Robert D. Lucas, Ph.D.
I have been doing some research on the development of degradable plastics locally. I have been able to develop an edible degradable plastic using glucose which is stable under certain conditions. There are certain challenges which have to be over come when using glucose. It is necessary to give some background on the status of degradable packaging and on how I became involved in the present research.
At present, there are four other methods of making degradable packaging. One of the methods, uses gelatinized starch which is molded under pressure with cellulose. In the second method, starch is extracted from maize, fermented to give lactic acid, which is then polymerized. Thirdly, there is the use of genetically modified bacteria, which are fed sugars. The latter process is complex and expensive. In the third method, use is made of methanotrophic (bacteria which utilize methane), in an aerated medium obtained from waste-water from plants (food, sewers etc.), to which has been added certain salts. Methane is then pumped through the system, and is polymerized by the bacteria.
I became involved in the research, as a result of a proposal of mine, which was entered in the National Council for Science and Technology (NCST’s) innovative competition. As a result, the Barbados Industrial Development Corporation (BIDC) became interested in my proposal. BIDC purchased some basic pieces of scientific equipment and the NCST allowed me the use of their forty-foot container which had previously been converted into a laboratory, located in the Ministry of Commerce’s yard. Apart from the BIDC’s equipment, I have funded all of the chemicals and other bits of equipment myself. I am not paid for doing the research; I want to make that absolutely clear.
Basically, cellulose is present in plants and paper. It is therefore easily available. Cellulose is a polymer, which is made up of thousands of glucose molecules joined together by β-1-4 glycosidic linkages .In nature, cellulose is surrounded by hemicelluloses and lignin polymers. Cellulose is resistant to degradation. Once cellulose is broken down, one has access to glucose, which can be utilized for the manufacture of plastics, alcohols and so on. The lignin and hemicelluloses by-products can be converted into other chemicals. Bagasse, a by-product of the sugar industry, contains lots of cellulose and it was felt that it should be utilized in the manufacture of by-products.
I made some mistakes initially, having not worked with sugars or plastics in the past. I gave myself six months to come up with some type of plastic. I achieved my aim before the six-month period. I started research in March and have been holding storage test since July. At present, there is an hiatus in the research, as I await the arrival of some chemicals. The plastic which I have made should be stored under the following conditions: 55-65°F and relative humidity of 65%. I have not been interested in storing under the conditions quoted. I have been storing at temperatures of 32.2°C ( 90° F) or more and relative humidity of 75-90%. Under the latter conditions, I have been able to maintain the integrity of the plastic for three-five months. Data were recorded hourly over a three-month period, using an Oakton plus temperature/humidity meter. The plastic product was subjectively judged. It exhibits the characteristic of a plastic. I had originally thought of using nano-particles to increase the rigidity of the plastic. Serendipitously, I have been able to increase the rigidity and at the same time maintain the plastic integrity of the product without having recourse to the use of nano-particles.
“One additional problem in using glucose was the presence of ants.”
Although the plastic has a low vapor pressure, the sensory capability of ants was such that they became a nuisance. I have used a series of masking molecules in the plastic product, which neutralizes the ant problem. I have not work with glucose derived from bagasse, because the equipment available to me could not break down cellulose. Instead, I worked with glucose purchased locally, which was in the α-1-4 configuration. This resulted in my having to use an anti-mycotic agent. I used one which is generally recognized as safe (GRAS). Anti-mycotics as a rule would not be required using glucose which is in β-1-4 configuration, since most molds and yeast do not have enzymes systems which can break down β-1-4 glycosidic linkages. As an adjunct, glucose in the β-1-4 configuration, can be used in slimming diets, since it cannot be metabolized in the human body. In the environment, filamentous fungii having the necessary enzyme systems are present, and can degrade the plastic. The unwanted plastic can be fed to ruminants as a source of energy; since the micro-organisms having the appropriate enzyme systems are present in the rumen.
I intend working on extending the storage-life of the product when it is held under extreme conditions. I have thought of some ways of doing so.
At a later stage of the research, objective tests such as: water vapor permeability(WVP), oxygen and carbon dioxide(OTandCO2) transmission rates; Young Modulus (YM); elongation at break(EB) and glass transition temperatures (Tg) will all have to be done according to the American Society for Testing and Materials(ASTM) methods.
In addition, bacteria will have to be genetically engineered to contain the gene for cellulase derived from extremophilic (organisms which live under extreme temperatures, pressures or toxicity) microbes. This has to be done, to increase the rate at which cellulose can be broken down. In this particular case, I am thinking about insertion of a gene which can be expressed at very high temperatures. The alternative is the use of acid and high temperatures and pressures to degrade cellulose. In the latter procedure, only about sixty percent of the available cellulose is obtainable. Hydrolysis with acid in the presence of high temperatures and pressures, results in some caramelization of glucose.
Robert D. Lucas, Ph.D.