Grafted Lactic Acid Oligomers on Lignocellulosic Filler towards Biocomposites

Lactic acid oligomers (OLAs) were in situ synthesized from lactic acid (LAc) and grafted onto chokeberry pomace (CP) particleboards by direct condensation. Biocomposites of poly (lactic acid) (PLA) and modified/unmodified CP particles containing different size fractions were obtained using a mini-extruder. To confirm the results of the grafting process, the FTIR spectra of filler particles were obtained. Performing 1HNMR spectroscopy allowed us to determine the chemical structure of synthesized OLAs. The thermal degradation of modified CP and biocomposites were studied using TGA, and the thermal characteristics of biocomposites were investigated using DSC. In order to analyse the adhesion between filler particles and PLA in biocomposites, SEM images of brittle fracture surfaces were registered. The mechanical properties of biocomposites were studied using a tensile testing machine. FTIR and 1HNMR analysis confirmed the successful grafting process of OLAs. The modified filler particles exhibited a better connection with hydrophobic PLA matrix alongside improved mechanical properties than the biocomposites with unmodified filler particles. Moreover, a DSC analysis of the biocomposites with modified CP showed a reduction in glass temperature on average by 9 °C compared to neat PLA. It confirms the plasticizing effect of grafted and ungrafted OLAs. The results are promising, and can contribute to increasing the use of agri-food lignocellulosic residue in manufacturing biodegradable packaging.

Experimental and Numerical Analysis of the Shear Properties of Honeycomb Cores Produced Using Additive Technologies

An approach to the experimental and computational study of the shear properties of honeycomb cores (HC) produced using Fused Deposition Modeling (FDM) technology is proposed. The experimental approach is based on a new sample type for testing HCs for shear. This sample contains two HCs and three steel plates. Shear tests are carried out in the TiraTest 2300 universal tensile testing machine. The HCs are made of ULTEM 9085 and PLA with FDM technology, which is implemented in the 3D Fortus 900 system. The tests resulted in obtaining the shear properties of the HCs by averaging the stress-strain curves of five samples. As follows from the analysis of the experimental results, brittle destruction of an HC is observed. Before its destruction, the value of shear deformation for samples made of PLA was 0.0134, and for samples made of ULTEM, 0.0257. The experimental analysis was accompanied by numerical finite element (FE) modeling of shear experiments, taking into account the deformation of the equipment. With the FE modeling of the experiments, to describe the behavior of the samples, it is necessary to take into account the influence, on the measurements of the shear properties, of the equipment and the deformation of each honeycomb cell. The deformation of three plates was taken into account; the elastic properties of the adhesive joint were not taken into account. A computer model of the deformation of the HCs with equipment was built using ANSYS Design Modeler. With FE modeling, only the elastic behavior of the HCs was considered.

A model study on the impact of metal ions on pre-vulcanization of concentrated natural rubber latex and dipped-products

A model study on the influence of some heavy metal ions on the stability and vulcanization efficiency of uncompounded and compounded high-ammonia natural rubber (HANR) latex was carried out by an exogenous addition and then determined by Brookfield viscometer, mechanical stability time (MST) tester, and tensile testing machine. The case of pre-vulcanized HANR latex with different aging times was determined by the change in the volatile fatty acid (VFA) number, MST, and viscosity. The compounded HANR latex was coagulated by adding Mn2+and Mg2+ while it was unaltered by adding Zn2+, Fe2+, and Cu2+ ions, leading to their colloidal stability. Therefore, these metal ions were chosen further to study the pre-vulcanization of compounded HANR latex. The presence of Zn2+, Fe2+, and Cu2+ in the latex is responsible for the delay in the vulcanization process and changes the appearance of compounded latex. Before compounding, the addition of such metal ions led to the reduction in tensile strength of the obtained gloves. At the same time, there was no effect on the tensile properties of the gloves made from the compounded HANR latex containing the metal ions.

Stress Corrosion Cracking Behavior of Fine-Grained Al5083 Alloys Processed by Equal-Channel Angular Pressing (ECAP)

In the present study, the stress corrosion cracking (SCC) behavior of ECAP Al5083 alloy was investigated in air as well as in 3.5 % NaCl solution using the slow strain rate tensile test (SSRT). The characteristics of grain boundary precipitates (GBPs), specifically the microchemistry of the SCC behavior of Al5083 alloys, both in “as-received” condition and when deformed by the ECAP process, were examined. The correlations between the SCC resistance and GBP microchemistry were examined. A microstructural evaluation was performed using an optical microscope. SCC tests were carried out using a universal tensile testing machine and the fracture surfaces were studied using scanning electron microscopy (SEM). A strain rate of 1×10−6 s−1 was applied for the SSRT. As the passes increased, the SCC susceptibility of the fine-grained ECAP Al5083 alloy also increased. Moreover, higher ultimate tensile strength and greater elongation were observed. This was due to grain refinement, high-density separations, and the expanded extent of high-density dislocations instigated by severe plastic deformation. Due to the high strength and elongation, the failure analysis showed a ductile mode of fracture. Electron backscattering diffraction (EBSD) analysis was performed to determine more clearly the nature of cracking. EBSD analysis showed that the crack propagation occurred in both transgranular and intergranular modes.

Portable universal tensile testing machine for studying mechanical properties of superelastic biomaterials

A portable universal tensile testing machine for single and cyclic loading of superelastic biomaterials is presented. It’s an alternative to large-sized stationary universal testing machines. The machine is designed to obtain uniaxial cyclic tension stress-strain curves of materials with a low elastic modulus, including biological tissues. Its portability allows using it in various conditions: classrooms, production laboratories, and in the field. An interface has been developed to connect it to a computer. Computer output of experimental data allows recording and displaying load-displacement curves, setting the number of cycles, limits, and rate of cyclic deformation. Several examples of testing various biomaterials are presented. The functional advantage of the device is the wide tensile testing speed range of 0.01-10 mm/s and cyclic loading, which allow capturing viscoelastic and superelastic behavior of biomaterials.

Effect of cooling rates after annealing on the microstructure and properties of 1000MPa grade automobile steel for cold forming

The effects of different cooling rates ( 0.05℃/s, 0.1℃/s, and 0.2℃/s ) on the microstructure and mechanical properties of 1000 MPa grade automobile steel for cold forming after two-phase annealing were studied. The microstructure of the experimental steel was observed by SEM and TEM, and its mechanical properties were tested by a universal tensile testing machine. The results showed that by increasing the cooling rate of two-phase annealing, more massive retained austenite, more uniform and fine ferrite, better elongation and higher ultimate tensile strength of steel can be obtained, so as to obtain better production of tensile strength and total elongation ( product of tensile strength and elongation, PSE ). The final result shows that after the test steel is quenched at 800℃ + 10 minutes and annealed in the two-phase region at 690℃ + 10 minutes, the faster the cooling rate, the better the mechanical properties. The mechanical properties of the steel plate are the best when the cooling rate reaches 0.2℃/s, and PSE can reach 27.44 GPa·%.

Enhanced Knittability of Paper Yarn from the Swedish Forest by Using Textile Finishing Materials

Friction between Swedish paper yarn and needles is a limiting factor that—together with the low yarn flexibility—is hindering the knitting and use of paper yarn as a sustainable textile material. To enhance the knittability, paper yarn was coated with textile finishing materials. The effect of six different textile finishing materials used for textiles processing (three different silicone-based, wax, glycerol, and soap) was evaluated. The treatment evaluation was done by determination of the friction coefficient, tensile testing, and knitting. The friction coefficient was determined by an adaption from the ASTM D3108-07 Standard Test Method for Coefficient of Friction, Yarn to Solid Material. The adaption meant using a specially designed rig, making it possible to simulate the yarn/needle friction during the knitting process and use a tensile testing machine to determine the friction coefficient. Through using the same angle for yarn movement during the knitting process in this adaptation, the effect of the flexibility of paper on the friction coefficient is integrated. Tensile testing was performed using a Tensolab 2512A/2512C electromechanical tensile tester, and knitting tests were performed using a Stoll CMS 822 HP knit and wear flat knitting machine with the E5.2 gauge. The results show that knittability is better for the yarns with lower coefficients of friction and can also be enhanced by spraying with regular water. The tensile properties of the yarn is degraded by the treatments. The wax- and soap-treated yarns were most challenging to knit. The silicone-based and glycerol-treated yarns showed enhanced knittability, where the glycerol treatment results in more protruding fibers compared to the other treatments. All treatments reduced the roughness in the feel of the knit. The results indicate that the Swedish paper yarn can be a future sustainable complement to polyester and cotton.

Lateral Translation of the Patella in MPFC Reconstruction: A Biomechanical Study of Three Surgical Techniques (210)

Objectives: Recurrent patellar instability (RPI) is a common knee disorder and can lead to chronic pain and functional disability. Surgically addressing recurrent patella instability has classically focused on reconstruction of the MPFL, which has widely become the standard of care either in isolation or concomitantly with other patellar realignment procedures. Complications following MPFL reconstruction include patellar fracture, articular surface penetration, and physeal injury in skeletally immature patients. In an effort to avoid these, other surgical techniques have been described. While these alternative MPFC reconstructions have anatomical support and the theoretical potential to reduce complications, it is unknown whether differences exist in lateral patellar translation and thus their effectiveness in adequately stabilizing the patella. The purpose of this study was to investigate whether differences exist in the ability to prevent lateral patellar translation between three distinct medial patellar stabilizing surgical procedures at varying knee flexion angles. Methods: Six cadaveric knee specimens were dissected, potted, and placed in a customized jig for testing. The quadricep muscle groups were separated into three components and loaded with a total of 175 N in anatomic directions using a weighted pulley system. Lateral patellar displacement was measured at 0°, 10°, 20°, 30°, 45°, 60°, and 90° of knee flexion using a tensile testing machine with a 20 N lateral force applied to the patella. Each specimen was tested with the MPFC intact and sectioned, and after each of the three reconstruction techniques: medial patellofemoral ligament (MPFL) reconstruction, hybrid (proximal medial patellar restraints - PMPR) reconstruction, and medial quadriceps-tendon femoral (MQTFL) reconstruction. Statistical analysis used the Friedman and Wilcoxon rank sum tests due to non-normally distributed data. Results: There was significantly increased lateral patellar displacement following MPFC sectioning when compared to the intact state in early degrees of flexion (10° to 30°) (p<0.05). All three reconstruction groups adequately restored patella stability and reduced lateral patellar displacement following medial soft tissue sectioning by 42%, 41% and 33% following MPFL, Hybrid and MQTFL reconstruction, respectively, from 0° to 30° of knee flexion (p<0.05 for each reconstruction group). When compared to the native, intact medial restraints group, all three reconstruction groups demonstrated reduced patella translation at full knee extension, while the MPFL and Hybrid reconstruction groups additionally demonstrated significant reduction of patella translation at 10° of flexion as well (p<0.05). When comparing patella displacement between reconstruction groups, no significant difference was observed at any degrees of flexion between the three groups. Conclusions: This biomechanical cadaveric study demonstrates the efficacy of three different MPFC reconstruction techniques in restoring patella stability following MPFC sectioning, especially at lower knee flexion angles where the medial soft tissue restraints play a more important role. Although all three reconstruction groups demonstrated less patella translation than the native MPFL intact knee, MPFL reconstruction appears to provide the most robust patella stabilization, whereas MQTFL reconstruction may be the most forgiving construct. Future clinical studies are needed to investigate the clinical correlation of these findings.

Research stand for microplasma surface treatment of materials at atmospheric pressure

A research stand for microplasma treatment of object surfaces with the ability to move the discharge zone along the object using a program-controlled linear stepper motor has been developed. The design of the stand allows the use of different types of plasma generation systems, as well as processing with feeding of various gases such as air, nitrogen, oxygen, etc. into the discharge zone. The research bench is equipped with measuring equipment for monitoring the electrical and physical characteristics of the discharge (digital oscilloscopes, optical emission spectrometer, air ion meter, etc.). A microhardness tester, goniometer, interference microscope, tribometer, tensile testing machine, etc. can be used to further evaluate the quality and characteristics of the treated surfaces. Examples of the electrical characteristics of discharge devices tested as part of the research stand, optical emission spectroscopy of plasma, and results of measurements of the contact angle of treated objects surfaces are given.

Effect of Doped Glass Fibers on Tensile and Shear Strengths and Microstructure of the Modified Shotcrete Material: An Experimental Study and a Simplified 2D Model

Shotcrete material has found extensive applications as a reinforcing material in the engineering sector. This study examined the effect of doped glass fibers on the mechanical performance of the modified shotcrete material composed of aeolian sand, fly ash, cement, quicklime, and doped glass fibers. Its tensile and shear strengths values were experimentally determined via a WAW-1000D computerized hydraulic universal tensile testing machine. Its microstructure was analyzed via a size analyzer, scanning electron microscope (SEM), and X-ray diffractometer (XRD). A 2D simplified mechanical model was elaborated to reflect the influence mechanism of the doped glass fibers on the mechanical performance of the modified shotcrete material. The experimental and mechanical analysis results indicated that, at the macroscopic scale, the experimental tensile and shear strengths of the shotcrete material doped with glass fibers were significantly higher than those of the undoped shotcrete material (by up to 310% and 596%, respectively). These results were in concert with the proposed model predictions, where the compound stresses in the shotcrete material were derived as the sum of the stress borne by the shotcrete material itself and the bridging stress exerted by the glass fibers. At the microscopic scale, SEM observations also revealed that the glass fibers were intertwined with each other and tightly enveloped by the shotcrete material particles within the modified shotcrete specimens, connecting the particles of different components into a whole and improving the overall mechanical strength. In addition, the relationships of the compound stress of the shotcrete material vs. embedment length, embedment angle, and cross-sectional area of the glass fibers were established. The research findings are considered instrumental in clarifying the mechanism by which the glass fibers influence the mechanical performance of shotcrete materials and optimize their solid waste (fly ash and quicklime) utilization.