Research

The main objective of the research part of the project is to develop a hybrid technology that enables the production of high-performance composite structures with a recyclable thermoplastic matrix. The proposed hybrid technology combines the advantages of three of the most promising processing techniques—thermoplastic resin transfer moulding (T-RTM) and/or injection moulding, and additive manufacturing, within the production of a single part.

Leader of research: Assoc. Prof. Dr. Irena Pulko

 

 

The research part of the project is divided into five tasks: 

1. Study of the interfacial bonding strength (Task 1.1)
2. Synthesis of covalent adaptable networks (CAN) using reactive extrusion and compounding (Task 1.2)
3. Study of improvement of interfacial bonding strength between different polymers (Task 1.3)
4. Use of CAN in hybrid technologies (Task 1.4)
5. Development of demonstrators (Task 1.5)

 

 

Study of the interfacial bonding strength (Task 1.1) 

As part of the IPPT_TWINN project researchers have developed an advanced mathematical model to predict the bonding strength between overmolded polymer components. This work addresses a critical challenge in hybrid polymer processing: ensuring the structural integrity of parts where different materials or layers meet.

Innovative Modeling Approach

Traditional bonding models often assume a uniform temperature across the contact interface, which rarely occurs in real-world overmolding. Our team developed a more accurate approach by:

• Integrating 3D Temperature Distribution: Using Finite Element Method (FEM) simulations to capture the complex, uneven temperature history at the interface.
• Applying Reptation Theory: The model utilizes the concept of "reptation time"—the time required for polymer chains to diffuse across the interface—calculated via the Williams-Landel-Ferry (WLF) equation and rheological measurements.
• Nodal-Based Calculations: Instead of a single value, the "Degree of Healing" (DoH) is calculated for specific pairs of coincident nodes on the contact surface, allowing for a precise mapping of local bonding strength.

Key Experimental Findings

The research involved extensive testing with materials such as ABS and PS to validate the model and explore methods for enhancing adhesion. Key results include:

• Critical Process Parameters: Melt and mold temperatures were identified as the most significant factors influencing bond strength. Higher melt temperatures consistently led to increased bonding due to enhanced molecular diffusion.
• Surface Modification: Plasma treatment was proven highly effective for joining dissimilar materials (e.g., ABS and PA6). By introducing new functional groups to the surface, plasma treatment enabled strong chemical bonding where none existed previously.
• 3D-Printed Substrates: Investigations into overmolding 3D-printed (FFF and SLS) parts showed that surface roughness has a negligible effect on bond strength because the high-temperature melt typically melts the top layer of the substrate. Instead, strategies like mechanical interlocking and optimizing infill density were found to be more effective for strengthening the joint.

The developed model shows a high degree of correlation with experimental data for both amorphous and semi-crystalline polymers¹². This tool allows engineers to optimize processing parameters and surface treatments in the simulation phase, significantly reducing the need for costly trial-and-error in the production of high-performance hybrid components.

 

Synthesis of covalent adaptable networks (CAN) using reactive extrusion and compounding (Task 1.2)

Researchers have successfully characterized a new generation of polymers known as Covalent Adaptable Networks (CANs). These materialsrepresent a paradigm shift in material science by combining the high mechanical and thermal stability of thermosets with the recyclability and processability of thermoplastics.

Advanced Material Development

The focus of Task 1.2 was the synthesis and analysis of CANs based on industrially relevant matrices, such as Maleic Anhydride grafted Polypropylene (PP-g-MAH) and Acrylonitrile Butadiene Styrene (ABS-g-MAH). The research team utilized several strategies:

• Reactive Extrusion: Using twin-screw extrusion to create dynamic cross-links within the polymer matrix, transforming standard plastics into high-performance adaptable networks.
• Dynamic Chemistry: Implementation of various exchange mechanisms, including transesterification and the use of specialized cross-linkers like tris(2-aminoethyl)amine and zinc-based catalysts.
• Functional Composites: Integration of Carbon Nanotubes (CNTs) and graphite to impart electrical and thermal conductivity, enabling "on-demand" triggering of the network's adaptability through external stimuli.

Key Findings and Technological Breakthroughs

• The "Reversible Glue" Concept: One of the most significant outcomes is the development of CANs that act as reversible adhesives. These materials allow for the welding of traditionally incompatible polymers and, crucially, enable the triggered "debonding" or separation of components, facilitating high-quality recycling.
• Enhanced Thermal Stability: Thermal analysis (DSC, TGA) confirmed that the cross-linking process improves the material's resistance to heat without sacrificing its ability to be reshaped or repaired.
• Mechanical Performance: Dynamic Mechanical Analysis (DMA) showed that CAN materials maintain structural integrity at temperatures where traditional thermoplastics would typically fail, thanks to the robust yet dynamic covalent network.
• Scalability: The project demonstrated that laboratory-scale chemical formulations could be successfully transitioned to pilot-scale reactive processing, proving their readiness for industrial application.

The characterization of CANs and their composites marks a step toward a circular economy in the polymer industry. By providing materials that are both durable and fully recyclable, the IPPT_TWINN project is helping to reduce plastic waste and energy consumption in the manufacturing of complex hybrid components.

 

 

Study of improvement of interfacial bonding strength between different polymers (Task 1.3)

Task 1.3 focused on evaluating the adhesive and self-healing properties of various overmolded and welded material combinations. This research is a cornerstone for selecting high-performance materials suitable for advanced additive manufacturing (AM) and hybrid processing technologies.

Advancing Material Synergy with CANs

The core of this task was the utilization of Covalent Adaptable Networks (CANs). These materials bridge the gap between thermosets and thermoplastics by using dynamic, reversible bond exchanges, which enable:

• Structural Reconfigurability: The ability to reshape and reprocess materials that traditionally could not be recycled.
• Weldability of Dissimilar Materials: Enhanced bonding between traditionally incompatible polymer counterparts.
• Autonomous Self-Healing: The capability to repair internal or surface damage triggered by external stimuli such as heat, light, or pH changes.

Key Experimental Outcomes

The collaborative effort between five EU project partners (FTPO, AITIIP, PCCL, BME, and IWK) yielded several results:

• Optimized Material Selection: Based on rigorous testing, the best-performing materials were identified.
• Enhanced Overmolding: The study explored overmolding processes (e.g., T-shape specimens), demonstrating how specific processing parameters like melt temperature and annealing influence the final weld strength.
• Functional Fillers: To enable advanced joining techniques like induction welding, materials were further modified with magnetite powder and carbon nanotubes. These functional fillers allow for spatially selective heating and triggered responses within the polymer matrix.
• Innovative Self-Healing: The project successfully demonstrated that CAN-based structures can recover their properties after damage through annealing, significantly extending the lifespan and durability of the components.

Specimens welded by ultrasonic welding

 

Use of CAN in hybrid technologies (Task 1.4)

In the final phase of the first work package (WP1) of the IPPT_TWINN project, Task 1.4 focused on evaluating the bonding strength of components produced through hybrid manufacturing. This task integrates the theoretical models, advanced CAN materials, and optimized processing parameters developed in previous steps to assess the real-world performance of multi-material structures.

Focus on Hybrid Manufacturing Interfaces

The research specifically addressed the challenges of joining different polymer types and the integration of additive manufacturing with traditional processing. Key areas of investigation included:

• Overmolding and Welding: Testing the bond integrity between injection-molded parts and substrates produced via Fused Filament Fabrication (FFF) and Selective Laser Sintering (SLS).
• CAN Material Performance: Evaluating how Covalent Adaptable Networks (vitrimers) enhance the interfacial strength compared to standard polymers, especially when subjected to thermal and mechanical stress.
• Surface Treatments: Final assessment of how surface preparation, such as plasma treatment or mechanical interlocking, contributes to the overall reliability of the hybrid joint.

Key Results and Validation

• Interfacial Strength: The evaluation confirmed that components utilizing CAN materials achieved significantly higher bonding strength during overmolding. This is attributed to the dynamic bond exchange that occurs at the interface during the high-temperature processing phase.
• Model Accuracy: The experimental results showed a high correlation with the mathematical models developed in Task 1.1. This validation proves that the simulation tools can accurately predict the failure points and strength of hybrid polymer joints.
• Impact of Processing Conditions: The study highlighted that precise control over the "holding pressure" and "cooling rate" is essential for minimizing residual stresses at the interface, which otherwise could lead to premature delamination.
• Demonstrator Success: Testing on complex demonstrator parts showed that hybrid technology can produce functional components that meet industrial standards for structural applications, while remaining potentially recyclable thanks to the reversible nature of the CAN joints.

Task 1.4 successfully demonstrates that hybrid processing, when combined with innovative material chemistry and accurate simulation, offers a viable pathway for manufacturing complex, durable, and sustainable polymer products.

 

Development of demonstrators (Task 1.5)

The final milestone of the first work package (WP1) in the IPPT_TWINN project was the development of a functional demonstrator. Task 1.5 aimed to consolidate the research on mathematical modeling, advanced CAN materials, and hybrid processing into a physical prototype.

From Concept to Functional Prototype

The demonstrator was designed to showcase the practical benefits of the technologies developed throughout the project. The development process focused on several key aspects:

• Integration of Hybrid Technologies: Combining different manufacturing methods—such as additive manufacturing (3D printing) and injection molding—into a single, cohesive part.
• Application of CAN Materials: Utilizing Covalent Adaptable Networks to enable properties that are typically unavailable in traditional plastic parts, specifically focusing on durability and structural integrity.
• Design for Performance: The geometry of the demonstrator was engineered to test the limits of interfacial bonding and to demonstrate how hybrid processing can solve complex engineering challenges.

Key Features and Breakthroughs

• Enhanced Mechanical Reliability: The demonstrator successfully reached the performance targets set during the simulation phase (Task 1.1). By using optimized processing parameters, the joint between the different material layers showed resistance to mechanical failure.
• Self-Healing and Repairability: A standout feature of the demonstrator is its ability to undergo "healing" processes. Thanks to the dynamic covalent bonds in the CAN materials, small surface damages or internal stresses can be mitigated through controlled thermal treatment, extending the product's operational life.
• Circular Design and Recyclability: Unlike traditional hybrid parts that are difficult to separate, this demonstrator was designed with the end-of-life in mind. The reversible nature of the bonds allows for the separation of different material components, proving that high-performance hybrid parts can be fully compatible with a circular economy.

This demonstrator stands as a proof of concept of repairable, reconfigurable, and sustainable polymer products, establishing a solid foundation for future scaling and industrial integration.

 

Schematic presentation of the demonstrator on left and physical demonstrator on the right