## 1 Introduction
The use of natural fibers in PA6 matrix not only provides better physical and mechanical properties to the composite but also there is excellent compatibility between the fibers and the matrix due to the hydrophilic nature of PA6, thus eliminating the need for any coupling agent [7; 16]. In North America, the market size of nylon-6 is estimated to grow as a result of environmental concerns by the plastic industry (Figure 1). This forecast is supported by the increase in demand for environmentally friendly wood based plastic composites. Correspondingly, PA6 has been considered as conventional matrix material for natural fiber-reinforced composites because of its beneficial thermo-mechanical properties [27]. With a view to increasing the mechanical properties of the final composite, it is important to understand the mechanics of microstructure of the composite. Von misses' criteria can be used to deduce that the strength of the composite is limited by the strength of the matrix [28]. The intrinsic tensile properties of the cellulose fibers can be imparted to the composites if there is qualitative interfacial bonding between the matrix and cellulose fibers. Addition to this, high degree of fiber  
Figure 1: USA nylon 6 and 66 market size, by product, 2014–2025 (USD Billion) [source: grandviewresearch.com]. orientation, fiber dispersion and distribution and shorter processing times are key factors to achieve PA6-cellulose composites [29]. Melt processing techniques for preparation of natural fibers thermoplastic composites has simplified scaling and shortening time for composite formation [30]. The morphology and properties of PA6 composites are significantly affected by the type of melt processing technique and also depends on the amount of shear produced [31]. The most common melt processing technique is the twin screw extrusion process through which high degree of filler dispersion can be obtained and thus, significant reinforcement and greater properties of the composites [32; 33]. However, cycle time is long and optimizing the extruder mixing conditions is a difficult task [34], which might lead to thermal degradation of the natural cellulose fibers. Even though there are some limitations such as level of dispersion and distribution or interfacial bonding with the matrix, these limitations can be overcome by melt processing with the Gelimat(r) mixer [35]. Gelimat is a compound/mixer based on the principle of high speed thermo-kinetic mixing. A final compound with excellent dispersion quality can be obtained in one cycle due to the high shear rate generated by the rotor [35]. The Gelimat equipment and a schematic of the Gelimat mixer is shown in Figure 2. When compared with the twin screw extruder, the Gelimat mixer produces higher dispersion [36] and the fiber length remains longer when compared to extruder or internal mixers, consequently improving strength of the composite [37]. Some studies indicate that several passes are required to obtain a biocomposite using an extruder with satisfactory dispersion level exposing the natural fibers to longer levels of processing time hence prone to thermal degradation [38; 39]. Instead, Gelimat kinetic-mixer compounds at shorter processing time and it helps fibrillation of fibers due to the high shear rate induced [30; 40]. These factors make it very suitable to manufacture extremely time-temperature sensitive biocomposites of cellulose and polymers such as polyamide-6. In this study the feasibility of reinforcing PA6 matrix with cellulose fibers by melt compounding with a thermo-kinetic mixer was studied. The thermal degradation temperature of cellulose together with the higher processing temperatures of PA6 are challenges for this study [14]. PA6 cellulose composites were prepared in the Gelimat mixer and injected to test samples.