1. 15 th Physical Chemistry Conference Introduction Introduction In recent years composites reinforced with nanoparticles have caught the attention of many researchers and engineers. In nano composite materials, the particles are dispersed through the polymer matrix in the nanometer range at least in one dimension. In polymer composites, nano silica is one of the widely used fillers. In recent years, there have been many publications dedicated exclusively to the effect of nano silica on mechanical properties of thermoplastic composite, however there are not many reports related to the effect of nano silica on mechanical properties of wood plastic composite [1,2]. In this study, the effect of nano silica particles on practical properties of wood plastic composite made of high density polyethylene and OCC fiber were investigated. To achieve this aim, OCC fiber were mixed with high density polyethylene at 30% by weight, and nano silica with 0, 1 and 3% respectively, also 2% of MAPE was used as the coupling agent in all formulation. Then samples were made in injection molding and mechanical properties were tested according to ASTM standard. Results indicated flexural properties, tensile properties, and hardness increased with nano silica loading, however impact strength was decreased by increasing of nano silica particles. Keywords : Composite, OCC fiber, HDPE, Nano silica, Mechanical properties Material Formulations of the mixes used for the respective mixes prepared have shown in Table 1. The components of each sample (HDPE, MAPE, and OCC fiber) were pre-mixed to prepare homogeneous compounds and were blended in a counter-rotating twin-screw extruder (Collin, Germany) at a screw speed of 80 rpm with profiles at 152-150-162-160- 165-170°C. The mix was cooled in water after removing from the mixing bowl and then, it was granulated into pellets. After that, the pellets were dried at 80°C for 24h before injection molding. Finally, the pellets were injection molded (Imen Machine Co., Iran) at 160°C. High density polyethylene (HDPE) was supplied by Tabriz Petrochemical Company, Iran, with grade of HD-5218UA. It had a density of 0.952 gr/cm3 and a MFI of 18 gr/10 min at 190°C. OCC fibers were prepared from municipal waste stream in Karaj, Iran. Maleic anhydride grafted polyethylene (MAPE) provided by Karangin Company, Iran, with trade name of KARABOND EHM and density of 0.935 gr/cm3 (MFI=1.1gr/10 min) was used as coupling agent. Fumed silica (Nano silica) was supplied by Degussa AG (Hanau, Germany) under the trade name AEROSIL 12000. The average primary particle size was 12 nm, the specific surface area 230 m2/g and the SiO2 content >99.8%. Composite preparation Result and discussion Figure 1. Effect of nano silica content on tensile properties The tensile modulus and tensile strength of the HDPE/OCC fiber composites increased with increasing nano silica content, however the impact strength of the composites decreased with increasing the nano silica loading. This project has shown that the composites treated with nano silica will be desirable as building materials due to their improved stability and strength properties. [1] Vladimirov, V., Betchev, C., Vassiliou, A., Papageorgiou, G., Bikiaris, D.; Dynamic mechanical and morphological studies of isotactic polypropylene/fumed silica nanocomposites with enhanced gas barrier properties; Composites Science and Technology; 66, 2935–2944; 2006. [2] Ghasemi, I. and Kord, B., Longterm; Water Absorption Behavior of Polypropylene/Wood Flour/Organoclay Hybrid Nanocomposite; Iranian Polymer Journal; 18, 683–691; 2009. [3] Lee, S.H., Kontopoulou, M., Park, C.B.; Effect of nanosilica on the co-continuous morphology of polypropylene/polyolefin elastomer blends; Polymer; 51, 1147-1155; 2010. [4] Deka, B.K., Maji, T.K.; Effect of Silica Nanopowder on the Properties of Wood Flour/Polymer Composite; Polymer engineering and science; 8, 1002-1012; 2012. Conclusion Reference Investigating the effect of nano silica particles on mechanical properties Investigating the effect of nano silica particles on mechanical properties of OCC fiber-HDPE Composite of OCC fiber-HDPE Composite A. Rashno *a, A. Eshghi a, S. Ahmadi b, R. Mohebi a a. Department of Wood and Paper Science, Karaj Branch, Islamic Azad University, Karaj, Iran b. Iran Polymer and Petrochemical Institute, Tehran, Iran Email: arashrashno@gmail.com Content (Wt. %) Sample Code HDPE MAPEOCC fiberNano silica 68 2300S0 67 2301S1 65 2303S3 Table 1. The materials used in making the OCC fiber /HDPE composite. Figure 1 shows the values of the tensile strength and modulus in the studied nano composites. It can be seen that the strength and modulus values of the nano composites increase in samples with 3% nano silica. The interaction between nano silica, polymer and fiber would restrict the movement of the polymer chains and as a result the tensile properties would be improved. This is consistent with the results reported by most authors [3,4]. Adding nano silica reduces the toughness and impact strength (Figure 2). Figure 2. Effect of nano silica content on impact strength