Thaís Larissa do Amaral Montanheiro

Preparation and Characterization of Maleic Anhydride Grafted Poly(Hydroxybutirate-CO-Hydroxyvalerate) – PHBV-g-MA

A compatibilizer agent was successfully produced by grafting maleic anhydride (MA) to poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) chains on a reactive processing by mechanical mixing, using a mixture of PHBV, MA and dicumyl peroxide (DCP) as initiator. The resulting PHBV grafted MA (PHBV-g-MA) was characterized by Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and gel permeation chromatography (GPC), and its properties were compared to neat PHBV. FTIR showed an absorption band at 699 cm-1 for PHBV-g-MA, related to CH group of grafted anhydride ring. The initial thermal degradation temperature of the compatibilizer agent was reduced when compared to neat PHBV. DSC analysis showed that after grafting MA onto PHBV the crystallization temperature was about 20oC higher than neat PHBV, and the degree of crystallinity was increased. GPC analysis showed that MA when grafted onto PHBV led to a reduction of molecular weight and polydispersity.

Nanocomposites of Polyhydroxyalkanoates Reinforced with Carbon Nanotubes: Chemical and Biological Properties

The polyhydroxyalkanoates (PHA) is one of the most investigated polymers in the development of eco-friendly nanocomposites. Biotechnology is used for their production and the mechanisms of their biodegradation make them very interesting polymers to replace conventional polymers in applications where the biodegradability is a desirable characteristic. PHA applications include medical field (suture fasteners, staples, screws, valves, orthopedic pins, etc.) besides agriculture and packaging sectors. The introduction of nanofillers in the polyhydroxyalkanoates matrixes is one of the ways used in an attempt to improve their properties or to reach new properties. With this goal, PHA/carbon nanotubes (CNT) nanocomposites have been quite studied. The remarkable properties shown by carbon nanotubes such as high Young’s modulus, high thermal stability and electrical conductivity, and their low chemical reactivity is the key to achieve excellent properties from PHA nanocomposites, and to maintaining the matrix biodegradability. CNT cause changes in PHA characteristics that can affect the biodegradation rate as crystallinity degree, porosity, surface roughness, and hydrophilicity of polymer matrix. Many researches have shown the effects and advances caused by CNT filler in the mechanical resistance, crystallinity degree, thermal properties, and other important characteristics of PHA nanocomposites. However, these works have disregarded the study of the biodegradation of PHA/CNT nanocomposites, what is essential to define the application field of final product.

Effect of Graphite Nanosheets on Properties of Poly(3-hydroxybutyrate-co-3-hydroxyvalerate)

The influence of different contents, 0.25, 0.50, and 1.00 wt%, of graphite nanosheets (GNS) on the properties of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) nanocomposites obtained by solution casting method has been studied. GNS were prepared by three steps: intercalation (chemical exfoliation), expansion (thermal treatment), and the GNS obtainment (physical treatment by ultrasonic exfoliation). X-ray diffraction (XRD), Raman spectroscopy, and field emission gun-scanning electron microscopy (FE-SEM) showed that the physical, chemical, and thermal treatments preserved the graphite sheets structure. XRD and Raman results also showed that GNS were dispersed in the PHBV matrix. The degree of crystallinity (X) of the nanocomposites did not change when the graphite nanosheets were added. However, the GNS acted as nucleation agent for crystallization; that is, in the second heating the samples containing GNS showed two melting peaks. The addition the GNS did not change the thermal stability of the PHBV.