC 17025 for laboratory testing, ISO/IEC 17020 for inspection and surveillance, and ISO/IEC 17021-1 and ISO/IEC 17065 for system and product certification. This chain ensures the reports and certificates issued are accepted worldwide.
Whether this test can be offered within accredited scope depends on your product and the standard applied; since accreditation is method-based, the scope is confirmed in writing at the quotation stage.
Scope and authorisationsRelated Regulations
- Pipe and geomembrane product standards
Plastics Testing — What Does This Testing Field Cover?
The section below describes the field that the Carbon Black test belongs to; the conditions and acceptance criteria of this particular test are given in the sections above. The scope specific to your product is confirmed in writing at the quotation stage.
Plastics testing determines the mechanical, thermal and burning behaviour of a polymer material. Unlike metals, plastics are VISCOELASTIC: their behaviour depends on loading rate, temperature and moisture. The same material therefore gives different results under different conditions, and the test conditions are an inseparable part of the result.
The practical consequence of viscoelasticity is this: a plastic part continues to deform over time under a constant load (creep) and the stress it carries at constant deformation falls over time (stress relaxation). A screwed joint loosens, a clamp loses its clamping force, a shelf sags over time. A short-term tensile test does not show this behaviour; a long-term test or an accelerated model is needed.
Thermal behaviour is the second main axis. Melt flow rate indicates the processability of the material and lot-to-lot consistency; heat deflection temperature and the Vicat softening point give a rough limit for service temperature. Thermal analysis (DSC, TGA, DMA) reveals the identity of the material: glass transition temperature, melting behaviour, crystallinity, filler content and decomposition temperature.
Burning behaviour is the third axis and ties directly into product standards. The UL 94 class and the limiting oxygen index are written into the material data sheet; a particular class is required for the housing of an electrical appliance, while a different classification system applies to a construction product.
Ageing is the most frequently skipped part of the field. Plastics degrade under UV, heat, moisture and oxygen: colour changes, the surface cracks, impact strength falls. For a part intended for outdoor use, what matters is not its values on day one but its values after ageing. Xenon arc and fluorescent UV equipment accelerate this degradation and allow comparison.
The output of this family is usually written into the material data sheet, and product standards refer to that sheet. But there can be a difference between the data sheet value and the behaviour of the actual part: orientation formed during moulding, weld lines and internal stresses make the part behave differently from the specimen.
The use of recycled content has added a new question to the field. Recycled resin varies from lot to lot; mechanical properties, colour and burning behaviour can shift between batches. For a manufacturer using recycled material, incoming material control is therefore not a choice but a necessity.
Method groups in this field
Mechanical
Tension, compression, bending, Charpy and Izod impact, hardness (Shore), creep and environmental stress cracking.
Thermal
Melt flow index (MFI), heat deflection temperature (HDT), Vicat softening temperature, linear thermal expansion.
Thermal analysis
Transition temperatures and crystallinity by DSC, composition and decomposition by TGA, dynamic mechanical behaviour by DMA.
Burning
UL 94 classification, limiting oxygen index (LOI), glow wire and needle flame tests.
Ageing
Accelerated ageing by xenon arc and fluorescent UV, hot air ageing, humidity and condensation.
Physical
Density, water absorption, ash content, gas and water vapour permeability of films and sheets.
Commonly confused in this field
- A plastics result without a stated test rate and temperature cannot be interpreted; viscoelastic behaviour depends on these parameters.
- A specimen result does not transfer directly to the actual part; moulding orientation and weld lines are decisive.
- HDT and Vicat values are NOT service temperatures; they are a rough indication of an upper limit and do not apply under load.
- The UL 94 class depends on thickness; a different wall thickness requires re-verification.
- For moisture-absorbing polymers (such as polyamide), results are misleading unless conditioning is carried out.
- ASTM D638 and ISO 527 results are not directly equivalent; the specimen geometries and rate definitions differ.
Which decisions these results support
- Material selection and supplier approval
- Meeting the flammability and thermal requirements of the product standard
- Verifying the use of recycled content and lot control
- Moulding process control and lot consistency
- Demonstrating ageing resistance for outdoor use
Related Tests
Frequently Asked Questions About Carbon Black
Can we say that if the carbon black ratio is correct, the distribution is also correct?
No. Even though the ratio is correct, a lumpy distribution both weakens UV protection and creates stress concentration points. The two measurements are made separately and carry separate acceptance criteria.