Evaluation of the Influence of Chemical Treatment on the Tensile Strength of Sisal Fibresby a Weibull Distribution Analysis

Mercerisation is a common chemical treatment for sisal fibres since it can be used to increase their interfacial adhesion to various polymeric matrices. The influence of this treatment on fibre tensile strength from the point of view of a Weibull distribution is reported. A hundred non-treated sisal fibres were individually tested and the accordance of their tensile strength to a Weibull distribution was analysed. The need to measure the diameter of each fibre being tested in order to estimate its tensile strength was studied. Sisal tensile strength was found to follow a Weibull distribution and to decay with the increase of the severity of the chemical treatment (0.25, 0.5, 1, 2, 5 and 10% w/w NaOH aqueous solution). The values showed an initial decrease of tensile strength, a plateau in the range of 3 to 6% and finally a steep decrease as the concentration was further increased. However, only the 10% treatment showed a statistically significant decrease of fibre tensile strength within a 90% confidence level. Comparisons are included throughout the paper regarding the widely used simplified statistical mean analysis when reporting fibre tensile strength values and its implications on the estimations.