How to Use Polymer Blends in Injection Molding

Injection molding is a highly efficient and versatile process that is particularly suitable for building plastic parts, whether for prototyping or final production. It’s also an ideal method for processing polymer blends. These blends—which combine two different polymers—can offer unique benefits such as enhanced material properties and recyclability, adding value to injection molded parts. In fact, over one-third of commercial polymers used for injection molding are blends, with the secondary polymer constituting at least 2% of the mixture’s total volume.

If you’re considering polymer blends for injection molding, here’s a comprehensive guide on these specialty polymers, their applications, and the processes involved in combining them.

Categories of polymer blends

Today, there’s a wide array of polymer blends categorized based on their constituent polymers. The five main types include:

  1. Thermoplastic-thermoplastic blends
  2. Thermoplastic-thermoset blends
  3. Thermoplastic-elastomer blends
  4. Polymer filler blends
  5. Elastomer-thermoset blends

Moreover, polymer blends are also classified based on their molecular compatibility into homogeneous (miscible) and heterogeneous (immiscible) blends. Most commercial polymer blends used in injection molded parts are immiscible, allowing each polymer to maintain its distinct properties. However, the resulting injection molded parts might exhibit different strengths and weaknesses in various phases.

Implementing polymer blends in injection molding

Various polymers are suitable for injection molding, each with specific requirements for pressure, clamping, and temperature. This process is equally effective for molding polymer blends.

Manufacturers often procure pre-mixed pellets, especially for blends like PC/ABS. Alternatively, they can blend two separate polymers just before the injection molding process using a precision gravimetric blender. This device accurately measures and weighs the materials, ensuring the correct ratio. It’s also useful for accurately adding additives and colorants. Regardless of the mixing technique, specialists in injection molding typically use a reciprocating screw injection machine for optimal efficiency.

To learn more about polymer blends for injection molded parts, consult with our experts at HLH Proto. We’re here to assist you in selecting the right polymers for your project and can offer design advice and a quote for our injection molding services.


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