ABS (Acrylonitrile Butadiene Styrene) is a widely used thermoplastic material known for its versatility and durability. It is found in applications from consumer goods to automotive components and electronic devices, with manufacturers typically using technologies like injection molding, CNC machining, and thermoforming to process it.

One key aspect of ABS that makes it suitable for these diverse applications is its moderate level of heat resistance. Though by no means a highly heat-resistant material, ABS’ heat resistance allows ABS products to maintain their integrity and performance when exposed to slightly elevated temperatures, which is crucial in industries such as automotive and electronics where components may be regularly subjected to residual heat from engines or batteries. In the world of FDM 3D printing, ABS is one of the most widely used 3D printing materials alongside PLA and PETG. ABS’ superior heat resistance to PLA is one of the material’s major advantages, although it means it must be extruded at higher temperatures.

This article serves as a comprehensive guide to ABS heat resistance, covering the composition of the material, ways to improve its heat resistance, and industry tests and standards.

1. Basics of ABS

1.1. Chemical Composition of ABS

Acrylonitrile Butadiene Styrene (ABS) is a copolymer composed of three distinct monomers: Acrylonitrile, Butadiene, and Styrene. Each of these monomers contributes specific characteristics to the final ABS material, and their relative proportions determine its overall properties.

The chemical composition of ABS

1. Acrylonitrile, a colorless volatile liquid, lends chemical resistance and rigidity to ABS. It has a high affinity for polar solvents, which contributes to the material's resistance to chemicals such as acids, alkalis, and various organic solvents. Perhaps most importantly, acrylonitrile is also the monomer that contributes most to the heat resistance of ABS. Typically, acrylonitrile makes up 15–35% of ABS by weight.

2. Butadiene, a colorless gas, provides toughness and impact resistance to the copolymer. It is a flexible and resilient material, which contributes to the overall durability of ABS. The proportion of butadiene in ABS ranges between 5–30% by weight.

3. Styrene, a colorless to yellowish oily liquid, is responsible for the ease of processing and good surface finish in ABS. It also contributes to the material's overall strength and dimensional stability. Styrene typically constitutes 40–60% of the ABS composition.

The polymerization process of ABS involves the formation of a copolymer through the reaction of these three monomers. The process begins with the polymerization of styrene and acrylonitrile, forming a styrene-acrylonitrile (SAN) copolymer. Subsequently, butadiene is grafted onto the SAN copolymer backbone, resulting in the formation of the ABS copolymer. The precise balance of these components dictates the physical and mechanical properties of the final ABS material, allowing manufacturers to fine-tune the material for specific applications.

1.2. Physical and Mechanical Properties of ABS

ABS has a natural ivory color

The physical properties of ABS make the material suitable for a wide range of applications. With a natural color varying between translucent ivory and opaque white, ABS has a typical density ranging between 1.03–1.07 g/cm³, making it a lightweight option compared to other plastics. The glass transition temperature of ABS is around 105 °C, allowing it to be processed using techniques such as injection molding, extrusion, and FDM 3D printing.

In terms of mechanical properties, ABS offers a good balance of strength, toughness, and rigidity. Its tensile strength is around 43 MPa, though this varies depending on the specific formulation and processing conditions. This strength allows ABS to withstand moderate loads without breaking or deforming. 

Impact resistance is another key characteristic of ABS, thanks to the presence of butadiene in its composition. This property is particularly crucial in applications where the material is subjected to sudden impacts or stress, such as automotive components or consumer electronics enclosures. The notched Izod impact strength of ABS is around 0.2 kJ/m, but this also depends on factors such as temperature, material formulation, and processing conditions.

In 3D printing, one of the most desirable physical properties of ABS is its score on the melt flow index (MFI), a method for “determining the rate of flow of molten polymer through a closely defined extrusion plastometer.”[1] Better melt flow facilitates better extrusion and easier 3D printing, especially at fast printing speeds.

The combination of these physical and mechanical properties makes ABS a popular choice for a wide range of applications, from consumer goods to industrial components. Its versatility, ease of processing, and relatively low cost contribute to its widespread use across different industries.

2. ABS Heat Resistance

2.1. Factors Affecting ABS Heat Resistance

The heat resistance of ABS is influenced by several factors, including its chemical composition, processing conditions, and the presence of additives. Understanding these factors is essential for optimizing the heat resistance of ABS products and ensuring their durability in high-temperature environments.

Chemical composition

As previously discussed, ABS consists of three primary monomers: acrylonitrile, butadiene, and styrene. The proportions of these monomers in the final ABS product can significantly impact its heat resistance. Higher acrylonitrile content generally results in increased heat resistance due to its high melting point and chemical stability. However, it is important to maintain a balance between the monomers to ensure optimal mechanical properties.

Processing conditions

The processing conditions, such as temperature, pressure, and cooling rate, can also affect the heat resistance of ABS. For example, injection molding ABS parts at high temperatures typically results in more heat-resistant parts (but at the expense of strength and impact resistance). Proper temperature control during the processing stage is essential to ensure the material's molecular structure remains intact and provides sufficient heat resistance. Cooling rate is another critical factor, as rapid cooling can lead to increased internal stresses, potentially reducing heat resistance.

Additives

The incorporation of additives can enhance the heat resistance of ABS. These additives include flame retardants, heat stabilizers, and reinforcing agents. Flame retardants, such as brominated compounds or phosphorus-based compounds, can minimize the flammability of ABS and reduce the risk of thermal degradation. Heat stabilizers, on the other hand, can protect ABS from oxidative degradation caused by prolonged exposure to elevated temperatures.

By considering these factors, manufacturers can fine-tune the heat resistance of ABS materials, ensuring their suitability for various high-temperature applications.

2.2. Heat Deflection Temperature (HDT) of ABS

Heat Deflection Temperature (HDT) is a crucial parameter used to evaluate the heat resistance of a plastic material like ABS. HDT refers to the temperature at which a standard test specimen deforms under a specified load (a stress of either 0.455 MPa or 1.82 MPa), usually measured in degrees Celsius. This value provides insight into the material's ability to maintain its shape and mechanical properties under heat and pressure.

The HDT of ABS typically ranges from 80 to 100 °C, depending on the specific formulation and processing conditions. This temperature range indicates that ABS can maintain its shape and structural integrity in moderate heat environments, outperforming a handful of other polymers such as polypropylene (PP), polyethylene (PE), and nylon 6 (PA6) but falling well short of heat-resistant polymers such as acetal (POM) and polycarbonate (PC). However, it is essential to note that HDT is not an absolute indicator of a material's performance in real-world applications, as it only represents a single point on the material's overall temperature-property curve.

Factors such as chemical composition, processing conditions, and additives, as previously discussed, can influence the HDT of ABS. By optimizing these factors, manufacturers can improve the HDT and overall heat resistance of ABS materials.

It is worth mentioning that HDT alone may not provide a comprehensive understanding of a material's performance in high-temperature applications. Other factors, such as thermal expansion, thermal conductivity, and specific heat capacity, should also be considered when evaluating the suitability of ABS for a particular application. Combining these parameters with the HDT can offer a more comprehensive picture of the material's performance and durability under heat and pressure.

2.3. ABS Heat Resistance and FDM 3D Printing

ABS filament is more heat-resistant than PLA filament

When considering the heat resistance of 3D printed ABS rather than ABS generally, other factors need to be considered. Any printed thermoplastic will behave in a different manner to a molded or formed thermoplastic, and the ABS filament is processed in a different way to ABS granules and other material forms.

In non-industrial FDM 3D printing, ABS is considered a fairly heat-resistant material due to its superior heat resistance to PLA filament and PETG filament, two other prominent 3D printer materials that can be bought at low prices. It may therefore be preferred for functional parts like electronics housings.

On the other hand, the higher glass transition temperature of ABS means it requires higher temperatures to extrude. This puts greater demands on the 3D printer while also making it necessary to use a heated print bed to minimize warping, which occurs to a greater extent with ABS printed parts than PLA or PETG parts.

For industrial applications, the best heat-resistant 3D printer filaments are high-quality engineering thermoplastics like PEEK, which have much better heat resistance than ABS in addition to high impact resistance and other desirable properties. However, due to their high melting temperature, these materials require specialist high-temperature hardware to print.

Recommended reading: ABS print temperature considerations: Nozzle, bed, enclosure

3. Enhancing ABS Heat Resistance

3.1. ABS Blends

One method to enhance ABS heat resistance is by combining it with other thermoplastics to create blends. These blends can significantly improve the overall heat resistance of the resulting material, while still retaining the desirable properties of ABS, such as impact resistance, processability, and surface finish. There are several ABS blend 3D printing filaments on the market,  

Polycarbonate (PC)

Polycarbonate (PC) is a thermoplastic material known for its high heat resistance, excellent mechanical properties, and optical clarity. By blending ABS with PC, manufacturers can create a material with better heat resistance than standard ABS, making it suitable for applications requiring higher thermal stability. The resulting ABS-PC blend often exhibits improved tensile strength, rigidity, and flame retardancy. Researchers have noted an increased heat deflection temperature and Vicat softening temperature as the proportion of PC is increased within the blend.[2] In 3D printing, PC is virtually the only material that is commonly blended with ABS to make filament. An example of such a filament is the 3DXMAX PC-ABS product from 3DXTech.

Polyamide (PA)

Polyamide (PA), commonly known as nylon, is a versatile thermoplastic with high mechanical strength and toughness. Some nylons have excellent heat resistance. When ABS is blended with a temperature-resistant grade of PA, the resulting material offers higher heat resistance and improved mechanical properties. ABS-PA blends can be employed in applications where higher operating temperatures and mechanical strength are required, such as automotive under-the-hood components and electronics enclosures. Though very rare, an example of an ABS-PA 3D printing filament was the 3DXION002 product from Sigma-Aldrich, now discontinued.

3.2. Heat-Resistant Additives for ABS

In addition to creating blends, another approach to enhancing ABS heat resistance is by incorporating heat-resistant additives into the base material. These additives can improve the thermal stability and performance of ABS without significantly altering its processability. In FDM 3D printing, an ABS filament containing a significant percentage of an additive is usually referred to as an ABS composite.

Inorganic Fillers

ABS can be enhanced with glass fibers and other additives

The incorporation of inorganic fillers such as glass fibers can lead to increased heat resistance in ABS. Glass fibers are particularly effective at improving both heat resistance and mechanical properties, as they create a more thermally stable network within the polymer matrix. The addition of glass fibers can increase the heat deflection temperature of ABS by up to 40°C, depending on the filler content. However, the presence of glass fibers may also increase the material's brittleness and decrease its impact strength. An example of a glass-filled ABS 3D printing filament is FibreX ABS+GF from 3DXTech.

Talc and mica, on the other hand, are plate-like fillers that can improve the heat resistance of ABS by forming a barrier to heat transfer within the material.[3] The use of talc or mica fillers can increase the heat deflection temperature by up to 15°C, depending on the filler content and particle size.

Flame Retardants

Some flame retardants, such as brominated compounds and phosphorus-based additives, can also contribute to the heat resistance of ABS. These additives not only improve the material's flame resistance but also increase its thermal stability by reducing the rate of thermal degradation at elevated temperatures. As a result, ABS with flame retardants exhibits higher heat deflection temperatures and reduced distortion under load when exposed to high temperatures.

Heat Stabilizers

Heat stabilizers are additives that help prevent the thermal degradation of ABS by minimizing the effects of heat-induced oxidation and molecular chain scission. Commonly used heat stabilizers include organotin compounds, hindered phenolic antioxidants, and phosphite esters. The use of heat stabilizers can improve the long-term heat resistance of ABS, allowing it to maintain its mechanical properties and dimensional stability at elevated temperatures for extended periods.

4. ABS Heat Resistance Testing and Standards

Ensuring the heat resistance of ABS materials is crucial for their successful application in various industries. To assess the heat resistance of ABS, various testing methods and industry standards have been developed. These tests help evaluate the performance of ABS materials under specific thermal conditions and guide engineers in selecting the most suitable ABS grades for their applications.

4.1. Testing Methods for ABS Heat Resistance

Heat Deflection Temperature Test

One of the most common testing methods for ABS heat resistance is the Heat Deflection Temperature (HDT) test, also known as the deflection temperature under load (DTUL) test. This test measures the temperature at which a standardized specimen deforms under a specified load. The HDT test is performed according to the ASTM D648 standard, which specifies two load levels: 0.455 MPa (66 psi) and 1.82 MPa (264 psi). The test results are essential for engineers to evaluate the suitability of ABS materials for applications with specific temperature and load requirements.

Vicat Softening Temperature Test

Another widely used test method for evaluating ABS heat resistance is the Vicat Softening Temperature (VST) test. This test measures the temperature at which a material starts to soften under the influence of heat and a specified load. The VST test is performed according to the ASTM D1525 standard, which requires a flat-ended needle to be applied to the surface of a specimen with a specified force. The temperature at which the needle penetrates a certain depth into the specimen is recorded as the Vicat Softening Temperature. VST results provide valuable information about the thermal stability of ABS materials and their resistance to deformation under load at elevated temperatures.

Thermal Gravimetric Analysis

Thermal Gravimetric Analysis (TGA) is another testing method used to assess the heat resistance of ABS materials. TGA measures the change in the mass of a specimen as a function of temperature, providing information about the material's thermal stability and degradation behavior. This method is conducted according to the ASTM E1131 standard, which specifies the temperature range, heating rate, and sample mass. TGA results help engineers evaluate the thermal stability of ABS materials and their suitability for high-temperature applications, as well as assess the effectiveness of heat-resistant additives and stabilizers.

4.2. Industry Standards and Regulations for ABS Heat Resistance

To ensure consistent quality and performance of ABS materials, various industry standards and regulations have been established to define the heat resistance properties of ABS. These standards serve as guidelines for manufacturers, allowing them to produce ABS materials with predictable performance in high-temperature applications.

UL 94 Standard for Flammability

One of the key industry standards related to ABS heat resistance is the UL 94 standard, which focuses on the flammability of plastic materials. Developed by Underwriters Laboratories (UL), the UL 94 standard classifies materials based on their burning behavior, including the time it takes for a material to extinguish and the dripping of burning particles. ABS materials must meet specific criteria in this standard to be considered suitable for certain applications, particularly those involving exposure to heat and potential ignition sources.

ISO 75-1 and ISO 75-2 for Heat Deflection Temperature

The International Organization for Standardization (ISO) has developed two standards for measuring the heat deflection temperature of plastics: ISO 75-1 and ISO 75-2. ISO 75-1 specifies the test method for determining the temperature at which a specimen deforms under a specified load, while ISO 75-2 defines the test conditions and requirements for the test method. Both of these standards are important for characterizing the heat resistance of ABS materials, as they provide consistent testing conditions and procedures, ensuring comparable results between different materials and manufacturers.

ISO 306 for Vicat Softening Temperature

Another crucial ISO standard for ABS heat resistance is ISO 306, which specifies the test method for determining the Vicat Softening Temperature of plastics. This standard defines the test conditions and requirements for measuring the temperature at which a material starts to soften under the influence of heat and a specified load. Compliance with ISO 306 allows manufacturers to provide consistent and reliable data on the thermal stability of ABS materials, enabling engineers to make informed decisions when selecting ABS grades for high-temperature applications.

Regulatory Compliance

Apart from industry standards, ABS materials may also be subject to specific regulations depending on the intended application and geographic location. For example, ABS materials used in automotive, aerospace, or medical applications may need to meet additional heat resistance requirements set by regulatory bodies such as the European Union's REACH (Registration, Evaluation, Authorization, and Restriction of Chemicals) regulation or the U.S. Food and Drug Administration (FDA). It is essential for manufacturers to be aware of and comply with all relevant regulations to ensure the safe and effective use of ABS materials in various applications.

Recommended reading: 5 Options to Get Heat-Resistant Parts in 3D Printing

5. Conclusion

Heat resistance is an important property of ABS materials that determines their suitability for various applications. Though ABS generally is not especially temperature-resistant, ABS filament is the most heat-resistant of the three major low-cost 3D printing filaments. To enhance ABS heat resistance, manufacturers can employ various strategies, such as creating ABS blends or incorporating heat-resistant additives. Industry standards and regulations, such as UL 94, ISO 75-1, ISO 75-2, and ISO 306, guide manufacturers in producing ABS materials with consistent heat resistance properties. Understanding the factors affecting ABS heat resistance and the methods to improve it is crucial for material selection and the development of innovative applications.

Frequently Asked Questions (FAQs)

What is the typical heat resistance of ABS?

The heat resistance of ABS can vary depending on factors such as its composition, processing conditions, and the presence of additives. Generally, the heat deflection temperature (HDT) of ABS ranges from 80 °C to 100 °C, while its Vicat Softening Temperature is around 100 °C.

How can ABS heat resistance be improved?

Improving ABS heat resistance can be achieved through blending ABS with other polymers, such as polycarbonate (PC). Additionally, incorporating heat-resistant additives such as glass fibers can enhance ABS heat resistance properties.

How is ABS heat resistance tested?

ABS heat resistance is commonly tested using methods specified in industry standards, such as the heat deflection temperature (HDT) test in ISO 75-1 and ISO 75-2, and the Vicat Softening Temperature test in ISO 306. These tests help determine the temperature at which ABS materials begin to deform or soften under specified loads, allowing for comparison of different ABS grades and materials.

Are there regulations governing ABS heat resistance?

Yes, there are various industry standards and regulations governing ABS heat resistance, such as UL 94 for flammability, ISO 75-1 and ISO 75-2 for HDT, and ISO 306 for Vicat Softening Temperature. Additionally, specific regulations may apply depending on the intended application and geographic location, such as REACH in the European Union or FDA requirements for medical applications in the United States.

References

[1] Shenoy AV, Saini DR. Melt flow index: More than just a quality control rheological parameter. Part I. Advances in Polymer Technology. 1986 Mar;6(1):1-58.

[2] Krache R, Debbah I. Some mechanical and thermal properties of PC/ABS blends. Materials Sciences and Applications. 2011 May 5;2(5):404-10.

[3] Ananthapadmanabha GS, Deshpande V. Influence of aspect ratio of fillers on the properties of acrylonitrile butadiene styrene composites. Journal of Applied Polymer Science. 2018 Mar 15;135(11):46023.