Mass loss determination of plastics during combustion is a fundamental fire-performance measurement that quantifies how quickly a polymeric material decomposes and volatilizes when exposed to a controlled radiant heat flux. Using techniques such as cone calorimetry in accordance with ISO 5660-1, ASTM E1354, and ASTM E2102, accredited third-party laboratories obtain mass loss rate data that directly supports flame-retardant material development, regulatory compliance, and fire safety engineering. This article explains the underlying principles, sample requirements, measured parameters, test procedures, and typical applications of combustion mass loss testing for plastic materials.
Technical Overview
Mass loss determination of plastics during combustion measures the continuous reduction in specimen mass as a material is heated by a calibrated radiant source, either in ambient air or under piloted/auto-ignition conditions. Because flaming combustion of polymers is sustained by the flux of combustible volatiles produced through thermal decomposition, the mass loss rate (MLR) is one of the most physically meaningful indicators of burning intensity. In practice, a specimen is placed on a precision load cell beneath a conical radiant heater, and its mass is recorded every second throughout exposure, ignition, flaming, and extinction.
The mass loss signal is a cornerstone of modern fire testing because it links directly to other critical fire hazard parameters. When combined with oxygen consumption measurements, the instantaneous mass loss rate allows calculation of the effective heat of combustion and, together with heat release rate data, provides a complete picture of the fire growth potential of a material. Mass loss data are also indispensable for evaluating char-forming and intumescent behavior, comparing flame-retardant formulations, and providing input data for fire dynamics modeling.
The principal standards governing this measurement include:
- ISO 5660-1 — Reaction-to-fire tests; heat release, smoke production and mass loss rate (cone calorimeter method)
- ASTM E1354 — Standard test method for heat and visible smoke release rates using an oxygen consumption calorimeter
- ASTM E2102 — Standard test method for measurement of mass loss and ignitability for screening purposes using a cone calorimeter
- ISO 13927 — Plastics; simple heat release test using a conical radiant heater and a thermopile (with mass loss measurement)
- GB/T 16172 — Chinese national standard adopting the ISO 5660-1 cone calorimeter methodology
Testing Samples
Standard Sheet and Plate Specimens
The reference specimen geometry for cone calorimeter-based mass loss measurement is a square plate of 100 mm × 100 mm, with a thickness typically between 6 mm and 50 mm. Specimens may be tested in the horizontal orientation with a retainer frame, or vertically with appropriate edge framing. Where the product thickness exceeds 50 mm, the specimen is cut down and the reduced thickness is reported.
Thermoplastic Materials
Common engineering and commodity thermoplastics such as polyethylene (PE), polypropylene (PP), polystyrene (PS), ABS, polyamide (PA), polycarbonate (PC), PMMA, and PVC are routinely tested. Because thermoplastics may melt, flow, and drip during exposure, wire grids are frequently placed over the specimen surface to maintain a stable burning configuration, and any melting behavior is documented in the report.
Thermosetting and Composite Materials
Cured epoxy, phenolic, and unsaturated polyester systems, as well as glass-fiber or carbon-fiber reinforced composites (SMC, BMC, GRP laminates), can be evaluated effectively. These materials often form a protective char layer, and mass loss data allow quantitative assessment of char yield and its stabilizing effect on the residual mass curve.
Foamed Plastics
Rigid and flexible polyurethane foams, expanded polystyrene (EPS), and extruded polystyrene (XPS) may be tested with appropriate preparation. Due to their low density, rapid pyrolysis, and possible shrinkage, foams require careful specimen mounting, and multiple replicate tests are recommended to characterize variability.
Finished Components and Parts
Specimens cut from finished products such as automotive interior trim, rail vehicle components, electrical equipment enclosures, cable sheathing compounds, and appliance housings can be assessed, provided a flat 100 mm × 100 mm section of representative thickness can be obtained from the part.
Unless otherwise specified, all specimens are conditioned to equilibrium at 23 ± 2 °C and 50 ± 5% relative humidity in accordance with ISO 291 prior to testing, and their initial mass is determined immediately before the test.
Testing Items
Depending on the selected standard and the client's objectives, the following quantities are typically determined and reported:
- Instantaneous mass loss rate (MLR, g/s) as a function of exposure time
- Peak mass loss rate (g/s) and the time at which it occurs
- Average mass loss rate over defined periods, such as 60 s, 180 s, and 300 s after ignition
- Total mass loss (g) and percentage mass loss relative to initial specimen mass
- Residual mass and char yield after flameout
- Specific mass loss rate normalized by exposed surface area (g/m²·s)
- Time to sustained ignition and time to flameout
- Effective heat of combustion (MJ/kg), derived from the ratio of heat release rate to mass loss rate
Testing Methods
Cone Calorimeter Method (ISO 5660-1 / ASTM E1354 / GB/T 16172)
The specimen, wrapped on its underside with aluminum foil and placed in a holder on the load cell, is exposed to a radiant heat flux selected in the range of 10 kW/m² to 100 kW/m², with 25, 35, 50, and 75 kW/m² being the most common levels. Piloted ignition is induced by an electric spark igniter, or auto-ignition conditions are applied when specified. The load cell records mass continuously at a resolution of typically 0.1 g or better, and the mass loss rate is obtained by numerical differentiation of the mass-time curve. The same test simultaneously yields heat release rate (by oxygen consumption) and smoke production data, making it the most information-rich single-specimen fire test available.
Screening Method (ASTM E2102)
This method is used for rapid screening of mass loss and ignitability under a fixed radiant exposure. It is well suited to comparing candidate formulations, evaluating the effect of additives, and ranking materials before full-scale reaction-to-fire qualification testing. The simpler protocol focuses on ignition time and mass loss behavior, reducing test cost and turnaround time.
Conical Radiant Heater with Thermopile (ISO 13927)
ISO 13927 provides a simplified apparatus in which a specimen is irradiated by a conical heater and mass loss is recorded while heat output is estimated using a thermopile rather than oxygen analysis. It is often applied as a research screening tool for plastic materials and precursor studies prior to full cone calorimeter characterization.
Typical Test Procedure
- Verify apparatus calibration, including load cell zero and span, radiant flux uniformity, and the oxygen analyzer
- Condition and weigh the specimen, mount it with aluminum foil backing and retainer frame, and position it on the load cell
- Apply the selected radiant flux and, where required, activate the spark igniter
- Record mass, ignition time, and visual burning observations continuously until flameout plus a defined post-exposure period
- Calculate mass loss rate, peak and average values, total mass lost, and char yield, and issue a test report with full test conditions
Applications
Combustion mass loss data for plastics serve a wide range of industrial and regulatory purposes:
- Flame-retardant formulation development, including halogenated, phosphorus-based, mineral filler, and intumescent systems, where MLR reduction is a primary performance metric
- Regulatory compliance and material qualification for railway applications under EN 45545-2, which incorporates ISO 5660-1 parameters in its classification scheme
- Building products, transportation interiors, aerospace components, and electrical and electronic equipment where reaction-to-fire evidence is required
- Quality control of incoming resins, compounds, and finished parts against established mass loss performance baselines
- Input data for fire growth modeling, hazard analysis, and equivalence studies replacing larger-scale fire tests
- Academic and industrial research into polymer pyrolysis kinetics, char formation mechanisms, and fire dynamics correlations
Complementary tests such as UL 94 vertical/horizontal burning, limiting oxygen index (ISO 4589), and glow-wire testing (IEC 60695-2 series) are frequently performed alongside mass loss determination to build a complete flammability profile of a material.
FAQ
What is the difference between mass loss rate and heat release rate?
Mass loss rate describes how quickly the material volatilizes, measured directly by the load cell, while heat release rate describes the energy released by combustion of those volatiles, measured by oxygen consumption. The ratio of heat release rate to mass loss rate gives the effective heat of combustion; the two parameters are complementary and are acquired simultaneously in a cone calorimeter test.
Which radiant heat flux level should be selected?
The choice depends on the fire scenario being simulated. Fluxes of 25–35 kW/m² are representative of early-stage or developing fires and are common for general screening, while 50–75 kW/m² approximate well-developed fire exposures. Many specifications require testing at more than one flux level to characterize sensitivity to exposure severity.
Does specimen thickness affect the results?
Yes. Thicker specimens act as a larger heat sink and fuel reservoir, generally extending burning duration and shifting the mass loss curve. Specimens should therefore always be tested at the thickness representative of the end-use product, and thickness must be stated in the report.
How many specimens should be tested?
ISO 5660-1 and ASTM E1354 require a minimum of three replicate specimens per condition. For heterogeneous materials, composites, or foams, additional replicates are strongly recommended to establish statistical confidence.
What is a typical turnaround time?
For a standard test matrix of three specimens at one heat flux level, including conditioning, calibration verification, testing, and reporting, results are typically available within five to ten working days at an accredited third-party laboratory, subject to sample queue and project scope.