Development of High Performance Cashew Nut Shell Liquid (CNSL) Based Surface Coatings Cross Linked with Styrene and Methyl Methacrylate

Abstract

The unmitigated volume of cashew nut shells produced annually along the production line poses a challenge for waste disposal. In Kenya the waste cashew nut shells are used as fuel which results in heavy pollution to the environment through emission of heavy dark smoke with particulate matter. Cashew nut shell liquid (CNSL), is a dark reddish brown liquid extracted from cashew nut shells and is an excellent source of natural resins. Therefore, it is wise to extract as much of the CNSL prior to disposal. This will ultimately help reduce the environmental load for the residual portion of the shell. It is hoped that this project will contribute significantly towards addressing this problem and reversing the trend. Being renewable, CNSL offers much advantage over synthetic materials. This research aimed at developing high performance surface coatings based on cross linking CNSL by means of suitable monomers such as styrene and Methyl Methacrylate (MMA). A high performance resin was formed by addition of formaldehyde to a solvent solution of CNSL in the presence of a catalyst and modified with styrene and MMA at different mole ratios. Tests for pH, viscosity, relative density, adhesion, pencil hardness and drying time were determined using the simulated standard procedures of the Association of Official Analytical Chemists (AOAC) and American Society for Testing and Materials (ASTM). Both physico-chemical and performance characteristics of the formulations were compared with the standards and conclusions were drawn. The results indicated that the estimated relative density (0.8691kg/m3) of CNSL-based coating compared to that of standard commercial coating (0.9294kg/m3). The FTIR analysis established that decarboxylation of raw CNSL was successful because both the ῡmax O-H stretch and ῡmax C=O symmetrical stretch of the Carboxylic acid having ῡmax O-H, at 2596.0 cm-1 and ῡmax C=O at 1647.1 cm-1 frequencies respectively had been cleared. The average pH (6.07) of CNSL-based coating also compared well to the standard (6.08). The optimization of temperature and heating time was determined using physico-chemical and performance characteristics and temperature of 70oC and heating time of 60 minutes were taken to be the optimum conditions. Polymerization was carried out under optimum conditions. Cross linking of the CNSL based coating with Styrene and MMA monomers, gave formulations with performance characteristics either improving or lowered, both adhesion and drying time properties were improved on different ratios of monomers that were added. Styrene monomers at lower ratios performed better in terms of adhesion and drying time, while MMA produced better formulations at higher ratios. Hardness characteristics for cross linked formulations were lowered compared to the standard. Generally, cross linking improved some performance characteristics and affected other characteristics negatively. Depending on the use of a given polymer, a suitable monomer can be used to effect the desirable performance characteristics. Successful implementation of the project would result into cleaner environment, job creation, increased returns to both producers and processors of the cashew nuts and net saving of foreign exchange to the country among other benefits. This research work was very successful as evidenced by the good results obtained. The study however, recommends further research to be done to determine other performance characteristics such as, impact resistance, corrosion resistance, flexibility and gloss.