JEC Group have brought together the international community of composites leaders and executives in our Composites Circle as an unique networking opportunity to meet with both peers and future partners.
Fibroline France has pioneered a radical new manufacturing approach to composites and fibre-reinforced materials in general. Its innovative dry powder impregnation technology greatly reduces direct material costs and the ecological footprint of composite manufacture, and enables the development of new products with specific functionalities and material characteristics.
(Published on December 2007 – JEC Magazine #37)
JÉRÔME VILLE, TECHNICO-COMMERCIAL RELATIONS FIBROLINE
The process uses a high-voltage generator to electrically charge powder particles in an AC current field and distribute them throughout any kind of porous structure (non-wovens, fabrics, foams, etc.). The types of powder include thermoplastics, thermosets, vegetal-based polymers, and a broad range of additives and functional powders.
A flexible process
This flexible process permits many different combinations of resin matrices and fibres (natural fibres, synthetic fibres, glass…). In addition to the application-specific process optimization, a key factor is the adaptation of the powder particle sizes to the porosity of the substrate. The main advantages of the dry powder impregnation process are the perfectly homogeneous powder distribution and the environmentally sensitive technology, which requires no water or solvents and reduces energy costs and the investment in pollution control processes.
The Fibroline team carries out feasibility and development studies. Initial experiments are performed on small samples (A4 size) whereby a powder is homogeneously distributed on the surface of a sample, which is then placed between two plate electrodes. The alternating field is applied and the powder starts to impregnate the porous substrate. To understand the homogenous distribution of the powder during the impregnation process, it suffices to place powder only between the plate electrodes. The electrically charged particles then form a cloud and fill the inter-dielectric space. Based on the lab trials, the team then defines the working process parameters and seeks to identify powders that would be of interest for the process at hand. To this end, a lab unit (1-m-wide pilot line) has been installed in France to validate the efficiency of the technology with the customer and to produce “industrial” prototype samples of a few m2. A fully automated inline unit located in Germany includes a winding/unwinding system, a flat-belt calender, and other post treatment. This line is mainly used for production-scale validation, and several industrial partners have already carried out pilot production to test the market or validate their product industrially. Since the line is used for a wide range of different applications, it was designed to offer maximum flexibility. Any customer equipment would be built to their specifications. The company does not manufacture equipment of its own, but subcontracts it to a Swiss equipment manufacturer (Strahm).
A biocomposite project (ACTRA) was carried out by several partners to investigate potential combinations of vegetalbased resins and natural fibre reinforcements. The project was coordinated by the French Institute of Textile and Clothing (IFTH) and the dry powder impregnation technology was selected to manufacture the tested materials. The partners involved in the project included two technical centres: the IFTH, which has a strong experience in the field of technical textiles and non-wovens, and the Cermav, a research centre experienced in the surface treatment of cellulosic fibres (for paper in particular) and willing to transfer its know-how to natural fibre reinforcements. The associated industrial partners were Visteon, a car-part manufacturer already working with natural fibres and seeking to innovate with vegetal materials, and Irisbus, also involved in the transportation industry (public transport mainly), an innovative company seeking to reduce the weight of vehicles while maintaining the performance of the products. The process partner was Fibroline. Selecting the polymer matrix according to the specifications of the industrial partners was the starting point of the project. The main requirements were thermal and mechanical performance, but also cost-effectiveness in relation to the transportation and automotive market. The following resins were selected: poly-lactic acid produced by Cargill, cellulosic acetate provided by Acetabel, cellulosic acetate by-products from Eastman such as cellulose acetate butyrate (CAB) and cellulose acetate propionate (CAP), and polyhydroxybutyrate (PHB) provided by Biomer. To be able to compare the manufactured samples with industrial products, polypropylene resin was also tested as a reference material. All natural fibre structures were manufactured (carding and needle punching) by IFTH and impregnated with 40% resin by weight.
Initial trials: mechanical characteristics and influence of the resin
Cellulosic acetate and PLA were selected for the initial trials. Threepoint bending tests gave the following results, showing significantly different ductilities between the resins tested. The results show that the mechanical properties of PLA resin are rather high, not so far from those of the glass-mat thermoplastic materials currently used in automotive applications. Cellulosic acetate materials show intermediate results between PP and PLA composites. The other materials tested, such as cellulosic acetate by-products and PHB, gave nearly the same results as the polypropylene matrix.
Material behaviour under wet conditions
To meet industrial requirements for the product and the main specifications of the industrial partners, ageing tests under wet conditions were carried out.
Samples were treated in water for 24 hours. The changes in mechanical properties (similar three-point bending tests) and weight of the product were studied with the following results: The mechanical results clearly demonstrate that the ageing treatment significantly impairs properties, in particular for hydrophilic resins (cellulosic acetate and PHB). This is not specific to bio-polymers and several studies are in progress to improve such properties in industrial products. Cellulosic acetate by-products show higher stability under wet conditions, but the cost price of such resins remains a strong disadvantage, in particular for transport applications.
To conclude, the potential of biocomposite materials in terms of technical characteristics was clearly demonstrated. Indeed, satisfying mechanical properties were obtained with such bioresins, even higher than those of more conventional materials for some of them.
In addition to those promising results, studies are currently in progress, at the Cermav in particular, to optimize surface adhesion so as to improve matrix compatibility in natural fibre structures. This is probably the way to improve strength under wet conditions while keeping in mind the cost price requirements of the automotive industry.