How Cross-Linkable Thermoplastics Boost Performance

plastic gears

The demands of part design optimization can sometimes exceed the capabilities of standard polyamide or polyester compounds. In such instances ultra-high performance polymers such as PEEK, PPS, and LCP are often deemed the necessary solution. While in most cases these ultra-polymers are a robust material solution, they are also expensive and, more often than not, over engineered.

Alternatively, manufacturers who choose cross-linked engineering thermoplastic materials over these ultra-polymers can realize cost savings up to 40% — without compromising part performance. Cross-linkable PA 6, PA 66, PPA, and PBT compounds are readily molded on standard processing equipment and, once cross-linked, are proven solutions for meeting demanding requirements.

Are cross-linkable thermoplastics right for your application?

The Cross-Linking Process

A cross-link is a bond that holds — or links — polymer chains together. In relation to thermoplastics, the goal of cross-linking is to interconnect long-chain molecules through covalent bonding in order to improve mechanical, thermal, electrical, and chemical performance. Typically, cross-linking is initiated either through e-beam radiation (irradiation) or chemical agents.

Teknor Apex supplies cross-linkable compounds in pellet form for processing on standard thermoplastic injection molding equipment. Molded parts are exposed to e-beam radiation, and a three-dimensional molecular network is formed within each part. The cross-linked parts remain unchanged in terms of size and appearance, but part performance is significantly improved.

The Benefits of Cross-Linked Thermoplastic Materials

Polyamide and other polyester compounds are semi-crystalline polymers. For most Polyamide 6 and 66 compounds the typical crystalline content after molding is in the 30-50% range, depending on a number of factors. The remaining 50-70% is amorphous content, which has a limiting/adverse effect on various properties of the materials. 

Cross-linking such semi-crystalline polymers creates a three-dimensional network, as explained above, binding the polymer chains together predominantly in the amorphous region of the material. Hence the gel rate after cross-linking can be increased to 70-80% for reinforced thermoplastics, and 60-70% for unreinforced materials — i.e. nearly full cross-linking of the amorphous content.

Thus, cross-linking standard engineering plastics leads to significant improvements in several attributes:

  • Improved tolerance for temporary temperature spikes exceeding the polymer melting point
  • Mechanical improvements to creep and stress crack resistance
  • Better abrasion resistance
  • Reduced solubility and swelling in various chemicals
  • Better weld line strength
  • Excellent thermal recovery from mechanical deformation
  • Increased flowability
  • Improved glass transition temperatures
  • Compatibility with traditional injection molding equipment

Additionally, these materials can be molded on standard injection molding machines with standard processing guidelines and procedures. The cross-linking reaction is triggered only via secondary irradiation process and does not affect the molding step. Depending on the material selected and the application, these benefits can translate to a cost savings of up to 40% over expensive ultra-high performance resins.

Part Design Optimization: Cross-Linking Success Stories

Cross-linking is highly technical, and the process isn’t always easily understood. However, results speak volumes as to its viability. Teknor Apex has helped manufacturers across industries resolve complex issues by introducing cross-linked engineering thermoplastics, as summarized in these success stories:

Providing Cost-Effective Materials for New Designs

GearsApplication:  Water pump gears 

Solution Sought:  Replacement for powder metal to reduce weight and cost

Key Application Requirements:

  • Tribological performance in 100° C oil
  • Lower gear noise
  • Reduced weight
  • Dimensional stability

Teknor Solution: V-Creamid® A3H9G6 1G6-  Cross-linked 30% glass fiber PA 66

Why Creamid® A Cross-Linked

  • Wear performance equivalent or slightly better than powder metal
  • Improved part to part consistency
  • Significant noise reduction
  • No noticeable change in dimensions or performance across operating conditions
RESULTS: 40% weight reduction ≅ 30% finished part cost savings

Meeting Demanding Product Development Timelines

Blow by tube Application:  Blow by tube coupling 

Solution Sought:  PA 6 was failing 8 weeks from SOP due to short-term exposure to 280° C air.

Key Application Requirements:

  • Withstand short-term exposure to 280° C air
  • Meet dimensional tolerances in a tool designed for nylon 6
  • Pass application-specific impact testing
  • Provide functional snap fit attachments

Teknor Solution: V-Creamid® B3H2G3ZB- Cross-linked 15% glass fiber, impact modified PA 6

Why Creamid® B Cross-Linked

  • Cross-linking allows the material to withstand short term exposure to 280° C (60° C above the melting point for PA 6)
  • Using cross-linked PA 6 allows for molding in the same mold to meet all dimensions
  • Process development support to optimize for cross-linking
  • Lower cost than other high temperature options
RESULTS: Cross-linking boosts temperature performance while maintaining part tolerances to help this customer meet SOP target

Solving Post-Tooling Performance Issues

Heavy VehicleApplication:  Heavy Vehicle Spring Bushings 

Post Tooling Problem:  Improved wear vs. Stanyl.  Parts were failing early in Stanyl.

Key Application Requirements:

  • Excellent abrasion resistance
  • Stable in a long term oil environment
  • Processability in current tooling
  • Cost neutral

Teknor Solution: V-Creamid® A4H9L05.2 -  Crosslinked internally lubricated  PA 66

Why Creamid® A Cross-Linked

  • Improved abrasive wear properties vs. Stanyl
  • Processing support to optimize cycle time and dimensions
  • Total cost was equivalent
RESULTS: Longer part life at equivalent part cost

Reducing Existing Part Cost: Vacuum Pump End Cap

pumpApplication:  Vane endcap for vacuum pump 

Solution Sought:  Cost reduction vs carbon fiber filled PEEK without compromising performance

Key Application Requirements:

  • Withstand short term temperature spikes as high as 350° C
  • Wear and friction equivalent to PEEK at all operating conditions
  • Significant cost reduction vs. PEEK

Teknor Solution: V-Creamid® A3H7 C6 - Cross-linked 30% carbon fiber, PA 66

Why Creamid® A Cross-Linked

  • Cross-linking allows carbon fiber-filled PA 66 to see short term temperature exposure in excess of 350° C
  • Cross-linking brings the tribological properties of carbon fiber filled PA 66 to the level of carbon fiber filled PEEK
  • Creamid® can be processed on standard injection molding equipment. PEEK needs special high-temperature machinery
RESULTS: ≅ 70% cost savings in the finished part

Cross-linked standard thermoplastics present opportunities for manufacturers to innovate or reimagine complex part designs in ways that are cost-effective and powerful alternatives to PEEK, PPS, and LCP. Contact the Teknor Apex team to learn more about cross-linking compounds, part design optimization, and solutions that can help get you to market faster and more profitably.