Development and Promotion of Starch-Based Biopolymers

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Objective(s)

The objective of this project led by the National Research Council Canada (NRC) was to develop and promote the use of starch-based materials in replacement of synthetic petroleum-based polymers particularly for short lifetime applications.

Description

An increase in the cost of petroleum, awareness of environmental issues, and international regulatory pressure banning non-biodegradable plastics in packaging applications has promoted the development of non-petroleum based materials and biodegradable packaging. Starch-based materials can be fabricated from a number of starch sources that are widely available in Canada including wheat and peas.

Logo of the International
Bioplastics Conference Organized
in Montreal in 2006 and 2007


Extrusion Work at NRC

Project activities include feedstock selection, ThermoPlastic Starch (TPS) fabrication, basic characterization of selected starches, and analysis of potential applications. In particular, the suitability and availability of different feedstock and starch modification routes for a starch-based material fabrication process were evaluated. In a first phase of the project, a first generation of application prototypes were developed. The materials comprised of starch, a plasticizer (glycerol), and a second polymer phase that was used to control the materials' hygroscopy. Wheat, pea, and rice were evaluated in combination with bio-based polymers such as PolyLactic Acid (PLA) and PolyHydroxyAlcanoates (PHA); and with petroleum-based polymers such as PolyCaproLactone (PCL) and ethylene-vinyl alcohol copolymers (EVOH). Over the last few years, PLA has become a true commercial success story and it became clear at the end of the first phase of the project that efforts should be directed towards TPS/PLA blends as a means to further extend the application window of PLA. PLA is made from the polymerization of lactic acid, which in turn is obtained from corn-dextrose fermentation. In the second phase of the project, efforts were dedicated towards the optimization of the PLA/TPS blends. The NRC research team was the first to report successful compatibilization of this blend through an interfacial modification strategy that resulted in lower interfacial tension and stronger bonding between TPS and PLA. A synergy resulting in outstanding elongation at break, a measure of material ductility, was found in the PLA/TPS blends. These findings were published in the high profile journal Polymer in January 2007. The next phase of the work was dedicated to the processing of these blends into several prototypes. The blends were injection moulded to verify if they could be used for the fabrication of common plastic objects. They were extruded into thin films and biaxially stretched to verify their potential as packaging films. They were foamed using carbon dioxide (CO₂) as a blowing agent to evaluate their potential as foamed sheets in replacement of polystyrene packaging. In all these cases, the properties and microstructural details of the produced prototypes were carefully examined and published in high profile scientific journals. On-going research includes the fabrication of multilayer packaging films comprising of a starch-rich inner layer, development of PHA/TPS blend family, and development of clay reinforced PLA/TPS composites. In Agriculture and Agri-Food Canada (AAFC) led work, the reinforcement of thermoplastic starch with carbon nanotubes and hemp nanocrystals was investigated, as well as the properties of plasticized starch/polyurethane blends. The work was also published in peer-reviewed polymer journals. At École Polytechnique, work related to the toughening mechanism in TPS/PE was carried out to give a better fundamental understanding of the underlying fracture mechanisms in starch-based materials.

Significant Outcomes

Starch-based materials have a reduced environmental impact in comparison to petroleum-based polymers. Project results indicate that various types of starch feedstock can be used for the fabrication of starch-based materials that can be shaped into moulded and extruded products. The project has been successful in producing a first generation of materials based on wheat and pea starches. A number of film, sheet, and moulded prototypes have been produced using conventional plastic processing equipment to demonstrate the feasibility and potential of these materials for the fabrication of consumer products. In terms of diffusion, the results of the CBIN-supported research have led to 10 publications in peer-reviewed scientific journals and over 20 conference presentations. The area of bio-based materials has also been promoted through 2 international symposia organized in 2006 and 2007 in Montreal. These events have attracted materials specialists as well as industrial representatives from over twenty countries.

Unmodified Controls
30% TPS / 70% PLA

After Compatibilization
30% TPS / 70% PLA

Unmodified Controls
60% TPS / 40% PLA

After Compatibilization
60% TPS / 40% PLA

Electron micrographs of blends comprising of TPS/PLA blends before and after using the reactive compatibilization strategy developed at NRC. The starch was selectively dissolved prior to observation and is thus represented by the dark zones. Note the important size change before and after compatibilization. Dispersed phase size reduction and blend homogeneity are important factors to obtain materials with good mechanical performance.