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Back to its origins

New processes simplify the cleaning and recovery of disposable plastic bottles

Blankets woven on a handloom, jeans, fruit trays, artificial leather and even bottles for non-foodstuff products have in common the same origin. They are products obtained mainly from plastic packaging known as PET, for soft drinks, water, cooking oil and household cleaning products, discarded after consumption and recycled. For them to start being reused, though, they have to go through a process that begins with the recovery of the material until it reaches the stage of transformation into the end product. In those cases in which the bottles are reprocessed into new packaging for holding food, besides the stage of conventional cleaning, they have to pass through a process of decontamination, to remove the dangerous substances that are absorbed by PET – as the Poly (ethylene terephthalate) is better known –, a cause of damage to human health, when ingested above certain limits. The substances generally come from the reuse of the containers by the consumer to hold fuel, pesticides, chemical products and products for cleaning. A new technique, more simple and economical than the methods currently used, has been developed and patented by the Materials Engineering Department (DEMa), of the Federal University of São Carlos (UFSCar). They have also developed a new process for the molecular recovery of PET, which is going to be of much assistance in the use of recycled material for making new bottles for water and soft drinks, for example, a situation that is unviable in Brazil today.

In the case of decontamination, the processes used by recycling companies currently use an extremely high industrial vacuum over several hours, or alkaline substances like caustic soda, to scrape the layers of the plastic nearest the surface, where the contaminants are deposited. The new process is much simpler: it needs just a flow of hot dry air for about 15 minutes, at a temperature range that runs from 130°C to 220°C. “The oxygen contained in the atmospheric air shows a reaction with the PET and, at the same time, a high diffusion power, facilitating the removal of the contaminant from the container in a short space of time”, says Professor Sati Manrich, the coordinator of the project, which is financed by FAPESP.

The simplicity of the new method has attracted the attention of five Brazilian and foreign companies, one of which has gone far ahead in the negotiations. Three of those interested are already working with superclean processes, as the methods employed in the decontamination of plastic packaging post-consumption are called. “These companies can incorporate the technology that we have developed to improve the process currently used, which will become far more economical”, says Sati. Another advantage of this technology is that it can be used by companies of any size, including micro and small ones. For the time being, in Brazil, the National Health Surveillance Agency (ANVISA) does not allow recycled plastics to come into contact with food, such as soft drinks, teas, juices cooking oils and other similar products. The recycled plastic bottles can be transformed again into bottles, provided that it is for holding cleaning products, chemicals, pesticides and others. “There are at least three Brazilian companies that have technology at their disposal for producing the recycled resin that could be transformed again into bottles to hold foodstuffs”, says Hermes Contesini, the communication director of the Brazilian Association of the PET Industry (Abipet), an entity that brings together the manufacturers of the resin and packaging and the recyclers of packaging. The technology available in the Brazilian industrial concerns is imported, for the time being. But it may gain reinforcement from the process developed at UFSCar.

Appropriate purity
In the United States, Canada, Australia and in Europe, recycled PET is also used in soft drink bottles, produced with varied percentages of the plastic resin. The Food and Drug Administration (FDA), the American regulatory agency for food and medicines, and the International Life Sciences Institute (ILSI), of the European Union, require the recycled material to have an appropriate purity, measured by specific rigorous parameters. “Tests carried out with the resin ground up in the form of flakes, previously contaminated with toluene, a solvent found in cleaning products and building materials, and other chemical products showed that our technology reduces the concentration of the contaminants to minimum levels and meets the requirements of the international regulatory bodies”, Sati says.

Versatile polymer
PET was developed in 1941, by two English chemists, Rex Whinfield and Dickson, from the ICI Laboratory, which started the production of fibers in 1950 in England. At the same time, production in the United States was beginning with DuPont, but the bottles produced with this polymer derived from petroleum only began to be manufactured in the 1970s. Recycling began ten years afterwards, when the United States and Canada started to collect the bottles, which were transformed into cushion filling. The quality of PET kept on improving and, with this, new applications arose, such as textiles and bottles for non-foodstuff products. It was only in the 1990s that the American government approved the use of the recycled material in food packaging. In Brazil, the polymer began to be used in 1988, in the textile industry to start with. It was only in 1993 that it began to be used in a significant way in the packaging market, mainly for soft drinks. The figures for 2003 translate this situation well. Of the 330 thousand tons produced in that year, 227 thousand had as their destination the soft drink industry, 65 thousand the mineral water industry, and 38 thousand the edible oil industry. The recycling of PET, besides taking plastic waste from the landfills, uses only 0.3% of the total energy needed for the production of the virgin resin. Furthermore, PET has the advantage of being able to be recycled several times for the manufacture of different high-quality products. The fibers are used for filling mattresses and pillows, for making eiderdowns and blankets, and the filaments for the manufacture of cords, broom and brush bristles. Part of this resin is also used in the paint industry, in hydraulic pipes, blow-molded parts and films for thermomolding, amongst other applications.

The fact that the Brazilian legislation bans the return to hold foodstuffs is not a hurdle to the growth of the recycling sector. “At the moment, we have other demands for all the PET recycled in Brazil”, says Contesini. According to Abipet, 173 thousand tons of plastic packaging were recycled in 2004, almost 50% of the 360 thousand tons produced in the year. In 2003, 141,500 tons were recycled, of the 330 thousand tons produced, which indicates a 43% level of reuse of the discarded material. The recycling rate could reach even higher figures if the National Policy on Solid Waste, a bill that has been running its course though the National Congress since 1997, had already been approved. For the time being, it is up to each city to establish its own policy for managing domestic and industrial waste. “All packaging materials would have a better recycling rate if selective collection were obligatory”, says Contesini.  Today, the majority of packaging leaves the hands of the consumer and goes straight into the domestic garbage, without any prior separation.

A survey carried out in 2004 by the Business Commitment to Recycling (Cempre in the Portuguese acronym), an association maintained by private companies from various sectors, indicates that the official programs of selective collection, under way in 237 of the country’s cities, concentrated on the regions of the Southeast and South, recover about a thousand tons a year. That is very little. “Generally speaking, a large part of the cities does not have any waste collection system, let alone a selective one”, says Contesini. According to the Brazilian Institute of Geography and Statistics (IBGE), 30% of the more than 5 thousand Brazilian cities do not have this waste removal service. The selective collection system that has recycling as its destination is carried out mainly by the pickers, people that in an informal manner gather recyclable material as a means of survival. After it is handed over to the cooperatives, it is forwarded to the recycling factory. The process of recycling discarded PET bottles begins with the separation of the packaging by color. Next, they are pressed, ground into flakes and then pass through an extrusion machine and transformed into granules, also called pellets. When the flakes are clean, the decontamination process developed at UFSCar is applied.

Closed circuit
The same project also covered another aspect related to the recovery of the physical properties of recycled PET and resulted in one more patent request. In the process of mechanical recycling of the bottles, which involves washing, crystallization, drying and granulation, the material loses some physical characteristics on account of being heated, amongst them those related to its molar mass – or size of the molecules –, which prevents its use in some kinds of products that call for resistance, such as a new bottle. “The greater the molar mass, the greater the material’s mechanical, chemical and thermal resistance”, Sati says. In the process developed at the university, the recovery of the molar mass is carried out in a single stage of crystallization, drying and polymerization on the solid state of the PET in the form of flakes, doing away with an additional stage of granulation, necessary for the production of new bottles. By this method, the flakes are submitted to a reaction of polymerization in the solid state, in which a flow of inert gas like nitrogen, or a vacuum, is applied at a temperature below the fusion point of the polymer.

The main advantages of the new process are that the time to recover the molar mass is reduced, and it is done in compact equipment, using a flow of inert gas that can be reused without any treatment, since the circuit is a closed one. As it is an economical process that does not call for much investment, it is recommended for micro and small businesses, whereas the processes currently used by the large industrial concerns needs a large quantity of gas, which has to undergo a purification treatment in other equipment before being reused. The process for recovering molar mass must be carried out straight after the decontamination of the PET, since the two stages are carried out in the same equipment. Once this process is concluded, the flakes pass through an extrusion machine, where granules are produced that are suitable for molding bottles or tire reinforcement cords.
The compact system can be used by companies connected with the recycling of PET, manufacturers of textile filaments and packaging. For the time being, no interested parties have yet appeared. But the growth of the recycling sector in Brazil shows that investing both in the decontamination of the plastic resin and in the recovery of its physical properties can be viable alternatives for small businessmen, and also rid the sanitary landfills of plastic bottles.

The Projects
1. Studies in recycling post-consumption PET for applications in foodstuff packaging
2. Process for decontamination and increasing molar mass of recycled PET
1. Regular Line of Research Grants
2. Intellectual Property Support Program
Sati Manrich – UFSCar
1. R$ 43,318.00 (FAPESP)
2. R$ 6,000.00 (FAPESP)