Impact Resistance of PP and ABS Regranulates – Safety, Testing, and Real-World Performance

of Dr. Magdalena Laabs January 24, 2026

A car bumper that fractures in a brittle manner under a minor impact, a pipe that gets damaged during installation, or a plastic component that behaves unpredictably at low temperatures—these are issues that end users encounter more often than is commonly assumed. In such cases, the key material parameter is impact resistance, defined as the ability of a polymer to absorb impact energy without sudden brittle failure.

At the same time, an increasing number of components used in vehicles and other technical products are now manufactured from recycled materials. For end users, this raises questions about safety and durability, while for producers and recyclers it creates the need for proper testing and control of regranulate impact resistance, so that the material performs in accordance with application requirements.

In the later part of this article, I move on to technical aspects relevant to recyclate producers and processors, including impact testing, standard requirements, and interpretation of test results in the context of specific applications.

Are recycled plastics used in cars and bumpers, and does this affect safety?

Yes. Modern automotive manufacturing widely uses recycled plastics, including in exterior vehicle components. This applies, among others, to bumpers, wheel arch liners, technical shields, as well as trim and finishing parts.

What matters most, however, is not whether the material comes from recycling, but whether it meets technical requirements, particularly those related to impact resistance and impact energy absorption.

Automotive bumpers are not made from pure ABS. In practice, they are most commonly produced from:

PP modified with elastomers (PP/EPDM, PP/TD)—materials specifically engineered for impact energy absorption,
less frequently, modified polymer blends tailored to specific crumple zones.

ABS, on the other hand, is widely used in exterior and semi-structural components, such as:

wheel covers,
technical housings,
protective panels,
styling and aerodynamic parts.

In these applications, ABS provides a balanced combination of stiffness, impact resistance, and surface appearance.

What about safety?

If a regranulate (i.e., recycled plastic):

is properly modified,
has controlled impact resistance,
has been tested in accordance with the applicable standard,

then it does not reduce vehicle safety.

Problems arise only when:

regranulates with insufficient impact resistance are used,
testing is omitted or test results are misinterpreted,
the material is applied outside the range of applications for which it was qualified.

For this reason, automotive manufacturers apply very strict impact testing requirements, and recycled materials used in vehicles are not selected at random—they must meet the same functional requirements as virgin materials.

What does this mean for the vehicle user?

For the driver and passengers, it does not matter whether a component is made from virgin material or recycled material. What matters is whether the component:

behaves predictably under impact,
does not fail in a brittle manner,
properly absorbs impact energy.

This is precisely why impact resistance of plastics is one of the key parameters in the design and material selection of automotive components.

Charpy and Izod methods, specimen preparation, standard requirements, and technological relevance

Impact resistance of PP and ABS regranulates is a parameter used when qualifying materials for applications where parts are exposed to impact loads, dynamic stresses, and assembly-related stresses. In industrial practice, this parameter determines whether a given regranulate can be used in a specific application or should be excluded from it.

Impact testing is performed on impact test specimens (commonly referred to in production practice as “test bars”), prepared in accordance with the requirements of the applicable standard. Compliance with the standard is determined by specimen dimensions, the method of specimen preparation, and the test conditions.

Impact testing methods: Charpy and Izod

Two impact testing methods are commonly used for PP and ABS regranulates: Charpy and Izod. These methods differ in specimen mounting and stress distribution during impact and are not equivalent.

In the Charpy method, the specimen is supported on two anvils and struck at its midpoint. In the Izod method, the specimen is clamped as a cantilever and struck at the free end.

Differences in the loading configuration result in different crack initiation and propagation mechanisms. For this reason, results obtained using Charpy and Izod methods must not be compared or converted. The selected method should be applied consistently within the quality control system.

In European industrial practice, particularly for PP and ABS regranulates, the Charpy method is more commonly used because it is more sensitive to material degradation and better differentiates between regranulate batches. The Izod method is applied when required by customer specifications or target markets.

Equipment used for Charpy and Izod testing

Impact testing using Charpy and Izod methods is carried out on pendulum impact testers, configured for the appropriate specimen support or clamping method.

A pendulum impact tester:

is equipped with interchangeable supports or clamps for Charpy or Izod testing,
allows selection of impact energy appropriate for the tested polymer,
records the energy absorbed by the specimen during impact.

For notched specimen testing, a notch cutter is required to produce a notch with geometry and dimensions specified by the standard. Without a correctly machined notch, the test does not comply with standard requirements.

If testing is conducted at temperatures other than ambient, specimens are conditioned in temperature-controlled chambers prior to testing.

Preparation of specimens for impact testing

In quality control of PP and ABS regranulates, the standard practice is to prepare specimens by injection molding using a mold compliant with the standard requirements. The regranulate is processed under defined and documented conditions, including barrel and mold temperatures, injection speed, holding pressure, and cooling time.

These parameters directly influence the measured impact resistance and are part of the test conditions. Any change in processing parameters constitutes a change in test conditions and may result in significant differences in impact values, even for the same material batch.

An alternative approach involves extruding sheets and cutting specimens from them; however, in industrial practice this method is mainly used for comparative or development studies. For routine quality control of regranulates, it is used less frequently due to higher result variability.

Notch as a material quality assessment tool

In impact testing of PP and ABS regranulates, notched specimens are most commonly used. The notch defines the crack initiation point and enables assessment of the material’s resistance to crack propagation.

Testing of notched specimens allows evaluation of:

effects of thermal degradation in PP,
the condition of the elastomeric phase in ABS,
the presence of contamination and material inhomogeneity.

The notch must be produced using a dedicated notch cutter and in accordance with the standard requirements. A manually produced notch or one made using unsuitable tools results in non-compliant test data.

Standard requirements and result comparability

The impact testing standard defines:

specimen dimensions,
notch geometry,
specimen support or clamping method,
test temperature,
calculation and reporting of results.

If test documentation lacks information on the applied method, standard, test temperature, or specimen preparation, the obtained result is not comparable between material batches or between different suppliers.

Changes in impact resistance after recycling

For PP, reduced impact resistance is most often the result of polymer chain degradation and changes in molecular weight distribution caused by the material’s thermal history. A regranulate may meet MFI requirements while simultaneously exhibiting reduced impact performance.

For ABS, the condition of the elastomeric phase is critical. Excessive processing temperatures, prolonged residence time, or repeated processing cycles reduce the material’s ability to absorb impact energy, directly lowering impact resistance.

Importance of impact resistance for end-use applications

High impact resistance of PP or ABS regranulates enables their use in components exposed to mechanical impacts, assembly stresses, or variable temperature conditions. Reduced impact resistance increases the risk of part cracking, quality instability, and customer complaints.

From the end user’s perspective, this parameter determines whether a material is suitable for a given application, regardless of whether it is virgin or recycled.

Practical conclusions

Declaring impact resistance for PP and ABS regranulates is meaningful only when:

a clearly defined test method (Charpy or Izod) is used,
specimens are prepared in accordance with standard requirements,
specimen preparation and test conditions are known and repeatable.

Otherwise, the test result does not represent reliable technical information for either the regranulate producer or the customer.

Impact resistance in specific industrial applications

The importance of impact resistance of PP and ABS regranulates is particularly evident in applications where components are subjected to dynamic loads or impacts during service.

For PP pipe manufacturers, impact resistance directly affects pipe performance during transport, storage, and installation, as well as material behavior at lower temperatures. Reduced impact resistance may lead to pipe cracking due to accidental impacts or drops, even when other parameters such as MFI remain within specification. In practice, this results in damage prior to system commissioning and issues during quality acceptance.

For ABS components such as bumpers, technical housings, and protective parts, impact resistance determines the material’s ability to absorb impact energy without brittle fracture. Reduced impact resistance after recycling, caused by degradation of the elastomeric phase, increases susceptibility to cracking under point impacts, low-energy collisions, or low-temperature service conditions. For manufacturers, this translates into application non-compliance and increased warranty claims.

In both cases, impact resistance is not an auxiliary parameter but a property that determines whether a regranulate is suitable for a specific application. Material with insufficient impact resistance, even if other parameters are within specification, does not meet functional requirements.

Impact resistance as a relevant parameter for other polymers

Although this article focuses primarily on PP and ABS regranulates, impact resistance is also a critical parameter for other polymers used in mechanical recycling.

In PS, impact resistance often determines whether the material can be used in technical components rather than only in simple packaging products. In PA, impact performance, particularly at low temperatures and in the presence of moisture, is essential for structural and technical components. In PET, impact resistance is relevant for applications requiring resistance to cracking and for modified technical recyclates. In PVC, impact resistance directly affects the durability of profiles, pipes, and construction elements, especially at low temperatures.

In all cases, the same principles apply: impact resistance must be tested in accordance with the standard, using specimens prepared according to standard requirements, and results must be interpreted in the context of processing history and intended application.

Additional information

I am currently preparing a publication titled “Additives in Mechanical Recycling of Plastics – Improving Quality and Stability of Recyclates”, which discusses:

impact modifiers in recyclates,
elastomers and copolymers as impact phases in recyclates,
mechanisms of improving resistance to crack initiation and propagation,
impact modification of ABS, PS, PA, and PET recyclates,
tailoring recyclate properties for structural applications.

The publication is in its final stage and will be released in print shortly.

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