Turning Product Requirements into Plastic & Plastic Part Specifications: The Key to Successful Material Selection!

Hello and welcome to a new blog post where we discuss an important material selection topic. 

When developing a plastic part, clear and meaningful specifications are essential—they help control variations in function, appearance, and cost. By translating product requirements into detailed plastic specifications, you set the foundation for selecting the optimal material and ensuring consistent quality. Also, the specifications will help for sourcing plastic parts with the correct material. 

What should a robust plastic specification and plastic part specification include? 

✔️ Material brand, grade, and generic name (e.g., Ryton® R-4-200BL, PPS)

✔️ Surface finish

✔️ Desired parting line location

✔️ Flash limitations

✔️ Permissible gating and weld line areas

✔️ Void intolerance zones

✔️ Allowable warpage

✔️ Tolerances

✔️ Color

✔️ Decorating needs

✔️ Performance criteria

Example of turning a product requirement into a plastic specification:

If your product requirement is “the part must withstand high temperatures, needs to have low tolerance, and have a glossy black finish,” this translates into a plastic specification such as:

• Material: Ryton® R-4-200BL (PPS) for heat resistance
• Color: Black, high-gloss surface finish
• Tolerance: ±0.05 mm
• No voids allowed in load-bearing areas
• Gating away from visible surfaces

Figure 1 demonstrates how plastic specifications act as a bridge between product requirements, material selection, and support for sourcing. First we turn product requirements into proper plastic specifications, which we can use for polymer selection. After identifying the plastic grade we can add it with commercial name to our specification list and use it for sourcing or to find alternativ materials, as well as sourcing the plastic parts themselfs. 

Figure 1: Plastic specifications as bridge between product requirements, material selection, and support for sourcing. 

Conclusions

Having proper specifications not only streamlines the material selection phase, but also greatly supports sourcing—especially when you need to identify or qualify alternative materials. Clear specifications ensure you can compare options confidently and maintain quality, even when supply chains change.

Getting these details right means your part will meet all functional, aesthetic, and economic goals. Start with clear specs—finish with a successful product!

Thanks for reading & #findoutaboutplastics

Greetings,

Herwig Juster

📚My Polymer Material Selection Book - Available Here

📊 Discover your Polymer Material Selection score by taking quick test here

🎥Join my YouTube channel community 

🔎Join my inner circle (monthly newsletter)

Literature:

[1] Herwig Juster - Polymer Material Selection, 2023

How Additives Make or Break Plastics - Examples PC and ABS (Rule of thumb)

Hello and welcome back, fellow explorers of the material world! Today, I invite you to join me on a journey behind the scenes of everyday plastics—a place where tiny additives can play the role of either hero or villain in the fate of your favorite products.

Chapter 1: The Perilous Partnership—Polycarbonate & Titanium Dioxide

Once upon a time, in the bustling world of manufacturing, Polycarbonate (PC) was the go-to plastic for making everything from monitor frames to sleek gadgets. It was strong, clear, and reliable. But every hero has a weakness, and for PC, it was its quest for the perfect color.

Enter Titanium Dioxide (TiO₂), the pigment famed for its ability to turn plastics dazzling white or vibrant in color. At first, the partnership seemed perfect. Products gleamed on store shelves, catching every eye. But beneath the surface, trouble was brewing.

As more TiO₂ was added, the very structure of PC began to change. Its molecular weight dropped, and with it, the material’s strength and fracture energy. What once was tough and resilient became brittle and prone to failure. The culprit? The very pigment that made it beautiful.

The lesson from this tale: Sometimes, the pursuit of perfection comes at a cost. If you want your PC products to last, consider alternative pigments that offer the same brilliance—without the heartbreak.

---

Chapter 2: The Unsung Guardians—ABS & Antioxidants

Now, let’s shift to a story of hope and protection. Meet Acrylonitrile Butadiene Styrene (ABS), a versatile plastic born from the union of acrylonitrile, styrene, and a dash of polybutadiene. ABS is everywhere—from car parts to LEGO bricks—thanks to its toughness and adaptability.

But ABS has a secret vulnerability: the polybutadiene phase, filled with unsaturated double bonds, is a magnet for environmental attackers like oxygen. When these bonds are struck, free radicals form, and the once-mighty ABS starts to crumble, losing its impact strength and behaving more like fragile styrene.

Enter the heroes: antioxidants! With just 0.5% of powerful defenders like benzophenone, benzotriazole UV stabilizers, or phenolic antioxidants (think Irganox 1010, 1076, 245), ABS gains a shield against the forces of degradation. These additives slow down the photo-oxidative process, especially when ABS faces the harsh outdoors.

For manufacturers, the moral is clear: choose ABS formulations fortified with antioxidants, and your products will stand strong against the test of time.

---

Chapter 3: The Detective’s Toolkit—FT-IR Spectroscopy

But how do we know our heroes are doing their job? Enter the detective: Fourier-Transform Infrared Spectroscopy (FT-IR). This tool lets us peer into the very soul of plastics, revealing the fingerprints of both the base polymer and its additives.

For example, when antioxidants like benzotriazole UV stabilizers are present, FT-IR shows unique peaks—C-H stretching at ~3053 cm⁻¹, N-H stretching at ~2848 cm⁻¹, and more. If you’re looking for Irganox 1076 in polyethylene, a clear peak at 1741 cm⁻¹ gives it away.

With FT-IR, we can confirm our heroes are present and ready for battle, and spot signs of degradation before disaster strikes.

FT-IR Example Irganox 1076 Quantitative Analysis in Polyethylene

Figure 1 shows the FT-IR spectra of a Polyethylene containing the anti-oxidant Irganox 1076. Clearly visible is the additive peak at 1741 cm-1.

Update - community feedback received: 

Chris DeArmitt, PhD gave the following feedback (many thanks!): The carbonyl peak at 1741 could also be Irganox 1135, 259, 245, 3125 or 1010 (1746 cm⁻¹). The peak at 1746 does not tell us whether the stabilizer is still active or consumed. GC-MS will tell you and so can OIT of you prepare a calibration curve with samples of known concentrations. An alternative proper extraction followed by HPLC will give u all insights of consumed and remaining AO and specifically 1076 content more precisely.

Figure 1: FT-IR Example Irganox 1076 Quantitative Analysis in Polyethylene [2].

---

Epilogue: Lessons from the Plastic Frontier

In the end, the story of plastics is one of balance—between beauty and strength, innovation and caution. By understanding how additives interact with polymers, we can craft materials that not only look good but last long.

So next time you hold a plastic part in your hand, remember: there’s a whole world of chemistry working behind the scenes, with heroes and villains shaping its destiny.

Thanks for reading & #findoutaboutplastics

Greetings,

Herwig Juster

📚My Polymer Material Selection Book - Available Here

📊 Discover your Polymer Material Selection score by taking quick test here

🎥Join my YouTube channel community 

🔎Join my inner circle (monthly newsletter)

Literature:

[1] https://www.mdpi.com/2073-4360/11/1/25

[2] https://tools.thermofisher.com/content/sfs/brochures/Fundamentals-Polymer-Analysis.pdf

[3] https://www.azom.com/article.aspx?ArticleID=12386

[4] https://www.linkedin.com/posts/herwigjuster_findoutaboutplastics-polymerengineering-polymermaterialselection-activity-7373264573338058753-48IH?utm_source=share&utm_medium=member_desktop&rcm=ACoAABCkmMcBev71cuhh4-jzEaiPHFO5VFb4aO0

[5] https://www.researchgate.net/publication/360735659_Infrared_Spectroscopy_Method_for_Detecting_the_Content_of_Antioxidant_Irganox_1076_in_Polypropylene

Design-to-Cost (DTC) in Plastic Part Design - Example housing for electronic device

Hello and welcome to a new post. In today's post we discuss the Design-to-Cost (DTC) approach in plastic part design.

Example housing for electronic device

A company is developing a new plastic housing for an electronic device. The target cost for the housing is €1.00 per unit, including material, manufacturing, and finishing.

Figure 1: 5 steps of a Design-to-cost approach for a plastic part design

Step 1: Set Cost Target

The project team establishes that the plastic housing must not exceed €1.00 per unit to remain competitive in the market.

Step 2: Analyze Cost Drivers

Material selection: Polycarbonate (PC) is initially considered, but its cost is relatively high.

Wall thickness: Thicker walls increase material usage and cycle time.

Part complexity: Complex geometries require more expensive tooling and longer molding cycles.

Surface finish: High-gloss or textured finishes may require additional processing.

Step 3: Generate Design Alternatives

Material: Evaluate switching from PC to a less expensive material, such as polypropylene (PP) or ABS, if performance requirements allow.

Wall thickness: Reduce wall thickness from 2.5 mm to 2.0 mm, maintaining structural integrity through ribbing and optimized geometry.

Geometry: Simplify the design by minimizing undercuts and eliminating unnecessary features, allowing the use of a simpler mold.

Surface finish: Specify a standard mold finish instead of a high-gloss or textured finish to reduce costs.

Step 4: Cost Estimation and Iteration

The team estimates the cost of each design alternative using supplier quotes and manufacturing simulations.

For example, switching to ABS and reducing wall thickness lowers material and cycle time costs, bringing the estimated cost to €0.95 per unit.

Step 5: Finalize Design

The design that meets both functional requirements and the cost target is selected.

The team documents the design choices and cost rationale for future reference.

Conclusions 

By applying the Design-to-Cost method, the team systematically reviewed material, geometry, and process options to ensure the plastic part meets its cost target without compromising essential performance.

Thanks for reading & #findoutaboutplastics!

Greetings, 

Herwig Juster

📚My Polymer Material Selection Book - Available Here

📊 Discover your Polymer Material Selection score by taking quick test here

🎥Join my YouTube channel community 

🔎Join my inner circle (monthly newsletter)

Literature: 

[1] https://www.megatron.de/en/category/plastic-housing.html

How many cavities should you choose for your injection molding tool? I Rule of Thumb Polymer Processing

Hello and welcome to a new post. In today's post we discuss a community question I received:

How many cavities should you choose for your injection molding tool?

It’s a question that can make or break your project’s budget. Go too low, and you’re missing out on efficiency. Go too high, and tooling costs skyrocket.

Figure 1 [1] compares the cost of the injection mold, material, and injection molding as function of the mold cavities.  The sweet spot is at eight cavities as the optimal cavity number before costs start to climb. It is a classic "bathtub" cost curve and allows one to balance between tooling investment and production savings. 

Figure 1: Choosing the optimal umbers of mold cavities [1].

Conclusions

This curve serves as a first orientation. Important is that you collect all your costs and create such a total cost curve on your own. It depends if you are molding a packaging part, where more than eight cavities are beneficial, or if you are molding an engineering part such as a connector with pin overmolding, where fewer cavities may lead to an optimum already. 

Update - I received an interesting feedback: Prof. Jozsef Kovacs from University of Budapest highlights that László Sors developed a comprehensive analytical method for cavity number optimization as early as 1966, including equations, practical examples, and a nomogram. Sors’s work also addressed prototype molds, tool cost-efficiency, and the integration of thermal, rheological, and electrical calculations into mold design—well before these became industry standards. Sors is recognized as a pioneering figure in polymer tooling and design, leaving a significant legacy in the field. He published his know-how in the 1966 book: Műanyag-alakító szerszámok.

More "Rules of Thumb" posts can be found under "start here".

Thanks for reading & #findoutaboutplastics!

Greetings, 

Herwig Juster

📚My Polymer Material Selection Book - Available Here

📊 Discover your Polymer Material Selection score by taking quick test here

🎥Join my YouTube channel community 

🔎Join my inner circle (monthly newsletter)

Literature: 

[1] A. Pouzada: Design and Manufacturing of Plastics Products: Integrating Traditional Methods With Additive Manufacturing

[2] H. Juster: Optimizing your injection moulding production – my 5+ How’s I Plastics processing tips