Flame retardancy of radiation cross-linked poly(vinyl chloride) (PVC) used as an insulating material for wire and cable A.A Basfar* Institute of Atomic Energy Research, King Abdulaziz City for Science and Technology (KACST), PO Box 6086, Riyadh 11442, Saudi Arabia Received 12 August 2001; received in revised form 24 October 2001; accepted 7 November 2001 Abstract Various formulations of radiation cross-linked poly(vinyl chloride) (PVC) were prepared to improve the flame retardancy for wire and cable insulation applications. Limiting oxygen index (LOI) was used to characterize the flammability of the developed formulations. The effect of different plasticizers, dioctyl phthalate (DOP), di-isodecyl phthalate (DIDP) and tri-2-ethylhexyl tri- mellitate (TOTM) and different flame-retardant fillers, Sb 2 O 3 , zinc borate, Al(OH) 3 and Mg(OH) 2 on the mechanical properties and flammability was investigated. The influence of radiation dose on the mechanical properties was minimal both at room temperature and after thermal aging for 168 h at 136  C. The highest LOI was 39% for PVC formulations containing DOP as a plasticizer and TMPTA at absorbed doses of 90 and 120 kGy. Both DTG peak maxima and temperature for loss of 50% mass decreased with increasing irradiation dose. No influence of plasticizer type or flame-retardant filler on the thermal properties was observed. # 2002 Elsevier Science Ltd. All rights reserved. Keywords: Flammability; PVC; Wire; Radiation crosslinking; Flame-retardant 1. Introduction Radiation crosslinking of wire and cable insulation was first introduced by RayChem Corp., USA. in 1957 [1]. It has been known to impart improved properties in various applications [2,3]. A unique advantage of this process is the capability of introducing a cross-linked structure to polymers at low temperatures. Among important properties of wire and cable insulation mate- rials are thermal stability, flammability and processa- bility. Poly(vinyl chloride) (PVC) with proven product performance, material processability, thermal stability and economic cost effectiveness has been an excellent choice as insulation material for wire and cable. In addition, PVC actually retards fires both from starting and from spreading because of the inherent flame- retardant nature of its chlorine content [4]. PVC com- pounds require much less fire retardant (FR) additives than other polymers even when highly plasticized. Lower amounts of FR fillers give PVC’s competitive cost structure and minimize the appearance and aging deficiencies, which most FR systems can cause in poly- mers. This, in turn, makes it possible for PVC to meet most stringent flame and smoke retardant standards. The flame retardancy of polymers can be improved by incorporating flame-retardant chemicals in two ways; first as additives, second as reactives. Additives are compounds, which are mechanically mixed with poly- mers [5]. On the other hand, reactives are chemically bound as an integral part of polymer structures. There are six elements, which are particularly associated with flame retardancy of polymers, namely; boron, alumi- nium, phosphorous, antimony, chlorine and bromine. These elements retard flames in different ways [6], which is not the subject of this paper. It is important to note that the addition of these elements may significantly influence mechanical, thermal and electrical properties. As a result, any investigation should include observing the influence of flame retardants on these properties. In addition, other metal compounds like magnesium hydroxide are frequently used as flame-retardants for polymers [7]. Synergistic combinations of the various ele- ments can also be considered for better performance [8]. 0141-3910/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved. PII: S0141-3910(02)00037-X Polymer Degradation and Stability 77 (2002) 221–226 www.elsevier.com/locate/polydegstab * Tel.: +1-481-3648; fax: +1-481-3887. E-mail address: abasfar@kacst.edu.sa