AA TECHNICAL STUDIES - UNUSUAL PERFORMANCES (2016)
Collaboration with Chong Yan Chuah
From Roman concrete to carbon fibre polymers, composite materials have been engineered to improve performance in the built environment, be it structural, environmental or aesthetic. Typically, when we talk about composites we imagine performance at a local scale, where the effect of the material’s properties is felt in its immediate surroundings. However, in every material is implied a set of properties at a much larger scale; the scale of the landscape. In every material is the story of its making – a supply chain which in today’s networked world often spans across the globe. Our composite – ‘Tainted Bone’ – aims to extend its performance to landscapes where it is made, choreographing into its production a positive, and much needed environmental change.
As you enter Hazaribagh the first thing you notice is the smell. It is the stench of thousands of animal carcasses, rotting in the open air. Beneath the smell of decay is a bitter, chemical taste in the air – chromium, sulphuric acid and sodium sulphide fumes. Scattered all around are animal bones, mixed with plastic bags and other trash from local shanty dwellings. Children play in the detritus, workers sift through rotting flesh with their bare hands. Hazaribagh, in Dhaka Bangladesh is one of the world’s primary leather tanneries. Sites like these supply prized leather to the luxury fashion markets of the world. Left behind, are piles of bone.
A truck, an old oil tanker to be exact, pulls up to a concrete trough at the outskirts of Pali, India. The driver gets out, and releases a valve to a plastic pipe protruding out of the back of the oil drum. Fluorescent green liquid sprays out, mixing into a purplish slurry flowing through the trough below. Next to it a row of other tankers do the same, blue, orange, black, red – it looks like soda at a candy store; but it’s not. It’s dye saturated effluent from the fabric dying factories of India. The trough leads straight to a pipe that opens out onto a river. Its banks are stained grey green. Grass withers and receded from the edges; a diagram of toxicity. The water is highly acidic, and tainted with heavy metals and iconic dyes used to give colour to our clothes. The river runs the colour of the next hot fashion trend.
CHOREOGRAPHY & AMBITION
Imagine a material that intervenes in these two sites, choreographing a careful and symbiotic relationship between the leather tanneries and the dyeing factories; a relationship that finds a use for Hazaribagh’s animal bones and Pali’s effluent. A composite that removes the waste from both these production landscapes and redistributes them as a product of beauty in the very consumer societies that motivate their making.
ADSORPTION & ACTIVATED CARBON
Due to the urgency and scale of the issue, the removal of polluting chemicals in dyeing effluent is a well-documented and researched topic. A common solution is the use of hyper-porous materials to ‘adsorb’ dissolved chemicals out of solution. [image of electron microscope scan of activated carbon] Adsorption is a chemical process where particles in solution (the solute) are attracted to adsorbent particles introduced to the liquid. Attraction occurs due to weak forces of electro-chemical and electro-static charge between the surface of the particles and the dissolved molecules of the solute. Therefore, a good adsorbent material will have a high surface area to volume ratio, meaning that small particles will have a large surface area and therefore large capacity to collect molecules of the target solute. The most common and effective adsorbent is activated carbon – a chemically prepared material made from burning carbon based materials (coal, timber, agricultural waste) under controlled pressure and chemical conditions. The resulting material has an extremely high surface area per volume in the region of 500 – 1500 m2 per gram (Shoba, n.d.). Typically, treatment of contaminated water using activated carbon is achieved by pumping the water through a column containing activated carbon, allowing high levels of contact between activated carbon granules and the contaminated solution. Treated water is then filtered/drained out (Lenntech.com, 2016).
In 2013, a team of researchers from the Amirkabir University of Techology in Tehran demonstrated that fish bone, when ground milled to a particle size of roughly 250µm could be used to effectively remove two basic (cationic) dyes from solution (Ebrahimi et al., 2013). Their experimentation demonstrated that with a dye concentration of 100ml per litre of water they were able to remove almost 90% of the dye with a concentration of 2.5g/L of the fishbone over 60 minutes. It was also found that increasing the pH of the solution aided adsorption, with best results at a pH of 11. Their findings proved that fish bone – itself naturally hyper porous, could adsorb large amounts of dye onto its surface.
otHer animal BONEs
We also consulted a number of other studies on bone as a low-cost adsorbent, using other (unspecified) animal bones. These other studies from the Suez Canal University in Egypt and The University of Bahrain found that pore size in animal bones could be optimised through a process of calcination – burning at a temperature between 600°C and 800°C in a furnace with a controlled oxygen content before being milled to particle sizes of 45-200µm (Shehata, 2013 and El Haddad et al., 2013). In both cases around 80-90% dye removal was also achieved through optimisation of both dye and adsorbent concentration.
STRUCTURAL COMPOSITES USING BONE
Parallel to our research into using bone as an adsorbent we also looked into several examples of composite materials that had used bone granules as an aggregate within various matrices (as our envisioned composite would need to be a coherent solid rather than a pile of toxic, free floating particles). One study aimed to produce a biodegradable plastic by encasing bone particles (under 1mm in size) in a matrix of polyhydroxyalkanoate polymer. The resultant bio-plastic was found to be more durable than ordinary plastics due to bone’s low hygroscopic expansion (inherent to its microporous structure), which meant it could absorb moisture with much lower levels of degradation than other plastics (Srubar and Billington, 2013). Finally, a study from the University of Lagos, Nigeria, found that pulverised bone could also be used as the aggregate in foam-aerated concrete, providing a low cost construction material (up to 36% cheaper than commercial alternatives) with adequate strength and water absorption for construction (Falade, Ikponmwasa and Fapohunda, 2013).
MILLED LAMB BONE
Lamb bone is naturally hyper-porous, with macro and micro pores of varying sizes. Based on the precedent studies we assume that the lamb bone would have a surface area of around 900 m2/g and a pore volume of 0.357ml/g. Average pore radius was expected to be roughly 8 Angstroms. Based on this, we expected that raw lamb bone would be able to provide adsorption but could potentially be increased through by calcining it before milling.
MILLED LAMB BONE AFTER ADSORPTION
It was not expected that adsorption of dyes would radically change the structural performance of ground bone particles as the aggregate in our composite. However, the particles would need to be well dried before being bound into the resin matrix to ensure proper curing of the resin. Furthermore, the dye coated milled bone would potentially be toxic, having taken on the dye. We were unsure as to whether the bone would be discoloured by the process, leaving open a potential aesthetic opportunity.
Various dyes were used in our experimentation. Natural indigo, obtained from India and Reactive Blue Fabric Dye, purchased in London. Natural indigo is extracted from Indigofera, a tropical plant. It is produced from a colourless amino-acid called Indican which hydrolyzes to produce glucose and indoxyl, which after oxidation produces the typical Indigo colour. Reactive Blue belongs to the family of reactive dyes – organic dyes that fix to fibres through covalent bonding. It was hoped that this chemical property would assist in the attraction between dissolved dye molecules and the bone particle surface.
Polyester Resin is a thermosetting plastic commonly used as a structural matrix in composite materials (particularly in the marine industry). The initial liquid state of the matrix before curing would allow us to completely encase our lamb-bone samples, whilst maintaining transparency to enable the material to take on the visual properties of the bone powder.
Bone was obtained from a local butchers and boiled for 8 hours to remove all excess meat and fat. The bones were washed and scoured under pure water until all visual signs of flesh were removed. The bones were then dried overnight at 100 degrees in an oven, then left in open air for 3 days for further drying to ensure we would get a powder on crushing rather than a sludge. Once dry, we manually broke the bone into small pieces. Half of our samples were calcined using a propane torch, so that we could assess the performance difference between burned and unburned bone. The bone samples were then ground to a fine powder in a commercial coffee grinder.
100ml samples of water with 2-3mg of the two test dyes (natural indigo and reactive blue) were used as tests. A control sample of water was kept in each case as a visual reference. Increasing quantities of both burned and unburned bone were mixed into the various solutions until colour change was noticed. The saturated bone samples were then removed from the liquid through filtration through tissue paper. These samples were then dried and mixed into liquid polyester resin. The lightweight nature of each of the particles and the viscosity of the setting resin ensure that the particulates remained suspended in the block with uniform distribution throughout the curing process.
GEOMETRY OF THE COMPOSITE
As our primary objective was to achieve adsorption, geometry was most relevant to us at the micro-scale. Based on precedent electron-microscopy imagery we produced a 3D model of a bone particle to visualise the high surface area nature of a hyper-porous material. It is the complex, folded geometric organisation inherent to bone that determined the success of our experimentation.
PROPERTIES OF THE COMPOSITE
The following images document the varying levels of dye removal we were able to achieve via bone adsorption. Unfortunately, due to limitations in the technology we had access too, our method for assessing dye removal was visual (electron microscopy and spectrometry were unavailable to us within our timeframe). To maintain some rigour in our analysis, we used a light table to light all our experiments evenly and recorded from a fixed location on a DSLR with fixed aperture, white balance, exposure and shutter speed. We then used RGB colour sampling of stills extracted from our recordings to compare the relative success of each of our tests. Some factors could potentially cloud our results, including discolouration added to the water from impurities in the bone samples, and limitation of light penetration into the water due to shadows cast by the particulates in water.
It was found that the most notable visual difference occurred when unburned bone was mixed with a dyed solution containing reactive blue in equal amounts (1 part bone to 1 part contaminated water). However, we suspect that the burned bone may have provided similar (if not better) results were it not for the fact that we did not clean the samples after calcination. A yellow discolouration occurred (although it appeared that the blue colour was removed from the water) which we believe may have been caused by ash created in the burning process.
When bound in resin, the resultant composite is a durable brick which can be polished to a smooth matte finish. In the case of the burned bone, the brick takes on an aesthetically pleasing neutral black colour. Unfortunately no discolouration of the bone itself was observable from the adsorption process, however we believe it is still reasonable that the composite could serve well as a finishing material for interior and exterior applications.
We initially speculated that the composite would be best suited as an aesthetic tile – perhaps used as a surface treatment in wet areas in residential buildings or as a feature piece on joinery – as counter tops, splashbacks or potentially even as a façade finish. However, there is also the possibility that the material, if bound in a breathable matrix might be able to continue functioning as an adsorbent (perhaps in air). If so (and of course this would depend on further experimentation) there could be the potential for the composite to adsorb contaminants in air, making it an ideal surface treatment on building facades in polluted urban areas, or inside specific building typologies with a need for clean air – hospitals, kitchens, laboratories etc. Whilst purely speculative, these applications bring an exciting set of possibilities to future iterations of this project.
CONCLUSIONS & FUTURE DEVELOPMENTS
We believe the experimentation covered here only scratches the surface of the potential for Tainted Bone. The project demonstrates that there could be significant financial motivation (through the creation of a new aesthetic finish for consumer countries) for positive environmental landscape change in the sites to which our waste materials are native – the leather tanneries of Hazaribagh and the contaminated rivers of Pali. Furthermore our choice in binding matrix for our composite was potentially restrictive for continued adsorption within our material. Possible future development would include a more detailed analysis of the observed adsorption process (through electron microscopy) and experimentation with binding the bone particles in a porous matrix – potentially aerated concrete. A potential problem is that while this would free up the particles to continue having contact with air/water allowing them to adsorb contaminants continuously, it would also involve continuous exposure of the particles to inhabited spaces – exposing humans to the toxic contaminants adsorbed.
However, given the short time frame and low-tech fabrication methodologies involved, we believe that Tainted Bone is a successful proof of concept composite, with potential to choreograph real and positive change in its polluted sites of production. It is a material with more than the story of its making embedded in its structure. It implies a whole new attitude toward environmental responsibility and materiality, poetically distributing the waste products unknowingly catalysed by consumer societies back into the homes of consumers.
Ebrahimi, A., Arami, M., Bahrami, H. and Pajootan, E. (2013). Fish Bone as a Low-Cost Adsorbent for Dye Removal from Wastewater: Response Surface Methodology and Classical Method. Environ Model Assess, 18(6), pp.661-670.
El Haddad, M., Slimani, R., Mamouni, R., ElAntri, S. and Lazar, S. (2013). Removal of two textile dyes from aqueous solutions onto calcined bones. Journal of the Association of Arab Universities for Basic and Applied Sciences, 14(1), pp.51-59.
Falade, F., Ikponmwosa, E. and Fapohunda, C. (2013). Low-Cost Construction through the Use of Pulverized Bone Foamed Aerated Concrete (PB-FAC). Civil and Environmental Research, 3(10), pp.107-113.
Lenntech.com. (2016). Adsorption / Active Carbon. [online] Available at: http://www.lenntech.com/library/adsorption/adsorption.htm [Accessed 15 Mar. 2016].
Shehata, A. (2013). Removal of Methylene Blue Dye from Aqueous Solutions by Using Treated Animal Bone as a Cheap Natural Adsorbent. International Journal of Emerging Technology and Advanced Engineering, 3(12), pp.507 - 513.
Shoba, J. (n.d.). Value Added Products from Gasification: Activated Carbon.
Srubar, W. and Billington, S. (2013). PHBV/Ground Bone Meal and Pumice Powder Engineered Biobased Composite Materials for Construction. US 8,507,588 B2.