Italian Researchers Characterize Polyetherimide (PEI, ULTEM) Based…

What is PEI/ULTEM in 3D Printing?

Polyetherimide (PEI), commercially known as ULTEM, represents one of the most advanced high-performance thermoplastics available for fused deposition modeling (FDM) 3D printing. This engineering thermoplastic is renowned for its exceptional thermal stability, outstanding mechanical strength, and flame resistance, making it a preferred choice for aerospace, automotive, and medical applications where performance under extreme conditions is non-negotiable.

ULTEM materials are categorized under ASTM PEEK-class high-temperature polymers, with glass transition temperatures typically exceeding 217°C and continuous use temperatures up to 170°C. The material’s unique molecular structure provides it with remarkable properties: high tensile strength (up to 110 MPa), excellent chemical resistance, low moisture absorption (0.25%), and inherent flame retardancy without additives. These characteristics make ULTEM particularly valuable for producing functional prototypes, end-use parts, and components that must withstand demanding environments.

The most common grades used in 3D printing include ULTEM 9085 (flame-rated, aerospace-qualified) and ULTEM 1010 (general-purpose high-strength). Both materials require specialized printing environments—typically an enclosed heated build chamber capable of maintaining temperatures between 150-170°C to prevent warping and ensure proper layer adhesion. The printing nozzle temperature typically ranges from 350-400°C, demanding printers with all-metal hotends capable of sustained high-temperature operation.

The Research Study: Methodology and Objectives

Italian researchers conducted a comprehensive study to address a critical gap in 3D printing material characterization: existing mechanical testing standards were developed for injection-molded or compression-molded polymers and don’t adequately account for the unique characteristics of FDM-printed parts. Their research, published in the journal “Applied Sciences,” aimed to develop and validate new testing methods specifically suited for evaluating PEI-based materials in additive manufacturing contexts.

The study’s primary objectives were threefold: first, to evaluate whether traditional mechanical testing standards could be effectively adapted for FDM parts; second, to investigate how specimen geometry affects mechanical properties in printed components; and third, to identify testing methods capable of differentiating between material variants that might appear similar under conventional analysis. The researchers focused on two commercial grades of ULTEM 9085—tan and black—which, while chemically similar, exhibited different thermal and mechanical behaviors during preliminary characterization.

Methodologically, the team employed a factorial experimental design, treating material type as Factor A (with two levels: tan and black ULTEM) and specimen geometry as Factor B (with two levels varying by test type). For tensile testing following ASTM D638 standards, they used Type I and Type IV specimen geometries. Flexural testing (ISO 178) and short-beam shear testing (ASTM D2344M) utilized specimen bars of different lengths (122mm and 165mm) to examine the effects of interlayer cooling on mechanical performance. All specimens were printed under controlled conditions using identical printing parameters to ensure consistency across test groups.

Before mechanical testing, the materials underwent thermal characterization using differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). These pre-tests revealed important differences in thermal behavior between the tan and black materials: the tan sample displayed a wide peak at 185°C with a shoulder at 140°C, while the black sample showed shifted peaks at 195°C and 148°C, respectively. These thermal transitions suggested potential differences in crystallinity and molecular structure that might affect mechanical performance.

Critical FDM Printing Parameters

The research highlighted several critical parameters that significantly influence the mechanical properties of FDM-printed PEI/ULTEM parts. Understanding and controlling these parameters is essential for achieving consistent, reliable results when working with high-performance thermoplastics.

Nozzle Diameter

Nozzle diameter directly affects the size of deposited filaments and consequently the void content and surface finish of printed parts. Smaller nozzles (0.2-0.3mm) provide higher resolution but require longer print times and may increase the risk of clogging with high-temperature materials like PEI. Larger nozzles (0.4-0.6mm) offer faster printing and better flow characteristics but at the expense of surface detail. For ULTEM printing, a 0.4mm nozzle is typically recommended as a balance between print quality and reliability.

Temperature Control

Temperature management is perhaps the most critical factor when printing PEI/ULTEM materials. This includes both nozzle temperature and bed temperature. The nozzle must reach 350-400°C to properly melt the high-viscosity ULTEM, while the heated bed should maintain 150-170°C to prevent warping and ensure first-layer adhesion. The ambient build chamber temperature is equally important—maintaining a stable environment minimizes thermal gradients that can cause residual stresses and part distortion.

Printing Speed and Feed Rate

Printing speed and feed rate must be carefully optimized for PEI materials. Too fast a speed can result in poor layer adhesion and increased void content, while too slow a speed may cause overheating and degradation of the polymer. Typical printing speeds for ULTEM range from 30-60mm/s, with lower speeds recommended for functional parts requiring maximum strength. The feed rate must match the extrusion rate to ensure consistent filament deposition and avoid under-extrusion or over-extrusion issues.

Layer Height and Raster Angle

Layer height determines the resolution and strength of printed parts in the Z-direction. Smaller layer heights (0.1-0.2mm) provide better surface finish and interlayer bonding but increase print time. Larger layer heights (0.3-0.4mm) print faster but may compromise mechanical properties. The raster angle—the orientation of deposited filaments within each layer—significantly affects anisotropic mechanical behavior. Alternating raster angles between layers (e.g., 0°/90° or 45°/-45°) helps distribute stresses more evenly and improves overall part strength.

Comparison Table 1: PEI/ULTEM vs Other High-Temperature Filaments

Material	Print Temp (°C)	Bed Temp (°C)	Tensile Strength (MPa)	Glass Transition (°C)	Flame Retardant	Price ($/kg)
ULTEM 9085	350-380	150-170	110	217	Yes (FST)	400-600
PEEK	400-450	120-140	90-100	343	No	600-800
PEKK	360-400	120-140	95-105	162	No	500-700
PETG	230-250	70-80	50-60	80-85	No	20-30
ABS	220-250	100-110	40-50	105	No	20-25

Table 1: Comparison of ULTEM 9085 with other high-temperature 3D printing filaments. FST = Flame, Smoke, and Toxicity rated for aerospace applications.

Testing Methods and Results

The researchers employed three distinct mechanical testing methodologies to evaluate the PEI materials, each providing unique insights into different aspects of material performance. The selection of these tests was strategic, targeting specific mechanical properties relevant to real-world applications of 3D printed parts.

Tensile Testing (ASTM D638)

Tensile testing is the most common method for evaluating a material’s strength and ductility under uniaxial loading. The ASTM D638 standard specifies specimen geometries and testing procedures for plastics. In this study, researchers used both Type I and Type IV specimen geometries to investigate the effect of specimen size on tensile properties. The tensile test measures ultimate tensile strength, yield strength, elongation at break, and modulus of elasticity—critical parameters for engineering design.

For the ULTEM materials tested, tensile testing revealed good baseline mechanical properties consistent with published data for PEI materials. However, the researchers noted that traditional tensile testing standards don’t adequately account for the anisotropic nature of FDM-printed parts. In printed components, strength varies significantly depending on the orientation of the deposited rasters relative to the applied load. Tensile strength is typically highest when the load is aligned with the raster direction and significantly lower when applied perpendicular to the rasters.

Flexural Testing (ISO 178)

Flexural testing evaluates a material’s stiffness and strength under bending loads. The ISO 178 standard describes a three-point bending test where a specimen is supported at two points and loaded at a third point between the supports. This test is particularly relevant for applications where parts experience bending, such as beams, brackets, and structural components. Flexural testing provides measurements of flexural strength and flexural modulus.

The flexural tests conducted in this study examined how specimen length (122mm vs. 165mm) affected flexural properties. Longer specimens are more susceptible to interlayer cooling effects during printing, which can influence the degree of fusion between layers. The researchers found that flexural testing provided useful data but, like tensile testing, was limited in its ability to differentiate between the two ULTEM material grades.

Short-Beam Shear Testing (ASTM D2344M)

The short-beam shear test proved to be the most valuable of the three testing methods for differentiating between PEI materials. This test specifically evaluates interlaminar shear strength—the ability of layers to bond to each other—by applying a load that induces shear stresses between layers. For FDM-printed parts, interlayer bonding is often the weakest point and determines many of the mechanical properties.

Unlike tensile and flexural tests, the short-beam shear test configuration privileges the effect of shear stress internal to the specimen, making it sensitive to differences in interlaminar bonding quality. The researchers found that this test was the only assessment capable of differentiating between the tan and black ULTEM materials. This discovery is significant because it demonstrates that interlaminar bonding varies between material variants even when other mechanical properties appear similar.

The ability to detect differences in interlayer bonding is crucial for quality control in additive manufacturing. Poor interlayer bonding leads to delamination, reduced mechanical strength, and premature failure under load. The short-beam shear test provides a practical method for quantifying this critical property and could become an important tool for material qualification in 3D printing applications.

Comparison Table 2: Testing Methods for FDM-Printed Parts

Test Method	Standard	Measures	Suitability for FDM	Can Differentiate Materials	Equipment Required
Short-Beam Shear	ASTM D2344M	Interlaminar shear strength	Excellent (FDM-specific)	Yes (✓)	Universal testing machine, 3-point fixture
Tensile	ASTM D638	Tensile strength, elongation, modulus	Moderate (adapted from injection molding)	Limited (✗)	Universal testing machine, grips
Flexural	ISO 178	Flexural strength, modulus	Moderate (adapted from injection molding)	Limited (✗)	Universal testing machine, 3-point fixture
Double Cantilever Beam	ASTM D5528	Mode I fracture toughness	Recommended for future research	Potential (?)	Universal testing machine, DCB fixture
End-Notched Flexure	ASTM D7903	Mode II fracture toughness	Recommended for future research	Potential (?)	Universal testing machine, ENF fixture

Table 2: Comparison of mechanical testing methods for characterizing FDM-printed parts. Short-beam shear testing emerged as the most effective method for differentiating between PEI/ULTEM material grades.

Thermal Analysis and Material Differences

Thermal characterization revealed important differences between the tan and black ULTEM 9085 materials. Using dynamic mechanical analysis (DMA), researchers measured the storage modulus, loss modulus, and tan δ (damping factor) as functions of temperature. These measurements provide insights into the viscoelastic behavior of materials and their thermal transitions.

The tan ULTEM sample displayed two distinct thermal transitions: a wide peak at 185°C with a shoulder at 140°C. This behavior suggests the presence of two molecular phases or crystalline structures within the material. The black ULTEM sample, in contrast, showed only one primary thermal transition, with peaks shifted to higher temperatures (195°C primary peak, 148°C shoulder). The shift to higher temperatures in the black material may indicate different thermal stabilizers, additives, or molecular weight distribution between the two color variants.

Differential scanning calorimetry (DSC) analysis complemented the DMA results by examining heat flow as a function of temperature. DSC can detect thermal transitions such as glass transitions, melting points, and crystallization events. However, the researchers noted that DSC was unable to resolve the thermal transitions observed in DMA, highlighting the importance of using multiple characterization techniques to fully understand material behavior.

The thermal differences between materials have practical implications for 3D printing. The black ULTEM’s higher thermal transition temperatures may require slightly higher nozzle temperatures to achieve proper flow and layer adhesion. Conversely, the tan material’s broader thermal transitions might provide a slightly wider processing window. These subtle differences underscore why material-specific parameter optimization is important when working with different grades or color variants of high-performance polymers.

Implications for FDM Standards and Future Research

The findings of this study have significant implications for the development of testing standards specific to additive manufacturing. Current mechanical testing standards (ASTM D638, ISO 178, etc.) were developed for injection-molded or compression-molded polymers—processes that produce isotropic parts with homogeneous microstructures. FDM printing, by contrast, creates anisotropic parts with inherent voids, layer lines, and varying interlayer bonding quality.

The researchers concluded that traditional standards don’t adequately account for these FDM-specific characteristics. Tensile and flexural tests, while useful for baseline characterization, fail to capture critical aspects of FDM part performance, particularly interlayer bonding strength. The short-beam shear test emerged as a more appropriate method for FDM materials, as it specifically evaluates the shear strength between layers—a key factor in printed part reliability.

Looking forward, the researchers identified several promising directions for continued research. See also: 3D Printing Safety Equipment Guide: Respirators, G…. Mechanical tests such as double cantilever beam (DCB) and end-notched flexure (ENF) could provide valuable insights into fracture toughness and interlaminar properties. These tests measure Mode I and Mode II fracture toughness, respectively, and are commonly used in composite material characterization. Their application to FDM parts could help establish new testing standards that better reflect real-world performance.

Additionally, the researchers emphasized the need for more comprehensive studies correlating printing parameters with mechanical properties. As additive manufacturing expands into structural applications requiring reinforced materials (e.g., carbon fiber-reinforced PEI), understanding anisotropic behavior becomes increasingly critical. The development of standardized test methods specific to FDM will enable better material qualification, quality control, and design confidence in 3D printed components.

Practical Applications for 3D Printing Users

For engineers, makers, and professionals working with PEI/ULTEM materials, this research offers several practical takeaways. First, the importance of interlayer bonding cannot be overstated. Parts with poor interlayer adhesion will fail prematurely regardless of the inherent material properties. Ensuring optimal print settings—particularly nozzle temperature, bed temperature, and chamber temperature—is essential for achieving strong interlayer bonds.

Second, material selection should consider more than just published datasheet values. As this study demonstrated, different grades or color variants of nominally the same material can exhibit different thermal and mechanical behaviors. When consistency is critical (e.g., for aerospace or medical applications), thorough material characterization and qualification are essential.

Third, for applications requiring maximum strength and reliability, consider design strategies that account for FDM anisotropy. Orienting parts to align critical load paths with the raster direction, using larger layer heights for better interlayer contact, and implementing post-processing techniques (e.g., annealing) can all help improve mechanical performance. The short-beam shear test provides a practical method for evaluating interlayer bonding quality and can serve as a valuable quality control tool for critical applications.

Finally, this research highlights the need for continued development of FDM-specific testing standards. As additive manufacturing matures and moves toward broader industrial adoption, standardized test methods will become increasingly important for material qualification, process validation, and regulatory compliance. Industry collaboration between researchers, equipment manufacturers, and standards organizations will be crucial for advancing the state of the art.

Frequently Asked Questions (FAQ)

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Where to Buy Filament

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• PEI: Hatchbox, eSUN, Overture
• PLA: Hatchbox

  Looking for Quick Answer: Key Findings from PEI/ULTEM Research
  Main Discovery: Italian researchers found that the short-beam shear test is the most effective method for distinguishing between different PEI/ULTEM materials in FDM 3D printing, as it specifically evaluates interlayer bonding—a critical factor in printed part strength.
  Materials Tested: Two grades of ULTEM 9085 (tan and black) – both aerospace-qualified high-performance thermoplastics.
  Tests Performed: Tensile testing, flexural testing, and short-beam shear testing under ASTM and ISO standards.
  Why It Matters: Current standard tests (developed for injection molding) don’t account for FDM-specific issues like voids and anisotropic behavior. This research paves the way for new testing standards specific to 3D printing.

  What is PEI/ULTEM in 3D Printing?
  Polyetherimide (PEI), commercially known as ULTEM, represents one of the most advanced high-performance thermoplastics available for fused deposition modeling (FDM) 3D printing. This engineering thermoplastic is renowned for its exceptional thermal stability, outstanding mechanical strength, and flame resistance, making it a preferred choice for aerospace, automotive, and medical applications where performance under extreme conditions is non-negotiable.
  ULTEM materials are categorized under ASTM PEEK-class high-temperature polymers, with glass transition temperatures typically exceeding 217°C and continuous use temperatures up to 170°C. The material’s unique molecular structure provides it with remarkable properties: high tensile strength (up to 110 MPa), excellent chemical resistance, low moisture absorption (0.25%), and inherent flame retardancy without additives. These characteristics make ULTEM particularly valuable for producing functional prototypes, end-use parts, and components that must withstand demanding environments.
  The most common grades used in 3D printing include ULTEM 9085 (flame-rated, aerospace-qualified) and ULTEM 1010 (general-purpose high-strength). Both materials require specialized printing environments—typically an enclosed heated build chamber capable of maintaining temperatures between 150-170°C to prevent warping and ensure proper layer adhesion. The printing nozzle temperature typically ranges from 350-400°C, demanding printers with all-metal hotends capable of sustained high-temperature operation.
  The Research Study: Methodology and Objectives
  Italian researchers conducted a comprehensive study to address a critical gap in 3D printing material characterization: existing mechanical testing standards were developed for injection-molded or compression-molded polymers and don’t adequately account for the unique characteristics of FDM-printed parts. Their research, published in the journal “Applied Sciences,” aimed to develop and validate new testing methods specifically suited for evaluating PEI-based materials in additive manufacturing contexts.
  The study’s primary objectives were threefold: first, to evaluate whether traditional mechanical testing standards could be effectively adapted for FDM parts; second, to investigate how specimen geometry affects mechanical properties in printed components; and third, to identify testing methods capable of differentiating between material variants that might appear similar under conventional analysis. The researchers focused on two commercial grades of ULTEM 9085—tan and black—which, while chemically similar, exhibited different thermal and mechanical behaviors during preliminary characterization.
  Methodologically, the team employed a factorial experimental design, treating material type as Factor A (with two levels: tan and black ULTEM) and specimen geometry as Factor B (with two levels varying by test type). For tensile testing following ASTM D638 standards, they used Type I and Type IV specimen geometries. Flexural testing (ISO 178) and short-beam shear testing (ASTM D2344M) utilized specimen bars of different lengths (122mm and 165mm) to examine the effects of interlayer cooling on mechanical performance. All specimens were printed under controlled conditions using identical printing parameters to ensure consistency across test groups.
  Before mechanical testing, the materials underwent thermal characterization using differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). These pre-tests revealed important differences in thermal behavior between the tan and black materials: the tan sample displayed a wide peak at 185°C with a shoulder at 140°C, while the black sample showed shifted peaks at 195°C and 148°C, respectively. These thermal transitions suggested potential differences in crystallinity and molecular structure that might affect mechanical performance.
  Critical FDM Printing Parameters
  The research highlighted several critical parameters that significantly influence the mechanical properties of FDM-printed PEI/ULTEM parts. Understanding and controlling these parameters is essential for achieving consistent, reliable results when working with high-performance thermoplastics.
  Nozzle Diameter
  Nozzle diameter directly affects the size of deposited filaments and consequently the void content and surface finish of printed parts. Smaller nozzles (0.2-0.3mm) provide higher resolution but require longer print times and may increase the risk of clogging with high-temperature materials like PEI. Larger nozzles (0.4-0.6mm) offer faster printing and better flow characteristics but at the expense of surface detail. For ULTEM printing, a 0.4mm nozzle is typically recommended as a balance between print quality and reliability.
  Temperature Control
  Temperature management is perhaps the most critical factor when printing PEI/ULTEM materials. This includes both nozzle temperature and bed temperature. The nozzle must reach 350-400°C to properly melt the high-viscosity ULTEM, while the heated bed should maintain 150-170°C to prevent warping and ensure first-layer adhesion. The ambient build chamber temperature is equally important—maintaining a stable environment minimizes thermal gradients that can cause residual stresses and part distortion.
  Printing Speed and Feed Rate
  Printing speed and feed rate must be carefully optimized for PEI materials. Too fast a speed can result in poor layer adhesion and increased void content, while too slow a speed may cause overheating and degradation of the polymer. Typical printing speeds for ULTEM range from 30-60mm/s, with lower speeds recommended for functional parts requiring maximum strength. The feed rate must match the extrusion rate to ensure consistent filament deposition and avoid under-extrusion or over-extrusion issues.
  Layer Height and Raster Angle
  Layer height determines the resolution and strength of printed parts in the Z-direction. Smaller layer heights (0.1-0.2mm) provide better surface finish and interlayer bonding but increase print time. Larger layer heights (0.3-0.4mm) print faster but may compromise mechanical properties. The raster angle—the orientation of deposited filaments within each layer—significantly affects anisotropic mechanical behavior. Alternating raster angles between layers (e.g., 0°/90° or 45°/-45°) helps distribute stresses more evenly and improves overall part strength.
  Comparison Table 1: PEI/ULTEM vs Other High-Temperature Filaments

  Material
  Print Temp (°C)
  Bed Temp (°C)
  Tensile Strength (MPa)
  Glass Transition (°C)
  Flame Retardant
  Price ($/kg)

  ULTEM 9085
  350-380
  150-170
  110
  217
  Yes (FST)
  400-600

  PEEK
  400-450
  120-140
  90-100
  343
  No
  600-800

  PEKK
  360-400
  120-140
  95-105
  162
  No
  500-700

  PETG
  230-250
  70-80
  50-60
  80-85
  No
  20-30

  ABS
  220-250
  100-110
  40-50
  105
  No
  20-25

  Table 1: Comparison of ULTEM 9085 with other high-temperature 3D printing filaments. FST = Flame, Smoke, and Toxicity rated for aerospace applications.
  Testing Methods and Results
  The researchers employed three distinct mechanical testing methodologies to evaluate the PEI materials, each providing unique insights into different aspects of material performance. The selection of these tests was strategic, targeting specific mechanical properties relevant to real-world applications of 3D printed parts.
  Tensile Testing (ASTM D638)
  Tensile testing is the most common method for evaluating a material’s strength and ductility under uniaxial loading. The ASTM D638 standard specifies specimen geometries and testing procedures for plastics. In this study, researchers used both Type I and Type IV specimen geometries to investigate the effect of specimen size on tensile properties. The tensile test measures ultimate tensile strength, yield strength, elongation at break, and modulus of elasticity—critical parameters for engineering design.
  For the ULTEM materials tested, tensile testing revealed good baseline mechanical properties consistent with published data for PEI materials. However, the researchers noted that traditional tensile testing standards don’t adequately account for the anisotropic nature of FDM-printed parts. In printed components, strength varies significantly depending on the orientation of the deposited rasters relative to the applied load. Tensile strength is typically highest when the load is aligned with the raster direction and significantly lower when applied perpendicular to the rasters.
  Flexural Testing (ISO 178)
  Flexural testing evaluates a material’s stiffness and strength under bending loads. The ISO 178 standard describes a three-point bending test where a specimen is supported at two points and loaded at a third point between the supports. This test is particularly relevant for applications where parts experience bending, such as beams, brackets, and structural components. Flexural testing provides measurements of flexural strength and flexural modulus.
  The flexural tests conducted in this study examined how specimen length (122mm vs. 165mm) affected flexural properties. Longer specimens are more susceptible to interlayer cooling effects during printing, which can influence the degree of fusion between layers. The researchers found that flexural testing provided useful data but, like tensile testing, was limited in its ability to differentiate between the two ULTEM material grades.
  Short-Beam Shear Testing (ASTM D2344M)
  The short-beam shear test proved to be the most valuable of the three testing methods for differentiating between PEI materials. This test specifically evaluates interlaminar shear strength—the ability of layers to bond to each other—by applying a load that induces shear stresses between layers. For FDM-printed parts, interlayer bonding is often the weakest point and determines many of the mechanical properties.
  Unlike tensile and flexural tests, the short-beam shear test configuration privileges the effect of shear stress internal to the specimen, making it sensitive to differences in interlaminar bonding quality. The researchers found that this test was the only assessment capable of differentiating between the tan and black ULTEM materials. This discovery is significant because it demonstrates that interlaminar bonding varies between material variants even when other mechanical properties appear similar.
  The ability to detect differences in interlayer bonding is crucial for quality control in additive manufacturing. Poor interlayer bonding leads to delamination, reduced mechanical strength, and premature failure under load. The short-beam shear test provides a practical method for quantifying this critical property and could become an important tool for material qualification in 3D printing applications.
  Comparison Table 2: Testing Methods for FDM-Printed Parts

  Test Method
  Standard
  Measures
  Suitability for FDM
  Can Differentiate Materials
  Equipment Required

  Short-Beam Shear
  ASTM D2344M
  Interlaminar shear strength
  Excellent (FDM-specific)
  Yes (✓)
  Universal testing machine, 3-point fixture

  Tensile
  ASTM D638
  Tensile strength, elongation, modulus
  Moderate (adapted from injection molding)
  Limited (✗)
  Universal testing machine, grips

  Flexural
  ISO 178
  Flexural strength, modulus
  Moderate (adapted from injection molding)
  Limited (✗)
  Universal testing machine, 3-point fixture

  Double Cantilever Beam
  ASTM D5528
  Mode I fracture toughness
  Recommended for future research
  Potential (?)
  Universal testing machine, DCB fixture

  End-Notched Flexure
  ASTM D7903
  Mode II fracture toughness
  Recommended for future research
  Potential (?)
  Universal testing machine, ENF fixture

  Table 2: Comparison of mechanical testing methods for characterizing FDM-printed parts. Short-beam shear testing emerged as the most effective method for differentiating between PEI/ULTEM material grades.
  Thermal Analysis and Material Differences
  Thermal characterization revealed important differences between the tan and black ULTEM 9085 materials. Using dynamic mechanical analysis (DMA), researchers measured the storage modulus, loss modulus, and tan δ (damping factor) as functions of temperature. These measurements provide insights into the viscoelastic behavior of materials and their thermal transitions.
  The tan ULTEM sample displayed two distinct thermal transitions: a wide peak at 185°C with a shoulder at 140°C. This behavior suggests the presence of two molecular phases or crystalline structures within the material. The black ULTEM sample, in contrast, showed only one primary thermal transition, with peaks shifted to higher temperatures (195°C primary peak, 148°C shoulder). The shift to higher temperatures in the black material may indicate different thermal stabilizers, additives, or molecular weight distribution between the two color variants.
  Differential scanning calorimetry (DSC) analysis complemented the DMA results by examining heat flow as a function of temperature. DSC can detect thermal transitions such as glass transitions, melting points, and crystallization events. However, the researchers noted that DSC was unable to resolve the thermal transitions observed in DMA, highlighting the importance of using multiple characterization techniques to fully understand material behavior.
  The thermal differences between materials have practical implications for 3D printing. The black ULTEM’s higher thermal transition temperatures may require slightly higher nozzle temperatures to achieve proper flow and layer adhesion. Conversely, the tan material’s broader thermal transitions might provide a slightly wider processing window. These subtle differences underscore why material-specific parameter optimization is important when working with different grades or color variants of high-performance polymers.
  Implications for FDM Standards and Future Research
  The findings of this study have significant implications for the development of testing standards specific to additive manufacturing. Current mechanical testing standards (ASTM D638, ISO 178, etc.) were developed for injection-molded or compression-molded polymers—processes that produce isotropic parts with homogeneous microstructures. FDM printing, by contrast, creates anisotropic parts with inherent voids, layer lines, and varying interlayer bonding quality.
  The researchers concluded that traditional standards don’t adequately account for these FDM-specific characteristics. Tensile and flexural tests, while useful for baseline characterization, fail to capture critical aspects of FDM part performance, particularly interlayer bonding strength. The short-beam shear test emerged as a more appropriate method for FDM materials, as it specifically evaluates the shear strength between layers—a key factor in printed part reliability.
  Looking forward, the researchers identified several promising directions for continued research. See also: 3D Printing Safety Equipment Guide: Respirators, G…. Mechanical tests such as double cantilever beam (DCB) and end-notched flexure (ENF) could provide valuable insights into fracture toughness and interlaminar properties. These tests measure Mode I and Mode II fracture toughness, respectively, and are commonly used in composite material characterization. Their application to FDM parts could help establish new testing standards that better reflect real-world performance.
  Additionally, the researchers emphasized the need for more comprehensive studies correlating printing parameters with mechanical properties. As additive manufacturing expands into structural applications requiring reinforced materials (e.g., carbon fiber-reinforced PEI), understanding anisotropic behavior becomes increasingly critical. The development of standardized test methods specific to FDM will enable better material qualification, quality control, and design confidence in 3D printed components.
  Practical Applications for 3D Printing Users
  For engineers, makers, and professionals working with PEI/ULTEM materials, this research offers several practical takeaways. First, the importance of interlayer bonding cannot be overstated. Parts with poor interlayer adhesion will fail prematurely regardless of the inherent material properties. Ensuring optimal print settings—particularly nozzle temperature, bed temperature, and chamber temperature—is essential for achieving strong interlayer bonds.
  Second, material selection should consider more than just published datasheet values. As this study demonstrated, different grades or color variants of nominally the same material can exhibit different thermal and mechanical behaviors. When consistency is critical (e.g., for aerospace or medical applications), thorough material characterization and qualification are essential.
  Third, for applications requiring maximum strength and reliability, consider design strategies that account for FDM anisotropy. Orienting parts to align critical load paths with the raster direction, using larger layer heights for better interlayer contact, and implementing post-processing techniques (e.g., annealing) can all help improve mechanical performance. The short-beam shear test provides a practical method for evaluating interlayer bonding quality and can serve as a valuable quality control tool for critical applications.
  Finally, this research highlights the need for continued development of FDM-specific testing standards. As additive manufacturing matures and moves toward broader industrial adoption, standardized test methods will become increasingly important for material qualification, process validation, and regulatory compliance. Industry collaboration between researchers, equipment manufacturers, and standards organizations will be crucial for advancing the state of the art.
  Frequently Asked Questions (FAQ)

  Q1: What makes PEI/ULTEM different from other 3D printing filaments?
  PEI/ULTEM stands apart from common filaments like PLA, ABS, or PETG due to its exceptional thermal and mechanical properties. With a glass transition temperature above 217°C and continuous use temperatures up to 170°C, ULTEM can withstand environments where other filaments would deform or degrade. It offers high tensile strength (up to 110 MPa), excellent chemical resistance, and inherent flame retardancy without additives. These properties make it ideal for aerospace, automotive, and medical applications where performance under extreme conditions is required. However, these advantages come with challenges: ULTEM requires specialized printing equipment with all-metal hotends capable of 350-400°C nozzle temperatures and enclosed heated build chambers to prevent warping.

  Q2: Why is the short-beam shear test better for FDM materials than tensile testing?
  The short-beam shear test is specifically designed to evaluate interlaminar shear strength—the strength of the bond between layers in FDM-printed parts. This is critical because layer bonding is typically the weakest point in printed components and determines many mechanical properties. Traditional tensile and flexural tests, while useful for measuring bulk material properties, don’t adequately account for FDM-specific issues like voids and anisotropic behavior. The short-beam shear test’s configuration specifically stresses the interlayer bonds, making it sensitive to differences in bonding quality. In this study, only the short-beam shear test could differentiate between tan and black ULTEM materials, demonstrating its superior suitability for FDM material characterization.

  Q3: What equipment do I need to print with ULTEM 9085?
  Printing with ULTEM 9085 requires specialized equipment beyond typical consumer-grade 3D printers. Essential requirements include: (1) An all-metal hotend capable of sustained temperatures of 350-400°C; (2) A heated build bed that can maintain 150-170°C; (3) An enclosed build chamber to maintain consistent ambient temperature and prevent warping; (4) Robust frame construction to minimize vibrations; (5) Adequate ventilation for potential fumes during high-temperature printing. Popular printers that can handle ULTEM include the Intamsys Funmat series, 3D Systems Figure series, and modified industrial printers. Additionally, you’ll need proper safety equipment including heat-resistant gloves, eye protection, and potentially a respirator or ventilation system depending on your printing environment.

  Q4: How does interlayer cooling affect ULTEM print quality?
  Interlayer cooling significantly impacts ULTEM print quality and mechanical properties. During FDM printing, the weld temperature (the temperature at the interface between newly deposited material and the previous layer) decreases rapidly—approximately 100°C per second according to literature. It remains above the glass transition temperature for only about 1 second. This brief window determines how well layers fuse together. Factors affecting interlayer cooling include print speed, layer height, and chamber temperature. Longer print paths allow more cooling time between layers of a given section, potentially reducing bonding quality. Maintaining a warm build chamber (150-170°C) slows the cooling rate and extends the fusion window, promoting better interlayer adhesion. This is why enclosed, heated chambers are essential for high-temperature materials like ULTEM.

  Q5: What are the main applications for PEI/ULTEM in 3D printing?
  PEI/ULTEM is primarily used in high-performance applications where standard materials cannot meet requirements. Key application areas include: (1) Aerospace components—brackets, ducts, and interior parts requiring FST (Flame, Smoke, Toxicity) certification; (2) Automotive under-hood components and functional prototypes that must withstand high temperatures; (3) Medical devices and sterilizable equipment due to chemical resistance and thermal stability; (4) Electrical insulators and connectors requiring high dielectric strength and thermal resistance; (5) Industrial tooling and manufacturing fixtures that must maintain dimensional stability under load and temperature. The material’s combination of strength, thermal stability, and flame retardancy makes it ideal for demanding applications where part failure is not an option. As 3D printing technology advances, we’re seeing increasing use of ULTEM for end-use production parts, not just prototyping.

  Q6: Why did the tan and black ULTEM samples behave differently in testing?
  The tan and black ULTEM 9085 samples exhibited different thermal and mechanical behaviors due to differences in their formulation and composition. Color additives, thermal stabilizers, and processing aids can all affect material properties. The thermal analysis revealed that the black sample had thermal transitions shifted approximately 10°C higher than the tan sample (195°C vs. 185°C peak, 148°C vs. 140°C shoulder). This suggests that the black formulation may include different stabilizers or additives that raise the glass transition temperature. Additionally, the tan sample showed two distinct thermal transitions while the black sample showed only one, indicating differences in molecular structure or crystallinity. These subtle differences highlight why material qualification is important—nominally identical materials can behave differently under the same conditions. For critical applications, thorough characterization of the specific material grade and lot is recommended.

  Q7: What future research directions did the researchers identify?
  The researchers identified several promising directions for future research in FDM material characterization: (1) Implementation of fracture toughness tests including double cantilever beam (DCB) and end-notched flexure (ENF) to better understand crack propagation and interlaminar properties; (2) Development of comprehensive correlations between printing parameters (nozzle temperature, bed temperature, printing speed, raster angle, etc.) and resulting mechanical properties; (3) Investigation of anisotropic behavior in reinforced materials (e.g., carbon fiber-reinforced PEI) which are increasingly used for structural components; (4) Creation of new testing standards specifically designed for additive manufacturing that account for void content, interlayer bonding, and mesostructural effects; (5) Study of the effects of post-processing techniques (annealing, chemical smoothing, etc.) on mechanical properties. The ultimate goal is to develop standardized test methods that enable better material qualification, quality control, and design confidence for 3D printed components.

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[Source: ‘Methods for the Characterization of Polyetherimide Based Materials Processed by Fused Deposition Modelling’, Applied Sciences, 2020]

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