Primary pvc plasticizers derived from vegetable oils, process for obtaining primary pvc plasticizers derived from vegetable oils and plasticized pvc composition

The present descriptive report refers to a patent of invention of PVC plasticizers composed of ethyl and/or isoamyl esters of vegetable oil fatty acids, obtained by transesterification and epoxidation and PVC compounds plasticized with bioesters, belonging to the technical field of polymer additives that were developed to improve the properties of PVC polymers, in addition to providing a lower cost for renewable compounds, such as those obtained with the use of vegetable oils.

Polyvinyl chloride (PVC) is a polymer well known for its wide range of industrial applications. Its natural rigidity, due to its molecular structure, requires the use of some additives to increase the range of useful applications. These compositions are commonly known as PVC compounds.

Among known compounds, plasticized PVC compounds present high flexibility and are used in films, wire and cable insulation, packaging, hoses, toys, etc. Plasticized PVC compounds are obtained by the addition, in different levels, of additives known as plasticizers, to provide the desired flexibility.

Plasticizers are, in general, high boiling point liquids with average molecular weight (between 300 and 600), linear or cyclic carbon chains (14 to 40 carbons) that, when added to the PVC resin allow for movement between the PVC molecules promoting flexibility to the final compound.

Currently, the major primary plasticizers used in the industry are the phthalates, obtained from petroleum. In addition to being dependent on the fluctuations of petroleum prices, phthalates are suspect of having adverse effects on human health.

As a result, a search was initiated to find alternatives that are technically and economically viable to replace petroleum based plasticizers. Epoxidized soybean oil was proposed as a primary plasticizer. However, its low compatibility with PVC limited its use to small quantities, keeping it from completely replacing phthalates as a primary plasticizer.

Another proposition was the use of epoxidized linseed oil, that in spite of having a similar molecular weight to soybean oil presents a higher oxirane index (8 to 12) and thus greater compatibility with PVC. However, its use is severely restricted due to its higher price.

As such, several initiatives have proposed the use of epoxidized bioesters, obtained from the transesterification or interesterification of vegetable oils combined with epoxidation, as primary plasticizers for PVC. Patent GB934689 describes the preparation of esters with high oxirane index (8,5 to 12,33) from vegetable oils with high linolenic acid contents (such as linseed oil) and high iodine index (175 to 200), that are transesterified with lower alcohols and subsequently epoxidized. Patents U.S. Pat. No. 4,421,886 and U.S. Pat. No. 5,886,072 propose the use of esters of soybean oil transesterified with pentaeritritol, whereas the latter patent proposes the use of these esters in a mixture with other plasticizers. Patent U.S. Pat. No. 4,605,694 describes the use of trimelitic acid and pentaeritritol esters, while the patent U.S. Pat. No. 5,430,108 proposes the use of esters of pentaeritritol with alcanoic acid. Finally, the Brazilian patent application BR 0111905-2 describes the use of soybean oil transesterified with methanol, ethylene glycol, propylene glycol, pentaeritritol, saccharose, and interesterified linseed oil.

Some of these esters (obtained from pentaeritritol, trimelitic acid, ethylene glycol, propylene glycol and interesterified linseed oil) as plasticizers present the drawback of having larger molecular weight and much higher cost when compared to phthalates. Others obtained from methanol, still have a price dependency on petroleum. Additionally, the proposed esters are composed by mixtures of esters with oxirane indexes greater than 8. Finally, with exception of the methanol esters, the other types of esters have been used as primary plasticizers for PVC only in laboratory tests, indicating the difficulty in obtaining an additive that is both technically and economically viable.

Therefore, the objective of the present invention is to obtain technically and economically viable alternatives of primary plasticizers for PVC compounds derived exclusively from renewable sources (vegetable oils, sugar cane ethanol and sugar cane isoamylic alcohol) that are completely compatible with the PVC resin.

With the purpose of overcoming the aforementioned problems and complying with the objectives previously described, the invention developed compositions of plasticizers obtained from the complete transesterification and epoxidation of vegetable oils, henceforth called epoxidized bioesters. Complete transesterification and epoxidation occur when the reactions achieve a minimum of 99% conversion. This invention differs from the state of the art by providing epoxidized bioester plasticizers, presenting low linolenic acid content, and oxirane indexes below 8. The epoxidized bioesters are obtained by the transesterification reaction of vegetable oils with mono-alcohols derived from sugar cane, such as ethanol and isoamylic alcohol, and subsequent epoxidation.

Vegetable oils are composed by triglycerides that contain glycerin molecules attached to three saturated, mono-unsaturated, di-unsaturated and tri-unsaturated acids such as palmitic, oleic, linoleic, and linolenic acids, among others. These fatty acids vary also in regards to the size of the carbon chain, presenting 14 to 18 carbon atoms for the oils referred in this invention.

The transesterification reaction of vegetable oils is employed to separate these fatty acids from the glycerin molecule and bond them to other alcohol molecules, providing superior properties when compared to those of the triglyceride. The transesterification reaction results in the formation of different esters (depending on the type of alcohol used), with a common alcohol termination. This wide range of ester varieties increases the possibilities of compatibility with PVC, in addition to allowing different properties in the plasticized PVC.

The epoxidation process, of public domain, introduces an atom of oxygen in the double bonds of the fatty acid carbon chain, forming an oxirane ring that makes the ester more polar and thus more compatible with the PVC resin. The greater the number of double bonds in the original ester, the greater the number of oxirane rings formed, and therefore increased compatibility with PVC. In addition, the substitution of the double bonds by the oxirane ring in the fatty acid chains increases the chemical and thermal stability of the resulting molecule.

The compatibility of the epoxidized bioesters with the PVC resin depends on the unsaturation of the original esters and the level of epoxidation of the double bonds. The bioesters of this invention present compatibility with PVC even when the resulting oxirane index is below 8, which is not foreseen in the current state of the art.

In a preferred embodiment the bioesters are obtained by the transesterification of a mixture of vegetable oils or one vegetable oil, such as soybean oil, with ethanol. After obtained, the bioesters are epoxidized. The vegetable oils are chosen among the oils with an iodine index between 120 and 170, such as soybean oil, corn oil, linseed oil, sunflower oil, or a mixture thereof.

In the transesterification reaction, the refined soybean oil reacts with anhydrous ethanol in the presence of sodium ethoxide based catalysts, in the molar proportion oil:alcohol of 1:10 to 1:30 and temperatures between 80° C. and 120° C. The glycerin formed in the reaction is separated and the soybean oil ethyl ester is obtained (ethyl soyate) with a high degree of purity. The new ester is then submitted to the epoxidation reaction, where the double bonds of the esters are broken in the presence of free oxygen under specific temperature and mixing condition to form the oxirane rings.

Another embodiment is the production of bioesters from the transesterification of a mixture of vegetable oils or one vegetable oil, with iodine index between 120 and 170 such as soybean oil, with isoamylic alcohol. The isoamylic alcohol is obtained from the residue of sugar cane based ethanol production (also known as fusel oil). After formed, the bioesters are epoxidized. The vegetable oils are chosen among the oils with an iodine index between 120 and 170, such as soybean oil, corn oil, linseed oil, sunflower oil, or a mixture thereof.

The transesterification process is similar to that used in the production of ethyl soyate, replacing the catalyst system by alkyl sodium oxides, and molar proportions oil:alcohol of 1:15 to 1:50 and temperatures in the range between 80° C. and 130° C. The resulting ester is submitted to the same epoxidation process used in the production of the epoxidized ethyl soyate.

The processes of preparation of the epoxidized ethyl and isoamyl bioesters are detailed below.

1—EPOXIDIZED ETHYL SOYATE