Plasticiser Effect of Oleic Acid Polyester on Polyethylene and Polypropylene
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View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Elsevier - Publisher Connector Polymer Testing 31 (2012) 1077–1082 Contents lists available at SciVerse ScienceDirect Polymer Testing journal homepage: www.elsevier.com/locate/polytest Material properties Plasticiser effect of oleic acid polyester on polyethylene and polypropylene Marcela Mantese Sander, Aline Nicolau, Rafael Guzatto, Dimitrios Samios* Laboratory of Instrumentation and Molecular Dynamics, Institute of Chemistry, Federal University of Rio Grande do Sul, Bento Gonçalves Avenue 9500, Postal Box 15003, Postal Code 91501-970 Porto Alegre, RS, Brazil article info abstract Article history: The potential application of a polymeric fatty acid derivative as a plasticiser for poly- Received 27 June 2012 ethylene and polypropylene was evaluated through the study of torque during melt pro- Accepted 14 August 2012 cessing, apparent crystallinity, crystalline plane orientation, plane strain compression and thermogravimetric analysis of polymer blends. The polymeric derivative is a polyester Keywords: produced from epoxidised oleic acid, cis-1,2-cyclohexanedicarboxylic anhydride and trie- fi Polyole n plasticiser thylamine as initiator. The results suggested that the oleic acid polymer had a plasticising Oleic acid polyester effect in blends with polyethylene (PE) and polypropylene (PP). Reduction of processing Crystallinity Plane strain compression torque, no loss of crystallinity, maintenance of mechanical properties and an improvement Thermal stability in thermal stability were observed for PP. For PE, a slight reduction of processing torque, crystallinity and mechanical resistance were observed. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction to their results, ELO improves migration transfer in PVC relative to the problems observed in PVC plasticised with The replacement of phthalates as plasticiser additives in traditional phthalates. the manufacture of plastics is of great importance for In the literature, there are few studies about the use applications such as food packaging, products for children, derivatives of renewable resources as co-processing mate- insect repellents, automotive products, blood storage bags rials for polyolefins. Sastry and co-workers [12] studied the and medical devices because these compounds present application of sunflower oil as a compatibiliser in potential risks to human health and the environment [1,2]. polyethylene-starch blends; they concluded that it acted as Some authors have investigated the suitability of alterna- a plasticiser (improved the film quality) and as a pro- tive plasticisers to replace phthalates [3–7]. Different oxidant (accelerated the film degradation). Other studies epoxidised vegetable oils were tested as plasticisers for regarding the processability and final properties of poly- polyvinyl chloride (PVC) [6–11]. Sun et al. [9] compared ethylene (PE)/vegetable oil derivative blends described epoxidised safflower oil with DEHP (Bis(2-ethylhexyl) their interaction, structure formation and thermal proper- phthalate) as plasticisers for PVC films, studying their ties [13,14]. Reports about blends of polypropylene (PP) resilience, elastic modulus, toughness and glass transition with vegetable oil derivatives showed that there were temperature. Bueno-Ferrer et al. [10] evaluated the interactions between both phases [15], and enhancement performance of epoxidised soybean oil (ESBO) as a plasti- of the PP mechanical properties such as tensile strength, ciser and stabiliser for PVC by means of structural and elongation at break, impact strength and tear strength [16]. thermal studies. Fenollar and co-authors [11] applied However, no evaluations of polymerised epoxy fatty acid epoxidised linseed oil (ELO) as a PVC plasticiser. According esters as co-processing materials for PE and PP have been published. * Corresponding author. Tel.: þ55 5133086290; fax: þ55 5133087304. A series of recent publications reported the synthesis E-mail address: [email protected] (D. Samios). and possible applications of materials derived from 0142-9418/$ – see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.polymertesting.2012.08.006 1078 M.M. Sander et al. / Polymer Testing 31 (2012) 1077–1082 epoxidised oils and biodiesel. Martini et al. [17] investi- The 1H and 13C NMR characterisation, which proves the gated polymers obtained from epoxidised linseed oil bio- epoxidation of oleic acid, was presented elsewhere [19,20]. diesel with different cyclic anhydrides. Reiznautt et al. [18] The OAP was prepared by reacting epoxidised oleic studied polyesters derived from sunflower oil biodiesel. acid (EOA) with cis-1,2-cyclohexanedicarboxylic anhy- Nicolau and co-authors reported the properties of linear dride (CH) and triethylamine (TEA) as the initiator. The polyesters produced from oleic acid and methyl oleate in molar composition of the reaction mixture was 0.5/0.5/ bulk [19] and in solution [20]. Roza and co-workers 0.0085 (EOA/CH/TEA). The mixture was placed in a glass prepared different types of polyesters from epoxidised beaker and heated in an oven at 165 Cfor3h.The soybean oil biodiesel, including biodiesel, as a green products were stored in desiccators at room temperature solvent. The polymerisation process [21] and the physico- [19,20]. chemical properties of the products were evaluated [22]. These materials possess important physicochemical prop- 2.3. Blend mixtures and torque evaluation erties. The olefinic chains of the fatty acids in these poly- mers suggest that it may be possible to apply them in The blends were prepared in a Haake Reomix 600p with blends with PE and PP. It is necessary to evaluate their two co-rotors. The composition of the PE and PP blends is plasticiser effects in this and other important applications. given in Table 1. The polyester was added in the mixing The properties of polyesters produced from epoxidised chamber as an ethyl acetate solution (30% w/v, polyester/ biodiesel depend on the type of vegetable oil used as ethyl acetate). The processing time was 10 min at 40 rpm, a starting material. Vegetable oils are fatty acid triglycer- the applied torque being monitored during this period. The ides that have different degrees of unsaturation. Fatty acids mixture temperature was 160 C for PE blends and 190 C differ in the length of their carbonic chains and the number for PP blends. This procedure guaranteed the evaporation and orientation of their double bonds. For example, linseed of ethyl acetate at the beginning of the process. and sunflower oils contain predominately polyunsaturated The blends were moulded as sheets with a Carver fatty acids; they form crosslinked materials when poly- Monarch model 3710 press, cut into small pieces and merised under optimum cure conditions. However, the injected with a Thermo Scientific Haake Minijet II to polymerisation of oleic acid, a monounsaturated fatty acid, produce the test specimens. The injection temperature was yields linear polyesters. 160 C for PE blends and 210 C for PP. The conditions were The aim of this work is to investigate the plasticiser as follows: injection at 280 bar for 4 s, followed by appli- action of oleic acid polyesters (OAP) in blends with PE and cation of pressure of 500 bar for 8 s and subsequent cooling. PP. The polyester was obtained from the polymerisation of The test specimens were 57 mm long, 12 mm wide and oleic acid, the main fatty acid component of olive and 3.2 mm thick. The PE and PP blend specimens were canola oils, with cis-1,2-cyclohexanedicarboxylic anhy- annealed at 120 C and 150 C, respectively, for 30 min and dride and triethylamine as initiator. cooled to room temperature. 2. Experimental 2.4. Differential scanning calorimetry experiments 2.1. Materials Differential scanning calorimetry (DSC) was used to determine the melting temperature (Tm), heat of fusion Oleic acid P.A., toluene (99.5%) and hydrogen peroxide (Hf) and crystallinity (Xc) of neat PP and PE and their (30% w/w) in water were purchased from Synth (São Paulo, blends with OAP. Approximately 5 mg of sample was Brazil). Triethylamine (99%), cis-1,2-cyclohexanedicarboxylic weighed in an aluminium capsule and analysed in a DSC anhydride (99%), formic acid (85%) and sulphuric acid (98%) 2920 apparatus from TA Instruments. The temperature were purchased from Aldrich Chemical Co. The blends were range was from 30 to 180 C for PE blends and from 30 to prepared with polyethylene HC 7260 and polypropylene H 200 C for PP blends. For both types of blends, the samples 301, both from Braskem S.A (São Paulo, Brazil). were heated at a rate of 10 C/min until the maximum temperature was reached, kept at an isothermal condition 2.2. Epoxidation and polymerisation of oleic acid for 2 min and then cooled to 30 C at a rate of À40 C/min. Then, samples were heated again at a rate of 10 C/min to The epoxidation of oleic acid was performed with for- their respective maximum temperature. This procedure mic acid generated in situ. The molar ratio of hydrogen erased the thermal history of the blends. The data from peroxide/formic acid/unsaturation (double bonds) was both heating cycles and the respective results are shown in 20/2/1. The oleic acid, toluene and concentrated formic acid Section 3.2, Table 2. were placed together in a well-stirred, round-bottom glass reactor kept at room temperature. Then, 30% (w/w) hydrogen peroxide was added dropwise. The reactor Table 1 temperature was raised slowly to 80 C to complete the Blend compositions in percentage (% w/w). reaction. This entire procedure took approximately 2 h. Afterwards, the organic layer (containing the epoxide) was Polymer PE0 PE1 PE3 PE5 PP0 PP1 PP3 PP5 PE 100 99 97 95 –– – – separated and washed with water to remove residual H2O2. PP –– – –100 99 97 95 Anhydrous sodium sulphate was used to dry traces of water OAP 01 3 5 01 3 5 and the epoxide was concentrated in a rotary evaporator. M.M. Sander et al.