Bacterial cellulose produced from Gluconacetobacter xilinus was used to produce cellulose nanocrystals by sulfuric acid hydrolysis. Hydrolysis was performed with 64% sulfuric acid at 50 ºC with the hydrolysis time ranging between 5 and 90 min. The production of nanocrystals was observed to have size distributions that were dependent on hydrolysis times up to 10 min, after which time the suspensions showed distributions closer in size. Results from thermal analysis and X-ray diffraction showed that the amorphous cellulose was removed, leaving only the crystalline portion. Self-supported films were formed from the suspension of nanocrystals and had iridescence characteristics. The films were characterized by microscopy measures and specular reflectance.

In this work, methylcellulose (MC) was produced from bacterial cellulose (BC), using dimethyl sulfate in a 3 h (MC3h) or 5 h (MC5h) reaction under heterogeneous conditions, with reagent substitution at each hour. MC3h showed a degree of substitution (DS) of 2.26 ± 0.13 and MC5h showed a DS of 2.33 ± 0.05. The two samples were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray powder diffraction (XRD), differential thermal analysis (DTA), thermal gravimetric analysis (TGA), 13C nuclear magnetic ressonance (NMR) and 1H NMR techniques. The FTIR spectra of the BC and MC samples present significant differences in the regions from 3750 to 2750 cm−1 and from 1500 to 750 cm−1, which evidence the methylation of the samples. Solid state NMR spectroscopy of the MC samples was used to identify the 13C NMR signals of substitution at sites C-2, C-3 or C-6 in the glucopyranose units. The modification of bacterial cellulose produced a material with a high DS, determined by three different techniques (chemically and using the liquid 1H and solid 13C NMR spectra). These samples also demonstrate high crystallinity and thermal stability. With the MC samples synthesized in this work, transparent and resistant films were prepared and also a highly porous sponge like material.

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.

Commercial copolymers based on styrene and divinylbenzene containing sulfonic acid groups were used as support for the incorporation of silver nanoparticles. These nanoparticles were obtained in situ by the reduction of Ag+ by using hydroxylamine in the presence of a protective agent. These materials were characterized with determination of the silver content and their morphological characteristics. The antibacterial activity of the final products against Escherichia coli was evaluated and the results show that the synthesized copolymers had antibacterial effect varying from 54 to 100%. The most efficient composite was made with small, well distributed particles.

O presente trabalho discute os recentes avanços na biossíntese e na produção de celulose bacteriana (CB) pela gram-negativa, aeróbia e aceto-ácida Gluconacetobacter. xylinus. A CB se difere de seu par vegetal, principalmente devido ao seu caráter de fibras nanométricas, contra o caráter micrométrico da vegetal, são extruídas através da parede celular de G. xylinus, com isso sua estrutura macroscópica é mecanicamente e fisicamente mais resistente, abrindo grandes oportunidades de aplicações tecnológicas e biológicas, muito além das obtidas pela celulose vegetal. O desafio atual está no aumento da produção de CB, que se debruça num maior entendimento de sua biossíntese para que seja possível uma posterior manipulação genético-bioquímica oriundas do recente avanço na biologia molecular e nos bioprocessos. São relacionados trabalhos utilizando a CB como base para produção de compósitos como também o que a está sendo feito de mais atual com este material biológico.

The present paper discusses the recent advances about the biosynthesis and production of bacterial cellulose (BC), from gram-negative, aerobic and acetic acid Gluconcetobacter xylinus (Gx). The BC differs from his vegetal pair, mainly due his feature of nanometric fibers, as opposed to micrometric feature of vegetal cellulose, are extruded through the cellular wall of Gx, thereby the macroscopic structure of BC is mechanically and physically more resistant, open big opportunities of biological and technological applications, apart from that obtained by vegetal cellulose. The actual challenge is in the grown of production of BC, which deals a superior understanding of his biosynthesis, to makes possible a later genetic-biochemical manipulation derived from recent advances in molecular biology. Are related works using the BC for production of composites and also what is being done of more actual with this biological material.

A simple method was developed to load a large amount of silver nanoparticles into bacterial cellulose (BC) produced by Gluconacetobacter xylinus in a controlled manner. Due to the high electron-rich oxygen density in the BC macromolecules and the large surface area of the BC nanoporous structure as an effective nanoreactor, the in situ direct metallization technique was successfully used to synthesize Ag nanoparticles with an average diameter of 30 nm and a loading content of at least 5 wt. (%), approximately. This novel procedure provides an easy and economical way to manufacture Ag nanoparticles supported on a porous membrane for various biomedical applications. These composite fibers showed nearly 100% antibacterial activity (elimination of microorganisms) against Escherichia coli because of the presence of the silver nanoparticles.