Project title: BIODEGRADABLE COATING MATERIALS FROM WATER DISPERSIBLE CO-POLYESTERS OBTAINED
BY CHEMICAL RECYCLING OF PET WASTES
Project number: 31-044
Financing: Governmental budget - Ministerul Educatiei, Cercetarii si Tineretului, Programul 4 - PARTENERIATE IN DOMENIILE PRIORITARE
Project category: PC
Project budget (including other sources): 1.300.000 lei
Contract budget (only governmental source): 1.300.000 lei
Contract period: 38 months (September 2007 - November 2010)
Contracting Authority: National Center of Programme Management (CNMP)
Coordinator: National Institute of Research and Development for Chemistry and Petrochemistry-ICECHIM
This project relates to biodegradable coating materials obtained from water dispersible co-polyesters, which might be used for coating fertilizers granules.
In order to avoid problems caused by the rapid dissolving process of most of the fertilizers in the moisture in the soil, often at a rate that exceeds the rate at which it can be used by plants, various slow and controlled release fertilizers have been developed.
Due to the slow process of biodegradation of the polyester-coating proposed by this project, the efficacy of the fertilizers increases, because the coated fertilizers release the substances which act as plant nutrients in a delayed manner and it can thus display its action over a prolonged period.
The coated fertilizers granules have to exhibit a relatively low tendency to stick and cake, even at elevated temperatures, and a good resistance to mechanical stress which occurs typically when being transferred and transported and in particular, when being applied by means of rapidly operating modern machinery.
In general, it should be possible for the polymers used as coatings to be applied to the fertilizer starting granules without resorting to the use of organic solvents. Such coatings are preferable from an environmental standpoint, since they are carried in water. They have superior water barrier characteristics, can be applied in relatively thin coating layers and they are also easier to handle.
The co-polyesters prepared in accordance with the present proposal must exhibit good film-forming properties, which means only small amounts of co-polyester to be required for producing a stable layer, ensuring economical advantages. In the mean time, the co-polyesters prepared according to the present proposal must disintegrate within an appropriate and measurable period of time when exposed to environment factors. On the other hand, the polymers used for the coating must not show undue hardness and brittleness, since the coating would otherwise be damaged, or could even chip off, when the coated fertilizer granules are exposed to mechanical stress as is the case, for example, during repackaging or, in particular, during mechanical spreading.
The proposed method of production utilizes recycled or reclaimed poly-ethylene terephthalate (PET) from plastic articles such as beverage bottles, as a raw material, following a chemical processing route. By reacting PET with either an alcohol or with an acid, it is possible to reduce the average chain length of the PET molecules. The chemical structure of PET backbone is modified using suitable co monomers which can provide both biodegradability and water dispersability for the resulted co-polyester. Preferably, the co-polyesters are produced through a melt polycondensation method. Thus, aromatic dicarboxylic acid component, (either as acids, esters, or mixtures thereof, aliphatic dicarboxylic acid component, (either as acids, esters, or mixtures thereof), other optional glycol component and optionally a polyfunctional branching agent, are combined in the presence of a catalyst at a temperature high enough and under full vacuum, such that the monomers combine to form esters and diesters, then oligomers, and finally polymers. The polymeric product at the end of the polymerisation process is a molten product.
Various monomer components can be charged to a polymerisation vessel along with polymerisation catalysts, for example, manganese and antimony catalyst, and subjected to poly condensation conditions to produce linear polyester in which the units are randomly distributed along the molecular chain. Specific catalyst or combination or sequence of catalysts used must be selected. The melt process conditions, particularly the amounts of monomers used, depend on the polymer composition that is desired.
The proposed procedure will provide achieving of ecological products, with low emission of organic volatile compounds upon the environment, with high performance properties and with large area of applications. In addition, this procedure uses PET wastes as raw materials, which is an important economical and ecological advantage. It provides the opportunity of recycling great amounts of poly-ethylene terephthalate derived from packaging materials, an attractive source of raw materials which can replace those derived from oil, providing thus resources–conservation.