1. Field of Invention
This invention relates to a novel process for sustainable materials development that combines polymer recycling with a new method in renewable polymer synthesis to achieve nanocomposite polymeric products with high-performance material capabilities. This process enables the simultaneous densification, purification, and recycling of polymeric substrates in a “one-pot” procedure. The invention includes solvent chemical compositions, polymeric formulations, recycling procedures, methods of synthesis, and fabrication methods of end-product recycled polymers.
2. Background
As consumer demands drive increased global production of plastic products and waste, the need for innovative strategies for improving environmental sustainability continues to grow. As long as non-environmentally degradable plastics are produced, the development of improved recycling techniques must continue in order to decrease additional material consumption and to reduce non-degradable plastic waste content in landfills. (W. Mueller, Waste Management 2013, 33, 508). There is hope that progress in polymer science will eventually give rise to alternative plastic materials that may eliminate the need for the production of petroleum-based and other non-degradable plastics altogether, and recent studies have investigated the development of naturally based polymers (C. J. Besset, A. T. Lonnecker, J. M. Streff, K. L. Wooley, Biomacromolecules 2011, 12, 2512), (P. A. Wilbon, F. Chu, C. Tang, Macromolecular Rapid Communications 2013, 34, 8), (Yao, C. Tang, Macromolecules 2013, 46, 1689).
One drawback that often surrounds sustainable materials development is the seemingly pervasive notion that improving the environmental suitability of materials comes with a sacrifice in material functionality. (H. Lewis, in Packaging for Sustainability, (Eds: K. Verghese, H. Lewis, L. Fitzpatrick), Springer London, 2012, 41). Studies reporting material selection strategies often weigh material capabilities against environmental sustainability, (T. Tambouratzis, D. Karalekas, N. Moustakas, Journal of Industrial Ecology 2013, 10.1111/jiec.12035), and many recycling processes in general are assumed to bring about some degree of material deterioration. (S. Rajendran, L. Scelsi, A. Hodzic, C. Soutis, M. A. Al-Maadeed, Resources, Conservation and Recycling 2012, 60, 131).
The present invention is based on an alternative premise, that the development of new sustainable materials with increased inherent value (i.e., well-engineered, value-driving material properties) is possible through innovative design at the materials engineering level. The successful bulk synthesis of a new naturally-derived polymer system is disclosed and mechanical properties in this polymer system are tailored and improved through the addition of recycled polymer additives to yield polyphasic nanocomposite products. The disclosed process enables the simultaneous densification, purification and reclamation of polymeric waste, and the reclamation step is achieved utilizing a breakthrough development in renewable polymer synthesis.
The present invention, although applicable to numerous recyclable polymers and corresponding solvent/monomer/co-monomer formulations, is demonstrated through a process for recycling expanded polystyrene (EPS) waste. The difficulties associated with EPS recycling have been widely publicized. It is estimated that over 3 million tons of EPS are produced each year globally, with roughly 70% of EPS products being single-use food and beverage packaging. (J. A. Bhatti, Columbia University, 2010). Because both transporting low-density EPS waste and cleaning it to remove contaminant residue greatly increase cost and time required for EPS recycling, an overwhelming majority of food-contaminated EPS waste (e.g., an EPS cup with residual soda inside it) is not recycled. (M. Boatwright, S. Leonard, M. McDanel, K. Raleigh, E. Wright, L. Barlow, 2010; S. M. Al-Salem, P. Lettieri, J. Baeyens, Waste Management 2009, 29, 2625).
EPS recycling is often sub-categorized using three groups: (1) material recycling, the reduction of EPS volume using compression or dissolution in solvent; (2) chemical recycling, the breaking of covalent bonds to re-generate monomers or other small molecules; and (3) thermal recycling, the combustion of EPS waste to generate energy. (A. Kan, R. Demirbo{hacek over (g)}a, Journal of Materials Processing Technology 2009, 209, 2994; T. Maharana, Y. S. Negi, B. Mohanty, Polymer-Plastics Technology and Engineering 2007, 46, 729). The present invention focuses on material recycling processes. Traditionally, the most cost-effective method of recycling EPS has been to heat non-contaminated EPS waste above its glass transition and/or compact it to produce densified, recycled polystyrene. Since mechanical densifiers require that EPS be contaminant free before compaction, mechanical densification is not ideal for recycling food or drink contaminated waste items and not practical for recycling the roughly 70% of EPS waste that is used for single-used food and beverage packaging.
It is known that an alternative material recycling method for EPS is a solvent-based approach, in which clean EPS waste is dissolved in a suitable organic solvent such as acetone. The dissolution process results in the densification of the EPS waste, and the removal of the solvent affords recycled polymeric products. Solvent-based recycling has been shown to be suitable for some contaminated EPS substrates because many contaminants are insoluble in solvents that dissolve EPS and can be removed using coarse filtration after EPS dissolution. (J. M. Seo, B. B. Hwang, “A Reappraisal of Various Compacting Processes for Wasted Expandable Polystyrene (EPS) Foam”, presented at Materials Science Forum, 2006). The solubility and behavior of EPS in multiple solvents has been previously reported. (M. T. García, I. Gracia, G. Duque, A. d. Lucas, J. F. Rodríguez, Waste Management 2009, 29, 1814; S. Shikata, T. Watanabe, K. Hattori, M. Aoyama, T. Miyakoshi, J Mater Cycles Waste Manag 2011, 13, 127). Polystyrene has been shown to be especially soluble in aromatic solvents such as toluene, and studies have also reported the solubility of PS in the naturally occurring citrus fruit extract D-limonene, (R. T. Mathers, K. C. McMahon, K. Damodaran, C. J. Retarides, D. J. Kelley, Macromolecules 2006, 39, 8982) which has a similar dielectric constant to that of toluene. (G. A. Thomas, J. E. Hawkins, Journal of the American Chemical Society 1954, 76, 4856). In the late 1990's and early 2000's Sony Corporation instituted a solvent-based recycling effort in Japan, in which D-limonene was used to recycle EPS waste, which was reclaimed from solution by evaporation of D-limonene. Sony's report of this recycling process is extremely in-depth, but this recycling effort appears to have been abandoned sometime between 2004 and 2006. (T. Noguchi, M. Miyashita, Y. Inagaki, H. Watanabe, Packaging Technology and Science 1998, 11, 19). Considering the low inherent value of recycled polystyrene, Sony's apparent decision to cease this recycling effort may have been financially motivated. Other studies have reported limonene-based recycling processes in which PS is reclaimed from solution in limonene using electrospinning or by precipitation by mixing with supercritical carbon dioxide. (C. Shin, G. G. Chase, Polymer Bulletin 2005, 55, 209 and C. Gutiérrez, M. García, I. Gracia, A. Lucas, J. Rodríguez, J Mater Cycles Waste Manag 2012, 14, 308).
The present invention is based on an alternative premise; that the development of new sustainable materials with increased inherent value (i.e., well-engineered, value-driving material properties) is possible through innovative design at the materials engineering level.