Increasing top layer share enhances recyclate cup performance in thermoforming

Why It Matters

This research offers practical strategies for designers and manufacturers looking to incorporate recycled plastics into high-volume products like cups. By understanding how to balance recyclate content with virgin material distribution, companies can achieve better product performance and meet sustainability goals without compromising quality.

Key Finding

Using recycled polypropylene in the core of thermoformed cups can reduce shrinkage but may lower strength. However, increasing the proportion of virgin material in the outer layers or blending the recyclate with virgin material can effectively improve strength and shrinkage, making the use of recyclates more viable.

Key Findings

• Post-consumer polypropylene recyclates exhibit lower stiffness but higher toughness due to polyethylene contamination.
• Thermoformed cups with recyclate core layers show reduced shrinkage compared to virgin material cups.
• Most cups with recycled content had lower top load strength than the control.
• Increasing the top layer share, blending recyclate with virgin material, or increasing overall film thickness all improved shrinkage and top load.
• Increasing overall film thickness was found to be economically unfeasible.

Research Evidence

Aim: How can the product properties of thermoformed multilayer cups, specifically shrinkage and top load strength, be improved when utilizing post-consumer polypropylene recyclates in the core layer?

Method: Experimental

Procedure: The study involved thermoforming multilayer cups using four different post-consumer polypropylene recyclates as the core layer and virgin polypropylene as the top layer. Material-level tests were conducted to assess mechanical properties. Product-level tests evaluated shrinkage and top load strength. Three improvement strategies were then tested: increasing the top layer share, blending recyclate with virgin polypropylene, and increasing overall film thickness. Performance metrics were compared against a control cup made solely from virgin polypropylene.

Context: Thermoformed packaging, specifically cups made from polypropylene.

Design Principle

Multilayer material construction allows for the optimization of product performance by strategically combining different material properties, such as using virgin materials for surface integrity and recyclates for bulk volume.

How to Apply

When designing thermoformed products with recycled content, consider a multilayer approach where the recyclate forms the core and virgin material constitutes a significant portion of the outer layers. Experiment with different ratios of virgin to recycled material in the layers to find an optimal balance between cost, performance, and sustainability.

Limitations

The study focused on specific commercially available recyclates and a particular multilayer structure; results may vary with different recyclate compositions or processing parameters. Economic feasibility of increasing overall film thickness was not fully explored beyond initial assessment.

Student Guide (IB Design Technology)

Simple Explanation: If you want to make cups from recycled plastic, using more of the new plastic on the outside and the recycled plastic on the inside helps make the cups stronger and less likely to shrink.

Why This Matters: This research shows how designers can use recycled materials in their projects without compromising the quality or performance of the final product, which is important for sustainable design.

Critical Thinking: While increasing the top layer share is effective, what are the economic implications of using a higher percentage of virgin material, and how can this be balanced with the environmental goals of using recyclates?

IA-Ready Paragraph: The research by Traxler et al. (2023) demonstrates that incorporating post-consumer polypropylene recyclates into the core layer of thermoformed cups can lead to reduced shrinkage but potentially lower top load strength. However, strategic adjustments, such as increasing the proportion of virgin polypropylene in the outer layers, can effectively enhance product performance, making the use of recyclates a viable option for sustainable design in packaging.

Project Tips

• When researching materials for your design project, consider how different types of recycled plastics behave in manufacturing processes.
• Investigate the potential for using multilayer structures to combine the benefits of virgin and recycled materials.

How to Use in IA

• Reference this study when discussing material selection for your design project, particularly if you are considering the use of recycled plastics.
• Use the findings to justify design choices related to material composition and manufacturing processes.

Examiner Tips

• Demonstrate an understanding of how material properties influence manufacturing processes and final product performance.
• Clearly articulate the trade-offs between using virgin and recycled materials and how design decisions can mitigate negative impacts.

Independent Variable: ["Proportion of virgin polypropylene in top layers","Blending of recyclate with virgin polypropylene","Overall film thickness"]

Dependent Variable: ["Shrinkage","Top load strength"]

Controlled Variables: ["Type of recyclate","Type of virgin polypropylene","Thermoforming process parameters"]

Strengths

• Investigated practical strategies for improving recyclate use.
• Tested both material and product level performance.
• Provided clear design implications for multilayer structures.

Critical Questions

• How would the results differ if other types of polymers or recyclates were used?
• What are the long-term durability implications of using recyclates in the core layer?

Extended Essay Application

• Investigate the feasibility of using advanced simulation tools to predict the performance of multilayer structures with varying recyclate content before physical prototyping.
• Explore the life cycle assessment (LCA) benefits and drawbacks of different strategies for incorporating recyclates into thermoformed products.

Source

Strategies for improving product properties of thermoformed multilayer cups with contents of post‐consumer polypropylene recyclates · Journal of Applied Polymer Science · 2023 · 10.1002/app.54451