PSI - Issue 68

Carlos Fernandes da Silva et al. / Procedia Structural Integrity 68 (2025) 1252–1258 C. F. das Silva et al. / Structural Integrity Procedia 00 (2024) 000–000

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pharmaceutic industry Utracki (2002); Padhan and Gupta (2015). PA, on the other hand, is a thermoplastic polymer, hygroscopic, with good thermal stability and strength, particularly after hydration Herna´ndez-Garcia et al. (2023); Marangoni Jr et al. (2023). The quality of the packaging material can be improved using di ff erent strategies, the food and pharmaceutic in dustries adopt basically two derived routes: the production of multilayered films by coextrusion ( e.g. refs. Herna´ndez Garcia et al. (2023); Marangoni Jr et al. (2023) and blending ( e.g ref. Yeh et al. (2009)). On economic grounds, blending is preferred Rosales et al. (2024) since the mixture of polymers can be done in a standard extruder, however, di ff erent polymers may not be compatible for mixing, degrading the properties of the film. The investigation of the dependence of properties like strength Zengin et al. (2023) and toughness Li et al. (2021) on blending is essential. The aim of the present work is to investigate the possibility of obtaining films of blends of PET and PA in terms of the obtained mechanical properties, targeting the viability and limitation of the blending process. The amounts of added PA will be 2.5 weight %, 5 weight %, 10 weight % and 20 weight %. PA will be added in the form of either a commercial PA 6.6 resin and of a modified PA resin (PA6T6I) which is an amorphous modification containing a terephtalate ring in it’s structure. The hypothesis here is that this modified structure will result in better compatibility with the PET base resin. The films will be produced by film extrusion in di ff erent thicknesses ranging from 0.15 to 0.35mm. The employed PET resin is a commercial bottle-grade PET, designated PET B90A by the producer, furnished in form of granules. It has density ρ = 1.4 g cm − 3 . A commercial PA 66 resin, designated Sollamid A 2700 by the producer, characterized as a standard PA 6.6 resin without additives and is also furnished in granules, its density is ρ = 1.14 g cm − 3 . Finally the modified PA resin, designated here PA 6T6I, receives the Grivory G1 designation by the producer. The main characteristic of this resin, compared with the standard PA 66 resin, is that the four methyl groups which are located between the cabonyl groups in PA66 are substituted by a cyclohexane ring, resembling the structure of the terephtalate group in PET. This change results in an amorphous resin, with density ρ = 1.18 g cm − 3 . The base material was also obtained in the form of granules. The molecular structures of the used resins can be found in standard textbooks for PET and PA66, e.g ref. Deopura et al. (2008). The molecular structure of PA 6T6I is described in ref. Djukic (2020). Prior to processing the three resins were submitted to a DSC test (DSC25, TA Instruments, polymer characterization lab., FATEC Maua´) to determine the appropriate processing temperatures. Previously to test the samples were dried in a standard mu ffl e at 80 ◦ C (353 K) for 12 hours under vacuum. Around 13 g of each resin was place in a sealed DSC crucible and the tests were conducted under a flowing N 2 atmosphere (flow rate of 50 ml min − 1 ). The tests were conducted under thermal cycles consisting of heating from 30 ◦ C (303 K) to 275 ◦ C (548 K) with a heating rate of 10 ◦ Cmin − 1 , holding at 275 ◦ C for 5 minutes, cooling to 30 ◦ at a rate of 10 ◦ Cmin − 1 , holding at 30 ◦ C for 5 minutes and then heating a second time to 275 ◦ C at a rate of 10 ◦ Cmin − 1 . Nine series of samples were prepared, according to Table 1. The PET samples is the only not corresponding to a blend and is introduced to produce a baseline for the behavior of the other samples. Series A corresponds to blends produced with the PA 66 resin and series B corresponds to blend produced with the PA 6T6I resin. The density was estimated as the mechanical mixture of the tabulated values for the base resins. The samples were prepared by weighting 3 kg of the resins in the appropriate proportions given in Table 1 using a digital scale, resolution was about 0.01 g. The groups corresponding to the blends (A1 to A4 and B1 to B4) were further homogenized using a revolving drum mixer (15 minutes, 15 rpm). The groups were then dried under vacuum at 80 ◦ C for 12 hours and then stored in vacuum sealed aluminum laminated polyethylene bags. The blends and the PET films were produced using a parallel double-screw extruder (NZ, processing lab., FATEC Mauaa´). The screws have a LD ratio of 20:1. The temperatures were set according to the DSC results to zone 1 - 260 2. Materials and methods 2.1. Materials 2.2. Sample preparation