Browsing by Author "Dias, Rolando"
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- 520b Dynamic prediction of microstructure and molecular size in coordination terpolymerizations including cross-linking and branchingPublication . Dias, Rolando; Costa, Mário RuiThe production of terpolymers using coordination catalysts is a subject with a great industrial importance, being the ethylene-propylene-diene (EPDM) the most representative chemical system within this class of polymers[1-4]. For technical reasons, only a very low content (less than 2 mol %) of diene monomer (such as ethylidene norbornene (ENB)) can usually be incorporated in the terpopolymer. Chain branching and cross-linking, leading eventually to gel formation are important limiting factors to increase the diene content as desired to obtain products with improved properties.
- Assessment of RAFT polymerization in the synthesis of crosslinked materials for energy storagePublication . Tristão, Paulo; Costa, Hugo Davide; Kadhirvel, Porkodi; Dias, Rolando; Costa, Mário RuiThe synthesis and characterization of two different classes of polymer crosslinked materials, useful for energy storage and improving energy efficiency, is here studied. Products resulting from the encapsulation of phase change materials (PCM), which can be used for thermal energy storage/release, are considered as first case study. For this purpose, different kinds of PCM can be considered in the encapsulation process, namely renewable based PCM such as natural fatty acids (e.g. stearic/palmitic acids). The sulfur inverse-vulcanization process, producing materials with useful electrochemical properties, is considered as second case study. This latter process takes advantage of the excess of elemental sulfur that is generated in petroleum refining and allows the synthesis of sulfur-rich copolymers to be applied (e.g.) as active materials in lithium-sulfur (Li-S) batteries.
- Branching and crosslinking in coordination terpolymerizationsPublication . Dias, Rolando; Costa, Mário RuiA general kinetic method, based upon population balances of generating functions, is applied to the prediction of the microstructure and molecular size of non-linear terpolymers obtained through the coordination polymerization of two monovinyl monomers and a non-conjugated diene. A rather complex kinetic scheme involving crosslinking and long-chain branching is considered. It is shown that even in these conditions it is possible to carry out the prediction of molecular size and mass distributions, sequence size distributions, and z-average mean-square radius of gyration of the polymers. The influence of some kinetic parameters on the properties of the products is studied, considering a homogeneous operation in a semi-batch reactor. The used simulation method is able to predict these properties before and after gelation whenever it occurs.
- Bulk crosslinking copolymerization: comparison of different modeling approachesPublication . Lazzari, Stefano; Hamzehlou, Shaghayegh; Reyes, Yuri; Leiza, Jose Ramon; Costa, Mário Rui; Dias, Rolando; Storti, GiuseppeThe predictions of four different models of crosslinking copolymerization, Kinetic Monte Carlo (KMC), statistic/kinetic Flory/Tobita (FT) model, and two kinetic approaches based on population balance equations (PBE) (solved with generating functions (GF) and numerical fractionation (MRNF), respectively), were compared. The approaches underlying more restrictive assumptions but asking for less computational effort, FT and MRNF, lead to very satisfactory predictions in terms of average properties (sol and gel fractions, degrees of polymerizations, crosslinking densities). On the other hand, fully detailed models (KMC) as well as more computationally demanding numerical solutions of the detailed PBE (GF) become necessary when the chain length distributions are required.
- Calculation of CLD using population balance equations of generating functions: linear and non-linear ideal controlled radical polymerizationPublication . Dias, Rolando; Costa, Mário RuiPopulation balance equations in terms of generating functions (GF) are used to predict chain length distributions (CLD) of linear and non-linear ideal controlled radical polymerization (CRP) systems. It is here shown that under simplified conditions analytical solutions for the CLD can be found and moreover the fundamental CLD derived by H. Tobita in 2006 is a limiting case of the more general solutions here presented. In order to deal with more complex CRP systems, solutions based upon the numerical inversion of GF are presented. These studies are also extended to the non-linear CRP of vinyl/divinyl monomers where multimodal CLDs are predicted to occur.
- Carbon-based hydrogelsPublication . Bzainia, Amir; Gomes, Catarina P.; Dias, Rolando; Costa, Mário RuiThis chapter intends to give insight into the use of carbon-based hydrogels for energy storage and/or conversion, which are becoming critical, given the ongoing need for decarbonization and growing renewable energy production. The ability to use sustainable materials and the added advantage to incorporate tailor-made, nontoxic, cheap, and electrochemically active functional moieties during their synthesis make them frontrunner materials in the field of green chemistry and energy applications. Here, after a brief introduction of graphene-, synthetic polymer-, and natural polymer-based hydrogels and many possibilities for their hybrid combination, a particular emphasis is given to their application to energy storage, energy conversion, and energy efficiency enhancement systems. Application examples concerning metal-air batteries, fuel cells, water electrolyzers, microbial fuel cells, photoelectrochemical water splitting, supercapacitors, lithium-ion batteries, and other metal-ion batteries, desalination, and water purification through solar vapor generation are highlighted.
- Chemical characterization and bioactive properties of different winemaking residues towards their valorizationPublication . Duarte, Cristina Nogueira; Dias, Maria Inês; Heleno, Sandrina A.; Dias, Rolando; Barros, Lillian; Amaral, Joana S.In the last decades, there has been an increasing concern in the search for strategies towards the valorization of agricultural residues. Annually, wine production is responsible for the generation of large quantities of phytotoxic waste, whose disposal is challenging as these residues can be hazardous to the environment when they are overused as fertilizers or simply discarded [1]. However, some of these residues can be a source of interesting compounds such as proteins, fibers, and phenolic compounds. In particular, the bioactive phenolic molecules have attracted considerable attention from the pharmaceutical, cosmetic, and food industries. Up until now, different studies have been conducted on the characterization of grape pomace and their components such as seeds, skins, and stems, particularly focusing on residues from red grape varieties [2]. However, less attention has been paid to other by-products generated during winemaking such as residues from white wine production, wine lees, and diatomaceous earth, which are used in the filtration of wine and represents approximately 250 tons/year of residues from the wine sector just in Portugal. In this context, as part of the project BacchusTech that seeks to develop a new innovative process, including the extraction, purification, and concentration of bioactive compounds present in winemaking residues, this work aimed in characterizing the pomace obtained from red and white wines production, the residues obtained after white pomace distillation, wine lees and diatomaceous earth in terms of phenolic compounds composition and extracts bioactivity. The residues were extracted using an hydroalcoholic solvent (80%, v/v), total phenolic compounds were estimated using the Folin-Ciocalteu reagent and individual phenolic compounds were identified and quantified by liquid chromatography coupled to mass spectrophotometry (HPLCDAD- ESI-MS/MS). Additionally, the biological activity was assessed through TBARS, DPPH, and reductive power assays to determine the antioxidant activity, and the antimicrobial activity was evaluated by broth microdilution against eight bacteria and two fungi. The non-anthocyanin and anthocyanin phenolic composition were in accordance with the previously reported by Sun et al. and He et al. [3,4], respectively, in red wines. Fifteen non-anthocyanin phenolic compounds were found, five phenolic acids (gallic acid and derivatives, p-hydroxybenzoic and p-coumaric acid), four flavan-3-ols (procyanidin dimers), two O-glycosilated flavanols (isorhamnetin and quercetin derivatives), three flavanol aglycones (quercetin, kaempherol, and myricetin), and one unknown compound. Regarding anthocyanins, five compounds were found, namely malvidin derivatives linked to acyl groups. Wine lees and white grape pomace before distillation presented the highest amounts of phenolic compounds; however, only diatomaceous earth sample reveal the presence of O-glycosylated flavonoids. All samples showed antibacterial and antifungal activity against most of the tested microorganisms, especially the red and white grape pomace before distillation and diatomaceous earth in the bacteriostatic activity and the wine lees in the fungistatic activity. In general, all samples showed promising antioxidant capacity, with very good results being obtained on TBARS assay, particularly for the white pomace after distillation (EC50 = 0.016±0.002 mg/mL), diatomaceous earth (EC50 = 0.063±0.001 mg/mL) and in red pomace before distillation (EC50 = 0.08±0.04 mg/mL). Overall, the obtained results demonstrated that the evaluated wastes are good sources of bioactive compounds, namely anthocyanins and other phenolic compounds, that can be used as raw materials for subsequent steps of concentration, purification and/or isolation of added-value compounds.
- Chemical characterization, antioxidant and antimicrobial activities of winemaking industry by-productsPublication . Duarte, Cristina Nogueira; Dias, Maria Inês; Heleno, Sandrina A.; Santos-Buelga, Celestino; Dias, Rolando; Barros, Lillian; Amaral, Joana S.The exploitation of bioactive compounds trom agri-food by-products has been attracting an increasing interest from different industries within a circular economy context since several of compounds may have health properties or be used as natural colorants or preservatives. So far, several studies have been developed on the characterization of red wine grape pomace and its components (seeds, skins, and stems). However, less attention has been paid to other by-products, such as grape pomace from white wine, the residues after distillation, wine lees, and diatomaceous earth, the latter used in the filtration of wine and corresponding to about 250 tons/year of waste in Portugal. In this work, samples of these by-products were evaluated for their chemical composition by HPLC-DAD-ESI-Msn and bioactivities (antioxidant activity by TBARS, DPPH, and reducing power assays, and antimicrobial activity against eight bacteria and two fungi). Fifteen non-anthocyanin phenolic compounds were found, including 5 phenolic acids, 4 flavan-3-0Is, 2 0- glycosylated flavanols, 3 flavanol aglycones, and one unknown. In the red wine byproducts 12 anthocyanins were detected, most being malvidin derivatives. Wine lees and white grape pomace before distillation presented the highest contents of phenolic compounds. Ali samples showed antibacterial and antifunga! activity against most of the tested microorganisms, with red and white grape pomace and diatomaceous earth having the best bacteriostatic activity, while the lees stood out against fungi. Ali samples showed promising antioxidant capacity, with very good results obtained on TBARS for the white pomace after distillation and diatomaceous earth. Overall, the results show that besides grape pomace other wine industry byproducts are also good sources of bioactive compounds with high potential for exploitation.
- Chemical composition and biological activity of different residues obtained from the wine industryPublication . Duarte, Cristina Nogueira; Dias, Maria Inês; Heleno, Sandrina A.; Santos-Buelga, Celestino; Dias, Rolando; Barros, Lillian; Amaral, Joana S.In recent years, the bioactive compounds present in agri-food sub-products have attracted increased attention due to their health benefits and advantages within a circular economy context. Annually, wine production is responsible for the production of large amounts of phytotoxic waste, which elimination is considered challenging since these residues can be hazardous to the environment when used as fertilizers or just discarded. Phenolic compounds are secondary metabolites processed by plants that have shown several health benefits, acting as antioxidants, antimicrobials, anticarcinogenic, or antidiabetics, among others. Bioactive phenolic molecules have attracted considerable attention from the pharmaceutical, cosmetic, and food industries. So far, several studies have been developed on the characterization of grape pomace and its components (seeds, skins, and stems), especially directed to the residues of red varieties.1 However, less attention has been paid to other by-products generated during winemaking, such as waste from the production of white wine, wine lees and diatomaceous earth. The latter is used in the filtration of wine and constitutes about 250 tons/year of waste from the wine sector in Portugal alone, making it a very pertinent residue with still scarce information being found in the literature. In this context, within the framework of the BacchusTech project that seeks to develop new innovative processes, comprising the extraction, purification, and concentration of bioactive compounds present in winemaking residues, different residues including pomace, lees and diatomaceous earth were evaluated for their chemical composition and bioactivities. Residues were extracted using an hydroalcoholic solvent (80%, v/v), total phenolic compounds were estimated using the Folin- Ciocalteu reagent and individual phenolic compounds were identified and quantified by liquid chromatography coupled to mass spectrophotometry (HPLC-DAD-ESI-MSn). Additionally, the biological activity was assessed through TBARS, DPPH, and reducing power assays to determine the antioxidant activity, and the antimicrobial activity was evaluated by broth microdilution against eight bacteria and two fungi. The phenolic composition was in accordance with the previously reported in red wines.2,3 Fifteen non-anthocyanin phenolic compounds were found, five phenolic acids (gallic acid and derivatives, p-hydroxybenzoic and p-coumaric acid), four flavan-3-ols (procyanidin dimers), two O-glycosylated flavanols (isorhamnetin and quercetin derivatives), three flavanol aglycones (quercetin, kaempferol, and myricetin), and one unknown compound. Regarding anthocyanins, five compounds were found, namely malvidin derivatives linked to acyl groups. Wine lees and white grape pomace before distillation presented the highest contents of phenolic compounds; however, only diatomaceous earth sample reveal the presence of O-glycosylated flavonoids. All samples showed antibacterial and antifungal activity against most of the tested microorganisms. The best bacteriostatic activity was evidenced by the red and white grape pomace before distillation and diatomaceous earth, while the wine lees stood out for their fungistatic activity. In general, all samples showed promising antioxidant capacity, with very good results being obtained on TBARS assay, particularly for the white pomace after distillation (EC50 = 0.016±0.002 mg/mL), diatomaceous earth (EC50 = 0.063±0.001 mg/mL) and red pomace before distillation (EC50 = 0.08±0.04 mg/mL). Overall, the results obtained showed that the residues analyzed are good sources of bioactive compounds, namely anthocyanins and other phenolic compounds, which can be used as raw materials for the steps of concentration, purification and/or isolation of compounds of added value.
- The combined use of orthogonal Laguerre expansions and numerical evaluation of generating functions for computing polymer chain-lenght distributionsPublication . Costa, Mário Rui; Dias, RolandoThe Combined Use of Orthogonal Laguerre Expansions and Numerical Evaluation of Generating Functions for Computing Polymer Chain-Lenght Distributions