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Cellulose nanocrystals (CNC) have been studied as rheological modulator in order to improve the printing performance of a novel polycaprolactone-polyethylene glycol (PCL-PEG) waterborne polyurethane urea (WBPUU) based ink for direct ink writing 3D-printing technology. The cellulose nanocrystals are chemically bonded to the WBPU, since they were added during the synthesis of a WBPUU, in order to tune the rheological properties of the ink and thus, improve the printing performances. The WBPUU-CNC inks have been extensively characterized from the rheological viewpoint and have been subsequently used to print different pieces. To determine the capacity of the CNC to improve the printing performance of this type of inks, we establish the relationship between the rheological properties of the inks and their printing viability by an optimal window of compositions of the inks. Additionally, we have measured the mechanical and thermomechanical properties of printed WBPUU-CNC pieces to evaluate the effective reinforcement of in situ incorporated CNC in the WBPUU-CNC inks. The results showed that the addition of CNC accentuates the shear-thinning behaviour, presenting lower tan δ, especially at the lowest CNC contents compared with the matrix, which resulted in inks with excellent printable properties. Moreover, the shape fidelity is increased by the solid-like behavior due to the filler effect of CNC and confirmed by SEM images. Finally, a large increase in Young’s modulus and thermal and thermomechanical stability were observed on the printed pieces that contained only 0.5 wt% CNC compared to the matrix, suggesting the formation of effective interactions between CNC and WBPUU, as corroborated by FTIR, that lead to a greater reinforcement.

In this work, shape-customized scaffolds based on waterborne polyurethane-urea (WBPUU) were prepared via the combination of direct ink writing 3D-printing and freeze-drying techniques. To improve the printing performance of the ink and guarantee a good shape fidelity of the scaffold, cellulose nanocrystals (CNC) were added during the synthesis of the WBPUU and some of the printed constructs were immersed in CaCl2 prior to the freeze-drying process to promote ionic crosslinking between calcium ions and the polyurethane. The results showed that apart from allowing the ink to be successfully printed, obtaining scaffolds with good shape fidelity, the addition of the CNC resulted in a greater homogeneity of the porous structure as well as an increase of the swelling capacity of the scaffolds. Additionally, the CNC has a reinforcement effect in the printed systems, presenting a higher compression modulus as the CNC content increases. In the case of samples crosslinked by calcium ions, a rigid shell was observed by scanning electron microscopy, which resulted in stiffer scaffolds that presented a lower water absorption capacity as well as an enhancement of the thermal stability. These results showed the potential of this type of post-printing process to tune the mechanical properties of the scaffold, thus widening the potential of this type of material. The financial support of the Basque Government within the framework of Grupos Consolidados (IT-1690-22) and the Spanish Ministry of Science and Innovation (MINCIN)—State Investigation Agency (AEI) (PID2019-105090RB-I00/AEI/10.13039/501100011033) is acknowledged.

In order to continue the development of inks valid for cold extrusion 3D printing, waterborne, polyurethane–urea (WBPUU) based inks with cellulose nanofibers (CNF), as a rheological modulator, were prepared by two incorporation methods, ex situ and in situ, in which the CNF were added after and during the synthesis process, respectively. Moreover, in order to improve the affinity of the reinforcement with the matrix, modified CNF was also employed. In the ex situ preparation, interactions between CNFs and water prevail over interactions between CNFs and WBPUU nanoparticles, resulting in strong gel-like structures. On the other hand, in situ addition allows the proximity of WBPUU particles and CNF, favoring interactions between both components and allowing the formation of chemical bonds. The fewer amount of CNF/water interactions present in the in situ formulations translates into weaker gel-like structures, with poorer rheological behavior for inks for 3D printing. Stronger gel-like behavior translated into 3D-printed parts with higher precision. However, the direct interactions present between the cellulose and the polyurethane–urea molecules in the in situ preparations, and more so in materials reinforced with carboxylated CNF, result in stronger mechanical properties of the final 3D parts. Financial support from the Basque Government (Grupos Consolidados (IT-1690-22), Elkartek (KK19-00048)) is acknowledged.

In this work, polycaprolactone–polyethylene glycol (PCL–PEG) based waterborne polyurethane–urea (WBPUU) inks have been developed for an extrusion-based 3D printing technology. The WBPUU, synthesized from an optimized ratio of hydrophobic polycaprolactone diol and hydrophilic polyethylene glycol (0.2:0.8) in the soft segment, is able to form a physical gel at low solid contents. WBPUU inks with different solid contents have been synthesized. The rheology of the prepared systems was studied and the WBPUUs were subsequently used in the printing of different pieces to demonstrate the relationship between their rheological properties and their printing viability, establishing an optimal window of compositions for the developed WBPUU based inks. The results showed that the increase in solid content results in more structured inks, presenting a higher storage modulus as well as lower tan δ values, allowing for the improvement of the ink’s shape fidelity. However, an increase in solid content also leads to an increase in the yield point and viscosity, leading to printability limitations. From among all printable systems, the WBPUU with a solid content of 32 wt% is proposed to be the more suitable ink for a successful printing performance, presenting both adequate printability and good shape fidelity, which leads to the realization of a recognizable and accurate 3D construct and an understanding of its relationship with rheological parameters. Financial support from the University of the Basque Country (UPV/EHU) (GIU18-216), Spanish Ministry of Economy and Competitiveness (MINECO) (MAT2016-76294R and PID2019-105090RB-I00) and the Basque Government (KK-2019/00048) are gratefully acknowledged. Julen Vadillo wishes to acknowledge both the University of Pau and Pays de l’Adour and the UPV/EHU for his PhD grant.

International audience; This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY; 3D printing has exponentially grown in popularity due to the personalization of each printed part it offers, making it extremely beneficial for the very demanding biomedical industry. This technique has been extensively developed and optimized and the advances that now reside in the development of new materials suitable for 3D printing, which may open the door to new applications. Fused deposition modeling (FDM) is the most commonly used 3D printing technique. However, filaments suitable for FDM must meet certain criteria for a successful printing process and thus the optimization of their properties in often necessary. The aim of this work was to prepare a flexible and printable polyurethane filament parting from a biocompatible waterborne polyurethane, which shows potential for biomedical applications. In order to improve filament properties and printability, cellulose nanofibers and graphene were employed to prepare polyurethane based nanocomposites. Prepared nanocomposite filaments showed altered properties which directly impacted their printability. Graphene containing nanocomposites presented sound enough thermal and mechanical properties for a good printing process. Moreover, these filaments were employed in FDM to obtained 3D printed parts, which showed good shape fidelity. Properties exhibited by polyurethane and graphene filaments show potential to be used in biomedical applications.

International audience; There has been an exponential rise in the interest for waterborne polyurethanes (WBPU), due to the easy customizability of their properties and their ecofriendly nature. Moreover, their aqueous state facilitates the incorporation of hydrophilic reinforcements. Cellulose nanofibers (CNFs) have shown great potential, thanks to their renewability, large natural availability, low cost and great specific properties. However, CNFs often require some modification to obtain optimal compatibility. In this work, standard bleached hardwood kraft pulp has been subjected to a carboxylation process followed by mechanical disintegration. Varying treatment times and passes, CNF samples with different carboxylation degrees have been obtained. WBPU/CNF nanocomposites with different CNF content have been prepared. The effect of the carboxylation degree on the CNFs and on the nanocomposites properties has been studied. Although carboxylation damaged the cellulose structure, decreasing the crystallinity degree of CNF and reducing the thermal stability of fibers, composites showed better thermal and thermomechanical stability and improved mechanical properties than the unreinforced matrix counterpart. A maximum increase of 1670% in modulus, 377% in stress at yield and 86% in stress at break has been achieved for composites reinforced with carboxylated fibers. Therefore, it was observed that carboxylation improved matrix/reinforcement interactions.

Optimization of a multivariate calibration process has been undertaken for a Visible-Near Infrared (400-1100nm) sensor system, applied in the monitoring of the fermentation process of the cider produced in the Basque Country (Spain). The main parameters that were monitored included alcoholic proof, l-lactic acid content, glucose+fructose and acetic acid content. The multivariate calibration was carried out using a combination of different variable selection techniques and the most suitable pre-processing strategies were selected based on the spectra characteristics obtained by the sensor system. The variable selection techniques studied in this work include Martens Uncertainty test, interval Partial Least Square Regression (iPLS) and Genetic Algorithm (GA). This procedure arises from the need to improve the calibration models prediction ability for cider monitoring.

Buildings are responsible for at least 40% of energy use in most countries. High reflectance outdoor coatings can bring significant energy savings for building applications. In this context, ultramarine blue pigment (UB) has been modified to increase its near infrared reflectance by depositing a reflecting film based on TiO 2 containing different types and concentrations of nanoparticles (alumina, titania and a mixture of them). The developed pigments were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and laser dispersion. For testing the performance of the modified pigments, they have been dispersed in a conventional waterborne paint at different percentages and characterized by UV–Vis-NIR spectrophotometry (measuring Total Solar Reflectance and CIE L × a × b × ). All the obtained paints increased the TSR in 2.65% when adding nanoparticles but the maximum value was obtained for an addition of 6 wt.% of titania nanoparticles. Higher contents of nanoparticles led to agglomeration reducing the reflectance in the final paint.

The present study covers the development and testing of polyurethane (PU) foams modified with phase change materials (PCMs) supported in inorganic silica containers. Two kind of inorganic supports (mesoporous silica and tight silica microcapsules) were selected as representative cases of two alternatives for the preparation of phase change composites: infiltration of PCMs on porous supports and microencapsulation of PCMs. The two types of phase change composites exhibit latent heats of 100–130 J·g−1 and PCM uptakes of 45–60%. The addition of the phase change composites to the formulation of a rigid PU foam promoted subtle changes in the foam growth process which were responsible of a cell-size contraction and of strengthening the compressive strength in a 27–30%. The thermal performance of the PU foams was tested under isothermal laboratory conditions showing higher thermal storage capacity in doped foams. Additionally, the higher energy storage capacity of the modified foams provides them greater thermal inertia. POLYM. COMPOS., 2016. © 2016 Society of Plastics Engineers