Natural Additives for Poly (Hydroxybutyrate–CO
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Materials Research. 2014; 17(5): 1145-1156 © 2014 DOI: http://dx.doi.org/10.1590/1516-1439.235613 Natural Additives for Poly (Hydroxybutyrate – CO - Hydroxyvalerate) – PHBV: Effect on Mechanical Properties and Biodegradation Daiane Gomes Brunela, Wagner Maurício Pachekoskib*, Carla Dalmolinc, José Augusto Marcondes Agnellia aDepartamento de Engenharia de Materiais, Universidade Federal de São Carlos – UFSCar, Rod. Washington Luis, Km 235, CEP 13565-905, São Carlos, SP, Brasil bUniversidade Federal de Santa Catarina – UFSC, Campus Joinville, Rua Presidente Prudente de Moraes, 406, CEP 89218-000, Joinville, SC, Brasil cDepartamento de Química, Centro de Ciências Tecnológicas – CCT, Universidade do Estado de Santa Catarina – UDESC, Rua Paulo Malschitzki, s/n, Campus Universitário Prof. Avelino Marcante, CEP 89219-710, Joinville, SC, Brasil Received: August 28, 2013; Revised: August 21, 2014 In this work, the improvement of mechanical properties in biodegradable materials was obtained through the incorporation of natural and also biodegradable plasticizers and nucleation agents into the PHBV copolymer. PHBV production with different quantities of additives was obtained by extrusion followed by injection. The additives in the copolymer were efficient, resulting in an adequate processing due to the presence of nucleate and an improvement of the mechanical properties of the resulting material provided by the action of the plasticizer. The formulation with the minimum amount of additive content, 5% epoxidized cottonseed oil and 0.1% Licowax, was the most effective showing 35% reduction in the elastic modulus, and 18% in the PHBV crystallinity; 58% increase in impact resistance and 46% increase in elongation. Furthermore, it is important to emphasize that the natural additives were very efficient for biodegradation, showing a mass loss higher of pure PHBV. Keywords: poly(hydroxybutyrate-co-hydroxyvalerate), PHBV, biodegradable polymers, additives, mechanical properties 1. Introduction Poly (3-hydroxybutyrate) – PHB – is a well-known with glucose, as a carbon source. The amount of propionic biologically derived and biodegradable polymer1. Since it acid that is found in the nourishment of the bacteria is can be produced from renewable resources, it has received responsible for the concentration of hydroxyvalerate increasing attention due to the potential applications such (HV) in the copolymer. As HV content increases, TG, TM as in environment-friendly products, tissue engineering, and crystallinity decrease, improving the processing and and control release devices2,3. Nowadays, bacterial toughness in PHB5. fermentation is the main source for PHB production. The By being thermoplastic, of renewable sources, process basically consists of two stages: a fermentative biodegradable, compostable and biocompatible, PHB and stage, in which the microorganisms are fed in reactors PHBV are of great interest in the production of fast usage containing butyric acid or fructose, where they metabolize products, such as disposable materials, packages, medical the sugar available and accumulate the PHB in the inner artifacts for human or veterinary, automobile industry cell as a power supply source; and the extraction stage, products, among others. To be suitable for these industrial where the polymer accumulated in the microorganism applications, however, PHB and PHBV should be processed inner cell is removed and purified with adequate solvents in large scale, mostly by melt processing techniques such 4 until obtaining the final product, that is solid and dry . as extrusion and/or injection. In this case, the polymeric However, the commercialization of these materials did not chains are submitted not only to high temperatures, but result in a major replacement of the conventional plastics also to shearing tension, which may lead to a scission on because of the higher costs of PHB, its brittleness, and a the polymeric chain, causing reduction in the molar mass narrow process window due to the lack of thermal stability. and characterizing a further degradation6. Incorporation The PHB copolymer, i.e. poly (3-hydroxybutyrate-co- of additives is another resource to modify some polymer 3-hydroxyvalerate) – PHBV – has been developed in an properties in order to achieve better processing or to adjust effort to improve its properties for industrial application. It their mechanical and thermal behavior. However, when is produced by a fermentative process similar to the PHB dealing with biodegradable polymers, it is preferable that process, only differing in the use of propionic acid, together these additives are biodegradable as well. Indeed, some *e-mail: [email protected] authors have reported the use of soybean oil7, β-carotene8 1146 Brunel et al. Materials Research and low molecular weight additives9 as plasticizing agents thread extruder. Next, the pelletized formulations were dried for PHB and PHBV in order to improve their mechanical in an oven at 60°C for 24h. The injection of impact and properties for industrial applications. Other approaches also tension specimen according to ASTM D-638[12] and D-256 include the use of nucleating agents and compatibilizers to standards13 was carried out in a 270V 300-120 Arburg All accelerate the crystallization process and refine morphology Rounder injector, with 12 cm3/s flow and 20 cm/s injection and thermal stabilizers, also known as antioxidants, which speed. can prevent various effects such as oxidation, chain scission An Instron 5569 Universal Test Machine, in ASTM and uncontrolled recombination that may occur during the D-638 standard12, with a 10 mm clutch gap, 5 mm/min process10. speed and 50 kN load cell was used to measure mechanical Among various natural biodegradable additives, an properties (Young’s modulus, stress and elongation at epoxidized cottonseed oil plasticizer and a nucleate based on break). The notched Izod impact test was carried out in fatty acids were efficient in the improvement of processing a 65451000 code CEAST Impact Machine, with a 2 J by extrusion and injection. Futhermore, the mechanical pendulum, under controlled temperature, according to properties and biodegradation increased when they were ASTM D-256 standard13. All procedures were done in 11 mixed together in a PHBV formulation . However, triplicate, three days after processing. optimized results still can be obtained through the study of The thermo gravimetric (TG) and the derived thermo the influence of both plasticizer and nucleating agent when gravimetric (DTG) curves were obtained in a TA Instrument their contents inside the formulation are changed. Therefore, TGA2950 at a 20°C.min–1 heating rate between room different PHBV formulations with an epoxidized cottonseed temperature (23°C) and 600°C, under N2 atmosphere oil as the plasticizer and a nucleate based on fatty acids (50 mL/min) in an alumina sample rest. A TA Instruments were processed by both extrusion and injection to result in DSC Q100 calorimeter was used for the DSC characterization materials with adequate mechanical properties for industrial ranging from –50 to 200°C at both a heating and cooling rate usage and composition with approximately 100% weight in of 20°C.min–1, under N atmosphere. The PHBV crystallinity biodegradable materials. To evaluate the better composition 2 was calculated by dividing the heat of fusion of each sample and the effect of additives in PHBV properties, specimens (ΔH ) and the heat of fusion of the hypothetically 100% with different formulations were tested by mechanical, M crystalline PHB, determined as 146 J/g[14]. thermal, microscopy and biodegradation analysis. The influence of nucleating agent contents in the 2. Experimental spherulites growth rate in relation to temperature was studied by optical microscopy with polarized light, PHBV – ( of 650,000 g/mol; 3.5% HV, 1.22 g/cm3) was using a heating plate. The optical microscope used had manufactured by biological fermentation from renewable a DMRXP Leica polarized light and a KAPPA webcam sugarcane carbohydrate at PHB Industrial S/A. P902 coupled to a computer with software for capturing images. (Logos Química Ltda), an epoxidized cottonseed oil, was To get the experiments into controlled temperatures, a chosen as the plasticizing agent, and the nucleating agent THMS 600 Linkan heating plate was used, monitored was the fatty acid based compound Licowax (Clariant). by a TMS92 Linkan temperature controller. The samples Contents of plasticizer (P) and nucleate (N) are listed in were heated at 50°C.min–1 up to 190°C and were kept at Table 1 for all formulations in this study. To guarantee this temperature for 3 minutes to guarantee the complete the homogeneity between both powder PHBV and liquid fusion of the spherulites, destroying the previous thermal plasticizer, the different blends were mixed into a Henschel history, but paying attention not to initiate a possible thermal blender for 10 minutes, with 450 rpm rotation. These degradation process. Subsequently, the samples were cooled compounds were dried in an air circulation oven (Soc. Fabbe down at 100°C.min–1, up to the isothermal crystallization 170) at 60°C for 24h. The different amounts of nucleating temperature (60°C, 70°C, 80°C, and 90°C), and were kept agents were manually blended. The pure copolymer and the there for 20 minutes. different formulations described in Table 1 were processed To evaluate the biodegradation of the processed in a DC-R 30:40 IF Imacom co-rotational double screw copolymer, the Sturm methodology