Tensile behaviour of dislocated/crystalline cellulose fibrils at the nano scale

Atomistic modelling of cellulose has widely been investigated for years using molecular dynamics simulations. In this paper, we model Iβ crystalline cellulose as well as develop a model including dislocations in between the crystal regions. The model including dislocations shows a tensile modulus of 109 GPa, 25% lower than that of the fully crystalline model (146 GPa). The change in dihedral angle preferences is analysed, and its effect on hydrogen bonding pattern is assessed. How presence of hydrogen bonds contributes to elastic properties of cellulose nano-fibrils is shown. Effect of water on the elastic modulus of fibrils is also investigated. Moreover, an illustration is given of how the tensile behaviour of fibrils is controlled by a synergy between the geometry changes occurring at the glycosidic linkage, reflected by specific torsional and glycosidic angles. These findings can be useful in further modelling of cellulosic fibrils at the atomistic and coarse-grained scales.status: publishe

Quasi-unidirectional flax composite reinforcement: Deformability and complex shape forming

Deformability and complex shape forming of a quasi-unidirectional flax reinforcement for composite materials (commercialized as FLAXPLY UD 180 by LINEO) are experimentally investigated. The first part of the study is focused on the understanding and measurement of the main deformation modes: in-plane tension, in-plane shear, and out-of-plane bending and compression, which are involved during draping of composite reinforcements. The second part is dedicated to the experimental study of a complex 3D shape forming, namely double-dome. The obtained results represent a complete data set for the characterisation of the deformation capabilities of the quasi-unidirectional flax reinforcement during complex 3D shape forming processes and provide benchmarking data for numerical predictions

3D-printed biodegradable gyroid scaffolds for tissue engineering applications

© 2018 Elsevier Ltd Fused deposition modeling (FDM), a low-cost and easy-to-use additive manufacturing technique, was used to produce poly(lactic acid) (PLA) gyroid scaffolds. Such morphology was selected for its spring shape, high porosity leading to good nutrient and waste diffusion, and favorable mechanical properties. Printing parameters were optimized and the need of a support material to improve printing was evidenced. The gyroid was compared to the common strut-based structure. Scaffold porosity was measured by micro-CT, and mechanical properties were determined by compression tests, taking into account the effect of geometry, printing resolution, and PLA crystallinity. The impact of scaffold geometry and crystallinity on its degradation was studied in vitro. Porosity of the gyroid structure was 71%, as expected from the printing model. The compression tests showed an isotropic behavior for the gyroid, in contrast with the strut-based scaffold. Upon aging in physiological conditions, gyroid scaffolds retained their integrity during 64 weeks, while control scaffolds lost struts starting from week 33, in a way that depended on crystallinity and printing resolution. Based on these results, the gyroid design is proposed as a suitable mesh architecture for tissue engineering scaffolds that can be elaborated using FDM techniques, to produce low-cost and personalized implants.status: publishe

3D-printed biodegradable gyroid scaffolds for tissue engineering applications

Fused deposition modeling (FDM), a low-cost and easy-to-use additive manufacturing technique, was used to produce poly(lactic acid) (PLA) gyroid scaffolds. Such morphology was selected for its spring shape, high porosity leading to good nutrient and waste diffusion, and favorable mechanical properties. Printing parameters were optimized and the need of a support material to improve printing was evidenced. The gyroid was compared to the common strut-based structure. Scaffold porosity was measured by micro-CT, and mechanical properties were determined by compression tests, taking into account the effect of geometry, printing resolution, and PLA crystallinity. The impact of scaffold geometry and crystallinity on its degradation was studied in vitro. Porosity of the gyroid structure was 71%, as expected from the printing model. The compression tests showed an isotropic behavior for the gyroid, in contrast with the strut-based scaffold. Upon aging in physiological conditions, gyroid scaffolds retained their integrity during 64 weeks, while control scaffolds lost struts starting from week 33, in a way that depended on crystallinity and printing resolution. Based on these results, the gyroid design is proposed as a suitable mesh architecture for tissue engineering scaffolds that can be elaborated using FDM techniques, to produce low-cost and personalized implants

Low-temperature compounding of flax fibers with polyamide 6 via solid-state shear pulverization: Towards viable natural fiber composites with engineering thermoplastics

© 2018 Society of Plastics Engineers Low-temperature compounding of natural fiber/thermoplastic composites via solid-state shear pulverization (SSSP) is explored for the first time, with a goal of processing temperature-sensitive natural fibers with high temperature-melting engineering thermoplastics without fiber degradation. The model study was based on polyamide 6 (PA6) as the matrix material and short flax fibers as the filler materials; flax fiber type was varied to provide a range of comparison. Composite structural characterization was conducted using computer tomography, optical microscopy, and scanning electron microscopy, while mechanical property measurements were performed on injection molded specimens in both tension and bending. SSSP demonstrated robust and effective processing results in model PA6/flax composites, especially when compared with conventional extrusion. SSSP was able to isolate unmodified scutched fibers into individual elementary fibers with minimal scission, and effectively distribute them in the polymer matrix in situ. The dispersed and distributed filler morphology led to mechanical property enhancements, including 230% and 40% increases in Young's modulus and tensile strength, respectively, compared with neat PA6, at a 20 vol% fiber content. POLYM. COMPOS., 2018. © 2018 Society of Plastics Engineers.status: publishe

Low-Temperature Compounding of Flax Fibers with Polyamide 6 via Solid-State Shear Pulverization (SSSP): Towards Viable Engineering Thermoplastic/Natural Fiber Composites

Low-temperature compounding of natural fiber/thermoplastic composites via solid-state shear pulverization (SSSP) is explored for the first time, with a goal of processing temperature-sensitive natural fibers with high temperature-melting engineering thermoplastics without fiber degradation. The model study was based on polyamide 6 (PA6) as the matrix material and short flax fibers as the filler materials; flax fiber type was varied to provide a range of comparison. Composite structural characterization was conducted using computer tomography, optical microscopy, and scanning electron microscopy, while mechanical property measurements were performed on injection molded specimens in both tension and bending. SSSP demonstrated robust and effective processing results in model PA6/flax composites, especially when compared with conventional extrusion. SSSP was able to isolate unmodified scutched fibers into individual elementary fibers with minimal scission, and effectively distribute them in the polymer matrix in situ. The dispersed and distributed filler morphology led to mechanical property enhancements, including 230% and 40% increases in Young’s modulus and tensile strength, respectively, compared with neat PA6, at a 20 vol% fiber content

Influence of Age and Harvesting Season on The Tensile Strength of Bamboo-Fibre-Reinforced Epoxy Composites

The purpose of this study was to measure the strength of various bamboo fibres and their epoxy composites based on the bamboo ages and harvesting seasons. Three representative samples of 1–3-year-old bamboo plants were collected in November and February. Bamboo fibres and their epoxy composites had the highest tensile strength and Young’s modulus at 2 years old and in November. The back-calculated tensile strengths using the “rule of mixture” of Injibara, Kombolcha, and Mekaneselam bamboo-fibre-reinforced epoxy composites were 548 ± 40–422 ± 33 MPa, 496 ± 16–339 ± 30 MPa, and 541 ± 21–399 ± 55 MPa, whereas the back-calculated Young’s moduli using the “rule of mixture” were 48 ± 5–37 ± 3 GPa, 36 ± 4–25 ± 3 GPa, and 44 ± 2–40 ± 2 GPa, respectively. The tensile strengths of the Injibara, Kombolcha, and Mekaneselam bamboo-fibre-reinforced epoxy composites were 227 ± 14–171 ± 22 MPa, 255 ± 18–129 ± 15 MPa, and 206 ± 19–151 ± 11 MPa, whereas Young’s moduli were 21 ± 2.9–16 ± 4.24 GPa, 18 ± 0.8–11 ± 0.51 GPa, and 18 ± 0.85–16 ± 0.82 GPa respectively. The highest to the lowest tensile strengths and Young’s moduli of bamboo fibres and their epoxy composites were Injibara, Mekaneselam, and Kombolcha, which were the local regional area names from these fibres were extracted. The intended functional application of the current research study is the automobile industries of headliners, which substitute the conventional materials of glass fibres

Mechanical Properties of Bambusa Oldhamii and Yushania-Alpina Bamboo Fibres Reinforced Polypropylene Composites

The current studies aim to measure the mechanical strength based on age, harvesting season and bamboo species in Ethiopia. The bamboo fibres are extracted using a roll milling machine, which was developed by the author. The age groups (1, 2 and 3 years), harvesting months (February and November), and bamboo species (Yushania alpina and Bambusa oldhamii) are the parameters of the current research studies. Prepregs and composites were produced from bamboo fibres and polypropylene. The mechanical properties of bamboo fibres and their composites in Ethiopia have not been investigated by researchers for the composite application so far. The tensile strength, Young’s modulus, and impact strength of injibara (Y. alpina) bamboo fibres reinforced PP composites from the ages of 1– 3 years old in November is 111 ± 9–125 ± 8 MPa, 15 ± 0.9–25 ± 0.72 GPa, and 47 ± 5 KJ/m2–57 ± 6 KJ/m2, whereas, in February, it is 86 ± 3.86–116 ± 10 MPa, 11 ± 0.71–23 ± 1.5 GPa, and 34 ± 4–52 ± 6 KJ/m2, respectively. Moreover, Kombolcha (B. oldhamii), bamboo fibres reinforced PP composites in November are 93 ± 7–111 ± 8 MPa, 7 ± 0.51–17 ± 2.56 GPa, and 39 ± 4–44 ± 5 KJ/m2, whereas, in February, it is 60 ± 5–104 ± 10 MPa, 12 ± 0.95–14 ± 0.92 GPa, and 26 ± 3 KJ/m2–38 ± 4 KJ/m2, respectively. Furthermore, Mekaneselam (Y. alpina) bamboo fibres reinforced PP composites in November are 99 ± 8–120 ± 11 MPa, 9 ± 0.82–16 ± 1.85 GPa, and 37 ± 4 KJ/m2–46 ± 5 KJ/m2, whereas, in February, it is 91 ± 8–110 ± 9 MPa, 8 ± 0.75–14 ± 1.86 GPa, and 34 ± 3 KJ/m2–40 ± 4 KJ/m2, respectively. At two years, November and Injibara bamboo have recorded the highest mechanical properties in the current research studies. Bamboo fiber strength in Ethiopia is comparable to the previous study of bamboo fibres and glass fibres used for composite materials in the automotive industry