3 Universidade Estadual de Santa Catarina - UDESC, Centro de Ciências Tecnológicas - CCT, Campus Universitário Prof. Avelino. Marcante s/n, Bairro Bom ...
Phase behavior of poly(3-hydroxybutyrate) / poly(3-hydroxybutyrate-co-3-hydroxyvalerate) blends Denise Santos Conti1, Maria Irene Yoshida2, Sérgio Henrique Pezzin3, Luiz Antônio Ferreira Coelho3* Sociedade Educacional de Santa Catarina - SOCIESC, Departamento de Materiais, Joinville, 89227-700, Santa Catarina, Brazil. 2 Universidade Federal de Minas Gerais - UFMG, ICEX, Depto de Química, Belo Horizonte, 31270-901, Minas Gerais, Brazil. 3 Universidade Estadual de Santa Catarina - UDESC, Centro de Ciências Tecnológicas - CCT, Campus Universitário Prof. Avelino Marcante s/n, Bairro Bom Retiro, Joinville, 89223-100, Santa Catarina, Brazil.
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The polymers of PHAs family more extensively studied are poly(3hydroxybutyrate), P(3HB) and the copolymer poly(3-hydroxybutyrate)-co-(3hydroxyvalerate) (P(3HB-co-3HV)). However, since P(3HB) is highly crystalline, forms large spherulites, and also has a relatively high Tg, the material itself is regarded as too brittle. Thus, there are many works attempting to blend P(3HB) with others polymers, with the aim of improving its mechanical properties and its utility in daily applications. However, blends of P(3HB) with P(3HB-co-3HV) have been barely studied in the literature (2). This paper focuses on P(3HB)/P(3HB-co3HV)-6%3HV blends to investigate the miscibility, molecular interactions and crystallinity by DSC and XRD. The Flory-Huggins interaction parameter of the P(3HB)/P3HB-co-3HV) blends was determined by the melting point depression method.
EXPERIMENTAL P(3HB) and P(3HB-co-3HV)-6%3HV, Biocycle® (PHB Industrial, Brazil), Mw = 492.0 and 294.2 kg.mol-1, respectively, were purified before use. P(3HB)/P(3HB-co-3HV)-6%3HV blends were prepared by casting from 1.0% w/v chloroform solutions in a saturated atmosphere.
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Figure 2. Melting temperatures (Tm) of P(3HB)/P(3HB-co-3HV)-6%3HV blends. It was detected that the Tg of the blends decreased with the increase of copolymer content (Figure 3). There is a very good agreement between the experimental data and the values provided by Fox Equation, indicating the blends can be miscible in the amorphous phase. 16,00 12,00
DSC analyses of the P(3HB)/P(3HB-co-3HV)-6%3HV were carried out on a Shimadzu DSC50 equipment at a rate of 10ºC.min-1 in He atmosphere. The samples were heated from -120ºC to 200ºC (first heating), cooled quickly to -140ºC and heated again to 200ºC (second heating). The experimental values of Tg were compared with the Tg calculated by Fox Equation.
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P(3HB-co- 3HV)-6%3HV content in the blend (%)
( 1 / TgAB ) = ( WA / TgA ) + ( WB / TgB ) where TgAB is the calculated value of Tg of the blend, WA and WB are the mass ratios of the components in the mixture, TgA and TgB are the values of Tg of the pure components determined by DSC. The crystallinity degree (Xc) of the blends was calculated by Xc = ( Hm / Hm0 ) 100 ,
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P(3HB-co- 3HV)-6%3HV content in the blend (%)
Experimental Tg (ºC)
Polyhydroxyalkanoates (PHAs) are thermoplastic polyesters made from bacterial fermentation using renewable resources. In the past two decades, PHAs have been the focus of extensive research considering their potential application as biocompatible and biodegradable thermoplastics (1).
Tm (ºC)
INTRODUCTION
From DSC data, it was obtained an linear relation between Tm1 versus copolymer content and Tm2 versus copolymer content (Figure 2). The linear correlation coefficient for those points (R2) indicates a very strong linear correlation between the variables. This is an indicative of the miscibility between the components of blends during the melting without phase separation. In addition, these results indicate that P(3HB) and P(3HB-co-3HV)6%3HV cocrystallized.
considering Hm0 =142 J.g-1.
Figure 3. Glass transition temperatures (Tg) of P(3HB)/P(3HB-co-3HV)-6%3HV blends. Tm1 and Tm2 of the P(3HB) are depressed systematically with the increase of the P(3HB-co3HV)-6%3HV content in the binary blends. This phenomenon is due to decrease of the chemical potential of the crystallizable polymer caused by the addition of the miscible diluent. The dependence of the melting point depression due only to thermodynamic effects on the blends composition is given by the Flory-Huggins theory modified by Nishi-Wang [4].
X-ray Diffraction analyses were carried out on Shimadzu XRD 6000 equipment. CuK radiation was used as the source and the patterns of were recorded in a 2 range of 5 – 50º at a scanning speed of 2º.min-1. The crystallinity degree was estimated according to the Ruland method [3].
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RESULTS AND DISCUSSION
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The results obtained for P(3HB) and P(3HB-co-3HV)-6%3HV (Fig 1) indicate that both biopolymers have P(3HB) homopolymer-type lattice. 1800
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CONCLUSIONS
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Figure 4. 1/Tm2 versus (w1)2 of P(3HB)/P(3HB-co-3HV)-6%3HV blends according to NishiWang theory. A negative polymer-polymer interaction parameter is obtained from the slope of the plot.
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Figure 1. X-ray Diffraction pattern of P(3HB) (a) and P(3HB-co-3HV)-6%3HV (b). The crystallinity degrees calculated according to the Ruland method [3] were 73.7% ( 5%) for the P(3HB) and 62.3% ( 5%) for the P(3HB-co-3HV)-6%3HV, indicating that both biopolymers are highly crystalline.
There was a linear relation between the melting peaks versus copolymer content, indicating miscibility and also a cocrystallization of the components in the blend. The Flory-Huggins polymer-polymer interaction parameter obtained from melting temperature depression analyses was negative, indicating that the miscibility of P(3HB-co3HV)-6%3HV with P(3HB) is promoted by effective polymer-polymer interactions.
ACKNOWLEDGEMENTS PHB Industrial Ltda., FINEP, GKSS, SOCIESC and PGCEM/UDESC.
REFERENCES [1] [2] [3] [4]
A. Steinbüchel, Macromol. Biosci. 1 (2001) 1-24. D.S. Conti, M.I. Yoshida, S.H. Pezzin, L.A.F. Coelho, Thermochim. Acta 450 (2006) 61-66. A. Keller, J. Polym. Sci. 17(84) (1955) 291-308. M.A. Silva, M. A. De Paoli, M.I. Felisberti, Polymer. 39(12) (1998) 2551-2556.
