Armando J.D. Silvestre

The quest for sustainable polyesters – insights into the future

Polyesters from renewable resources are an expanding area with a burgeoning scientific activity, nevertheless little has been reviewed about this particular class of polymers. The present appraisal intends to contribute to fill this literature gap by reviewing recent aspects related to the most promising renewable-based polyesters. Emphasis will be placed on bio-based polyesters that, given their comparable properties, may replace polymers derived from fossil fuel feedstock, and on bio-based polyesters with completely innovative properties for novel applications. Furthermore, the sources of renewable monomers will also be reviewed, together with the most relevant eco-friendly synthetic approaches used in polycondensation reactions leading to polyesters.

Materials from renewable resources based on furan monomers and furan chemistry: work in progress

The polymerisation of furan monomers and the exploitation of some of the chemical peculiarities of the furan heterocycle have generated a wide diversity of macromolecular materials based on renewable resources. We present here recent contributions to this field, including ongoing studies on the synthesis and characterisation of novel furan polyesters and on the application of the Diels–Alder reaction to the preparation of linear and branched thermally reversible polyadducts.

Biobased polyesters and other polymers from 2,5-furandicarboxylic acid: a tribute to furan excellency

Motivated by the general concern about sustainability and environmental issues, an intense search for renewable-based polymers has grown exponentially in recent years. This search definitely spotlighted polyesters derived from 2,5-furandicarboxylic acid, among other polymers, as some of the most promising, especially due to the resemblance of this renewable monomer to the well-known petroleum-based terephthalic acid, as well as owing to the possibility of preparing innovative materials. The huge number of recent papers and patents about this family of polymers explore aspects as diverse as synthesis with other renewable-based monomers, leading to the preparation of materials with enhanced thermo-mechanical, biodegradability and liquid crystalline properties, among other features. Additional aspects pursued in such studies are innovation in the synthetic approaches or their optimisation, as well as the development of applications for everyday-life objects for example packaging materials, especially bottles, textiles, coating, and toners, among many other uses. Despite this intense activity, little has been reviewed recently about this unique family of polyesters or derived polymers, as the only reviews on the subject date back to the last century. In this perspective, the present review aims at contributing to filling this literature gap, covering recent aspects related with challenges in developing polyesters, polyamides, or other polymers from 2,5-furandicarboxylic acid and their precursors. Emphasis is placed on monomer synthesis, polymerisation reactions, catalysts and applications.

Novel transparent nanocomposite films based on chitosan and bacterial cellulose

New nanocomposite films based on different chitosan matrices (two chitosans with different DPs and one water soluble derivative) and bacterial cellulose were prepared by a fully green procedure by casting a water based suspension of chitosan and bacterial cellulose nanofibrils. The films were characterized by several techniques, namely SEM, AFM, X-ray diffraction, TGA, tensile assays and visible spectroscopy. They were highly transparent, flexible and displayed better mechanical properties than the corresponding unfilled chitosan films. These new renewable nanocomposite materials also presented reasonable thermal stability and low O2 permeability.

Electrostatic assembly of Ag nanoparticles onto nanofibrillated cellulose for antibacterial paper products

Nanofibrillated cellulose offers new technological solutions for the development of paper products. Here, composites of nanofibrillated cellulose (NFC) and Ag nanoparticles (NP) were prepared for the first time via the electrostatic assembly of Ag NP (aqueous colloids) onto NFC. Distinct polyelectrolytes have been investigated as macromolecular linkers in order to evaluate their effects on the building-up of Ag modified NFC and also on the final properties of the NFC/Ag composite materials. The NFC/Ag nanocomposites were first investigated for their antibacterial properties towards S. aureus and K. pneumoniae microorganisms as compared to NFC modified by polyelectrolytes linkers without Ag. Subsequently, the antibacterial NFC/Ag nanocomposites were used as fillers in starch based coating formulations for Eucalyptus globulus-based paper sheets. The potential of this approach to produce antimicrobial paper products will be discussed on the basis of complementary optical, air barrier and mechanical data.

Cork suberin as a new source of chemicals.: 1. Isolation and chemical characterization of its composition

Extractive-free cork from Quercus suber L. was submitted to a solvolysis treatment with methanolic NaOH which yielded 37% (o.d. cork) of suberin. This mixture of compounds was thoroughly characterized by FTIR, 1H- and 13C-NMR, gas chromatography coupled with mass spectrometric (GC-MS) analysis, vapour pressure osmometry (VPO), mass spectrography (MS) and gel permeation chromatography (GPC). After derivatization, the main components of the volatile fraction, representing less than half of the total, were found to be omega-hydroxymonocarboxylates, alpha, omega-dicarboxylates, simple alkanoates and 1-alkanols, all with chain lengths ranging from C16 to C24. A second fraction, with an average molecular weight about three times higher, was detected by VPO, MS and GPC. The presence of this important fraction in cork suberin had not been recognized in earlier studies. Both fractions constitute interesting precursors for the elaboration of new materials.

Comparative studies of fungal degradation of single or mixed bioaccessible reactive azo dyes

A screening using several fungi (Phanerochaete chrysosporium, Pleurotus ostreatus, Trametes versicolor and Aureobasidium pullulans) was performed on the degradation of syringol derivatives of azo dyes possessing either carboxylic or sulphonic groups, under optimized conditions previously established by us. T. versicolor showed the best biodegradation performance and its potential was confirmed by the degradation of differently substituted fungal bioaccessible dyes. Enzymatic assays (lignin peroxidase, manganese peroxidase, laccase, proteases and glyoxal oxidase) and GC-MS analysis were performed upon the assay obtained using the most degraded dye. The identification of hydroxylated metabolites allowed us to propose a possible metabolic pathway. Biodegradation assays using mixtures of these bioaccessible dyes were performed to evaluate the possibility of a fungal wastewater treatment for textile industries.

Characterization of Phenolic Components in Polar Extracts of Eucalyptus globulus Labill. Bark by High-Performance Liquid Chromatography–Mass Spectrometry

High-performance liquid chromatography-electrospray ionization mass spectrometry (HPLC-ESI-MS) and tandem mass spectrometry (MS(n)) were used to investigate the phenolic constituents in methanol, water, and methanol/water extracts of Eucalyptus globulus Labill. bark. Twenty-nine phenolic compounds were identified, 16 of them referenced for the first time as constituents of E. globulus bark, namely, quinic, dihydroxyphenylacetic, and caffeic acids, bis(hexahydroxydiphenoyl (HHDP))-glucose, galloyl-bis(HHDP)-glucose, galloyl-HHDP-glucose, isorhamentin-hexoside, quercetin-hexoside, methylellagic acid (EA)-pentose conjugate, myricetin-rhamnoside, isorhamnetin-rhamnoside, mearnsetin, phloridzin, mearnsetin-hexoside, luteolin, and a proanthocyanidin B-type dimer. Digalloylglucose was identified as the major compound in the methanol and methanol/water extracts, followed by isorhamnetin-rhamnoside in the methanol extract and by catechin in the methanol/water extract, whereas in the water extract catechin and galloyl- HHDP-glucose were identified as the predominant components. The methanol/water extract was shown be the most efficient to isolate phenolic compounds identified in E. globulus bark.

Transparent bionanocomposites with improved properties prepared from acetylated bacterial cellulose and poly(lactic acid) through a simple approach

The preparation and characterization of biocomposite materials with improved properties based on poly(lactic acid) (PLA) and bacterial cellulose, and, for comparative purposes, vegetal cellulose fibers, both in their pristine form or after acetylation, is reported. The composite materials were obtained through the simple and green mechanical compounding of a PLA matrix and bacterial cellulose nanofibrils (or vegetable fibers), and were characterized by TGA, DSC, tensile assays, DMA, SEM and water uptake. The bionanocomposites obtained from PLA and acetylated bacterial cellulose were particularly interesting, given the considerable improvement in thermal and mechanical properties, as evidenced by the significant increase in both elastic and Young moduli, and in the tensile strength (increments of about 100, 40 and 25%, respectively) at very low nanofiller loadings (up to 6%). These nanocomposites also showed low hygroscopicity and considerable transparency, features reported here for the first time.

Utilization of residues from agro-forest industries in the production of high value bacterial cellulose.

Bacterial cellulose (BC), a very peculiar form of cellulose, is gaining considerable importance due to its unique properties. In this study, several residues, from agro-forestry industries, namely grape skins aqueous extract, cheese whey, crude glycerol and sulfite pulping liquor were evaluated as economic carbon and nutrient sources for the production of BC. The most relevant BC amounts attained with the residues from the wine and pulp industries were 0.6 and 0.3 g/L, respectively, followed by biodiesel crude residue and cheese whey with productions of about, 0.1 g/L after 96 h of incubation. Preliminary results on the addition of other nutrient sources (yeast extract, nitrogen and phosphate) to the residues-based culture media indicated that, in general, these BC productions could be increased by ~200% and ~100% for the crude glycerol and grape skins, respectively, after the addition organic or inorganic nitrogen.