Polymer Degradation and Stability最新文献

As the most widely used sealing component in hydrogen systems, rubber seals are affected by hydrogen over long-term service. Hydrogen molecules can dissolve into rubber materials and diffuse through the material. Studies have shown that adding fillers can enhance rubber's performance, improve its compatibility with hydrogen, and reduce the damage caused by hydrogen diffusion. Therefore, this study integrates experimental hydrogen permeation research with finite element modeling for nitrile butadiene rubber (NBR). The aim is to investigate the influence of filler properties on the microstructure, hydrogen permeation behavior, and hydrogen concentration distribution within NBR. Ultimately, the study elucidates the mechanisms governing hydrogen distribution evolution and permeation in NBR under hydrogen environments. The results indicate that the crosslink density of NBR filled with carbon black (NBR-CB) and silica (NBR-SC) is directly proportional to the filler content. NBR with higher filler content exhibits a lower hydrogen permeation coefficient and superior hydrogen barrier properties. In contrast to silica fillers, carbon black fillers demonstrate strong adsorption and a more pronounced barrier effect against hydrogen molecules, thereby enhancing the hydrogen barrier efficiency. The increase in carbon black's hydrogen solubility (from 2.2 × 10^-4 to 16.9 × 10^-4 cc(STP)·cm^-3(polymer)·cmHg^-1) effectively reduces the hydrogen permeation coefficient. In contrast, the rise in carbon black's hydrogen diffusion coefficient (from 0.1 × 10^-6 to 4.1 × 10^-6 cm^2·s^-1) exacerbates the overall hydrogen permeation coefficient of NBR-CB, thereby intensifying the hydrogen permeation process.

Copper-cyclodextrin metal-organic framework (Cu-CD-MOF) prepared via the vapour diffusion method was applied as an environmentally friendly catalyst for the pyrolysis process of nitrocellulose (NC). The structural and thermal properties of Cu-CD-MOF were comprehensively and meticulously characterized. Differential scanning calorimetry results disclosed the good compatibility of Cu-CD-MOF toward NC. The NC/Cu-CD-MOF mixture exhibited a decrease of 21.6 KJ/mol in energy barrier, which was resulted from the catalytic characteristics. The TG-FTIR measurement confirmed the maximum pyrolysis rate temperatures of NC/Cu-CD-MOF mixture was decreased by 0.9 °C than NC. Furthermore, Cu-CD-MOF was able to accelerate the rupture of the –O–NO₂ bond and the secondary self-catalytic reaction. The toxic and harmful gas concentrations were also reduced. This work provided a now path to design green catalysts for NC-based materials.

Polypropylene (PP) has the advantages of excellent mechanical properties and easy molding, but its shortcomings such as high flammability and poor ultraviolet (UV) resistance cannot be ignored. In this paper, APP was used as the core, 1, 10-diamino-decane (DA) was used as a "bridge" to connect TA to the surface of APP, obtaining TAPP through oxidation self-polymerization. The addition of TAPP greatly improved the flame retardancy and UV resistance of PP matrix. The limiting oxygen index of the PP/22.5 %TAPP sample was increased to 31.0 %, and it was able to pass the UL-94 V-0 rating without droplet produced. Compared with PP samples, the peak heat release rate and peak smoke release rate of PP/22.5 %TAPP sample were reduced by 65.0 % and 44.7 %, respectively. In addition, the tensile strength and impact strength of PP/22.5 %TAPP samples decreased by only 2.7 % and 15.0 % after 60 h UV irradiation. The results showed that the addition of TAPP effectively improved the flame retardancy and UV aging resistance of PP. This study provides a feasible method for the preparation of anti-UV aging and flame-retardant PP composites.

The phosphorus-containing flame retardant that can enter the interior of cotton fiber and has self-crosslinking ability was designed and synthesized. The flame retardant contains two components, 2-(1-(dimethoxy phosphoryl)-2,5, 8-Triazectridecyl) phosphonate starch (PTPS) and 4-(hydroxymethyl)-10-((3-((5-(hydroxymethyl)-10-((3-((tris(hydroxymethyl)phosphonio)methyl)ureido)methyl)-2,6,8,12,14,18-hexaaza-4,10,16-Triphosphanonadecane (BPTP). The structure of PTPS and BPTP were detected by NMR and FTIR, and the results showed that the synthesis of PTPS and BPTP was successful. During the treatment, cellulose was first endowed with -NH groups. Then PTPS molecule and BPTP molecule were grafted onto cellulose through the reaction of P-CH₂-OH groups and -NH groups. After 50 laundering cycles (NFPA2112-2012 standard), the limiting oxygen indexes (LOIs) of the fabrics treated with 35 wt% CFN-PB and 30 wt% CFN-PB were 28.80 % and 27.30 %, respectively, and passed the vertical flame test (VFT). Compared with the raw cotton, the peak heat release rate (PHRR), the total heat rate (THR) and the flame growth rate (FGR) of the CNF-PB treatment fabric were reduced by 62.90%, 29.43% and 62.91% respectively. These indicate that the flame retardant PB could be firmly fixed on the fibers and show good flame retardancy durability. In the VFT, and cone calorimetry test, the CFN-PB treated fabric showed the condensed phase flame retardant mechanism.

Textile wastes rapidly grow into a challenge when a significant portion of them are processed by landfilling or incineration, leading to hazardous solid and volatile pollutants. This work investigated the utilization of wasted cellulose fiber by recycling it with calcium alginate fiber into a fireproof composite filler as a circular economy strategy, followed by the modification with MXene dispersion to further enhance its fire resistance and offer it the electromagnetic interference shielding ability. A comprehensive investigation elucidated the flame retardant mechanism of the composite felt via studying its combustion behavior, the microstructural morphology of residue char, and the gasous compounds produced. The results indicated that this composite felt generated a large number of nonflammable gas species and fibrous residue char, serving as a natural barrier to impede the fuel supply and suppress heat diffusion, thereby endowing the composite felt with an outstanding fire retardant performance and reduced carbon footprint. Compared to other textile waste recycling processes, the opening-carding-needling punch technique employed in this study was more energy-efficient and environmentally friendly. The recycling of waste cellulose fiber into functional fireproof composites not only extended the practical applications of waste resources but also mitigated the negative environmental impact of textile disposal.

As one of the most commonly used thermosetting resins, the flammability of epoxy resins (EPs) has become a key factor limiting the expansion of their application range. Herein, a novel phosphorous-containing epoxy monomer (EDPPO) was synthesized using diallyl amine and diphenyl phosphoryl chloride as the starting materials. Subsequently, EDPPO was thermally cured with two diamine hardeners, 4, 4′-diaminodiphenyl sulfone (DDS) and 4,4′-dithiodianiline (DTDA). Additionally, commercial diglycidyl ether of bisphenol A (DGEBA)-type epoxy pre-polymers were cured with DDS and DTDA as comparative samples. The cured EDPPO-based thermosets showed excellent flame-retardant properties coupled with smoke suppression. Specifically, the limiting oxygen index (LOI) for the EDPPO/DDS (P content 6.4 wt.%) reached 32.0 %, and the UL-94 vertical burning test reached a V-0 rating. In addition, the PHRR, THR, and TSP values of EDPPO/DDS were 61.6 %, 49.1 %, and 58.5 % lower than those of DGEBA/DDS, respectively. The flame retardant mechanism analysis indicated that the excellent flame retardancy for cured EDPPO-based thermosets was attributed to the combined modes of action in condensed (promoting the charring capacity) and gaseous phases (quenching the active radicals). More importantly, EDPPO/DDS and EDPPO/DTDA exhibited lower dielectric constant and dielectric loss than DGEBA/DDS and DGEBA/DTDA. This work provided novel phosphorous-containing epoxy thermosets with improved anti-flammability, smoke suppression, and dielectric properties.

The excellent oxidation and ablation resistance of silicone rubber thermal protection system (TPS) materials have made them extensively utilized in large-area thermal protection applications, such as ramjet engines and spacecraft reentry capsules, where air is present in the service environment. The ablation resistance is significantly influenced by the pyrolysis reactions, which serves as the foundation for subsequent ceramic transformation and the development of anti-erosion structures. The majority of previous research has been conducted in inert gas environments. To investigate the pyrolysis mechanism of silicone rubber TPS materials in realistic service environments, thermal analysis tests were performed using a range of analytical instruments including a thermal analyzer, mass spectrometer, infrared spectrometer, and X-ray photoelectron spectrometer from room temperature up to 1300 K in air atmosphere and compared with the results in argon atmosphere. The results demonstrate that silicone rubber TPS materials undergo both pyrolysis and oxidation reactions in air atmosphere. The primary pyrolysis of the matrix is attributed to cyclization reactions and side-chain cross-linking reactions. In comparison to argon atmosphere, the oxidation reaction produces a greater amount of organic gases, thereby diminishing the extent of cross-linking reaction and the thermal stability of the pyrolysis residue. The prolonged exposure to elevated temperatures allows for an extended duration of oxidation reactions, consequently diminishing the long-term thermal stability of TPS materials. The increase in mass of TPS materials at temperatures exceeding 1100 K can be attributed, in part, to the formation of new organic groups through oxidation reactions. The observed morphology of the residue, along with the weight gain from oxidation and SiO₂ formation, promotes ceramic transformation of the materials at elevated temperatures.

Epoxy resins are used in various applications where environmental factors can interact and degrade the material. Thermo-oxidation is one of the degradation processes that can lead to both mechanical and chemical changes. This work aims to present a technique for characterizing thermo-oxidative degradation based on color analysis. The UV–vis spectroscopy reveals the direct link between the chemical modification and the color variation. The color difference $\Delta E_{ab}^{*}$ between a virgin and an aged sample (in CIELAB color space) provides an excellent indicator of oxidation degree. Calibration correlations have been developed based on reference samples aged under known conditions of temperature and pressure, translating color differences into an oxidation equivalent duration, represented as an equivalent time $t^{*}$ or to directly estimate mechanical properties. The $t^{*}$ parameter is the time that the sample should be exposed to the reference conditions to undergo the same oxidation level (equivalent to the same color difference change and then, degradation). Nanoindentation measurements were performed to validate the color measurement method. Some limitations were identified, including the poor correlation under non-equivalent time-temperature-pressure conditions, poor relevance for assessing high oxidation levels, and the impact of light scattering in areas with strong color gradients. The spatial resolution of color measurement is ten times higher than nanoindentation. Furthermore, the color measurement is non-destructive, can be conducted in situ, and is suitable for monitoring the aging of industrial components.

This study details a novel approach to enhance the dimensional stability of foamed polyvinyl chloride (PVC) materials through the introduction of a reversible cross-linking network. This is achieved via the carboxylation of acrylate polymers (ACR) utilizing the hydrolysis reaction of maleic anhydride (MAH) during the extrusion of PVC foam sheets. Subsequently, an ionic cross-linking network is formed using calcium-zinc (Ca-Zn) stabilizers. This paper elucidates the process of cell formation and the mechanisms underpinning the ACR/MAH ion network formation. Cell morphology of the foamed PVC was characterized using SEM, and the effects of ionic cross-linking on the plasticizing time, dimensional stability, and mechanical properties were analyzed through cell diameter distribution measurements and rheometry. The longitudinal and transverse dimensional shrinkage of PVC-F/MAH1 was reduced by 28.0 % and 28.9 %, respectively. The construction of the ACR/MAH ion cross-linking network not only augments the mechanical properties but also substantially enhances the dimensional stability of the material. This approach underscores the viability of ion cross-linking networks in advancing the performance parameters of PVC foams, suggesting a promising avenue for future research and development in polymer processing technology, and potentially expanding their application spectrum.

The intrinsic flammability of polyamide 6 (PA6) has significantly impeded its broad application regardless of its balanced physical properties. Aluminum diethylphosphinate (ADP), as a P-containing fire retardant, has been demonstrated to be effective in reducing flammability of PA6 because of its dual-phase modes of action by creating an intact protective char layer and inhibiting the burning process. However, the efficiency of ADP needs to be further improved for creating cost-effective fire-retardant PA6, in addition to its relatively high cost. To boost its efficiency, we, here, report a P/N/B-containing aggregate (MBA) as an effective synergist via green self-assembly of melamine (MA), boric acid (BA) and amino trimethylene phosphonic acid (ATMP) in an aqueous medium. The results show that the inclusion of 5 wt% MBA and 10 wt% ADP leads to a significantly reduced peak heat release rate (PHRR) by 52.5% compared to neat PA6, in addition to a desired UL-94 V-0 rating. A synergistic effect of 55.4 % is observed between MBA and ADP in terms of the PHRR value. This work provides a facile green strategy for developing eco-friendly multiple elements-containing fire retardants, which can be used as fire retardants alone or high-efficiency synergists for other fire retardants.