Tuesday 21 March 2023

2 Component Injection Moulding: How TPS (SEBS) Can Stick to Polyamide or Polycarbonate Without Using Additional Adhesive?

Overmoulding PA and PC with PC - 2 component moulding

Hello and welcome to a new blog post in which we discuss how TPS can stick to Polyamide or Polycarbonate in 2 component injection moulding. 

During polymer material selection, one scenario can be that a solid plastic housing, made out of Polyamide, needs to have a sealing moulded on it. The selected sealing material is a styrene-ethylene-butylene-styrene (SEBS) from the thermoplastic elastomer class. A two-phase block copolymer with hard and soft segments forms the basis of SEBS. 

SEBS (Figure 1)  is used in different applications such as footwear, and seals which have low requirements towards chemicals and (heat) aging. Furthermore SEBS has excellent weatherability making it useful for many outdoor applications. It is also known for its ability to uptake oil and soften its Shore hardness. SEBS is non-polar leading to a harder adherence on polar polymers such as Polyamide. 

Figure 1: Structural formula of SEBS.

How can we increase the adherence of SEBS towards PA and PC?

There is a chemical trick one can apply: grafting maleic anhydride (= acid anhydride of maleic acid) onto the ethylene butadiene mid-blocks allows for better connection. The functional groups enable an adherence to polar PA or PC. 2 component overmoulding applications can be done and no additional usage of adhesives is needed.

Thanks for reading!


Herwig Juster

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[1] https://www.hexpol.com/tpe/resources/tpe-academy/what-is-tpe/what-is-tps/

[2] http://plasticnotes.blogspot.com/2009/11/polymer-polarity.html?q=polar

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