Browsing by Author "Miettinen, Arttu"

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Black Bioinks from Superstructured Carbonized Lignin Particles
(2023-11-02) Dufau Mattos, Bruno; Jäntti, Noora; Khakalo, Sergei; Zhu, Ya; Miettinen, Arttu; Parkkonen, Joni; Khakalo, Alexey; Rojas, Orlando; Ago, Mariko
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
A renewable source of carbon black is introduced by the processing of lignin from agro-forestry residues. Lignin side streams are converted into spherical particles by direct aerosolization followed by carbonization. The obtained submicron black carbon is combined with cellulose nanofibers, which act as a binder and rheology modifier, resulting in a new type of colloidal bioink. The bioinks are tested in handwriting and direct ink writing. After consolidation, the black bioinks display total light reflectance (%R) at least three times lower than commercial black inks (reduction from 12 to 4%R). A loading of up to 20% of nanofibers positively affects the cohesion of the dried bioink (1 to 16 MPa), with no significant reduction in light reflectance. This is a result of the superstructuring of the ink components, which disrupts particle packing, intensifies colloidal interactions, introduces light absorption, and non-reflective multiple scattering.
Decontamination of a surgical mask with UV-C irradiation : analysis of experimental results with optical simulations
(2024-09-01) Kiiskinen, Titta; Mangs, Oliver; Virkajärvi, Jussi; Elsehrawy, Farid; Salo, Satu; Miettinen, Arttu; Halme, Janne; Harlin, Ali; Ketoja, Jukka A.
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
The suitability of ultraviolet-C (UV-C) irradiation for the decontamination of a surgical face mask was studied by decontamination experiments and carried out using Staphylococcus aureus and MS2 microbes. A moderate dosage level of 0.22 J/cm2 achieved within 2 min led to an over 6-log10 reduction in viable microbe contamination of the inner filtering layer. The underlying reason for this effective decontamination of fibers with small external UV-C dosage was explored with ray-tracing optical simulations, supported by optical measurements on reflection and transmission. The model 3D fiber network was constructed from X-ray tomography images of the layered mask structure consisting of polypropylene fibers. Both simulations and optical measurements indicated that UV light was able to penetrate even the deepest material regions. The simulations show that, despite radiation reflection from the outer mask layer, microbes in the actual filtering layer are affected by the radiation with increased probability due to multiple refraction and scattering of UV light from the inner fibers.
A detailed investigation of acetylated cellulose nanofiber films as a substrate for printed electronics
(2024-09) Wiklund, Jenny; Miettinen, Arttu; Parkkonen, Joni; Mela, Lauri; Karakoç, Alp; Paltakari, Jouni
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
The increased interest in printed electronics necessitates the development of suitable sustainable substrates for them. In this study, the suitability of acetylated cellulose nanofiber (ACNF) films as substrates for printed electronics were examined through (I) the ink-substrates interaction, (II) print quality, and (III) electrical and (IV) mechanical properties of the printed pattern on the ACNF substrates. The results have been compared with cellulose nanofiber (CNF) and commercial reference material (CRM) substrates. The wetting of the silver nanoparticle (AgNP) ink on the ACNF substrate was found out to be excellent. The thickness of the printed pattern increased and the hole area fraction decreased with each consecutive layer of ink. The comparative investigations demonstrated that the electrical properties of the printed patterns were almost as good for 4 layers of ink on the ACNF substrate (1.6 Ω resistance) as the ones on the CRM substrate (1.2 Ω resistance). Additionally, the printed pattern on the ACNF substrate endured the adhesion and bending tests significantly better compared to the CRM substrate. Therefore, this study demonstrates that ACNF substrates could be a suitable candidate for printed electronics, which are more sustainable yet with similar functionalities in comparison with the conventional fossil based substrates.
Effective elastic properties of biocomposites using 3D computational homogenization and X-ray microcomputed tomography
(2021-10-01) Karakoç, Alp; Miettinen, Arttu; Virkajärvi, Jussi; Joffe, Roberts
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
A 3D computational homogenization method based on X-ray microcomputed tomography (μCT) was proposed and implemented to investigate how the fiber weight fraction, orthotropy and orientation distribution affect the effective elastic properties of regenerated cellulose fiber-polylactic acid (PLA) biocomposites. Three-dimensional microstructures reconstructed by means of the X-ray μCT were used as the representative volume elements (RVEs) and incorporated into the finite element solver within the computational homogenization framework. The present method used Euclidean bipartite matching technique so as to eliminate the generation of artificial periodic boundaries and use the in-situ solution domains. In addition, a reconstruction algorithm enabled finding the volume and surface descriptions for each individual fiber in a semi-automatic manner, aiming at reducing the time and labor required for fiber labeling. A case study was presented, through which the method was compared and validated with the experimental investigations. The present study is thus believed to give a precise picture of microstructural heterogeneities for biocomposites of complex fiber networks and to provide an insight into the influences of the individual fibers and their networks on the effective elastic properties.
Microstructural evaluation and recommendations for face masks in community use to reduce the transmission of respiratory infectious diseases
(2022-11) Karakoç, Alp; Miettinen, Arttu; Sözümert, Emrah; Evans, Llion; Ali, Yusein; Bostanci, Başak; Taciroğlu, Ertuğrul; Jäntti, Riku
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Background and Objective: Recommendations for the use of face masks to prevent and protect against the aerosols (≤5µm) and respiratory droplet particles (≥5µm), which can carry and transmit respiratory infections including severe acute respiratory syndrome coronavirus (SARS-CoV-2), have been in effect since the early stages of the coronavirus disease 2019 (COVID-19). The particle filtration efficiency (PFE) and air permeability are the most crucial factors affecting the level of pathogen transmission and breathability, i.e. wearer comfort, which should be investigated in detail. Methods: In this context, this article presents a novel assessment framework for face masks combining X-ray microtomography and computational fluid dynamics simulations. In consideration to their widespread public use, two types of face masks were assessed: (I) two layer non-woven face masks and (II) the surgical masks (made out of a melt-blown fabric layer covered with two non-woven fabric layers). Results: The results demonstrate that the surgical masks provide PFEs over 75% for particles with diameter over 0.1µm while two layer face masks are found out to have insufficient PFEs, even for the particles with diameter over 2µm (corresponding PFE is computed as 47.2%). Thus, existence of both the non-woven fabric layers for mechanical filtration and insertion of melt-blown fabric layer(s) for electrostatic filtration in the face masks were found to be highly critical to prevent the airborne pathogen transmission. Conclusions: The present framework would assist in computational assessment of commonly used face mask types based on their microstructural characteristics including fiber diameter, orientation distributions and fiber network density. Therefore, it would be also possible to provide new yet feasible design routes for face masks to ensure reliable personal protection and optimal breathability.
Multiscale microstructural characterization of particulate-reinforced composite with non-destructive X-ray micro- and nanotomography
(2018-06-15) Nafar Dastgerdi, J.; Miettinen, Arttu; Parkkonen, J.; Remes, H.
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Methods based on X-ray tomography are developed to study the relevant statistical quantities describing the microstructural inhomogeneity of particulate reinforced composites. The developed methods are applied in estimating microstructural inhomogeneity parameters of composites containing metallic glass particles in metal matrix, extruded in varying pressure loads. This study indicates that the critical characteristics with regard to the effect of particle clustering are cluster size and shape, local volume fraction of particles in the cluster and the distance between clusters. The results demonstrate that the spatial distribution of reinforcement is very uneven and the amount of particle clustering varies with amount of reinforcement. Moreover, X-ray nanotomography was used to investigate the structure of individual clusters and the results suggest that high extrusion load may cause break-up of individual particle clusters so that their shape changes from solid and spherical to broken and ellipsoidal.
Wood-based superblack
(2023-12-05) Zhao, Bin; Shi, Xuetong; Khakalo, Sergei; Meng, Yang; Miettinen, Arttu; Turpeinen, Tuomas; Mi, Shuyi; Sun, Zhipei; Khakalo, Alexey; Rojas Gaona, Orlando; Dufau Mattos, Bruno
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Light is a powerful and sustainable resource, but it can be detrimental to the performance and longevity of optical devices. Materials with near-zero light reflectance, i.e. superblack materials, are sought to improve the performance of several light-centered technologies. Here we report a simple top-down strategy, guided by computational methods, to develop robust superblack materials following metal-free wood delignification and carbonization (1500 °C). Subwavelength severed cells evolve under shrinkage stresses, yielding vertically aligned carbon microfiber arrays with a thickness of ~100 µm and light reflectance as low as 0.36% and independent of the incidence angle. The formation of such structures is rationalized based on delignification method, lignin content, carbonization temperature and wood density. Moreover, our measurements indicate a laser beam reflectivity lower than commercial light stoppers in current use. Overall, the wood-based superblack material is introduced as a mechanically robust surrogate for microfabricated carbon nanotube arrays.