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2006 Progress Report: Sustainable Biodegradable Green Nanocomposites From Bacterial Bioplastic For Automotive Applications
EPA Grant Number: R830904Title: Sustainable Biodegradable Green Nanocomposites From Bacterial Bioplastic For Automotive Applications
Investigators: Drzal, Lawrence T. , Joshi, Satish , Miloaga, Dana G. , Misra, Manjusri , Mohanty, Amar K. , Paruleka, Yashodhan
Institution: Michigan State University
EPA Project Officer: Lasat, Mitch
Project Period: January 1, 2004 through December 31, 2006 (Extended to December 31, 2007)
Project Period Covered by this Report: January 1, 2005 through December 31, 2006
Project Amount: $369,613
RFA: Environmental Futures Research in Nanoscale Science Engineering and Technology (2002)
Research Category: Nanotechnology
Description:
Objective:The objective of this research project is to replace/substitute existing petroleum derived polypropylene (PP)/thermoplastic olefin-based nanocomposites with ecofriendly, biobased nanocomposites produced from compatibilized clay reinforced bacterial bioplastic (polyhydroxyalkanoate) for automotive applications. The ‘green’ nanocomposites that are the subject of this project are ‘sustainable’ materials because they are: recyclable, stable in use but can be ‘triggered’ to biodegrade under composting conditions, environmentally benign, and commercially viable. Compatibilization between the exfoliated clay and the bioplastic is the key to achieving success. This project has a goal of synergistically combining ‘green’ materials technology and nanotechnology to produce a new generation of sustainable materials for industrial applications that will have a positive impact upon the environment. To achieve ‘sustainability,’ this project integrates the environmental, economic, life cycle analysis (LCA), energy, and education components critical to achieving sustainability. Our original aims/objectives remain unchanged.
In addition, we are addressing the issue of brittleness of poly(hydroxybutyrate) (PHB) from two different perspectives: the low nucleation density and the need for plasticization. In this context, expanded graphite nanoplatelets (xGnP) were proven to act as extremely good nucleating agents for PHB, being at the same time efficient reinforcements capable of imparting electrical conductivity to the PHB matrix. Ionic liquids (ILs) were shown to plasticize PHB. As a result, a part of the present study will address the adsorption of ILs onto xGnP surfaces and the implications on the mechanical properties of the resulted bionanocomposites. This study aims to compare and contrast the effect of xGnP on the crystallinity of PHB and polylactic acid (PLA) and to determine the fundamental physical and chemical interactions responsible for the changes induced in polymers’ crystallization behavior and the mechanical properties of the nanocomposites obtained. The results are particularly important because they may be applied to similar semicrystalline polymers. Understanding how xGnP affects the nanoscale structure of the polymers and interferes with nucleation, lamellar structure, and crystallization rates will allow the optimization of the processing conditions leading nanocomposites with controllable mechanical properties.
We also are investigating novel ecofriendly techniques for surface modification of the nano reinforcements. In general practices, these modifications by quaternary complexes are reported using aromatic solvents that are toxic and environmentally persistent. We have addressed this problem by two techniques; one is by using an aliphatic solvent having similar characteristics as the aromatic solvent but significantly more environmentally benign and secondly by developing a solventless technique using ultrasonic atomization of the modifier directly onto the surface.
Progress Summary:The crystallization of PHB and PLA in the presence of xGnP was compared and contrasted with a goal of understanding the nanoscale interaction between xGnP and these semicrystalline biopolyesters and the effects caused by xGnP on the mechanical properties of the nanocomposites obtained. Two aspects of PHB/xGnP and PLA/xGnP nanocomposites were analyzed in the view of the nucleating effect of xGnP: the rate of overall crystallization as a function of the amount of xGnP and the influence of xGnP on the morphology and properties of the nanocomposites. The preliminary results obtained PHB/xGnP and PLA/xGnP systems show different extents of the nucleating effect of xGnP, depending on each polymer’s crystallization behavior. Injection-molded PLA/xGnP nanocomposites showed an improvement in the flexural modulus up to 68 percent (for 10 % wt xGnP-1), as well as an enhanced electrical conductivity. These results lead to further investigation of PLA/xGnP systems to assess the factors responsible for the dispersion of xGnP in the polymer matrix, as well as their interference with the nanoscale crystalline structure. A quantitative evaluation of the melting and crystallization behavior of PLA/xGnP-1 composites was performed, and the main factors affecting crystallization were identified as melting time and melting temperature.
Nano-thermal analysis (TA) was evaluated as a potential alternative thermal analysis technique to be used in the characterization of polymer nanocomposites. Nano-TA is a novel local thermal analysis technique used in combination with traditional atomic force microscopy (AFM) with the aim of understanding the thermal behavior of materials at nanoscale dimensions. A study compared nano-TA results with traditional differential scanning calorimetry (DSC), and the implications of localized heating and melting versus complete melting were analyzed. Although DSC gives quantitative information regarding the dependence of the degree of crystallinity on cooling rates, nano-TA offers the unique advantages of in situ observation of the polymer’s morphology under the same conditions, providing valuable information for practical applications. In this study, we selected calibration standards, set up calibration procedures for the nano-TA tips to be used in the temperature range of interest for PHB and PLA, and collected data for PP nanocomposites containing different nanofillers; these data will be used to determine the relationships between the thermal and electrical conductivities of the nanofillers and the properties of the nanocomposites. A nano-TA study of the PLA/xGnP interface and the changes in the crystallization behavior in the presence of increased amounts of xGnP is ongoing.
Novel surface modifications of the clay reinforcement to achieve improved exfoliation/intercalation and matrix-clay compatibility also were investigated. The fundamental scientific investigations on structure-property correlation of organo-clay are quite valuable in understanding the interface chemistry needed to design and engineer the most effective polymer-clay nanocomposites systems. Organo alkyl-titanate derivatives were used as reagents for the surface modification of pristine montmorillonite clay platelets. This surface modification was validated through coordinated characterization techniques that include X-ray photoelectron spectroscopy (XPS), contact angle measurements, X-ray diffraction (XRD), and thermogravimetric analysis (TGA). By fine-tuning the surface characteristics (controlling the hydrophilicity), effective nanodispersion in polymers by intercalation or delamination can be accomplished. The titanate-coupling agent increased the water contact angle of the clay from 6° to 44° denoting significant decrease in hydrophilicity. Similarly, XRD studies revealed the increased intergallery spacing from 9.8 Å to 12.7 Å. The grafting of titanate modifier on to clay surface is quantified through XPS elemental analysis and co-related with TGA. This new surface-modification method provides an effective technique to convert the hydrophilic surface of the montmorillonite clay into organophillic for polymer-clay nanocomposites.
Optimization of the elastomer-toughened PHB materials included experiments on developing an effective vulcanization system. We investigated different vulcanizing systems (sulfur-based, N,N'-m-phenylenedimaleimide-based) and used dynamic vulcanization to optimally cross-link the elastomeric portion of the blend.
Another phase of this project involved incorporation of different plasticization systems into unplasticized PHB powder. Three different plasticizers (dibutyl sebacate, tributyl citrate, and hydroxyl terminated epoxidized polybutadiene) were investigated along with an antioxidant to determine their ability to increase the elongation and toughness of the PHB. The plasticizers were unsuccessful in improving the extension of PHB and also faced problems of leaching and incompatibility. Hence, we investigated different nucleating agents in the above plasticized PHB so as to inhibit spherulite growth and thus enhance elongation and mechanical properties of the materials. Four different nucleating agents (boron nitride, talc, clay, and saccharin) were studied, but these also gave limited success in improving the toughness of PHB.
Another part of this project focused on finding a flexible partner for PHB, which will give synergistic properties sufficient for film applications. PHB was blended with a flexible petroleum-based biodegradable polymer (e.g., Poly-(butylene adipate-co-terephthalate) [PBAT]) by twin-screw extrusion. PHB-PBAT blends of varying compositions were reinforced with organically modified montmorillonite clay. These blends and their nanocomposites were fabricated into films using a single screw extruder equipped with a blown film line. The blends and nanocomposites were characterized through thermo-physical and mechanical analysis. This material combination is ideal for film making (requisite mechanical properties) and shows oxygen barrier between that of polyolefins (low-density polyethylene, high-density polyethylene, oriented PP, and polystyrene) and nylon.
Future Activities:Part I
Toughening of PHB by blending with a tough and flexible blending partner, PBAT, gave promising results and fundamental studies of the toughening mechanism are in progress. We intend to investigate the thermo-physical, mechanical, and barrier properties of such materials for commercial packaging applications. Specific models and equations that can predict the barrier and mechanical behavior of these materials are being developed so as to correlate experimental findings with theoretical predictions.
Part II
We will continue to investigate the nucleating effects of xGnP on PHB and PLA and the nanoscale interaction between xGnP and IL surface treated xGnP and the polymers, as well as the effects of xGnP on mechanical properties, mainly moduli and fracture toughness. The final scope is to determine the fundamental interactions governing mechanical properties. A combined AFM/nano-TA study of the xGnP-polymer interfaces will be done, and the results will be correlated with traditional characterization techniques, such as DSC.
All the above blends and nanocomposites will be processed mainly using a DSM micro-extruder and injection molder (15 cm3 capacity), Werner-Pfleidderer ZSK 30 mm Twin Screw Extruder L/D 26:1; Killion blown film line (Killion, New Jersey) single screw extruder attached with a blown film die, 1 inch screw diameter, 25:1 L/D (multiplayer and single layer); and Killion cast film line single screw extruder (Killion, New Jersey), 1 inch screw diameter, 25:1 L/D attached with a cast blown film die with chill roll. Mechanical properties will be measured using United Test System and Testing Machines Inc. equipment, according to specified American Society for Testing and Materials (ASTM) standards. Thermal properties (DSC, TGA, dynamic mechanical analysis, and thermomechanical analysis) will be observed using TA equipment as per the ASTM standards. Polymer morphology and crystallization behavior will be observed using Olympus optical microscopes equipped with a hot stage (from Mettler Toledo). Fracture surfaces will be analyzed by environmental scanning electron microscopy and energy dispersive X-ray spectroscopy (EDS). Perkin-Elmer Spectrum 2000 Fourier transform infrared spectroscopy will be used for infrared characterizations of blends and nanocomposites. XRD by RIGAKU 200B (rotating anode) and Nanoscope IV AFM from Digital Instruments, transmission electron microscopes (TEM), JEOL 2100FEF field emission TEM, scanning TEM, high-angle annular dark-field (Z-contrast imaging), EDS, Omega energy filter for energy filtered imaging and electron energy loss spectroscopy equipment will be used to study the nanostructures of the blends and nanocomposites. The water contact angles for the modified clays were measured on a CAHN 322 microbalance (ThermoCahn, Wisconsin) in the wicking mode using a modified Washburn equation. Surface elemental analysis will be performed on an XPS using a Physical Electronics PHI-5400 ESCA workstation.
A nano-TA instrument (from Anasys Instruments, California) will be used in combination with the Nanoscope IV AFM for the characterization of the crystalline structures and morphology of the nanocomposites.
Part III
LCA on the PHB blends and clay nanocomposites is in progress.
Journal Articles on this Report: 2 Displayed | Download in RIS Format
| Other project views: | All 21 publications | 2 publications in selected types | All 2 journal articles |
| Type | Citation | ||
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Parulekar Y, Mohanty AK. Effect of titanate-based surface on hydrophilicity and interlayer spacing of montmorillonite clay for polymer nanocomposites. Journal of Nanoscience and Nanotechnology 2005;5(12):2138-2143. |
R830904 (2005) R830904 (2006) |
not available |
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Parulekar Y, Mohanty AK. Biodegradable toughened polymers from renewable resources: blends of polyhydroxybutyrate with epoxidized natural rubber and maleated polybutadiene. Green Chemistry 2006;8(2):206-213. |
R830904 (2005) R830904 (2006) |
not available |
green chemistry, material science, innovative technology, waste reduction, socio-economic, transportation, ecosystem, eco-friendly materials, environmentally conscious manufacturing, life-cycle analysis, sustainable development, innovative technology,
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INTERNATIONAL COOPERATION, TREATMENT/CONTROL, Sustainable Industry/Business, Scientific Discipline, RFA, POLLUTION PREVENTION, Technology for Sustainable Environment, Sustainable Environment, Technology, Energy, Chemicals Management, Environmental Engineering, Environmental Chemistry, Chemistry and Materials Science, energy conservation, nanotechnology, environmentally applicable nanoparticles, environmental sustainability, environmental conscious construction, cleaner production, clean technologies, green design, automotive industry, green chemistry, Design for Environment, nanoparticles, environmentally conscious manufacturing, biopolymers, nanomaterials, alternative materials, air pollution control, environmentally friendly green products, environmentally conscious design, nanocomposite, polypropylene substitute, environmentally benign alternative, automotive interior parts, clean manufacturing, biodegradable plastics
Relevant Websites:
http://www.egr.msu.edu/cmsc/biomaterials/star/star.htm 
Progress and Final Reports:
2005 Progress Report
Original Abstract