Biobased polyurethanes and nanocomposites. From structure/properties relationship to shape-memory behavior

325 p.This work deals with the increase of the renewability of different porous and solid (thermoplastic and crosslinked) polyurethanes and bionanocomposites, by the incorporation of different reactants and nanoentities from renewable sources. Moreover, the influence of the nature of the reactants and nanoentities and their content on the final properties has been deeply studied.Besides, the synthesized solid polyurethanes and bionanocomposites have shown shape-memory properties. Therefore, the effect of the programming conditions, content of the reactants and, in the case of the bionanocomposites, nanoentity nature and content on shape-memory properties has been thoroughly analyzed.GMT.Materials + Technologies Research Grou

Effect of the catalyst system on the reactivity of a polyurethane resin system for RTM manufacturing of structural composites

The high versatility of polyurethanes (PU’s) is encouraging the development of new formulations for new appli cations, like their use as a matrix for structural composites. PU’s based technology offers some advantages, such as fatigue resistance and fast curing cycles. However, their high reactivity hinders some manufacturing processes like Resin Transfer Moulding (RTM). This work aimed to achieve a PU resin (PUR) formulation with the required latency and reactivity for the RTM. For this purpose, different catalytic systems based on an epoxide and LiCl were investigated. The reactivity of the systems was evaluated through Differential Scanning Calorimetry (DSC) and rheology tests, and the curing reaction and viscosity were modelled. Furthermore, the RTM process of a representative composite part was simulated. Results demon strated the processability improvements when the LiCl was incorporated into the isocyanate component of the formulation combined with a monool or a diol. It was observed that these combinations contribute to the encapsulation of the LiCl between the as formed urethane groups by hydrogen bonding, providing the desired latency and acting as a delayed action catalyst. Once the reaction started and the encapsulation was deactivated, an alkoxide was formed to act as a catalyst. En capsulation was more effective with the diol, providing a higher latency.We gratefully acknowledge the Basque Government for the fi nancial support through the ELKARTEK 2020 (ProjectAVAN SITE New generation of sustainable composites for advanced manufacturing KK2020/00019) program. The authors also ac knowledge the University of the Basque Country (UPV/EHU) in the frame of GIU18/216 Research Group and the Macrobe havior-Mesostructure-Nanotechnology SGIker unit

Nonwoven Mats Based on Segmented Biopolyurethanes Filled with MWCNT Prepared by Solution Blow Spinning

To prepare nonwoven mats constituted by submicrometric fibers of thermally responsive biopolyurethanes (TPU) modified with multiwalled carbon nanotubes (MWCNT), solution blow spinning (SBS) was used. The TPU was the product of synthesis using poly(butylene sebacate)diol, PBSD, ethyl ester L-lysine diisocyanate (LDI), and 1,3-propanediol (PD) (PBSe:LDI:PD) as reactants. TPU was modified by adding different amounts of MWCNT (0, 0.5, 1, 2, and 3 wt.%). The effect of the presence and amount of MWCNT on the morphology and structure of the materials was studied using field-emission scanning electron microscopy (FESEM) and Fourier-transform infrared spectroscopy (FTIR), respectively, while their influence on the thermal and electric behaviors was studied using differential scanning calorimetry (DSC) and capacitance measurements, respectively. The addition of MWCNT by SBS induced morphological changes in the fibrous materials, affecting the relative amount and size of submicrometric fibers and, therefore, the porosity. As the MWCNT content increased, the diameter of the fibers increased and their relative amount with respect to all morphological microfeatures increased, leading to a more compact microstructure with lower porosity. The highly porous fibrous morphology of TPU-based materials achieved by SBS allowed turning a hydrophilic material to a highly hydrophobic one. Percolation of MWCNT was attained between 2 and 3 wt.%, affecting not only the electric properties of the materials but also their thermal behavior.This research was funded by the Fondos de Investigación de Fco. Javier González Benito, política de reinversión de costes generales, Universidad Carlos III de Madrid [2012/00130/004], the Acción Estratégica en Acción Estratégica en Materiales nanocompuestos multifuncionales, Universidad Carlos III de Madrid [2011/00287/003], and the Project PID2020-112713RB-C22–C21 supported by AEI [Ministerio de Ciencia e Innovación of Spain], the University of the Basque Country (UPV/EHU) and (GIU18/216 Research Group)

Design of a Waterborne Polyurethane-Urea Ink for Direct Ink Writing 3D Printing

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

Residues from rigid foams and graphene for the synthesis of hybrid polyurethane flexible foams composites

Hybrid biobased polyurethane flexible foam composites containing a residue from surf industry (polyurethane powder) as filler and graphite or graphene residue were synthe-sized. It was observed that the addition of the powder at low contents did not modify the final properties considerably, since the cell structure was not compromised. Moreover, the powder increased the capacity of the foams to retain the carbonaceous fillers. The compressive properties of the hybrid foams were not altered with the addition of the graphite and graphene. Finally, hybrid composites showed selective absorption capacity since the presence of the carbonaceous fillers provided the foams oil absorption capacity without modifying the hydrophobic nature of the matrix foams. (C) 2021 The Author(s). Published by Elsevier B.V.Authors thank the University of the Basque Country (UPV/EHU) (GIU18/216 Research Group), the Basque Government (PIBA19-0044 project) and the Provincial Country of Gipuzkoa (DG 19/28 Support Program for the Guipuzcoan Science, Technology and Innovation Network 2019) for the financial support. We also acknowledge the "Macrobehavior-Mesostructure-Nanotechnology " SGIker unit from the UPV/EHU, for their technical support and Olatu S.A. (Gipuzkoa) for providing the PUP. T.C-C. thanks the Provincial Country of Gipuzkoa (2017-BE01-000002-01) and the UPV/EHU (ESPDOC19/41)

Enhancing the Mechanical Properties of 3D-Printed Waterborne Polyurethane-Urea and Cellulose Nanocrystal Scaffolds through Crosslinking

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

Lignocellulosic Biomass as a Source of Raw Materials for the Synthesis of Polyurethanes

Precursors have been satisfactorily synthesized from lignocellulosic biomass for later use in the synthesis of polyurethanes resulting in competitive final properties with those of petroleum derived polyurethanesWe thank the Basque Government (IT-776-13, ELKARTEK-KK2017/00003) for the financial support. We also wish to acknowledge the “Macrobehavior-Mesostructure-Nanotechnology” SGIker unit from the University of the Basque Country, for their technical support

Towards Circular Economy: Different Strategies for Polyurethane Waste Recycling and the Obtaining of New Products

As a consequence of the high production and simultaneous consumption of polyurethanes (PU) a great volume of PU waste is landfilled. In this scenario, suitable and efficient routes for PU waste recycling have been searched for many years. In this work two series of PUs using different recycled PU sources were synthesized: a thermoplastic PU series using a glycolysated polyol obtained from the glycolysis of elastomeric PU waste (chemical recycling) and a PU flexible foam series loaded with PU dust waste created in the shaping of PU surf tables (mechanical recycling). Results showed that the incorporation of recycled components in the formulation improved mechanical properties both in the case of thermoplastic polyurethanes and polyurethane foams. The optimum glycolysated polyol was fixed in 15% over the total polyol weight for thermoplastic PUs. In the case of foams, a maximum of 20% PU dust over the polyol weight was incorporated.We thank the Basque Government (IT-776-13) for the financial support. We also thank for technical and human support provided by SGIker of UPV/EHU and European funding (ERDF and ESF), and Olatu S.A (Gipuzkoa) for providing the PU dust. T.C.-C. thanks the University of the Basque Country (DOCREC17/13) and Provincial Country of Gipuzkoa (2017-BE01-000002-01)

Effect of Cellulose Nanofibers’ Structure and Incorporation Route in Waterborne Polyurethane–Urea Based Nanocomposite Inks

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

Cellulose and Graphene Based Polyurethane Nanocomposites for FDM 3D Printing: Filament Properties and Printability

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