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Efficacy of Spirulina sp. polyhydroxyalkanoates extraction methods and influence on polymer properties and composition

Costa, Samantha Serra, Miranda, Andréa Lobo, Assis, Denilson de Jesus, Souza, Carolina Oliveira, de Morais, Michele Greque, Costa, Jorge Alberto Vieira, Druzian, Janice Izabel
Algal research 2018 v.33 pp. 231-238
Fourier transform infrared spectroscopy, Spirulina, composite polymers, crystal structure, methanol, microalgae, molecular weight, polyhydroxyalkanoates, sodium hypochlorite
The objective of this study was to evaluate the efficacy of methods used to extract polyhydroxyalkanoates from Spirulina sp. LEB-18 microalgae and to examine the influence of these methods on the purity, properties, and composition of the polymers. Polyhydroxyalkanoates were characterized by Fourier transform infrared spectroscopy (FTIR), molecular mass, degree of crystallinity, and monomer composition. The efficacy of the extraction methods varied, with polyhydroxyalkanoate accumulation.between 6.10 and 9.80%, and degrees of purity between 63.51 and 93.62%. Using sodium hypochlorite in the initial stage of the extraction increased accumulation, while using methanol at the end of the process increased the purity of the polymers. The molecular mass and crystallinity index of the polyhydroxyalkanoates varied, showing that the extraction methods interfered with polymer properties. The composition of polyhydroxyalkanoates was also influenced by the extraction, with varying percentages of monomers identified. The copolymers of the polyhydroxyalkanoates obtained are formed by the monomers 11-hydroxyhexadecanoate, in a higher proportion, hydroxyheptanoate and hydroxytetradecanoate, demonstrating that Spirulina sp. LEB-18 is capable of producing medium and long chain polymers. The detection of these monomer blocks in the polyhydroxyalkanoate structure of this microalga is an important scientific novelty because these monomer blocks are constituents of new polymers. An indirect relationship (R2 = 0.8044) was observed between the percentage of the 11-hydroxyhexadecanoate monomer and the degree of crystallinity of polyhydroxyalkanoates obtained by the different methods. This suggests that obtaining the polymer with medium- and long-chain monomers contributes to reduction of crystallinity.