Infections by pathogenic microorganisms (bacteria, viruses and fungi) are of great concern in many fields, particularly in medical devices, water purification systems, textiles, food packaging and storage, etc. Many efforts have been made by both academic and industrial research in order to struggle infections and polymeric materials are of great interest in this sense thanks to their non-toxicity. There is a multitude of antimicrobial systems, but, among those, polymers exhibiting intrinsic antimicrobial activity are of particular interest. The advantage is the longer-term antimicrobial ability, respect for example to systems containing low molecular weight biocides, which could be released through the polymeric matrix . In this sense, a very interesting polymer is poly(ricinoleic acid) (PRA) (Figure 1), coming from the self-polycondensation of ricinoleic acid (RA), the main constituent of castor oil, which derives from the beans of the castor plant, Ricinus Communis, of the Euphorbiaceae family. PRA is a viscous liquid, with a glass transition temperature of about -67 °C, i.e. significantly low, indicating a very flexible chain. It contains an hydroxyl and carboxyl group, as well as a 9 unsaturation and an aliphatic side chain [2, 3]. The biocidal efficiency of RA is attested by many articles, describing the behaviour of the extract from Ricinus Communis seeds against some human pathogens [2-4]. On the other hand mechanical properties are quite insufficient for whatever application, thus copolymerization is often required. In this work, some polyesters based on 1,3 propandiol (PD), such as poly(propylene terephthalate) (PPT) and poly(propylene isophthalate) (PPI), were chosen to that end. PPT is synthesized starting from terephthalic acid and PD, both derivable from renewable resources [5, 6]. It has become an engineering thermoplastic because many of its properties are between those of poly(ethylene terephthalate) (PET) and poly(butylene terephthalate) (PBT). PPT can be used in applications including films, mechanical parts, and mainly fibers. Such fibers combine the advantageous properties of polyesters and polyamides. They are distinguished for their high elasticity, excellent recovery rate, strain resistance, high UV stability, low water absorption, and low electrostatic charging. In addition, PPT films show good barrier properties .
On the other hand, a limited number of works have been published about PPI [8, 9]. Unlike PPT, PPI is an amorphous polyester, useful in soft packaging.
In order to achieve safe materials, non-cytotoxic, with potent and broad range of antimicrobial activity, long-last response and even reusable, in this work a series of random copolymers based on PRA, PPT and PPI were synthesized starting from monomers (Figure 2-3). Different content of ricinoleic acid have been tested, such as 10 and 25 mol% respect to the comonomer (terephthalic or isophthalic acid), in order to evaluate the lower composition able to confer antibacterial activity. The materials prepared were tested against Staphilococcus aureus and Escherichia coli. Furthermore, thermal properties were investigated. DSC and TGA data of copolymers showed that the thermal properties tended to those of PPT or PPI as a function of composition. All the chemical structures were confirmed by 1H NMR.
These materials could be suitable for textile fibers and/or film engineering thermoplastic applications.
Figure 1. Poly(ricinoleic acid), PRA.
Figure 2. Poly(propylene terephthalate-co-ricinoleic acid), P(PT-co-RA).
Figure 3. Poly(propylene isophthalate-co-ricinoleic acid), P(PI-co-RA).
1) A. Munoz-Bonilla, M. Fernández-García, Prog Polym Sci 37 (2012) 281– 339;
2) G. Totaro, L. Cruciani, M. Vannini, A. Celli, G. Mazzola, D. Di Gioia, L. Sisti, Synthesis of castor oil-derived polyesters with antimicrobial activity, Europ Polym J 56 (2014) 174-184;
3) G. Totaro, L. Paltrinieri, G. Mazzola, M. Vannini, L. Sisti, C. Gualandi, A Ballestrazzi, S. Valeri, A. Pollicino, A. Celli, D. Di Gioia, M. L. Focarete, Macromol Mater Eng 300 (2015) 1085–1095;
4) K. Poonam, S. K. Pratap, Int Res J Pharmacy 3 (2012) 209-210;
5) Y. Tachibana, S. Kimura, Ken-ichi Kasuya, Sci Rep 5 (2015) 8249 (1-4);
6) M. Colonna, C. Berti, M. Fiorini, E. Binassi, M. Mazzacurati, M. Vannini, S Karanam, Green Chem, 13 (2011) 2543-2548;
7) C. P. Roupakias, D. N. Bikiaris, G. P. Karayannidis, Journal of Polymer Science: Part A: Polymer Chemistry 43 (2005) 3998–4011;
8) C. Perez, J. Guzman, E. Riande, J. G. De la Campa, J. De Abajo, Makromol Chem, 189 (1988) 691–699;
9) C. P. Roupakias, G. Z. Papageorgiou, G. P. Karajannidis, J Macromol Sci Part A: Pure Appl Chem, 40 (2003) 791.
Grazia Totaro, born in 1976, has a degree in Chemistry (University of Ferrara), a Master’s Degree in Science, Technology & Management with a specialization in Environmental Chemistry (University of Ferrara) and a PhD in Materials Engineering (University of Bologna).
She worked at the R&D Centre of Basell Polyolefins in Ferrara for 2 years in the frame of a project addressed to the development of a novel methodology for qualitative and quantitative analysis of additives in polymers. She also worked at ARPA, Regional Agency for Environment in Ferrara, division Water Analysis. Then she started working at the school of Engineering of the University of Bologna for a Ph.D. in Materials Engineering (2007-2010). After that, she had a scholarship "Spinner 2013" in cooperation with Reagens spa (San Giorgio di Piano, Bologna) on novel poly(vinyl chloride) nanocomposites. Now she is post-doc fellow at the same school and her research work is related to new polymer-based nanocomposites from renewable sources and inorganic fillers. She also worked at the laboratoire de Chimie et Biochimie Pharmacologique et Toxicologique (Université Réné Descartes) in Paris in 2001 and she was visiting professor at the Ecole Nationale Superieure de Chimie (Université Blaise Pascal, Clermont Ferrand, FR) in 2012 and 2015. Dr. Totaro has about 25 scientific papers and several participations at conferences and scientific schools. She is guest editor for Environmental Engineering and Management Journal and Procedia-Environmental Engineering and Management Journal. She is supervisor of students and referee of several journals. Moreover, she collaborates for Ecomondo from 2013.