Sustainable acoustic and thermal insulation materials from elastomeric waste residues H. Benkreira n , A. Khan, K.V. Horoshenkov School of Engineering, Design and Technology, University of Bradford, UK article info Article history: Received 9 March 2011 Received in revised form 27 May 2011 Accepted 28 May 2011 Available online 7 June 2011 Keywords: Materials processing Porous media Foam Particulates processes Microstructure Environment abstract This study presents the data elements to develop a new processing route to transform elastomeric waste residue (particulates) into acoustic and thermal insulation materials that can compete with commercial products. The approach is to bind these grain and fibre particulates with a foaming polyurethane or a similar polymer, the chemistry of which can be manipulated to control the structure stiffness and the evolution of the foaming gas into open or closed cells. Here the study uses two examples of such residues, tyre and carpet shreds both composed of fibres trapping grains of either rubber or PVC. Compounds were made from these systems with different PU binders and the structural properties (density, porosity, air flow resistivity, tortuosity and stiffness) and performance properties (sound absorption, sound transmission, impact sound insulation and thermal conductivity) were measured as a function of binder loading and chemistry. The data obtained show clearly that performance can be tailored by tailoring structural properties resulting with materials that match or even outperform commercial products. The data set obtained here can be usefully exploited with available acoustic and thermal insulation materials model to take the approach further and extended to other waste systems. & 2011 Elsevier Ltd. All rights reserved. 1. Introduction The sustainability agenda now espoused throughout the world requires industry and local authorities to cease dumping waste in landfills and treat it as a resource that should be valorized, just like any other potential starting material, to develop new products that can compete in performance and price with established products made from our dwindling reserve of natural resources. Scrap products containing plastic and/or rubber provide such an opportu- nity with an abundant supply deriving from scrap tyres, cars parts, post industrial and consumer carpets, etc. Although much effort is now being made worldwide to recycle or re-use most of the plastic and/or rubber components of these wastes, a large amount remains difficult to separate and this is what is termed here as residue. This residue is predominantly in the form of plastic fibres trapping rubber particulates (see Fig. 1) and it is this structure coupled with their dust state that makes complete separation very difficult thus uneconomical to consider as a potential basis material to develop new products. Unless new technological routes for reusing these wastes residues, as they are, are found, they will continue being disposed to landfills, stockpiles or illegal dumps and the burden on the environment will increase. A sustainability challenge therefore is to develop from these elastomeric fibre-granular waste residues and dust new performance and price competing products to replace products currently manufactured from diminishing raw resources. This paper takes up precisely this challenge and describes how such wastes residues can be compounded and structured into cheaper acoustic and thermal insulation materials of properties similar or better than current commercial products. The acoustic and thermal material applications targeted are for noise absorption and heat insulation around buildings, industrial and domestic appliances and transport vehicles, reflection or noise barriers against traffic noise and impact sound insulation in flooring underlays. Clearly, and on the basis of well established physical principles, the final material structure, its elasticity and porous features are at the heart of acoustic and thermal properties. Material density is the prime consideration of acoustic reflection and an intimate binding of the particulates will thus be required for noise barrier materials. An open pore structure in which the pores are interconnected is the key to noise absorption as such structure increases air flow resistivity and consequently the dissipation of noise energy. A closed pore structure, in which gas is trapped, is the prime requisite for heat insulating materials. For impact sound insulation, the essential structural aspect is the ability to dissipate the vibrational energy of the impact, most suitably achieved when the receiving material has a low elastic modulus as is the case with the waste elastomers used in this study. In this research, the marriage of acoustic and/or heat insulation properties derives from the low thermal conductivity Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/ces Chemical Engineering Science 0009-2509/$ - see front matter & 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.ces.2011.05.047 n Corresponding author. Tel.: þ44 1274 233 721; fax: þ44 1274 235 700. E-mail address: H.Benkreira@bradford.ac.uk (H. Benkreira). Chemical Engineering Science 66 (2011) 4157–4171