Comparing the adsorption of methyl orange and malachite green on similar yet distinct polyamide microplastics: Uncovering hydrogen bond interactions.
作者: Kangkang Wang ; Yuli Kou ; Kefu Wang ; Siqi Liang ; Changyan Guo ; Wei Wang ; Yi Lu ; Jide Wang
Microplastics (MPs) and dye pollutants are widespread in aquatic environments. Here, the adsorption characteristics of anionic dye methyl orange (MO) and cationic dye malachite green (MG) on polyamide 6 (PA6) and polyamide 66 (PA66) MPs were investigated, including kinetics, isotherm equilibrium and thermodynamics. The co-adsorption of MO and MG under different pH was also evaluated. The results reveal that the adsorption process of MO and MG is suitably expounded by a pseudo-second-order kinetic model. The process can be characterized by two stages: internal diffusion and external diffusion. The isothermal adsorption equilibrium of MO and MG can be effectively described using the Langmuir model, signifying monolayer adsorption. Furthermore, the thermodynamic results indicated that the adsorption was spontaneous with exothermic and endothermic properties, respectively. The results of binary systems reveal that MO dominates the adsorption at low pH (2-5), while MG dominates at high pH (8-10). Strong competitive adsorption was observed between MO and MG in neutral conditions (pH 6-8). The desorption experiments confirm that PA6 and PA66 could serve as potential carriers of MO and MG. The interaction between dyes and polyamide MPs is primarily mediated through hydrogen bonds and electrostatic attraction. The results reveal that PA6 formed more hydrogen bonds with the dyes, resulting in higher adsorption capacity than that of PA66. This difference can be attributed to the disparities in the synthesis process and polymerization method. Our study uncovered the adsorption mechanism of dye pollutants on PA6 and PA66, and provided a more comprehensive theoretical basis for the risk assessment concerning different types of polyamide MPs in aquatic environments.
Comparison of the Properties of a Random Copolymer and a Molten Blend PA6/PA6.9.
This study compares the thermal and mechanical properties of two different materials, obtained via two diverse synthetic pathways. The first one is a mixed blend of PA6/PA6.9, while the second is a random copolymer (PA6.9-ran-PA6, obtained via copolymerization of its monomers, i.e., caprolactam, hexamethylenediamine and azelaic acid). Several tests are carried out according to the aforementioned pathways, varying the relative ratio between the two polymeric building blocks. The role of the synthetized plastic is to be coupled to polyamide material, such as PA6, to confer its better properties. The synthetized random copolymer, besides displaying ease of processability with respect to conventional methods, exhibits interesting features. It has a low melting point (135 °C, PA6.9-ran-PA6 50:50) and therefore it might be used as a hot-melt adhesive in composite material. Owing to its low crystallinity content, the material displays a rubber-like behavior and may be employed to confer elastomeric properties to PA6 matrix, in place of non-amidic material (for example elastomeric polyurethanes). This leads to a further advantage in terms of chemical recyclability of the end-of-life material, since the additive increases the percentage of PA6 in waste material and, consequently, the yield of caprolactam recovery.
2022-09-29·International journal of biological macromolecules
Characterization of the keratin/polyamide 6 composite fiber's structure and performance prepared by the optimized spinning process based on the rheological analysis.
作者: Bo Li ; Yanli Sun ; Jinbo Yao ; Yanqin Shen ; Hailiang Wu ; Jiaying Li ; Meihui Yang
The complex chemical structure of polypeptide and the imperfection of processing technology cause the mechanical properties of regenerated keratin to be hard and brittle. This defect seriously affects the application prospects of keratin materials. To solve the above problems, α-lipoic acid modified keratin (KER) was blended with Polyamide 6 (PA6) and prepared into composite fibers via the wet-spinning method in this work. The spinnability and spinning conditions of the KER/PA6 blend solution were analyzed by rheological theory. The results illustrated that keratin solution will easily form a gel state under certain temperatures and concentrations, which was not conducive to the preparation of regenerated fiber. When the temperature was 45 °C and the mass fraction was 10 %, the viscosity and rheology of the solution were appropriate. The rheological properties of the blend solution showed that too much keratin would make the solution easy to gel, which was not conducive to the preparation of regenerated fibers and may affect the fiber properties. On this basis, the prepared composite fibers were characterized to explore the macromolecular aggregation state of keratin and PA6 in fibers. FT-IR and XRD results proved that there was no chemical reaction between keratin and PA6 in the composite fibers, which belonged to physical blending. At the same time, the two polymers had good compatibility and can be blended at the molecular level. SEM, DSC, and tensile strength test results indicated that when the proportion of keratin was too high, the structure and properties of the composite fibers will have obvious defects, which was consistent with the rheological analysis. Therefore, the blend ratio of keratin/PA6 was determined to be 3:7. Under this condition, the fibers exhibited a homogeneous structure and good thermal properties, especially its mechanical properties were close to wool fibers. The KER/PA6 composite fibers show important research value and can also provide technical reference for the development of regenerated biomass materials.