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EUROLAB Laboratory Services

Plastics Testing · Polimer

Density

ISO 1183-1 (immersion, liquid pycnometer and titration methods)ISO 1183-2 (density gradient column method)ASTM D792 (density by displacement method)ISO 845 (apparent density of cellular plastics and rubber)
Plastics Testing laboratory work

What Is Density?

Density is mass per unit volume. The most common method for plastics is immersion (Archimedes): the sample is weighed in air and in a liquid of known density, and the difference gives the volume.

Purpose of Density

The purpose is to verify raw material identity, monitor filler ratio, and control production consistency. An unexpected change in density is the earliest sign of a formulation or process shift.

Which Products Is Density Applied To?

  • Thermoplastic granules and parts
  • Filled and reinforced compounds
  • Pipe and profile products
  • Films and sheets
  • Foam materials (apparent density)

In Which Sectors Is Density Used?

PlasticsPackagingAutomotiveElectronicsConstruction

Standards Related to Density

  • ISO 1183-1 (immersion, liquid pycnometer and titration methods)
  • ISO 1183-2 (density gradient column method)
  • ASTM D792 (density by displacement method)
  • ISO 845 (apparent density of cellular plastics and rubber)

Density Conditions

Method
Immersion, pycnometer or density gradient column
Temperature
The measurement is made at constant temperature and is indicated in the report
immersion liquid
Liquid of known density that does not affect the sample
Specimen
It should not contain any voids or air bubbles.

Equipment for Density

  • Analytical balance with density measurement setup
  • Temperature-controlled liquid bath
  • Pycnometer set
  • Density gradient column
  • Vacuum degassing setup

Sample Requirements for Density

  • The sample must be taken so as to represent the batch or production run.
  • Sample description, material type, and production direction if any, must be stated.
  • The standard to be applied and any customer specification must be provided together with the sample.
  • The test may be destructive; the required number of samples must be confirmed in advance.
  • Surfaces that will be tested must be protected during transport.

Duration of Density

Measurement, including conditioning, is generally completed within the same working day.

Density Procedure

  1. 1The sample is conditioned and its surface cleaned.
  2. 2The sample is weighed in air.
  3. 3It is immersed in the immersion liquid; air bubbles are removed.
  4. 4It is weighed in the liquid.
  5. 5The temperature and density of the liquid are recorded.
  6. 6Density is calculated.
  7. 7The measurement is repeated and averaged.

Density Acceptance Criteria

The method standard defines how the test is performed, not what the result must be. The acceptance limit comes from the material or product standard, the customer specification, or the relevant regulation; this page therefore does not give a numerical limit.

Evaluation of Results

The result is compared against the range in the raw material technical data sheet or product specification. Deviation in density is explained by causes such as a change in filler ratio, moisture, or voids in the product.

Density Report

  • Sample description, material/product information, and batch number if any
  • Sample preparation method and conditioning conditions
  • Standard and test conditions applied
  • Instrument used and calibration status
  • Measurement results and units
  • Measurement uncertainty (if requested)
  • A statement that the result applies only to the specimen submitted for testing

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 authorisations

Related Regulations

  • Harmonised standards applied according to the product family
  • EU 765/2008 (market surveillance and accreditation framework)
  • Relevant product regulations and customer specifications

Plastics Testing — What Does This Testing Field Cover?

The section below describes the field that the Density 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 Density

Is the same method used for foam materials?

No. In cellular materials the liquid fills the pores; for these products the apparent density calculated from dimensions and mass per ISO 845 is used.

Why is temperature reported?

Both the sample's and the immersion liquid's density change with temperature. A density value given without stating temperature cannot be compared.

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