Effects of Temperature, Packaging and Electron Beam Irradiation Processing Conditions on the Property Behaviour of Poly (Ether-Block-Amide) Blends

Materials Science and Engineering C 39 (2014) 380–394

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Materials Science and Engineering C

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Effects of temperature, packaging and electron beam irradiation processing conditions on the property behaviour of Poly (ether-block-amide) blends

Kieran A. Murray a, James E. Kennedy a, Brian McEvoy b, Olivier Vrain b, Damien Ryan b, Richard Cowman b, Clement L. Higginbotham a,⁎ a Materials Research Institute, Athlone Institute of Technology, Dublin Road, Athlone, Co. Westmeath, Ireland b Synergy Health, IDA Business & Technology Park, Sragh, Tullamore, Co. Offaly, Ireland article info abstract

Article history: The radiation stability of Poly (ether-block-amide) (PEBA) blended with a multifunctional phenolic antioxidant Received 17 December 2013 and a hindered amide light stabiliser was examined under various temperatures, packaging and electron beam Received in revised form 6 February 2014 processing conditions. FTIR revealed that there were slight alterations to the PEBA before irradiation; however, Accepted 7 March 2014 these became more pronounced following irradiation. The effect of varying the temperature, packaging and Available online 16 March 2014 processing conditions on the resultant PEBA properties was apparent. For example, rheology demonstrated that the structural properties could be enhanced by manipulating the aforementioned criteria. Mechanical testing Keywords: Electron beam irradiation exhibited less radiation resistance when the PEBA samples were vacuum packed and exposed to irradiation. MFI Poly (ether-block-amide) and AFM conﬁrmed that the melting strength and surface topography could be reduced/increased depending on Crosslinking and chain scission the conditions employed. From this study it was concluded that virgin PEBA submerged in dry ice with non- Mechanical, thermal, structural and surface vacuum packaging during the irradiation process, provided excellent radiation resistance (20.9% improvement) properties in contrast to the traditional method. Stabilisers © 2014 Published by Elsevier B.V. Packaging and processing conditions

1. Introduction material is extensively used in the biomedical industry for a range of applications from catheter bodies to angioplasty balloons [8]. For this reason Poly (ether-block-amides) (PEBAs) are thermoplastic elastomers it is important that these end products are sterilised before use. Converse- which are composed of linear chains of rigid polyamide segments linked ly, such sterilisation processes like high energy irradiation, dry steam and to flexible polyether segments via ester groups [1–3]. PEBAs were first heat can have unfavourable effects on medical grade polymers such as introduced by Atochem in the early 1980s, which are sold under the plastic deformation and extensive material degradation [9–11]. Sterilising trade name PEBAX®. There are many types of polyamides that are techniques can either act physically or chemically leading to modifica- used to synthesise PEBAX, including nylon 6, nylon 66, nylon 11, tions of the structure or function of macromolecules which can result in nylon 6/11, nylon 12 and nylon 6/12. In terms of polyethers, these crosslinking, chain scission, oxidation, melting and hydrolysis. With include poly (propylene glycol), poly(tetramethylene ether glycol) regards to high energy radiation, it is vital that the material properties and poly(ethylene glycol) [4]. These block copolymers are synthesised are not impaired by the sterilisation process [12]. Radiation exposure via a metallic Ti(OR)4 catalyst which helps the melt polycondensation can result in both chain scission and crosslinking; however, one generally of carboxylic acid terminated amide blocks with polyoxyalkylene predominates over the other [13]. The dominance of one process over an- glycols. This polymerisation reaction is performed at elevated tempera- other is determined by the overall structure of the polymer [17] and the tures and under high vacuum [5–7]. irradiation processing conditions [18]. Chain scission can consequently Due to the invaluable properties that the PEBA material has to offer, lead to a reduction in the molar mass, whereas crosslinking increases for instance elasticity and thermal stability at body temperatures, this the molar mass leading to a less flexible product [15]. The yield of oxidative products plays an important role in the extent to which crosslinking and chain scission processes affects the polymer ⁎ Corresponding author. properties. Earlier work performed on polyethylene oxide identified E-mail addresses: [email protected] (K.A. Murray), [email protected] that chain scission predominates when electron beam irradiation is (J.E. Kennedy), [email protected] (B. McEvoy), [email protected] (O. Vrain), [email protected] carried out in air whilst crosslinking predominates when irradiated in (D. Ryan), [email protected] (R. Cowman), [email protected] vacuum [14]. While with polyamides, crosslinking has been proposed (C.L. Higginbotham). as the main consequence of damage leading to the loss of crystallinity

H O polyamide (PA) blocks covalently linked to soft polyether (PE) blocks via ester groups. The PE blocks have a molecular weight that varies H N C H C O C H OH from approximately 400 to 3000 g/mol, whereas the PA blocks have 11 22 4 8 a molecular weight that varies from about 500 to 5000 g/mol [7]. The chemical structure for this block copolymer is illustrated in Fig. 1 n [13,20]. Polymer stabilisers such as Irganox 565 (multifunctional phenolic antioxidant) and Tinuvin 783 (hindered amide light stabiliser)

Fig. 1. Chemical structure of Poly (ether-block-amide) [20]. were kindly supplied by Heterochem (Dist) Ltd (Ireland). These stabilisers were selected for the current study based on the outcome of previous work performed by Murray et al. [21] and design of [15]. Degradation normally occurs where the samples are irradiated in experiments (DOE). All material was used as received with no further the presence of air and this contributes to the formation of such oxida- treatment. tive products as ketones, peroxides, alcohols, aldehydes, peracids, acids, γ peresters or lactones. Elevated temperature and heat would play a 2.2. Processing and packaging significant role in supporting oxidation and this is generally detected during the irradiation process where the severity of the rise in temper- 2.2.1. Hot melt extrusion ature is highly dependent on the material type and irradiation dose used The compounding of the materials in this study was performed on a [16]. Dramatic advances in material susceptibility to radiation oxidation Micro 27 laboratory twinscrew extruder (Leistritiz Ltd) which incorpo- fi and post irradiation oxidation have been accomplished by modi ed rated a screw diameter of 27 mm and a 38/1 length-to-diameter processing conditions [17]. Furthermore, it is possible to achieve ratio. Feeding of the polymer and additives was accomplished by stabilisation at the different stages of degradation by blending antioxi- independent KiTron gravimetric feeders. Prior to compounding the dants, radical scavengers and hydroperoxide decomposers with a base base material (PEBA) was dried in a Piovan desiccant dryer according polymer like PEBA. Hindered phenols are extremely effective at to the manufacturers specifications (6 h at 75 °C). All batches were protecting the physical properties of a polymer like PEBA, however; at drawn through a water bath and pelletised to produce a material the expense of a yellowish colour formation [18].With regards to suitable for injection moulding and further analysis. Table 1 displays hindered amine stabilisers (HAS), they provide remarkable resistance the hot melt extrusion conditions. In this study, two different batches towards UV degradation and long term heat exposure. Over the past of material were compounded. (1) Virgin PEBA 6333 at 100% and few years, blending of phenolic antioxidants with various stabilisers (2) PEBA 6333 at 99.8% compounded with Irganox 565 at 0.1% and fi has developed into an fascinating eld of research [19]. Tinuvin 783 at 0.1% [21]. This is the first study to report blending of PEBA with a multifunctional phenolic antioxidant and a hindered amide light stabiliser to 2.2.2. Injection moulding improve its radiation stability properties. In this work, virgin PEBA and Drying of the virgin and compounded PEBA material was performed PEBA compounded with Irganox 565 and Tinuvin 783 were exposed in accordance to the manufacturer's specifications (6 hrs at 75 °C). A to a number of different packaging and processing conditions to moisture content test was conducted on the dried materials prior to eliminate/reduce chain scission, crosslinking and oxidative reactions injection moulding. This was to ensure the moisture content was during and after the electron beam irradiation process. A comparative below a specified limit (typically below 0.02%) to avoid defects during study was conducted in order to compare non-vacuum packed samples the processing of the samples. An Arburg injection moulding machine to vacuum packed samples following irradiation in room temperature, was utilised in manufacturing type IV (American society for testing dry ice and annealing (annealing was performed post processing). and materials) ASTM D638 testing specimens. The machine had a max- This is the first study in the literature to ever report such a comparative imum clamping force of 38 tonne with a screw diameter of 25 mm. study in the radiation industry for all polymeric applications. The inten- Table 2 shows the injection moulding parameters that were used. tion of the dry ice conditions was to reduce/eliminate the formation of reactive intermediates during the irradiation process, whereas the annealing process was used after irradiation to reduce/eliminate the 2.2.3. Packaging reactive intermediates that were generated during the irradiation pro- fi cess. Overall, this study is aimed at identifying which sample provides 2.2.3.1. Non-vacuum packed. Sample preparation plays a signi cant role the best radiation resistance. during the electron beam process as this controls the uniformity of the irradiation dose on the samples. Each of the samples (virgin PEBA 6333 and PEBA 6333 compounded with Irganox 565 and Tinuvin 783) 2. Materials and methods i.e. tensile specimens and pellets were placed into sealable LDPE bags where the sample size, density, weight and orientation remained the 2.1. Materials same for each type to facilitate uniform irradiation.

PEBA (polyether-block-amide) 6333 virgin medical grade polymer 2.2.3.2. Vacuum packed. Vacuuming packing was conducted on the virgin was manufactured by Arkema Ltd (France) and purchased from the PEBA 6333 and PEBA 6333 compounded with Irganox 565 and Tinuvin National Chemical Company (Ireland). A density of 1.01 g/cm3 was 783 in the ﬁnal section of this work. This was completed at the SteriPack speciﬁed for the material with a melting temperature of 169 °C. The facility (Clara, Co. Offaly, Ireland). Vacuum packing was performed to material was supplied in granular form and was stored under vacuum ensure the samples were contained in a controlled environment. at ambient temperature until use. PEBA contains linear chains of hard Again the sample size, weight and orientation remained the same in

Table 1 Melt extrusion conditions.

Screw speed (RPM) Temperature (°C)

Zone 1 Zone 2 Zone 3 Zone 4 Zone 5 Zone 6 &7 Zone 8 Zone 9 Zone 10

180 80 100 148 150 163 160 171 172 174 Download English Version: https://daneshyari.com/en/article/1428800

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