Polymer最新文献

To address the issues of poor thermal stability and thermal conductivity in polyurethane (PU) shell microencapsulated phase change materials (MEPCMs), this study prepared PU/SiO₂-MEPCMs using an interfacial polymerization method combined with electrostatic self-assembly technology. First, the PU shell was synthesized via an interfacial polymerization reaction between isophorone diisocyanate (IPDI) and triethanolamine (TEA). Subsequently, the hydrolyzed product of tetraethyl orthosilicate (TEOS), monosilicic acid (Si (OH)₄), was adsorbed onto the PU shell surface using electrostatic self-assembly technology and reacted with the –NCO groups to form an SiO₂ shell. The effects of the PU/SiO₂ composite shell on the surface morphology, chemical structure, compactness, thermal stability, phase transition performance, thermal conductivity, and thermal cycling stability of MEPCMs were investigated. The results showed that the formation of the PU/SiO₂ composite shell significantly improved the thermal stability, compactness, thermal conductivity, and cyclic stability of MEPCMs. After continuous treatment at 150°C for 120 min, the leakage rate of the core material decreased from 12.13 % to 3.74 %, and the heat-resistant temperature (T_95 %) increased by 30°C. Even after 1000 thermal cycles, MEPCMs still exhibited excellent heat storage performance. Additionally, even under high temperature conditions of 257°C (where pure butyl stearate completely decomposes), the PU/SiO₂-MEPCMs still maintained a stable core-shell structure. The introduction of the SiO₂ shell greatly enhanced the thermal conductivity of MEPCMs, aligning the phase change temperature more closely with that of the core material and effectively reducing the supercooling phenomenon. Furthermore, the stable energy storage system formed by MEPCMs on the finished fabric surface can endow it with excellent temperature regulation functionality.

Reprocessable, repairable, and recyclable (“3R”) vitrimers have experienced rapid development over the past decade and demonstrate significant potential for diverse applications. The creep performance of vitrimers is crucial for their dimensional stability under load-bearing conditions at relatively low temperatures and serves as a key metric for evaluating their reprocessability at high temperatures. However, the impact of dynamic covalent polymer networks (DCPNs) on vitrimer mechanics, particularly creep properties, remains debated. Systematic experimental studies on the creep of vitrimers across a wide temperature range are lacking. We use the classic epoxy vitrimer as a model system to investigate the impact of DCPNs on vitrimer mechanics, especially focusing on the creep and recovery behavior across a wide temperature range, spanning from room temperature to the glass transition temperature (T_g) and further to the topology freezing transition temperature (T_v). We systematically examined the effects of temperature, stress, and catalysts on vitrimer creep, revealing the influence of DCPNs. Our findings demonstrate significant thermo-chemo-mechanical coupling effects in the creep mechanics of vitrimers, a facet not comprehensively acknowledged in existing studies. In addition, at temperatures below T_g, vitrimers exhibit superior creep resistance compared to pure epoxy resin due to metal coordination, ensuring excellent dimensional stability under load-bearing conditions. Conversely, at high temperatures, active bond exchange reactions in vitrimers accelerate creep and result in greater residual deformation, highlighting exceptional reprocessability. This study provides new insights into the materials and mechanics of vitrimers.

It has been a challenge to improve the performance of epoxy insulation in the whole life cycle by achieving the reduction of residual stress during manufacturing, the healing of damages during application, and the recycling after decommissioning. In this paper, a novel recyclable epoxy resin (SEP) with releasable residual stress and synergistically enhanced dielectric properties and healing ability was successfully developed by introducing dynamic thiocarbamate bonds (DTBs). A reduction in residual stresses by 45 % was detected after SEP was annealed at 30 °C below the glassy transition temperature (T_g) for 8 h, during which the mechanical properties remained unchanged. Synergistically improved dielectric properties and damage-healing ability were also observed in SEP. A high healing efficiency of 94.4 % for electrical breakdown damage was found in SEP, meanwhile its dielectric properties were superior to commercial epoxy resin. Additionally, SEP featured good recyclability, including reprocessability and degradability. All those excellent properties were ascribed to the dissociation and recombination of DTBs triggered by thermal stimulation. This work provides an effective solution to a series of issues throughout the full lifecycle of epoxy materials.

The rough contact plays an important role in the adhesion of carbon fiber/polymer matrix interface and interface modeling techniques are integral to quantify the effects of roughness factors on material properties. Taking the popular CF/PEEK materials as the object, an atomic method is proposed to construct CF/PEEK rough interfaces in this paper, which adopts a sinusoidal form to change the roughness regularly. Based on molecular dynamics (MD) simulations, CF/PEEK tensile separation experiment is processed and the response of the CF/PEEK interfaces with different roughness under mechanical loading are investigated. Based on the recorded CF/PEEK atomic force-displacement behavior, innovating roughness parameters, a traction separation law for the interface region is proposed. This study found the contact area between the two phases, which can be greatly improved through rough structures, determines the interfacial adhesion strength. In addition, this study observes interesting phenomena through the capturing atomic states, such as the polymer chains at the boundary between the two phases are greatly stretched.

While numerous studies have explored the potential of shape memory materials in medical applications, the current research output is not enough for significant productivity in industrial products. In this research, a type of shape memory orthopedic plaster was fabricated by using epoxy/polyurethane interpenetrating networks modified with epoxidized soybean oil (ESO) and then compared with some commercial plasters. Polymer networks that were produced could be tailored to have glass transition temperatures (Tgs) within the range of 70–90 °C by changing the percentage composition of polyurethane and soybean oil. Shape recovery and fixity ratios in all samples were above 95 and 97 %. DMA results showed that IPNs with variable amount of soybean oil had lower glass transition temperature (Tg) and cross-link densities compared to IPNs without soybean oil. Based on the tensile test results, most samples exhibited an elastic modulus in the range of 280–400MPa, a level deemed somewhat acceptable when compared to commercial samples. Light microscope images had shown that the increase of polyurethane led to the phase separation of polymers, which was improved by the addition of soybean oil.

Electro-blow spinning represents a novel and emerging hybridised technology for producing high-quality, large-scale nanofibers. The applied pressure, accompanied by an electric field, functions as a drafting force to generate ultrafine, homogeneous nanofibers. Herein, we utilised a sustainable solvent to produce polylactic acid nanofibers via the electro-blow spinning technique. A parametric study investigating the effect of polymer concentration, pressure, and voltage on the characteristics of the produced nanofibers was thoroughly conducted. The produced nanofibers were tested using scanning electron microscopy, Fourier-transform infrared spectroscopy, differential scanning calorimetry, and tensile test. The findings revealed that air pressure plays a crucial role in the electro-blow spinning process, while introducing electric field enhances the spinnability and stretchability of nanofibers. Increasing the applied pressure and voltage led to finer fibres with improved crystallinity and mechanical strength. However, excessive pressure or voltage can cause jet instability, resulting in defects such as fused or broken fibres. Our study suggests that the most recommended parameters for uniform and high-quality nanofibers are 10 wt%, 5 bar, and 20 kV. Moreover, the polylactic acid nanofibers were further evaluated for air filtration performance using a customised filtration setup to determine their suitability as a facemask material. The results indicated a notably high filtration efficiency, reaching up to 98 %, with a corresponding pressure drop between 137 and 163 Pa. These preliminary findings strongly suggest that produced nanofibers are highly promising candidates for medical textile applications, particularly in the development of facemasks.

Anionic polyamide 6 (aPA6), synthesized via the ring-opening polymerization of ε-caprolactam, has emerged as a promising matrix for high-performance thermoplastic composites, offering advantages over conventional thermoplastics and thermosets. However, optimizing the microstructure and mechanical properties of aPA6 requires a comprehensive understanding of how processing conditions influence polymerization kinetics and resulting material characteristics. This work systematically investigates the interplay between two critical processing parameters, i.e., the mold temperature and catalysts concentration, on the microstructural and thermomechanical properties of aPA6, via a combined experimental and statistical approach. Increasing the mold temperature from 145 °C to 175 °C and the catalysts concentration led to a reduction in crystallinity, due to the promotion of polymerization over crystallization. Higher temperatures and concentrations also slightly anticipated thermal degradation onset from 388 °C to 327 °C. The elastic modulus decreased from 3.4 GPa to 2.7 GPa as temperature increased, primarily governed by the diminishing crystallinity. Similarly, the ultimate tensile strength declined from 80 MPa to 68 MPa with rising temperature. Interestingly, the strain at break exhibited a complex dependence, peaking at 48 % for an intermediate temperature of 165 °C and lower catalysts concentration, suggesting an optimal balance of crystallinity, branching, and high molecular weight. Statistical empirical models captured these relationships, enabling prediction and tailoring of aPA6 properties by tuning processing conditions. These insights pave the way for optimized manufacturing of high-performance aPA6 composites via techniques like thermoplastic resin transfer molding and expand potential applications to thermally sensitive reinforcements like natural fibers.

Epoxidized natural rubber (ENR) is a modified natural rubber (NR) prepared by the epoxidation of NR. Dispersion of silica in the ENR nanocomposite is crucial for the performance, but there is not a definite relationship among ENR and silane coupling agent bis(γ-triethoxysilylpropyl) tetrasulfide (TESPT) and silica. In this work, ENR/silica with different amounts of TESPT nanocomposites (ENR/silica-xT) were prepared, and the structure and critical properties of ENR/silica-xT for tire tread applications were investigated and compared with NR/silica-TESPT nanocomposite. There is a competitive relationship between TESPT and epoxy groups on the rubber molecular chain in improving silica dispersion. Epoxy groups produce stronger filler-rubber interaction while TESPT provides more chemical crosslinking density. Accordingly, as the amount of TESPT increases, the tear strength, tensile strength, wet-skid resistance, abrasion resistance, as well as rolling resistance performance of ENR/silica-xT improves. The ENR/silica-6T demonstrates significant improvements compared to NR/silica-6T, with a 207 % enhancement in wet-skid resistance, a 29 % increase in abrasion resistance, and a 29 % reduction in rolling resistance. This work will be of significance in guiding the preparation of green tire tread.

Phenyl-containing polysiloxanes have better thermal stability, low-temperature flexibility, and room-temperature damping performance than polydimethylsiloxanes. Poly [dimethylsiloxane-co-methyl (phenyl)siloxane] and poly (dimethylsiloxane-co-diphenylsiloxane) were synthesized through a bulk copolymerization of octamethylcyclotetrasiloxane and methylphenylcyclosiloxane mixture or octaphenylcyclotetrasiloxane, and the structure and properties of the copolysiloxanes were comparatively studied. The phenyl content in poly [dimethylsiloxane-co-methyl (phenyl)siloxane] can be as high as 50 mol%. With the increment of the phenyl content, the thermal stability of the copolysiloxanes is dramatically improved as evaluated by thermal gravimetric analysis. At a given phenyl content, poly [dimethylsiloxane-co-methyl (phenyl)siloxane] has higher thermal stability than poly (dimethylsiloxane-co-diphenylsiloxane). The former is more difficult to crystalline at low temperatures and has lower room temperature viscosity than the latter as confirmed by differential scanning calorimetry and rotational rheometer. The copolysiloxanes is mixed with hydrogen-containing polysiloxane and silica, and vulcanized at elevated temperature to get copolysiloxane composites with good damping properties, oil resistance, and low-temperature resistance. This study not only enriches the fundamental academic research on functional polysiloxanes, but also provides useful technical references for practical applications of phenyl silicone rubber.

Polyurethane has emerged as an excellent potential candidate for shape memory materials due to its microphase-separated structure with alternately connected hard and soft segments. In this study, SMPU of different molecular weights were prepared with poly(caprolactone) diol (PCL), hexamethylene diisocyanate (HDI), 1, 6-hexanediamine (HMDA), trimethylolpropane tris (3-mercaptopropionate) (TMPMP), and Dilauroyl peroxide (LPO). LPO as a chemical cross-linking agent can induce secondary cross-linking, which leads to the formation of a strong and stable secondary cross-linking network, and this network can be transformed into a supplier of internal stresses, so that the network exhibits excellent bidirectional shape memory effects. The effects of thermal and shape memory properties were investigated by TGA, DSC and DMA tests, the phase transition temperature of the SMPU was studied and the shape recovery process was recorded. The results show that the SMPU synthesized by PCL_2k has good shape memory performance, with a reversible strain of up to 16.1 %, and the average shape fixation and recovery rates of 92.83 % and 99.98 %, respectively, with good shape memory performance, which is expected to show a wide range of application prospects and value of use in the fields of smart fabrics, biomedicine, sensing drive, aerospace and so on.