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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.

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.

Polylactic acid (PLA) is a biodegradable polymer from renewable resources with mechanical properties comparable to traditional polymers, but with a higher cost. A solution to this issue is the production of bio-based composites to partially replace the PLA matrix with industrial wastes characterized by a zero-cost, e.g., linoleum, to also valorize them in a circular economy perspective. Linoleum heterogeneous nature deriving from the simultaneous presence of lignocellulosic and inorganic fillers and oil/rosin binders, made the evaluation of matrix/filler compatibilization strategies necessary. Two approaches were considered, one from the filler perspective with NaOH and silane treatments, and the other one from the matrix perspective by adding a chain extender (C.E.). The first approach marginally improved tensile stiffness (by 1.6 %) compared to neat PLA but caused a significant decrease of 32.8 % in strength. Considering this, the costs and disposal of the chemicals and the increased environmental impact of the process, this approach was discarded. One the contrary, the introduction of C.E. does not modify the manufacturing process and increases tensile stiffness and elongation at break of 7.2 % and 415.5 % compared to neat PLA with a tolerable reduction in strength, i.e., 16.6 %, thus being a suitable way to exploit linoleum as zero-cost filler.

Rigid polypropylene is mechanically recycled but flexible polypropylene is mostly used in energetic valorization because of the poor properties of the recycled polymer. A recycled polypropylene-based composite with outstanding properties for flexible food packaging was developed. For the first time, the influence of maleated polypropylene copolymer addition and the fumed silica/copolymer ratio on the packaging properties of recycled flexible polypropylene under the effects of silica hydrophilicity was investigated. The structural, morphological, thermal, mechanical, melt flow, overall migration, water vapor barrier and sealing properties of the developed nanocomposites were analyzed. Prominently, the addition of 1:1 maleated polypropylene and hydrophobic nanosilica improved the global performance of all tested methods. The recycled polypropylene had an overall migration to olive oil of 17 mg dm−2, exceeding the limit allowed for food packaging, but the developed added-value composite reduced it to the tolerance limit according EU legislation. The seal strength was drastically increased by 50 % with adhesive peeling, high thermal stability, and well-dispersed particles without affecting the ductility.

Epoxy/glass fibre composites possess excellent mechanical and electrical properties and are widely utilised in electrical and electronic power equipment. However, the composites exhibit relatively poor thermal conductivity, causing the temperature of the composites to increase during the operation of power equipment, resulting in a significant reduction in the electrical breakdown strength. Although the effects of thermal aging on polymeric materials have been widely studied, its influence on electrical strength mechanisms has not been investigated at the molecular level. In this study, epoxy/glass fibre composite specimens were subjected to accelerated thermal aging treatment for 360 h at 180 °C. Functional groups, molecular chain dynamics, and electrical breakdown are characterised using infrared spectroscopy, dielectric spectroscopy, and breakdown measurement. Subsequently, electrical breakdown mechanism and life prediction of the thermally aged composites are discussed. During thermal aging, the epoxy resin molecular chains undergo continuous oxidation and chain scission, which generate numerous polar functional groups and short chains and an increase in the free volume. This triggers an enhancement in the chain segmental dynamics, thereby significantly reducing the activation energy of the epoxy resin. After 360 h, activation energy decreased from 0.78 eV to 0.67 eV. The DC breakdown voltages of the specimens decreased from 168.28 kV/mm to 134.91 kV/mm. An insulation life prediction model for thermally aged epoxy/glass fibre composites is established based on the time-temperature equivalence theory. The prediction results indicate that the service life of the operational composites is approximately 11.2 years at 353 K, which is consistent with engineering experience.

In the context of the increasing effect of carbon dioxide emissions on the global climate biodiesel produced from renewable sources has emerged as a promising contender replacing fossil fuels, especially in long-range transport vehicles, using existing engines and infrastructure.High-density polyethylene is one of the prevailing materials for pipe and container applications for storage and transport of such fuels, both, from fossil and renewable resources. The contact with the respective fuels raises questions concerning material compatibility as biodiesel exhibits significant differences compared to conventional diesel fuel affecting its sorption and plasticization behavior in polyethylene. In this study, its behavior with respect to environmental stress cracking, considered one of the most frequent damage mechanisms leading to failure of polymer parts and packaging, was evaluated using the well-established Full Notch Creep Test. This approach allows for a detailed fracture surface analysis using imaging techniques, such as optical and laser scanning microscopy, as well as infrared spectroscopy. Comparing the environmental stress cracking behavior in standard surfactant solutions with that in biodiesel and diesel, respective crack propagation rates, showing different levels of acceleration, were determined and details of the underlying mechanisms could be revealed. Furthermore, the specific infrared absorption of the biodiesel's ester functionality allows its semi-quantitative determination on the fracture surface of the tested specimens after failure. Thus, a preferred uptake of sorptive fluids in the fracture zone due to local morphological changes of the polyethylene could be directly evidenced by infrared spectroscopy.

The intricate failure modes and the yet unclear rate dependency of carbon fiber reinforced plain weave composite materials pose a challenge to mechanics researchers. This study establishes an energy-based evolution mechanism for the compressive failure modes of plain weave composite materials as the strain rate varies. This mechanism illustrates how the rate dependency of failure modes arises from the competitive relationship between strain potential energy and deformation kinetic energy. At low loading rates, the specimen exhibits a progressive crushing failure mode characterized by low peak stress and significant geometric deformation. As the loading strain rate increases, the energy required for this geometric deformation also increases. When the energy expenditure surpasses that needed to elevate the stress level of the specimen, it transitions to an instantaneous failure mode with high peak stress. In this mode, the specimen fractures into multiple small fragments immediately upon failure, lacking the large geometric deformations observed at lower rates. Through calculating this energy mechanism, a transition strain rate of 180 s−1 was determined for both failure modes. The accuracy of this mechanism was further verified by tests conducted near the critical strain rate. The energy-based evolution mechanism for failure modes provides a simplified and concise framework for simplifying complex models of composite material failures.

The synthesis and characterization of PVA-chitosan-NiO, PVA-chitosan-TiO2, and PVA-chitosan-TiO2@NiO films have opened avenues for tailoring materials with specific electrical, dielectric, and optical properties. The synergistic effects arising from the combination of polymers and metal oxides offer a platform for further optimization and application-specific tuning. The synthesis process successfully incorporated NiO and TiO2 nanoparticles into the PVA-chitosan matrix, creating three distinct films: PVA-chitosan-NiO, PVA-chitosan-TiO2, and PVA-chitosan-TiO2@NiO. Structural analyses, including X-ray diffraction (XRD) and scanning electron microscopy (SEM), revealed well-defined nanostructures with crystalline metal oxide dispersions. Dielectric characterization demonstrated frequency-dependent behavior, elucidating the influence of metal oxides on dielectric constants and loss tangents. Cole–Cole plots provide insights into relaxation processes and can guide applications in capacitors and energy storage devices. Conductivity measurements highlight the enhanced electrical performance of NiO and TiO2. This study provides a foundation for future research on the development of advanced functional materials for a wide range of technological applications. The insights gained from this work contribute to the growing body of knowledge on polymer-metal oxide composites and pave the way for innovations in electronic, optoelectronic, and energy-related technologies.

Using the solution casting procedure, poly (vinyl alcohol)/carboxymethyl cellulose/polypyrene/milled multiwall carbon nanotubes, PVA/CMC/PPy/x wt% milled MWCNTs blended polymers were formed. X-ray diffraction and scanning electron microscopy were employed to inspect the structure and morphology of the resulted blends. The lowest direct and indirect optical band gaps are (5, 4.3) eV and (4.37, 3.38) eV, respectively, achieved when the MWCNTs content in the doped blend was 0.25 wt %. By incorporating varying quantities of milled MWCNTs into the PVA/CMC/PPy blended polymer, consistent enhancements were observed in the optical dielectric constant and optical conductivity values. The blend with 0.25 wt% MWCNTs exhibited the maximum values of refractive index. The maximum electric dielectric constant and energy density values were attained as x = 0.15. The temperature impacted the dielectric constants and energy storage values. All blends fit with the CBH model. The impact of MWCNTs doping level and the temperature on the impedance spectroscopy and electric modulus of the host blend was explored. The sample with x = 0.15 has the smallest relaxation time. The impact of MWCNTs doping level on the dc conductivity, activation energy and conductivity mechanism of the host blend was explored. The doped blends with x = 0.15 is viable materials for energy storage purposes.

The IR absorption mapping of two multiblock copolymers based on poly(ethylene glycol) and poly(ε-caprolactone) segments (PEG-b-PCL) in poly(acid lactic) and poly(ε-caprolactone) blends (PLA/PCL) was performed via AFM nanoscale IR spectroscopy. These copolymers, having the same number average molar masses (Mn‾) but varying block sizes, were added into the blend in different amounts (1 and 5 wt%) using a co-rotating twin-screw extrusion. The results revealed that copolymers with smaller blocks are preferentially located near the interface when incorporated in small quantities. Increasing the copolymer content led to preferential diffusion into the PLA matrix. Compatibilization with the longer block-size copolymers also led to preferential diffusion in the PLA matrix, albeit with a tendency to form micelles. This hampers the overall mechanical properties of the blend, making the compatibilized blend more brittle than neat PLA. Compatibilization with the short block-size copolymers showed no micellization and improved the mechanical behavior of PLA/PCL.

In this study, a novel fluorine-containing carbon nanosphere was synthesized by high-temperature carbonization of waste fluororubber trimmings, and its mixing method with fluororubber was investigated. It was found that the solution mixing method resulted in the highest tensile strength (7.6 %) and modulus at 100 % strain (13.3 %) of fluororubber compared to the mechanical mixing method. Furthermore, the addition of fluorine-containing carbon nanosphere can significantly enhance fluororubber's heat resistance, inhibit its thermal degradation, and increase its ultimate service temperature (266.3 °C, 2 years). This work provides new insights into the preparation of high-performance fluororubber composites.

Electroactive polyvinylidene fluoride (PVDF) with predominantly the β-phase is now challenging the fabricating of PVDF toward energy storage applications. Here, the comprehensive effect of BaTiO3 nano-particles and mechanical stretching on the improvement of the β-phase of PVDF was investigated. In situ synchrotron wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS) measurements were performed to investigate this behavior. Consequently, the transformation rate of β-crystal for both pure PVDF (BT0) and PVDF/BaTiO3 (90/10) nanocomposites (BT1) decreases as the stretching temperature increases, implying that the high temperature is unfavorable to the formation of β-crystal phase. A synergistic enhancement of the β-phase of nano-particle additives and stretching was discovered. It was surprisingly observed that α-phase of PVDF would completely transform into β-crystal in BT1 sample at 100 °C during stretching. The mechanism of the synergistic effect of BaTiO3 nano-particles and mechanical stretching was proposed. Moreover, machine learning was implemented to predict the fraction of β-crystal phase (F(β)) of the PVDF/BaTiO3 composites under various uni-axial stretching conditions by Python 3.8. The results show that the machine learning technique can rapidly and efficiently discover the ideal value of F(β) and the optimal multivariate coupling conditions.

Polydioxanone (PPDX) has gained significant attention as a biocompatible and absorbable polymer used in various medical applications, such as sutures and tissue scaffolds. This research presents a thorough investigation into the degradation mechanisms of PPDX under low pH conditions, simulating physiological environments, e.g., esophagus and stomach. It mainly focuses on the dependence of the PPDX degradation rate on various ambient pH values (7.4 and below), which is a substantial knowledge for successful gastrointestinal treatment. The PPDX suture samples were degraded for up to 6 weeks and analyzed using size exclusion chromatography, differential scanning calorimetry, Raman spectroscopy, scanning electron microscopy, X-ray microtomography, and mechanical property measurements. The results show that the PPDX degradation is significantly accelerated at pH below 1.67. Correlations of the molecular weight, crystallinity, glass transition temperature, Young's modulus, shear modulus, tensile strength, and the 1733 cm−1 Raman peak shoulder area (RPSA1733) indicate that the degradation mechanism does not change with increasing acidity. Measurements of tensile strength, shear modulus, and RPSA1733 were found to be the most suitable parameters for characterizing the PPDX filament's macroscopic integrity. Raman spectroscopy is of particular interest in this regard due to its rapidity and practically no requirements on the sample preparation.

In this work polyurethane (PU) and phenolic foam (PF) panels were mechanically grinded and incorporated within an expanded polyurethane matrix utilized for thermal insulation, in order to reduce the use of virgin material and to promote a circular re-utilization of recycled materials. As observed by scanning electron microscopy, the formulations containing both recyclates showed a rather homogeneous cell structure, however their presence led to a strong reduction of the closed porosity. This reflected in a slight increase in the thermal conductivity, reaching maximum values of 0.030 W/m∙K in foams with 7.5%wt of PF particles. The introduction of the recyclates slightly improved the thermal stability of the PU foams and led to a general decrease in flexural and compression properties. Cone calorimetry tests demonstrated that the inclusion of PF particles reduced the peak heat release rate up to 28 % compared to neat PU foam, enhancing the fire safety of the insulating panels.

The leachate generation is an inevitable consequence of landfill disposal, and thus it is critically important to acquire effective approach to preventing contamination of the underlying soils and groundwater aquifers. Currently, there is no consensus on the best approach; the biological treatment and the membrane technology are widely tested but each has its own drawbacks. On the other hand, superabsorbent polymers are nowadays widely used in many liquid-absorbing applications but have rarely been assessed for the application of landfill leachate treatment. In this study, a comprehensive analysis of the physicochemical parameters, ionic parameters, and trace elements of the collected leachate was carried out, and four commercially available superabsorbent polymers with different chemical compositions were tested in respect of their kinetics of adsorption and desorption, both load-free and under-load, in deionized water, tap water, and leachate, respectively. The results are of significant importance in elucidating the application potential of commercially available superabsorbent polymers in landfill leachate treatment.

Collagen is one of the main constituents of mammalian extracellular matrix and is used extensively as a coating for tissue culture dishes and medical implants to promote cell growth and proliferation. By modulating the topography of the collagen coating at the nanometer to micrometer length scales, it is possible to achieve spatial control over cell growth and morphology. In this work, we are exploring the self-assembly of a thin collagen film on a glass substrate as a way to create new nanoscale surface features. By controlling the collagen concentration and adding an oscillatory flow, we are able to enrich the collagen film surface with a localized pattern of ripples oriented perpendicular to the flow direction. We propose that these ripples are the result of dewetting of the collagen film that leads to the formation of adjacent holes. We observe that individual holes form with an anisotropic rim due to the microstructure of the deposited collagen fibril network. This intrinsic anisotropy and the oscillatory flow yield new holes being formed in the film next to existing rims. As holes keep growing deeper, the rims extend along the flow direction, and the holes appear rectangular in shape, which gives the linear array of holes the apparent morphology of a ripple. Overall, we are able to create localized ripples at the surface of collagen films that would be difficult to produce via standard nanofabrication techniques.

The widespread adoption of plastics has led to substantial production and waste generation, raising environmental concerns. Chemical recycling offers a promising solution to enhance recycling rates, with microwave heating emerging as an attractive technology for polymer breakdown. This paper investigates the dielectric properties of various polymers and their temperature dependencies, providing insight into the effectiveness of microwave heating. Results indicate that while polymers may show low dielectric loss at room temperature, those with polar segments exhibit increasing loss at high temperatures, indicating that additional susceptors may not always necessary for effective microwave heating. Three key transitions are identified with respect to their significant impact on the dielectric properties of polymers at elevated temperatures: the glass transition temperature, the decomposition temperature, and the point where the dispersion/displacement peak exceeds the measurement frequency. Additionally, this paper introduces a new approach for utilising microwave heating for the selective, multistage recycling of mixed plastics.

Though existing studies had continuously improved the hydrogel printing resolution by facilitating ink solidification, it was literally challenging to exceed the size limit of the printing needle even if there was an ideal ink that could solidify instantaneously. One possible solution to this hurdle is to stretch the hydrogel ink with a high printing speed and try maintaining its deformation without strain recovery. In this study, a gelatin/alginate/hydroxyapatite(HA) ink was printed at multiple temperatures, and a much lower yielding strain occurred at −1 °C than 2–5 °C according to our rheological tests. At −1 °C, the hydrogel ink could be highly stretched to produce an ultrahigh resolution at 81 ± 13 μm while maintaining uniform and continuous. Furthermore, our biological tests found a high scaffold resolution greatly promoted cell adhesion, proliferation, osteogenic differentiation and biomineralization. We stepped further from existing studies, by coming up with a new concept of utilizing ink stress-yielding in improving printing resolution, which would broaden our understanding to the processing-structure-property relationship in hydrogel-based 3D printing.

The thin film composite (TFC) membrane possesses the highest commercial application potential among all types of forward osmosis (FO) membranes. The support layer of the membrane plays a crucial role in both bearing mechanical loads and facilitating the active layer formation. Herein, we addressed the issues of low permeability and poor mechanical strength of the conventional TFC FO membrane by selecting suitable fabrics and optimizing membrane design and preparation. Polyester (PS) woven fabric, with its high strength, low thickness, and high porosity, served as an excellent material for reinforcing the strength of the FO membrane. We employed a novel double-blade casting method to address the defect issue associated with the conventional single-blade casting method. The influencing factors and quality control strategies of the fabric-reinforced substrate were systematically investigated. Furthermore, membrane characterization techniques, including scanning electron microscopy (SEM), liquid-liquid displacement porometer, and cross-flow FO system, were used to reveal the influences of different substrates, including polysulfone (PSU), polyacrylonitrile (PAN), and polyetherimide (PEI), on the structure and performance of the fabric-reinforced TFC-FO membrane. Compared to commercial FO membranes, the TFC/PSU membrane exhibited superior FO performance, with a water flux of 24.1 LMH, and outstanding mechanical strength that was more than 10-times higher than that of free-standing membranes. This study demonstrates a new pathway for engineering robust TFC-FO membranes with low structural parameters as well as excellent scalability of the membrane fabrication method.

Biodegradable polymers are susceptible to environmental degradation, particularly when exposed to factors such as moisture, temperature, light, and microorganisms. To mitigate these aging and degradation processes, the incorporation of anti-aging substances is crucial. While the polymer industry has traditionally relied on synthetic stabilizers, there is a growing interest in naturally occurring compounds as environmentally friendly alternatives. Hemp extract, the focus of this study, is a promising natural stabilizer mixture that is readily available. Hemp-derived stabilizers represent a relatively new area of research on polymeric materials, with limited studies evaluating the impact of hemp extract on degradation processes. This study investigated the effects of weathering and thermo-oxidative aging on PLA matrices containing hemp extract using infrared spectroscopy, spectrophotometry, static mechanical testing, and surface free energy analysis. These findings demonstrate that hemp extract effectively inhibits thermo-oxidative aging but has a catalytic effect on atmospheric aging. This difference can be attributed to distinct oxidation and reduction reactions under varying conditions, resulting in different decomposition products. Further research in this area is warranted due to the increasing interest in hemp and its derivatives as functional materials and substances, as well as the growing amount of waste materials generated during their production.

In this work, the effect of temperature on interfaces with viscoelastic behavior was investigated using experimental and theoretical means. In particular, rubber/woven fabrics with thickness of 0.5 mm were subjected to self-designed shear tests at temperatures ranging from 263.15 to 383.15 K. Derived interface cyclic regeneration was observed through shear tests. Subsequently, a bi-linear cohesive zone model (CZM) was used to describe the shear test data. A novel image processing algorithm was developed to analyze the damaged morphology of the rubber/weave interface. It was found that hairniness amount decreased by 68.4 % when the temperature increased from 263.15 to 383.15 K. In addition, by combining the bi-linear CZM with the Kohlrausch–William–Watts law, Wiliams-Landel-Ferry equation and BK criterion, a 3D temperature-dependent constitutive model (KBW) was developed. The model successfully simulated the viscoelasticity of interfaces at different temperatures with margin of error less than 9 %. Thus, this study provides a strategy for elucidating the temperature dependence of interfaces with viscoelastic behavior.

Halloysite nanotubes (HNTs) and polypropylene-grafted maleic anhydride (PP-g-MA) were studied for their effects in blends of polystyrene (PS) and polyolefin elastomer (POE). The method used to prepare PS/POE blends (90/10 and 80/20 wt/wt) containing 1, 3, and 5 phr HNTs with or without PP-g-MA (a compatibilizer) was melt blending. Structural and morphological studies using X-ray diffraction analysis (XRD), scanning electron microscopy assisted energy dispersive X-ray spectroscopy (SEM-EDS), and transmission electron microscopy (TEM) confirmed a matrix-droplet morphology and the sample containing compatibilizer has better microstructure than the other formulations. The presence of both PP-g-MA and HNTs together has been discovered to improve the viscoelastic properties of the solid, as evidenced by increased storage modulus and complex viscosity. A notable change occurred in the rheological behavior of the PS/POE blends containing 5 phr of PP-g-MA and HNTs. The dependence of zero-shear viscosity on HNTs loading (0–5 phr) was approximated as a polynomial curve by fitting the experimental data with the Carreau-Yasuda model. Computational fluid dynamics (CFD) simulations were also used to study the effects of HNTs loading on changes in fluid flow patterns and shear rates. The calculated effective viscosities at a given shear rate (0.05 1/s) were in qualitative agreement with the experimental results. Moreover, we utilized various machine-learning techniques to predict the complex viscosity of PS/POE blends and their nanocomposites. The results showed that Extreme Gradient Boosting (XGBoost) outperformed other predictive models based on evaluation metrics. Four-point probe measurements found that the samples containing 5 phr HNT had the lowest conductivities due to the presence of aggregated structures. However, the homogeneous distribution of HNT led to a sudden rise in conductivity in the samples containing 5 phr of PP-g-MA. Computer modeling results of samples with uniform and non-uniform HNT distributions showed that the conductivity decreased with HNT loading and decreased considerably compared to the uniform distribution.

This study explores the structure-property relationships in colorless polyimides (CPIs) synthesized from stereoisomeric (exo- and endo-form) alicyclic dianhydrides, combined with various diamines. The structural configurations of 5,5’-(1,4-phenylene)bis[hexahydro-(3aR,4R,5R,7S,7aS)-rel-4,7-Methanoisobenzofuran-1,3-dione] (BzDA-exo) and 5,5-(1,4-phenylene)bis(hexahydro-4,7-methanoisobenzofuran-1,3-dione) (BzDA-endo) were confirmed as exo- and endo-forms, respectively, through 1H NMR and 2D NOESY NMR analyses. Wide-angle X-ray scattering (WAXS) data revealed that stereoisomeric structures influence polymer chain packing in synthesized CPIs. The investigation extended to the chemical and physical structure-dependent properties such as physical, thermal and optical properties of the PIs. Notably, structure-dependent physical and thermal properties were evident, with a particularly strong structure-property relationship manifesting in the coloration and yellow index (Y.I.) of PIs. These systematic characterizations offer profound insights into the design and optimization of chemical and physical structures in CPIs, highlighting the versatility of stereoisomeric monomers for various applications.

Accurate size measurements of nanosized polymer chains in dilute solutions is important for understanding polymer behavior, however, these measurements can be challenging to implement accurately, and are technique dependent. Here we explore the use of Fluorescence Correlation Spectroscopy (FCS) to determine the size of single polymer chains in dilute solutions (

Nitrile rubber (NBR) and polysulfides are two classes of polymers known for their resistance against swelling when in direct contact with hydrocarbon-based oils and non-polar solvents. In this study nitrile rubber (NBR) and a cyclic tetrasulfide (CTS) are combined with a goal of achieving a rubber blend that has superior properties than of each component. The role of CTS in the blend is discussed, as it presents several functions. This study represents a fundamental analysis of NBR-CTS blends, starting with polymeric phase analysis by Scanning Electron Microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy (EDX). Thermodynamic compatibility studies are deployed in this study to illustrate the materials’ compatibility. Mechanical properties with an emphasis on Payne effect were also studied for blends of NBR-CTS. The synergistic effect found between NBR and CTS can be further expanded in a practical application of rapid gas decompression test as a side-by-side comparison for NBR and NBR-CTS blend compounds. This type of polymer blend represents a potential replacement of fluoroelastomers.

Hydrogels are among the most promising materials for biological applications mainly because of their ability to absorb large volumes of water and carry as well as deliver biologically active substances. A challenge is to make them appropriately responsive to environmental triggering factors simply and reliably. In this work, we present a basic approach of modification of a commonly used, low-cost poly (acrylic acid) – PAA – hydrogel with biocompatible surfactants regarding their possible thermoresponsive activity.Viscoelasticity, hydration, and molecular diffusion processes, in relation to the morphology of the hydrogel and its mixture with nonionic surfactant Brij 58, are studied systematically using oscillatory rheometry, NMR diffusiometry and imaging, and cryoSEM. Our results contribute to the understanding of interactions between weak PAA and nonionic surfactants. The changes of the hydrogel microstructure caused by nonionic and bio-safe surfactant or thermal induction are clearly reflected in their mechanical response as well as the translational mobility of water molecules entrapped within the hydrogel's network. The structural modification induced by adding nonionic surfactant gives rise to a decrease in hydrogel elasticity.

Bioplastics like poly(lactic acid) or PLA have received significant attention over the last years, triggered by global environmental and climate concerns linked to the use of petroleum-based plastics. However, the ester bonds in PLA that are responsible for its biodegradable character are also vulnerable linkages during polymer processing. Melt processing of polymers typically involves high temperatures and shear loading. Hence, understanding degradation of PLA in the melt phase is crucial to minimize the molecular weight decrease, since it is directly linked to deterioration of mechanical, thermal and rheological properties. In this study, we performed a 24 full factorial design to investigate melt-phase degradation using a parallel plate rheometer. We investigated the effect of four parameters on the molecular weight: moisture content in the PLA, processing temperature, residence time, and shear stress. In addition, we explored whether the percentage of d-isomer significantly influences the degradation, through selecting three PLA-grades with different optical purity. The results showed that moisture content is the dominant factor in the molecular weight decrease, followed by a significant effect of processing temperature. Notably, the significant interaction between moisture content and processing temperature highlights the importance of studying interaction effects, an aspect often overlooked in current literature. Moreover, only the effect of moisture content is influenced by the percentage of d-isomer, whereas the numerical values of other significant effects are similar across the three PLA-grades. The small, yet significant effect of residence time, along with the unexpected insignificant effect of shear stress, may be explained by the use of small amplitude oscillatory deformations in a parallel plate rheometer as testing method in this study. In conclusion, the findings of this study offer polymer processors and researchers valuable insights, which can help with the selection and prediction of processing conditions that minimize degradation, ultimately saving time and raw materials during production.

Artificial materials for the potential treatment of bone defects are very trendy in such research fields. To investigate a hydrogel scaffold with better mechanical strength and osteoinductivity is always a challenge since brittle and soft properties are always the problems in traditional hydrogels. In our study, a novel gelatin/chitosan hydrogel crosslinked by a double network filled with lignin and calcium silicate is fabricated. Enhancements of mechanical strength, low swelling ratio, and improvement in osteoinductivity were achieved in this composite double network hydrogels. The results revealed that lignin was a key factor in raising the compressive strength and stability of the hydrogel because more hydrogen bonds were formed between lignin and the crosslinking network. Even after swelling equilibrium, the compressive strength remained almost unchanged. In addition, the hydrogel groups with a higher ratio of lignin also had lower cytotoxicity and improved osteoinductivity of pre-osteoblasts while the increasing concentration of calcium silicate progressively weakened these performances. Therefore, the gelatin/chitosan double network hydrogel reinforced by lignin would be a potential bone tissue-engineered artificial material.

Plastic scintillators in the form of microspheres (PSm) have emerged as a sustainable solution for the determination of alpha and beta radioactivity, reducing hazardous wastes and improved selectivity when combined with selective extractants (PSresin). To overcome challenges like solubility in organic solvents, researchers have developed crosslinked scintillating microspheres (CPSm) using divinylbenzene (DVB) as a crosslinking agent. This study focuses on optimizing CPSm synthesis and assessing their morphological characteristics, resistance and scintillation capabilities. The findings indicate that increasing the DVB proportion in the monomeric mixture leads to a reduction in microsphere size while maintaining high detection efficiency. CPSm demonstrate enhanced resilience to temperature and organic solvents compared to PSm. Despite some solute extraction by specific solvents, CPSm maintain their essential properties. In summary, CPSm provide similar scintillation performance to linear polystyrene PSm while offering increased durability, broadening their applicability and facilitating further advancements in plastic scintillator technology.

Herein, we study comparatively the crystal structure, orientation, and residual stress of polypropylene (PP) films processed by uniaxial constant width (UCW) and uniaxial free width (UFW) stretching modes, respectively. Compared with UFW PP film, UCW PP film exhibits broad lamellar thickness distribution with thinner average lamellar thickness, and accordingly lower melting temperature region. UCW PP film also has larger lateral lamellar size with high orientation along stretching direction. In addition, a preferential orientation of b-axis perpendicular to the surface exists in the UCW PP film, while a cylindrical symmetry around the stretching direction is in UFW PP film. A new single tilt X-ray diffraction method is utilized to measure the residual stress of PP films. The direction of maximum principal tensile residual stress is approximately along stretching direction for both films, while tensile residual stress occurs in UCW PP film and compressive residual stress in UFW PP film in transverse direction. Good correlation of the direction of maximum residual stress with crystal orientation is found in both PP films.

This paper presents the development of multilayered carbon nanotube (CNT)/adhesive (MLCA) films for human body signal detection sensors using a spray-coating method. The chemical composition, adhesion properties, and electrical conductivity of the films were investigated using various adhesives, with the acrylate-based adhesive (ABA) exhibiting superior performance. The surface roughness, thickness, and electrical properties of the films were characterized, and the tunability was demonstrated by adjusting the number of coating layers. Tribological tests were performed to assess the wear resistance and friction behavior of the films. The adhesion stabilities and conformabilities of the films on various substrates were investigated. The films were combined with polydimethylsiloxane (PDMS) and surfactants to create biocompatible and durable sensors. The PDMS-surfactant composite was characterized, and the MLCA film/PDMS-surfactant-based sensor exhibited excellent stability under deformation and biocompatibility. The impedance behavior, temperature, humidity, and strain-sensing capabilities of the sensors were evaluated. The capability of the sensor to detect vital signs was validated by accurately capturing the electrocardiogram (ECG) waveforms. This study provides valuable insights into the design and fabrication of CNT-based conductive films for human body signal-detection sensors, offering a promising approach for the development of flexible and wearable electronic devices.

Wearable glucose sensors have attracted significant attention for enabling non-invasive blood glucose measurement without discomfort and risk of infection. However, it is a challenge to simultaneously realize wearable adaptability, biodegradability, and excellent sensing performance. Herein, a cellulose paper-based non-invasive biosensor relying on reverse iontophoresis was designed to detect glucose in interstitial fluid (ISF), and two different enzyme immobilization strategies have been compared. The results showed inkjet-printed cellulose paper-based biosensor (IPB) performances better than the drop-coated cellulose paper-based biosensor (DPB). IPB has twice response current more than DPB in detection range (0–10 mM). In sensitivity, IPB is 1.170 μA/mM three times higher than the DPB (0.376 μA/mM). Besides, IPB's electron-transfer resistance (Rct) is 7.27 kΩ smaller than DPB (Rct = 10.51 kΩ) about 30 %. More importantly, IPB exhibited a good reproducibility (RSD, 4.82 %), which was much less than DPB (RSD, 18.35 %). Furthermore, the IPB realizes noninvasive continuous glucose monitoring over 6 h in volunteer experiments with great analytical performance comparable to commercial devices (Pearson correlation 0.732). Cellulose paper-based glucose sensors with inkjet printing provide non-invasive access to statistically significant diagnostic information, simple and cost-effective, which promotes the application of flexible, wearable, degradable bioelectrodes in continuous glucose monitoring at home, providing a concept for full integration in a compact and portable way in the future.

The present study examined the nonlinear time-dependent behavior of rheodictic polymers, a class of noncrosslinked materials that exhibit flow. Such behavior was addressed with extended Schapery's nonlinear viscoelastic model by introducing new physical quantities, i.e., the flow term Φflow and corresponding nonlinear shift parameter g2,flow. While Φflow portrays irrecoverable deformation, g2,flow depicts a nonlinear contribution to flow acceleration. This theory was accompanied by analytical and experimental methodologies for identifying all the parameters in the linear and nonlinear viscoelastic domains. Predictions of long-term time-dependent behavior (in shear) at various stress states show excellent agreement with the experimental data, i.e., within 5% error, obtained for polycarbonate at 130°C. Surprisingly, the newly introduced g2,flow indicates that flow retardation occurs with increasing stress, implying that a highly deformed entangled system hinders molecular reptation/disentanglement. Nevertheless, the proposed extension of Schapery's nonlinear viscoelastic model not only allows accurate predictions of the nonlinear time-dependent behavior of rheodictic polymers but also enables a detailed outlook on the underlying molecular mechanisms under severe environmental and loading conditions.

Carbon fiber reinforced polyetheretherketone (CF-PEEK) samples were fabricated using material extrusion. These additive manufactured green bodies are later processed to their final application as ceramic matrix composites (CMC) by the liquid silicon infiltration (LSI) route. Past studies showed that the application of material extrusion for the fabrication of CMC requires an additional stabilization-step after 3D-printing in order to prevent the remelting of CF-PEEK during the high temperature process of pyrolysis. The thermally induced crosslinking of the CF-PEEK parts ensured shape accuracy and avoided remelting during the pyrolysis afterwards but is limited by the melting temperature of PEEK (Tm ∼ 343 °C). The study revealed a correlation between the annealing conditions time and temperature and the degree of crosslinking. Based on the analytical results from differential scanning calorimetry (DSC), a kinetic model was calculated, allowing predictions in dependence of the annealing temperature and time. Rheological and shape stability investigations of thermally annealed specimens verified the analytic results. The main findings of the study highlight an increasing degree of crosslinking with increasing annealing temperature and time.

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.

The present study focuses on investigating the effect of incorporating silica aerogel on the electrical characteristics and sensing capabilities of carbon nanotube (CNT)-embedded PDMS nanocomposites. Initially, the concept of developing nanohybrid clusters composed of CNT and silica aerogel was introduced, followed by comprehensive evaluations of their formation including zeta potential, Raman spectra and FT-IR spectrum. Subsequently, the nanocomposites with varied silica aerogel contents from 0.5 to 2 % by polymer mass were assessed for their sensing capability. It is observed that porosity has exerts perceptible influence on the overall effective electrical conductivity of the sensor below the percolation thresholds, while it does not have any impact beyond this threshold. In addition, the effective medium proposition theory has been modified to analyze both the effective electrical conductivity and the piezoelectric properties of the sensors fabricated. Based on the theoretical and experimental results, the developed CNT@aerogel nanohybrid clusters displayed the potential to enhance sensing sensitivity and increase linearity during stretching condition.

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.

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.

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.

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.

The increased use of plastics and the associated environmental impact has catalyzed research on the development of bio-derived polymers. Bio-based polyesters have gained increased attention due to the abundance of their starting materials and ease of processing. Lignin is naturally occurring in biomass with rich carbon content, whose functionality and rigidity make it an ideal bio-derived candidate for bio-based polyesters. Herein, a lignin-based polyester with good thermal stability and self-repairability was synthesized from carboxylated lignin and epoxidized soybean oil. The synthesized lignin/epoxidized soybean oil (ESO) vitrimer was brittle such that its mechanical performance could not be recorded. However, when polyethylene glycol (PEG) was incorporated as a plasticizer, polymer samples exhibited acceptable ductility. From thermomechanical analysis of the synthesized polyesters, the plasticizer did not impair thermal stability of polymers, but greatly enhanced mechanical properties. Notably, all samples exhibited stability at high temperatures, and good glass transition temperatures (51.0 ± 0.9–78.0 ± 1.2 °C). The highest tensile strength (3.983 ± 0.1 MPa) and storage modulus (1463.67 ± 12.6 MPa) were recorded for the polyester containing 6 % w/w PEG. Moreover, the polymer samples exhibited self-healing capability at 180 °C. This work expands on valorization of lignin through the synthesis of bio-derived materials.

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.

A low-carbon and sustainable green rigid polyurethane foam was prepared by compounding montmorillonite (MMT) with homemade barium phytate (BAPA). The flame retardancy, thermal stability and mechanical properties of the modified RPUFs investigated using the limiting oxygen index (LOI) method, cone calorimetry (CONE) and thermogravimetry. The results showed that the BAPA/MMT2 composite containing 2 wt% MMT had the highest LOI (25.1 %), and its peak heat release rate (PHRR) and total heat release (THR) were reduced by 14.33 % and 34.68 %, respectively, compared with that of the BAPA/MMT0 material without added MMT. In addition, the smoke production rate (SPR) and total smoke release (TSR) were reduced by 20.54 % and 30.77 %, respectively. BAPA/MMT2 had good flame retardancy and smoke suppression effect. The mechanical properties of BAPA/MMT2 with 2 wt% MMT were improved. The flame retardant mechanism confirmed that BAPA and MMT synergistically improved the quality of the carbon layer. At the same time, phosphorus-containing compounds (PO·), CO2 and water vapor were produced, which diluted the combustible gas in the gas phase and inhibit the flames spread. The current results provided a new strategy for the preparation of high-performance RPUFs.

This research is devoted to developing a finite element model using Abaqus code for the computer simulation of an in-house developed and manufactured rubber bearing subjected to static vertical and cyclic horizontal loads. A high-damping rubber compound was designed. The material behavior of the rubber was assumed to be described by the hyper-viscoelastic model. Both linear (Prony series) and nonlinear (strain hardening power law) viscoelastic relationships were used in conjunction with the Ogden-Roxburgh equation to take the addition of the stress softening phenomenon or Mullins effect into consideration. The parameters of the material model were determined using MCalibration code in which an optimization technique was used, and data obtained in experiments carried out on test specimens were fitted into the selected model. The results of the simulations were compared with their corresponding experimental data carried out on the rubber bearing. The force-displacement behavior, stress and strain fields, and computed energy were presented and discussed. It is shown that the nonlinear viscoelastic model accompanied by the Mullins effect gives the best results. Moreover, the model could accurately predict the energy variations during the earthquake loading.

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 (Tg) 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 102 and 103 rad/s for 5 wt% CNT/PEI and CNT/PEEK, respectively.

Petroleum-based epoxy resin is commonly used in electrical equipment due to its outstanding performance and affordability. However, its non-melting characteristics present challenges for recycling, leading to significant resource waste and environmental pollution. To address this issue, this study prepared and synthesized a kind of vitrimer epoxy resin polymer material based on disulfide bonds with 2,2′-Diaminodiphenyl disulphide as the curing agent. The research investigated the impact of the curing agent ratio on the resin's structure and properties. The resin was mechanically recovered through hot pressing at high temperature and pressure, and its chemical degradation and recovery were achieved via the reduction reaction of the thiol and disulfide bond. The findings revealed that a curing agent to epoxy group material ratio of 0.75 improved the resin system's electrothermal properties. The electrical insulation property retention rate after hot pressing recovery reached 95 %, with a mechanical property retention rate of 85 %. The disulfide bonds can be reoxidized and crosslinked to realize the recovery and reuse of vitrimer resin degradation solution. Vitrimer epoxy resin based on disulfide bonds is a significant way to realize the environmental protection of epoxy electrical equipment.

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.