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Extramural Research

Final Report: Environmentally Benign Polymeric Packaging from Renewable Resources

EPA Grant Number: R826733
Title: Environmentally Benign Polymeric Packaging from Renewable Resources
Investigators: Dorgan, John R. , Knauss, Daniel M.
Institution: Colorado School of Mines
EPA Project Officer: Richards, April
Project Period: November 1, 1998 through October 31, 2001 (Extended to June 14, 2003)
Project Amount: $275,000
RFA: Technology for a Sustainable Environment (1999)
Research Category: Nanotechnology , Pollution Prevention/Sustainable Development

Description:

Objective:

Polylactides (PLA) are a family of environmentally benign plastics based on a monomer produced by the fermentation of corn. The environmental advantages of these polyesters are numerous and include: (1) production of the monomer from a renewable resource (biomass); (2) sequestration of vast quantities of the greenhouse gas carbon dioxide; (3) energy savings and accompanying pollution prevention; and (4) reduction of municipal landfill volumes.

This research project set out to determine a number of fundamental physical properties of PLA that were hitherto unknown. Although the focus was on melt rheology, permeation, and processing properties also were elucidated. This ongoing scientific work led to a close collaboration with Cargill-Dow Polymers and matching financial support.

Cargill-Dow Polymers is a joint venture formed to produce and market these materials and as of December 2002, it began operating a chemical plant in Blair, Nebraska, to produce 140 thousand metric tons per year of PLA. PLA polymers have a unique combination of economic, energy, and environmental benefits. Based on a comprehensive "cradle-to-grave" Life Cycle Inventory (LCI) for PLA using methodology enabling "apples-to-apples" comparisons with petrochemical-based thermoplastics, the most notable benefits of PLA are reductions in both fossil fuel use and global warming potential. For example, compared to polyethylene (PET) and Nylon, PLA uses 30-50 percent less fossil resources that results in 50-70 percent less CO2 emissions. PLA now has obvious commercial significance, and foreign companies around the globe are pursuing the same objective. Because of this U.S. Environmental Protection Agency (EPA)-sponsored research project, a better quantitative understanding of PLA exists, which can help optimize its adoption and facilitate the transition to this renewable and degradable material.

The objectives of this research project were to: (1) chemically synthesize PLA homopolymers and copolymers having well-controlled molecular structure with varying molecular weight, optical composition, and chain architectures; (2) determine the effects of the L-to-D monomeric ratio and sequencing in PLA on the characteristic ratio and melt rheological properties; (3) investigate the rheological, permeation, and degradation properties of the above novel polymers, copolymers, and their blends; and (4) educate chemists and chemical engineers at an advanced level in the science and technology of an extremely important class of environmentally benign polymeric materials, which are available from sustainable natural resources.

Summary/Accomplishments (Outputs/Outcomes):

Several seminal journal articles in the PLA field were produced under the support of the research project. In addition, two M.S. degrees in chemical engineering were granted. The information presented in the publications is broadly applicable to a variety of manufacturers of plastic articles. Briefly, the work can be subdivided into four different properties: (1) solution properties; (2) melt rheological (flow) properties; (3) permeation properties; and (4) physical properties of PLA blends.

Solution Properties. Although PLAs have been known for several decades, the literature on basic chain properties and solution characterization is disjointed and inconsistent. In this research project, a comprehensive and well-controlled set of experiments was combined with consistent numerical analyses to resolve existing apparent contradictions. Homopolymers and copolymers spanning wide ranges of molecular mass and stereoisomer proportions were prepared by ring opening polymerizations of pure or mixed L- and D-lactide stereoisomeric dimers. The polymer products were characterized by means of: (1) dilute-solution viscometry in three different solvents; (2) size-exclusion chromatography in Tetrahydrofuran (THF) with light-scattering detection; (3) static multiangle light scattering in a mixed acetonitrile-dichloromethane solvent; (4) variable-angle spectroscopic ellipsometry; and (5) melt rheology.

The data imply that polylactides are typical linear flexible polymers; unperturbed PLA chain dimensions are describable in terms of a characteristic ratio in the range 6.5 ± 0.9, regardless of stereoisomeric composition. Precise Mark-Houwink and Schulz-Blaschke constants for dilute PLA solutions in chloroform and in THF were determined; for chloroform at 30°C, K = 0.0131 mL/g, a = 0.777, and kSB = 0.302; for THF, K = 0.0174 mL/g, a = 0.736, and kSB = 0.289. Data for the intrinsic viscosity of PLAs of varying optical compositions in chloroform are given in Figure 1, where it is apparent that no optical composition dependence exists.

Figure 1. Intrinsic Viscosity of PLAs in Chloroform.

Melt Rheology Properties. The melt rheological properties of PLA have been studied in a comprehensive fashion. This has led to the development of a software simulation package that allows the prediction of the flow properties of PLA. This software technology has been transferred to Cargill-Dow for distribution to their customers. It will facilitate process change-over from traditional petrochemical sourced plastics such as polyethylene and polypropylene to the new environmentally benign PLA.

Melt rheology properties are summarized in Table 1. The scaling of the zero shear viscosity with molecular weight is presented in Figure 2 for a wide variety of optical compositions. Again, it is observed that within the experimental variation, there is no systematic trend of the melt viscosity with changing composition.

Table 1. Melt Rheology Properties of PLA.

Property Value
M1, g/mol
(molecular weight per skeletal bond)
24.02
rho, g/cm3 1.117
GN0, MPa 1.0
Me = rhoRT/GN0, (kg/mol) 4.21 = 175M1
Mc =(p*/p)Me, kg/mol 9.60 = 400M1
<r2>/M, Å2·mol/g 0.57
Characteristic Ratio 6.7 +/- 7%
MKuhn, g/mol 237 = 9.85M1


Figure 2. Zero Shear Viscosity Versus Weight Averaged Molecular Weight for PLAs of Varying L/D Ratio.

Permeation Properties. The permeabilities of several permanent gases of interest to food and other packaging applications were measured for PLAs of different optical composition. For carbon dioxide, the permeability at 30°C is 1.1 Barrers, the diffusivity is 4.4 x 10-9 cm2/s, and the solubility is 0.025 cm3(STP)/cm3 cm Hg. The activation energy of carbon dioxide permeation is 18.5 kJ/mol. For oxygen, the permeability at 30°C is 0.14 Barrers, the diffusivity is 3.6x10-8 cm2/s, and the solubility is 0.0004 cm3(STP)/cm3 cm Hg. The activation energy of oxygen permeation is 24.9 kJ/mol. For nitrogen, the permeability at 30°C is 0.05 Barrers, and the activation energy of oxygen permeation is 34.6 kJ/mol.

Physical Properties of PLA Blends. Although PLA has sufficient physical properties for a variety of applications, it is a relatively brittle plastic (low elongation to break) with poor impact properties (Notched Izod Impact test). This precludes the use of PLA in many applications. Based on the rheological studies pursued under this grant, a flow modifier was developed. Application of this flow modifier to blends of PLA with a secondary biodegradable plastic (Eastar BioGP from Eastman Chemicals) improves its mechanical strength; this effect is shown in Figure 3.

Figure 3. Mechanical Properties of the New Biobased Polymer Blends. The flow modifier dramatically increases mechanical properties.

Conclusions:

This research project successfully met and exceeded the objectives of the proposal. It has developed a scientific and engineering technical basis for understanding several fundamental properties of PLA in a quantitative manner. Resulting software technology, based on this technical understanding, has been transferred to industry and is being made widely available to manufacturers interested in changing over to this new commercially relevant environmentally benign packaging material from renewable resources.


Journal Articles on this Report : 10 Displayed | Download in RIS Format

Other project views: All 16 publications 10 publications in selected types All 10 journal articles

Type Citation Project Document Sources
Journal Article Cicero JA, Dorgan JR. Physical properties and fiber morphology of poly(lactic acid) obtained from continuous two-step melt spinning. Journal of Polymers and the Environment 2001;9(1):1-10. R826733 (Final)
R826732 (Final)
  • Abstract: Springer-Abstract
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  • Journal Article Cicero JA, Dorgan JR, Garrett J, Runt J, Lin JS. Effects of molecular architecture on two-step, melt-spun poly(lactic acid) fibers. Journal of Applied Polymer Science 2002;86(11):2839-2846. R826733 (Final)
    R826732 (Final)
  • Abstract: Wiley-Abstract
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  • Journal Article Cicero JA, Dorgan JR, Janzen J, Garrett J, Runt J, Lin JS. Supramolecular morphology of two-step, melt-spun poly(lactic acid) fibers. Journal of Applied Polymer Science 2002;86(11):2828-2838. R826733 (Final)
    R826732 (Final)
  • Abstract: Wiley Online - Abstract
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  • Journal Article Cicero JA, Dorgan JR, Dec SF, Knauss DM. Phosphite stabilization effects on two-step melt-spun fibers of polylactide. Polymer Degradation and Stability 2002;78(1):95-105. R826733 (Final)
    R826732 (Final)
  • Full-text: Research Gate - Abstract & Full Text PDF
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  • Abstract: ScienceDIrect-Abstract
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  • Journal Article Dorgan JR, Williams JS, Lewis DN. Melt rheology of poly(lactic acid): entanglement and chain architecture effects. Journal of Rheology 1999;43(5):1141-1155. R826733 (2000)
    R826733 (Final)
    R826732 (Final)
  • Full-text: Research Gate - Abstract & Full Text PDF
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  • Abstract: AIP-Abstract
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  • Journal Article Dorgan JR, Lehermeier H, Mang M. Thermal and rheological properties of commercial-grade poly(lactic acid)s. Journal of Polymers and the Environment 2000;8(1):1-9. R826733 (2000)
    R826733 (Final)
    R826732 (Final)
  • Abstract: Springer-Abstract
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  • Journal Article Dorgan JR, Lehermeier HJ, Palade L-I, Cicero J. Polylactides: properties and prospects of an environmentally benign plastic from renewable resources. Macromolecular Symposia 2001;175(1):55-66. R826733 (Final)
    R826732 (Final)
  • Abstract: Wiley-Abstract
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  • Journal Article Dorgan JR, Janzen J, Knauss DM, Hait SB, Limoges BR, Hutchinson MH. Fundamental solution and single-chain properties of polylactides. Journal of Polymer Science Part B–Polymer Physics 2005;43(21):3100-3111. R826733 (Final)
    R826732 (Final)
  • Abstract: Wiley-Abstract
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  • Journal Article Lehermeier HJ, Dorgan JR, Way JD. Gas permeation properties of poly(lactic acid). Journal of Membrane Science 2001;190(2):243-251. R826733 (Final)
    R826732 (Final)
  • Full-text: ScienceDirect-Full Text HTML
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  • Abstract: ScienceDIrect-Abstract
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  • Other: ScienceDirect-Full Text PDF
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  • Journal Article Mierzwa M, Floudas G, Dorgan J, Knauss D, Wegner J. Local and global dynamics of polylactides: a dielectric spectroscopy study. Journal of Non-Crystalline Solids 2002;307-310:296-303. R826733 (Final)
    R826732 (Final)
  • Abstract: ScienceDirect-Abstract
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  • Supplemental Keywords:

    green chemistry, renewable resources, global warming, plastics, solid waste, renewable, sustainable development, alternatives, clean technologies, innovative technologies, waste reduction, waste minimization, environmentally conscious manufacturing, biomass, pollution prevention, life-cycle analysis., RFA, Scientific Discipline, Sustainable Industry/Business, Chemical Engineering, cleaner production/pollution prevention, Environmental Chemistry, Sustainable Environment, Technology for Sustainable Environment, Environmental Engineering, life cycle analysis, hydrolysis, environmentally benign packaging, toxic monomeric components, cleaner production, sustainable development, waste minimization, waste reduction, environmentally conscious manufacturing, biodegradable materials, innovative technology, life cycle assessment, pollution prevention, polymeric packaging, polymer design

    Relevant Websites:

    http://www.cdpoly.com Exit

    Progress and Final Reports:
    Original Abstract
    2000 Progress Report

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    The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.

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