Why natural-based bioactive coatings?

The design of bioactive coatings through combining green strategies and natural formulations prevails over conventional synthetic systems. These approaches address the need to provide biofunctional properties through alternative solutions. Green strategies include methodologies that involve lower environmental impact, namely by using green solvents and reagents, or low-cost and low-toxic processes, promoting an optimized life assessment of the product, among other features. It is important to note that most recent methodologies (e.g., 3D printing, electrospinning, layer-by-layer deposition, or dip coating) enable the design of novel and tailor-made structures, whose assemblies/morphology can be essential to guarantee the formulation’s functionality.The authors are grateful to the Foundation for Science and Technology (FCT, Portugal) for financial support through national funds FCT/MCTES (PIDDAC) to CIMO ((UIDB/00690/2020 and UIDP/00690/2020)) and SusTEC (LA/P/0007/2021). National funding by FCT, through the institutional scientific employment program-contract with Arantzazu Santamaria-Echart.info:eu-repo/semantics/publishedVersio

Advances in waterborne polyurethane and polyurethane-urea dispersions and their eco-friendly derivatives: a review

Polyurethanes and polyurethane-ureas, particularly their water-based dispersions, have gained relevance as an extremely versatile area based on environmentally friendly approaches. The evolution of their synthesis methods, and the nature of the reactants (or compounds involved in the process) towards increasingly sustainable pathways, has positioned these dispersions as a relevant and essential product for diverse application frameworks. Therefore, in this work, it is intended to show the progress in the field of polyurethane and polyurethane-urea dispersions over decades, since their initial synthesis approaches. Thus, the review covers from the basic concepts of polyure-thane chemistry to the evolution of the dispersion’s preparation strategies. Moreover, an analysis of the recent trends of using renewable reactants and enhanced green strategies, including the current legislation, directed to limit the toxicity and potentiate the sustainability of dispersions, is described. The review also highlights the strengths of the dispersions added with diverse renewable additives, namely, cellulose, starch or chitosan, providing some noteworthy results. Similarly, dispersion’s potential to be processed by diverse methods is shown, evidencing, with different examples, their suitability in a variety of scenarios, outstanding their versatility even for high requirement applications.This research was funded by the University of the Basque Country (UPV/EHU) (GIU18/216 Research Group), the Spanish Ministry of Science, Innovation and Universities and European Union (MICINN/EU/FEDER) (MAT2016-76294-R and PID2019-105090RB-I00). Also, the Foundation for Science and Technology (FCT, Portugal) funded by financial support by national funds FCT/MCTES to CIMO (UIDB/00690/2020). National funding by FCT- Foundation for Science and Technology, through the institutional scientific employment program-contract with I.F.info:eu-repo/semantics/publishedVersio

Evaluating the potential of natural polymers for water-dispersible curcumin-based solid dispersion colourant systems for food applications

Solid dispersion (SD) technology, a strategy through which a hydrophobic compound is molecularly dispersed into a hydrophilic carrier, is raising interest in food applications to surpass natural colourants’ low water solubility. Motivated by the importance of using natural solutions, five natural polymers (k-carrageenan (KC), maltodextrin (MD), Arabic gum (AG), potato starch (PS), and pectin (PC) were evaluated against the synthetic benchmark polyvinylpyrrolidone (PVP)). Targeting a stable yellow hue, pH 6 was used, and the effect of salt addition on crystallinity was evaluated. Comparatively with PVP, used as a synthetic polymer reference, SDs based on MD, AG, and PC presented a deeper orange shade. Similar size distributions were achieved for the produced samples except for PS-based SDs, which showed higher sizes in volume. For all systems, polymer-curcumin hydrogen bonding was perceptible and reflected in the curcumin crystallinity modification/reduction, particularly if produced under natural pH conditions. The water solubility was significantly improved compared to free curcumin, from 1 μg/mL to 25–37 μg/mL (pH 6, PVP - 24.54 μg/mL) and 18–86 μg/mL (without pH control, PVP - 28.34 μg/mL), highlighting the favourable effect of natural polymers.The authors are grateful to the Foundation for Science and Technology (FCT, Portugal) and FEDER under Programme PT2020 for financial support to CIMO (UIDB/00690/2020 and UIDP/00690/2020) and SusTEC (LA/P/0007/2021), LSRE-LCM (UIDB/50020/2020 and UIDP/00690/2020) and ALiCE (LA/P/0045/2020). FCT for the Research grant SFRH/BD/147326/2019 of Stephany C. de Rezende and national funding by FCT, PI, through the institutional scientific employment program contract for Arantzazu Santamaria-Echart. In addition, the technical support provided by I3Bs- Research Institute on Biomaterials, Biodegradables and Biomimetics of the University of Minho is also acknowledgedinfo:eu-repo/semantics/publishedVersio

Different environmentaly-friendly strategies for loading waterborne polyurethane and polyurethane-urea dispersions

The environmental awareness has increased the research and development of eco-friendly green synthesis routes for many different applications, such as the waterborne polymer systems. Among others, waterborne polyurethanes (WBPU) and waterborne polyurethane-ureas (WBPUU) have gained attention due to their versatility in terms of composition and properties, making them suitable in a wide range of applications [1]. WBPU and WBPUU synthesis process is based on the incorporation of internal emulsifiers covalently bonded to the polymer obtaining stable water dispersions over months. Furthermore, the waterborne character of the dispersions provides the opportunity of incorporating water dispersible nanoentities and water soluble additives, enhancing or even providing additional properties. In this context, the use of renewable derivatives opens the possibility of enhancing the environmentally-friendly character. Among them, cellulose nanocrystals (CNC) are presented as a suitable candidate for the preparation of nanocomposites, considering their unique properties in the nanoscale dimension, provided by their high length/diameter aspect ratio and high specific mechanical properties [2]. Otherwise, the incorporation of natural water soluble additives has focused attention on extracts obtained from plants, consisting in biologically active compounds [3], whose antimicrobial character can determine the antimicrobial behavior of the WBPU and WBPUU. Therefore, in this work, different strategies have been analyzed for the preparation of WBPU-CNC nanocomposites and WBPUU-plant extracts varying their content as well as their incorporation route.info:eu-repo/semantics/publishedVersio

Development of waterborne polyurethane-ureas added with plant extracts: Study of different incorporation routes and their influence on particle size, thermal, mechanical and antibacterial properties

Polyurethane-ureas are a versatile family of polymers which can be employed in a wide range of applications. Among them, waterborne polyurethane-urea (WBPUU) dispersions are gaining relevance in the field of environmentally-friendly products since their productive process adopts green synthesis routes, avoiding the use of organic solvents. Furthermore, their waterborne character can be exploited to incorporate several water compatible ingredients able to confer functional properties to the final materials. Among them, plant extracts, which are known to have relevant bioactivities, can be viewed as interesting candidates. Therefore, in this work, two extracts known to present antimicrobial activity (Melissa officinalis L. and Salvia officinalis L.) were obtained by the infusion method and incorporated into the WBPUU (1, 3 and 5 wt%) following different incorporation routes comprising its adding during different phases of the productive process (post-, in-situ and pre- methods). Thereafter films were prepared by solvent-casting and characterized from the viewpoint of physicochemical, thermal, mechanical, thermomechanical and antibacterial properties and morphologically. The studied incorporation routes resulted in different intercalation mechanisms that varied from extract positioned among the polyurethane-urea nanoparticles (post-method) to extract partially embedded inside them (in-situ and pre-methods), which produced stiffening or flexibilizing effects in the produced films, enhancing in general the antimicrobial characteristics of films after 4 days of incubation comparing with base WBPUU, especially when the extract is embedded.Financial support from the Basque Government (IT-776-13), the Spanish Ministry of Economy and Competitiveness (MINECO) (MAT2016-76294-R), POCI-01-0145-FEDER-006984 (LA LSRE-LCM) funded by ERDF through POCI-COMPETE2020 and FCT and NORTE-01-0145-FEDER-000006, funded by NORTE 2020, under PT2020 through ERDF is gratefully acknowledged. We also wish to acknowledge the “Macrobehaviour- Mesostructure-Nanotechnology” SGIker units from the University of the Basque Country, for their technical support. A.S-E thanks the University of the Basque Country for Ph.D. grant (PIF/UPV/12/201).Financial support from the Basque Government (IT-776-13), the Spanish Ministry of Economy and Competitiveness (MINECO) (MAT2016-76294-R), POCI-01-0145-FEDER-006984 (LA LSRE-LCM) funded by ERDF through POCI-COMPETE2020 and FCT and NORTE- 01-0145-FEDER-000006, funded by NORTE 2020, under PT2020 through ERDF is gratefully acknowledged. We also wish to acknowledge the “Macrobehaviour- Mesostructure-Nanotechnology” SGIker units from the University of the Basque Country, for their technical support. A.S-E thanks the University of the Basque Country for Ph.D. grant (PIF/UPV/12/201).info:eu-repo/semantics/publishedVersio

Bioinks functionalized with natural extracts for 3D printing

In the search of materials valid for direct ink writing (DIW) 3D printing and with special interest for the biomedical and pharmaceutical applications, the development of bioactive inks for DIW is of great interest. For that purpose, in this work bioactive waterborne polyurethane–urea inks were prepared by addition of natural extracts (logwood, chestnut, and alder buckthorn) and cellulose nanofibers (CNF). The rheological behavior of the inks proved to be strongly dependent on the extract type and content, and the addition route used. Inks prepared by ex-situ incorporation of the extracts showed a strong gel-like behavior, as did inks prepared with chestnut and alder buckthorn extracts, which, in turn, hindered a continuous flow during the printing process, resulting in 3D printed parts with poor shape fidelity. On the other hand, inks prepared insitu and with logwood extract showed more facility to flow and higher homogeneity, which translated in better printability and better shape fidelity, further enhanced for CNF containing inks. 3D printed composites showed reinforced mechanical behavior, as well as in materials with enhanced antibacterial behavior. Overall, the possibility to successfully prepare bioactive inks valid for 3D printing was proven.Open Access funding provided thanks to the CRUE-CSIC agreement with Springer Nature. Financial support from the Basque Government (Grupos Consolidados (IT-1690-22), Elkartek (KK19-00048)) is acknowledged.info:eu-repo/semantics/publishedVersio

Green nanocomposites from Salvia-based waterborne polyurethane-urea dispersions reinforced with nanocellulose

Waterborne polyurethane-urea (WBPUU) dispersions, products having none or low contents of organic solvents, depending on the used synthesis process, can provide suitable environmentally-friendly strategies to prepare novel materials. Moreover, waterborne systems enable the incorporation of aqueous dispersible nanoentities and soluble additives, which provides a strategy to design versatile functional materials with tailored properties. Having demonstrated in previous work the bacteriostatic properties of a 3 wt% Salvia-based WBPUU against Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa, this work is focused in the preparation of Salvia-based WBPUU added with cellulose nanocrystals (CNC) tackling the preparation of functional green nanocomposite films with increased mechanical properties. Through this strategy, nanocomposites loaded with 1, 3 and 5 wt% of CNC were prepared, showing an effective CNC incorporation avoiding agglomerates. CNC addition is able to modulate soft and hard phase's segregation, inducing enhanced mechanical stiffness, together with improved deformability, while retarding thermomechanical instability to higher temperatures.Financial support from the University of the Basque Country (UPV/ EHU) (GIU18/216 Research Group), the Spanish Ministry of Economy and Competitiveness (MINECO) (MAT2016-76294-R). Foundation for Science and Technology (FCT, Portugal) for financial support by national funds FCT/MCTES to CIMO (UIDB/00690/2020). National funding by FCT- Foundation for Science and Technology, through the institutional scientific employment program-contract with I.P. Fernandes. We also wish to acknowledge the “Macrobehaviour-Mesostructure- Nanotechnology” SGIker units from the UPV/EHU, for their technical supporinfo:eu-repo/semantics/publishedVersio

Development of water-in-oil emulsions as delivery vehicles and testing with a natural antimicrobial extract

Water-in-oil (W/O) emulsions have high potential for several industrial areas as delivery systems of hydrophilic compounds. In general, they are less studied than oil-in-water (O/W) systems, namely in what concerns the so-called fluid systems, partly due to problems of instability. In this context, this work aimed to produce stable W/O emulsions from a natural oil, sweet almond oil, to be further tested as vehicles of natural hydrophilic extracts, here exemplified with an aqueous cinnamon extract. Firstly, a baseW/O emulsion using a high-water content (40/60, v/v) was developed by testing di erent mixtures of emulsifiers, namely Tween 80 combined with Span 80 or Span 85 at di erent contents. Among the tested systems, the one using a 54/46 (v/v) Span 80/Tween 80 mixture, and subjected to 12 high-pressure homogenizer (HPH) cycles, revealed to be stable up to 6 months, being chosen for the subsequent functionalization tests with cinnamon extract (1.25–5%; w/v; water-basis). The presence of cinnamon extract leaded to changes in the microstructure as well as in the stability. The antimicrobial and antioxidant analysis were evidenced, and a sustained behavior compatible with an extract distribution within the two phases, oil and water, in particular for the higher extract concentration, was observed.Base Funding—UIDB/00690/2020 of CIMO—Mountain Research Center—funded by national funds through FCT/MCTES (PIDDAC). Base Funding—UIDB/50020/2020 of the Associate Laboratory LSRE-LCM—funded by national funds through FCT/MCTES (PIDDAC).info:eu-repo/semantics/publishedVersio

Thermomechanical behaviour of bonded joints of wood and wood-based panels at room and elevated temperatures

Wood is a natural material traditionally used in the construction industry. In recent decades, developments in scientific research have turned wood into a high-tech construction material. Increased interest in bonded joints in wood construction is due to the advantages of adhesive technology compared to traditional mechanical joining techniques. It is very important to understand the influence of elevated temperatures on adhesives due to their use in multilayer systems such as compartmentation walls and fire-resistant doors, which require adequate mechanical and thermal resistance in fire situations. The purpose of this study is to investigate the mechanical behaviour of different structural adhesives on bonded connections of wood and wood-based panels at room and elevated temperatures through experimental testing. The performance of the adhesives was evaluated at room temperature and at 50 °C, 100 °C, 150 °C, and 200 °C.info:eu-repo/semantics/publishedVersio

Thermomechanical behaviour of bonding joints of wood and wood-based panels at room temperature and elevated temperatures

Wood is a natural material traditionally used in the construction industry. In recent decades, developments in scientific research have turned wood into a high-tech construction resource. Increased interest in bonded joints in wood construction is due to the advantages of adhesive technology compared to traditional mechanical joining techniques. It is very important to understand the influence of elevated temperatures on adhesives due to their use in multilayer systems such as compartmentation walls and fire-resistant doors, which require adequate mechanical and thermal resistance in fire situations. The purpose of this study is to investigate the mechanical behaviour of different structural adhesives on bonded connections of wood and wood-based panels at room and elevated temperatures through experimental testing. The performance of the adhesives was evaluated at room temperature and at 50 °C, 100 °C, 150 °C, and 200 °C. The resins tested were a polyurethane prepolymer resulting from the reaction between polyols and diphenylmethane diisocyanate (MDI), Flexpur151, and urea resin glue for hot pressing. The tensile shear tests with lap joints were performed using combinations of pinewood-pinewood and MDF-MDF. The experimental tests were done according to EN 205:2016, which allows for determining the tensile shear strength of bonded joints. The failure mode of the tested specimens was classified according to ASTM D5573. The results show that the bonding strength and the displacement of the specimens decrease with the increase of the temperature. The failure mode presents a different result for different temperatures. For example, for the urea resin, the shear resistance of MDF-MDF panels decreases about 50 % when exposed to 100 ºC with the failure mode usually occurring on the panel, and 98 % when exposed to 200 ºC with the failure mode in the adhesion plane. For the MDI based resin, the shear resistance of MDF-MDF panels decreases about 35 % when exposed to 100 ºC with the failure usually occurring on the panel, and 65 % when exposed to 200 ºC with the failure mode occurring in the adhesion plane.This work was developed within the scope of the project NORTE-01-0247-FEDER-072225, supported by North Portugal Regional Operational Programme (NORTE 2020), under the PORTUGAL 2020 Partnership Agreement, through the European Regional Development Fund (ERDF), CIMO (UIDB/00690/2020) funded by FCT/MCTES (PIDDAC), FCT, P.I., through the institutional scientific employment program-contract for Arantzazu Santamaria.info:eu-repo/semantics/publishedVersio