Anionic Polyamide Research Articles

Decoding the interplay of mold temperature and catalysts concentration on the crystallinity and mechanical properties of anionic polyamide 6: a combined experimental and statistical approach

Anionic polyamide 6 (aPA6), synthesized via the ring-opening polymerization of ε-caprolactam, has emerged as a promising matrix for high-performance thermoplastic composites, offering advantages over conventional thermoplastics and thermosets. However, optimizing the microstructure and mechanical properties of aPA6 requires a comprehensive understanding of how processing conditions influence polymerization kinetics and resulting material characteristics. This work systematically investigates the interplay between two critical processing parameters, i.e., the mold temperature and catalysts concentration, on the microstructural and thermomechanical properties of aPA6, via a combined experimental and statistical approach. Increasing the mold temperature from 145 °C to 175 °C and the catalysts concentration led to a reduction in crystallinity, due to the promotion of polymerization over crystallization. Higher temperatures and concentrations also slightly anticipated thermal degradation onset from 388 °C to 327 °C. The elastic modulus decreased from 3.4 GPa to 2.7 GPa as temperature increased, primarily governed by the diminishing crystallinity. Similarly, the ultimate tensile strength declined from 80 MPa to 68 MPa with rising temperature. Interestingly, the strain at break exhibited a complex dependence, peaking at 48 % for an intermediate temperature of 165 °C and lower catalysts concentration, suggesting an optimal balance of crystallinity, branching, and high molecular weight. Statistical empirical models captured these relationships, enabling prediction and tailoring of aPA6 properties by tuning processing conditions. These insights pave the way for optimized manufacturing of high-performance aPA6 composites via techniques like thermoplastic resin transfer molding and expand potential applications to thermally sensitive reinforcements like natural fibers.

Influence of silane interfacial chemistry on the curing process of anionic Polyamide 6 in glass reinforced composites

The manufacturing of composites based on reactive thermoplastic polyamide 6 (PA6), reinforced with glass particles or fibers for structural applications, is quite sensitive to the state of the interface. Surface hydroxyls present at the glass surface can completely inhibit both the PA6 polymerization and crystallization processes. Care must then be exerted when tuning the interfacial chemistry in this system. This work demonstrates how an adequate choice of silane coupling agent, combined with a precise surface grafting methodology and tight control of hydroxyl groups density on glass particulates, yields kinetics and degrees of polymerization and crystallization comparable to the pure PA6 resin. Various silanes were grafted onto the microparticles and their surfaces were characterized by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, thermogravimetric analysis, confocal laser scanning microscopy and contact angle measurements. The activator was also grafted onto the glass surface to initiate polymerization directly from the surface. The results showed that all treated glass particles surfaces allowed obtaining a high degree of conversion but with varying polymerization and crystallization kinetics. The results provide fundamental information on the role of the surface chemistry of glass reinforcements on the polymerization and crystallization of PA6, which are essential for the proper control of composite manufacturing.

Water-soluble anionic polychloramide biocides based on maleic anhydride copolymers

Our goal was to develop film-forming polymers to extend the antimicrobial lifetimes of cleaned and disinfected surfaces. Antimicrobial polymers were prepared by first reacting poly(ethylene-alt-maleic anhydride) with isopropylamine, partially consuming the anhydride groups, followed by hydrolysis to give water-soluble, highly anionic polyamide PC3. Chlorination with NaOCl gave PC3Cl with oxidative chlorine contents up to 9 wt%. Dried, 5 µm thick, PC3Cl films, gave log 4 reductions in the concentration of Escherichia coli or Staphylococcus aureus exposed to films. A unique feature of the maleic anhydride copolymer platform was the ability to form covalent grafts to surfaces via anhydride reactions. PC3 solution was impregnated into cellulosic filter paper, heated to form ester linkages with cellulose, followed by chlorination with sodium dichloroisocyanurate dihydrate giving grafted PC3Cl. The treated paper (0.3 wt% PC3Cl) gave a log 4 reduction of E. coli concentration in 30 min

Improvement of the process of the direct synthesis of polyamide to obtain a high properties material

Under the NANOTEK+ project, POLIFLUOR and TECNALIA propose to develop and scale industrially a polyamide obtained by direct synthesis. These properties, mainly thermal ones, have to be improved by the addition of nanoparticles. To this end, it has been worked in the  dispersión of the nanoparticles and the process of polymerization, and in the industrial production process and its evaluation from the point of view of the health security. In-situ polymerization process of anionic polyamide 6 offers important advantages for the incorporation of nanoparticles because the low viscosity of the monomer make easier the dispersion of the nanoscale reinforcemenet. Several parameters of the process  have to be taken into account during the up scaling: Selection of the suitable nanoparticles and their percentage, taking into account the dispersion ability in the matrix and their chemical compatibility. Percentage of catalytic system, which can be affected by the nature of the nanoparticles. Melting, feeding and polymerization temperatures, which should not degrade the nanoparticle. Mixing rates, since the dispersion of the nanoparticles by mechanical stirring can produce air inside the obtaindes polymer. The distribution of the nanomaterial in the polymer matrix and the adhesion degree between both, have studied under formulated material, using techniques such as SEM/EDS. The correct distribution of the nanoparticles in the polyamide 6 has been observed thoughout the industrialization.

Moisture Adsorption and Desorption Behavior of Raw Materials for the T-RTM Process

The use of fiber reinforced plastics (FRPs) has significant potential to reduce the weight of components. As regards the sustainability of these components, thermoplastic matrices offer more potential for recycling than thermoset ones. A possible manufacturing process for the production of thermoplastic FRPs is thermoplastic resin transfer molding (T-RTM). In this very moisture-sensitive process, ε-caprolactam in addition to an activator and catalyst polymerizes anionically to polyamide 6 (aPA6). The anionic polymerization of aPA6 is slowed down or even completely blocked by the presence of water. This study analyses the sorption behavior of the matrix, fiber, binder and core materials for the production of anionic polyamide 6 composites, which are processed in the thermoplastic RTM process. Water vapor sorption measurements are used to determine the adsorption and desorption behavior of the materials. The maximum moisture loading of the materials provides information about the water adsorption capacity of the material. This knowledge is crucial for correct handling of the materials to achieve a fast process and good properties of the final product.

Optical biosensor for catechol determination based on laccase‐immobilized anionic polyamide 6 microparticles

AbstractThis work presents the preparation, optimization, and testing of an enzyme‐based optical biosensor for catechol determination. The sensing area is attached to a glass support and contains: anionic polyamide 6 (PA6) porous microparticles supporting laccase from Trametes Versicolor, embedded in a Pebax® MH1657 polymer binder that contains the optical indicator dye 3‐methyl‐2‐benzothiazolinone hydrazone (MBTH), responsible for the optical transduction. The catechol analyte, after its enzymatic oxidation, forms o‐benzoquinone that can be detected by oxidative coupling with MBTH giving rise to a colored product. The latter can be quantified measuring the UV/VIS absorbance at 500 nm. The PA6 microparticles performed as useful laccase carriers reaching high immobilization yields of up to 99.8% and preserving the enzyme catalytic activity. This permitted the preparation of a new biosensor presenting a detection limit of 11 μM and responding linearly to up to 118 μM of catechol. Biosensor applicability was tested in spiked natural water samples from river and spring. The recovery rates observed were in the range of 97–108% that proves the good accuracy of the proposed biosensor.

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.

Manufacture and Performance of Textile-ramie Fiber Reinforced Anionic Polyamide 6 Composites

A vacuum assistant resin infusion moulding (VARIM) was adopted to prepare a new-style and environmental friendly thermoplastic composite consisting of anionic polyamide-6 (APA-6) and textile-ramie fiber. However, the intensive polymerization-inhibition and fiber-discoloration phenomena were found in the reactive processing. In order to overcome these problems, two methods were used to suppress the reaction between the ramie fiber and APA-6, which are the surface modification of ramie fiber and a new initiator with a low activity. Finally, the inhibition and discoloration phenomena were suppressed significantly, which overcame the major challenge during the preparation of ramie fiber reinforced APA-6 composites by reactive processing. The composites showed a good polymerization during VARIM process. The tensile strength and flexural modulus of the obtained composites were increased by 21 % and 26 % respectively compared with that of pure APA-6. It is important to find that there were some interactions between APA-6 and ramie fiber, which produced a good interface characters. This work not only opens new avenues for the development of renewable composites, but also further broadens the applications of the natural fibers.

Comparative Structural and Mechanical Studies on Polyamide 6 Knitted‐Reinforced Single Polymer Composites Prepared by Different Reactive Processing Techniques

Single polymer laminate composites based on anionic polyamide 6 (PA6) matrix‐reinforced by PA6 knitted textile structures (KSPC) were produced by nylon reactive injection molding and powder coating/compression molding (PCCM) processing techniques. The effect of the reinforcement's structure and the fiber volume fraction on the mechanical properties of the knitted‐reinforced PA6 composites resulting from the two methods were investigated and compared. The morphology and the crystalline structure of KSPC materials were studied to identify the main factors determining the tensile properties. The results showed that the PCCM method produced laminate composites with higher Young's modulus and mechanical strength in tension. Microscopy, differential scanning calorimetry and X‐ray diffraction experiments were carried out to correlate the morphology and crystalline structure of the composites and their precursors with the different tensile behavior of KSPC prepared using the two techniques. The microscopy and X‐ray scattering studies suggested the formation of a transcrystalline layer at the matrix/reinforcement interface. POLYM. COMPOS., 40:E886–E897, 2019. © 2018 Society of Plastics Engineers

Enhanced synthesis of poly gamma glutamic acid by increasing the intracellular reactive oxygen species in the Bacillus licheniformis Δ1-pyrroline-5-carboxylate dehydrogenase gene ycgN-deficient strain.

Poly gamma glutamic acid (γ-PGA) is an anionic polyamide with numerous applications. Previous studies revealed that L-proline metabolism is implicated in a wide range of cellular processes by increasing intercellular reactive oxygen species (ROS) generation. However, the relationship between L-proline metabolism and γ-PGA synthesis has not yet been analyzed. In this study, our results confirmed that deletion of Δ1-pyrroline-5-carboxylate dehydrogenase gene ycgN in Bacillus licheniformis WX-02 increased γ-PGA yield to 13.91gL-1, 85.22% higher than that of the wild type (7.51gL-1). However, deletion of proline dehydrogenase gene ycgM had no effect on γ-PGA synthesis. Furthermore, a 2.92-fold higher P5C content (19.24μmolgDCW-1) was detected in the ycgN deficient strain WXΔycgN, while the P5C levels of WXΔycgM and the double mutant strain WXΔycgMN showed no difference, compared to WX-02. Moreover, the ROS level of WXΔycgN was increased by 1.18-fold, and addition of n-acetylcysteine (antioxidant) decreased its ROS level, which further reduced γ-PGA synthesis capability of WXΔycgN. Collectively, our results demonstrated that proline catabolism played an important role in maintaining ROS homeostasis, and deletion of ycgN-enhanced P5C accumulation, which induced a transient ROS signal to promote γ-PGA synthesis in B. licheniformis.

The influence of montmorillonite on the processing and properties of anionic polyamide 6/montmorillonite composites via vacuum assisted resin infusion

In this article, the vacuum assisted resin infusion (VARI) process was employed to prepare anionic polyamide 6/montmorillonite (APA6/MMT) nanocomposites. The ɛ‐caprolactam and MMT mixture are infused into the mold by vacuum. At the same time, the anionic polymerization of ɛ‐caprolactam proceeds all the way which results in fast viscosity rise. To make the VARI process has more practical application value, enough infusion time is necessary. Three types of MMT were chosen in this paper: Na+‐MMT, OMMT‐CTAB, and OMMT‐AUA. In order to study the effects of MMT on infusion process and material's performance, conversion, and temperature test, X‐ray diffraction analysis, transmission electronic microscopy, thermogravimetric analysis, Molau test, and mechanical test were performed. The results indicated that the OMMT‐AUA can both further improve the material's performance and has longer infusion time for VARI process. POLYM. COMPOS., 40:1481–1491, 2019. © 2018 Society of Plastics Engineers

The reactive compatibilization effect of copolymer macroactivator for immiscible anionic polyamide 6/polystyrene blends via in situ polymerization

ABSTRACTIn this article, a novel method has been successfully developed to prepare the anionic polyamide 6/polystyrene (APA6/PS) blends. The macroactivator P(St‐co‐IEM) was synthesized by the free radical polymerization of 2‐isocyanatoethyl methacrylate and styrene (St), then the graft copolymer of PS and APA6 (PS‐g‐APA6) can be obtained by the anionic polymerization of ɛ‐caprolactam activated by the macroactivator P(St‐co‐IEM). The X‐ray diffraction analysis, differential scanning calorimetry, scanning electron microscopy analysis, contact angle measurement, water absorption measurement, molau test, thermogravimetric analysis, and mechanical properties test were performed separately to study the effects of P(St‐co‐IEM) on crystallinity, morphology, water resistance, thermal stability, and mechanical properties. The results indicate the synthesis of macroactivator can promote the formation of the γ‐phase. Moreover, it can improve the interfacial compatibility, water resistance, thermal stability, and toughness. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46302.

Hexaphenoxycyclotriphosphazene as FR for CFR anionic PA6 via T‐RTM: a study of mechanical and thermal properties

SummaryThe production of carbon fiber reinforced (CFR) anionic polyamide 6 (APA6) plates by thermoplastic resin transfer molding (T‐RTM) processing is highly sensitive to the presence of polymer additives such as flame retardants (FRs). However, APA6 is flammable, and therefore, it is mandatory to protect the polymer matrix, especially if the produced materials are intended for aerospace applications. Typically used FR for PA6 cannot be incorporated in the T‐RTM processes. With hexaphenoxycyclotriphosphazene, an incorporable and effective FR additive for CFR APA6 was discovered. Cone calorimetry measurements indicate a char formation‐based mechanism, and the flame retardancy was further confirmed with limiting oxygen index tests, classification by UL94 (V‐0), and FAR25 tests. The influence of this FR on the thermal (thermogravimetric analysis and differential scanning calorimetry) and mechanical behavior (flexural, compressive and ultimate tensile strength, and Charpy impact tests) on CFR APA6 produced via T‐RTM processing is evaluated and indicates no interaction with the APA6; it works as a passive filler. Copyright © 2016 John Wiley & Sons, Ltd.

Some new perspectives of anionic polyamide 6 (APA 6) synthesis

The anionic polymerization of ε‐caprolactam in the bulk is now enriched by a new member belonging to the family of very fast activators, represented by blocked (triethoxysilyl)propylisocyanate. The activator is able to allow polymerization completion in a few tens of seconds in quasi‐adiabatic conditions starting from ca. 150°C. The most relevant and unexpected feature of its role in ε‐caprolactam activated anionic polymerization arises from the observation that the resultant APA 6 is extensively crosslinked in situ up to ca. 80% despite the isocyanate monofunctionality of the activator. Comparison with the behavior of a commercial trifunctional activator/crosslinker is carried out and possible explanation of (triethoxysilyl)propylisocyanate role as a crosslinker is put forward. Optimization of the procedure to properly evaluate the degree of APA 6 crosslinking in comparison with a literature method is established. Other tested silane derivatives do not behave similarly in the same experimental conditions of synthesis. The strong adhesion, due to the triethoxysilyl group, to glass fibers introduced in the polymerizing medium is a relevant additional advantage of the quoted activator. Possible industrial applications can be foreseen. Copyright © 2015 John Wiley & Sons, Ltd.

A numerical simulation of woven/anionic polyamide 6 composite part manufacturing using structural reactive injection moulding process

In this work, a structural reactive injection moulding process using reactive anionic polyamide 6 (APA-6) is studied. Semi-empirical equations for the prediction of the APA-6 reaction kinetics and an advection equation for void transport are used in the numerical scheme. A complex numerical simulation of reactive injection of ε-caprolactam was developed for a three-dimensional industrial part. The validity of the approach is demonstrated for determining an effective injection strategy, including the position of vents and gates and the most effective parameter values for minimum mould filling time without the formation of voids.

Temperature Evolution During Processing of Thick-Walled Anionic Polyamide 6 Composites: Experiment and Simulation

A 1-D through-the-thickness transient heat transfer model is built to simulate the curing process of thick-walled glass-fibre-reinforced anionic polyamide-6 (APA-6) composites. The temperature and the degree of polymerisation through the thickness of the composite are calculated and compared to the experimentally obtained results. The kinetic models describing the polymerisation behaviour of APA-6 are implemented in the model. The kinetic model not taking into account the convection in the polymerisation process shows the best results. It is found that the predicted temperature profiles agree well with the experimental data.

Structure, Morphology and Properties of a Novel Molecular Composite by In‐Situ Blending of Anionic Polyamide 6 with a Polyamide Copolymer Containing Rigid Segments

AbstractMolten caprolactam, in which a polyamide copolymer (HPN) containing rigid segments was dissolved, was polymerized by means of anionic ROP to in produce polyamide (PA, nylon) 6 blends with HPN in situ. A novel molecular composite was achieved in which toughness and strength were simultaneously improved, as well as modulus, compared to virgin PA6. In view of the interchange reaction between PA6 and PA1212 (and PA66) in blends fabricated in the same way, it was deduced that a similar reaction between PA6 and HPN took place during the blending and led to copolymerization between the two components. The formation of copolymers was verified by their single glass transition and single melting peak, measured through DMA and DSC, respectively. DSC analysis also showed that the occurrence of the interchange reaction inhibited the crystallization and suppressed the melting point of PA6. Analysis by FT‐IR spectroscopy indicated that the difference in the distance between the amide groups for PA6 and HPN induced a decrease in the amount and strength of hydrogen bonding. Moreover, characterization by POM and XRD revealed that the spherulite size of the PA6 crystals decreased dramatically and the amount of γ crystal increased slightly with the majority of crystallites being α crystals. Furthermore, it was found through the observation of the morphology by SEM that no phase separation existed in the composites. On the basis of detailed analysis and a comparison between the in situ PA6/PA66 and PA6/HPN blends, it is believed that the combination of markedly decreasing spherulite size and similar segmental mobility resulted in the simultaneous improvement of mechanical properties for the in situ PA6/HPN blends.magnified image