Evaluation of Bast Fibres of the Stem of Carica papaya L. for Application as Reinforcing Material in Green Composites

Aims: The production of green composites based on natural fibres is rising with regard to increasing environmental problems and declining fossil raw materials. Bast fibres of papaya (Carica papaya L.) accumulate on plantations at a large scale but remain an unused resource. The characterisation of the bast allows a first evaluation of the potential of papaya-fibres for use in composites.
Study Design: Material testing.
Place and Duration of Study: Institute for Botany, Technische Universität Dresden and Fraunhofer Institute for Nondestructive Testing Dresden (IZFP-D), 2011 and 2013.
Methodology: The anatomic structure of fibre cells and the microfibril angle of the cell walls were determined as well as a chemical analysis to determine the proportion of cellulose, lignin and hemicelluloses of the fibre cells. In addition, samples of fibres were subjected to static uniaxial tension tests revealing Young's modulus, tensile strength and breaking strain at different plant ages and of two origins.
Results: Fibres of a two-year-old plant exhibited a Young's modulus of 10.7 GPa, a tensile strength of 101 MPa and a breaking strain of 1.2%, on average. Fibres from six-months-old plants, grown under greenhouse conditions had a mean Young's modulus of 4.4 GPa, tensile strength of 49 MPa and a breaking strain of 1.4%. Having one of the lowest fibre densities with ca. 0.85 g/cm³, papaya fibres exhibit noteworthy specific mechanical properties among all studied natural fibers.
Conclusion: These data allow us a first estimation for a potentail use in green composites as reinforcing material.