Hardness Values Research Articles

The impact of BBr3/TiCl4 ratios on the microstructural and mechanical characteristics of TiBN coatings deposited using a pulsed-PACVD technique

This study aimed to investigate the impact of precursor ratios on both the microstructural and tribological characteristics of TiBN coatings. Using the PACVD process, TiN, TiB2, and three variations of TiBN coatings with adjusted BBr3/TiCl4 ratios were applied onto H13 substrates. The coatings were characterized using XRD, FESEM, TEM, AFM, nanoindentation, and nanoscratch methods to analyze their microstructural properties, surface morphology, and mechanical behavior. The findings revealed that the TiBN coatings possessed a nanocomposite structure with TiN crystals dispersed within the BN matrix, which is amorphous. Moreover, the augmentation of the BBr3/TiCl4 ratio from 0 to 1/3 resulted in a significant rise in the hardness value, from 13.4 GPa to 25.7 GPa. However, a further increase in the ratio from 1/3 to 3/3 resulted in a decrease in hardness to 14.4 GPa because cracks were formed in the deposited coating. In comparison, the TiB2 coating exhibited a higher hardness of 19.7 GPa due to strong TiB bonds within the coating. The TiBN coating, applied with a BBr3/TiCl4 ratio of 1/3, demonstrated the lowest wear volume of 0.10 × 10−18 m3, attributed to its higher hardness and smoother surface texture.

Microstructural and mechanical characterizations of weld metal of S960QL ultra high strength steel joints obtained with different multi-pass laying techniques using GMAW

Abstract 15 mm thick ultra-high strength steel plates with 960MPa yield strength were welded using different multi-pass laying techniques (i.e., stringer and weaving beads) with torch manipulation. Weld metals obtained were compared using different mechanical (i.e., micro tensile tests and Vickers hardness maps) and microstructural (i.e., optical microscope, scanning electron microscope, X-ray diffraction, electron backscatter diffraction) characterization techniques. Coarser grains and acicular ferrite were observed in weld metal obtained with weaving pass procedure. There were hardness differences in face and root passes of both weld metals. Yet, hardness values were 19% and 11% higher for face and root regions of the joint obtained by stringer pass procedure, respectively. Fractographs of micro tensile test specimens revealed dimples depicting ductile network structure for both joints.

Wear and corrosion properties of mechanically coated 316 stainless Steel-TiC nanocomposites

The mechanical coating (MC) method was used to deposit 316 stainless steel (SS316), TiC, and SS 316-TiC nanocomposite coatings on SS 316 substrates using a ball mill machine at milling durations of 1, 2, 5, 10, and 15 h using relatively cheap and abundant raw material. The chemical composition of the SS 316, TiC, and SS 316-xTiC (x = 20, 50, 80 wt%) nanocomposite coatings deposited by the mechanical coating method has been investigated and the hardness values and the wear and corrosion mechanisms were presented. Dense and uniform coatings were obtained using a ball-to-powder weight ratio (BPR) of 20:1 and an MC duration of 5 h. Among the samples, the SS316-20 wt%TiC coating exhibited the best wear and corrosion resistance. The least mean coefficient of friction was 0.3 for the SS316-20 wt%TiC deposited sample while the largest mean coefficient was for the SS316-80 % TiC sample to be 0.76. The SS 316-20 wt% TiC sample had the lowest wear rate where the highest value was for the %100SS 316 sample being 0.36 × 10−6 and 19 × 10−6 (mm3/Nm), respectively. Corrosion tests revealed that the SS316-20%TiC sample had the best corrosion resistance among the composite samples having a corrosion resistance of 4.9358 μm/Y. The corrosion resistance decreased with the increase of TiC whereas the 80 % TiC coating had severe pitting. Cracks and pores present in the non-uniform 100 % TiC coating resulted in lower corrosion resistance compared to the 100 % SS 316 and composite coatings.

Experimental, Density Functional Theory, Molecular Docking and ADMET Analyses on the Role of Different Plant Extracts of Aronia melanocarpa (Michx) Elliot Species on Acetylcholinesterase Enzyme Activity

In the present study, different extracts obtained in different solvents from the fruits collected from the Aronia melanocarpa (Michx.) were prepared. The inhibition performances of these extracts on the inhibition of the acetylcholinesterase enzyme were checked via both theoretical and experimental analyses. Although all extracts used in experimental studies showed high inhibitory activity, it was observed that the extract obtained in methanol had higher inhibitory activity than the others. According to the enzyme activity results presented in the light of Ellman method, IC50 values were found between 0.0311-0.0857 mg/mL. Conceptual Density Functional Theory (CDFT) and Molecular Docking calculations were performed to identify the component or components of the extract with high inhibitory activity. Conceptual Density Functional Theoretical based data commented through popular electronic structure principles such as Maximum Hardness and Minimum Electrophilicity Principles showed that the most reactive one among studied dominant components of the extract is Malvin molecule. The interactions between studied molecules and AChE and mechanisms of these interactions were illuminated via Molecular Docking analyses and ADMET studies. As a result, it was shown that the most reactive molecule Malvin (with lowest hardness and the highest electrophilicity) interacts more powerful with AChE compared to other molecules. Within the framework of the theoretical analyses made, it was proposed that in the design and introduction of new AChE inhibitors, structures with low hardness and high electrophilicity values ​​should be preferred.

Additively manufactured carbon fiber reinforced-polyamide component: a study based on statistical modeling and regression analysis

This paper presents the experimental assessment of the hardness characteristic of additively manufactured polyamide (PA 6) composite reinforced with carbon micro-fibers. The carbon fiber-reinforced polyamide (CFPA) components were manufactured using the additive manufacturing technique—fused deposition modeling (FDM). The experiments were conducted for testing the hardness of the samples using a Shore-D hardness tester. The novel contributions of the work towards the manufacturing fraternity include selecting a scantly researched material like CFPA, and the elaborative investigation of hardness variation with the alteration of the prime parameters pertaining to FDM. The effect of the print-related parameters, namely, layer height (LH), infill density (ID), and raster orientation (RO) on the hardness of the CFPA component was studied, and the results were analyzed using statistical analysis tool ‘analysis of variance (ANOVA)’. Moreover, a regression model was developed to predict the output response, i.e. hardness for different combinations of the input parameters. Considering an ID of 100% and an RO of 0°, the hardness value of 93.89 at 0.1 mm LH reduced to 88.44 at 0.3 mm LH, depicting a reduction of 5.81%. An increasing trend was observed for hardness with the increase in ID for all the levels of LH and RO. The highest value of hardness (93.89) was achieved at an ID of 100%, with the LH and RO values kept at 0.1 mm and 0°, respectively. The ANOVA suggested that the effect of all three parameters is significant in the study, ID being the most affecting parameter with an effect contribution of 37.88%. The fitness of the adopted model was well justified by the high R-sq value of 0.9618 and significantly low error values in the range of 0.002–0.08.

Influence of titanium carbide particles on the characteristics of microarc oxidation layer on Ti6Al4V alloy

The Microarc Oxidation (MAO) layer on titanium alloy was mainly composed of TiO2, and there were some defects, such as holes and cracks, which made the performance of the MAO layer not ideal. To enhance the properties of the MAO layer, titanium carbide (TiC) particles were added to the electrolyte of a phosphate–silicate system as an additive. Consequently, the MAO layers containing the TiC phase on Ti6Al4V alloy were produced. The MAO process, composition, microstructure, and hardness of the MAO layer were comprehensively analyzed. Their frictional performance was assessed under reciprocating friction conditions without lubrication. The findings suggested that added TiC particles in the electrolyte played a significant role in creating the MAO layer, enhancing its thickness. The electrolyte without TiC particles produced an MAO layer primarily composed of TiO2 in two different mineral forms (rutile and anatase). Adding TiC particles resulted in the presence of TiC within the MAO layer, thereby facilitating the formation of a reinforced oxide layer. This addition also led to an improvement in the densification of the layer and a reduction in porosity. Notably, corrosion resistance testing indicated that incorporating 6 g l−1 TiC into the electrolyte resulted in superior performance compared with that obtained from the base electrolyte alone by achieving 1.4 times higher corrosion resistance. Moreover, a hardness value of 690 HV for the MAO layer was attained at a content level of 9 g l−1 TiC, demonstrating a significant 65% enhancement compared to the base oxide layer. This finding also demonstrated significantly enhanced friction property with a wear-volume reduction to 0.81 mm3. The findings on the relationship between the preparation of the MAO layer and its structure and properties can provide valuable guidance for designing and preparing the MAO layer.

Influence of B, Si, Ge, and As impurities on the electronic properties of graphene quantum dot: A density functional theory study

The electronic features of chemically functionalized graphene quantum dots (GQDs) are investigated using density functional theory (DFT). The fabrication of nanoscale devices needs to enhance- the electronic performance of customized GQDs, which is crucial in many applications. GQDs can be used as a model with the molecule C24H12. We investigated the effects of adding metalloid impurities) boron B, silicon Si, germanium Ge, and arsenic As) on the structure and electronic properties of the dots at the B3LYP/6–31 level using the Gaussian 09 program package. The obtained results show efficient adding impurities B, Si, Ge, and As on the structure and electronic properties of GQDs, where it is noted that the energy gap change with -3.085, -12.340, -13.907, and -66.846 %, respectively.These results not only advance our knowledge of the mechanisms behind chemical doping, which may change the electronic features of quantum dots, but they also provide support for the development of nanodevices that have better electronic performance. As observed with As/GQD, it is anticipated that this system, which has the lowest possible chemical hardness values, will function as an effective corrosion inhibitor.

The microstructure and mechanical properties of the laser-welded joints of as-hot rolled AlCoCrFeNi2.1 high entropy alloy

AlCoCrFeNi2.1 hot-rolled eutectic high entropy alloys were welded by laser welding, yielding a free-defect laser-welded connection. With the use of optical microscopy, EDS, EBSD, and XRD, the microstructure of the base metal (BM), fusion zone (FZ), and heat-affected zone (HAZ) of the joint was examined. The produced joint underwent tensile and micro-hardness testing as well as a fracture morphology examination. A similar tensile strength in the FZ and BM is measured, while a decrease in the elongation. The typical layered lamellar structures, in particular an FCC + BCC dual-phase structure, were all visible in the HAZ, BM, and FZ zones. The α-fiber and γ-fiber as well as other textures are determined by the ODF figure, indicating a potential orientation distribution of the as-hot rolled AlCoCrFeNi2.1 joint. A clear grain refinement characteristics in the fusion zone as a result of the uneven thermal cycling during the welding process. The results of the mechanical test demonstrate the base metal has the highest hardness value, i.e. 500–550 HV0.2, within the welded joint zone. The welded joint has a tensile strength ∼1200 MPa, which is marginally higher than ∼1150 MPa in the base metal, and an elongation that decreases by 20 % from base metal to welded joint, indicating a decrease in the plasticity of the welded joint. A combination of brittle and ductile fracture occurs in welded joints during tensile failure. This study may give possibilities for the engineering application of laser welding of AlCoCrFeNi2.1 eutectic high entropy alloy in the future.

Effect of ultra-high temperature treatment on the rolled pure molybdenum for nuclear thermal propulsion

Molybdenum (Mo)-based uranium dioxide (UO2) fuel is considered one of the most promising fuel forms for deep-space exploration. The rolling process has been proposed for the preparation of Mo matrix due to its excellent performance. However, there has been limited research on the ultra-high temperature stability of Mo matrix used in nuclear thermal propulsion (NTP). Therefore, in this study, annealing experiments were carried out on rolled Mo plates within a relatively wide temperature range of 1200 to 2300 °C for 1 h to investigate the effects of temperature on the phase composition, microstructure, and mechanical property. The results showed that, despite the body-centered cubic structure of the Mo plates remaining unchanged without undergoing phase transition after high-temperatures, the intensity of the crystal diffraction peaks experienced a significant increase. The preferred growth orientation shifted from the (110) direction at lower temperatures to the (200) direction at 2300 °C. The grain shape of the rolled Mo plates changed from elongated to equiaxed after annealing, and the grain size increased from the initial 1 μm to tens of microns. No discernible surface pores or fracture bubbles were observed when annealed at 1200 to 2100 °C. However, subsequent annealing at 2300 °C revealed a proliferation of polyhedral bubbles, ranging in size from tens of nanometers to several microns, distributed both in grain boundaries and within grains. Nevertheless, there is no apparent change in the density from 1200 to 2300 °C. Bright-field TEM micrographs show that after annealing at 2300 °C, the dislocation density is significantly reduced, and the dislocation shape evolves from screw dislocation to long and straight line. In addition, the Vickers hardness value of the rolled Mo plates undergoes a significant decrease, from 247.1 to 199.6 Hv, after annealing at 1200 °C. Subsequently, in the temperature range of 1200 to 2300 °C, a gradual decline in the hardness value is observed. This work will deepen our understanding of the high-temperature resistance of rolled Mo plates and provide data to support their applications in ultra-high-temperature conditions.

A good balance between the efficiency of ionizing radiation shielding and mechanical performance of various tin-based alloys: Comparative analysis

The Sn-Bix (x = 30, 40, 50, 60 and 70%) radiation shielding alloys were prepared using a melting process of the alloying material in a ceramic crucible at 200 °C for 120 min. The structural characterization for synthesized samples was carried out using X-ray Diffraction technique (XRD). The hardness and elastic properties of the prepared alloys was measured using micro-indentation creep technology and tensile test machine respectively. XRD pattern indicated that that the crystal size of Sn phase is lowered by increasing Bi concentration in the Sn matrix. The hardness decreases as the dwell time increases. The hardness values and elastic properties (in terms of young modulus) were significantly improved due to the decrease in the crystallite size by increasing Bi content. The stress exponent (n) value increase by increasing Bi content which mean that the mechanical properties improved due to increment of resistance. Furthermore, the produced alloys' nuclear shielding ability was investigated. The μm values were calculated using MCNP simulation code and XCOM software over a broad energy range of 0.015 MeV–15 MeV with good agreement between them. Several characteristics are estimated in order to properly understand the researched alloy's radiation and properties of neutron shielding. The findings showed that a higher Bi concentration causes the crystal size to decrease, improving the radiation shielding and mechanical qualities. The alloy Sn-70% Bi has a maximum increase of vicker hardness, tensile strength, and young's modulus. The findings of the shielding parameters indicate that the alloys under study are efficient gamma shielding materials in contrast to other typical shielding materials and materials that have been examined recently. The highest mechanical efficiency and rather strong gamma-ray shielding capabilities are found in the Sn–70Bi alloy. Owing to its ability to effectively balance mechanical performance and shielding, the Sn–70Bi are approved for use in radiation protection. In addition, when compared to all other manufactured alloys, typical neutron shielding materials, and recently investigated materials, the results further demonstrate that the Sn–70Bi alloy has the best neutron attenuation capability. Furthermore, in terms of mass stopping power (MSP) and projected range (PR), the Sn–70Bi alloy demonstrates the most effective attenuation for alpha particles (He+2) and protons (H+1). These results imply that the Sn–70Bi alloy provide superior mechanical performance and nuclear shielding for a range of applications including industrial, medicinal, and nuclear waste storage in the future.

Improving the Mechanical Properties of Glass Ionomer Cement With Nanocrystalline Cellulose From Rice Husk.

This study aimed to evaluate the effect of incorporating nanocrystalline cellulose (NCC) sourced from rice husk on the mechanical properties of a commercial glass ionomer cement (GIC). NCC was isolated through acid hydrolysis, and its crystallinity, chemical structure, and morphology were characterized through x-ray diffractometry, Fourier-transform infrared spectroscopy, and transmission electron microscopy, respectively. Various concentrations of NCC (0%, 0.5%, 1%, and 1.5%) were added to reinforce the GIC matrix. Mechanical tests including compressive strength, flexural strength, hardness, and shear bond strength were conducted on the modified GIC samples. The addition of NCC resulted in increased hardness and shear bond strength values, with 1% NCC showing the highest values compared to other concentrations. However, there was no significant improvement observed in the compressive and flexural strength of the modified GIC. Failure mode test revealed a reduction in adhesive failure with the addition of NCC. Incorporating small amounts of NCC (0.5%-1%) suggests a promising and affordable modification of GIC restorative material using biomass residue, resulting in improved mechanical properties.

Graphene nanoplatelet reinforced Al-based composites prepared from recycled powders via mechanical alloying and pressureless sintering

This study reports on the powder metallurgy preparation and characterization of aluminum-graphene nanoplatelet (Al-GNP) composites synthesized using recycled Al powders. Recycled Al and GNP powders (0.1–1 wt%) were mechanically alloyed (MA'd) for 4 h, followed by cold pressing (at 450 MPa) and pressureless sintering at 590 °C for 2 h. Starting powders were analyzed using an optical emission spectrometer (OES) and a Raman spectrometer. Also, MA'd powders and sintered samples were characterized using an X-ray diffractometer (XRD), a scanning electron microscope/energy dispersive spectrometer (SEM/EDS), and a differential scanning calorimeter (DSC). Particle size analyses, pycnometer, and Archimedes' densities, Vickers microhardness, dry-sliding wear, and compression tests were also conducted. The Al4C3 formation was observed in the XRD patterns of sintered compositions. The highest and lowest relative densities were measured for the 1 wt% and 0.1 wt% GNP reinforced samples as 97 % and 92 %, respectively. The highest hardness value was obtained as approximately 1.31 GPa for 1 wt% GNP reinforced. With the addition of reinforcement GNP, the wear rate developed to approximately 0.00225 mm3/Nm. The compressive strength increased from nearly 70 MPa to 162 MPa.

Effect of ultrasonic pretreatment on physicochemical, thermal, and rheological properties of chemically modified corn starch

This study investigated the effects of ultrasonic and three chemical individual and dual modification treatments on corn starch's physicochemical, thermal, and rheological properties. Ultrasonication and the three chemical treatments disrupted the starch granules with a decrease in particle size and a significant increase in the ζ-potential. The hydrophilicity of ultrasonic-oxidized dual-modified starch (U-O-CS) was the highest, at 0.854 g/g. The lipophilicity of ultrasonic-esterified dual-modified starch (U-E-CS) was the highest, at 1.485 g/g. The gelatinization temperature of ultrasonic, oxidation, and cross-linking modified starches increased significantly, with cross-linking starches being the largest. Oxidative treatment significantly decreased the starch's G' and G" and weakened the textural properties. The rheological properties of U-O-CS were further weakened. The G' of the starch decreased after the esterification treatment, while the G" increased, and the textural properties were cut. The maximum rheological and textural properties were obtained for crosslinked modification, with a hardness value of 284.70 g.

Comparison of the hardness value and microstructure of Al6061 in horizontal centrifugal casting with and without mold cooling

The object of this research is the horizontal centrifugal casting process of the Al6061 alloy. Usually, cast products experience some casting defects, so the horizontal centrifugal casting process is applied to reduce the possibility of casting defects arising. In some casting processes, especially in the production of cylindrical specimens, casting defects such as porosity are encountered. Therefore, horizontal centrifugal casting was applied to overcome this problem. The test results show that the average hardness value for aluminum 6061 specimens resulting from centrifugal casting products with water cooling was 73.3 HRE, while the average hardness value for aluminum 6061 specimens resulting from centrifugal casting products without water cooling was 86.4 HRE. The microstructure results show that the grain size of centrifugal casting products with water cooling was 82.5 µm, whereas without water cooling it was 75 µm. Higher hardness values were obtained in specimens without mold cooling, this is because the conductivity in molds without cooling was higher compared to molds that experienced water cooling. The higher the heat conductivity of the mold, the faster the cooling process of the cast product. The casting process using the horizontal centrifugal method can be carried out to produce cylindrical spare parts

Microstructure and mechanical properties of similar and dissimilar resistance spot welded DC04 and HRP6222 (DD11) steels

Abstract Low carbon steels are frequently preferred in the automotive industry. The most preferred welding method in vehicle body manufacturing is resistance spot welding (RSW). In this study, RSW joints of DC04 and HRP6222 steels were carried out at two different electrode forces (2.1 kN, 2.4 kN) and three different welding currents (4 kA, 6 kA, 8 kA). The effects of different welding parameters on microstructure, tensile shear force, failure mode and microhardness were investigated. So, the focus was on optimizing the welding parameters. As a result, the RSW process caused the formation of three different regions in the microstructure (the base metal, the heat affected zone and the weld metal). It was observed that the tensile shear force increased as the welding current and electrode force increased. After the tensile shear tests, two different failure modes occurred (interface and pull-out type). Hardness values showed a linear relationship with tensile shear force results. In addition, a significant increase in hardness values was observed from the base metal to the weld metal in all welding parameters.

Composition design and mechanical properties of B4C/Al-Zn-Mg-Cu functionally graded materials prepared by laser additive manufacturing

In this study, three types of three-layer functionally graded materials (FGMs) were designed by mainting the average content of the reinforcement constant and changing the span of the composition. The B4C particle-reinforced Al-matrix FGMs and a homogeneous composite (HC) with the same average composition were prepared using the laser additive manufacturing technique. The FGMs had a higher average secondary-phase content and grain size than the HC. Large (black) and reticulated (white) secondary phases corresponding to B4C phase, T phase, and MgZn2 were observed in the as-deposited FGM samples. The content of the secondary phase in the middle layer was generally low. The bottom layer, which was in direct contact with the substrate, exhibited the smallest grain size. The hardness and wear resistance significantly improved owing to the high B4C content in the top layer. The flexural behaviors of each layer of the FGM in different directions were systematically studied. The plasticity of the single-layer material decreased with increase in the B4C content. When the bottom layer had a high B4C content, the flexural ability significantly reduced. Among all the samples, G2 with 8% B4C particle content in the top layer exhibited the best comprehensive mechanical properties. The hardness value, wear rate of the top layer, maximum bending stress, and maximum bending strain of the FGM were 177.5 HV, 0.367 × 10−3mm3/(N·m), 585.6 MPa, and 7.36%, respectively. This study can provide a reference value for the future design and development of wear-resistant gradient materials for aerospace applications.

The important factors for structure and mechanical properties in the repair of iron base metal component by thermal spray and welding processes

Cast iron is widely used in the manufacturing industry due to its high strength and wear resistance properties. However, cast iron's brittle nature results in frequent failure of cracks during formation or use. Among the repair methods that can be used are thermal spray and the welding process. Even though both welding and thermal spray have been implemented for various metal repairs processes, however very limited technical reports as well as scientific papers are found for this topic. Therefore, the optimum condition of metal repair by both processes is still needed to be explored. The present works focus on the comparison between thermal spray and welding method for cast iron repairs purposes. In the experiment of thermal spray process focus has been given in optimizing spraying distance on microstructure and hardness properties. On the other hand, in the welding experimental works focus has been given on the influence of groove design on microstructure and hardness. Each research variable is carried out to obtain optimal crack repair results. It was observed that thermal spray process produces less Heat Affected Zone (HAZ) area compared to the welding process therefore having less critical area. The highest hardness value of thermal spray method is 101.33 shown by 30 cm spraying distance. Meanwhile, the highest hardness value of HAZ area of welding method is 600 HV shown by specimen A. It was obtained that from the present experimental works, thermal spray process produces better results than welding process. However, the value of the specimen hardness produced by the welding and thermal spray method depends on the type of coating material used

Evaluation of dry sliding wear characteristics of hybrid a356 composite

As advancements in lightweight and synthetic materials have evolved, our ability to tailor materials to meet societal demands has expanded. Aluminium alloys, known for their high strength-to-weight ratio and cost-effectiveness, are extensively utilized in engineering applications, including structural casting and automotive components. This study employed the stir casting method to investigate the impact of silicon carbide (SiC) and graphite (Gr) on a hybrid A356 composite, aiming to enhance its tribological applicability. SiC and Gr particles were processed using a vibratory ball milling machine for two hours, followed by composite fabrication with varying particle sizes. Microstructural investigation using optical microscopy revealed maximum hardness values of 127 BHN and 125 BHN for A356 composites reinforced with 12.50% SiC, 15.50% Gr, and 11.43% SiC, 15.86% Gr, respectively. Wear rate analysis demonstrated that reinforced A356 composites exhibited higher wear resistance compared to unreinforced alloys. Notably, the sample reinforced with 11.43% SiC and 15.86% Gr displayed exceptional wear resistance. Photo micrographs of A356-SiC-Gr samples at different sliding distances, velocities, and loads revealed minimal plastic deformation during wear testing, resulting in abrasive and cohesive wear. Overall, this study underscores the effectiveness of graphite (Gr) and silicon carbide (SiC) as reinforcement materials for enhancing the tribological properties of A356 composites.

Antimicrobial Coatings Based on a Photoreactive (Meth)acrylate Syrup and Ferulic Acid-The Effectiveness against Staphylococcus epidermidis.

A novel photopolymerizable (meth)acrylate oligomer syrup modified with ferulic acid (FA) was verified as an antimicrobial coating binder against a biofilm of Staphylococcus epidermidis. A solution-free UV-LED-initiated photopolymerization process of aliphatic (meth)acrylates and styrene was performed to prepare the oligomer syrup. The influence of ferulic acid on the UV crosslinking process of the varnish coatings (kinetic studies using photo-DSC) as well as their chemical structure (FTIR) and mechanical (adhesion, hardness), optical (gloss, DOI parameter), and antibacterial properties against S. epidermidis were investigated. The photo-DSC results revealed that FA has a positive effect on reducing the early occurrence of slowing processes and has a favorable effect on the monomer conversion increment. It turned out, unexpectedly, that the more FA in the coating, the greater its adhesion to a glass substrate and hardness. The coating containing 0.9 wt. part of FA exhibited excellent antimicrobial properties against S. epidermidis, i.e., the bacterial number after 24 h was only 1.98 log CFU/mL. All the coatings showed relatively high hardness, gloss (>80 G.U.), and DOI parameter values (30-50 a.u.).

Repetitive recycling effects on mechanical characteristics of poly‐lactic acid and PLA/spent coffee grounds composite used for 3D printing filament

AbstractDue to its biodegradability, biocompatibility, and mechanical properties, poly‐lactic acid (PLA) is a leading biomaterial for numerous applications, especially for fused deposition modeling and fused filament fabrication. Nonetheless, the absence of a comprehensive recycling strategy may emerge as a significant source of plastic pollution in the future. Indeed, the polymer undergoes deterioration during melt recycling, resulting in a decrease in some mechanical properties that can compromise recyclability. To improve the properties of recycled PLA, the utilization of organic fillers coming from renewable materials can be considered as a sustainable solution. The objective of this work is then to evaluate the effect of recycling (reprocessing) on a virgin raw material as well as on biocomposites based on spent coffee grounds (incorporating 5% of spend coffee grounds in weight). The different types of filaments are extruded and re‐extruded and characterized under tensile, melt flow index, and hardness tests. The results show that the increase in the number of extrusions whether for virgin PLA or the composite contributes to the diameter fluctuation. Regarding the tensile properties, the rise in the frequency of recycling shows a weakness in the tensile strength and the elongation at break. On the other hand, Young's modulus values exhibit fluctuations. Concerning the addition of the spent coffee grounds filler, no major enhancement is observed in the tensile strength and the elongation at break, which is attributed to the poor adhesion between the matrix and the filler. The recycling process affects the hardness values of PLA, leading to an increase in these values, as well as those of the composite, which can be associated with the increased crystallinity caused by the recycling process and the SCG incorporation.Highlights Recycling and reusability strategy for poly‐lactic acid (PLA) and PLA/spent coffee grounds (SCG) filaments. Assessment of recycling effects on PLA and PLA/SCG. Mechanical characterization through tensile and hardness testing.