Hybridisation of short-fibre reinforcement in composites for injection moulding – ways to provide improvement in mechanical performance

Significance 

Recent advancement in technology resulted in many applications that demand more sophisticated material properties. As such, material composites have been identified as promising solution owing to their capability of achieving the desired property by combining individual materials with distinct properties. Several methods for improving the mechanical properties of composites have been developed. Among them, hybridization of reinforcement may enhance, for instance, the Youngs modulus, elongation, strength among others. Apart from property improvement, it is also cost-effective thus reducing the overall cost of the reinforcement process. In a recently published literature, the possibility of using softwood flour to effectively hybridize short-fiber thermoplastics reinforced with man-made cellulose have been proved [1]. It is consequently a reliable means of reducing the reinforcement cost as well as obtaining higher absorption energy in the injection molded composites [2].

Recently, Piotr Franciszczak (PhD candidate) at the West Pomeranian University of Technology Szczecin in collaboration with Dr. K. Kalniņš at Riga Technical University investigated the effects of reinforcement hybridization on the mechanical properties of the misaligned short-fiber composites. Also, they purposed to determine the relationship between the stress-strain characteristics, geometry characteristics and the hybrid reinforced components. They used two types of fibres with different stress-strain characteristics (man-made cellulose and E-glass) – these were hybridized with glass and cellulose fillers during compounding. The manufactured compounds were injection molded and investigated. The reinforcements and compatibilizer contents were proportionally maintained to enable examination of the relation of the filling ratios, reinforcement geometry and mechanical properties of the resulting hybrids. The work is published in the journal, Composites Part B Engineering.

The authors observed that the mechanical performance of a hybrid composite was highly influenced by the fiber, filler E-moduli and the geometries since the interface of the fiber and the filler-matrix had almost equal strength. For instance, the addition of a second filler to short-fibers significantly increased the flexural strength owing to the high response to compressive stresses during bending. This however required Young’s modulus to be within the desired range or higher than that of the fibers. In addition, transfer of the stress from the matrix to the filler depended on the aspect ratio of the filler. For example, a high aspect ratio resulted in the module gain and much higher tensile and flexural strength. Furthermore, the authors noted that stiffer fibers are more susceptible to damages and shortening during compounding and injection molding processes and especially for thermoplastic composite.

The study successfully investigated the influence of reinforcement hybridization on the mechanical properties of short-fiber composites. Based on the experimental results, the developed model to predict mechanical properties of hybridized thermoplastic composites also proved to be effective for obtaining calculations results similar to those provided in theory. However, according to the authors, mechanical properties of hybrids can be further enhanced by using mathematical models that combine the performance of single reinforced composites, effective stress transfer as well as the average fiber aspect ratio. The study will, therefore, advance fabrication of reinforced fiber composites with the desired applications to fit the numerous available applications. Enhanced mechanical properties will also significantly reduce mechanical failures thus resulting in highly efficient and reliable components and structures.

Hybridisation of short-fibre reinforcement in composites for injection moulding – ways to provide improvement in mechanical performance - Advances in Engineering

About the author

Piotr Franciszczak – is currently preparing his Ph.D. thesis on hybridisation of reinforcement in polypropylene based short-fibre composites. In recent years his work at the West Pomeranian University of Technology, Szczecin has been focused on composites for injection moulding.

He developed a method for selective tailoring of interphases in PP/man-made cellulose hybrids with improved impact energy absorption and applied hybridisation for material cost reduction in these composites.

References

Franciszczak, P., Kalniņš, K., & Błędzki, A. (2018). Hybridisation of man-made cellulose and glass reinforcement in short-fiber composites for injection molding – Effects on mechanical performance. Composites Part B: Engineering, 145, 14-27.

Go To Composites Part B: Engineering

 Bledzki, A.K., Franciszczak, P., Meljon, A. (2015). High performance hybrid PP and PLA biocomposites reinforced with short man-made cellulose fibres and softwood flour. Composites Part A: Applied Science and Manufacturing, 74,  132-139.

 Franciszczak, P., Bledzki, A.K. (2016) Tailoring of dual-interface in high tenacity PP composites – Toughening with positive hybrid effect. Composites Part A: Applied Science and Manufacturing, 83, 185-192.

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