What is the difference between crosslinking, branching, and chain scissioning?

[embedyt] https://www.youtube.com/watch?v=UdiX3oW1sxM[/embedyt]
In the latest Crash Course, the E-BEAM team talks about the difference between three different types of polymer modification: crosslinking, branching, and chain scissioning.

Crosslinking

Crosslinking occurs during the e-beam process when the bonds between molecules in a polymer break, and then reform as stronger bonds.
Why would someone be looking for crosslinking? Well, crosslinking helps improve the mechanical properties, like increased temperature resistance and abrasion resistance, of many polymers.
E-beam crosslinking provides all of chemical crosslinking’s advantages of having a thermoplastic turn into a thermoset–without the use of harmful chemicals.

Some Everyday Applications include:

  • Gaskets and seals
  • Automotive parts
  • Connectors
  • Mouthguards
  • Medical casts
  • Plumbing components
  • Ice maker tubing
  • Risers
  • Manifolds

Branching

Branching is used to modify the molecular processability and melt properties of polymer pellets. The e-beam irradiation creates side chains and can increase the molecular weight, all without creating a 3D network like during the crosslinking process.

Crosslinking is generally performed on molded parts, whereas branching is performed on pellets. A much lower dose is needed for long-chain branching than for crosslinking.

Why would someone be looking for branching? Well, when the side chains entangle, it increases the melt strength of the polymer, allowing for downgauging, long draw thermoforming, creation of lower density foams, and other applications. Essentially, when you’re looking to improve the properties of a polymer before it’s molded.

Some Everyday Applications include:

  • Foam
  • Film
  • Extrusion coating
  • Extrusion blow molding
  • Thermoformed trays and containers
  • Automotive interiors

Chain Scissioning

Chain scissioning is another method of polymer modification. During the chain scissioning process, bonds between molecules are broken and not reformed in controlled degradation.

For example, PTFE can be processed to create a micro powder that can be brought to a specific particle size. Specific particle sizes are increasingly useful in products such as inks, coatings and lubricants.

Some everyday applications include:

  • Injection molding (reduced warping)
  • Films (improved opticals)
  • Fiber/textiles
  • Packaging
  • Cellulosic materials
  • Natural rubbers
 

If you want to look at it another way, crosslinking can be seen as taking different pieces of fabric and stitching them together to make a piece of clothing. Branching is taking that fabric and holding it together using Velcro instead of stitching. And chain scissioning is taking the finished piece of clothing and taking it apart to turn it into something else useful.

As always, if you have any questions, feel free to reach out to our Technical Services team at ebeam@ebeamservices.com!

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