Poly(acrylamide-acrylic acid) (P(AM-co-AA)) was synthesized via the copolymerization of acrylamide and acrylic acid and well characterized by Fourier transform infrared spectroscopy. Afterward, the obtained P(AM-co-AA) was blended with flame retardants to prepare transparent flame-retardant hydrogel applied in the fireproof glass. The influence of poly(acrylamide-acrylic acid) on fire resistance and anti-aging properties of the transparent flame-retardant hydrogels were studied by assorted analysis methods. The optical transparency analysis shows that the light transmittance of the transparent flame-retardant hydrogel gradually decreases with the decreasing mass ratio of acrylamide to acrylic acid in P(AM-co-AA). Heat insulation testing shows that the heat insulation performance of fireproof glass applying the transparent flame-retardant hydrogel firstly decreases and then increases with decreasing mass ratio of acrylamide to acrylic acid in P(AM-co-AA). When the mass ratio of acrylamide to acrylic acid is 1:2, the obtained P(AM-co-AA) endows the resulting flame-retardant hydrogel applied in fireproof glass with the lowest light transmittance of 81.3% and lowest backside temperature of 131.4 °C at 60 min among the samples, which is attributed to the formation of a more dense and expanded char to prevent the heat transfer during combustion, as supported by the digital photos of char residues. The results of TG analysis indicate that P(AM-co-AA) imparts high thermal stability to the resulting hydrogels due to the hydrogen bonds between carboxyl and amide groups. The accelerated aging test shows that the transparent flame-retardant hydrogel containing P(AM-co-AA) is less affected by aging conditions. Especially, when the mass ratio of acrylamide to acrylic acid in P(AM-co-AA) is 4:1, the resulting transparent flame-retardant hydrogel shows a light transmittance of 82.9% and backside temperature of 173.1 °C at 60 min after 7 aging cycles, exhibiting the best comprehensive properties among the samples.
Polymer blending is a simple and cost-effective method to improve the gas separation performance of polyimide membranes, thereby potentially overcoming the inherent permeability/selectivity trade-off effect. However, its application still faces challenges, since only a few polymers are miscible with polyimides, and the mechanical property of the membranes usually reduces significantly after polymer blending. Herein, we prepare membranes by blending polyimide containing bulky isopropyl substituents with a small amount of polar polymers such as polyacrylonitrile (PAN). The resultant blend membranes using PAN as additive not only possess excellent gas separation performance but also maintain good mechanical property. For example, when 0.8 wt% PAN is added, the corresponding blend membrane displays a high CO 2 permeability of 632.2 Barrer and a high CO 2 /CH 4 selectivity of 23.4 under humidified condition, close to the 2008 Robeson upper bound, which is attributed to the formation of micro-phase separation structure within the blend membranes. Moreover, the tensile strength of the blend membranes using 0.8 wt% PAN as additive is only 12 % lower than that of the pure polyimide membrane. In addition, the blend membranes using PAN as additive show remarkable stability against physical aging and outstanding long-term operation stability, suggesting their great prospect for natural gas purification and biogas upgrading.
Rubber materials are frequently degraded by environmental factors such as light, heat and oxygen during service. Conventional protective approaches, however, often involve adding antioxidants during processing, which not only causes significant environmental pollution but also limits the applicability of rubber products in the biomedical field. Therefore, developing robust aging mitigation strategies constitutes a critical imperative to ensure material longevity. This study proposes a feasible and effective strategy: inducing network rearrangement in rubber through pre-stretching to achieve a more stable crosslinked structure, thereby enhancing its thermo-oxidative stability. During vulcanization, polysulfide and disulfide bonds are formed in the crosslinking network of rubber. Pre-stretching preferentially broke weaker bonds, inducing the conversion of polysulfide bonds to disulfide bonds during the stretching process. This strain-induced network rearrangement enhanced the rigidity and stability of rubber. At elevated temperatures, this mechanism became more pronounced. Pre-stretching triggered rapid conversion of polysulfide to disulfide bonds during the initial stages of thermo-oxidative aging. Given the higher bond energy and stability of disulfide bonds under thermal-oxidative conditions, the aging resistance of rubber is significantly improved. Both atomic force microscopy tests and mechanical tests demonstrated that stretching induced dynamic transformation of sulfur bonds in the crosslinking network, leading to significant changes in spatial heterogeneity under thermo-oxidative conditions. As a result, the thermo-oxidative resistance of natural rubber was enhanced, with the retention of tensile strength increasing from 58.6 % to 81.1 % after 24 h of thermo-oxidative aging. This study not only provided important guidance for the general design of thermo-oxidation-resistant elastomers but also advanced the understanding of rubber network evolution mechanisms under thermo-mechanical coupling conditions.
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