This study shows that the leaching caprolactam (CPL) in PA6 microplastics significantly enhanced methane production in anaerobic digestion of WAS.
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•PA6 microplastics motivate methane ...production in WAS anaerobic digestion.•PA6 microplastics offer marginal effect on solubilization and hydrolysis.•PA6 microplastics promote acidification and methanogenesis.•PA6 microplastics mainly affect anaerobic digestion by leaching caprolactam.
Polyamide 6 (PA6) as a typical emerging microplastic pollutant has frequently been featured in wastewater treatment plants (WWTPs), yet its associated impact on waste activated sludge (WAS) anaerobic digestion process have not been fully understood. This study identified the key role of PA6 microplastics (5–50 particles/g TS) in methane production during anaerobic digestion through biochemical methane production testing and model-based analysis, and explored the mechanism involved by monitoring the conversion of metabolic intermediates, the activity of key enzymes, and the effects of leachate caprolactam (CPL). Unlike other microplastics that normally inhibit anaerobic digestion, PA6 significantly enhanced methane production due to the effect of CPL. The presence of 10 particles PA6/g TS improved methane production by 39.5% (from 124 ± 6 to 173 ± 8 L CH4/kg VS). Model-based analysis showed that PA6 promoted methane production potential and volatile solids destruction. PA6 offered marginal effect on the solubilization and hydrolysis of WAS, the leaching of CPL improved acidification and methanogenesis due to the promotion of key enzyme activities, which is the main reason why PA6 increased methane production. These findings indicate that PA6 is less toxic to WAS anaerobic digestion than other microplastics, which prompts an understanding of the dual role of microplastics in WWTPs.
This study investigates the enhancement of flame-retardant properties in polyamide 6 (PA6) composites through the incorporation of nanofibrillated polyphenylene sulfide (PPS) and a flame retardant, ...ammonium sulfamate (AS). By strategically combining a fibrillar PPS component (15 wt%) with a minimal AS concentration (1 wt%), the composite achieves a UL 94-V0 rating and a heightened limiting oxygen index (LOI) of 33.8 %. Rheological analyses reveal the formation of an entangled fibril network, contributing to a solid-like response that effectively suppresses flame propagation and prevents dripping. Micro-combustion calorimetry (MCC) results demonstrate a synergistic effect between the PPS nanofibril network and AS, leading to a significant 17 % reduction in peak heat release rate (PHRR) in PA6-nanofibrillated PPS-AS composites, showcasing improved flame-retardant properties compared to neat PA6. Despite a trade-off in mechanical properties, this research presents a promising strategy for enhancing the flame-retardant performance of PA6 composites, offering valuable insights for addressing fire safety challenges in PA6 applications.
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•PA6 composites with 15 % nanofibrillated PPS and 1 % AS achieve UL 94-V0 and 33.8 % LOI.•Rheological analysis confirms formation of fibril network.•Char analysis shows PA6-nanofibrillated PPS-AS forms a flame-protective char layer.•MCC indicates 17 % PHRR reduction in PA6-nanofibrillated PPS-AS composites.•Despite mechanical property trade-offs, this strategy enhances fire safety of PA6.
Prepared nanofiber matrices based on polyamide 6 and polyamide 6/chitosan with numerous amine groups were tested on enzyme immobilization. Laccase from Trametes versicolor was immobilized on both ...nanofiber sheets either via glutaraldehyde and hexamethylenediamine activation, or via adsorption followed by glutaraldehyde crosslinking. Both types of the attachment were successful, however, the adsorption method provided immobilized laccase with enhanced operational stability.
Herein, the modification of polydopamine (PDA) surface improved the high temperature stability of polysulfone (PSF)/PAO40 microcapsules (D-microcapsules), which achieved the potential application of ...microcapsules in polyamide 6 (PA6). The D-microcapsules in PA6 for lubricative application has been investigated by ball-on-disc friction tests. In particular, the inclusion of 9 wt% D-microcapsules yielded the best tribological properties where the value of COF (0.088) was largely decreased as compared with that of the neat PA6(0.41). Moreover, the wear rate was found to be decreased from 4 × 10−3 mm3/Nm to 4.3 × 10−6 mm3/Nm. It has been demonstrated that better antifriction performance was associated with the lubricating film generated by PAO40. Therefore, the prepared PA6-based self-lubricating composites can be further applied in the field of self-lubricating materials.
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In the polymerization of caprolactam, the stoichiometry of carboxyl groups and amine groups in the process of melt polycondensation needs to be balanced, which greatly limits the copolymerization ...modification of polyamide 6. In this paper, by combining the characteristics of the polyester polymerization process, a simple and flexible synthetic route is proposed. A polyamide 6-based polymer can be prepared by combining caprolactam hydrolysis polymerization with transesterification. First, a carboxyl-terminated polyamide 6-based prepolymer is obtained by a caprolactam hydrolysis polymerization process using a dibasic acid as a blocking agent. Subsequently, ethylene glycol is added for esterification to form a glycol-terminated polyamide 6-based prepolymer. Finally, a transesterification reaction is carried out to prepare a polyamide 6-based polymer. In this paper, a series of polyamide 6-based polymers with different molecular weight blocks were prepared by adjusting the amount and type of dibasic acid added, and the effects of different control methods on the structural properties of the final product are analyzed. The results showed that compared with the traditional polymerization method of polyamide 6, the novel synthetic strategy developed in this paper can flexibly design prepolymers with different molecular weights and end groups to meet different application requirements. In addition, the polyamide 6-based polymer maintains excellent mechanical and hygroscopic properties. Furthermore, the molecular weight increase in the polyamide 6 polymer is no longer dependent on the metering balance of the end groups, providing a new synthetic route for the copolymerization of polyamide 6 copolymer.
Poor interfacial compatibility is the main factor restricting the improvement of mechanical properties of carbon fiber (CF) reinforced polyamide 6 (PA6) composites. In this paper, we exploited the ...feature that polydopamine (PDA) can be rapidly synthesized under hypoxic conditions by ultrasound, and the PDA coating was generated quickly and uniformly on CF to modify the interface of the composites. The results show that CF could be entirely coated by impregnating CF in PDA-Tris solution for 1 h under the ultrasound. The introduction of PDA coating significantly enhanced the wettability of the CF surface. The application of ultrasound greatly improved the coating efficiency of PDA on CF, especially on the inner layer of the CF bundle. Compared with desized CF/PA6 composites, the interlaminar shear properties of PDA-modified CF/PA6 composites are improved by 21.07%. The PDA coating binds well to both CF and PA6, so when the composites were exposed to shear force, the interlayer cracks spread along the PDA and PA6 layers instead of the CF surface, resulting in greater resistance to crack propagation. It is the primary reason for improving the composites’ interface performance. Therefore, ultrasound-assisted rapid synthesis PDA on CF can effectively improve the interface characteristics of CF/PA6 composites.
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•Coating polydopamine (PDA) on carbon fiber (CF) improved the CF's wettability and tensile strength.•Ultrasound-assisted significantly accelerated the production rate of PDA on CF.•The ultrasound’s cavitation effect greatly reduced the difference between the inner and outer coatings of fiber bundle.•The aggregation state of PDA can evolve farther toward self-assembly with the ultrasound.•After modification, the interlaminar shear strength of CF/PA6 composites was increased by 21.07%.
With the number of vehicles increases every year, the demand for flame retardant and thermal oxidative stabilized PA6 has also surged significantly. Therefore, it is crucial to improve the flame ...retardancy and thermal oxidative stability of PA6. In this regard, a novel dual-functional cuprous diethylphosphinate (CuDP) was successfully prepared through an ion exchange reaction and was used to prepare PA6 composites. The effects of CuDP on the flame retardancy and thermal oxidative stability of PA6 composites were studied in detail. In contrast with an LOI value of 22.6, pHRR of 911.3 kW m−2, and THR of 109.2 MJ m−2 for pure PA6, the addition of 15 wt% of CuDP upgrades the LOI value to 28.2 and reached UL-94 V-0 rating. Meanwhile, there was a 43.8 %, 22.3 % and 17.9 % decrease in pHRR, THR and av-CO2Y, respectively. In addition, the flame retardant mechanism of CuDP was explored in detail, where CuDP can encourage PA6 to form a protective char layer in the condense phase and quench free radicals in the gas phase. Moreover, the incorporation of CuDP helped maintain the mechanical properties of PA6 composites during accelerated thermal oxidative aging experiments. This work presents a new approach for enhancing the flame retardancy and thermal oxidative stability of PA6 composites, which paves the way for its broader application.
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•CuDP as a flame-retardant and potential antioxidant is successfully prepared.•The thermal oxidative stability of PA6 composites was improved.•The flame-retardant and thermal oxidative stabilized mechanism of the CuDP in PA6 has been revealed.
Polyamide 6 is a widely used engineering plastic; however, its thermomechanical properties are not well understood, particularly at medium and high strain rates. In this research, the ...thermomechanical properties of Polyamide 6 were extensively characterized. Differential Scanning Calorimetry was performed to investigate the glass transition temperature and crystallinity. Frequency sweep Dynamic Mechanical Analysis was carried out through the secondary- and glass-transitions, and the temperature dependent storage moduli obtained from different sweep frequencies were used to construct a master curve. Quasi-static tensile tests at two loading speeds were conducted with digital image correlation for full-field strain mapping. Compression properties were measured at strain rates between 0.001 and 6000 s−1 at room temperature, and temperatures between −60 and 200 °C at 0.01 s−1. The mechanical response is highly rate- and temperature-dependent; at large strains and elevated rates, apparent softening occurs owing to heat generation, which was quantified using an infrared camera.
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•Polyamide 6 characterised from −60 to 200 °C and 0.001–6000 s−1 in compression.•Tensile tests performed with digital image correlation.•High speed infrared camera measured temperature rise in compression.•Time-temperature equivalence gives insights into rate dependence.
In this study, our primary aim was to increase the presence of amine groups in polyamide 6 fibers. To achieve this, we employed a functionalization process that mainly depended on increasing the ...number of reactive sites via acid-catalyzed hydrolysis. The effects of several acids were rigorously examined, including hydrochloric acid (HCl), sulfuric acid (H2SO4), and formic acid (HCOOH). Following this comprehensive acid-based treatment, the method that demonstrated the most significant increase in amine groups was selected for further evaluation in dyeing experiments and full characterization. The quantification of amino groups was performed using potentiometry, evaluating the equilibrium state of acid removal from the fibers. To corroborate these results, the acid dye Levaset Blue 2R was employed, which measured the amount of dye bound to the fibers during the dyeing process. Characterization of the polyamide 6 fiber structural changes was conducted using multiple techniques, including tensile tests, Fourier transform infrared (FTIR) spectroscopy, and differential scanning calorimetry (DSC). Among the acid treatments, the 11% HCl treatment exhibited the most significant increase in amine groups, amounting to an approximately 110% increase as measured by potentiometry and an approximately 150% increase using the dyeing method. During the dyeing process, the 11% HCl-treated fibers absorbed 91% of the dye from the dye bath, indicating enhanced color intensity and K/S value, thus affirming the efficacy of the amine group increasing. Tensile testing revealed a decrease in the strength of the functionalized fiber. In the FTIR spectra, there was a notable increase in the intensity of bands associated with the fiber's crystalline regions and hydrogen bonds. DSC tests validated the FTIR results, demonstrating a 9% increase in crystallinity. Furthermore, SEM micrographs depicted surface alterations induced by the hydrolysis process. These results collectively highlight the effectiveness of hydrolysis in introducing functional groups, enhancing color intensity during dyeing with acid dyes, and reducing dye content in the bath. Additionally, the potentiometric method for quantifying amine group demonstrated practicality and accuracy, serving as a valuable contribution to the field.
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•Increase the amount of amine groups in polyamide (PA) 6 fiber via acid hydrolysis.•Comparison between the potentiometric and dyeing method to quantify amine groups.•Acid hydrolysis increases the crystallinity and color intensity of the polyamides.•The increase in the amount of amines in PA promotes better exhaustion of the dyebath.•Hydrolysis may serce as an alternative to improve dyeing properties of polyamides.
•Wear abrasion of polyamide 6 and glass fiber- polyamide 6 under hydrothermal aging.•Conditioned samples in water at different temperatures are tested at the saturation state.•Mass loss of ...conditioned specimens does not increase compared to unconditioned ones.•Conditioning causes a reduction in tensile modulus and strength.
Polymer composites are increasingly used in applications where they are subjected to abrasive wear. The bulk of prior research has focused on the performance of polymers under sliding wear conditions and in some cases resulted in a contradiction, particularly when it comes to the effect of reinforcing fibers on the wear performance. Another omission is the absence of pre-conditioning or accelerated aging which is clearly an important factor from an application standpoint. This work aims to highlight the influence of hydrothermal aging on the tribological and mechanical performance of polyamide 6 (PA6) and glass fiber-reinforced polyamide 6 (PA6-GF). The friction and abrasion wear behavior of unconditioned and conditioned PA6 and PA6-GF composites are measured against silicon carbide grinding paper on a pin-on-disk tribometer in a demineralized water medium at 60 °C. Specimens are conditioned in demineralized water at room temperature (RT) 25, 40, and 60 °C to investigate the effects of moisture and temperature. The presence of up to 25 wt.% glass fiber (GF) in PA6-based composites exhibits an increasing trend in abrasion wear mass loss and a reduction in coefficient of friction (COF). Interestingly, the mass loss of specimens conditioned to saturation does not increase compared to that of unconditioned samples. The FTIR spectroscopy is used to study the polymer degradation during hydrothermal aging.
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