Wednesday, 17 June 2026

Plastics Testing & Analysis - The Importance of Understanding Measurement Uncertainty and Measurement Error (Rule of Thumb)

Hello and welcome to an new Rule of Thumb post in which we have a closer look at understanding Measurement uncertainty and measurement error in plastics. 

Back at University during my polymer engineering study, I remember, there was a paper hanging on the wall of the rheology lab which I kept all the years in my mind. On the paper was a quote, if I remind correctly, from David Packard and it stated the following: 

"You are always measuring wrong, you just have to know by how much"

That quote captures a fundamental truth in polymer engineering, and physics: perfect measurement does not exist. Every measurement contains some degree of error, and the key to precision is understanding and quantifying that error.

This brings me to the standard deviation (σ) which measures the dispersion or spread of data points around their arithmetic mean. A low σ indicates data clusters tightly near the average, while a high σ shows wide scattering. It carries the same units as the data, making it highly interpretable (Figure 1).

Figure 1: The importance of mean and standard deviation in plastics testsing and analysis including an example of PP tensile strength measurement. 

Example - Standard deviation σ in polymer analysis

Standard deviation σ in polymer analysis directly quantifies the absolute spread of polymer chain lengths or molecular weights around the mean. It is critical for predicting physical properties like viscosity, tensile strength, and melting point, providing a more precise measure of chain variation than the standard Polydispersity Index (PDI).

What a high σ tells you - more examples

  • Plastics testing: Tensile strength of injection molded Polyproyplene (PP) specimen measured under the same conditions. A high σ indicates an incosnistent process with greater part variability and higher risk of outliers (Figure 1).
  • Molding inconsistencies: Fluctuations in barrel temperature or cooling rates.
  • Operator variance: Poor grip alignment or extensometer slippage during ⁠measurment

Ok, and what I can do to have the standard deviation under control?

Here is a quick Troubleshooting Checklist:

  • Sample prep: Are specimens conditioned to eliminate moisture variance.
  • Calibration: Verify force cells and displacement transducers strictly meet ISO/ASTM requirements.
  • Sample size: Ensure you test at least 5 representative specimens for a statistically sound mean.

In conclusion 
One only truly understand polymers when you connect: 

polymeric material → processing → structure → failure.

Great polymer engineers don not just know materials —they understand the interaction between design, processing, and degradation.

Check out more Rule of Thumb posts in my Start here section.

Thanks for reading & #findoutaboutplastics

Greetings, 

Herwig 



Literature: 

[1] https://onlinelibrary.wiley.com/doi/book/10.1002/0470100427

[2] https://www.hanser-fachbuch.de/Kunststoffpruefung/978-3-446-48105-3

[3] https://www.philmckinney.com/10-quotes-from-bill-hewlett-and-david-packard-that-every-executive-should-read/
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Tuesday, 2 June 2026

Cyanoacrylates - Eastman 910 & Super Glue: The Most Famous "Happy Accidents" in Science

Hello and welcome to a new post in which we uncover the story of Super Glue. It is one of the most famous "happy accidents" in science, involving not just one, but two accidental discoveries by the same man before it reached the public. 

Let us start chronologically: 

1. The Initial "Failure" (1942)

During World War II, Dr. Harry Coover was a chemist at Eastman Kodak working on a project to develop clear plastic for precision gun sights. He discovered a class of chemicals called cyanoacrylates. 

The Problem: The substance was a disaster for gun sights because it was "infuriatingly sticky" and bonded to everything it touched.

The Result: Coover and his team rejected the compound and "threw away the formula," considering it a failed attempt at clear plastic. 

2. The Rediscovery (1951)

Nearly a decade later, Coover was overseeing a new project at Eastman Kodak to create heat-resistant polymers for jet plane canopies. 

The "Aha!" Moment: His colleague, Fred Joyner, was testing the optical properties of a cyanoacrylate sample and spread a thin layer between two expensive glass refractometer prisms. The prisms fused together instantly, permanently bonding the equipment.

The Realization: While Joyner initially panicked over the ruined prisms, Coover recognized that they had not created a failed plastic—they had discovered an incredible, fast-acting adhesive that required no heat or pressure to bond. 

3. Commercial Success and Marketing (1958)

The product was first sold commercially in 1958 under the name Eastman 910. 

The TV Stunt: To prove its strength, Coover appeared on the TV show "I’ve Got a Secret," where he used just one drop of the glue between two metal plates to lift the show's host off the ground.

The Rebranding: It was eventually rebranded as "Super Glue" in the 1970s. 

4. A Life-Saving Evolution

Beyond household repairs, the adhesive found a critical use during the Vietnam War. 

Battlefield Medics: Medics began using a spray version of the glue to instantly seal battlefield wounds. It stopped catastrophic bleeding long enough for wounded soldiers to be transported to a hospital, saving countless lives.

Modern Medicine: This accidental military application led to the development of FDA-approved medical-grade adhesives used in hospitals today, such as Dermabond. 

5. How the Bonding Strength Compares

Vs. Epoxies & Structural Acrylics: Two-part epoxies and acrylics have comparable or slightly higher tensile strength (12–25 MPa), but they heavily outperform Eastman 910 in impact, heat, and moisture resistance. Epoxies are highly resilient under mechanical stress, whereas cyanoacrylates are relatively brittle. Eastman 910 is a high-strength, original methyl-cyanoacrylate (super glue) that cures rapidly. It boasts tensile shear strengths of 20–30 MPa on metals like steel. An overview on the achievable shear strength by metal type is shown in Figure 1.

Figure 1: Eastman 910 / Permabond 910 - shear strength by metal type.

Vs. Modern Cyanoacrylates: Because Eastman 910 is an unmodified methyl-cyanoacrylate, its true strength peaks on tight metal-to-metal joints. Modern cyanoacrylate formulations (such as Loctite 401 or Permabond 731) offer similar shear strength but include "toughening" agents that vastly improve flexibility and peel resistance.

Vs. Wood Glues & Hot Melts: Eastman 910 is much stronger in dead tension than traditional wood glues, hot melts, or silicones. However, it fails on porous or rough surfaces, where wood or polyurethane glues excel.

In conclusion - Strengths & Weaknesses

What it does best: Creates an incredibly strong, instantaneous bond in seconds with a very low volume of adhesive required. It is excellent at resisting straight tension/pulling.

Where it falls short: It is brittle, performs poorly under vibration or sudden impact, and has low heat resistance (usually weakening past 80°C).

Which "happy accidents" leading to new polymers are you aware? Let me know in the comments below.

Thanks for reading & #findoutaboutplastics

Greetings, 

Herwig 



Literature: 

[1] https://lemelson.mit.edu/resources/harry-coover#:~:text=Super%20Glue%E2%84%A2,moved%20on%20with%20their%20research.

[2] https://custom-powder.com/accidental-invention-super-glue/#:~:text=In%201942%2C%20chemist%20Dr.,its%20extraordinary%20strength%20and%20reliability.

[3] https://tacticsjournal.com/opinion/2025/01/31/eastman-910-adhesive/

[4] https://www.silitech.ch/en/blog/wissenszentrum-7/permabond-klebstoffe-sortiment-technische-daten-loctite-vergleich-31

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Friday, 8 May 2026

Polymer Injection Molding – The Effect of Pressure on Viscosity [infographic]

Hello and welcome to a new blog post. 

How much does pressure really affect polymer viscosity in injection molding?

When we talk about melt viscosity, most of us immediately think about temperature and shear rate. But pressure also matters — and for some polymers, it matters a lot more than many people expect.

The infographic below highlights a key point: the viscosity of thermoplastics depends not only on temperature, shear rate, and pressure, but also on chemical structure and physical conditions.

A good example is the difference between amorphous and semi-crystalline polymers:

  • Polystyrene (PS): at 200 bar, viscosity can increase by about 22%
  • Polyethylene (PE): at the same pressure, viscosity increases by only about 3–4%

Calculation in detail

The pressure dependence of polymer viscosity, often analyzed using methods like those proposed by Dudvani and Klein [2,3], is significant for polystyrene (PS) at high pressures.

Exponential Model: The effect of pressure P on the viscosity Eta of PS is generally described using the exponential formula: Eta = Eta_0 exp (P + Alpha).

Pressure Coefficient (Alpha): For atactic and syndiotactic polystyrene, studies show the average pressure coefficient Alpha is in the range of  1–3 x10^(-8) Pa^-1.

At 200 bar (200 x 10^5 Pa) with Alpha of 10^-8 Pa, viscosity increases to 1.2214 (22%). 

Mechanism: Increased pressure decreases the free volume available for polymer chain movement, increasing the intermolecular friction and thus the viscosity.

Conclusions

That is an important reminder for injection molding, where pressure effects can strongly influence filling behavior and process stability. In extrusion, by contrast, the effect of pressure on viscosity is often much less relevant.

Figure 1: The Effect of Pressure on Thermoplastic Viscosity.

Thanks for reading & #findoutaboutplastics

Greetings, 

Herwig 



Literature: 

[1] Rao Natti - Design Formulas for Plastics Engineers

[2] https://www.researchgate.net/publication/285636168_Comparison_of_Measurement_Techniques_for_Evaluating_the_Pressure_Dependence_of_the_Viscosity

[3] Dudvani I.J. and I. Klein: Analyis of Polymer MeltFlow  in  Capillaries  Including  Pressure  Effects,SPE Journal (1967) 41-45

[4] https://link.springer.com/chapter/10.1007/978-3-662-41458-3_31

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Wednesday, 6 May 2026

🎯Getting Tolerances Right in Injection Molding: Why Standards Matter! (ISO 20457 & ISO 3302)

Figure 1: Overview of ISO 20457 for thermoplastics and ISO 3302 for rubber injection molded parts.

Hello and welcome to a new blog post. When it comes to plastic and rubber parts, achieving the right tolerances is key to ensuring quality, fit, and function. But did you know there are specific ISO standards that guide this process?

🔹 ISO 20457 for Plastics:

This standard provides clear guidelines for defining tolerances and acceptance conditions for dimensions of plastic parts produced by processes like injection molding, extrusion, or thermoforming.

Different tolerance groups (TG) are defined:

TG 6 for packaging parts

TG 5 for housing parts

TG 4 for precision parts (like gears)

Note: ISO 20457 applies only to unfilled thermoplastics.

🔹 ISO 3302 for Rubber:

For molded rubber parts, ISO 3302 is the go-to standard. It divides molded parts into four tolerance classes, from M1 (fine) to M4 (coarse). For most technical molded rubber parts, M3 (medium) is typically used.

In conclusion

Understanding and applying the right tolerance standards helps ensure your parts meet performance expectations and manufacturing requirements—saving time, reducing costs, and boosting customer satisfaction. 

As a rule of thumb, for precision injection molded parts such as gears, ISO 20457 TG 4can be applied. For housing parts TG 5 and packaging parts TG 3. For rubber molded parts,  ISO 3302 is key, and in particular M1 (fine) to M4 (coarse) (Figure 1).

Check out this post too, where tolerances are important to turn product requirements into plastic & plastic part specifications: read full post.

Thanks for reading & #findoutaboutplastics

Greetings, 

Herwig 



Literature: 

[1] https://maxnext.io/de/blog/allgemeintoleranzen-im-spritzguss-nach-din-iso-20457-ehemals-din-16742-2/

[2] https://www.nh-technology.de/download/Design-Construction-Guide-Plastic-Parts.pdf

[3] https://www.zorge.com/gummi-lexikon/din-iso-3302-1/

[4] https://www.toleranzen-beratung.de/unternehmen/aktuelles/ansicht/iso-204572018-toleranzen-fuer-kunststoff-formteile-informationen-zur-neuen-norm/

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