Tensile strength of pine needles and their feasibility as reinforcement in composite materials

Abstract

A feasibility study concerning the use of pine needles from Maritime Pine (Pinus pinaster) trees as reinforcement in composite materials has been presented in this paper with the tensile strength being investigated for a total of 150 specimens at three gauge lengths, namely 50, 75 and 100 mm. In order to calculate the tensile strength for each specimen, a correlation was obtained between the cross-sectional area and external dimensions of the individual pine needles. The mean value of the tensile strength was noted to vary only slightly between 33.4 MPa for the 50 mm gauge length and 31.4 MPa for the 100 mm case with a minimum and maximum of 15 and 65 MPa, respectively. Analysis of the data using the standard Weibull model indicated the Weibull strength to vary between 33.5 and 36.0 MPa whereas the Weibull modulus varied between approximately 3.5 and 4.5. Further analysis using the Weibull model indicated the presence of a bimodal strength distribution at each gauge length that was consistent with the presence of two distinct flaw populations operating within the pine needles. Overall, it was concluded that the strength of the pine needles was sufficient for inclusion in polymer matrix composites subject to low stress or non-load bearing applications such as fibreboard and thermal or acoustic insulation.