Fibers and Polymers 2013, Vol.14, No.2, 304-310 304 Effect of Nanoclay and Magnesium Hydroxide on Some Properties of HDPE/Wheat Straw Composites Yaghob Liany 1 , Asghar Tabei 1 , Mohammad Farsi*, and Mostafa Madanipour 1 Department of Wood and Paper Science and Technology, Sari Branch, Islamic Azad University, Sari, Iran 1 Department of Wood and Paper Science and Technology, Astara Branch, Islamic Azad University, Astara, Iran (Received February 25, 2012; Revised July 27, 2012; Accepted August 3, 2012) Abstract: Since natural fiber/polymer composites are increasingly used, the development of safe and environmental friendly flame retarding bio-based composites is of great importance. But this issue must maintain the mechanical performance of these composites. To study these objectives, four levels of magnesium hydroxide Mg(OH) 2 of (0, 10, 20, 30 phc) and two levels of nanoclay (0, 3 phc) were considered and incorporated into HDPE/wheat straw composites. Maleic anhydride grafted polyethylene (PE-g-MA) was also used as a compatibilizer at constant content. The samples were prepared by melt compounding and injection molding processes, respectively. The some properties of samples including burning rate and mechanical properties (tensile and impact strengths) were tested based on the ASTM standard. The results showed that the burning rate of samples decreased with increasing the nanoclay and Mg(OH) 2 content. The tensile and impact strengths showed a marginal reduction by adding Mg(OH) 2 from 10 phc to 30 phc and the tensile modulus and impact strength revealed an increase by increasing the amount of nanoclay up to 3 phc. Generally, these results confirmed that the fire retarding and mechanical properties of HDPE/wheat straw composites could be significantly improved with an appropriate combination of the nanoclay and Mg(OH) 2 in the composites. Keywords: Composites, Flame retardant, Nanoclay, Magnesium hydroxide, Burning rate, Mechanical properties Introduction The use of agricultural residues as filler or reinforcement in polymers is a prospective commercial application that would unlock the potentiality of these underutilized renewable materials and provide a non-food based market for the agricultural industry [1]. Lack of hazard to the environment, renewability, low cost, and biodegradability are just some instances of their advantages as fillers or fibers [2]. Wheat straw is particularly an abundant source of plant fiber which is produced in large quantities every year in the world. The importance of this issue becomes clear when we know, at present, that this potentially valuable resource is greatly under-exploited and the total worldwide production of cereal straw is estimated to exceed 2900 million tons per year [3]. A review of literature shows that there are a limited number of useful studies on the use of wheat straw fibers for composite production which are based on mechanical properties [1,4-7], but all these research showed some limitations on their applications. To meet their widespread applications in industry, the mechanical properties, thermal stability and flame retardant properties of polymeric materials or composites which are made from agriculture residues need to be improved. There are still many gaps in information and knowledge of composites made from agriculture residues, which must be filled in order to stimulate commercial production of these novel materials. Generally, the decomposition of burning polymeric materials includes the production of combustible gases, non-combustible gases, liquids, solids (usually char), and entrained solid particles (smoke) [8]. Because of easy flammability of both natural fibers and plastics incorporated in lignocellulosic filled polymer composites and the demands of fire protection in their use, flame retardancy of natural fiber-polymer composites with flame retardant agents is more important topic in its applications. Additive type flame retardants are added to the plastic melt during processing and come in many forms, although most are particles or powders. Additive type flame retardants can improve fire performance through the following mechanisms; 1) redirecting the decomposition and combustion reactions toward the evolution of non-combustible gases, or heavy gases that interfere with the interchange of combustion gases and air, 2) redirecting the decomposition and combustion reactions toward reducing the heat of combustion, 3) maintaining the physical integrity of the material, and 4) increasing the specific heat or thermal conductivity [8]. There are many inorganic materials such as magnesium hydroxide [9-11], ammonium polyphosphate [12], aluminium phosphinate [13,14], decabromodiphenyl oxide [11], melamine phosphate [12], boric acid and zinc borate [9], and also nanoparticles such as carbon nanotubes [15,16], and nanoclays [17-20] as flame retardant which are applied into composites. Magnesium hydroxide is endothermic flame retardant [21], which is decomposed by the endothermic reaction as follows: (1) Mg OH ( ) 2 MgO H 2 O + → *Corresponding author: moh_farsi@iausari.ac.ir DOI 10.1007/s12221-013-0304-3