Study of the hydrolytic degradation of poly-3-hydroxybutyrate in the development of blends and polymeric bionanocomposites

Abstract

Bionanocomposites of poly-3-hydroxybutyrate (PHB), polyethylene glycol (PEG), and organophilic vermiculite (VMT) clay were prepared at 95/5/3% and 90/10/3%and blends at 95/5% and 90/10% PHB/PEG in the form of films obtained via solution intercalation. The films were submitted to hydrolytic degradation according to the ASTM F1635-11. X-ray diffraction (XRD) analysis, mass loss, visual inspection, and Fourier transform infrared (FTIR) spectroscopy evaluated the properties of films. XRD analysis showed that the polymer chains were intercalated into the organoclay layers, and some degree of exfoliation was observed from this analysis. FTIR was performed to calculate the carbonyl index and to quantify the causing group of the degradation process. The visual inspection results showed that the film surfaces were whitened and brittle. This characteristic was more evident for the 90/10% PHB/PEG blend and 90/10/3% PHB/PEG/VMT composite. The addition of the organophilic VMT clay at 95/5/3% (PHB/PEG/VMT) displayed a larger mass loss; FTIR showed that degradation of pure PHB occurred in the amorphous regions and that the presence of PEG and VMT increased the polymer degradation, decreasing crystallinity.

Accelerated Weathering Effects on Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and PHBV/TiO2 Nanocomposites

“…The chemical structure changes of the PHBV and the PHBV/TiO 2 samples before and after the weathering test were investigated by FTIR. It can be seen in Figure 6 , the PHBV presents the characteristic bands of the neat polymer identified in previous works [ 25 , 31 , 32 , 34 , 72 , 73 , 93 ], i.e., the observed region of 3000–2800 cm −1 is assigned to the asymmetric and symmetric deformations in the methylene chains (–CH 2 –), and the bands at 1472, 1448, 1425, 1338, 1335 and 1313 cm −1 are due to the CH 2 and CH 3 asymmetric and symmetric deformations, and the C–O stretching characteristic bands are seen at 1255–1245 cm −1 for the crystalline domains, while the amorphous phase is indicated by the 1180 cm −1 peak. The strong absorbance peaks at 1713 and 1720 cm −1 are attributed to the stretching vibrations of the crystalline C=O carbonyl groups, while the absorption bands at 1730 and 1740 cm −1 are assigned to the amorphous C=O stretching.…”

“…To further confirm the extent of the degradation of each phase, the carbonyl index (ratio of the intensity heights of C=O/CH 3 ) was quantified before and after accelerated weathering. The absorbance ratios of 1720/1388 and 1713/1388 cm −1 were used to quantify the crystalline C=O of the PHBV and its nanocomposites, whereas 1730/1388 and 1740/1388 cm −1 were used to measure the amorphous carbonyl content [ 31 , 32 , 72 , 73 ]. The quantitative analysis of the carbonyl index and the ratio of crystalline/amorphous phases are presented in Table 1 .…”

“…In addition, a quantitative analysis of the ratio of the crystalline/amorphous phases was conducted. The absorbance ratios of the 1720/1388 and 1713/1388 cm −1 were used to quantify the crystalline carbonyl (C=O) content, while 1730/1388 and 1740/1388 cm −1 were used to calculate the amorphous C=O content of PHBV and its composites [ 31 , 32 , 72 , 73 ].…”

“…Extensive research efforts have been focusing on the PHBV degradation characteristics and mechanisms when subjected to soil and microorganisms [ 11 , 15 , 16 , 17 , 18 , 19 , 20 , 21 ], ultraviolet (UV) radiation [ 22 , 23 , 24 , 25 , 26 ], hydrolytic [ 25 , 27 , 28 , 29 , 30 , 31 , 32 ] and thermal [ 16 , 33 ] conditions. The degradation of PHBV includes several competing mechanisms: the hydrolysis of the ester group, series of reactions initiated by free radicals, crosslinking reactions, and Norrish I and II mechanisms are the most described processes [ 22 , 34 ].…”

“…The degradation of PHBV includes several competing mechanisms: the hydrolysis of the ester group, series of reactions initiated by free radicals, crosslinking reactions, and Norrish I and II mechanisms are the most described processes [ 22 , 34 ]. Due to the chain cleavage of the polymer during degradation, the molar mass, crystallinity and crystal structure, as well as the chemical/thermal/mechanical properties, are affected [ 11 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 ]. The degradation rates of PHBV under simultaneous conditions can be significant.…”