Water Uptake Behavior and Young Modulus Prediction of Composites Based on Treated Sisal Fibers and Poly(Lactic Acid)

The main aim of this work was to study the effect of sisal fiber surface treatments on water uptake behavior of composites based on untreated and treated fibers. For this purpose, sisal fibers were treated with different chemical treatments. All surface treatments delayed the water absorption of fibers only for a short time of period. No significant differences were observed in water uptake profiles of composites based on fibers with different surface treatments. After water uptake period, tensile strength and Young modulus values of sisal fiber/poly(lactic acid) (PLA) composites were decreased. On the other hand, composites based on NaOH + silane treated fibers showed the lowest diffusion coefficient values, suggesting that this treatment seemed to be the most effective treatment to reduce water diffusion rate into the composites. Finally, Young modulus values of composites, before water uptake period, were predicted using different micromechanical models and were compared with experimental data.The authors are grateful for the financial support from the Basque Country Government in the frame of Consolidated Groups (IT-776-13) and Elkartek 2015 FORPLA3D project. Technical and human support provided by SGIker (Universidad del Pais Vasco-Euskal Herriko Unibertsitatea (UPV/EHU), Ministerio de Economia y Competitividad (MINECO), Gobierno Vasco-Eusko Jaurlaritza (GV/EJ), European Regional Development Fund (ERDF) and European Science Foundation (ESF)) is also gratefully acknowledged

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

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

Biocomposites Based on Poly(Lactic Acid) Matrix and Reinforced with Lignocellulosic Fibers: The Effect of Fiber Type and Matrix Modification

in composite materials, two or more different components are combined to produce a new material with different characteristics from the individual components. In recent years, due to environmental concerns, the development of biocomposites based on natural fibers has attracted great interest of researchers. The mechanical properties of biocomposites are dependent, among other parameters, on matrix properties, fiber properties as well as fiber/matrix adhesion. There are different approaches to improve fiber/matrix adhesion, such as, the use of fiber surface treatments and the use of matrix modifiers, i.e.,: coupling agents. In this work, poly(lactic acid) matrix composites reinforced with two different lignocellulosic fibers (sisal and flax) were prepared and the mechanical properties of both types of composites were compared. On the other hand, poly(lactic acid) polymer was modified with maleic anhydride in the presence of dicumyl peroxide. The mechanical properties of PLA/lignocellulosic fiber composites modified with maleic anhydride-modified poly(lactic acid) were also studied.Authors are grateful for the financial support from the Basque Country Government in the frame of Elkartek “Provimat” KK-2018/00046 and PIBA19-0044 projects and from the University of the Basque Country in the frame of GIU 18/216 project. The authors also thank for technical and human support provided by SGIker of UPV/ EHU and European funding (ERDF and ESF). 6. Reference

Biocomposites Based on Poly(Lactic Acid) Matrix and Reinforced with Lignocellulosic Fibers: The Effect of Fiber Type and Matrix Modification

In composite materials, two or more different components are combined to produce a new material with different characteristics from the individual components. In recent years, due to environmental concerns, the development of biocomposites based on natural fibers has attracted great interest of researchers. The mechanical properties of biocomposites are dependent, among other parameters, on matrix properties, fiber properties as well as fiber/matrix adhesion. There are different approaches to improve fiber/matrix adhesion, such as, the use of fiber surface treatments and the use of matrix modifiers, i.e.,: coupling agents. In this work, poly(lactic acid) matrix composites reinforced with two different lignocellulosic fibers (sisal and flax) were prepared and the mechanical properties of both types of composites were compared. On the other hand, poly(lactic acid) polymer was modified with maleic anhydride in the presence of dicumyl peroxide. The mechanical properties of PLA/lignocellulosic fiber composites modified with maleic anhydride-modified poly(lactic acid) were also studied

Natural Fiber–Reinforced Cement Mortar Composite Physicomechanical Properties: From Cellulose Microfibers to Nanocellulose

Using asbestos in building materials is a risk to human health, which has driven the interest in utilizing other natural fibers, such as cellulosic fibers, in cement-based building materials. There have been studies on cement-based composites reinforced with cellulose microfibers or nanocellulose. However, to the best of our knowledge, the effect of cellulose fiber reinforcement, at different scales (micro and nano), on cement-based composite properties has not yet been studied, from raw natural fiber to nanocellulose. Moreover, comparing data from the literature on cellulose-reinforced cement composites is difficult because there are many variables (e.g., matrix, cement, sand, dosification, water:cement ratio, superplasticizer, and fabrication method) that affect the final composite performance. In the current work, different cement-based composite properties reinforced with cellulose fiber were compared using the same variables and fabrication method. After the addition of microfibers, the strength of mortar decreased compared with plain mortar, the reduction being higher as the fiber content was increased. On the other hand, after the addition of nanocellulose fiber, the density hardly changed compared with unreinforced mortar. Contrary to microfiber addition, the presence of 0.25% by weight nanocellulose in mortar slightly increased the flexural strength. The mechanical properties obtained in the current study were compared with literature data for similar systems.Financial support from the Basque Country Government in the frame of Grupos Consolidados (IT-1690-22) is gratefully acknowledged

Fast Simulation of Laser Heating Processes on Thin Metal Plates with FFT Using CPU/GPU Hardware

In flexible manufacturing systems, fast feedback from simulation solutions is required for effective tool path planning and parameter optimization. In the particular sub-domain of laser heating/cutting of thin rectangular plates, current state-of-the-art methods include frequency-domain (spectral) analytic solutions that greatly reduce the required computational time in comparison to industry standard finite element based approaches. However, these spectral solutions have not been presented previously in terms of Fourier methods and Fast Fourier Transform (FFT) implementations. This manuscript presents four different schemes that translate the problem of laser heating of rectangular plates into equivalent FFT problems. The presented schemes make use of the FFT algorithm to reduce the computational time complexity of the problem from O(M2N2) to O(MN log(MN)) (with M× N being the discretization size of the plate). The test results show that the implemented schemes outperform previous non-FFT approaches both in CPU and GPU hardware, resulting in 100× faster runs. Future work addresses thermal/stress analysis, non-rectangular geometries and non-linear interactions (such as material melting/ablation, convection and radiation heat transfer). © 2020 by the authors

Water Uptake Behavior and Young Modulus Prediction of Composites Based on Treated Sisal Fibers and Poly(Lactic Acid)

The main aim of this work was to study the effect of sisal fiber surface treatments on water uptake behavior of composites based on untreated and treated fibers. For this purpose, sisal fibers were treated with different chemical treatments. All surface treatments delayed the water absorption of fibers only for a short time of period. No significant differences were observed in water uptake profiles of composites based on fibers with different surface treatments. After water uptake period, tensile strength and Young modulus values of sisal fiber/poly(lactic acid) (PLA) composites were decreased. On the other hand, composites based on NaOH + silane treated fibers showed the lowest diffusion coefficient values, suggesting that this treatment seemed to be the most effective treatment to reduce water diffusion rate into the composites. Finally, Young modulus values of composites, before water uptake period, were predicted using different micromechanical models and were compared with experimental data