Synthesize of crumb rubber using pulsed laser ablation in liquid

Abstract

A novel crumb rubber production technique incorporating laser technology is introduced as an alternative to mechanical grinding and cryogenic processing techniques. This technique offers solution to major drawbacks of the existing techniques in terms of the size of the crumb rubber particles. The effectiveness of utilizing the produced crumb rubber as oil absorbent applied in oil spilled recovery application has been explored. A nanosecond Nd:YAG pulse laser with 1064 nm wavelength was used as a light source in the pulse laser ablation in liquid (PLAL) technique. The rubber target used in this work is a piece of scrap tyre immersed in the liquid medium comprising acidic, neutral and base solutions. Two chosen acidic solutions were the D-limonene and acetic acid, while sodium hydroxide (NaOH) and sodium chloride (NaCl) were selected for base solutions. A high-speed photography system with femtosecond laser and CCD camera was used to capture the mechanism involving the crumb rubber production. This technique was successfully conducted in producing finer crumb rubber particles. The shock wave and water jet from the cavitation bubble were identified as the main mechanisms responsible for the fragmentation of rubber surface after interacting with laser. The highest concentration of crumb rubber (1.97 g ml-1) was achieved in acetic acid solution generated with 300 mJ laser pulse at repetition rate of 3 Hz. Ablation of rubber sample in NaOH solutions produced crumb rubber particles with average diameter about 12000 mesh (1.44 μm) which is smaller than the average size of crumb rubber produced from conventional techniques. The energy-dispersive X-ray spectroscopy analysis indicated that crumb rubber consists of carbon, oxygen, zinc, sulphur and silicon which is similar to the element composition of the target sample. Results from field-emission scanning electron microscope showed that the generated crumb rubber particles have irregular shape. The crumb rubber was then immersed into cooking oil and illuminated by a diode pumped solid state laser to measure the oil absorption efficiency. The absorption was found to be dependent on two main parameters namely the crumb rubber size and the time interaction. Crumb rubber particles with average diameter 10, 60 and 3650 mesh were tested, and the measured absorption coefficients were 485 m-1, 769 m-1 and 2906 m-1 respectively. This result shows that smaller crumb rubber particles have higher absorption coefficients. In conclusion, controllable, safe and environmental friendly technique of crumb rubber production based on PLAL is a promising technique to be used in oil spill recovery.