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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Tuesday, 5 May 2026

Estimating Maximum Injection Pressure in Plastic Injection Molding (Rule of Thumb Plastics Processing)

Hello and welcome to a new blog post in which we’re sharing a practical rule of thumb for estimating the maximum injection pressure in plastics injection molding. 

It’s straightforward: take the minimum necessary injection pressure of your chosen polymer and simply multiply by 1.2. 

The result? Your maximum injection pressure.

Examples applying this rule

Let us look at a few examples with standard parts and medium-viscosity polymers:

  • Polyamide: Minimum pressure = 110 MPa → Maximum = 130 MPa
  • Polyethylene: Minimum = 100 MPa → Maximum = 120 MPa
  • Polycarbonate: Minimum = 120 MPa → Maximum = 150 MPa
Benefits:
  • It is a quick and easy way to estimate directly at your machine
  • Improves the process stability
  • Protects the machine and the mold

This simple approach helps you quickly estimate your injection molding parameters and ensures smoother processing—every time!

More Rules of Thumb can be found in my "start here" section. 

Thanks for reading & #findoutaboutplastics

Greetings, 

Herwig 



Literature: 

[1] Natti Rao: https://www.hanser-elibrary.com/doi/pdf/10.3139/9783446431492.fm

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Sunday, 3 May 2026

High Performance Thermoplastic Selection - Part 2D: Liquid Crystal Polymers (LCP) and High-performance Polyesters (Polycyclohexylene terephthalate - PCT)

Hello and welcome to Part 2D of my  High Performance Thermoplastics Selection blog series. 

Overview - 6 major high performance thermoplastics families (“the magnificent six”) 

In this blog post series we discuss six major high performance thermoplastics families (“the magnificent six”) which are outlined in the following enumeration

1. Introduction to High Performance Polymers

2. Short profile of the "magnificent six" families:

-Part 2A: Polysulfides (Polyphenylene sulfide - PPS), Polysulfones (PSU, PESU, PPSU), and Polyarylates (PAR)

-Part 2B: Imide-Based Polymers (PEI, PAI, PESI, TPI, PI) and Polybenzimidazoles (PBI, PBI+PEEK, PBI+PEKK)

-Part 2C: Polyether (PPE)

-Part 2C: Polyether (PAEK, PEEK, PEKK)

-Part 2D: Liquid Crystal Polymers (LCP) and High-performance Polyesters (Polycyclohexylene terephthalate - PCT)

-Part 2E: Semi- and Fully Aromatic Polyamides (PARA, PPA, Aramid)

-Part 2F: Polyhalogenolefins (PTFE, PCTFE, FEP, PVDF, ECTFE)

3. Key properties and design data for selection

4. Polymer Material Selection 4-stage funnel methodology (POMS-Funnel-Method)

5. Examples for Ultra- and high performance polymer selection

Let's start with LCP. 

1) Liquid Crystal Polymers (LCP)

1.1 Introduction

Liquid Crystal Polymers (LCPs) are a class of high-performance thermoplastics characterized by their ability to form ordered (liquid crystalline) structures in the melt phase. This molecular alignment leads to exceptional mechanical and thermal properties, even at elevated temperatures.

LCPs are considered super engineering plastics and are widely used in electronics, automotive, and precision components.

Discovery of LCP - Friedrich Reinitzer and Otto Lehmann

In 1888, Friedrich Reinitzer, an Austrian chemist and botanist, observed unusual temperature-dependent behavior in cholesteryl benzoate. He noticed it melted into a hazy liquid at one temperature and then became clear at a higher temperature, exhibiting color changes upon cooling before solidifying. Puzzled by these two melting points, Reinitzer sent his findings and the material to German physicist Otto Lehmann. Lehmann used a heated microscope to further investigate and identified the hazy liquid as a new state of matter with crystalline properties, which he named a "liquid crystal." While this discovery by Reinitzer and Lehmann around the turn of the 20th century generated initial scientific interest and the identification of nearly 200 similar compounds, practical applications were not immediately apparent, leading to a decline in research focus.

1.2 Chemistry and Production

Not to be overlooked is the fact that every LCP has a unique chemical structure. This implies that although the term "liquid crystalline polymer" refers to the overall set of features, each manufacturer of LCP may have unique chemical structures and this is similar to polyamides. For example, PA6 and PA 4.6 show significantly differing thermal resistance, yet they both absorb more water than polyesters and have poorer dimension stability. While each polyamide has a unique chemical structure that determines its different thermal resistance, the amide-bonding group determines the increased water absorption property.

Looking into the literature [1] of polymer chemistry, we can distinguish between

-Type I LCP (HDT a 1.82 MPa > 260°C), 

-Type II LCP (HDT = 210-260°C), and

-Type III (HDT < 210°C). 

All three types contain a p-hydroxybenzoic group and are called  “thermotropic” LCP ( in contract to “lyotropic” LCP = liquid crystals can be seen in solvent as a solution; most well known lyotrpic LCP is based on PARA-Aramid). The crystals stay solid in the melt phase and can be modelled as matchsticks during the injection moulding filling process. Applying shear to the polymer will result in a very good alignment of the matchsticks.

LCPs are typically aromatic polyesters or polyester-amides, which are built from rigid rod-like monomers (e.g., hydroxybenzoic acid, terephthalic acid derivatives).

Polymerization via:

  • Melt polycondensation
  • Occasionally solution polymerization

Key structural feature:

  • Highly anisotropic molecular chains
  • Self-aligning during processing → liquid crystalline phase

Some more history on the commercialization of LCP - Example Xydar

Xydar Liquid Crystal Polymer (LCP) is a high-performance thermoplastic, commercially introduced by Dartco Manufacturing Company in 1984. It is notable as one of the first melt-processable aromatic polyesters, characterized by its ability to form ordered, rigid-rod structures in the melt phase, providing superior high-temperature performance (melting points > 300°C) and chemical resistance.

The technology originated from research in the 1970s, with Dartco (a subsidiary of Dart Industries) obtaining a license for production from Carborundum.

  • Composition: Xydar is a Type I LCP, generally based on a copolymer of p-hydroxybenzoic acid (HBA) and related monomers, designed for high heat distortion temperatures (HDT).
  • Industrialization (1984): Dartco launched Xydar as a commercial product, targeting high-heat applications. In 1985, Dartco licensed Xydar to Nippon Petrochemical, which after establishing the JX Nippon group is since 2021 on the market as Eneos LC. Eneos focus selling LCP in China (80%), Japan and rest of Asia.
  • Amoco Acquisition (1987): At the end of 1987, Amoco Chemical Company acquired the patent rights to Xydar from Dartco.
  • Further Ownership Changes: The product line was later part of Solvay Advanced Polymers and is currently associated with Syensqo (formerly Solvay).

Xydar was part of the first wave of commercial liquid crystal polymers in the mid-1980s (alongside Celanese’s Vectra in 1985). 

History of Kevlar invented by Stephanie Kwolek from Dupont in 1965

In 1965, DuPont chemist Stephanie Kwolek invented Kevlar, a lightweight, high-strength synthetic fiber five times stronger than steel by weight, while researching durable tire materials. Her accidental discovery of a milky, liquid crystalline solution—later spun into fiber—revolutionized materials science and led to widespread use in bullet-resistant vests, protective gear, and aerospace components. 

Initially called "Fiber B," the material was later named Kevlar. It is an aramid fiber (para-phenylenediamine and terephthaloyl chloride) known for extreme strength, stiffness, and heat resistance.

The remarkable strength and energy absorption of Kevlar stem from its dense network of hydrogen bonds between polymer chains and its rigid aromatic rings, which inhibit chain twisting and impart a characteristic rod-like structure. 

Table 1 compares thermotropic LCP to lyotropic LCP. 

Table 1: Comparison of thermotropic LCP vs lyotropic LCP. 

1.3 Properties of LCP

  • Thermal properties: CUT vs. HDT of LCP 

The short term temperature resistance of engineering polymers can be improved by adding glass-fiber reinforcement, however the long term temperature resistance stays on a similar level. This is different with high heat plastics such as PEEK, PPS, LCP, Polyarylates (PAR), Polysulfones (PSU, PESU, PPSU), and Polyimides (PEI, PAI, PI). They combine a high short- and long term thermal resistance. Figure 1 compares the Continuous Use temperature (CUT) to the Heat Deflection Temperature (HDT; short term temperature resistance) of high performance and engineering polymers.  LCP has an excellent short- and long-term temperature stability.

Figure 1: Thermal properties of LCP - comparison of short and long temperature. 

  • Dynamic Mechanical Analysis (DMA):

LCP has a high heat deflection temperature (HDT; e.g. LCP-GF30: 282 °C at 1.8 MPa) and continuous use temperatures (CUT) up to ~200–300°CLCPs do not have a “glass transition” temperature in the classical way of definition (Alpha temperature transition enabling the movement of more than 40 C-atoms in backbone [3]). They have a liquid crystal temperature. Figure 2 shows the DMA curves of PESU (amorphous; Tg = 220°C), PEEK (semi-crystalline; Tg=143°C; Tm =334°C), and LCP (Tlc = 300-380°C). LCP does not have a glass transition temperature, nor a melting temperature. It has a liquid crystalline temperature where the crystals  remain solid, however the linkages between the solid crystals can move [1]. If you examine in detail the literature, a small transition temperature of LCP was found at 120°C. LCP can keep a high mechanical strength level up to 300 °C, outperforming PEEK and PESU. 

Figure 2: Dynamic Mechanical Analysis (DMA) of LCP, PEEK, and PESU.

  • Mechanical properties

LCP has a very high stiffness and strength with a self-reinforcing effect and as an example is the relationship of wall thickness and tensile strength of LCP:

The skin layer's thickness of LCP is almost 200 μm and is a result of the strong orientation of the solid crystal elements (“matchsticks”). The ratio of the skin layer to the total thickness increases proportionately as the thickness decreases. The skin layer has strong mechanical properties since it is made up of highly aligned fibrous semi-crystals of stiff rod molecules. Because of this, LCP's strength will progressively rise as its thickness decreases. Figure 3 shows this relationship of a LCP, and comparing it to a PBT and PESU. This is a common and unique feature of LCP that isn't seen in traditional polymers. 

Figure 3: Relationship of wall thickness and tensile strength of LCP.

  • Low creep and excellent fatigue resistance
  • Highly anisotropic properties (direction-dependent)
  • Excellent dimensional stability
  • Thermal conductivity
Figure 4 shows the thermal conductivity of LCP+PTFE, LCP+MF30, LCP+GF30, and LCP+CF30 [9]. The thermal conductivity increases slightly for glass fiber reinforced LCP. 

Figure 4: Thermal conductivity of different filled LCP grades as function of the temperature [9].

  • Electrical: Very low dielectric constant and loss (Figure 5), making LCP ideal for high-frequency (5G, RF) applications.

Figure 5: Dielectric constant of different LCPs [9].

  • Chemical: Excellent chemical resistance
  • Low moisture absorption
  • Unique feature: Self-reinforcing behavior due to molecular orientation. Know how in part design and material selection is needed to unfold the full potential of LCP. 

1.4 Processing Methods

  • Injection molding (primary method)
  • Extrusion (films, fibers)
  • Thin-wall molding capability
  • Very low viscosity in melt → high flowability
  • Key processing aspect: Properties strongly depend on flow direction and orientation

1.5 Applications

  • Electrical & electronics: Connectors, sockets, SMT components, Lead-free reflow soldering of LEDs
  • High-frequency electronics: 5G antennas, RF components
  • Automotive: Sensor housings, ignition components
  • Industrial: Precision gears, micro-components

1.6 Economic Aspects

Higher costs compared to standard engineering plastics

Cost is justified by:

  • Miniaturization capability
  • High performance in demanding environments
  • Often replaces metals or ceramics in niche applications

1.7 Suppliers / Trade Names

Major global thermotropic LCP suppliers include:

  • Celanese – Vectra®, Zenite®
  • Toray – SIVERAS™
  • Sumitomo Chemical - SUMIKASUPER ™ LCP
  • Polyplastics - Laperos®
  • Syensqo - Xydar® 

2) Polycyclohexylene Terephthalate (PCT)

2.1 Introduction

PCT is a high-temperature, semi-crystalline polyester belonging to the engineering thermoplastics family. It is structurally similar to PET and PBT but offers higher thermal resistance and hydrolysis stability.

It is often positioned as a high-performance polyester for electrical and automotive applications.

Discovery of PCT

PCT was developed by Eastman Kodak and introduced in the early 1950s under the trade name KODEL II. While similar in structure to Polyethylene Terephthalate (PET), PCT features a cyclohexylene ring within its structure. This modification gives it a higher melting point (approximately 285°C), and better hydrolysis resistance. In 1980, General Electric Co. commercialized extrusion-grade PCT for use in construction materials and high-strength panels. 

While initial applications were in fibers, PCT gained traction as a specialized injection molding resin due to its superior heat performance and ability to remain dimensionally stable. PCTs have high initial whiteness which can be further modified by additives. This results in high reflective values (>95% @ 460 nm). Therefore, PCTs are good material candidates for LED applications, where high reflectivity, combined with  luminosity retention over the product service life is needed. 

Replacing thermoset Electric and Electronic applications is possible too.

2.2 Chemistry and Production

  • Polymer: Polycyclohexylene dimethylene terephthalate

Produced by polycondensation of:

  • Terephthalic acid (TPA)
  • Cyclohexanedimethanol (CHDM)

Structure:

  • Aromatic + cycloaliphatic backbone

→ Provides:

  • High rigidity
  • Improved thermal resistance vs PET/PBT, excellent chemical resistance, and high crystallinity.

2.3 Properties of PCT

  • Thermal: high-temperature form stability (up to 256°C shortly), high melting point (~285°C), and excellent resistance to reflow soldering (~255°C). Also, good long-term heat resistance.
  • Optical properties: Figure 6 shows the high reflectance values according ASTM E1331 of two Lavanta® HPP grades [10]. 

Figure 6: Optical properties (Reflectance) of Lavanta® High Performance Polyester [10].

  • Mechanical: High stiffness and dimensional stability (PCT-GF15 reach a tensile modulus of 7 GPa with a tensile strength of 70 MPa and 1.2 % tensile strain).
  • Good creep resistance
  • Chemical: Resistant to automotive fluids and cleaning agents.
  • Good hydrolysis resistance (better than PET)
  • Electrical: High dielectric strength and High CTI (comparative tracking index).
  • Moisture behavior: Low water and moisture absorption, resulting in stable properties. (water absorption after 24 hours is typically 0.057 %; ASTM D570)
Figure 7 shows an engineering comparison for typical unfilled, semicrystalline Polyesters which can be used during material selection.

Figure 7: Engineering comparison for typical unfilled, semicrystalline Polyesters (PET, PBT, and PCT) which can be used during material selection.

2.4 Processing Methods

  • Injection molding (main process)
  • Fast cycle times (good flow behavior)

Compatible with:

  • Glass fiber reinforcement (20–30%)
  • Flame-retardant formulations

2.5 Applications

  • Electrical & electronics: Connectors, switches, relays
  • Automotive: Sensor housings, connectors, interior components which require high reflectivity 
  • Lighting: LED reflectors (color stability advantage)
  • Industrial: High-temperature components as well as filaments and fibers (industrial use).

2.6 Economic Aspects

  • More expensive than PET/PBT
  • Less expensive than LCP

Attractive for:

  • High-temperature polyester niche with re-flow soldering
  • Drop-in replacement for PBT in some cases
  • Replacement of thermosets

Short material selection guide

PET: choose when higher strength/stiffness is needed and managing processing in careful way is possible.

PBT: choose when the best molding productivity and a strong all-round property balance is needed.

PCT: choose when thermal margin, hydrolysis resistance, high reflectivity (LEDs) and dimensional stability at high temperature matter most.

2.7 Suppliers / Trade Names

Key suppliers include:

  • Syensqo - Lavanta®
  • Celanese – Thermx®
  • Eastman – Eastar®
  • SK Chemicals – SkyPURA®

LCP and PCT: Key Comparison Insight 

Figure 8 compares LCP and PCT for having a quick overview on the main properties. 

Figure 8: Comparison of LCP and PCT.

Practical selection guidance for LCP and PCT

Choose LCP when:

When very high flow, very thin walls, micro-molding, excellent dimensional accuracy, or high-frequency electrical performance is needed. LCPs are also attractive when self-reinforcing behavior and low CTE are beneficial, and when the design can tolerate or exploit anisotropy.

Choose PCT when:

When a high-temperature polyester with more conventional semi-crystalline behavior, strong chemical resistance, good electrical performance, and compatibility with standard injection molding practice is needed. PCT is especially compelling for electrical and automotive connector applications where solder resistance matters but LCP-level miniaturization is not mandatory.

Final Engineering Takeaway

LCP = highest flow, highest miniaturization potential, anisotropic performance, premium cost → Best for electronics, RF, precision parts

PCT = high-temperature semi-crystalline polyester, balanced connector material, easier substitution path from other engineering polyesters → Best for connectors, automotive, and electrical applications

Check out the other parts of this series too: 

The 11 Functional Groups of Polymers — A Primer for Polymer Engineers

-Part 2A: Polysulfides (Polyphenylene sulfide - PPS), Polysulfones (PSU, PESU, PPSU), and Polyarylates (PAR)

-Part 2B: Imide-Based Polymers (PEI, PAI, PESI, TPI, PI) and Polybenzimidazoles (PBI, PBI+PEEK, PBI+PEKK)

-Part 2C: Polyether (PPE)

-Part 2C: Polyether (PAEK, PEEK, PEKK)

Thanks for reading & #findoutaboutplastics

Greetings, 

Herwig 



Literature: 

[1] https://www.sumitomo-chem.co.jp/sep/english/products/pdf/lcp_users_manual_v31_e.pdf

[2] https://www.findoutaboutplastics.com/2026/01/high-performance-thermoplastic.html

[3] https://youtube.com/shorts/OIwTTClNroE

[4] https://www.findoutaboutplastics.com/2024/03/high-heat-plastics-selection-liquid.html

[5] https://www.findoutaboutplastics.com/2018/12/dynamic-mechanical-analysis-dma-as.html

[6] https://www.azom.com/article.aspx?ArticleID=13872

[7] https://www.ptonline.com/articles/tracing-the-history-of-polymeric-materials-part-27-lcp

[8] Zeus- Introduction to LCP 

[9] https://www.celanese.com/products/lcp-vectra-zenite

[10] https://www.syensqo.com/en/brands/lavanta-hpp/properties

[11] https://www.polymermaterialselection.com

[12] https://www.justerexpertwitness.com

[13] https://www.pbs.org/newshour/show/the-life-and-achievements-of-chemist-stephanie-kwolek-inventor-of-kevlar

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Influence of fillers on the efficiency of Antioxidants in Polypropylene (PP)

Hello and welcome to a new blog post in which we discuss the influence of fillers on the efficiency of Antioxidans additives in Polypropylene (PP). 

Fillers and Antioxidant Efficiency in Polypropylene

The Figure 1 highlights an important point about the long-term thermo-oxidative stability of polypropylene (PP): not all fillers are neutral in their effect on ageing performance. 

Under oven ageing at 160°C, the results show a clear reduction in time to embrittlement for PP filled with talc and calcium carbonate (CaCO₃) compared with unfilled PP. 

In other words, both fillers have a negative impact on long-term stability under these conditions, with talc showing the strongest reduction. The figure is a useful reminder that filler selection must be considered not only from a cost and stiffness perspective, but also from the standpoint of antioxidant efficiency and durability.


A note on testing for plastics embrittlement

The standards ASTM D5510 (Standard Practice for Heat Aging of Oxidatively Degradable Plastics) and ASTM D3045 (Standard Practice for Heat Aging of Plastics Without Load) were used with regular tensile testing during oven aging (ISO 527 / ASTM D882). Focus is not so much on tensile strength, but more on Elongation-at-break which is the most direct indicator of embrittlement. 

A sharp drop (often to <50% of its original value) indicates the PP has become brittle. A brittle PP might maintain its tensile strength, it will snap almost immediately when bent or stretched. 

Check out my other posts on additives here:

The Important Role of Additives: Enhancing Polymer Properties for High Performance Applications (Part 1)

Thanks for reading & #findoutaboutplastics!

Greetings, 

Herwig 



Literature: 

[1] https://www.linkedin.com/posts/herwigjuster_findoutaboutplastics-share-7454851060814348289-PnnQ?utm_source=share&utm_medium=member_desktop&rcm=ACoAABCkmMcBev71cuhh4-jzEaiPHFO5VFb4aO0

[2] M. Bonnet - Kunststoffe in der Ingenieuranwendung

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Friday, 17 April 2026

Condensation Polymers - The Importance of Resin Drying prior to Processing (Rule of Thumb)

Hello and welcome to a new Rule of Thumb post. 

For condensation polymers—such as PET, PC, PA, and PU proper resin drying is absolutely critical before processing. Why? These polymers contain reactive groups in their backbone (ester, amide, carbonate, or urethane) that can interact with even tiny amounts of moisture. 

If not thoroughly dried, water can trigger chain scission during processing at high temperatures (250–300°C), leading to a significant drop in molecular weight (Mw) and, ultimately, a loss of part performance and properties.

Even as little as 0.01% water can have a major impact, so special care must also be taken with regrind material, which can introduce additional moisture into the system. 


Figure 1: Polyester, Polyamide, Polycarbonate, and Polyurethane - Example of Chain Scission Due to Hydrolysis

As a rule of thumb, the molecular weight of condensation polymers should not decrease by more than 10%, since a 5% drop in Mw can already reduce properties by 10%. 

In contrast, addition polymers like PE and PP are more tolerant to molecular weight reduction, showing only minor property losses (5% property drop).

Understanding and controlling moisture is key to ensuring the quality and durability of your finished parts and prevent part failure. 

Check out my deep dive on functional groups here.

Thanks for reading & #findoutaboutplastics!

Greetings, 

Herwig 



Literature: 

[1] Ezrin M.: Plastics Failure Guide https://www.hanser-elibrary.com/doi/book/10.3139/9783446428829

[2] https://www.findoutaboutplastics.com/2026/04/the-11-functional-groups-of-polymers.html

[3] https://www.justerexpertwitness.com/case-directory

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Monday, 13 April 2026

Insights from the KPA Trade Fair: The Power of Glass Fibers in Plastics

Recently, I had the opportunity to visit the KPA trade fair in Ulm, Germany where I stopped by the booth of Technoform—a specialist in the extrusion of highly filled plastics. I was joined by Dirk from Technoform, and together we explored the fascinating world of glass fibers and their integration into plastics.

Dirk (left) from Technoform Tailored Solutions discussing with Herwig the importance of glass fibers integration into plastics. 

Why Glass Fibers?

Our discussion centered on the advantages of incorporating glass fibers into plastic materials. Dirk explained that glass fibers are not only cost-effective but also significantly enhance the mechanical properties of plastics. When used as a compound, glass fibers reinforce the plastic, making it stronger and more durable.

Types of Glass Fibers and Their Applications

There are several ways to integrate glass fibers into plastics:

-Short Glass Fibers: Ideal for optimizing component properties at a relatively low cost. These are commonly used when a balance between performance and cost is needed.

-Long Glass Fibers: Preferred when higher impact resistance or damping effects are required.

-Continuous Glass Fibers: Used specifically for components that demand increased stiffness.

Dirk highlighted that the choice of fiber type depends on the specific requirements of the component being produced.

A Practical Example: The Child Seat Frame

One of the most interesting examples we discussed was a child seat frame made of polypropylene. In this application, both short and continuous glass fibers are combined. The short glass fibers provide the general mechanical strength, while continuous fibers are strategically placed at weak points to reinforce rib structures. This targeted approach results in local stiffening, which further stabilizes the entire component mechanically. They used their pultrusion technology to create thin polypropylene profile with unidirectional glas fiber reinforcement. The cut profiles where placed in the injection molding tool and overmolded with polypropylene. 

Takeaways

This conversation with Dirk offered valuable insights into how the right combination of glass fibers can optimize the performance of plastic components. By understanding the unique benefits of each fiber type, we can better tailor our materials to meet specific application needs.

Thank you to Dirk and the Technoform team for sharing their expertise and practical examples. I look forward to bringing more of these industry insights to our polymer engineering community in the future!

Check out our other exchanges too: More Than Just Profiles: Unlocking the Diverse Potential of Technoform's Flexible Pultrusion

Thanks for reading & #findoutaboutplastics

Greetings, 

Herwig 



Literature: 

[1] https://www.technoform.com/en/pultrusion

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Tuesday, 7 April 2026

Estimation of Clamping Force in Injection Molding (Rule of Thumb)

Estimation of Clamping Force in Injection Molding - Rule of Thumb

Welcome to our latest blog post! 

If you’ve ever wondered how to choose the right injection molding machine for your project, understanding clamping force is key. 

Today, we’ll break down how to calculate the clamping force required for parts with wall thicknesses both below and above 1.5 mm. Mastering this calculation not only ensures high-quality parts but also helps you make smarter, more efficient equipment choices. 

Let’s dive in!

Case 1: part wall thickness below 1.5 mm

Clamping force F [kN] = projected area A [m2] * filling pressure pf [bar] / 100 

Filling pressure pf [bar] = Flow factor kf [bar/mm] * wall thickness factor kw [/] * flow length [mm]

Note: 1 bar = 1x10^5 Pa; Pa = N/m^2 = kg/(m x s^2) 

Flow factors kf depending which material one is using:

ABS: 2.0

PA: 2.0

PA+GF: 2.4

PBT: 2.0

PBT+GF: 2.3

PC: 2.0

PC+GF: 3.3

PE: 1.8

PESU: 3.7

PMMA: 1.8

POM: 2.4

PP: 1.2

PPO: 1.9

PPO+GF: 3.2

SAN: 1.8

PK (Polyketone): 1.2


Wall thickness factor kw:

0.4 mm: 11.9

0.5 mm: 9.2

0.6 mm: 7.3

0.8 mm: 4.5

1.0 mm: 3.0

1.2 mm: 2.1

1.4 mm: 1.5

1.6 mm: 1.1

Case 2: part wall thickness above 1.5 mm

Clamping force F [kN] = projected area A [m2] * pressure p [bar] / 100

Insert for pressure p:

Thermoplastics = 350 - 400 bar

Thermosets = 450 - 500 bar

Rubbers = 500 bar

Figure 1: Overview on clamping force estimation in injection molding.


Check out other Rules of Thumb posts here. 

Thanks for reading & #findoutaboutplastics

Greetings, 

Herwig 



Literature: 

[1] https://manuelkuehner.de/wp-content/uploads/2015/04/formelsammlung_polymertechnik_kunststofftechnik_hhn_manuel_kuehner.pdf

[2] https://firstmold.com/de/tips/clamping-force/

[3] https://prototool.com/de/injection-molding-formulas/

[4] https://www.justerexpertwitness.com/case-directory

[5] https://polymermaterialselection.com

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Wednesday, 1 April 2026

The 11 Functional Groups of Polymers — A Primer for Polymer Engineers

Hello and welcome to this new blog post in which we discuss the functional groups of polymers. 

Introduction — why functional groups matter

Figure 1: Overview of the functional groups of polymers. 

Functional groups are the recurring atom clusters in organic molecules whose chemistry largely determines material properties (polarity, hydrogen-bonding, thermal stability, chemical resistance, chain rigidity, degradability, etc.). 

In polymers, the functional group(s) present in the backbone or pendant positions control bulk properties and processing behaviour, so identifying the dominant functional group is a quick route to predicting performance during material selection. 

What are the 11 functional groups we will discuss in this post:

  • Imide group
  • Sulfone Group
  • Amide Group
  • Ester Group
  • Ketone Group
  • Sulfide Group
  • Ether Group
  • Arene Group
  • Alcohol Group
  • Alkane Group
  • Haloalkane Group
Let us get starting!

1) Imide group — structure: –CO–N–CO– (cyclic or linear imide)
Figure 1: Functional groups of polymers: Imide group.

What it gives: outstanding high-temperature stability, good chemical resistance, high glass transition (rigid backbone), low creep.
Typical polymers / examples: Polyimides (e.g., Kapton®, Vespel®) used for high-T films, electrical insulation, aerospace parts. Polyimides are classic high-performance plastics made from dianhydride + diamine routes. 
Notes: Alkyl groups (R-) are saturated, non-aromatic hydrocarbon chains derived from alkanes (e.g., methyl, ethyl).
Aryl groups (Ar-) are aromatic rings derived from compounds like benzene.

2) Sulfone group — structure: –SO2– (often between aryl groups)
Figure 2: Functional groups of polymers: Sulfone group.

What it gives: high thermal stability, hydrolytic stability, rigidity and flame resistance; good dimensional stability and toughness in amorphous engineering resins.
Typical polymers / examples: Polysulfones / Polyethersulfones / Polyphenylsulfone (PSU, PES/PESU, PPSU — trade names include Ultrason®, Radel®). Widely used in medical devices, plumbing/valves, electrical components and under-the-bonnet automotive parts. 

3) Amide group — structure: –CONH–
Figure 3: Functional groups of polymers: Amide group.

What it gives: strong intermolecular hydrogen bonding resulting in high strength and toughness, relatively high melting point, moisture uptake (hydrophilicity increases with amide density), good abrasion resistance.
Typical polymers / examples: Polyamides (Nylons) — PA6, PA66, PA11, PA12; Semi-aromatic polyamides such as PPA, and fully-aromatic polyamides (aramids) such as Kevlar® for ballistic & high-strength uses. Use in fibers, gears, bearings, structural components. 

4) Ester group — structure: –COO– (ester linkage in backbone)
Figure 4: Functional groups of polymers: Ester group.

What it gives: backbone polarity (good mechanical strength), susceptibility to hydrolysis (hence biodegradability for some), good melt processability (thermoplastic polyesters).
Typical polymers / examples: Polyesters — PET (polyethylene terephthalate), PBT, PLA (polylactide). Used for fibers, bottles, films, engineering thermoplastics and (for some aliphatic esters) biodegradable medical devices. 
Example: Carbonate functional group
If the organic rest "R1" is replaced by a oxygen,  R-O-C(=O)-O-R2, we obtain a carbonate ester, which are utilized in the creation of polycarbonate (PC). 

5) Ketone group — structure: –CO– (ketone carbonyl in backbone or adjacent to aromatic units)
Figure 5: Functional groups of polymers: Ketone group.

What it gives: increased backbone polarity and stiffness; when combined with ether linkages in high-performance families it confers elevated Tg and chemical resistance.
Typical polymers / examples: Poly(aryl ether ketone) family (PAEK) — includes PEEK, PEK, PEKK — used for high-temperature structural parts, bearings, medical implants, and additive manufacturing in demanding applications. PAEKs combine aryl, ether and ketone functionalities giving excellent thermo-oxidative stability. 

6) Sulfide group — structure: –S– (or disulfide –S–S– / polysulfide –Sx–)
Figure 6: Functional groups of polymers: Sulfide group.


What it gives: enhanced temperature resistance, chemical and solvent resistance; excellent flow for injection molding; inherent flame retardant properties; excellent dimensional stability; 
Typical polymers / examples: Polyphenylene sulfide (PPS) trade names include Ryton®, Fortron®.

7) Ether group — structure: –O– (alkyl or aryl ether linkages)
Figure 7: Functional groups of polymers: Ether group.

What it gives: flexibility (aliphatic ethers), good low-temperature toughness, and for aromatic ether linkages (polyarylethers) increased thermal stability and oxidative resistance. Ethers reduce crystallinity when in backbone and improve chain mobility.
Typical polymers / examples: Polyethers (polyethylene glycol PEG/PEO; polypropylene oxide PPO), polyetherimide (PEI), polyethersulfone (PES), epoxy networks (contain ether linkages after cure). Applications span elastomers, polyurethanes (polyether polyols), and engineering plastics. Trade names include Noryl® PPE, Ultem® PEI, Veradel® PESU.

8) Arene (aromatic ring) group — structure: –Ar– (phenyl, substituted phenyl rings in backbone or pendant)
Figure 8: Functional groups of polymers: Arene group.

What it gives: backbone rigidity (high modulus), thermal stability, UV interaction (often poor UV resistance unless stabilized), pi-stacking that influences mechanical and barrier properties. Aromatic content generally increases glass transition and heat resistance.
Typical polymers / examples: Polystyrene (PS) — aromatic pendant phenyls on a saturated backbone; poly(phenylene), polyaryls and many high-performance polymers with aromatic repeat units (e.g., polyimides, PAEK family). Polystyrene is a major commodity aromatic polymer used for foams, rigid packaging and consumer products. 

9) Alcohol (hydroxyl) group — structure: –OH (pendant or chain-end hydroxyls)
Figure 9: Functional groups of polymers: Alcohol group.

What it gives: hydrogen bonding, polarity, water solubility (if dense), reactivity for crosslinking (e.g., with isocyanates to form polyurethanes) or functional modification. Hydroxyls raise surface energy and adhesion.
Typical polymers / examples: Polyvinyl alcohol (PVA, PVOH) — water-soluble, used in films, adhesives and hydrogels; alcohol endgroups in polyols (polyether or polyester polyols) are core building blocks for polyurethanes. 

10) Alkane group (saturated hydrocarbon backbone) — structure: –CH2–CH2– etc. (non-functional hydrocarbon chain)
Figure 10: Functional groups of polymers: Alkane group.

What it gives: low polarity results in low surface energy, excellent chemical resistance to polar solvents, high flexibility (especially in low Tg aliphatic polyolefins), good electrical insulating properties and very high production volumes (commodity plastics).
Typical polymers / examples: Polyethylene (PE), Polypropylene (PP). These are the polyolefin family used for films, containers, piping, and fibers. Expect low density, good toughness, and simple processing. 

11) Haloalkane group (alkyl halide pendant or backbone) — structure: –C–X (X = Cl, Br, F)
Figure 11: Functional groups of polymers: Haloalkane group.

What it gives: increased flame retardance (e.g., chlorinated polymers), increased polarity and density, and ready sites for nucleophilic substitution or further modification; halogens can also raise refractive index and change dielectric properties.
Typical polymers / examples: Polyvinyl chloride (PVC) — chlorine on backbone carbons; fluoropolymers (e.g., PTFE — where fluorine dominates) are extreme cases with outstanding chemical resistance and low friction. PVC is used in construction, pipes, cable insulation and flooring; fluoropolymers are used where chemical inertness and high T performance are needed. 

Mixed-functionality polymers & location of the group
  • Backbone vs pendant vs endgroup: a functional group in the backbone (repeat unit) typically dominates bulk mechanical/thermal behaviour. Pendant groups (e.g., the phenyl in polystyrene or the chloro in PVC) tune Tg, polarity and solubility. Endgroups mainly affect surface chemistry and reactivity. 
  • Combinations are common: many engineering polymers combine functional groups (for example, PAEKs include arene, ether and ketone motifs; polysulfones include aryl, ether and sulfone units), which gives the unique combined property sets. 
Overview of all the 11 functional groups of polymers

Figure 12: Overview of the functional groups of polymers.

Check out my video on functional groups too: 


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Monday, 23 March 2026

ISO 1043 / ISO 11469 Plastic Part Marking Code Example - Metal fillers, Elastomers, or special Fillers (MEF)

Hello an welcome to a new blog post. In plastic part design, proper material selection and processability are essential considerations. Additionally, part marking plays a crucial role, as it enables more efficient sorting and recycling of plastic components. The two primary standards governing part marking are ISO 1043 and ISO 11469.

Example >PARA-(CF+MEF(x))<

Based on ISO 1043 (specifically ISO 1043-1 regarding plastics symbols), the notation >PARA-(CF+MEF(x))< is a part marking code used to identify the material composition of a molded plastic component made out of PolyarylAmide (PARA; PA-MXD6). 

Figure 1: Plastic part marking example with focus on special additives. 

Here is the breakdown of that marking:

PARA: PolyArylAmide (PA-MXD6) - the base polymer.

CF: Carbon Fiber

MEF: This indicates a specific, likely proprietary, modification or additive blend. In the context of this material, it refers to special filler package, potentially containing Metal fillers, Elastomers, or special Fillers (MEF) which are used to enable EMI-shielding.

(x): Often followed by a number (e.g., in a technical data sheet, it might appear as >PARA-MEF(1)7<, this indicates the specific grade or a percentage/variant within the supplier's internal classification system.

> <: The angled brackets indicate that the part is marked in accordance with ISO 11469 for identification and recycling, as required for parts over a certain weight. ISO 11469 does not define a universal minimum weight for marking; however, industry standards (e.g., in automotive) generally require marking for parts weighing more than 100 grams. Smaller components, often those under 25 grams or with a surface area smaller than, are usually exempt from this marking requirement. 

Check out my other part marking posts too: 

Plastic Part Marking – Overview Codes and Standards (incl. miniguide for downloading)

Thanks for reading and #findoutaboutplastics

Greetings, 

Herwig 



Literature:

[1] https://www.findoutaboutplastics.com/2020/12/plastic-part-marking-overview-codes-and.html

[2] https://rsjtechnical.com/dqr/rules/code161/

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