The multi-level engineering principles can serve as guideline to develop engineering routes for the mass production of CNTs. CNTs with tunable wall number, super-long length, and a low cost have been available for many researchers. Their large-scale applications have been successfully explored and related CNT based products have been well developed. As a replacement of high performance carbon black, high conductive CNTs with thousands of production capacity have been commercially used in Li ion battery and nanocomposites, which offers the opportunity for rapid growth of CNT industry.
The CNT industry is growing rapidly, and more and more kinds of CNTs are now available from the markets to explore and commercialize new type of CNT products. The engineering science summarized in this review intended to provide the methodology and guideline for CNT production in a sustainable way.
The high end use based on bulk CNTs for Li ion batteries is a great success. However, the CNTs for limited add value products (e.g. tyres, conductive plastics for pipes, absorbent) is still hindered by its high prices: the available MWCNTs are still expensive than bulk chemical products and other raw materials (such as normal carbon blacks, PE, PP, PET, PI, PC, etc.). Compared with traditional bulk chemicals, the controllable synthesis and large-scale applications (on the order of millions of tons) of CNTs is still far from being achieved because of the difficulty of both synthesis and the subsequent product treatments. The CNT synthesis with controllable chirality, super-alignment, and predetermined size and length still remains great challenges.
Furthermore, the strong coupling among CNT structures, production processes, properties, post-treatments, and applications are still difficulties for the production of certain type CNTs. Environment, health, safety, and ecological considerations for CNTs also must be considered to ensure the development of intrinsically safe, high efficiency, and economical processes. The growth of CNT industry also brings new concept for traditional materials industry.
Up to now, many delicate scientific research works have been carried out for CNT industry while few industrial trials have been set up. There is still a huge gap between the basic scientific research and industrial development. The CNTs are an extraordinary structural platform to demonstrate the power of nanotechnology. With multidisciplinary scientific researches, the production of advanced CNT-based materials can help us to develop a wonderful and sustainable society.