•Influence of Energy Density and scanning speed is studied in Selective Laser Melting.•Identified the correlation between product density and Energy Density.•Pore formation mechanisms based on Energy ...Density and scanning speed are described.•Hierarchical α′ structure is observed Ti-6Al-4V product in Selective Laser Melting.
Improving the metallurgical properties of the products fabricated by the Selective laser melting (SLM) process is still a challenge focusing on processing parameters and Energy Density (ED). In this study, the density, porosity and microstructure of cuboid Ti-6Al-4V alloy samples fabricated by the SLM process were investigated, paying particular attention to the manufacturing key factor ED. Seven different EDs between 39 J/mm3 and 260 J/mm3 were achieved by varying the scanning speed from 1000 mm/s to 150 mm/s. The results show the ED, as well as cooling conditions, have a great influence on the above mentioned metallurgical properties. Significantly different densities have been observed, with different Eds where the difference between the sample with the highest relative density and the sample with the lowest relative density was almost 2.45%. The highest relative product density of almost 99.45% was obtained at the ED value of 65 J/mm3. The volume, shape and numbers of pores were different with different EDs. The resultant microstructure consisted of four typical hierarchical α′ martensites, namely, primary, secondary, tertiary and quartic α′ martensites within columnar prior β grains.
•Terminal aldehyde groups are formed during the isolation of CNFs.•140% additional C6-located aldehydes are created using laccase/4-Amino TEMPO.•Only C6-aldehydes are transformed to carboxyl's using ...Cannizzaro reaction.•Covalent hemiacetal linkages between C6-aldehydes and hydroxyls may be formed.
The chemo-enzymatic modification of cellulose nanofibers (CNFs) using laccase as biocatalysts and TEMPO or 4-Amino-TEMPO as mediators under mild aqueous conditions (pH 5, 30°C) has been investigated to introduce surface active aldehyde groups. 4-Amino TEMPO turned out to be kinetically 0.5-times (50%) more active mediator, resulting to oxoammonium cation intermediacy generated and its in situ regeneration during the modification of CNFs. Accordingly, beside of around 750mmol/kg terminally-located aldehydes, originated during CNFs isolation, the reaction resulted to about 140% increase of C6-located aldehydes at optimal conditions, without reducing CNFs crystallinity. While only the C6-aldehydes were wholly transformed into the carboxyls after additional post-treatment using NaOH according to the Cannizzaro reaction, the post-oxidation with air-oxygen in EtOH/water medium or NaClO2 resulted to no- or very small amounts of carboxyls created, respectively, at a simultaneous loss of all C6- and some terminal-aldehydes in the latter due to the formation of highly-resistant hemiacetal covalent linkages with available cellulose hydroxyls. The results indicated a new way of preparing and stabilizing highly reactive C6-aldehydes on cellulose, and their exploitation in the development of new nanocellulose-based materials.
Single-walled carbon nanotubes (SWCNTs) and phosphorylated nanocellulose fibrils (PCNFs) were used as functional screen-print coatings on flame-retardant (FR) fabric, to improve its thermal ...resistance and thermophysiological comfort (wetting, water vapour and heat transmission) properties, while inducing it with electrical conductivity and UV protection. The effect of PCNF printing, followed by applying a hydrophobic polyacrylate (AP), on the same (back/B, turned outwards) or other (front/F, turned towards skin) side of the fabric, with and without the addition of 0.1–0.4 wt% SWCNTs, was studied by determining the amount of applied coating and its distribution (microscopic imaging), and measuring the fabric’s colour, air permeability, thickness, mechanical, flame and abrasion resistance properties. Due to the synergistic effect of PCNF and SWCNTs, both-sided printed fabric (front-side printed with PCNF and back-side with SWCNTs within AP) resulted in an increased heat transfer (25%) and an improved thermal resistance (shift of degradation temperature by up to 18 °C towards a higher value) and UV protection (UPF of 109) without changing the colour of the fabric. Such treatment also affected the moisture management properties with an increased water-vapour transfer (17%), reduced water uptake (39%) and asymmetric wettability due to the hydrophilic front (Contact Angle 46°) and hydrophobic back (129°) side. The increased tensile (16%) and tear (39%) strengths were also assessed in the warp direction, without worsening the abrasion resistance of the front-side. A pressure-sensing electrical conductivity (up to 4.9∙10−4 S/cm with an increase to 12.0∙10−4 S/cm at 2 bars) of the SWCNT-printed side ranks the fabric among the antistatic, electrostatic discharge (ESD) or electromagnetic interference (EMI) shielding protectives.
In recent years, nanocellulose (NC) has also attracted a great deal of attention in drug delivery systems due to its unique physical properties, specific surface area, low risk of cytotoxicity, and ...excellent biological properties. This review is focused on nanocellulose based systems acting as carriers to be used in drug or antimicrobial delivery by providing different but controlled and sustained release of drugs or antimicrobial agents, respectively, thus showing potential for different routes of applications and administration. Microorganisms are increasingly resistant to antibiotics, and because, generally, the used metal or metal oxide nanoparticles at some concentration have toxic effects, more research has focused on finding biocompatible antimicrobial agents that have been obtained from natural sources. Our review contains the latest research from the last five years that tested nanocellulose-based materials in the field of drug delivery and antimicrobial activity.
Differently structured aluminum (tri/mono) hydroxide (Al(OH)
3
/AlO(OH)) nanoparticles were prepared and used as thermal-management additives to microfibrillated cellulose (MFC), cast-dried in ...thin-layer films. Both particles increased the thermal stability of the MFC film, yielding 20–23% residue at 600 °C, and up to 57% lowered enthalpy (to 5.5–7.5 kJ/g) at 0.15 wt% of loading, while transforming to alumina (Al
2
O
3
). However, the film containing 40 nm large Al(OH)
3
particles decomposed in a one-step process, and released up to 20% more energy between 300 and 400 °C as compared to the films prepared from smaller (21 nm) and meta-stable AlO(OH), which decomposed gradually with an exothermic peak shifted to 480 °C. The latter resulted in a highly flexible, optically transparent (95%), and mechanically stronger (5.7 GPa) film with a much lower specific heat capacity (0.31–0.28 J/gK compared to 0.68–0.89 J/gK for MFC-Al(OH)
3
and 0.87–1.26 for MFC films), which rendered it as an effective heat-dissipating material to be used in flexible opto-electronics. Low oxygen permeability (2192.8 cm
3
/m
2
day) and a hydrophobic surface (> 60°) also rendered such a film useful in ecologically-benign and thermosensitive packaging.
The fabrication of biomaterials to be used in segmental bone defects, mimicking the bone's organic-inorganic architecture and mechanical properties to induce osteogenesis, persists as a key ...challenge. The purpose of this study was to elucidate the effect of a lightweight, morphologically graded, and multiphase self-standing scaffold structure prepared from a combination of gelatine (Gel), collagen type 1 (Col) and/or hydroxyapatite (HAP) nanoparticles by a unidirectional freeze-casting process at different temperatures (−20, −40, −60 °C), followed by carbodiimide induced cross-linking, on their in-vitro mechanical stability and bioactive properties. In addition, the rheological study of differently formulated Gel solutions has been performed to determine the effect of Col and HAP content on their microstructural arrangement, which, together with the freezing kinetic, affects Gel/Col orientation and cross-linking, and, thus, the scaffold's mechanical strength and stability.
A bone-like anisotropic, interconnected, and graded porosity (from 120 to a few μm) scaffold structure with up to 30% total porosity and ~61 μm average pores' diameter is obtained by using a higher Col content (Col: Gel = 2:5) and freezing temperature (−20 °C) while forming a few μm thick close-to-parallel lamellae, separated with a 10–100 μm space when prepared at −60 °C. Such a structure influenced in-vitro stability strongly (lower swelling without weight loss), being accompanied with a ~76% increase of compression strength (to 37 kPa) and ~67% decrease of elastic modulus (to 17 kPa) when prepared with HAP and incubated in HBSS for 7 days. On the other hand, a significant reduction of both strength (~78%, to 15 kPa) and elasticity (~95%, to 5 kPa) was noted for a scaffold prepared with HAP at −60 °C, being related to faster degradation and the formation of a highly opened structure on the bottom, required to stimulate the bone ingrowth, while a more closed network structure on the top to adhere with the surrounding soft tissue. None of the scaffolds induced cytotoxicity to human bone-derived osteoblasts, even after 19 days of incubation, but rather improved their viability while promoting cells' adhesions, proliferation, and differentiation, being supported with an increased alkaline phosphatase activity and rod-like CaP formation.
•Multiphase and gradient micro-porous scaffolds from gelatine/collagen/hydroxyapatite by unidirectional freeze-casting.•The freezing temperature systematically alters porous microstructure with heterogeneous and interconnected pores.•The scaffold has improved the adhesion, proliferation, and differentiation of human bone-derived osteoblast cells.
Low moisture absorbency of hydrophobically coated flame-resistant (FR) fabrics do not correlate well with the thermophysiological comfort. In this frame, we were the first to study the effect of ...screen-printed microfibrillated cellulose (MFC) on fabric’s breathability and moisture build-up and transfer as user-friendly and wear-related comfortable coating. The amount of MFC applied and its patterning was varied using different printing parameters, the density and thickness of FR fabric, and studied by add-on measurement and microscopic imaging. The effect of MFC coating and its durability (attachment) after a post-printing of hydrophobic polyacrylate on the same (layer-by-layer) or other side of the fabrics was considered, thus to maintain one side of the fabric (facing towards the wearer) hydrophilic while keeping the other side (facing outward) hydrophobic. The results showed that MFC provides uniform and repeatable printing, which gave homogeneous patterning with good layering on the fabrics, although, resulting in the MFC concentration, squeegee’ pressure, and fabric’ structure dependent add-on, its imprinting and co-crosslinking within the polyacrylate. This slightly reduced the fabric air-permeability, but increased it surfaces wetting, moisture uptake kinetic and capacity (hydroscopicity), without affecting the water vapour transfer. Besides, the polyacrylate could fix the MFC pre-printed on the other side of the fabric, thus maintaining its hydrophilicity, being more pronounced in the case of less open and thicker fabric, while improving its tensile/tear strengths and abrasion resistance, without deterioration of the fabric`s flammability.
The cellulose-binding domain (CBD) is the second important and the most wide-spread element of cellulase structure involved in cellulose transformation with a great structural diversity and a range ...of adsorption behavior toward different types of cellulosic materials. The effect of the CBD from
Clostridium cellulovorans on the supramolecular structure of three different sources of cellulose (cotton cellulose, spruce dissolving pulp, and cellulose linters) was studied. Fourier-transform infrared spectroscopy (FTIR) was used to record amides I and II absorption bands of cotton cellulose treated with CBD. Structural changes as weakening and splitting of the hydrogen bonds within the cellulose chains after CBD adsorption were observed. The decrease of relative crystallinity index of the treated celluloses was confirmed by FTIR spectroscopy and X-ray diffraction (XRD). X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) were used to confirm the binding of the CBD on the cellulose surface and the changing of the cellulose morphology.
Bio-based, renewable and biodegradable products with multifunctional properties are also becoming basic trends in the textile sector. In this frame, cellulose nanofibrils (CNFs) have been surface ...modified with hexamethylenediamine/HMDA and used as an antimicrobial additive to a ring-spun viscose yarn. The CNF-HMDA suspension was first characterized in relation to its skin irritation potential, antimicrobial properties, and technical performance (dispersability and suspensability in different media) to optimize its sprayability on a viscose fiber sliver with the lowest sticking, thus to enable its spinning without flowing and tearing problems. The impact of CNF-HMDA content has been examined on the yarn`s fineness, tensile strength, surface chemistry, wettability and antimicrobial properties. The yarn`s antimicrobial properties were increasing with the content of CNF-HMDA, given a 99% reduction for
S. aureus
and
C. albicans
(log 1.6–2.1) in up to 3 h of exposure at minimum 33 mg/g, and for
E. coli
(log 0.69–2.95) at 100 mg/g of its addition, yielding 45–21% of bactericidal efficacy. Such an effect is related to homogeneously distributed CNF-HMDA when sprayed from a fast-evaporated bi-polar medium and using small (0.4 mm) nozzle opennings, thus giving a high positive charge (0.663 mmol/g) without affecting the yarn`s tenacity and fineness, but improving its wettability. However, a non-ionic surfactant being used in the durability testing of functionalized yarn to 10-washing cycles, adheres onto it hydrophobically via the methylene chain of the HMDA, thus blocking its amino groups, and, as such, decreasing its antibacterial efficiency, which was slightly affected in the case when the washing was carried out without using it.
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