Transforming the resource base: new bioplastics

Poly(lactic acid) combined with nylon-11, a polymer from castor oil, creates a new family of 100 renewable plastic materials.Plastics is the third largest industry in the United States with an annual value of goods shipped exceeding $374 billion.1 It employs…

Poly(lactic acid) combined with nylon-11, a polymer from castor oil, creates a new family of 100 renewable plastic materials.Plastics is the third largest industry in the United States with an annual value of goods shipped exceeding $374 billion.1 It employs 1.1 million workers in 18,500 facilities distributed across the country.2 Large quantities of petroleum (roughly 10% of the total) are used to produce plastics, but global development is making oil more expensive.3 Importantly, significant pollution results from the manufacture, use, and disposal of plastic materials, and greenhouse gases such as carbon dioxide are now a primary concern. Moreover, as the Gulf of Mexico oil spill demonstrates, the increased demand for petroleum is forcing us to drill under challenging offshore conditions and in environmentally sensitive areas. Simultaneously, carbon-intensive lower-grade ‘heavy’ crude oils like the Canadian tar sands are being increasingly used. However, plastics offer profound societal benefits, including increased agricultural production, reduced food spoilage, reduced fuel consumption in lighter-weight vehicles, better health care, and low-cost net shape manufacturing. We need plastics, but a lack of truly sustainable practices is a real threat to our long term well-being.Colleagues and I have been working to assist a transition to more sustainable plastic materials with quantitatively better environmental performance as measured using life cycle analysis (LCA). For example, LCAs for poly(lactic acid) (PLA) show reductions in both fossil fuel use and global warming potential.4–6 Compared to the common polymer polyethylene terephthalate (PET), PLA uses 30–50% less fossil resource and emits 50–70% less carbon dioxide. However, PLA alone does not have all of the properties needed for the multitude of applications in which plastics are used. Accordingly, blending PLA with other polymers is an important undertaking and a number of blends have been reported. Unfortunately, by blending with petroleum-based plastics, some of the sustainability advantages of the material are lost. We combined PLA with poly(undecanoic acid) also known as polyamide-11(PA11) or nylon-11. This polyamide is produced using renewable castor oil as the feedstock, so the blends produced are 100% biorenewable. (It is worth noting that the use of renewable resources is one of the 12 key principles of green chemistry.7)Figure 1.Field emission scanning electron microscopy images of base etched for poly(lactic acid) blends with polyamide-11 (PA11, also known as nylon-11) prepared at 205°Cwith 20min of melt-blending time: compositions of (a) 25/75; b) 50/50; and (c) 75/25wt%.We used a specialized reactive blending approach to melt blend PA11 with polylactide(PLA), with titanium isopropoxide as a catalyst to investigate potential compatibilizing reactions. We measured blend properties using differential scanning calorimetry (DSC), thermo-gravimetric analysis (TGA), dynamic mechanical thermal analysis (DMTA), and tensile and impact testing. DSC shows two separate glass transition temperatures indicating only partial miscibility. As shown in Figure 1, base etching to remove PLA domains followed by field emission scanning electron microscopy (FE-SEM) confirms the two-phase nature of the blends. Two phases are observed in each of the blends, confirming the basic immiscible nature of the PLA/PA11 blends. A ‘droplet morphology’ is observed in all the blends with a continuous matrix or ‘major’ phase and a separate dispersed or ‘minor’ phase. For example, in the 25/75wt% PLA/PA11 blend, the PLA is the minor phase dispersed in the PA11 major phase matrix. The PLA phase appears as small holes because of the base etching procedure. Similarly, the 50/50wt% blend shows a minor PLA phase due to its greater density, and therefore smaller volume. At 75wt% PLA, the morphology is very different. The etching procedure removes the major phase, and distinct droplets of the PA11 of approximate size 0.5–1μm are observable. Accordingly, Figure 1 reveals the transition from a PA11 major phase to a PLA major phase as the proportion of PA11 increases.We also investigated mechanical properties and found that the storage and tensile moduli of the blends increase monotonically with increasing PLA content. Values of shear and the elongation modulus as well as tensile strength show close to monotonic behavior with blend composition. Toughness and impact strength are relatively insensitive to composition. These later trends are attributed to a poorly compatibilized two-phase morphology. We used carbon-13 nuclear magnetic resonance spectroscopy to further investigate the compatibilization and interchange reactions during reactive mixing.8 The analysis shows little evidence of interchange reactions. At the upper end of the temperature range investigated, significant degradation is observed. The combined results indicate that degradation reactions dominate over compatibilizing reactions.In summary, there is an increasing interest in 100% biorenewable plastics, thanks to a number of factors.9We used reactive blending to develop such materials from PLA/PA11 polymer blends. Intermediate physical properties between the two homopolymers were observed, but degradation limited the improvements possible. Given the increasing number of new biobased plastics originating out of biotechnological routes to renewable monomers, there is a vital need to investigate various blends and nanocomposites from new and novel materials. Our activities encompass permeation,10–13rheological,8,14–18 and processing studies.19–23 We have investigated the use of biobased cellulosic nanowhiskers24,25 to make 100% biodegradable nanocomposites26 and developed other novel supramolecular systems.27–31 Recently, we have been investigating biorenewable blends of different types of polyamides (nylons) and have found that such blends have properties that are superior to the individual homopolymers. These studies will appear in the near future. Given the pressing needs for humanity to develop systems to meet the grand challenges of sustainability, the field of biorenewable plastic materials is sure to see significant developments in the years ahead.AuthorJohn R. DorganColorado School of Mines (CSM)Professor Dorgan is a member of the faculty. He holds a BS from UMass Amherst and a PhD from the University of California, Berkeley, both in chemical engineering. His postdoctoral studies were completed at the Max Planck Institute for Polymer Research, Mainz, Germany. He is a past-president of the Bioenvironmental Polymer Society.ReferencesR. Patel, D. A. Ruehle, J. R. Dorgan, P. Halley and D. Martin, Biorenewable blends of polyamide-11 and polylactide, Polym. Eng. Sci., 2013. Published online in advance of print Size and Impact of the U.S. Plastics Industry, 2010. Executive Summary available at http://www.plasticsindustry.org/AboutPlastics/content.cfm?ItemNumber=787&navItemNumber=1280.K. S. Deffeyes, Hubbert’s Peak: The Impending World Oil Shortage, Princeton University Press, 2001. E. T. H. Vink, D. A. Glassner, J. J. Kolstad, R. J. Wooley and R. P. O’Connor, The eco-profiles for current and near-future NatureWorks®
polylactide (PLA) production, Indust. Biotechnol. 3, pp. 58-81, 2007. E. T. H. Vinka, K. R. Rá bago, D. A. Glassner and P. R. Gruber, Applications of life cycle assessment to NatureWorks polylactide (PLA) production, Polym. Degrad. Stabil. 80, pp. 403-419, 2003. M. Weiss, J. Haufe, M. Carus, M. Brandão, S. Bringezu and B. Hermann, A review of the environmental impacts of biobased materials, J. Ind. Ecol. 16, pp. S169-S181. P. T. Anastas and J. C. Warner, Green Chemistry: Theory and Practice, Oxford University Press, New York, 2000. J. R. Dorgan, J. Janzen, D. M. Knauss, S. B. Hait, B. R. Limoges and M. H. Hutchinson, Fundamental solution and single-chain properties of polylactides, J. Polym. Sci. B: Polym. Phys. 43, pp. 3100-3111, 2005. J. R. Dorgan, H. J. Lehermeier, L. I. Palade and J. Cicero, Polylactides: properties and prospects of an environmentally benign plastic from renewable resources, Macromol. Symp., pp. 55-66, 2001. N. Oliveira, J. Dorgan, J. Coutinho, A. Ferreira, J. Daridon and I. Marrucho, Gas solubility of carbon dioxide in poly (lactic acid) at high pressures, J. Polym. Sci. B: Polym. Phys. 44, pp. 1010-1019, 2006. N. Oliveira, J. Dorgan, J. Coutinho, A. Ferreira, J. Daridon and I. M. Marrucho, Gas solubility of carbon dioxide in poly (lactic acid) at high pressures: Thermal treatment
effect, J. Polym. Sci. B: Polym. Phys. 45, pp. 616-625, 2007. N. Oliveira, C. Goncalves, J. Coutinho, A. Ferreira, J. Dorgan and I. Marrucho, Carbon dioxide, ethylene and water vapor sorption in poly(lactic acid), Fluid Phase Equil. 250, pp. 116-124, 2006. N. S. Oliveira, J. Oliveira, T. Gomes, A. Ferreira, J. Dorgan and I. Marrucho, Gas sorption in poly (lactic acid) and packaging materials, Fluid Phase Equil. 222, pp. 317-324, 2004. J. R. Dorgan, J. Janzen, M. P. Clayton, S. B. Hait and D. M. Knauss, Melt rheology of variable L-content poly(lactic acid), J. Rheol. 49, pp. 607, 2005. J. R. Dorgan, H. Lehermeier and M. Mang, Thermal and rheological properties of commercial-grade poly (lactic acid) s, J. Polym. Env. 8, pp. 1-9, 2000. J. R. Dorgan, J. S. Williams and D. N. Lewis, Melt rheology of poly (lactic acid): Entanglement and chain architecture effects, J. Rheol. 43, pp. 1141, 1999. H. J. Lehermeier and J. R. Dorgan, Melt rheology of poly (lactic acid): Consequences of blending chain architectures, Polym. Eng. Sci. 41, pp. 2172-2184, 2001. L.-I. Palade, H. J. Lehermeier and J. R. Dorgan, Melt rheology of high L-content poly (lactic acid), Macromolecules 34, pp. 1384-1390, 2001. J. A. Cicero and J. R. Dorgan, Physical properties and fiber morphology of poly(lactic acid) obtained from continuous two-step melt spinning, J. Polym. Env. 9, pp. 1-10, 2001. J. A. Cicero, J. R. Dorgan, S. F. Dec and D. M. Knauss, Phosphite stabilization effects on two-step melt-spun fibers of polylactide, Polym. Degrad. Stabil. 78, pp. 95-105, 2002. J. A. Cicero, J. R. Dorgan, J. Garrett, J. Runt and J. S. Lin, Effects of molecular architecture on two-step melt-spun poly(lactic acid) fibers, J. Appld. Polym Sci. 86, pp. 2839-2846, 2002. J. A. Cicero, J. R. Dorgan, J. Janzen, J. Garrett, J. Runt and J. S. Lin, Supramolecular morphology of two-step melt-spun poly(lactic acid) fibers, J. Appl. Polym Sc 86, pp. 2828-2838, 2002. B. Braun, J. R. Dorgan and S. F. Dec, Infrared spectroscopic determination of lactide concentration in polylactide: An improved methodology, Macromolecules 39, pp. 9302-9310, 2006. B. Braun and J. R. Dorgan, Single-step method for the isolation and surface functionalization of cellulosic nanowhiskers, Biomacromolecules 10, pp. 334-341, 2009. B. Braun, J. R. Dorgan and J. P. Chandler, Cellulosic nanowhiskers. theory and application of light scattering from polydisperse spheroids in the Rayleigh-Gans-Debye regime, Biomacromolecules 9, pp. 1255-1263, 2008. B. Braun, J. R. Dorgan and L. O. Hollingsworth, Supra-Molecular EcoBioNanocomposites Based on Polylactide and Cellulosic Nanowhiskers: Synthesis and Properties, Biomacromolecules 13, pp. 2013-2019, 2012. M. J. Sobkowicz, B. Braun and J. R. Dorgan, Decorating in green: surface esterification of carbon and cellulosic nanoparticles, Green Chem. 11, pp. 680-682, 2009. M. J. Sobkowicz, J. R. Dorgan, K. W. Gneshin, A. M. Herring and J. T. McKinnon, Renewable cellulose derived carbon nanospheres as nucleating agents for polylactide and polypropylene, J. Polym. Env. 16, pp. 131-140, 2008. M. J. Sobkowicz, J. R. Dorgan, K. W. Gneshin, A. M. Herring and J. T. McKinnon, Controlled dispersion of carbon nanospheres through surface functionalization, Carbon 47, pp. 622-628, 2009. M. J. Sobkowicz, J. R. Dorgan, K. W. Gneshin, A. M. Herring and J. T. McKinnon, Supramolecular bionanocomposites: grafting of biobased polylactide to carbon nanoparticle surfaces, Austral. J. Chem. 62, pp. 865-870, 2009. M. J. Sobkowicz, E. A. White and J. R. Dorgan, Supramolecular bionanocomposites 3: Effects of surface functionality on electrical and mechanical percolation, J. Appl. Polym. Sci. 122, pp. 2563-2572, 2011. DOI:  10.2417/spepro.005111

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