ASTM D638 Research Articles

3D Printed Stent from Graphene-Polyethylene Glycol Diacrylate Using Digital Light Processing Technique

Abstract This paper presents the development of the photocurable resin material based on the graphene reinforced polyethylene glycol diacrylate (gPEGDA) for vascular stent fabrication using a commercial 3D printer. 3D printing with digital light processing (DLP) technique is an attractive alternative for low-cost fast fabrication with high accuracy. Four photocurable resin compositions were prepared by mixing PEGDA and varied composition of graphene and the photoinitiator according to the design of experiment of 22 full factorial design. The diphenyl (2,4,6-trimethylbenzoyl) phosphine oxide (TPO) photoinitiator was adopted to meet the required 405 nm UV-light source wavelength of the 3D printer for stent fabrication. Material characterization of the UV-absorbance and viscosity tests were conducted and optimized to obtain resin printability. Mechanical characteristics tests were conducted to obtain the best resin composition for stent application. For this purpose, the tensile tests were conducted according to the ASTM D638 standard using the type-V specimen size. The test specimens were 3D printed with varied UV exposure time 20 and 30 seconds. Finally, the stents were successfully fabricated using a commercial 3D printer DLP with the bottom parameter time setting of 60 seconds, and the UV exposure time of 30 seconds. The resin material was applicable for 3D printing of the stent. The result has shown that 3D printer with DLP technique is suitable for stent fabrication with excellent surface quality. Moreover, the innovative bioresorbable stent materials and fabrication approach could open up new possibilities in the development of medical devices, particularly in the treatment of vascular diseases.

An investigation of clay percentage variation on composite materials sustainability identification by digital image correlation

ABSTRACT The study focuses on stress and strain evaluation of composite resin material with the reinforcement of clay in the glass-reinforced epoxy composite (GREC). The strain measurement used the DIC technique. The tensile test specimens were prepared from the laminate sheets as per ASTM D638 standard. The influence of nano clay weight percentage such as 2.5%, 3.5%, and 4.5% during preparation of GREC is studied in the article. The fibre orientation angles are 90°, and the fibre volume percentage is 45%. Hand lay-up methods are used to prepare the composite resin material. The samples were tested as per the standardised procedures. The specimen rupture at a localised strain reached a maximum value of 0.01293, 0.01571, and 0.0143 with 2.5%, 3.5% and 4.5% Nano clay, respectively. The material behaviour in terms of major strain (εyy), Poisson’s ratio (µ) and thickness strain (Δt) is evaluated at the gauge length of the specimen. DIC strain measurement clearly demonstrates the 3.5% percentage of clay addition as it yields better results as elastic modulus and tensile strength have improved. The composite resin with clay addition could be used in various applications, such as low-cost housing, structural works, medical devices, automotive panels, etc

Mechanically robust and durable polyurethane-based superhydrophobic coating containing silica nanoparticles derived from hydrothermal assisted sol–gel method

In the current study, a suspension of hydrothermal assisted sol–gel synthesised superhydrophobic silica nanoparticles (h-SNPs) are sprayed over apartially cured polyurethane (PUR) surface on aluminium substrate. The surface exhibited superhydrophobic (SH) property with a water contact angle of 166 ± 2° and awater sliding angle of < 5°. X-ray diffraction study confirmed the formation of amorphous silica nanoparticles. The particle size determined by field emission scanning electron microscope is about 19–21 nm. The roughness of the coating is 3.5 µm as characterised using a surface profilometer. X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy investigations indicated the presence of urethane linkages from PUR and siloxane stretching from h-SNPs. The adhesion of the coating tested with a cross-hatch cutter as per ASTM D3359 shows a rating of 5B. The coating qualified mandrel bend test conducted according to ASTM D255. No cracks are observed at the deformed areas and water drops roll off the surface, demonstrating the integrity of the coating and its superhydrophobicity. The coating exhibits high robustness as evident from sandpaper abrasion and tape peel tests. When compared to superhydrophobic polyurethane (SH PUR) coating developed using commercial silica as reported in our previous work, the developed h-SNPs coating is much more durable as confirmed by accelerated weathering test and anti-icing test. The SH coating also exhibits superhydrophobicity even after 200 h of accelerated weathering test and 16 de-icing cycles. The coating withstands 15 days of water immersion and also displays self-cleaning property.

A New Method for Compression Testing of Reinforced Polymers

Compressive testing of specimens taken from relatively thin composite plates is difficult, especially due to the occurrence of buckling. To prevent buckling, the central portion of the specimens used for the compression test has smaller dimensions, and the specimens can be guided along their entire length. For these reasons, optical methods, such as digital image correlation (DIC), cannot be used for the compression test and strain rosettes cannot be glued onto the samples to determine Poisson’s ratio. In this study, compression tests of a glass fiber-reinforced polymer (GFRP) were conducted using both the ASTM D695 (Boeing version) and a newly proposed method. The new method involves using special specimens that allow T-type rosettes to be bonded to determine Poisson’s ratio, whose value of 0.14 was thus determined. SEM images of the failure surfaces were presented and interpreted. A finite element analysis (FEA) of the specimens tested in compression is also presented. The first analyzed case considers the homogeneous and orthotropic composite, loaded with a uniformly distributed force. The normal stress in the central section of the specimen, determined with FEA, has an error of 6.52% compared to that determined experimentally. Additionally, the strain in the center of the strain gauge, determined with FEA, has an error of 4.76% compared to the measured one. In the second case studied with FEA, the sample is loaded with a quasi-concentrated force, which can move in the direction of the symmetry axes of the cross-section, to study the effect of the eccentricity of the compression force on the state of stress. It was shown that the eccentricity of the force has a great influence: the stress distribution in the section of the specimen becomes strongly non-uniform. For a force eccentricity of 0.4 mm in the direction of the OX axis, the minimum stress decreases by 53.7%, and the maximum stress increases by 55.4%. In order to analyze the influence of some manufacturing defects, two other cases were analyzed by FEA, in which it was assumed that the thicknesses of the outer resin layers were modified, making them asymmetrical. For this final FEA, the specimen was considered to be composed of laminates. These results demonstrate the special attention that must be paid to the centric application of force in compression testing.

Optimizing Thermoplastic Starch Film with Heteroscedastic Gaussian Processes in Bayesian Experimental Design Framework

The development of thermoplastic starch (TPS) films is crucial for fabricating sustainable and compostable plastics with desirable mechanical properties. However, traditional design of experiments (DOE) methods used in TPS development are often inefficient. They require extensive time and resources while frequently failing to identify optimal material formulations. As an alternative, adaptive experimental design methods based on Bayesian optimization (BO) principles have been recently proposed to streamline material development by iteratively refining experiments based on prior results. However, most implementations are not suited to manage the heteroscedastic noise inherently present in physical experiments. This work introduces a heteroscedastic Gaussian process (HGP) model within the BO framework to account for varying levels of uncertainty in the data, improve the accuracy of the predictions, and increase the overall experimental efficiency. The aim is to find the optimal TPS film composition that maximizes its elongation at break and tensile strength. To demonstrate the effectiveness of this approach, TPS films were prepared by mixing potato starch, distilled water, glycerol as a plasticizer, and acetic acid as a catalyst. After gelation, the mixture was degassed via centrifugation and molded into films, which were dried at room temperature. Tensile tests were conducted according to ASTM D638 standards. After five iterations and 30 experiments, the films containing 4.5 wt% plasticizer and 2.0 wt% starch exhibited the highest elongation at break (M = 96.7%, SD = 5.6%), while the films with 0.5 wt% plasticizer and 7.0 wt% starch demonstrated the highest tensile strength (M = 2.77 MPa, SD = 1.54 MPa). These results demonstrate the potential of the HGP model within a BO framework to improve material development efficiency and performance in TPS film and other potential material formulations.

Efficacy of jute-glass hybrid laminate composite wrapping under flexural loading

The demand for sustainable engineering materials has catalyzed interest in hybrid composites that combine natural fibers like jute with synthetic fibers such as E-glass. This study investigates the flexural strength of jute/E-glass/epoxy hybrid composite laminates under different stacking sequences, employing the ANOVA method to analyze their mechanical performance. The materials, including jute fabric, E-glass fabric, and epoxy resin, were arranged in various configurations and tested for flexural strength following ASTM D790 standards. The results indicated significant variability, with the GJGJ configuration exhibiting the highest average flexural strength of 71.20 MPa, while the GJG configuration had the lowest at 26.33 MPa. The ANOVA analysis confirmed a statistically significant effect of laminate configuration on flexural strength (F = 6.41, p = 0.004). These findings underscore the critical role of laminate arrangement in enhancing the mechanical properties of hybrid composites. The superior performance of the GJGJ configuration suggests that alternating layers of jute and E-glass fibers can effectively distribute stress and enhance load-bearing capacity. Conversely, suboptimal configurations like GJG demonstrated lower performance, highlighting the importance of strategic fiber arrangement. This research contributes to the development of optimized hybrid composites for various engineering applications, providing valuable insights into the interplay between natural and synthetic fibers within a composite matrix. The study's conclusions support the broader use of hybrid composites in industries such as automotive, construction, and aerospace, where material sustainability and performance are paramount. Future research should explore further optimization of stacking sequences and volume fractions of fibers, as well as investigate other mechanical properties such as tensile and impact strength, to fully realize the potential of hybrid composites in advanced engineering applications

Fatigue Analysis of Polylactide Manufactured by Fused Deposition Method of 3D Printing

Nowadays, 3D printing technology has gained popularity in various industrial sectors, especially in the field of developing new products. This technology allows for the layer-by-layer construction of 3D prototypes. This research primarily focuses on the fatigue performance of 3D-printed components made of Polylactide (PLA). PLA is a versatile material and has a diverse range of applications in packaging, medical, household items, etc. The specimens were made following the ASTM D638 standard using the Fused Deposition Modeling (FDM) technique. A fatigue test was carried out to investigate fatigue performance by fluctuating the loads and speed of the rotating beam fatigue tester. The finding reveals that materials break under variable strains at a stress magnitude is less than the material's ultimate tensile strength. Furthermore, it was discovered that the degree of the stress triggering fatigue failure reduces as the number of stress cycles increases. Fatigue failure is characterized as a time-delayed fracture due to cyclic stress. The finding reveals that PLA has a low fatigue strength of 19.62N.

Damage sensing in multi-functional nanocomposite polymer bonded energetics with embedded multi-walled carbon nanotube sensing networks

Abstract This experimental investigation evaluates the strain and damage sensing abilities of multi-walled carbon nanotube (MWCNT) networks embedded in the binder phase of polymer-bonded energetics (PBEs). PBEs are a special class of particulate composite materials that consist of energetic crystals bound by a polymer matrix, wherein the polymer matrix serves to maintain the composite’s shape and form. The structural health monitoring (SHM) approach presented in this work exploits the piezoresistive properties of the distributed MWCNT networks. Major challenges faced during such implementation include the low binder concentrations of PBEs, the presence of conductive/non-conductive particulate phases, the high degree of heterogeneity in the PBE microstructure, and achieving the optimal MWCNT dispersion. In this study, ammonium perchlorate (AP) crystals as the oxidizer, Aluminum grains as the metallic fuel, and Polydimethylsiloxane (PDMS) as the binder are used as the constituents for fabricating PBEs. To study the effect of each constituent on the MWCNT network’s SHM abilities, various materials systems are comprehensively studied: MWCNT/PDMS materials are first evaluated to study the binder’s electromechanical response, followed by AP/MWCNT/PDMS to assess the impact of AP addition, and finally, AP/AL/MWCNT/PDMS to evaluate the impact of adding conductive aluminum grains. Compression samples (ASTM D695) were fabricated and subjected to monotonic compression. Electrical resistance is recorded in conjunction with the mechanical test via an LCR meter. Gauge factors relating to the change in normalized resistance to applied strain are calculated to quantify the electromechanical response. MWCNT dispersions and mechanical failure modes are analyzed via scanning electron microscopy imaging of the fracture surfaces. Correlations between the electrical behavior in response to the mechanical behavior are presented, and possible mechanisms that influence the electromechanical behavior are discussed. The results presented herein demonstrate the successful ability of MWCNT networks as SHM sensors capable of real-time strain and damage assessment of PBEs.

Investigation of The Effect of CNC Milling Cutting Process on The Tensile Test of PLA Samples Produced Using Two Different 3D Printers with The FDM Method

One of the most commonly used materials in additive manufacturing with the fused deposition modeling (FDM) method is polylactic acid (PLA) filaments. In 3-dimensional (3D) printed products, an external wall is also used in addition to the internal structure pattern. The exterior wall pattern differs from the interior structure pattern. The 3D products obtained by this method contain two different pattern structures, which is not desired when determining the mechanical properties. In this study, tensile test specimens were produced with two different 3D printers using 1.75 mm and 2.85 mm diameter PLA filaments. Some tensile test specimens were directly produced in ASTM D638-14 Type 1 dimensions and subjected to tensile testing. The rest of the specimens were produced in a rectangular shape with 19 mm x 165 mm dimensions and the side edges of those specimens, produced in rectangular shape, were cut with CNC milling to bring their dimensions to ASTM D638-14 Type 1. All tensile test specimens were manufactured with a thickness of 4 mm. The test specimens cut with CNC milling after 3D printing were compared with the specimens tested only by 3D printing. The effects of CNC milling cutting on the tensile test properties of specimens produced on two different 3D printers using 1.75 mm and 2.85 mm diameter PLA filaments were investigated. Consequently, it was observed that cutting the side edges with CNC milling eliminated irregularities caused by 3D printing due to the tensile stress in those areas and allowed for more regular and consistent fractures of test specimens. When compared with only the 3D-printed specimens, the elongation at break of the tensile test specimens whose side edges were cut with CNC milling resulted in 13.45% and 33.55% higher using 1.75 mm and 2.85 mm PLA filaments, respectively. It was determined that the toughness of the samples cut by CNC milling was higher than the test samples that were only 3D printed.

Evaluation of mechanical properties of natural fiber based polymer composite

Natural fiber based polymer composites are eco-friendly alternatives to synthetic materials, with greater mechanical properties, biodegradability, availability, ease of access, and affordability. Jute fiber is widely recognized as one of the most important and beneficial natural fibers due to its strength, durability, and biodegradability. In this study, the jute composite is designed and fabricated using a 5-layer jute and epoxy resin, utilizing the manual hand lay-up technique. The combination of 52.5 % jute and 47.5 % of epoxy resin and harder is found optimized to achieve the goals of improving the tensile strength and flexural strength, reducing the cost of epoxy resin, and promoting eco-friendliness and sustainability. Tensile testing was performed on a universal testing machine, while flexural testing was done with a three-point bending test. Experimentally, the composites reinforced with jute and epoxy resin were capable of achieving the required levels of tensile strength (42.91 MPa) and bending strength (69.30 MPa). To validate and visualize specimens, numerical analysis was performed on the ABAQUS simulation software. The numerical simulation utilized ASTM D3039 and ASTM D7264 as the specified requirements for tensile and flexural behavior. For validation, these tensile and flexural test results were then numerically analyzed and compared to the experimental data. Finally, composite design, fabrication, and optimization can improve mechanical properties, reduce composite weight, lower resin cost, and increase sustainability. The proposed design and composition can be implemented to achieve lightweight properties in various applications, such as car components, door handle sheets, bicycle seat backs, and luggage covers.

Effect of different parameters on mode I fracture toughness of resin samples manufactured by DLP

Abstract Additive manufacturing is spreading rapidly in almost all industries, from household to advanced engineering. Components produced by Digital Light Processing (DLP) are not comprehensively characterized, but exceed the capabilities of many AM processes. Its advantages include the ability to produce highly complex designs, superior precision, fast printing and lower operating costs. The present paper investigates the mode I fracture toughness (KIC) of UV-sensitive resin specimens obtained through DLP process. Single edge notch bending (SENB) specimen were 3D printed and tested according to the ASTM D5045 standard. The influence of printing orientation-PO (0°, 45° and 90°), resin color-RC (white, black and transparent) and corrosive environment-CE (air, water and saline solution) was studied. It was observed that all the studied parameters have some effect on the fracture properties. The highest KIC values were obtained for 45°-PO, white-RC (1.88 MPa•m0.5) and saline solution-CE (2.24 MPa•m0.5). However, the greatest influence is highlighted by RC (∼92%), while CE (∼32%) shows a minimal effect. The fracture surface of the investigated samples is influenced by the printing parameters.

Acoustic Emission based determination of delamination initiation in GFRP laminates

Acoustic Emission (AE) has the potential to identify delamination initiation in quasi-static Mode I fracture tests on glass fiber-reinforced polymer-matrix (GFRP) laminates. It had been shown that a combined AE activity and intensity criterion yields critical Mode I delamination resistance values GIC for an AS4/PEEK carbon fiber thermoplastic composite that are comparable to those from data analysis according to ASTM D5528. However, the AE historic index also allows for detection of delamination initiation under Mode I and Mode II loading of carbon fiber reinforced thermoplastics and thermosets. In the present study, these AE criteria for initiation under Mode I, Mode II and Mixed Mode I/II loading of GFRP epoxy laminates are compared with AE signal energy as additional initiation criterion. Initiation under Mode II and Mixed Mode I/II at a ratio of 4:3 was determined with two different set ups for each Mode. For some test configurations noise signals make unambiguous initiation detection difficult. Determination by means of AE energy or AE activity and intensity yields more conservative GC values compared with the AE historic index or criteria defined in the standards, however, with similar repeatability.

Influence of Silver Nanoparticle Integration on the Composition and Surface Properties of Acrylic Dental Resins Employed in Temporary Bridges

Background: Recognized widely for its irreversible effects, periodontal disease stands as one of the most prevalent conditions, particularly emphasizing the potential for permanent damage caused by gingivitis, extending to encompass the entirety of the supportive complex, including the connective tissue and alveolar bone. Patients necessitating comprehensive periodontal and prosthetic treatments require an interdisciplinary approach, involving the coordination of pre-treatment procedures and appropriate prosthetic strategies. The adoption of advanced materials and techniques can prove beneficial in addressing complex dental issues. (2) Methods: Forty specimens were prepared using the prescribed procedure, with 20 acting as controls and the other 20 integrating AgNPs. The initial step involved crafting wax patterns of distinct shapes: dumbbell shapes for tensile testing and rectangular shapes for roughness assessments. These dimensions were aligned with ASTM D-638 and ISO 527-2 standards and adjusted to match the specifications of the analysis device for mechanical properties. (3) Results: In this case, the results indicate minimal differences in heat-curing acrylic resins compared to the control samples at a 5% concentration. However, notable disparities arise at concentrations of 10% and 20%. (4) Conclusions: Temporary prosthetic constructions are essential for preventing functional imbalances and complications. Incorporating AgNPs at a 5% concentration maintains mechanical properties while providing antibacterial effects for long-term interim prosthodontic restorations. Higher nanoparticle concentrations may reduce resin mechanical properties without affecting material surface condition

Exploring how 3D printing parameters affect the flexural strength of ABS materials

: This research focuses on testing the flexural strength of Acrylonitrile Butadiene Styrene (ABS) materials used in 3D printing by the Fused Deposition Modeling (FDM) method. The objective of this study was to evaluate the mechanical strength of ABS using a full factorial experimental design, applying three main factors such as layer height, infill density and infill pattern. Flexural testing was conducted following ASTM D790 standards. A total of 27 specimens were made by varying the layer height, infill density and infill pattern. The results showed that layer height was the most influential factor on flexural strength, with the highest value of 41.815 Mpa at 0.2 mm layer height, 100% infill density, and line infill pattern. ANOVA analysis supported this conclusion with p values &lt;0.05 for layer height, while infill pattern and infill density showed no significant effect. This study provides guidelines for the use of optimal parameters in ABS-based 3D printing processes.

Pattern optimization for 3D printing of composite filament materials with natural fibers and polylactic acid

Composite fiber materials developed through Fused Deposit Modeling (FDM) in high demand in fabricating automotive, machinery components such as bearings, sleeves, bumpers, windshields, etc. In this article, a new composite filament with natural fiber (Flax) and polylactic acid was prepared and their mechanical properties were analyzed. Taguchi approaches L27 orthogonal array was used to optimize the process parameters layer thickness (0.15, 0.25, 0.35 mm) for 0.4 mm nozzle with filling structure (L1—lines, L2—triangles, L3—octet), speed of nozzle movement (80,100,120 mm/s) and occupancy ratios (20%, 40%, 60%) were chosen as process parameters. Tensile and Impacts test have been carried with American Society of Testing and Materials Standard (ASTM D638 and ASTM D256) to evaluate the tensile strength, percentage of elongation and impacts strength of the fabricated specimens. The results emphasized that layer thickness significant influences the tensile characteristics as compared to better process parameters. The occupancy ratio at 20% and 40% with triangle and octet filling structure, nozzle speed of 100 mm/s at constant extruder temperature of 200°C have been found to optimize 3D printing parameters in this work. They were calculated as tensile strength 61.13 MPa, percentage of elongation is 4.43% and Izod impact test is 12.77 kJ/m2.

Evaluation of Different ZX Tensile Coupon Designs in Additive Manufacturing of Amorphous and Semi-Crystalline Polymer Composites

The layer-by-layer deposition of molten polymer filament in fused deposition modeling (FDM) has evolved as a disruptive technology for building complex parts. This technology has drawbacks such as the anisotropic property of the printed parts resulting in lower strength for parts printed in the vertical Z direction compared with the other two planes. In this manuscript, we attempt to address these challenges as well as the lack of standardization in sample preparation and mechanical testing of the printed parts. The paper focuses on process parameters and design optimization of the ZX build orientation. Type I tensile bars in ZX orientation were printed as per the ASTM D638 standard using two (2B) and four (4B) tensile bar designs. The proposed design reduces material loss and post-processing to extract the test coupons. Printing a type I tensile bar in the ZX orientation is more challenging than type IV and type V due to the increased length of the specimen and changes in additional heat buildup during layer-by-layer deposition. Three different polymer composite systems were studied: fast-crystallizing nanofiller-based high-temperature nylon (HTN), slow-crystallizing nanofiller-based polycyclohexylene diethylene terephthalate glycol-modified (PCTG), and amorphous carbon fiber-filled polyetherimide (PEI-CF). For all the polymer composite systems, the 2B showed the highest strength properties due to the shorter layer time aiding the diffusion in the interlayers. Further, rheological studies and SEM imaging were carried out to understand the influence of the two designs on fracture mechanics and interlayer bonding, providing valuable insights for the field of additive manufacturing and material science.

EXPERIMENTAL TESTS OF RED MERANTI (SHOREA SPP.) DOWEL BEARING STRENGTH AT AN ANGLE TO THE GRAIN

The angle to the grain has a significant influence on timber bearing strength. As the grain angle increases the bearing strength decreases. The aim of this research was to obtain the dowel bearing strength of the red meranti (Shorea spp.) timber at an angle to the grain. The scope of this research was as follows the specimens were made according to ASTM D143, the grain angle ranged from 0° to 12°, and the dowel bearing tests were displacement controlled in accordance with ASTM D5764. Results of this research was an empirical equation of dowel bearing strength (in MPa) in terms of an angle to grain θ (in degrees) namely Fe = 32.74 - 4.701θ + 0.2064θ2. The importance of studying the influence of the grain angle to the dowel bearing strength for timber connection design is because the direction of the timber grain is not perfectly 0°.

Investigation on Tensile Properties of Polylactide-Nanoclay (PLA/ MMT) Surface Modification Nanocomposites

Polylactic acid (PLA) has gained significant attention as an environmentally friendly biopolymer, but its limited mechanical properties have hindered broader applications. Nanoparticles such as montmorillonite (MMT) offer a promising approach to address this limitation. The intercalation of MMT with polymer chains can significantly impact the mechanical properties of the nanocomposites. Hence, this paper investigated the effect of surface-modified montmorillonite (MMT) nanoparticles on the mechanical properties of polylactic acid (PLA) nanocomposites. The acetylation process of MMT was carried out followed by neutralisation process with NaOH. PLA granules and acetylated-modified MMT were mixed, crushed into granular form, and moulded. The effect of varying concentrations of modified MMTs on the tensile strength, elongation at break, and maximum force of PLA/MMT nanocomposites was evaluated using the ASTM D638 standard. FTIR results showed shifts in peak intensities in regions 2750 cm-1- 2810 cm-1 led to changes in the aliphatic and aromatic regions, which confirmed the presence of acetylation. Controlled surface modification improved interfacial interactions and load distribution, enhancing overall mechanical performance. The incorporation of surface-modified MMT in PLA/MMT nanocomposite increased the maximum force, Young's modulus, elongation at breaks and tensile strength. PLA/1wt% MMT and the PLA/7wt% MMT compositions exhibited good mechanical properties. However, the PLA/5 wt% MMT blendis deemed more suitable for food applications, such as disposable cups, plates, and cutleries, due to its lower elongation point. In conclusion, the hydrophilic properties of MMT and the hydrophobic properties of PLA are compatible due to the synergistic effects during surface modification which enhance the overall performance of the nanocomposites.

An Advanced Surface Treatment Technique for Coating Three-Dimensional-Printed Polyamide 12 by Hydroxyapatite

Polymer 3D printing has is used in a wide range of applications in the medical field. Polyamide 12 (PA12) is a versatile synthetic polymer that has been used to reconstruct bony defects. Coating its surface with calcium phosphate compounds, such as hydroxyapatite (HA), could enhance its bonding with bone. The aim of this study was to coat 3D-printed polyamide 12 specimens with hydroxyapatite by a simple innovative surface treatment using light-cured resin cement. Polyamide 12 powder was printed by selective laser sintering to produce 80 disc-shaped specimens (15 mm diameter × 1.5 mm thickness). The specimens were divided randomly into two main groups: (1) control group (untreated), where the surface of the specimens was left without any modifications; (2) treated group, where the surface of the specimens was coated with hydroxyapatite by a new method using a light-cured dental cement. The coated specimens were characterised by both Fourier transform infrared spectroscopy (FTIR) and Transmission Electron Microscopy (TEM), (n = 10/test). The control and treated groups were further randomly subdivided into two subgroups according to the immersion in phosphate-buffered saline (PBS). The first subgroup was not immersed in PBS and was left as 3D-printed, while the second subgroup was immersed in PBS for 15 days (n = 10/subgroup). The surfaces of the control and treated specimens were examined using an environmental scanning electron microscope (SEM) and energy dispersive X-ray analysis (EDXA) before and after immersion in PBS. Following the standard American Society for Testing and Materials (ASTM D3359), a cross-cut adhesion test was performed. The results of the FTIR spectroscopy of the coated specimens were confirmed the HA bands. The TEM micrograph revealed agglomerated particles in the coat. The SEM micrographs of the control 3D-printed polyamide 12 specimens illustrated the sintered 3D-printed particles with minimal porosity. Their EDXA revealed the presence of carbon, nitrogen, and oxygen as atomic%: 52.1, 23.8, 24.1 respectively. After immersion in PBS, there were no major changes in the control specimens as detected by SEM and EDXA. The microstructure of the coated specimens showed deposited clusters of calcium and phosphorus on the surface, in addition to carbon, nitrogen, and oxygen, with atomic%: 9.5, 5.9, 7.2, 30.9, and 46.5, respectively. This coat was stable after immersion, as observed by SEM and EDXA. The coat adhesion test demonstrated a stable coat with just a few loose coating flakes (area removed &lt;5%) on the surface of the HA-coated specimens. It could be concluded that the 3D-printed polyamide 12 could be coated with hydroxyapatite using light-cured resin cement.

Evaluation of Mechanical Properties of Composite Material with a Thermoplastic Matrix Reinforced with Cellulose Acetate Microfibers.

Low-density polyethylene (LDPE) has been widely used in various applications due to its flexibility, lightness, and low production cost. However, its massive use in disposable products has raised environmental concerns, prompting the search for more sustainable alternatives. This study aims to investigate the mechanical properties achievable in a composite material utilizing low-density polyethylene (LDPE), potato starch (PS), and cellulose microfibrils (MFCA) at loadings of 0.05%, 0.15%, and 0.30%. Initially, the cellulose acetate microfibrils (MFCA) were produced via an electrospinning process. Subsequently, a dispersive mixture of the aforementioned materials was created through the extrusion and pelletizing process to form pellets. These pellets were then molded by injection molding to produce test specimens in accordance with ASTM D 638, the standard for tensile strength testing. The evaluation of the properties was conducted through mechanical tensile tests (ASTM D638), hardness tests (ASTM D 2240), melt flow index (ASTM D1238), and scanning electron microscopy (SEM). This study determined the influence of cellulose acetate microfibril loadings below 0.3% as reinforcement within a thermoplastic LDPE matrix. It was demonstrated that these microfibrils, due to their length-to-diameter ratio, contribute to an enhancement in the mechanical properties.