Anionic Polymerization Of Ε-caprolactam Research Articles

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.

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.

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.

Simultaneous study of anionic polymerization of ε-caprolactam and crystallization of polyamide 6 in an isothermal process by in situ WAXS

We directly observed the polymerization and crystallization of polyamide 6 (PA6) via anionic polymerization with a combination of in situ wide-angle X-ray scattering (WAXS), temperature measurements, and real-time visualization. In situ WAXS discriminated polymerization and the crystallization of PA6. The peak temperatures produced by exothermic polymerization and crystallization were identified during the temperature measurements. Visual observations were consistent with the WAXS spectral changes. The WAXS results indicated that the molding process consisted of three stages: (1) polymerization induction, (2) polymerization, and (3) crystallization. We compared the polymerization rate, crystallization rate, and crystallinity at each molding temperature. Both polymerization and crystallization were slow at temperatures below 127 °C. Polymerization was fast at temperatures exceeding 166 °C, but PA6 was gelated, and the crystallization rate and crystallinity were low. In contrast, polymerization was fast at 139, 148, and 155 °C, and crystallization was faster at 148 and 155 °C than at 139 °C. Therefore, the total molding time of PA6 was shorter at 148 and 155 °C than at other temperatures. The crystallinity of PA6 decreased with increasing temperature due to increasing molecular weights. We concluded that molding temperatures between 148 and 155 °C were suitable for providing PA6 with high productivities and good properties. The polymerization and crystallization of polyamide 6 (PA6) via anionic polymerization was observed using a combination of in situ wide-angle X-ray scattering (WAXS), temperature measurement, and real-time visualization at 119–182 °C. In-situ WAXS discriminated between polymerization and the crystallization of PA6. The WAXS results indicated that polymerization was fast at 139–155 °C, and crystallization was fast at 148–155 °C. The crystallinity of PA6 decreased with increasing temperature. We concluded that molding temperatures between 148 and 155 °C were suitable for high productivities of PA6 with good properties.

Rheological and mechanical properties of a novel polyamide 6 synthesized by anionic polymerization of ε-caprolactam in a twin-screw extruder

In this study, we successfully synthesized a novel polyamide 6 (PA6, nylon 6) with a linking agent (a diepoxide) by in-situ reactive extrusion. In order to vary the physical properties of the polymer, a unique strategy was introduced. The linking agent reacted with growing PA6 chains during the anionic polymerization in the extruder. The extrudates appear to have a different structure (chain branching) without forming a network structure, causing a remarkable enhancement in the rheological properties as well as the mechanical properties of the nylon 6 produced. The molar ratio of linking agent to initiator was optimal at 0.1 and the produced polymers exhibit remarkably enhanced physical properties, though their molar masses was not appreciably varied. The melt viscosity of the produced PA6 including the optimum linking agent increased by almost 200 times that of the neat PA6 melt at low shear rate. The dynamic moduli also increased by more than 100 times that of the neat nylon 6. In addition, the mechanical properties were significantly improved with the addition of the linking agent. The elongation at break was almost doubled compared to neat PA6. The optimum compound showed a high toughness behavior.

Facile and cost-effective strategy for fabrication of polyamide 6 wrapped multi-walled carbon nanotube via anionic melt polymerization of ε-caprolactam

There is a growing demand for the development of a melt process-based nanocomposite manufacturing process capable of minimizing the incorporation of expensive carbon nanotubes (CNTs) by inducing a uniform dispersion of multi-walled CNTs (MWNTs). In this study, we proposed a nanocomposite manufacturing process that includes both physical particle mixing using high-speed rotation and anionic polymerization of ε-caprolactam (CL) to induce a uniform dispersion of MWNTs. MWNTs were uniformly dispersed by powder mixing and then wrapped with polyamide 6 polymers by in-situ polymerization of CL. The synergistic effect of the two sub-processes resulted in an enhanced dispersion of MWNTs and prevented aggregation of the MWNTs. The composites fabricated by the proposed process exhibited electrical conductivities of 4.49 × 10−5 S/m and 1.45 × 10 S/m at 1 wt% and 3 wt% MWNTs, respectively, indicating that by applying the proposed process it is possible to incorporate a smaller amount of MWNT to achieve electrical conductivities applicable for electrostatic discharge (ESD) (>1 X 10−5 S/m) and electromagnetic interference shielding effectiveness (EMI SE) (>10 S/m) applications. An ESD chip tray and EMI SE mobile phone case were fabricated using the prepared composite, and it was verified that the ESD and EMI SE performances can be realized.

The reactive compatibilized effect of SMA for immiscible APA6/PS blends via in-Situ polymerization

Styrene maleic anhydride (SMA)-g-APA6 copolymer was firstly synthesized by free radical polymerization of styrene and followed by anionic polymerization of ε-caprolactam. The polyamide 6 (APA6)/polystyrene (PS) blends were successfully prepared via anion polymerization. Among in, SMA was acted as both compatibilizer and macromolecular activator. A series of APA6/PS blends with different SMA addition amounts were synthesized to study the effect of SMA on crystallinity, morphology, water resistance, thermal stability and mechanical properties using X-ray diffraction analysis, differential scanning calorimetry, scanning electron microscopy analysis, contact angle measurement, water absorption measurement, molau test, thermogravimetric analysis, stretching and impact test. Correlational analysis proved that the obtained SMA-g-APA6 copolymer has good dispersion with PS. In addition, APA6/PS blends possess good mechanical properties, thermostability and hydrophobic property.

High crystalline, porous polyamide 6 by anionic polymerization

Polyamide 6 (PA6), also known as Nylon 6 is a widely used industrial polymer. The structural properties of PA6 play an important role in its potential commercial applications. We report that the anionic polymerization of ε-caprolactam in the presence of liquid additives such as o-Xylene, m-Xylene, p-Xylene and toluene at a critical concentration led to the formation of high crystalline, porous polyamide 6 (aPA6). Porous aPA6 samples possess hierarchical spherulitic morphology where 10 μm size spherulitic granules are interconnected by submicron size fibrillated domains. The size and shape of spherulitic domains change with the type of liquid additives used during the synthesis of porous aPA6. The presence of liquid additives influences the kinetics of the exothermal processes during polymerization, which ultimately leads to a solid-liquid phase separation prior to the formation of porous networks of spherulites. Such process also leads to thickening of lamella and formation of second order crystals that contributed to highest crystallinity in porous aPA6 ever reported. Differential scanning calorimetric along with wide-angle X-ray scattering study reveal ∼60% crystallinity in all porous aPA6, which is about 60% increase in comparison with the neat aPA6 (∼40%). Higher crystallinity in porous aPA6 also exhibited 50% reduction in moisture uptake in comparison with the neat aPA6.

A kinetic model of viscosity development for in situ ring-opening anionic polymerization of ϵ-caprolactam

The in situ polymerization of ∈-caprolactam in a carbon fiber mat is a promising technology for the production of carbon fiber-reinforced polyamide 6 (CFRPA6) parts. There is a strong demand for a kinetic model of viscosity development of polyamide 6 (PA6) in computer-aided engineering applications. In this study, a viscosity model was developed by modifying the Castro-Macosko model to include simultaneous polymerization and crystallization effects. Differential scanning calorimetry (DSC) was used to measure a heat flow curve that involved the polymerization and crystallization kinetics from 50 to 250 °C at various heating rates. The peak separation of the measured heat flow curves was used to elucidate the individual polymerization and crystallization heat flow curves. The Kamal and generalized Avrami models were used to obtain kinetic parameters by fitting the heat flow curves of polymerization and crystallization, respectively. An isothermal rheological measurement was performed to measure the increase in viscosity caused by the polymerization and crystallization at a steady shear rate at reaction temperatures from 100 to 200 °C (at 10 °C intervals). A modified Castro-Macosko model was useful to fit the viscosity data at 110 and 140 °C to determine parameters using the monomer conversion estimation from the Kamal model and the degree of crystallization from the generalized Avrami model.

Effect of single-walled carbon nanotubes with imide cycles on the synthesis and properties of polycaproamide

The anionic polymerization of e-caprolactam in the presence of single-walled carbon nanotubes with grafted acyllactam groups or polyimide macromolecules is performed. It is shown that the polymerization of e-caprolactam slows down with an increase in the filler concentration. The introduction of 0.01 wt % nanotubes with polyimide fragments into polycaproamide leads to a 25% increase in the compressive modulus. In this case, the Izod impact strength is 10 kJ/m2, that is, 150% higher than that for an unfilled polycaproamide or polycaproamide containing other types of nanotubes.

Preparation of Mg–Al layered double hydroxide/polyamide 6 nanocomposites using Mg–Al–taurate LDH as nanofiller

A novel method using Mg–Al layered double hydroxide (LDH) intercalated with taurate (2-aminoethanesulfonate acid) was applied for preparation of LDH/polyamide 6 nanocomposites via in situ intercalative polymerization. Two polymerization mechanisms were used — hydrolytic and anionic polymerization of ε-caprolactam, in which the Mg–Al LDH intercalated with taurate was dispersed. The obtained LDH/polyamide 6 nanocomposites were characterized by a combination of wide- and small-angle X-ray scattering, transmission electron microscopy, differential scanning calorimetry and thermogravimetric analysis. It was found that LDH filler was exfoliated in the polymer matrix and the LDH/polyamide 6 nanocomposites were successfully prepared by anionic polymerization of ε-caprolactam in the presence of dispersed LDH.

Carbon nanotubes bearing imide groups for anionic polymerization of ε-caprolactam

Acyllactam groups and aromatic polyimides were grafted to the surface of single walled carbon nanotubes. The modified nanotubes were characterized by X-ray photoelectron spectroscopy, scanning electron microscopy, thermogravimetric analysis, and elemental analysis. It was shown that the nanotubes with grafted acyllactam groups or polyimide macromolecules form homogeneous stable in time dispersions in a melt of e-caprolactam.

Modeling the influence of flow phenomena on the polymerization of ϵ-Caprolactam

In order to describe the influence of a flowing system on the anionic polymerization of ϵ-Caprolactam, a model comprising of classical Malkin kinetics which is embedded in the framework of computational fluid dynamics (CFD) is established and validated with results from different experimental setups, which cover different polymerization temperatures and catalytic systems. As test geometry for a flowing system a plate shaped mold with a single injection point is employed. The main focus of this study lies on fast reactions in order to assess mainly the influence of the flow on the polymerization process and to circumvent any influences of a possible simultaneously happening crystallization. Governed by the flow, local inhomogeneities regarding the polymer conversion arise during the mold filling phase that influence the further course of the reaction and are found to be significant for the entire process far beyond the filling phase.

Fast-activated anionic polymerization of ε-caprolactam in the bulk under quasi-adiabatic conditions: Comparison of different kinetic models

The kinetics of e-caprolactam fast-activated anionic polymerization in the bulk under quasi-adiabatic conditions is analyzed in terms of three semiempirical schemes. Malkin's model, the most frequently quoted approach in the literature, provides an excellent simulation of the polymerization kinetics in our experimental conditions, but the values of the derived parameters do not remain constant, as predicted by the model when different experimental conditions are chosen, and do not allow any correlation with the physical and chemical aspects of the reaction. The same limit exists for Lin's model, with a poorer agreement between simulation and experimental data. Only Kamal–Sourour's model provides almost constant values of the parameters present in the equation and can be considered a valid approach for the description of the whole course of the reaction in our experimental conditions. The relevance of the auto acceleration step is compared for two very fast activators and related to the most accredited interpretation of its occurrence. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 4474–4480

Modyfikowany silseskwioksanem (POSS) poliamid 6 wytwarzany metoda anionowej polimeryzacji e-kaprolaktamu

Modyfikowany silseskwioksanem (POSS) poliamid 6 wytwarzany metoda anionowej polimeryzacji e-kaprolaktamu

SiO2 Nanofiller impact on crystallization kinetics during adiabatic anionic polymerization of ε-caprolactam

AbstractAnion activated adiabatic polymerization of ε-caprolactam was investigated in the presence of various quantities of nano-SiO2. The parallel processes of crystallization and polymerization are separated first. Based on the crystallization kinetics and electron microscopic investigations it was shown that nano-SiO2 particles are heterogeneous nuclei for the crystallization of poly-ε-caprolactam. Further the time dependence of mean length of amorphous polymer macromolecules is determined experimentally.

Effects of carbon nanotubes and their state of dispersion on the anionic polymerization of ϵ‐caprolactam: 1. Calorimetry

AbstractThis work reports, for the first time, on the effect of carbon nanotubes (CNT) on the kinetics of the activated polymerization of lactams. Differential scanning calorimetry (DSC) was chosen to study the kinetics of the activated anionic polymerization of ε‐caprolactam in the presence of multiwalled carbon nanotubes (MWCNT). A statistical test was carried out to confirm the validity of the experimental approach. The presence of the MWCNT slowed down the polymerization rate. This inhibiting effect depended not only on the MWCNT content but also on its state of dispersion in the polymerizing system. An autocatalytic model coupled with an evolutionary algorithm showed that the MWCNT content had an effect on the autocatalysis while its state of dispersion had an effect on the apparent polymerization kinetic constant. POLYM. ENG. SCI., 2010. © 2010 Society of Plastics Engineers

All-polyamide composites prepared by resin transfer molding

Resin transfer molding (RTM) was used to manufacture all-polyamide (all-PA) composites in which PA6 matrix was in situ formed by the anionic polymerization of e-caprolactam (CL). Influence of molding temperature (T M), a critical process parameter, on the structure and properties of all-PA composites was investigated using TGA, DSC, SEM, and tensile, flexural test. Increasing T M resulted in the decrease of CL conversion and the enhancement of fiber/matrix interface bonding. By comparing the mechanical properties of all-PA composites prepared at different T M (140–200 °C), an optimal T M (180 °C) was found in this temperature range. As a whole, the complete consolidation of all-PA composites and the remarkable reinforcing effect of PA66 fibers on PA6 matrix were assured by low-void fraction, high-CL conversion and strong interface performance though in a wide T M range.

Copolymers Obtained by ε-Caprolactam and Methyl Methacrylate Polymerization in the Presence of Polyimides

New copolymers have been synthesized by anionic or radical photopolymerization of ε-caprolactam or methyl methacrylate (MMA) in the presence of dissolved polyimides bearing hexafluoroisopropylidene, fluorene or other groups. Using diimides as models it was shown that the kinetics of anionic polymerization of ε-caprolactam depends on the nature of spacer between the imide cycles. The mechanical and tribological properties of copolymers, their water absorbance and the microstructure of copolymer films were studied. It was found that upon the selection of polyimide activator it was possible to gain the desirable control over the polymer properties, namely, the gel fraction content, phase composition, compression modulus, notched Izod impact strength, friction coefficient and temperature of frictional contact. The kinetics of radical polymerization of MMA in the presence of polyimide and model diimide has been studied by differential scanning photocalorimetry and infrared spectroscopy. From the results of the reaction kinetics and the study of polymer structures by Fourier transform infrared spectroscopy, nuclear magnetic resonance, size-exclusion chromatography and thermogravimetric analysis it has been established that radical photopolymerization of MMA in the presence of polyimide leads to the formation of copolymers owing to chain transfer reactions and/or chain termination by the relevant condensation polymer. It has been established that the imide cycles play a significant role in the formation of both copolymers with ε-caprolactam and MMA, respectively.

Homoionic inorganic montmorillonites as fillers for polyamide 6 nanocomposites

The homoionic montmorillonites Ca-MMT, Mg-MMT, Ba-MMT and Ca-MMT intercalated with ε-caprolactam – Ca-MMT·CL were prepared from commercial Na-MMT and characterized by WAXS and TGA. They were used as fillers for nanocomposites of polyamide 6 synthesized either by anionic polymerization of ε-caprolactam (monomer casting) or by melt blending. WAXS analysis showed that the intercalation of MMT by the polyamide was complete for all nanocomposites, with only a very small fraction of exfoliated platelets being detected by TEM. The decrease in the number of layers in the MMT tactoids suggests that tactoid splitting was lower for the blended nanocomposites than for the polymerized ones. Both the rate of polymerization and the polyamide yield in the nanocomposites were comparable to those of an unfilled system. The MMT fillers, the density of which was more than twice that of the ε-caprolactam in which they were suspended, sedimented during the first stage of polymerization. TGA was used to determine the degree of sedimentation at various levels of the resulting mold. In line with the coordination of polyamide chains to the surface cations of MMT particles, the sedimentation level increased in the following sequence: Mg-MMT < Ba-MMT < Ca-MMT·CL << Na-MMT. Ca-MMT was found to be the only non-sedimenting filler suitable for use in the synthesis of polyamide nanocomposites by either monomer casting or the use of reactive injection molding (RIM) technologies.