Fraunhofer Institute for Casting, Composite and Processing Technology IGCV
Fraunhofer Institute for Casting, Composite and Processing Technology IGCV

PuLaCell – Bio-Based Polyurethane Reinforcement Lamella with Cellulose Fibers for Wood Structures

»PULaCell« Successfully Completed: Bio-based Reinforcing Lamella Produced on an Industrial Scale

As part of the »PULaCell« research project funded by the BMEL, researchers succeeded in developing a bio-based reinforcing lamella for wood structures, demonstrating its production using a continuous pultrusion process, and scaling it up to an industrial-scale facility. The stable processing of the developed material system was demonstrated during a 24-hour production run. The project results also lay an important foundation for the use of bio-based fiber-reinforced composites in other industrial applications.

Fiber-reinforced lamellas can be used in structural timber construction to absorb high tensile forces and specifically enhance the mechanical performance of timber structures. Conventional fiber-reinforced composites are currently based primarily on petrochemical raw materials.

The collaborative project »PULaCell«—Bio-based Polyurethane Reinforcement Lamella with Cellulose Fibers for Wooden Structures therefore took a new approach: The goal was to develop a reinforcement laminate that was as bio-based as possible and that met the mechanical and functional properties required for exterior applications in the construction sector.

For this purpose, a newly developed bio-based aliphatic polyurethane resin system was combined with regenerated cellulose fibers or hybrid fibers and processed using a continuous pultrusion process.

Material and Process Developed Jointly

The processing of new bio-based material systems presented the project team with various technical challenges. For the large-scale processing of the partially bio-based polyisocyanates, the viscosity, the miscibility of the individual resin components, and the reactivity of the system, in particular, had to be adapted to the pultrusion process. The material had to remain processable for a sufficiently long time while also curing reliably within the continuous process.

At the same time, suitable bio-based reinforcing fibers and corresponding fiber sizing systems were investigated. Complete impregnation of the fibers with the polymer matrix is crucial for achieving perfect force transmission between the fiber and the matrix and, thereby, the required mechanical properties of the composite material.

Within the collaborative project, Fraunhofer IGCV focused in particular on process development for the continuous production of reinforcing lamellae using the pultrusion process. The findings from material and fiber development were gradually incorporated into the pultrusion process. Through numerous processing campaigns in the pultrusion process, a stable and continuous process was ultimately established. This subsequently enabled the transfer of the technology to an industrial setting.

24-Hour Production Demonstrates Suitability for Industrial Use

A key success of the project was the successful processing of the novel bio-based polymer system using the pultrusion process. Various types of fibers (glass, natural fibers, hybrid fibers) were used during the course of the development work. Toward the end of the project, the successful transfer of the development work to an industrial pultrusion line was demonstrated. There, the developed material system was processed in a 24-hour continuous production run, thereby demonstrating the stability of the pultrusion process under industrially relevant conditions.

The consortium was thus able to demonstrate the technical feasibility of processing a bio-based reinforcement lamella for wood structures. In addition, the developed manufacturing process underwent a life cycle assessment and an economic feasibility analysis. Initial potential applications of the manufactured profiles were also tested. Various configurations of the FRP lamellas were bonded to glued laminated timber beams and subjected to mechanical testing. The expected significant performance gain of the wood-FRP hybrid beams was verified.

Technically successful –economically challenging

The project results show that the developed solution is both technically feasible and environmentally sound (LCA). At the same time, the economic analysis (LCCA) revealed that the currently high costs of the required bio-based raw materials still pose an obstacle to their economic use as reinforcing lamellas for laminated wood products.

Regardless, the project yielded extensive scientific and technical insights into the processing of bio-based aliphatic polyurethanes, the impregnation of bio-based fibers, and industrial pultrusion. These findings are already being incorporated into further development and production activities by the participating partners.

Potential Beyond Wood Construction

The material and process expertise developed in the project is not limited to applications in timber construction. Further opportunities for application are emerging, particularly in industries where lightweight construction, resource efficiency, and the use of renewable raw materials are playing an increasingly important role.

The project partners are therefore investigating potential applications in industries such as the automotive, energy, and sporting goods sectors. As a result, »PULaCell« provides an important technological foundation for the further development of bio-based composite materials and their transition to industrial applications.

The »PULaCell« collaborative project ran from August 1, 2017, to December 31, 2020, and brought together expertise across the entire process chain – from the development of the bio-based resin system and reinforcing fibers, through pultrusion process development, to industrial demonstration and evaluation.