You are here

Mechanical properties of natural-fibre-reinforced composites

News International-French

22 Feb 2011

Natural fibres are now considered as a suitable alternative to glass fibre, due to their advantages, which include low cost, high strength-to-weight ratio, and recyclability. Combining natural fibres with glass fibre also decreases the usage of glass fibre. In this investigation, hybrid glass-/sisal-fibre composites were fabricated using the hand lay-up method. The tensile, flexural and impact strength of the resulting composites were tested using a universal testing machine (UTM). It was concluded that the sisal-glass hybrid composites exhibit better tensile, flexural and compression strength.





Natural fibres are now regarded as a serious alternative to glass fibre for use as reinforcements in composite materials. Their advantages include low cost, low density, high strength-to-weight ratio, resistance to breakage during processing, low energy content and recyclability. The properties of natural-fibre-based composites can be affected or modified by a number of factors such as fibre combinations, processing method, fibre volume fraction, aspect ratio, water absorption, etc. The process parameters and their influence on the final properties vary with different fibre-matrix combinations. The fabrication method has a significant impact on the resulting properties. Various processing methods, e.g. compression moulding, injection moulding, extrusion moulding, and hand lay-up, are available for naturalfibre composite materials. Injection moulding improves the fibre dispersion, hence increasing the tensile and flexural properties. However, extrusion and injection moulding have detrimental effects on the properties of natural fibres.


The objectives of this work were 1) to fabricate natural-fibre-reinforced composites with various layer configurations and 2) to analyze properties like tensile, flexural and impact strength.


A Life Cycle Assessment was then performed on these materials in connection with an application for plastic transport pallets.


Manufacturing process


The manufacturing process used involved the use of hand lay-up to produce composites with different layer configurations. The materials used were a general-purpose polyester resin, a methyl ethyl ketone accelerator, a cobalt catalyst, polyvinyl/polyethylene sheets, glass plates, glass fibres, and sisal fibres. A double-layer composite and two types of triple-layer composite were produced.



Double-layer system



For the double-layer system, both sisal and glass fibre were used as reinforcement, and a polymer-based resin as matrix. The fabrication process consisted in pouring a resin mixture over a polyethylene sheet, placing the sisal fibre over it, pouring more resin mixture over that, applying the glass fibre, pouring more resin mixture again, and then covering these layers with another polyethylene sheet.


Triple-layer system

For the triple-layer system, the reinforcement consisted either of two layers of sisal with a layer of glass fibre in between, or a layer of sisal fibre between two layers of glass fibre. A polymer-based resin was used as matrix.


Two sisal layers/one glass-fibre layer


For this type of triple-layer composite, the resin mixture was poured over the polyethylene sheet, then covered with a layer each of sisal fibre, resin, glass fibre, resin, sisal fibre, and resin. This sandwich was then covered with another polyvinyl/polyethylene sheet.


Two glass layers/one sisal layer

For this type of triple-layer composite, the resin mixture was poured over the polyethylene sheet, covered with a layer each of glass fibre, resin, sisal fibre, resin, glass fibre, and resin. This sandwich was covered with a polyethylene sheet.


Results and discussion

Tensile test

The test was carried out on a cured specimen 15 cm x 1.5 cm x 0.4 cm. The following figures show the displacement curves for the different layers and the variations of several parameters with respect to the layers.


Flexural test



The tensile tests demonstrate that the composite combining two sisal layers and a glass layer has better tensile strength. The flexural tests show that the one glass/one sisal layered composite has better flexural strength. The impact tests with and without moisture show that the two glass/one sisal layered composite has high impact strength. The dispersion of hard particles on the layers does not show any improvement over sisal-fibre composites.




  1. A. K. Bledzki, J. Gassan: Composites reinforced with cellulose base fibres, Progr Polym Sci; 24, 1999, 224-74.
  2. J. Bolton: The potential of plant fibres as corps for industrial use, Outlook Agric. 24, 1995, 85-9.
  3. A. K. Mohanthy, A. Wibowo, M. Misra and L. T. Drzal: Effect of process engineering on the performance of natural fibre cellulose acetate biocomposites, Compos: Part 1 – Applied Science, 35, 2004, 1781- 1873.
  4. O. S. Carneiro and J. M. Maia: Rheological behaviour of carbon fibre / thermoplastic composites, Part 1: The influence of fibre type, processing conditions and level of incorporation, PolymCompos, 21 (6), 2000, 960-969.
  5. L. Wanjun, L. T. Drazal, A. K. Mohanthy and M. Misra: Influence of processing methods and fibre length on physical properties of kenaf fibre reinforced soy based biocomposites, Composites: Part B, 38(11), 2007, 352-359.
  6. H. Y. Sastra, J. P. Siregar, S. M. Sapuan and M. M. Hamdan: Tensile properties of arenga pinnata fibrereinforced epoxy composites, Polymer-Plastics Technology and Engineering, 45 (11), 2006, 149-155.
  7. K. Okubo, T. Fujii and Y. Yamamoto: Development of bamboo-based polymer composites and their mechanical properties, Composites Part A: Applied Science and Manufacturing, 35 (3), 2004, 377-383.
  8. P. Antich, A. Vazquez, I. Mondragon and C. Bernal: Mechanical behaviour of high impact polystyrene reinforced with short sisal fibres, Composites: Part A, 37, 2006, 139-150.
  9. T.-T.-L. Doan, S.-L. Gao and E. Mäder: Jute/polypropylene composites I. Effect of matrix modification, Composites Science and Technology, 66, 7-8, 2006, 952-963.
  10. X. Lu, M. Q. Zhang, M. Z. Rong, D. L. Yue and G. C. Yang: Environmental degradability of self-reinforced composites made from sisal, Composites Science and Technology, 64, 9, 2004, 1301-1310.