Enhancement of flame retardancy and mechanical properties of HDPE/EPM based radiation shielding composites by electron beam irradiation Duckbong Seo a , Jaewoo Kim a,⇑ , Phil-Hyun Kang b , Chang Eui Seo c , Jun-Hyung Lee a , Hyun-Jin Kim a a Nuclear Materials Research Division, Korea Atomic Energy Research Institute, 1045 Daeduckdaero, Yuseong-Gu, Daejeon 303-305, Republic of Korea b Advanced Radiation Technology Institute, Korea Atomic Energy Research Institute, 1045 Daeduckdaero, Yuseong-Gu, Daejeon 303-305, Republic of Korea c Agency for Defense Development, 488 Bukyuseongdaero, Yuseong-Gu, Daejeon 305-152, Republic of Korea article info Article history: Received 14 March 2012 Accepted 21 May 2012 Available online 28 May 2012 abstract Radiation shielding materials based on polymer or its composites require higher material properties to endure the harsh radiation environments. In this investigation, electron beam (E-beam) irradiation and/or cross-linking agent triallyl cyanurate (TAC) were applied into the composites of a high density polyethylene (HDPE)/ethylene propylene monomer (EPM) blend containing B 2 O 3 and/or PbO. The tensile strength increased as much as twice while the elongation enhanced more than 5 times by irradiation of 150 kGy with 10 MeV E-beam. Further enhancement of the tensile and elongation properties was achieved by applying both 1 wt.% TAC and E-beam irradiation, while use of 1 wt.% TAC alone decreased the mechanical properties. Flame retardancy of the polymer composites by mean of limit oxygen index (LOI) also achieved to higher than 21 without using any flame retardant additive. Ó 2012 Elsevier B.V. All rights reserved. 1. Introduction Polymer is an essential material as a component or a complete product in modern industrial era. It can be used by itself or as a blend with the other polymers. It can also be mixed with various organic or inorganic particles from nano- to micro-scales in making the polymer composites. While polymers possess superior physical and chemical properties, there are some weaknesses in the mechanical toughness and thermal stability compared with competing materials such as wood and metal. As the needs for applications of polymeric materials increase, the demand for enhancement of their material properties also increases. Among others, polymers or polymer composites based radiation shields require higher material properties in addition to radiation endurance. Particularly, they should have mechanically tougher, thermally more stable, and radiation resistant properties to endure harsh radiation environments [1–3]. Hydrogen rich polymers such as polyethylene (PE) or epoxy containing neutron absorbers such as boron, lithium, or gadolinium are commonly used as a neutron shield, while polymers mixed with high density elements such as Fe, Pb, or W can be used as a gamma (or X-ray) radiation shield [4–6]. However, uses of these types of materials in those extreme environments are restricted because of their high flammability and low mechanical strengths. In these regards, it is necessary to enhance the flammability resistancy and/or mechanical properties of polymeric materials while lowering production cost and simpli- fying manufacture processes. Applying flame retardant additives based on phosphorous compounds [7–10] or metal oxides/hydrox- ides [11–14] into polymeric materials is a common method to re- duce the flammability of polymers, while the uses of the halogenated compounds are not recommended currently due to their adverse health and environmental effects. Adding foreign fill- ers into polymeric materials generates severe degradation of the material properties, since the flame retardant additives usually act as an impurity reducing the materials properties [15,16]. To en- hance the thermal and/or mechanical properties, the polymer com- posites containing various nanoparticles are recently explored [17– 21]. Also, radiation induced cross-linking of polymeric materials due to its fast and convenient process have long been investigated to enhance the material properties [22–28]. More importantly for the radiation involved process, material purity can be maintained while the mechanical properties could be enhanced. In this inves- tigation, we applied electron beam (E-beam) irradiation together with a small amount of cross-linking agent triallyl cyanurate (TAC) without any flame retardant additives into polymeric radia- tion shielding materials, and achieved the enhancement of the flame retardancy as well as the mechanical strengths. 2. Experimental A polymer blend and its composites that can be used as a radi- ation shielding material were prepared, and the mechanical prop- erties in terms of the tensile strength and elongation, and the flame 0022-3115/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jnucmat.2012.05.036 ⇑ Corresponding author. E-mail address: kimj@kaeri.re.kr (J. Kim). Journal of Nuclear Materials 429 (2012) 99–104 Contents lists available at SciVerse ScienceDirect Journal of Nuclear Materials journal homepage: www.elsevier.com/locate/jnucmat