Polymerization Of E-caprolactam Research Articles

Anionic Ring-Opening Polymerization of ε-Caprolactam above the Crystallization Temperature of Polyamide 6: A Study on the Effects of the Activator and Catalyst

Anionic Ring-Opening Polymerization of ε-Caprolactam above the Crystallization Temperature of Polyamide 6: A Study on the Effects of the Activator and Catalyst

The degradation during recycling of polyamide 6 produced by anionic ring-opening polymerization of ε-caprolactam

As the plastics industry continues to grow, the amount of plastic waste is also increasing. The European Union is controlling plastic waste through various regulations, focusing primarily on recyclability. A good alternative to traditional thermoset composites is thermoplastic polyamide 6 composites produced by Thermoplastic Resin Transfer Molding (T-RTM). Polyamide 6 has high strength and is produced by in-situ anionic ring-opening polymerization in T-RTM. Products made with this technology can replace traditional thermoset composites in many areas, which greatly increases recyclability. In this paper, the recyclability of the high molecular weight polyamide 6 matrix material of T-RTM composites is investigated. Products were mechanically recycled and then processed by injection molding. Thermal, mechanical and rheological properties of the samples were compared with the properties of the original product, as well as a general injection molding–grade PA6. Results show that the parts prepared with this innovative technology can be mechanically recycled and reprocessed by injection molding without a processing aid. After reprocessing, a significant reduction in properties is observed due to degradation, but the properties of the resulting product are in good agreement with those of a conventional commercially available injection molding grade PA6 material.

Synthesis and properties of oil-filled polycaproamide

The effect of antifriction additives on the process of ε-caprolactam anionic polymerization and on the properties of the synthesized samples has been studied. Motor oil, vacuum oil, household lubricating oil and polymethyl-siloxane fluid were used as antifriction additives. It has been shown that the introduction of antifriction additives at the stage of synthesis of oil-filled polycaproamide reduces the rate of anionic polymerization of ε-caprolactam. The influence of oils on the complex of physico-mechanical, thermal and operational properties has also been studied. It was found that the use of oils at the synthesis stage helps to reduce the coefficient of friction of the samples compared with the control sample. The best effect is observed when using 5 7 wt.% of petroleum oils (a decrease of 50 66% compared to the control sample). The water absorption of oil-filled polycaproamide samples containing petroleum oils is also reduced (by 37% compared to the control sample). At the same time, there is a deterioration in the physical and mechanical properties and an increase in oil and petrol absorption.

Biodegradation of polyamide 6 by Lysinibacillus sp, Alcaligene faecalis and Enterococcus faecalis

Polyamide 6 (PA6, polycaprolactam, Nylon 6) is a thermoplastic polymer widely used in construction, automotive, packaging, etc. It is a semi-crystalline polymer known for its good mechanical properties, and chemical, and thermal stability, with a low price, compared to the other polyamides. PA6 can be synthesized by anionic polymerization of ε-caprolactam, initiated by sodium hydride, and activated by N-acetylcaprolactam. This poorly biodegradable material has quickly proven to be a source of considerable pollution both visually and in terms of ecosystem preservation, particularly due to its increasing annual global production. This issue raises the need to develop environmentally friendly protocols for the degradation of this waste. One of the methods that can prove to be effective is the degradation by microorganisms. The objective of our research is to study the degradation of PA6 by the bacteria Lysinibacillus sp. (LB), Alcaligene faecalis (AF), and Enterococcus faecalis (EF) isolated from the landfill. The three bacteria, isolated and previously identified, were able to show proliferation in minimal media using PA6 as the sole source of carbon and nitrogen. The weight loss of the PA6 pellets was evaluated at 21% for L. bacillus, 27% for A. faecalis, and 13% for E. faecalis after 48 days of incubation. The biodegradation of PA6 was also confirmed by FTIR and SEM coupled to the elemental detector scanning EDS, which revealed the structural, morphological, and elemental changes that PA6 underwent.

Photochromic Polyamide 6 Based on Spiropyran Synthesized via Hydrolyzed Ring-Opening Polymerization.

We report photochromic polyamide 6 (PA6) which was synthesized by hydrolyzed ring-opening polymerization of ε-caprolactam with spiropyran (SP) embedded in the polymer chains. It indicated that crystallinity degree of the resulting copolymers was decreased since only PA6 segments can crystallize with increasing content of SP modifier. Meanwhile, toughness of photochromic PA6 was decreased. The photochromic property analysis indicated that the sample with more flexibility and more content of SP was more sensitive to UV light at the beginning of irradiation than other samples and its color after being irradiated for 1 min tended to reddish. Investigation revealed that the UV-vis absorbance of SP-PA6-3 had negligible decay after 10 cycles, which indicated SP-modified PA6 possessed excellent photoresponse reversibility and fatigue resistance.

Interfacial enhancements between a three-dimensionally printed Honeycomb-Truss core and woven carbon fiber/polyamide-6 facesheets in sandwich-structured composites

A novel sandwich-structured composite comprising a three-dimensionally (3D) printed core and a woven carbon fiber/polyamide-6 facesheet was fabricated and characterized. By using selective laser sintering, which is a 3D printing technology, a structurally reinforced honeycomb-truss hybrid core was produced, which had superior compressive stiffness in various directions compared with conventional honeycomb cores. The interface between the core and the facesheet was enhanced by laser power control during the sintering as well as plasma surface treatment. The sandwich composite was produced by the reactive thermoplastic resin transfer molding (T-RTM) technique using anionic polymerization of ε-caprolactam, which has an ultra-low viscosity in the molten state. This in-situ polymerization not only enabled manufacturing process simplification by combining fabrication and bonding processes of the facesheet, but also provided excellent resin impregnation into the fiber fabrics and core surface. Therefore, the 3D printing technology, interfacial strengthening techniques, and T-RTM process induced synergistic effects on mechanical properties of the sandwich composite by forming structural reinforcement and strong mechanical and chemical interactions. The edgewise compressive properties of the hybrid core were significantly better than those of a normal honeycomb core. In addition, the interlaminar fracture toughness, impact energy absorption, and penetration limit of the sandwich composite consisting of the structurally and interfacially strengthened hybrid core increased by 76, 77, and 125%, respectively, compared to those of a nonreinforced sandwich composite.

Fabrication of highly thermal conductive PA6/hBN composites via in-situ polymerization process

In this research, thermally conductive polyamide 6/hexagonal boron nitride (PA6/hBN) nanocomposites waaere fabricated via an in-situ ring-opening polymerization of e-caprolactam. The hBN filler was exfoliated through a co-solvent exfoliation process and then chemically modified to form an e-caprolactam-grafted BN (cBN). After that, PA6 was introduced onto the cBN surface using a grafting from method. The thermal conductivities of the PA6/cBN composites significantly increased up to 180 % when the BN content was 16.5 wt%. The tensile strength and Young’s modulus of the PA6/cBN composites with 16.5 wt% hBN increased by 30 % and 92 %, respectively, compared to the pristine PA6. The grafted PA6 on BN composites exhibited strong polymer-filler interfacial interactions. Overall, this study provides a facile method of fabricating high-performance PA6 with improved thermal and mechanical properties and higher thermal conductivity.

Characterization of Polyamide 6/Multilayer Graphene Nanoplatelet Composite Textile Filaments Obtained Via In Situ Polymerization and Melt Spinning.

Studies of the production of fiber-forming polyamide 6 (PA6)/graphene composite material and melt-spun textile fibers are scarce, but research to date reveals that achieving the high dispersion state of graphene is the main challenge to nanocomposite production. Considering the significant progress made in the industrial mass production of graphene nanoplatelets (GnPs), this study explored the feasibility of production of PA6/GnPs composite fibers using the commercially available few-layer GnPs. To this aim, the GnPs were pre-dispersed in molten ε-caprolactam at concentrations equal to 1 and 2 wt %, and incorporated into the PA6 matrix by the in situ water-catalyzed ring-opening polymerization of ε-caprolactam, which was followed by melt spinning. The results showed that the incorporated GnPs did not markedly influence the melting temperature of PA6 but affected the crystallization temperature, fiber bulk structure, crystallinity, and mechanical properties. Furthermore, GnPs increased the PA6 complex viscosity, which resulted in the need to adjust the parameters of melt spinning to enable continuous filament production. Although the incorporation of GnPs did not provide a reinforcing effect of PA6 fibers and reduced fiber tensile properties, the thermal stability of the PA6 fiber increased. The increased melt viscosity and graphene anti-dripping properties postponed melt dripping in the vertical flame spread test, which consequently prolonged burning within the samples.

Effects of carbon nanofibers on carbon fiber reinforced thermoplastics made with in situ polymerizable polyamide 6

The effects of carbon nanofibers (CNFs) on the mechanical properties of carbon fiber reinforced thermoplastics (CFRTPs) made with in situ polymerizable polyamide 6 (PA6), which are derived through the polymerization of ε-caprolactam, were discussed. Although it is difficult to disperse CNFs in solvents, including molten polymers, ε-caprolactam was successfully obtained with good CNF dispersibility. CFRTPs with good dispersion of CNFs were molded while maintaining moldability below the CNF weight fraction of 0.5 wt%. Furthermore, it was revealed that CNFs increased the molecular weight of PA6, and the elastic modulus of the matrix polymer increased. As a result, the stress transfer ability increased, and the bending properties of the CFRTPs, particularly the bending strength, also increased.

Post-Polymerization Heat Effect in the Production of Polyamide 6 by Bulk Quasiliving Anionic Ring-Opening Polymerization of ε-Caprolactam with Industrial Components: A Green Processing Technique

Bulk, solventless anionic ring-opening polymerization (AROP) of ε-caprolactam (CPL) with high yields, without side products and with short reaction times, initiated by caprolactamate-carbamoylcaprolactam initiating systems belong to green polymerization processes, leading to poly(ε-caprolactam) (Polyamide 6, PA6, Nylon 6). However, the effect of post-polymerization heat (i.e., slow, technically feasible cooling) on the fundamental characteristics of the resulting polymers such as yield and molecular weight distributions (MWDs) have not been revealed thus far. Significant post-polymerization effect was found by us in terms of both monomer conversions and MWDs by carrying out CPL polymerization with industrial components under conditions mimicking thermoplastic reaction transfer molding (T-RTM). Remarkably, higher monomer conversions and molecular weights (MWs) were obtained for Polyamide 6 samples prepared without quenching than that for the quenched polymers at the same reaction times. Independent of quenching or non-quenching, Mn of the resulting polymers as a function of conversion fell in the theoretical line of quasiliving AROP of CPL. At high monomer conversions, significant increase of the MW and broadening of the MWDs occurred, indicating pronounced chain–chain coupling. These findings have fundamental importance for designing processing conditions for in situ polymerization processes of ε-caprolactam by various techniques such as T-RTM, reaction injection molding (RIM), and other processing methods of Polyamide 6.

Effect of Temperature on the Mechanical Properties and Polymerization Kinetics of Polyamide-6 Composites.

This work reports the preparation of carbon fiber reinforced thermoplastic composites via the in situ anionic ring opening polymerization of ε-caprolactam. Vacuum assisted resin transfer molding was used to fabricate polyamide-6/carbon fiber composites at different molding temperatures. As a result, the higher polymerization of ε-caprolactam was observed with the condition at 140 °C for satisfactory impregnation. Regarding molding temperature, the physical properties of polyamide-6/carbon fiber were observed that the bending and impact strengths at 140 °C were higher than those to at other molding temperatures. The polymerization kinetics of polyamide-6 was analyzed using differential scanning calorimetry by experimentally acquiring kinetic parameters according to model fitting approaches. Polymerization and crystallization, which occur simultaneously throughout the whole process, were separated using Gaussian and Maxwell–Boltzmann distributions to study polymerization kinetics. The result of the developed model was in good agreement with the experimental data for the presented first order autocatalytic reaction model.

Enhanced Tensile Properties of Multi-Walled Carbon Nanotubes Filled Polyamide 6 Composites Based on Interface Modification and Reactive Extrusion.

To induce uniform dispersion and excellent interfacial properties, we adopted a strategy of combining both polyamide 6 (PA6) grafting for multi-walled carbon nanotubes (MWCNTs) and reactive extrusion of PA6 matrix, based on anionic ring-opening polymerization of ε-caprolactam (CL). Compared to –COOH and –NCO treatments of MWCNTs, enhanced MWCNT dispersion and tensile properties of the composites were achieved using the applied strategy, and the tensile strength and modulus of the PA6-grafted MWCNT-filled PA6 composites were 5.3% and 20.5% higher than those of the purified MWCNT-filled PA6 composites, respectively. In addition, they were almost similar to the theoretical ones calculated by the modified Mori–Tanaka method (MTM) assuming a perfect interface, indicating that the tensile properties of MWCNT-filled PA6 composites can be optimized by PA6 grafting and reactive extrusion based on the anionic ring-opening polymerization of CL due to uniform MWCNT dispersion and excellent interfacial property.

Development of polyamide 6 based single polymer composites reinforced by novel stitched plain fabrics

In the present study, novel woven reinforced single polymer composites (WSPC) based on polyamide 6 (PA6) is developed via a combination of powder-coating of PA6 textile reinforcements with PA6 empty microcapsules (EMC) and compression molding techniques. Activated anionic ring-opening polymerization of ε-caprolactam was employed to synthesize the PA6-EMC which was transformed during the compression molding into WSPC matrix without damaging the PA6 textile reinforcements. A promising novel class of PA6 woven fabrics, stitched plain, which are patented by Jakob Müller company AG® were used as reinforcements. The tensile properties of stitched plain reinforced WSPC were studied and compared to ones reinforced by the plain-woven structure and the PA6 neat matrix reference materials. The parametric studies are performed on the stress field along the elements of reinforcements, using image processing to correlate the influence of reinforcement architectures with the failure mechanism of WSPC.

Effect of Different Flame-Retardant Bridged DOPO Derivatives on Properties of in Situ Produced Fiber-Forming Polyamide 6.

The production of sustainable and effective flame retardant (FR) polyamide 6 (PA6) fibrous materials requires the establishment of a novel approach for the production of polyamide 6/FR nanodispersed systems. This research work explores the influence of three different flame-retardant bridged 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) derivatives on the comprehensive properties of in situ produced PA6/FR systems. To this end, in situ water-catalyzed ring-opening polymerization of ε-caprolactam was conducted in the presence of three different bridged DOPO derivatives, e.g., one P−N bond phosphonamidate derivative and two P−C bond phosphinate derivatives. The selected bridged DOPO derivatives mainly act in the gas phase at the temperatures that relatively match the PA6 pyrolysis specifics. The effects of the FRs on the dispersion state, morphological, molecular, structural, melt-rheological, and thermal properties of the in situ synthesized PA6 were evaluated. The specific advantage of this approach is one-step production of PA6 with uniformly distributed nanodispersed FR, which was obtained in the case of all three applied FRs. However, the applied FRs differently interacted with monomer and polymer during the polymerization, which was reflected in the length of PA6 chains, crystalline structure, and melt-rheological properties. The applied FRs provided a comparable effect on the thermal stability of PA6 and stabilization of the PA6/FR systems above 450 °C in the oxygen-assisted pyrolysis. However, only with the specifically designed FR molecule were the comprehensive properties of the fiber-forming PA6 satisfied for the continuous conduction of the melt-spinning process.

Influence of the Structure of Polyimide Macromolecules on the Reinforcement of Polycaproamide

Aromatic polyimides used in the anionic polymerization of e-caprolactam as polyfunctional activators are considered effective reinforcing agents of polycaproamide formed in their presence. It is shown that the nature of polyimide, the rigidity of its macromolecules, makes the dominant contribution to the strength characteristics of copolymers. It is found that molecular composites containing up to 5 wt % of the rigid-chain polyimide have a unique specific impact strength that is several times higher than the corresponding values for both polycaproamide and its copolymers with flexible-chain polyimides.

Enhanced electrical conductivity of polymer nanocomposite based on edge-selectively functionalized graphene nanoplatelets

Achieving high filler dispersion in a polymer composite is very important for effectively and efficiently imparting several advantages of functional fillers to the composite. To this end, we have suggested a synthesis of polyamide 6 via in situ ring-opening polymerization of ε-caprolactam and edge-selectively functionalized graphene nanoplatelets without defects on its basal plane synthesized by a ball-mill process with dry ice. As a consequence, the final graphene nanocomposite possesses highly dispersed filler and has enhanced electrical conductivity due to its undistorted sp2 hybridization after functionalization. This approach is a promising way of incorporating filler into polymer composites, effectively implementing highly electrical conducting graphene without its aggregation and damage to its inherent properties after functionalization.

Anionic Polymerization of ε-Caprolactam under the Influence of Water: 2. Kinetic Model

The reaction kinetics of anionic polymerization for the production of anionic polyamide 6 (aPA6) are widely understood. It is also known that this reaction is very sensitive to external influences such as water. This paper analyzes and quantifies the influence of water on the reaction of ε-caprolactam to anionic polyamide 6. A kinetic model is developed in which the reactive molecules of the activator and catalyst are defined as variables and the concentrations of activator and catalyst as well as water content are considered. A model for the calculation of the reaction kinetics is established and validated with experimental data. The developed model can be used to predict the influence and compensation of water by addition of surplus activator and catalyst during the polymerization of ε-caprolactam.

Compensation of Water Influence on Anionic Polymerization of ε-Caprolactam: 1. Chemistry and Experiments

The activated anionic ring opening polymerization of ε-caprolactam to polyamide 6 is highly sensitive to external influences such as water. Based on an initial theory, preliminary reaction kinetic tests are carried out with the aim of compensating the influence of the water by increasing the activator and catalyst concentration. Different formulations of activator and catalyst were studied to understand the influence of water on the concentration of activator and catalyst. It was found that the compensation of added water with activator and catalyst restores the original reaction time. The test plates produced are examined with regard to their mechanical characteristics and the polymer properties. The results of the mechanical characterization show no significant impairment after compensation of the added water. The physical properties of the matrix show degradation with repeated compensation. However, the residual ε-caprolactam content remains below the critical value of 1% for three of the four investigated formulations.

Development and characterization of single polymer composites prepared by compression molding of polyamide 6 empty microcapsules and novel woven textile structures

In the present study, novel polyamide 6 based woven single polymer composites (WSPC) were developed by powder-coating of woven textile structures with polyamide 6 empty microcapsules (EMC) and subsequent compression molding. To synthesize EMC, activated anionic ring-opening polymerization of ε-caprolactam by solution/precipitation was applied. Stitched plain fabrics that are promising novel class of woven fabrics and two conventional woven patterns (plain and satin-5 harness) were used as textile reinforcements. The thermal and mechanical properties of all composites were characterized and related to the reinforcements´ morphology, fiber volume fraction and ply orientation. For better understanding of the bonding state at the matrix-fiber interface, stereo-optical microscopy and SEM image analysis by image processing were performed. The data obtained confirmed the existence of a transcrystalline layer (TCL) in the interface region. The mechanical behavior of the composites was related also to the PA6 polymorph content of the samples and their crystallinity indexes determined by wide-angle X-ray diffraction experiments.

Preparation of Poly(phenylene sulfide)/Nylon 6 Grafted Graphene Oxide Nanocomposites with Enhanced Mechanical and Thermal Properties

Poly(phenylene sulfide) (PPS) is an attractive polymer in engineering plastics because of its high mechanical strength and thermal stability. Herein, poly(phenylene sulfide)/nylon 6 grafted graphene oxide (PPS/NGO) nanocomposites were prepared by micro-compounding, where NGO is prepared via ring-opening polymerization of e-caprolactam on the graphene oxide (GO), which has carboxylic acid groups that can act as an initiator. Since nylon 6 is known to be able to blend with commercial PPS, nylon 6 moiety in NGO can increase mechanical properties of PPS, especially by forming PPS/NGO nanocomposites with improved toughness. Moreover, graphene nanosheets can provide improved mechanical strength and thermal stability because of their mechanically reinforcing and thermal barrier effects. For example, if a PPS/NGO nanocomposite with 0.03 wt% of NGO was prepared, the tensile strength and elongation at break values increased by 32% and 30%, respectively, compared to neat PPS. Also, the thermal decomposition temperature for 5% weight loss increased from 481 to 488 °C, indicating the improved thermal stability. These improved properties can be attributed to the well-dispersed NGO in the PPS matrix, as confirmed by the morphological studies using SEM and EDS mapping.