Article pubs.acs.org/IECR
Potential of a Pyrolytic Coconut Shell as a Sustainable Biofiller for Styrene−Butadiene Rubber Yiran Fan,*,† Geoffrey D. Fowler,*,† and Chris Norris‡ †
Department of Civil and Environmental Engineering, Imperial College London, London SW7 2AZ, United Kingdom Artis Ltd., Hampton Park West, Semington Road, Melksham, Wiltshire SN12 6NB, United Kingdom
‡
ABSTRACT: This paper presents research undertaken on pyrolytic coconut shell char to evaluate its potential as a sustainable and renewable substitute filler for carbon black in rubber. Carbon black is the most widely used filler in rubber. Its manufacture from nonrenewable feedstock is unsustainable and energy-consuming and contributes significantly to global CO2 emissions. The pyrolytic properties of coconut shell were evaluated; response surface methodology was applied to model the relationship between the pyrolysis conditions and char properties. Coconut shells were pyrolyzed using a laboratory-scale furnace under various temperatures (400−800 °C), residence times (0−2 h), and atmospheric flow rates. Comparisons were made between the char and commercial carbon blacks for their physical and chemical properties (surface area and pH). Comparable char pH and surface area properties were achieved (optimal char exhibited 300 m2/g surface area). Selected samples were tested in-rubber, with the performance of the filled styrene−butadiene rubber showing 2 MPa at M100%.
1. INTRODUCTION Carbon black is widely used as a filler and additive in the fields of rubber and materials production. Over 12 million tonnes of carbon black are used every year in tire manufacture alone. The carbon filler in rubber can make up over 30% of the material by weight. The key property of the filler is its ability to bond with rubber components, hence providing mechanical strength as well as imparting durability to the material.1 However, the methods used to manufacture carbon black require the partial combustion of fossil-origin hydrocarbon fuels (heavy oil, coal tars, etc.) under reduced oxygen conditions. Not only is this energy-intensive, it is unsustainable in the long term as a source of feedstock to make carbon black. Given the increasing pressures toward the cessation of using nonrenewable feedstock in industrial and manufacturing processes, through the adoption of a circular economy model, there is an exciting and innovative opportunity to develop alternative materials to act as rubber fillers. Recently, more and more attention has been given to “green” fillers, which come from industrial byproducts and other waste materials having potential “renewability”.2 The use of biobased fillers would further help to reduce the dependence upon fossil fuel and move toward a sustainable material basis for rubber filler production. © XXXX American Chemical Society
It is widely known that coconut shell can be used as a biofuel and is also a commercial source of charcoal and activated carbon. In fact, the activated carbon made from coconut shell is considered to be superior to those obtained from other feedstock because of its highly microporous and complementary mesoporous structure. In particular, the mesopores make it potentially suitable for in-rubber applications. Thus, research into this potential application for coconut shell char is needed.3−6 With the aforementioned pressures on reducing waste disposal and a growing emphasis on resource recovery, more and more attention has been paid to reusing materials that would otherwise be discarded. There have been several studies reported in the literature using alternative materials as fillers in rubber materials, although most of this work has focused on using recovered rubber, pyrolytic rubber, or naturally occurring materials such as lignin, nut shells, egg shells, fly ash, or rice husks.2,7−10 The results show that the performance of the “green fillers” in the rubber matrix and the production Received: Revised: Accepted: Published: A
January 27, 2017 April 6, 2017 April 10, 2017 April 10, 2017 DOI: 10.1021/acs.iecr.7b00405 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX
Article
Industrial & Engineering Chemistry Research requirements have limited their application in rubber manufacturing. Only under some production conditions can a comparable performance be achieved; for example, the tensile strength of a rubber material containing 20 phr of treated rice husk ash can reach 26.0 MPa compared to 22.0 MPa obtained by commercial carbon black N774.2 The physical properties, such as the tensile strength and modulus, obtained by these papers indicate that the fillers can be grouped as semi- to nonreinforcing fillers. This paper reports for the first time an analysis of coconut shell char as a novel and sustainable filler for rubber and related materials.
Table 1. Proximate Analysis Protocol temperature (°C)
2. MATERIALS AND EXPERIMENTS 2.1. Materials. 2.1.1. Coconut shell. The coconut shells used in this project had already been broken into random large pieces (approximately 15 mm × 15 mm) by the supplier and were further crushed using a laboratory-scale hammer mill (Glen Creston, U.K.) in order to pass a 10 mm screen. The small pieces of coconut shell were then dried at 105 °C to constant weight. 2.1.2. Commercial Carbon Black. Two commercial carbon black samples to be used as the reference materials in this research were sourced from the manufacturers: N330 (Cabot Corp.) and N772 (Degussa AG). Both of the samples are made using the furnace procedure and received in pellet form. Type N330 is a highly active furnace black, which is widely used in the manufacture of tires showing good wear resistance. It was used as the reference material in the later in-rubber tests. Type N772 belongs to the family of low-dispersion, middle-active grades of carbon black. It can give the mixtures high elasticity and superior dynamic performance when used in tire frames and technical rubber products.11 2.2. Experiments. 2.2.1. Thermal Analysis of Coconut Shell. Thermogravimetric analysis (TGA) was used to identify some of the key pyrolysis parameters, such as the most suitable temperature(s) and heating rates, for the raw feedstock to produce char fillers. The thermal analysis experiments were carried out using a Rheometric Scientific STA 1500 simultaneous [TGA/differential scanning calorimetry (DSC)] thermal analyzer. For TGA, approximately 15 mg of the ground coconut shell sample (
