A cleaner enzymatic approach for producing non-phthalate plasticiser to replace toxic-based phthalates

Abstract

Dioctyl phthalate (DOP) is industrially commonly used as a polyvinyl chloride (PVC) plasticiser. As DOP does not form a chemical link with PVC, it migrates from flexible PVC segments into the media in contact, a matter that arose concerns due to its noxious effect. Despite the introduction of several non-DOP-based plasticisers recently, most of these new plasticisers are petroleum derived, which is a non-renewable resource. Accordingly, this research aims to produce a natural-based plasticiser using clean production method. Epoxidised 2-ethylhexyl oleate (E-2-EHO) was produced through an esterification and epoxidation reaction between oleic acid and 2-ethyl hexanol; both reactions occur simultaneously, in the presence of hydrogen peroxide as oxygen donor in a solvent-free environment. Candida antarctica lipase (Novozym 435) was used as a cleaner biocatalyst. Several reaction parameters that affect the synthesis of (E-2-EHO) were analysed using response surface methodology based on full factorial central composite design for four variables. The maximum experimental conversion was 94.2% while the value of the predicted conversion was 95.3%. The operation conditions were a temperature of 65 °C, enzyme load of 4 wt%, alcohol-to-oleic acid molar ratio of 4:1, hydrogen peroxide-to-C=C molar ratio of 0.5:1, molecular sieve/g acid of 0.425 g and reaction time of 2 h. In addition, the plasticising effectiveness of (E-2-EHO) to substitute toxic DOP was studied. Comparison with conventional DOP highlighted that (E-2-EHO) had superior and significantly reduced glass transition temperature (tg) and improved mechanical properties. In the proposed study, (E-2-EHO) was proved to be an efficient substitute to DOP by replacing up to 80% of the total plasticiser. Moreover, the product yield obtained in a short time reaction along with the proven stability of Novozym 435 during operation both showed that this ecofriendly and maintainable alternative is favourable when used in large-scale applications.