Tucumã (Astrocaryum aculeatum) pulp presents a large number of secondary metabolites that can mediate the synthesis of metallic nanoparticles through a greener and more sustainable synthetic route than traditional ones. This study investigated the production of silver nanoparticles (AgNPs) mediated by aqueous extracts of tucumã pulp assessing different parameters, such as temperature, concentration of extract, and pH values of the reaction media. The alkaline reaction media produced the most intense and well-defined bands around 400 nm in the electronic spectra, indicating the formation of AgNPs in the three concentrations of tucumã pulp evaluated. The increase in the temperature of the reaction media also enhanced the surface plasmon resonance band of AgNPs but it increased the polydispersivity of produced nanoparticles according to the dynamic light scattering (DLS) and transmission electron microscopy (TEM) data. Zeta potential results indicated moderate stability of the AgNPs (close to -30 mV). Antimicrobial assessment of the colloidal metal particles indicated microbicide activity against the Gram-negative Escherichia coli bacterium.

Synthetic conditions were evaluated to intercalate norbixin into layered double hydroxides (LDH). Norbixin was isolated from a hydrosoluble commercial annatto extract. LDH samples comprising M2+/Al3+ (M = Mg, Zn) were synthesized by coprecipitation and characterized by X-ray diffraction, thermal analysis coupled to mass spectrometry, vibrational spectroscopies, and solid-state 13C nuclear magnetic resonance. Radical scavenging activity of LDH hybrids was monitored by electron paramagnetic resonance towards the stable radical DPPH (1,1-diphenyl-2-picrylhydrazyl). LDH hosts presented more than 50 wt.% of norbixin and d-spacing (003) values of about 2.5 or 3.0 nm depending of the cation LDH composition. Vibrational spectra assignment (supported by density functional theory calculations) confirmed the chemical integrity of norbixin after intercalation into LDH. The inorganic layers were found to enhance the thermal stability of norbixin upon intercalation. The free radical scavenging capacity of norbixin was retained when immobilized into LDH. Considering that zinc and magnesium-LDH matrices are biocompatible and that norbixin presents biological activity, the hybrid materials appear as promising systems for biomedical assessment.

Organic-inorganic nanocomposites based on cassava starch, glycerol and chitosan-modified Veegum® HS clay mineral at two different low polymer-to-clay ratios (2.5 and 5.0 wt.%) were prepared by extrusion producing flexible, transparent and homogeneous plastics as potential candidates for agricultural purposes. X-ray diffraction and transmission electron microscopy images revealed the presence of both intercalated and exfoliated nanocomposites in all samples, in which exfoliation is the predominant type of microscopic structure. Statistically significant improvements of over 20% on the tensile strength and Young's modulus were observed for samples containing chitosan-modified clay in comparison to pristine thermoplastic starch. Chitosan deeply affects the conversion of polymer carbon to CO2 through biodegradation. Mineralization values for the sample loaded with 5.0 wt.% of chitosan-modified clay in simulated compost soil showed a reduction of almost 40% in comparison to thermoplastic starch, benefiting applications where delay degradation is required.

Celulose bacteriana (BC) foi utilizada nesse estudo como molde na preparação de compostos do tipo hidrotalcita ou hidróxidos duplos lamelares (LDHs) pelo método da co-precipitação e submetida a três tempos de envelhecimento distintos. Os compósitos isolados contendo LDH suportado na BC (BC-LDH) foram calcinados para remoção da matriz orgânica. Os óxidos metálicos mistos formados após a decomposição térmica sofreram reação de reconstrução na presença de uma solução de Na2CO3 para produzirem novamente materiais do tipo hidrotalcita (RBC-LDH). Para avaliar a influência da BC na formação do LDH, também foram analisadas as frações de LDH que não aderiram às fibras da BC e, também, o LDH sintetizado na ausência da membrana polimérica. Os difratogramas de raios X dos compósitos BC-LDH exibem picos alargados relacionados com a matriz orgânica semi-cristalina, indicando um grande nível de interação entre as fases orgânica e inorgânica. A interação também é evidenciada pelas mudanças nos perfis de decomposição dos compósitos com relação ao polímero prístino. As imagens de microscopia eletrônica de varredura mostraram a formação de partículas arredondadas submicrométricas de LDH após a remoção da membrana (RBC-LDH), diferentemente do hábito de rosetas exibido pelo LDH prístino. O envelhecimento é uma componente chave no processo de crescimento de todas as amostras de LDH produzidas, resultando na formação de partículas inorgânicas maiores à medida que o tempo aumenta. O compósito RBC-LDH envelhecido por três dias apresenta um aumento significativo na área superficial (mais do que três vezes) se comparado ao LDH preparado na ausência de BC.

Bacterial cellulose (BC) was used as a template for preparation of Hydrotalcite-type compounds or layered double hydroxides (LDHs) by co-precipitation method, and submitted to three aging times. Isolated composites containing LDH supported on BC (BC-LDH) were calcined to remove the organic matrix. Mixed metal oxides formed after thermal decomposition underwent reconstruction reaction in Na2CO3 solution producing again hydrotalcite-like materials (RBC-LDH). To evaluate the influence of BC on the LDH formation, it was also analyzed LDH fractions not attached to the BC fibers and LDH synthesized in absence of the polymeric membrane. XRD pattern of BC-LDH composites show broadened peaks related to the organic semi-crystalline matrix, indicating a deep level of interaction between organic and inorganic phases. Interaction is also evidenced by changes in the composites thermal decomposition profiles compared to pristine polymer. SEM images revealed formation of submicrometrical round-shaped LDH particles after removal of membrane (RBC-LDH), differently from the plate-habit exhibited by pristine LDH. Aging plays a key role in growth of all LDHs samples, leading to the formation of larger inorganic particles as time is increased. RBC-LDH aging for three days shows significant improvement in the surface area (more than three times) if contrasted to LDH prepared in BC absence.

Nanocompósitos à base de amido de mandioca, argila sintética hectorita e açúcar invertido (plastificante) foram preparados por processo em meio aquoso (casting) produzindo filmes transparentes e homogêneos. Pequenas quantidades de argila (5-15% em massa) produzem principalmente nanocompósitos esfoliados, enquanto grandes quantidades (30% em massa) promovem a formação de nanocompósitos intercalados. Os espectros FT-Raman mostram que bandas sensíveis à ligação de hidrogênio em grânulos de amido são progressivamente deslocadas para frequências menores quando o teor de argila é aumentado. Os nanocompósitos mostram um comportamento térmico semelhante até 320 ºC, enquanto a decomposição da biomolécula em cerca de 500 ºC é dependente do teor de argila. A liberação de CO2 em aproximadamente 300 ºC (decomposição não oxidativa das cadeias poliméricas) diminui se comparada com o desprendimento desse gás em 500 ºC quando a quantidade de argila é aumentada. Filmes com teor de argila maior que 10% não mostram melhora substancial nas propriedades de alongamento ou resistência.

Polymer-clay nanocomposites (PCN) based on cassava starch, synthetic hectorite clay and inverted sugar cane syrup (plasticizer) were prepared by solvent-assisted (casting) process producing transparent and homogeneous films. Small amounts of clay (5-15 wt.%) resulted mainly in exfoliated nanocomposites while large amounts (30 wt.%) promote the intercalated nanocomposites formation. FT-Raman bands sensitive to hydrogen bonding in starch granules are progressively shifted to lower wavenumbers as the clay content is raised. Nanocomposites show a similar thermal behavior up to 320 ºC while the biomolecule decomposition at about 500 ºC is dependent on the clay content. CO2 release at about 300 ºC (non-oxidative decomposition of polymeric chains) decreases if compared to the gas delivery at ca. 500 ºC, as the clay content is increased. Films with clay content higher than 10 wt.% show no substantial benefit for either elongation or resistance properties.