Grantee Research Project Results
Final Report: Novel Feedstock for Biodegradable Plastic
EPA Contract Number: EPD06050Title: Novel Feedstock for Biodegradable Plastic
Investigators: Combie, Joan
Small Business: Montana Biotech SE Inc.
EPA Contact: Richards, April
Phase: I
Project Period: March 1, 2006 through August 31, 2006
Project Amount: $69,035
RFA: Small Business Innovation Research (SBIR) - Phase I (2006) RFA Text | Recipients Lists
Research Category: Safer Chemicals , SBIR - Pollution Prevention , Small Business Innovation Research (SBIR)
Description:
In a world increasingly conscious of the shortcomings related to non-degradable but disposable plastics, there has been a growing demand for more environmentally friendly materials. Unexpected price increases for petrochemicals (used to make traditional plastics) have convinced some plastics manufacturers to look at alternative feedstocks, bringing attention to commodities such as levan.
In this Phase I project, funded by the U.S. Environmental Protection Agency, Montana Polysaccarides Corporation investigated levan (a polysaccharide) as a new feedstock for use as a biodegradable plastic. As an exopolymer, no costly separation steps are needed for levan production, giving it a price advantage over other biomaterials when sold at equivalent volumes. Levan is produced by fermentation of low-cost sucrose. This fructose polymer is an ideal raw material for the production of green plastics.
The objective was to develop material formulations and the corresponding technical know-how to produce a form of thermoplastic levan that could serve as the basis of subsequent product development. Building on the Phase I experience, the eventual goal in Phase II will be to make products with properties rivaling select petrochemical-based plastics. With increased production volume and the falling cost of the levan, these bio-based products can replace the less environmentally friendly counterparts. Experiments focused on production of levan-based plastics as cast films in extruded formats.
One goal of this research was to make levan-based, clear, flexible films that were water resistant for at least 12 hours and could be considered a biodegradable plastic. Films with good oxygen barrier properties also were desired. Additionally, extruded items were of interest.
The main technical hurdle in this program was that levan, in its original form, will not melt and flow like traditional thermoplastic polymers. It was, therefore, necessary to develop blends of levan with suitable plasticizers and other additives.
Summary/Accomplishments (Outputs/Outcomes):
It was clearly shown that levan could be converted into plastic products. Films were made by casting, extrusion, and a press method. Samples of levan-based items were made on both twin- and single-screw extruders.
Cast Films. Although cast films generally use solvents, the water solubility of levan allowed films to be formulated in water. This was a quick method to determine how various additives interacted with levan while simultaneously making a plastic film that could be used as an example of a levan-based plastic product.
Flexibility. Although levan is a good film former, it is not bendable. For packaging, especially as a plastic wrap, it was necessary to add flexibility to the characteristics of levan films. One to 2 percent glycerol added to cast film formulations or 15 to 20 percent glycerol added to material to be extruded enhanced the flexibility of levan-based products. Sodium montmorillonite (Cloisite®) tended to give these films more pliability. The most flexible films were made with a synthetic layered hydrous magnesium silicate (Laponite®XLG).
Stretchability. Laponite®also was found to make finished films much more stretchable. Because polylactide (PLA) typically can be stretched by 30 percent, a levan-based film with this synthetic magnesium silicate added could be stretched by 128 percent before it broke.
Water Resistance. Levan-based films are readily water soluble, making them useful for applications such as detergent tablets, pre-packaging chemicals, and disposable laundry bags; many other uses call for a water-resistant material. It was found that 20 to 30 percent well exfoliated sodium montmorillonite made films that could be soaked in water up to 2 days before beginning to break up.
Barrier. Levan films consisting of 10 percent montmorillonite and 5 percent polyethylene glycol (PEG) were tested as a barrier to oxygen at 0 percent relative humidity and 23°C. Prior to testing, the films were conditioned at 25 percent relative humidity for 3 weeks. Results on 110 micron (4 mil) films showed an oxygen permeability under 0.05 cc/m2 per day. The film allowed passage of water vapor. The average water vapor transmission rate was 123 g/m2 per day.
Biodegradation. One requirement for a biodegradable plastic is that 30 percent or more of the polymer carbon must be converted to carbon dioxide. Levan attained this level of mineralization in a few days.
Extrusion. The semicrystalline structure of levan interferes with melting, necessitating use of a plasticizer. Glycerol was found to facilitate conversion of levan into a homogeneous, flowing material. Using temperature-modulated differential scanning calorimetry, it was found that the addition of 15 percent glycerol dropped the glass transition temperature to 35°C. Optimal conditions for extruding levan-based strands from a laboratory-scale twin screw extruder were at 130°C, 110 rpm using levan blended with 20 percent glycerol. The strands were homogeneous and showed little evidence of thermal degradation.
Work directed toward making extruded films also used a blend of 80 percent levan and 20 percent glycerol. These materials were mixed in a Henschel high-intensity mixer for 5 minutes at 1000 rpm. The resultant mixture was tacky on the surface and formed clumps when exposed to room temperature. Feeding of the material into the extruder in this form was nearly impossible. To feed the material into the extruder, the mixture was chilled with liquid nitrogen and milled into a powder-like material. The powdered levan/glycerol was immediately fed into the extruder. Cryogenic extrusion is a well-established technology for certain applications. Freezing the feedstock, however, milling it to a powder and then feeding the frozen material into standard equipment requires a little different approach. Conditions employed here were 60 rpm screw speed, final barrel temperature of 110°C, and a film roll temperature of 15°C. These 37 mil films dissolved in water in 30 minutes. Bent crosswise, the films could withstand an average of 187 repetitions at 90°C, while bending length-wise allowed an average 314 repetitions at 90°C.
It also was possible to extrude levan from a single screw extruder with some adjustments in conditions.
Conclusions:
The most water resistant films were those made with a substantial amount of montmorillonite added to the levan. It was found that 20 to 30 percent sodium montmorillonite enhanced water resistance and improved flexibility. As long as there was not too much plasticizer present, films retained their shape for 48 hours. Microbial activity would be expected to increase the degradation rate of this polysaccharide as compared with results under sterile conditions in the laboratory.
The extruded films were even more flexible than the cast films, withstanding up to 314 repetitions when folded parallel to the length-wise axis. Among cast films, inclusion of 2 percent Laponite®withstood the 90°C bends better than any other formulation. This film could be bent back and forth to 90°C for a total of 180 times prior to breaking. A close second was the
1 percent cellulose in the levan film, which took 170 repetitions. Without montmorillonite in the formulation, these films were water soluble, dissolving in 30 minutes.
The 98 percent levan, 2 percent Laponite®film could be stretched by 128 percent over its original length before breaking. This property was not part of the original objectives but when noted for this formulation, it was added because this opens the door for additional applications.
The film formulation making the best oxygen barrier had 85 percent levan, 10 percent montmorillonite, and 5 percent PEG.
|
Levan |
Cloisite® |
Glycerol |
Laponite® |
PEG |
Results |
Water Resistance |
60 |
40 |
|
|
|
Initial breakup: 2 days |
Flexibility |
80 |
|
20 |
2 |
|
314 repetitions |
Stretchable |
98 |
|
|
2 |
|
128% increase in length |
O2 Barrier |
85 |
10 |
|
|
5 |
<0.05 cc/m2-day O2 at 0% RH, 28°C |
Table 1. Formulations for Levan-Based Products
Levan has not been available in large quantities until now. Although it has very useful properties and the Phase I work showed it can be used to make plastics, its current biggest drawback is that most potential users have never heard of levan. With some data on how to convert levan into various biodegradable products in hand, efforts were initiated to introduce levan to plastics manufacturers. A number of presentations were made at trade and technical shows. Also samples of levan were given to prospective users for testing in their own laboratories and local companies were contacted.
Journal Articles:
No journal articles submitted with this report: View all 5 publications for this projectSupplemental Keywords:
small business, SBIR, levan-based plastic, levan for food packaging, polysaccharide plastic wrap, natural polymer, biodegradable plastic, polysaccharide formulation, green chemistry, bioplastic, petrochemicals, green plastic, sugar monomers, pollution reduction, sustainable environment, biodegradable materials, biodegradable plastics, environmentally conscious manufacturing, innovative technology, life cycle analysis, life cycle assessment, pollution prevention, polymer design, polysaccharide, sustainable development, waste minimization,, RFA, Scientific Discipline, Sustainable Industry/Business, Chemical Engineering, Environmental Chemistry, Sustainable Environment, Technology for Sustainable Environment, Environmental Engineering, life cycle analysis, biodegradable plastics, sustainable development, waste minimization, waste reduction, environmentally conscious manufacturing, biodegradable materials, innovative technology, life cycle assessment, pollution prevention, polymer design, polysaccharideThe 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.