Fibre reinforced polymer composites are being used in almost every type of applications in our daily life and its usage continues to grow at an impressive rate. The manufacture, use and removal of traditional composite structures usually made of glass, carbon and aramid fibres are considered critically because of the growing environmental consciousness . In recent years, there has been a growing interest in the use of biofibres as reinforcing components for thermoplastics and thermosets. Coconut fibre (coir), a member of the palm family is a biodegradable and environmental friendly crop. Moreover, coir is a strong, stable and versatile material and it has been recognized as an important source of fibres for composites [2–4].
It is generally accepted that the tensile properties of fibre-reinforced polymer composites are controlled by factors such as nature of matrix, fibre-matrix interface, fibre volume fraction, fibre aspect ratio. Many scientists are working in this field and the reinforcement of polymer with coconut coir fibres has been widely reported [5–12]. A further attempt to use coir fibres as reinforcement for high temperature and pressurize vessel applications has been found in the literature . Manikandan Naira et al.  studied the thermal behaviour of polystyrene composites reinforced with randomly matted coconut coir fibres by means of thermogravimetric and dynamic mechanical thermal analysis. It has been found  that matrix cracking, fibre bridging, fibre breakage and pull-out are the major fracture modes of coconut coir fibre reinforced composites with pre-cracks under the static loading condition. However, despite the fact that several methods have been used and great strides have been made, there is still some lack of knowledge about tensile strength property of coconut coir fibre reinforced polymer composites.
Cashew nut shell liquid resins (CNSL) are the most prominent examples of the class of thermosetting resins usually referred to as bio-resins , even though new research efforts are needed to address to offset its major disadvantage. The use of CNSL as a major resin matrix by the composite products industry is due to a number of advantages, including low cost, ease of use under a wide variety of curing conditions, low cure temperatures, water solubility, resistance to microorganisms and to abrasion, hardness, and excellent thermal properties.
The present work dealt with the changes in the tensile properties of coir/CNSL blend composite as a function of fibre size, weight fraction and surface treatments of coconut coir fibre. In addition to this, the effect of coconut coir fibre loading on water absorption tendencies of the composites has also been examined. Meanwhile, the surface modifications is studied and described. This study was initiated to determine whether the compatibility between CNSL and coconut coir fibre is strong or weak, and to evaluate the tensile performances of the composites. It is anticipated that this study may open the way for future investigations in the use of coconut coir fibre in fibre composites so that the range of natural fibre potential applications can be widened.