BIOPOL-2013
SAXS MEASUREMENTS OF PBAT/TPS BLENDS AND ITS NANOCOMPOSITES WITH CELLULOSE NANOCRYSTALS Jânia Betânia da Silva1, Janice Izabel Druzian1, Fabiano Vargas Pereira2, Cesar Augusto Gonçalves Beatrice3, Juliano Marini3, Rosario Elida Suman Bretas3, Alessandra de Almeida Lucas3 1 – Universidade Federal da Bahia, Departamento de Engenharia Química, Salvador, BA, Brasil. 2 – Universidade Federal de Minas Gerais, Departamento de Química, MG, Brasil. 3 – Universidade Federal de São Carlos, Departamento de Engenharia de Materiais, Rod. Washington Luís, km 235, ZIP Code: 13565-905, São Carlos, SP, Brasil, e-mail:
[email protected].
Introduction In a previous work [1], blends of PBAT/ TPS reinforced with cellulose nanocrystals (CNC) were processed and evaluated. Very good improvements on the mechanical properties of the PBAT/TPS system was observed, about 170% on the Young Modulus, simultaneously with 76% on the tensile strength and 67% on the elongation at rupture. The SEM morphology of the systems showed the formation of a network of nanofibrils in the TPS phase, under stretching, responsible for the improvement of the mechanical properties. In this paper SAXS 2D measuremnets are used to investigate the lamellae morphology of PBAT and PBAT/TPS films, as extruded and stretched. Materials and Methods Cellulose nanocrystals (CNC) were obtained from acid hydrolysis of eucalyptus fibers (final mean dimensions: 145 ± 25 (L) and 6.0 ± 1.5 nm (D), respectively), resulting in an aspect ratio (L/D) of approximately 24. Cassava starch was donated by Cargill Agrícola S.A, (Porto Ferreira, SP, Brazil), Glycerol from NEON Química (São Paulo, Brazil) and water were used as plasticizers. PBAT (poly(butylene adipate co-terephthalate), Ecoflex® (film grade), was supplied by BASF (Ludwigshafen, Germany). The blends were prepared in three steps. In the first one, 30% glycerol TPS-CNC nanocomposites were processed in twin screw extruder (B&P Process Equipment and Systems, model MP19 – TC, L/D = 25, diameter: 19 mm), barrel temperature profile set at 130º ⁄140º ⁄145º/145º ⁄150 ºC, from the feeding zone (zone 1) to the die zone (zone 5), and screw speed of 100 rpm. The amount of CNC in TPS phase was varied from 1 to 10 % w. In the second step PBAT/TPSCNC (70/30 w/w) blends were prepared at the same conditions. In the third step, flat films were extruded (single extruder, from AX Plásticos, Brazil) using a screw speed of 40 rpm. The SAXS measurements were performed at LNLS, (Campinas, Brazil), using a two-dimensional detector located at 1509.3 mm of distance from the sample. The wavelength of the incident beam was 0.15498 nm. Because the films were thin, it was necessary to stack them one over another. This stacking process was carefully conducted, ensuring proper alignment of the films in relation to the processing directions (MD and TD, machine and transversal directions, respectively). The films were also further stretched in the MD direction at a low constant speed (around 1 mm/s) to the point immediately preceding the rupture of the sample, in order to evaluate possible alterations on the elongation process of the PBAT lamellae phase. Results and Discussion The PBAT SAXS pattern indicates a lamella structure, with preferential orientation slightly higher in MD, Figure 1a. After stretching at this direction, it can be noted that PBAT lamellae get
completely oriented parallel to MD, figure 1b. The addition of TPS to PBAT changes completely the SAXS pattern of the film, figure 1c, and after the stretching process the orientation of PBAT lamellae is no longer observed in the MD direction, as can be seen on Figure 1d, being suppressed by the presence of TPS. Instead, an orientation on TD is observed. The same qualitative behavior can be observed when (TPS + NCC) nanocomposites are added to PBAT.
PBAT (a)
PBAT – Stretched (b)
PBAT/TPS (c)
PBAT/TPS – Stretched (d)
PBAT/(TPS + 4% NCC)
PBAT/(TPS + 4% NCC) Stretched (f)
PBAT/(TPS + 10% NCC)
PBAT/(TPS + 10% NCC) Stretched (h)
MD TD
(e)
(g)
Figure 1 – 2D SAXS patterns obtained for the samples. Conclusion From the 2D SAXS measurements, it was possible to observe that the presence of TPS as a second phase suppressed the lamellae orientation of PBAT in the MD direction, even without the presence of cellulose whiskers. The quantitative analysis of these scattering patterns, including lamellae orientation function, long period and lamellae thicknesses is under way and will help us to elucidate this phenomenon. Acknowledgments The authors would like to thank CAPES/Rede Nanobiotec Brasil (#13) for the financial support. References 1. BR 10 2012 04512 (2012), J. B. Silva; J. I. Druzian; F. V. Pereira; C. S. Miranda; N. M. José; R. E. S. Bretas; D. C. Horácio; A. A. Lucas (invs.)
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