Polymer Testing最新文献

The South China Sea contains many coral reefs, and there is a lot of discussion about the best way to dispose of them. Finding ways to use these materials effectively in marine engineering could help address the shortage of natural aggregates in coastal engineering. One potential solution is using coral concrete, which offers cost-effective and enhanced properties. A type of coral fiber concrete using sea sand is created by combining coral rock, sea sand, seawater, PVA fiber, and PP fiber. The findings indicate that by utilizing the optimal ratio of the two fibers (3 kg PVA + 1 kg PP and 2 kg PVA + 2 kg PP), the cubic and axial compressive strength of the new concrete can be increased by 10 % and 20 %, respectively compared to ordinary coral concrete. Furthermore, incorporating these fibers can also reduce axial displacement, resulting in an elastic modulus that is 30–50 % higher than non-fiber variants while enhancing axial toughness. Finally, this study examines stress-strain curves at three different stages through analysis of macroscopic and microscopic failure mechanisms. It was found that there exists a correlation exceeding 0.9 between two mathematical models and measured stress-strain curves from this study. The effective use of composite plastic fiber significantly enhances concrete material performance while providing valuable data support for marine economic facilities construction.

This research explores the potential of PE-based mono-material flexible packaging as a sustainable alternative to traditional designs, emphasizing its efficient mechanical recyclability. Typically, non-PE materials are used in the outer layers of multilayer flexible packaging to ensure adequate stiffness and barrier properties. The stiffness of PE films can be significantly improved through the machine direction orientation (MDO) process. Our study investigates the influence of key polyethylene (PE) resin parameters, specifically, resin density and short-chain branching (SCB) distribution, with indications of molecular weight on lab-scale MDO film stretching and its subsequent effects on mechanical properties. We processed 5 distinct PE resins and blends in a lab-scale setup to produce compression molded base sheets and further MDO-PE films, characterizing them using shear rheology, GPC, DSC, and iCCD analyses. Tensile testing provided insights into the mechanical characteristics, while X-ray scattering (SAXS and WAXS) and AFM studies analysed structural evolution and morphology. Uniaxial stretching notably enhanced the tensile modulus of MDO-PE films along the machine direction, particularly in higher density blends, comparable to conventionally used polymers. Challenges related to extremely high-density base sheets led to localized stretching and breakage. Certain resin compositions exhibited unique molecular architecture, facilitating enhanced tensile modulus and axial stiffness. Our study offers insights into the microstructural changes and surface morphology of MDO-PE films, underscoring the potential use of stiffness-enhanced MDO-PE films as outer layers in PE-based flexible packaging designs.

Polymer composites reinforced with natural fibers have made great strides in industrial appliance use owing to the fibers exceptional composite properties, low environmental impact, and long lifespan. Five natural fibers-banana, sugar cane, coir, wood, and rice husk—are employed as short fibers in this experiment. The electrical and thermal properties of hybrid filler polymer (HFP) composites are also examined in relation to the thermal conductivity nano hBN filler weight ratio. HFP composites are prepared using the Taguchi design to select nano filler ratios and fifteen tests. Experimental results demonstrate that HFP composites with the maximum h-BN content are the most electrically and thermally robust. HFP composite material has the highest thermal conductivity and electrical resistance of 1.01 W/m-K and 346.91 Giga-Ohms respectively, with 5 % nano hBN and 2 % RH (sample 6). Nano h-BN fillers positively increase the thermal conductivity and electrical resistance of the composite structures. An improvement in thermal conductivity and electrical resistance is evident for the sample 6 composite, which increased by 16.09 % and 154.05 %, respectively, compared to the S1 interlaced multiphase hybrid polymer composite. Sample 4, containing rice husk fiber, achieves the minimal dielectric constant of 0.94, whereas sample 12, containing banana fiber, achieves a dielectric constant of 0.98. ANOVA is used to determine how such variables affect output variables. Performance measures are determined using the adaptive neuro-fuzzy inference system model with a hybrid grey base. Using the adaptive network-based fuzzy inference system, the input-output relation is modeled. After comparing experimental and ANFIS-anticipated data, the latter accurately predicted HFP composite behaviour. The combination of h-BN and natural fiber composites holds significant potential for various electrical and thermal applications due to their exceptional overall properties.

In environments with high humidity or water exposure, the performance of polyurethane materials could be adversely affected by water and its penetration, which could compromise their long-term utility. The influence of water on polyurethane materials is affected by water transport and various factors. This article summarizes the factors affecting the water absorption of polyurethane, introduces research methods for water transport in polyurethane, analyzes the pathways of water transport, and reviews the influence of water on the mechanical properties of polyurethane and its composite materials. The ultimate goal of this paper is to furnish a comprehensive theoretical foundation and a valuable reference for the research and practical application of polyurethane materials in water environments.

The sustainability and additive manufacturing of dielectric insulators are the development direction of the power system. Introducing dynamic covalent bonds in light-based 3D printing have attracted considerable attention as the reversible crosslinks allow for the reprocessing of printed objects. However, there generally exists a trade-off between mechanical strength, glass transition temperature (T_g), and reconfigurability for dynamic covalent networks. The reconfiguring process of the dynamic covalent network often requires high mobility of molecular chains and large free volumes, which in turn decreases the mechanical strength, T_g, and electrical insulating performance. Herein, we demonstrate a novel strategy for developing a kind of mechanically robust and sustainable vitrimer by building a rigid-flexible coupling inter-penetration network (IPN). Specifically, a two-stage curing approach was used to prepare high-performance 3D-printing vitrimers by using the plant oil-epoxy hybrid resin, which brings a lot of ester bonds and β-hydroxyl ester for the crosslinking network. Computational techniques with molecular dynamics calculation are used for the design and optimization of the crosslinking network, and then the optimized IPN is prepared by digital light processing 3D printing and subsequent heat curing. In the IPN, the epoxy backbone is rigid to enhance the T_g and tensile strength, while the plant-based methacrylate is flexible to guarantee topological rearrangement at elevated temperatures. Compared to reported epoxy vitrimers, the resultant IPN exhibits simultaneous high T_g (111 °C), outstanding tensile strength and toughness (tensile strength of 70 MPa, elongation at break of 17.58 %), good topological rearrangement, and excellent dielectric properties (permittivity less than 4, breakdown strength of 49.3 kV/mm). This work provides a new strategy for balancing the strength, toughness, electrical insulating and sustainability of 3D-printed thermosets.

The melamine-formaldehyde (MF) resin adhesive was modified by graphene oxide (GO), the chemical structure, wettability, bonding performance, tensile properties, curing performance and thermal properties of the modified resin were analyzed, and the toughening mechanism was also discussed in this study. The results showed that: (1) The MF resin with a high molar ratio possessed stable methylene ether bonds, which could easily generate parallel folding in space to form a π-π stacking supramolecular self-assembly special structure, with the potential of enhancing the toughness of molecular structures. (2) GO contained a large number of oxygen-containing reactive functional groups, which could further lower the curing temperature of the MF resin. A dense cross-linked network structure improved the thermal stability of the resin. (3) The bonding strength and toughness of the resin were significantly improved when the content of GO was 0.1 wt%. However, due to the large specific surface area and the intense π-π interaction between sheets, GO was easy to agglomerate, and the properties of the resin with GO content of 0.4 wt% degraded sharply. (4) The crystallinity of the MF resin modified by GO decreased, and the surface energy and plastic deformation energy increased due to the increased fracture crack path and fracture surface of the resin, which was the macro-reason for the improvement of toughness. (5) The strong π-π interaction between GO sheets and π-π accumulation between triazine rings were like parallel “springs” in the molecular structure of the resin, which might be the internal reason for the improvement of toughness. In addition, it was also proved that this special structure could limit the activity of hydroxymethyl and the release of free formaldehyde in the resin.

Polylactic acid (PLA) has become desirable for biomedical applications, particularly implantable devices. However, the degradation of PLA in biological environments under mechanical stress remains incompletely understood and requires further investigation. This study compared the plain fatigue (PF) and the biodegraded fatigue (BDF) behavior of 3D-printed PLA. For this purpose, two sets of standard fatigue specimens were additively manufactured by the fused filament fabrication (FFF) method. One set was used for plain fatigue testing, and the other was immersed for 330 days in simulated body fluid (SBF). After immersion, the samples were dried and weighed before fatigue testing. The fully reversed rotary bending fatigue tests were conducted on both sets of specimens, and the stress-lifetime (S-N) curves were obtained. Additionally, the fatigue properties of PF and BDF specimens were evaluated. Moreover, the fracture behaviors of the materials were studied using field emission scanning electron microscopy (FESEM). The outcomes implied that the weight of the samples extended during the immersion period, primarily due to water absorption by the PLA. However, after drying, the final weights did not change compared to the weights before immersion. The SBF immersion significantly reduced the fatigue performance of the biodegraded samples comparing the PF result.

Polyurethane elastomers (PUEs) will experience different strain rates in different application scenarios. Therefore, it is of great significance to study the mechanical properties of PUE under a wide range of strain rates and establish a constitutive model that considers strain rates with high accuracy and few parameters. In this study, the quasi-static and dynamic compression tests of two types of PUEs (PUE55 and PUE85) were carried out, and investigated the strain rate effect of the materials. Based on the Mooney-Rivlin hyperelastic model and the Prony series, a compressible visco-hyperelastic constitutive model for PUE was established. Different from the conventional constant relaxation time in Prony series, two relaxation times that vary exponentially with principal stretch were proposed based on the relaxation test to describe the strain rate effect of the material at low and high strain rate respectively. In addition, using the visco-hyperelastic constitutive model to obtain the model inputs of the Simplified rubber/foam model in LS-DYNA, the impact process of the Metal/PUE composite projectile was reproduced under different impact conditions through the finite element simulation. Simulation results verified the visco-hyperelastic model in generating numerical model material parameters and the rationality of the Simplified rubber/foam model in describing PUEs.

Surface-modified nanoparticles are commonly used to improve the mechanical properties and wear resistance of polytetrafluoroethylene (PTFE). However, fewer studies have been devoted to quantitatively revealing the action mechanism of graphene (Gr) modified with different functional groups on the mechanical and tribological properties of PTFE. Herein, the effects of four functional groups (−OH, −NH₂, −COOH, and −COOCH₃ functional groups) on the surface of Gr nanosheets on the mechanical and tribological properties of PTFE nanocomposites are studied using molecular dynamics simulations. The results indicate that the incorporation of functional groups to the Gr surface is able to significantly improve the mechanical properties and wear resistance of the nanocomposites, and the COOH-functionalized Gr nanosheet shows the best reinforcing effect due to the synergistic effect of its own high surface roughness and strong interfacial interaction between itself and the matrix. It is also found that the friction coefficient of the nanocomposites is obviously increased by the inclusion of functionalized Gr nanosheets, and the greater the surface roughness of the functionalized Gr nanosheet, the more significant the growth of the friction coefficient of the nanocomposites. The pull-out test and confined shear simulation reveal that due to the increased interfacial shear strength and the isolation of functional groups, an inhomogeneous transfer film is formed at the friction interface, leading to a decreased anti-friction property. This study provides some guidance for the future design and development of polymer nanocomposites with excellent mechanical and tribological performance for use in extreme service conditions.