ARKPEEK-1000 Properties: MFR and Elongation at Break

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Introduction

Polyether ether ketone (PEEK) is a high-performance, semi-crystalline thermoplastic widely used in aerospace, medical, semiconductor, automotive, and analytical instrumentation applications. Among the many material parameters used to evaluate PEEK, Melt Flow Rate (MFR) and Elongation at Break are two of the most important indicators of processability, molecular structure, and mechanical behavior.

This article explains how PEEK MFR values are measured, how they vary across commercial grades, and how they relate to elongation at break and crystallinity. ARKPEEK-1000 is used as a representative example of a low-flow, high-molecular-weight PEEK grade.

What Is PEEK Melt Flow Rate (MFR)?

Definition

Melt Flow Rate (MFR) measures the amount of molten polymer that flows through a standardized capillary under defined temperature and load conditions within 10 minutes.
It is expressed as g/10 min.

For PEEK, MFR is typically measured under high-temperature conditions due to its high melting point, most commonly:

  • 380°C / 5 kg

  • 400°C / 2.16 kg

The reported MFR value is entirely dependent on the test condition and standard used (ISO 1133 or ASTM D1238). Therefore, MFR values must always be compared under identical test conditions.

Typical PEEK MFR Value Ranges

PEEK grades show an exceptionally wide MFR range, reflecting differences in molecular weight and intended processing method.

Low Flow (High Molecular Weight) PEEK Grades

These grades exhibit low MFR and high melt viscosity, making them ideal for applications requiring maximum toughness, impact resistance, and fatigue performance.

  • Typical MFR range: 8 – 15 g/10 min (380°C / 5 kg)

  • Example industry reference:
    A well-known low-flow PEEK grade shows an MFR of approximately 8.5 g/10 min at 380°C / 5 kg

Key characteristics:

  • High molecular weight

  • Excellent elongation and toughness

  • Preferred for extrusion, compression molding, and structural parts

High Flow (Low Molecular Weight) PEEK Grades

High-flow PEEK grades are designed for injection molding of thin-walled or complex geometries.

  • Typical MFR range: 50 – 140+ g/10 min (380°C / 5 kg)

  • Example industry reference:
    A high-flow injection molding grade may reach ~75 g/10 min under the same test condition

Key characteristics:

  • Lower melt viscosity

  • Improved mold filling

  • Reduced toughness and impact resistance compared to low-flow grades

Summary of Commercial PEEK MFR Spectrum

Across the market, commercial PEEK materials can range from:

  • ~8 g/10 min (very low flow, ultra-high molecular weight)

  • To >140 g/10 min (very high flow, low molecular weight)

This wide spectrum allows engineers to select PEEK grades precisely matched to processing method and performance requirements.

ARKPEEK-1000 MFR Value Explained

ARKPEEK-1000 is a 100% virgin, unfilled PEEK grade positioned in the low-flow, high-molecular-weight category.

  • MFR = 10 g/10 min

This value places ARKPEEK-1000 very close to classic low-flow structural PEEK grades.

What MFR = 10 Means in Practice

  • High melt viscosity

  • Strong molecular entanglement

  • Excellent mechanical integrity

  • Optimized for:

    • Extrusion

    • Compression molding

    • Injection molding of mechanically demanding parts (with appropriate tooling)

ARKPEEK-1000 prioritizes toughness and durability over extreme flowability.

What Is Elongation at Break in PEEK?

Elongation at break is the percentage strain a material experiences before fracture in a tensile test. It is one of the most important indicators of ductility and toughness.

In PEEK, elongation at break is governed primarily by:

  • Molecular weight

  • Degree of crystallinity

  • Thermal history and processing conditions

  • Presence or absence of fillers

Typical Elongation at Break Values for PEEK

Unfilled (Virgin) PEEK

  • Typical range: 30% – 50%

  • Ductile failure behavior

  • High resistance to cracking and fatigue

Reinforced PEEK Grades

  • Glass fiber reinforced PEEK: ~2% – 5%

  • Carbon fiber reinforced PEEK: ~1.5% – 4%

Reinforcement dramatically increases stiffness but significantly reduces elongation and toughness.

ARKPEEK-1000 Elongation at Break and Crystallinity

For ARKPEEK-1000, elongation at break is:

  • 30% – 50%, depending on degree of crystallinity

Influence of Crystallinity

As a semi-crystalline polymer, PEEK’s mechanical response is highly sensitive to crystallinity:

  • Lower crystallinity

    • Higher elongation

    • Greater toughness

    • Better impact resistance

  • Higher crystallinity

    • Lower elongation

    • Higher stiffness

    • Improved dimensional and thermal stability

Processing parameters such as cooling rate, mold temperature, and post-annealing directly influence crystallinity and therefore elongation performance.

Relationship Between MFR and Elongation at Break

MFR and elongation at break are both indirect indicators of molecular weight, but they influence performance differently:

  • Lower MFR (higher molecular weight)

    • Higher elongation

    • Better toughness

    • Higher impact resistance

  • Higher MFR (lower molecular weight)

    • Easier processing

    • Higher stiffness and strength

    • Reduced elongation and toughness

ARKPEEK-1000, with MFR = 10 and elongation up to 50%, represents a balanced high-performance structural PEEK grade.

Application Areas Benefiting from This Balance

PEEK materials with low MFR and high elongation, such as ARKPEEK-1000, are commonly used in:

  • Medical device components

  • Analytical and fluid handling parts

  • Semiconductor processing equipment

  • Aerospace structural components

  • High-load mechanical parts

  • Electrical insulation and connectors

These applications demand long-term reliability, fatigue resistance, and mechanical stability.

Conclusion

Melt Flow Rate (MFR) and Elongation at Break are two of the most critical parameters when selecting a PEEK material.

  • MFR defines processing behavior and molecular weight level

  • Elongation at break reflects ductility, toughness, and structural resilience

With an MFR of 10 g/10 min and an elongation at break of 30%–50% depending on crystallinity, ARKPEEK-1000 is a representative low-flow, high-molecular-weight PEEK grade optimized for demanding engineering applications where toughness and durability are essential.

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