Fluoropolymers are often described as “dream materials” for advanced industries. They can withstand high temperatures, resist aggressive chemicals, and maintain stable performance in harsh environments. Among them, PFA (perfluoroalkoxy alkane) is widely used in applications where reliability and cleanliness are essential—such as semiconductor manufacturing, chemical processing, electronic machinery, and medical devices.
However, fluoropolymers also come with a well-known drawback. Their surfaces are so chemically stable and “non-stick” that they are notoriously difficult to bond to other materials. In fact, the same surface property that prevents contamination and chemical attack often prevents practical assembly. This creates a serious engineering challenge when fluoropolymers must be integrated with rubber, which is required for flexibility, sealing performance, vibration tolerance, and robust mechanical design.
Why we started this research
In many industrial systems, tubing must do much more than simply “transport fluids.” It must endure bending, thermal cycling, pressure fluctuations, and long-term operation without failure. Rubber layers are valuable because they provide flexibility and sealing, while fluoropolymers provide chemical resistance, oxidation resistance, and durability. A composite structure combining both materials is therefore highly attractive.
But there is one major obstacle: weak interfacial adhesion. If the bond between a fluoropolymer and rubber is insufficient, the layers can peel apart during operation. This can result in leakage, loss of sealing, mechanical failure, or reduced service life. In short, poor adhesion can prevent fluoropolymers from being fully utilized in multi-material designs—even when their bulk properties are ideal.
Traditionally, wet chemical etching has been widely used to improve fluoropolymer adhesion. While effective, such methods can require aggressive chemicals and may generate liquid waste, raising concerns about environmental impact and sustainable manufacturing. These practical issues motivated us to explore a “dry” alternative.
Our guiding question was simple:
Can we achieve strong fluoropolymer–rubber adhesion using a dry process that avoids wet chemical etching?
Our approach: nonthermal plasma surface modification
We focused on nonthermal plasma (NTP), a form of plasma in which electrons are highly energetic while the overall gas temperature remains relatively low. This is a powerful advantage for polymer processing: it enables surface activation and chemical modification without melting or damaging the polymer bulk.
To treat PFA tubes, we applied dielectric barrier discharge (DBD) in a cylindrical reactor configuration. DBD is well known for generating stable nonthermal plasma under atmospheric or near-atmospheric conditions and has been widely used in surface treatment applications.
However, plasma exposure alone is not always sufficient for stable and strong bonding on fluoropolymers. To further enhance the effect, we introduced acrylic acid vapor into the treatment atmosphere. Under these conditions, plasma-induced polymerization can occur, enabling formation of a functionalized surface layer that supports stronger interaction with rubber during bonding.
Our aim was to develop a method that is:
- Dry, avoiding liquid waste and wet chemical handling
- Practical for tubular components
- Effective for notoriously difficult-to-bond fluoropolymer surfaces
Dry surface modification of PFA tubes using dielectric barrier discharge (DBD) under acrylic acid vapor.
From plasma treatment to composite tube fabrication
Our experimental process was designed to be straightforward but industrially relevant.
First, PFA tubes were treated in a cylindrical DBD reactor under an acrylic acid vapor atmosphere. The goal was to tailor the surface chemistry of the PFA tube and create a thin functional layer that could support strong bonding.
Next, the treated PFA tubes were bonded to white ethylene acrylic elastomer (AEM) rubber using hot-press bonding. This step represents a realistic route toward composite fabrication where both chemical surface interactions and mechanical consolidation contribute to final interfacial strength.
Finally, we evaluated the bonding performance by 180° peel tests, which provide a clear and quantitative measure of interfacial adhesion. Peel testing is commonly used in both research and industry to assess bonding reliability, and it also allows observation of how failure occurs during separation.
Key findings: strong adhesion and reliable failure behavior
The nonthermal plasma treatment significantly enhanced adhesion between the fluoropolymer tube and rubber. Under optimized conditions, we achieved a maximum peel strength of ≥ 7 N/mm. This level of adhesion is remarkably strong for a fluoropolymer–rubber interface and indicates that the surface treatment effectively transformed the bonding performance of PFA.
Equally important, we assessed the fracture behavior after peeling. In many cases, the failure occurred predominantly within the rubber rather than at the fluoropolymer–rubber interface. This is a meaningful sign of interfacial reliability: when adhesion is weak, separation occurs cleanly at the interface; when adhesion is strong, the bonded interface can exceed the cohesive strength of one of the materials.
As a result, we successfully prepared a PFA–rubber composite material with extremely strong interfacial adhesion, using a dry plasma process instead of wet chemical etching. This achievement supports the potential for more sustainable and scalable manufacturing of fluoropolymer-based hybrid structures.
Overall view of the DBD surface-treatment system used to modify PFA tubes under acrylic acid vapor.
Why this matters beyond the lab
At first glance, “adhesion improvement” might sound like a narrow technical topic. But in many real products, interfaces determine reliability. Even if a material has outstanding heat and chemical resistance, it cannot be fully utilized if it cannot be integrated into practical components.
A strong fluoropolymer–rubber interface enables new design possibilities such as:
- Durable composite tubing with improved flexibility and sealing
- Compact integration of chemically resistant and elastomeric functions
- Reduced risk of delamination during bending and long-term use
- Cleaner manufacturing routes by reducing reliance on wet chemical treatments
This is especially relevant in fields where fluoropolymers play a critical role. In semiconductor manufacturing, for example, fluid delivery systems often require extremely high chemical purity and corrosion resistance. In chemical industries, tubing must maintain performance under aggressive conditions. Medical and electronic machinery applications also demand stable materials and reliable component interfaces.
By enabling strong bonding through dry surface modification, fluoropolymers can potentially be applied in broader multi-material designs—expanding their industrial value.
Collaboration and real-world motivation
This achievement was made possible through a close collaboration with Togawa Rubber Co., Ltd. Their application-driven perspective helped us focus on practical requirements, while our research team contributed plasma processing expertise and materials evaluation. We believe that bridging industrial needs with scientific methods is essential for translating surface engineering into real manufacturing improvements.
Looking ahead
This work demonstrates that dry nonthermal plasma polymerization treatment can dramatically improve the adhesion performance of fluoropolymer–rubber composites. Our next goals include expanding the approach to other fluoropolymers and elastomer systems, evaluating long-term durability under realistic operating environments, and improving process optimization for wider deployment.
If you work in plasma processing, polymer surface engineering, fluoropolymer applications, or industrial rubber systems, we would be happy to connect and exchange ideas.