A raw material extracted from several vegetable sources, with many chemical and physical modification possibilities, starch is a polysaccharide that can be transformed into a promising biopolymer for the development of biodegradable packaging, plastic films and other products for agricultural use. At the Federal University of São Carlos (UFSCar), in inner-state São Paulo, a new material for making pots for seedlings and other applications was developed from a biodegradable plastic made of cornstarch and vegetable waste such as coconut fiber, wood shavings and cassava skin. The result is a stiff plastic that, once buried in soil, degrades in six months.
The project arose from the need of the firm Corn Product Brasil to expand its applications for a biodegradable plastic called Ecobras, already on the market and developed jointly with Basf. Ecobras is a flexible plastic used, for instance, to make supermarket bags. Its formulation combines cornstarch and a polymeric thermoplastic resin called Ecoflex, obtained by Basf from petrochemicals. “Blending 51 percent of corn starch paste with Ecoflex resulted in Ecobras, a biodegradable flexible plastic”, says professor Elias Hage Júnior, from the Department of Materials Engineering at UFSCar, and coordinator of the project that led to a third compound, stiff biodegradable plastic. “By adding cassava skin to Ecobras, it acquires stiffness, whereas coconut fiber gives it better mechanical resistance, making it less susceptible to breaking”, says Hage Júnior.
The material’s biodegradation trials were conducted in a sort of aquarium, in which the material being tested is buried in soil and periodically removed for analysis. “We found that the trials with Ecobras plastic combined with cassava skin and coconut fiber disappeared completely in six months”, Hage Júnior reports. In other words, if the material is used for containers such as pots for reforestation seedlings it can be buried in the soil along with the seedlings and it will degrade as the plant grows.
The pots made from conventional plastic, such as polypropylene, cannot be re-used, especially in the case of large-scale planting, because if they are contaminated with fungi or bacteria the diseases will probably be transmitted to the next generation of plants. The project, initiated in 2008 as a service provided by UFSCar, ended in 2009. The first stage of the research, which led to the rigid biodegradable plastic, came to an end and the results were transferred to the firm. At the university, however, research continues, looking for new applications for this bioplastic film, including the incorporation of substances that might, for example, interact with foodstuffs.
At the State University of Londrina (UEL), in Paraná state, researchers developed a formulation that consists of cassava starch (80 percent) and sugarcane fiber (20 percent) to make trays for dry products such as bread, fruit and vegetables. “It’s a product with good mechanical properties, that is biodegradable and cheap to make”, says professor Suzana Mali de Oliveira, from the Department of Biochemistry and Biotechnology of UEL, who is the coordinator of the research project on developing biodegradable trays. Ten years ago, the UEL research group focused only on cassava starch, but in the last four years, they began blending it with fibers. The incorporation of fibers such as sugarcane bagasse gave rise to a stiff material, with low density, that looks similar to expanded polystyrene and can be thermoformically molded. However, for the time being, it can only be used with dry products, as moisture can cause the packaging to degrade.
Another line of research headed by Suzana concerns developing food trays made out of cassava starch strengthened with nanocomposites. “We have been using nanoclays, powders derived from decomposing volcanic ash, at a concentration of 2.5 percent to 5 percent, mixed with vegetable fibers”, says the researcher, who is testing several formulations with different concentrations. The time that the material stays in the environment varies according to the conditions. “When subject to a fair amount of moisture, certain materials degrade totally in 45 days”, says the researcher. The project, called Application of nanocomposites in the development of biodegradable food packaging, is part of the Young Researchers in Nanotechnology program, released by CNPq (the National Council for Scientific and Technological Development).
Manioc starch is also used in the formulation of plastic biodegradable films developed by the research group coordinated by professor Maria Victória Eiras Grossmann, from the Department of Food Science and Technology at UEL. These films can be used to package seedlings, protect fruit in the field or cover the soil in the farming of fruit and vegetables. To improve the mechanical properties of the films, the researchers have used glycerol (a by-product of biodiesel production) in the amount of 5 to 30 percent. “Glycerol works like a plastifying agent that makes the material less stiff”, says professor Fabio Yamashita, a member of the research team. Better known by the commercial name of glycerin, glycerol can be obtained from both vegetable oils and petroleum products. “We’re testing glycerols from the biodiesel industry, with various degrees of purity, to assess the performance of each”, says Yamashita. “We want to find out whether the degree of purity does or does not influence the mechanical properties and the films’ barrier properties regarding water and gases.”
The biodegradable plastic films are obtained by the extrusion process, the same as is used to produce conventional synthetic packaging made out of polyethylene, polypropylene and other oil products. “Our work consists of making Ecoflex and starch blends with some additives and compatibility agents to improve the mechanical and barrier properties”, explains Yamashita. The films with selective permeability to gases, for example, can be used to control the breathing of fruit and vegetables, working as packaging in a modified atmosphere. Or to produce small bags to wrap fruit in the field, protecting them from pests. Trials with guavas showed that the fruit developed very well wrapped in biodegradable film bags. The trials also involved planting medicinal seedlings in bags of a plastic made out of Ecoflex, cassava starch and glycerol. They resisted 120 days on average. “The chief advantage of this material is that because it is biodegradable, one doesn’t need to take the seedling out to plant it in the ground, which, depending on the plant, can damage its roots”, says Yamashita.
When it is used to cover the ground, the film protects vegetables, fruit and flowers from direct contact with the soil. In addition, it discourages the growth of weeds that compete with the production of foods.
Today, farmers are using a plastic cover also known as mulch to do this. The blend of starch, Ecoflex and glycerol varies depending on the application. “To line the ground for strawberries, we work with formulations that have 30 to 70 percent of thermoplastic starch”, says Yamashita. The best results have been achieved with a mixture that includes 30 percent of thermoplastic starch. The useful life of the material depends on its application. For strawberry plantations, the soil covering started degrading after three months.
A new line of bioplastic research has been started at UEL recently. This involves poly (lactic acid) or polylactide, a biodegradable polymer also known as PLA. “Our objective is to develop a PLA with as much as 70 percent of cassava, glycerol and compatibilizers, to produce films for several types of packaging”, says Yamashita. Films that include the starch from corn, potatoes and wheat are already being produced on an industrial scale by the Italian company Novamont, under the trademark Mater-Bi. However, the formulation details are a well-guarded industrial secret. The company announces that the product, in the form of granules, can be used to make garbage bags. It can also be used in other applications, such as bottles, plates, cutlery and toys.
MALI, S.; DEBIAGI, F. et al. Starch, sugarcane bagasse fibre, and polyvinyl alcohol effects on extruded foam properties: A mixture design approach. Industrial Crops and Products. v. 32, p. 353-59. 2010.
MALI, S.; SAKANAKA, L.S. et al. Water sorption and mechanical properties of cassava starch films and their relation to plasticizing effect. Carbohydrate Polymers. v. 60, p. 283-89. 2005.
BRANDELERO, R. P. H.; YAMASHITA, F.; GROSSMANN, M. V. E. The effect of surfactant Tween 80 on the hydrophilicity, water vapor permeation, and the mechanical properties of cassava starch and poly (butylene adipate-co-terephthalate) (PBAT) blend films. Carbohydrate Polymers. v. 82, p. 1.102-09. 2010.