Polymer Testing最新文献

Shape-memory polyurethanes (SMPUs) are promising materials that change shape in response to external heat. These polymers have a dual-segment structure: a hard segment for netpoint and a soft segment for molecular switch. Understanding the molecular behavior of each segment and microphase-separated morphology is crucial for comprehending the shape-memory mechanism. This study aimed to understand the shape-memory behavior by observing the phase separation of SMPU using mesoscale models based on dissipative particle dynamics (DPD) simulations. The SMPU copolymer was modeled using 4,4′-diphenylmethane diisocyanate (MDI, hard segment) and poly(ethylene oxide) (PEO, soft segment). By calculating segment solubility and repulsion parameters, we found that the hard-segment domain changes from isolated form to a lamellar and interconnected structure and eventually to a continuous form as its content increases. Combining these insights with shape-memory performance models can enhance our understanding of better SMPU design and contribute significantly to the optimization of smart stimuli-responsive materials.

Under environmental exposure, the mechanical properties of elastomers change due to ageing, all while enduring mechanical service loading conditions. The influence of ageing on the multiaxial mechanical response of elastomers remains an understudied question, lacking exploration in both experimental evidence and modelling proposals. The present study describes an experimental/numerical approach to characterize the multiaxial behaviour of elastomers with consideration of ageing. This technique associates complex experimental tests conducted with a hexapod device, with a Data-Driven Identification (DDI) algorithm. Practically, heterogeneous strain fields are measured by Digital Image Correlation (DIC), and the corresponding stress and energy fields are calculated by DDI. These fields are visualized through three-dimensional maps, encompassing kinematical quantities and strain energy density. These maps convincingly capture the stiffening induced by ageing, in different deformation modes. Finally, the coupling between ageing and multiaxiality is foregathered in a material database that can be fitted for further modelling purposes.

As the demand for innovative electronic devices continues to grow, flexible electronic products which offer a solution capable of adapting to various shapes and deformations, are increasingly gaining prominence. This study innovatively uses electrospun polyvinylidene fluoride (PVDF) nanofibers as substrates and employs reactive inkjet printing (RIP) technology to deposit and instantaneously reduce graphene oxide (GO), fabricating ultralight flexible all-solid-state supercapacitors. To verify that PVDF nanofibers as substrates can facilitate the uniform deposition of GO ink during inkjet printing and prevent the dispersion of GO into the internal structure, thereby achieving good capacitive performance with the fewest layers of printing, this study analyzes and compares the capacitive performance differences among 1rGO/PVDF, 3rGO/PVDF, and 5rGO/PVDF samples. The results have been confirmed that the GO ink was effectively instantaneously in-situ reduced by l-ascorbic acid (AA) to rGO by RIP system, and the specific capacitance of 1rGO/PVDF electrode was founded of 83.29 F/g at a current density of 2 A/g from the GCD analysis with a corresponding energy density of 7.5 Wh kg⁻¹ and power density of 1.04 kW kg⁻¹. The 1rGO/PVDF supercapacitor exhibits excellent electrochemical stability, maintaining 93 % efficiency after 4000 charge-discharge cycles at a current density of 2 A/g.

A hybrid methodology was developed and implemented for estimation of polymeric mechanical properties in rotational moulding process. The considered polymer in this study is linear low-density polyethylene, known as LLDPE, which has extensive application in plastic industry. The mechanical properties of the polymer were assessed and correlated to the oven residence time to build the predictive model of moulding process. A tiny dataset containing only 25 data rows via a number of machine learning models were assessed. Oven residence time is the only input, while the LLDPE's properties including tensile strength, impact strength, and flexure strength are the outputs considered in the machine learning models. We used tree-based ensemble methods for modeling in this work and they are tuned using FA (Firefly Algorithm) optimizer to find optimal hyper-parameters of them. Finally, the optimal models had shown a great performance to predict the output accurately. For tensile strength, the best model (FA-ET) has an R² value of 0.9994, this score is 0.9995 for impact strength and 0.9968 for flexure strength. The tree-based models tuned in this study revealed to be robust in estimation of polymeric properties and can be used to obtain the products with the best quality.

In this work, the structural battery composite (SBC) full-cells based on carbon fiber (CFs) were fabricated using a three-step hot pressing method. LiFePO₄ (LFP) was loaded onto CF fabrics considering the influences of hot pressing parameters including the pressure and the temperature. The SBC full-cells were subsequently fabricated using the LFP loaded CF cathode, the CF anode, the glass fiber (GF) separator via a structural electrolyte (SE) filming process, followed by the second hot pressing. The multifunctional efficiencies were assessed for SBCs with SE containing different components. To reduce the capacity loss, the SBC was eventually encapsulated with the GF/Vinyl Ester prepreg and thermally cured in the third hot pressing. The capacity retention of the SBC was significantly improved after encapsulation. This work could be seen as a further step forward the engineering fabrication of the SBC full-cells based on both CF anodes and cathodes.

Multifunctionality brought by nanomaterials such as carbon nanotubes (CNTs) to high-performance thermoplastics brings several opportunities for tuning the properties in advanced applications. Here, polyetherimide (PEI) and polyether ether ketone (PEEK), amorphous and semi-crystalline polymers, were chosen to explore the thermal transitions and rheology linked to morphological properties of CNT-reinforced PEI and PEEK nanocomposites. A custom-built twin-screw extruder was employed to manufacture the CNT/PEI and CNT/PEEK nanocomposites at 1, 3, and 5 wt%. The thermal stability and glass transition temperature ($T_g$) of nanocomposites were not significantly affected; however, the crystallization ratio of the PEEK nanocomposites was increased to 29.3% for 1 wt% CNT/PEEK. Rheological analysis showed that storage modulus was enhanced in both polymers. Rheological percolation was considered to be below 1 wt% CNT for both PEI and PEEK. The lowest shear-thinning exponents were found as 0.35 and 0.26 between $10^2$ and $10^3$ rad/s for 5 wt% CNT/PEI and CNT/PEEK, respectively.

Understanding the impact-induced ignition properties and energy release behavior of polymer-bonded explosives (PBXs) is critical for the safety of explosive systems. In this study, a new impact test component was designed using a light gas gun to quantify the ignition mechanism and chemical reaction of micro-damaged PBXs under different inertial loading conditions. A constitutive model was developed to describe the mechanical-thermal-chemical response of the PBXs. This model was employed to further investigate the correlation between microcracks, debonding, hot spots, and chemical reactions. The results show that the stress state of the material is not uniformly distributed due to the micro-inhomogeneities and structural defects of PBXs. The shear friction of the microcracks contributes to localized hot spots, thereby inducing ignition. The critical loading condition for ignition is the length of the steel pillar is 32 mm. The damage and hotspot temperatures of the anterior lateral and posterior lateral regions are greater than those of other locations. The ignition response is accentuated with longer steel pillars, resulting in a more violent release of energy.

Considering wide applications of Additive Manufacturing (AM), profound knowledge on the mechanical performance of AMed components is a necessity. In the present study, the mechanical behavior of AMed polymer parts under static and dynamic tests has been investigated. To this end, cantilever beams with three different mesostructure cells were designed and fabricated via ABS Carbon material based on the fused deposition modeling process. The specimens were subjected to a series of static bending tests and free vibration experiments. In addition, numerical models have been presented for both static bending and the dynamic tests. In the current study, digital image correlation technique has been employed to determine strain field and validate the numerical results. The experimental findings and numerical outcomes have been compared and the convergence has been investigated. Based on the applications of AM in fabrication of structural elements with complex geometries, the results of the current study are useful for new designs of AMed parts with customized mechanical strength and enhanced structural performance.

Fast scanning chip calorimetry (FSC) allows subjecting polymer melts to well-defined vitrification, crystal nucleation, and crystal growth pathways and, therefore, precise control of morphologies, from fully amorphous glassy states to semicrystalline structures containing perfect crystals. Due to the required use of nanogram-sized samples, needed to achieve high cooling rates, their mechanical properties, in order to establish structure-property relations, are difficult to assess. In this work, indentation modulus and indentation hardness of FSC samples are successfully determined on example of semicrystalline poly (ʟ-lactic acid) (PLLA) containing spherulitically grown disorder α′- or rather perfect α-crystals, with the correctness of the applied preparation and analyses routes confirmed by nanoindentation measurements on milligram-sized samples prepared through hotstage microscopy, and by applying both static single-step and quasi-continuous stiffness measurements. Modulus and hardness data are consistent with prior analyses of bulk samples, confirming that semicrystalline PLLA containing α-crystals exhibits around 10–20 % higher values of these properties compared to PLLA containing α′-crystals, related to the different molecular-chain packing in the crystal lattice. This work demonstrates that combination of FSC and nanoindentation techniques is an effective tool for determining mechanical properties of samples solidified at specific thermal pathways which otherwise cannot be realized.