Final Report: Sustainable Polymeric NanocompositesEPA Contract Number: EPD07088
Title: Sustainable Polymeric Nanocomposites
Investigators: Hollingsworth, Laura O.
Small Business: PolyNew, Inc.
EPA Contact: Manager, SBIR Program
Project Period: May 1, 2007 through May 31, 2009
Project Amount: $224,988
RFA: Small Business Innovation Research (SBIR) - Phase II (2007) Recipients Lists
Research Category: Nanotechnology , Small Business Innovation Research (SBIR) , SBIR - Nanotechnology
Petroleum is finite in supply and as more world economies develop, it will be both more rare and more expensive.1 As a result, less desirable crude oils containing heavy metals such as mercury and contaminants like sulfur will be processed. The resulting extensive pollution along with concerns over climate change due to carbon dioxide emissions make it highly desirable to find alternative sources for plastics. Many communities are also choking on solid wastes—plastic water bottles in California are filling up available dumping space and when released into the ocean cause a multitude of problems.2 Finally, during the production of plastics and particularly of foamed plastic articles, significant quantities of volatile organic compounds (VOCs) are generated. The purpose of this research project is to enhance biobased green polymers using nanotechnology to address these many ecological concerns. The resulting ecobionanocomposites can compete on a price-performance basis with environmentally deleterious petro-plastics.
Polylactide (PLA) is a biobased material presently made from corn but available from any fermentable biomass resource including plentiful cellulosics. Comprehensive Life Cycle Inventory (LCI) for PLA3 shows multiple environmental benefits over petroleum-based plastics. The property window of PLA, however, is limited because the heat distortion temperature (HDT) is too low. In this project, nanotechnology was used to successfully overcome this limitation.
A series of formulations containing cellulosic nanowhiskers (CNWs) was produced. The material properties of the formulations were evaluated, and the environmental characteristics of the best performing materials were quantified. An immediate application for PLA with an enhanced HDT is in solid and foamed trays. Presently, polystyrene is largely used for these applications and foamed with approximately 5 weight percent hydrocarbons. PLA can be foamed with carbon dioxide, so the new technology has the ability to displace at least 1 million pounds of VOCs per year.
The objective of the Phase II project was to develop nanocomposite materials suitable for solid and foamed trays for microwaveable food and other packaging applications.
The basic technical approach pursued in Phase II was experimental. Formulations were pursued to meet the materials properties requirements through addition of CNWs and appropriate additives. The research plan was executed as planned, with minor modifications as reported in the first monthly report, working in conjunction with the academic group of Professor John R. Dorgan at the Colorado School of Mines.
The needed property improvements can be categorized into four areas: (1) heat distortion, (2) impact properties, (3) color, and (4) cost. The work plan provided measurable goals against which progress was assessed. Additionally, the sustainability of the novel nanocomposites was quantified using the tools of Life Cycle Analysis (LCA) along similar lines as in Phase I.
Task A. Nanowhisker Synthesis and Dispersion
A one-step method that allows the synthesis of surface-modified CNWs as depicted in Figure 1 was developed. The addition of cotton linter to a mixture of an organic acid (acetic and butyric were demonstrated) and water in the presence of a catalytic amount of hydrochloric acid led to surface-substituted CNWs with increased hydrophobicity.
Figure 1. Reaction scheme illustrating simultaneous hydrolysis of amorphous cellulose and esterification of surface hydroxyl groups using an acetic and hydrochloric acid mixture.
The single-step method for the simultaneous isolation and functionalization of CNWs led to the conceptual design of a process for producing such materials at industrial scales. The process is schematically depicted in Figure 2 and serves as the basis for the LCA performed as part of the project.
Figure 2. New process for isolation of functionalized CNW.
Task B – Nanocomposite Manufacturing
To explore the reinforcement effects of functionalized and well-dispersed CNW in PLA, a series of laboratory scale experiments was performed. The data obtained are extremely valuable for economic scale-up because they provide guidance for attaining optimal manufacturing conditions for producing the degree of desirable dispersion. Nanocomposites were prepared by solution blending, melt-mixing, and reactive processing techniques; each included experimentally based trial and error optimization.
Task C – Nanocomposite Property Evaluation
C1. Measure Thermo-Mechanical Properties
The HDTs of various nanocomposites are shown in Figure 3. Remarkable improvements are observed as the CNW loading level increases beyond 7wt% in nanocomposites prepared via solution and bulk polymerization. Incorporation of 7wt% CNW results in a 10°C improvement of the HDT for these composites. HDT values exceeding 110°C are achievable with 10 wt% CNW, and a further increase in CNW loading to 15 wt% leads to a material with an HDT of 155°C when prepared by solution polymerization.
Materials prepared by solution blending conceptually show the same trend as in situ polymerized materials; the increase in HDT, however, is not observed for CNW loading levels below 25 wt%. A 120°C HDT material is obtained when 35 wt% filler is incorporated into the polymer matrix. This is likely to be caused by aggregation of the nanofiller, leading to a larger value of filler to reach the so-called percolation threshold where properties start increasing dramatically. Quantitative modeling of percolation phenomena was completed as part of the project.
Figure 3. Heat distortion temperature for composite materials obtained from reactive processing in solution and bulk compared to solution-blended materials.
Figure 4. HDT vs. CNW content with Biomax addition.
The effects of Biomax impact modifier addition are shown in Figure 4. Here simple melt-mixed composite materials have been used due to the simplicity of their preparation. For a 25% CNW loading level, the HDT decreases from above 110°C to approximately 90°C with the addition of 5% Biomax. Referring back to Figure 3, PolyNEW interprets this to mean that the solution-polymerized nanocomposites would decrease from 120°C to 100°C upon the addition of Biomax. That is, both the HDT and impact strength technical targets have been met.
C2. Evaluation of Environmental Properties
LCA is a technique for assessing the environmental aspects and potential impacts associated with a product. A series of ISO standards, 14040 to 14043, provides detailed guidelines for conducting LCA.4-6 LCA studies the environmental aspects and potential impacts throughout a product’s life from raw material acquisition through production, use, and end-of-life management options such as recycling, incineration, and disposal.
To set the stage for the analysis, the system to be analyzed was first identified. The system generally includes:
- Functionalized CNW production
▪ Acid hydrolysis/functionalization of cotton linter
▪ Separation of acid solution from digested cellulose
▪ Neutralization and washing of cellulose
▪ Drying of cellulose
- PLA pellet production
- Blending of acetic acid functionalized CNWs with PLA
The system for producing PLA is the system presented by Vink, et al.3 for the LCA of PLA.
Summarizing the results of the LCA, it was determined that the nanocomposite properties exceeded targets and are extremely promising for commercial development. The LCA shows that the nanocomposite environmental footprint is comparable to the green plastic PLA alone and, therefore, is superior to existing petroleum-based materials.
The Phase II project has been an enormous success—all technical tasks were completed. It was demonstrated that the nanocomposite materials do have the requisite physical and environmental properties to serve the microwaveable food packaging application. In Phase III, final cost properties must be established as the processes for manufacturing the materials are scaled up. Patents on various aspects of the work have been filed. Presently, financing is being sought to pursue the commercialization of these materials.
1. Deffeyes, K. S., Hubbert's Peak: The Impending World Oil Shortage. ed.; Princeton University Press: Princeton, NJ, 2001; 'Vol.' p.
2. Wilson, E.; Oldfield, M.; Drysdale, D., http://www.consrv.ca.gov/index/news/2003%20News%20Releases/NR2003-13_Water_Bottle_Crisis.htm. In ed.; ENVIRONMENT, S. I. B. W. P. T.
3. Vink, E. T. H.; Ra´ bago, K. R.; Glassner, D. A.; Gruber, P. R. Polymer Degradation and Stability 2003, 80, 403-419.
4. International Standards Organization, ISO 1440 (1997).
5. International Standards Organization, ISO 1441 (1998).
6. International Standards Organization, ISO 1442 (2000).
Journal Articles on this Report : 2 Displayed | Download in RIS Format
|Other project views:||All 2 publications||2 publications in selected types||All 2 journal articles|
||Braun B, Dorgan JR. Single-step method for the isolation and surface functionalization of cellulosic nanowhiskers. Biomacromolecules 2009;10(2):334-341.||
||Sobkowicz MJ, Braun B, Dorgan JR. Decorating in green: surface esterification of carbon and cellulosic nanoparticles. Green Chemistry 2009;11(5):680-682.||