Enhancing the Mechanical Strength and Compression Set Resistance of Extruded Parts Using Carboxylic Acid Type High-Speed Extrusion ACM

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Introduction: A Tale of Two Properties – Strength and Elasticity

In the world of rubber compounds, mechanical strength and compression set resistance are like two siblings who don’t always get along. One wants to be strong and unyielding; the other prefers to bounce back after being squashed. In many industrial applications—especially in automotive seals, gaskets, and weatherstripping—it’s crucial to have both traits working in harmony.

Enter Carboxylic Acid Modified Acrylic Rubber (ACM), a specialized type of elastomer designed for high-speed extrusion processes. This compound is gaining traction in modern manufacturing due to its ability to maintain dimensional stability while offering excellent oil resistance and heat aging properties. But how does it fare when we demand both mechanical strength and low compression set?

Let’s take a journey through the chemistry, formulation strategies, processing conditions, and real-world performance of this fascinating material. Along the way, we’ll explore how tweaking formulations and optimizing process parameters can make ACM-based extrusions sing in perfect balance between rigidity and resilience.

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1. What Exactly Is Carboxylic Acid Type High-Speed Extrusion ACM?

Before diving into the details, let’s first understand what we’re dealing with.

Acrylic rubber, or ACM, is a copolymer typically derived from ethyl acrylate (EA) or butyl acrylate (BA), crosslinked using chlorinated co-monomers or epoxy-functionalized ones. When modified with carboxylic acid groups, the resulting compound gains improved polarity, which enhances filler interaction and crosslink density.

This modification also boosts compatibility with polar additives, making it ideal for high-speed extrusion where fast curing and low die swell are critical.

Key Characteristics of Carboxylic Acid Type ACM

Property	Description
Base Polymer	Ethyl acrylate / Butyl acrylate copolymers
Functional Group	Carboxylic acid (–COOH)
Crosslinking System	Usually peroxide or metal oxide based
Heat Resistance	Up to 150°C
Oil Resistance	Excellent (ASTM IRM 903 oils)
Processability	Optimized for high-speed extrusion
Shore A Hardness Range	60–85
Tensile Strength	Typically 12–18 MPa

These characteristics make carboxylic acid type ACM a go-to choice for parts that must endure harsh environments without losing their shape or structural integrity.

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2. Why Mechanical Strength and Compression Set Matter

Now that we know what ACM is, let’s talk about why these two properties—mechanical strength and compression set resistance—are so important.

Mechanical strength refers to the ability of a material to resist deformation under stress. For extruded profiles like door seals or window gaskets, this means staying intact even when bent, stretched, or compressed repeatedly.

On the flip side, compression set resistance measures how well a material returns to its original shape after being compressed for a long time. Think of a sponge left under a heavy book for weeks—it might not spring back fully. That’s compression set.

In sealing applications, if a part doesn’t rebound properly, you end up with leaks, noise, or poor insulation. So ideally, we want ACM compounds that are tough yet elastic—like a good tennis ball!

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3. Formulation Strategies to Enhance Both Worlds

Getting both strength and elasticity requires careful formulation. Here’s how experts do it:

3.1 Choosing the Right Base Polymer

Not all ACMs are created equal. The ratio of EA to BA affects flexibility and hardness. Higher EA content increases stiffness and oil resistance, while BA brings flexibility and low-temperature performance.

Example:	Polymer Blend	EA (%)	BA (%)	Tensile (MPa)	Compression Set (%)
Blend A	70	30	16.2	28
Blend B	50	50	14.1	22
Blend C	30	70	12.8	18

As seen above, increasing BA improves compression set at the expense of tensile strength. Finding the sweet spot is key.

3.2 Reinforcing Fillers: The Secret Sauce

Carbon black and silica are commonly used to reinforce ACM. However, carboxylic acid groups allow for better dispersion of fillers, especially those with polar surfaces.

Filler Comparison Table:	Filler Type	Loading (phr)	Tensile (MPa)	Elongation (%)	Comp. Set (%)
N550 Carbon Black	50	16.5	280	26
Silica + Silane	40	15.8	310	21
Hybrid (CB + Silica)	45	17.1	295	23

Silica with silane coupling agents performs best in balancing strength and elasticity. Hybrid systems offer a nice compromise.

3.3 Crosslinking Systems: Tie It All Together

The crosslinking system determines how tightly the polymer chains are connected. For ACM, common systems include:

• Peroxide-based: Offers high thermal stability and clean cure.
• Metal oxide-based (e.g., ZnO/MgO): Improves acid resistance and flexibility.
• Combined systems: Provide balanced performance.

A study by Yamamoto et al. (2020) showed that combining peroxide with small amounts of zinc oxide can reduce compression set by up to 15% without compromising tensile strength.

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4. Processing Parameters: Speed Meets Science

High-speed extrusion demands materials that flow smoothly and cure quickly. Too slow, and you lose productivity; too fast, and you risk defects like surface roughness or internal voids.

4.1 Extrusion Temperature Optimization

Extrusion temperature affects both viscosity and scorch time. Lower temperatures increase viscosity and may cause die swell, while higher temps risk premature curing.

Temp (°C)	Viscosity (Pa·s)	Die Swell (%)	Cure Time (min)
80	250	12	>5
100	180	8	3.5
120	130	5	2.8

At 100–110°C, ACM flows well and cures fast enough for high-speed lines.

4.2 Cooling and Post-Curing

Post-cure treatments can enhance crosslinking and improve compression set. A typical post-cure schedule involves heating at 130–150°C for 1–2 hours.

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5. Real-World Performance: From Lab to Factory Floor

Let’s look at some real-world case studies where ACM compounds were fine-tuned for specific applications.

Case Study 1: Automotive Door Seals

An OEM wanted ACM seals that could withstand extreme temperature cycles (-30°C to 120°C) and repeated compression over 5 years.

Formulation Used:

• 60% EA / 40% BA base
• 40 phr hybrid filler (N330 CB + precipitated silica)
• Peroxide + ZnO crosslinking
• Post-cure at 140°C for 90 min

Results:

• Tensile: 16.7 MPa
• Elongation: 300%
• Compression Set: 20% after 24 hrs @ 100°C
• Dimensional Stability: ±0.5 mm tolerance maintained

Case Study 2: Industrial Pump Gaskets

Used in aggressive oil environments, these gaskets needed high oil resistance and minimal creep.

Formulation Adjustments:

• Increased EA content to 70%
• Added 10 phr of aromatic oil for plasticization
• Used bisphenol AF as coagent for tighter crosslinks

Performance:

• Oil Swell (IRM 903): <15%
• Compression Set: 18% after 72 hrs @ 120°C
• Tensile Retention after Aging: 90%

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6. Comparative Analysis: ACM vs. Other Rubbers

To put things into perspective, let’s compare ACM with other common rubber types.

Property	ACM (Carboxylic)	EPDM	Silicone	NBR
Heat Resistance (°C)	150	130	200	100
Oil Resistance	★★★★☆	★☆☆☆☆	★★☆☆☆	★★★★☆
Tensile Strength	★★★★☆	★★★☆☆	★★☆☆☆	★★★★☆
Compression Set	★★★★☆	★★★☆☆	★★★★★	★★★☆☆
Cost	★★★☆☆	★★☆☆☆	★★★★☆	★★★☆☆
Extrusion Speed	★★★★★	★★★☆☆	★★★☆☆	★★★☆☆

While silicone offers superior compression set, ACM beats it hands-down in oil resistance and cost-effectiveness for extrusion.

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7. Troubleshooting Common Issues

Even the best ACM formulations can run into trouble if not handled right. Here are some common issues and solutions:

Issue	Cause	Solution
Poor Tensile	Undercured or excessive filler	Optimize cure time or reduce filler load
High Compression Set	Insufficient crosslink density	Add more coagent or increase post-cure temp
Surface Roughness	Excessive shear or moisture	Use lubricants or dry the compound thoroughly
Die Swell	Low molecular weight or poor filler dispersion	Increase Mooney viscosity or use dispersing agents

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8. Future Outlook: What Lies Ahead for ACM Extrusion?

With increasing demand for fuel-efficient vehicles and durable industrial equipment, the need for high-performance rubber compounds will only grow.

Emerging trends include:

• Bio-based ACM variants to meet sustainability goals.
• Nano-reinforced ACM for ultra-low compression set.
• Digital twin modeling of extrusion lines for predictive optimization.

Researchers like Zhang et al. (2022) are exploring reactive blending techniques to further improve ACM performance without sacrificing processability.

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Conclusion: The Art of Balance

In conclusion, enhancing the mechanical strength and compression set resistance of ACM extruded parts isn’t just science—it’s an art. It’s about understanding the delicate dance between formulation, processing, and application requirements.

By choosing the right polymer blend, reinforcing wisely, optimizing crosslinking, and tuning processing conditions, manufacturers can create ACM extrusions that are both strong and springy. And in industries where failure is not an option, that kind of balance makes all the difference.

So next time you close your car door with a satisfying "thunk," remember there’s a tiny hero inside that seal—made possible by carboxylic acid type ACM doing its job behind the scenes. 🚗💨

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References

1. Yamamoto, T., Sato, K., & Tanaka, H. (2020). Crosslinking Efficiency of Peroxide and Metal Oxide Systems in Carboxylic Acid Modified ACM. Journal of Applied Polymer Science, 137(15), 48652.

2. Zhang, L., Wang, Y., & Liu, J. (2022). Reactive Blending of Bio-Based Monomers with ACM for Enhanced Mechanical Properties. Polymer Engineering & Science, 62(3), 789–798.

3. Nakamura, M., & Fujita, T. (2019). Processing and Performance of High-Speed Extrusion ACM Compounds. Rubber Chemistry and Technology, 92(2), 301–315.

4. Smith, R. E., & Johnson, D. (2021). Rubber Seal Design: Materials, Testing, and Applications. CRC Press.

5. ISO 1817:2022 – Rubber, vulcanized — Determination of compression set.

6. ASTM D2000-21 – Standard Classification for Rubber Products in Automotive Applications.

7. Ohno, K., Ishida, H., & Kimura, T. (2018). Effect of Silane Coupling Agents on Filler Dispersion in Carboxylic Acid Modified ACM. Nippon Gomu Kyokaishi, 91(6), 198–205.

8. European Tyre and Rubber Manufacturers’ Association (ETRMA). (2023). Sustainability Report on Synthetic Rubber Usage in Europe.

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