Phosphorylated silica/polyamide 6 nanocomposites synthesis by in situ sol–gel method in molten conditions: Impact on the fire-retardancy

Polyamide 6 (PA6)/phosphorylated silica nanocomposites were synthesized during PA6 extrusion through in situ formation of the inorganic phase without solvent. This synthesis is based on the hydrolysis-condensation reactions of diethylphosphatoethyltriethoxysilane (SiP) as a functional inorganic precursor in combination with or without tetraethoxysilane (TEOS) dispersed in the molten PA6. This synthesis is carried out during PA 6 matrix extrusion that means at high temperature and under shear. The characterization of the in situ synthesized PA6/phosphorylated silica nanocomposites by solid ²⁹Si Nuclear Magnetic Resonance (NMR), Small Angle X-ray Scattering (SAXS) and Transmission Electron Microscopy (TEM) coupled with Energy Dispersive X-ray spectroscopy (EDX) demonstrated the possibility to directly create in less than 5 min at 220 °C a phosphorylated silica uniformly dispersed in the PA6, i.e. in the form of well dispersed particles or aggregates of sub-micron range. The influence of silicon and phosphorus on the thermal and fire retardant behaviour was investigated by thermogravimetric analysis (TGA), cone calorimeter and UL94 tests. The fire retardant behaviour was modified with a formation of a char and a peak heat release rate (PHRR) decrease by more than 50% for the SiP based nanocomposite compared to the pure PA6.     

Modeling and optimizing toughness and rigidity of PA6/SBR: Using compatibilizer and response surface methodology

The improvement of miscibility between toughened Polyamide-6 (PA6) and Styrene-Butadiene Rubber (SBR) was carried out using grafted Glycidyl Methacrylate (SBR-g-GMA). At first, the compatibilizers were prepared using different comonomers, Styrene, and N-vinyl pyrrolidone. Central composited design (CCD) was distinctly applied to study the influence of Glycidyl Methacrylate (GMA) content and comonomer/GMA on the process of compatibilizer preparation. Four models were developed for Gel content and Degree of grafting for both comonomers using Design-expert software. The models were used to calculate the optimum operating conditions and according to the Flory-Huggins parameter and obtained results, SBR-co-NVP-g-GMA was chosen as an effective compatibilizer. Afterward, another CCD was employed to scrutinize the effect of various amounts and grafting degree of compatibilizer on morphology and mechanical properties of PA6/SBR. The Interparticle distance and polydispersity were studied using a Scanning electron microscope (SEM) and also the Izod impact test inspected in order to evaluate the mechanical properties. Finally, modulus and impact strength were optimized to minimize the former and maximize the latter. Also, the most practical terms in the fitted model are statistically specified using F-value. The root causes for the improvement of blend properties were attributed to a chemical reaction between epoxy groups in SBR-g-GMA and both the carboxylic and amine groups in PA6. Impact strength (539.8 J/m) and modulus (2017.2 N/mm²) of the optimum blend indicate an excellent agreement with the amounts predicted by the models.     

The effect of short glass fibers on the process behavior of polyamide 12 during selective laser beam melting

In additive manufacturing, polymer composites are used for setting tailored properties. Short glass fibers can be used as fillers for polyamide 12 for enhancing stiffness or tensile strength as well as for reducing shrinkage. In this paper, the effects of short glass fibers on polyamide 12 concerning powder properties, process behavior and part properties in laser beam melting of polymers (SLS) are investigated. It could be shown that by increasing the short glass fiber content powder properties as well as part properties are immensely affected. By adding glass fibers, powder properties, like flowability and diffuse reflection decrease. The isothermal crystallization changes resulting in a narrower processing window. Concerning mechanical properties, short glass fibers allow for a higher stiffness until a critical limit of filler concentration within this study is reached, after which the tensile strength decreases. The elongation of break decreases by rising the filler content.     

Multiscale characterization and constitutive parameters identification of polyamide (PA12) processed via selective laser sintering

This study is focused on multiscale characterization and constitutive parameters identification of selectively laser sintered PA12 specimens. The process parameters and change in crystallinity due to 3D printing were identified via differential scanning calorimetry (DSC). Tension, compression, shear, flexural and fracture tests performed on samples fabricated, both in 0° and 90° directions reveal that the tensile toughness of samples printed in 0° orientation, outperform samples printed in 90° orientation by an average of 24%. Cryogenically fractured samples were analyzed via SEM and micro-computed tomography to analyze 2D/3D defects and correlate the microstructure with macroscopic properties. The constitutive parameters for a strain-rate and temperature-dependent Three Network (TN) material model were identified using the measured mechanical properties. Furthermore, mechanical response of micro-architected Kelvin lattice structure was analyzed by Finite Element Method employing the TN constitutive model and the predictions were corroborated with measurements.     

In-situ thermal crosslinked PA66/β-cyclodextrin/PA66 nanofibrous membranes with high mechanical strength for removal of heavy metal ions by flow through adsorption

β-cyclodextrin (β-CD) based materials have been studied widely as adsorbents and filter membranes for removing pollutants in air or water applications. The present study aimed to develop a sandwich structure of eletrospun nanofibrous membrane based on β-cyclodextrin and PA66 to achieve the high mechanical strength and flow-through adsorption of heavy metal ions in water. The surface and cross section morphology of PA66/β-cyclodextrin/PA66 nanofibrous membranes (PA66/β-CD/PA66 NMs) were examined using scanning electron microscopy (SEM). The physicochemical and mechanical properties of PA66/β-CD/PA66 NMs were analyzed by differential scanning calorimetry (DSC), thermogravimetric (TG) analysis and universal testing machine. The diameter of β-CD and PA66 electrospun fibers are 300–400 nm and 20–40 nm respectively. PA66/β-CD/PA66 NMs show a loosely arranged fibers and layer by layer structure. The tensile strength increases remarkably for PA66/β-CD/PA66 NMs, from 1.33 MPa of β-CD NMs to 23.17 MPa and the Young's modulus increases from 34.8 MPa to 253.3 MPa. The mechanical behavior of PA66/β-CD/PA66 NMs is a typical brittle fracture, and its microcosmic fracture diagrams are also involved. TGA/DSC results confirm the thermal crosslinking reaction is effective and complete. On the basis of SEM, DSC, TG and mechanical behavior analysis results, the molecular mechanism of in situ thermal crosslinking reaction is discussed. Fe³⁺、Ni²⁺ were used to confirm the ability to absorb heavy metal ions of PA66/β-CD/PA66 NMs. In conclusion, PA66/β-CD/PA66 NMs could be a promising solution for removal of metal ions by flow-through adsorption.     

In situ fibrillation of polyamide 6 in isotactic polypropylene occurring in the laminating‐multiplying die

The polyamide 6 (PA6)/isotactic polypropylene (iPP) in situ fibrillation composites are prepared by a novel extrusion die with an assembly of laminating‐multiplying elements (LMEs). The scanning electron micrographs illustrate that the dividing‐multiplying processes in LMEs elongate, break, and stabilize the dispersed PA6 phase in the iPP matrix along the flowing direction (FD). The morphology development of PA6 with different LME numbers greatly affects the rheological properties, crystalline behaviors, and mechanical properties. The dynamic rheological test performed at 195°C shows that the increased spatial restriction of the high‐aspect‐ratio PA6 particles increases the viscoelastic moduli, complex viscosity, and relaxation time. The crystalline analysis reveals that the heterogeneous nucleation becomes predominant and the transcrystalline morphology is observed in those samples produced by more LMEs. The tensile tests indicate that both, breaking strength and elongation, enhanced simultaneously because of the fibrillation of dispersed phase and the improvement in interfacial adhesion between the fibers and the matrix. Copyright © 2009 John Wiley & Sons, Ltd.     

Largely enhanced ductility of immiscible high density polyethylene/polyamide 6 blends via nano‐bridge effect of functionalized multiwalled carbon nanotubes

Immiscible polymer blends usually exhibit negative deviation in mechanical properties compared with the corresponding pure polymers due to the weak interfacial bonding between the two polymers. Due to the bridge effect of the oriented carbon nanotubes (CNTs) on the craze and crack development at the load of stress, CNTs have been proved to be efficient toughening agent for polymers. In this work, functionalized multiwalled carbon nanotubes (FMWCNTs) have been introduced into immiscible high density polyethylene/polyamide 6 (HDPE/PA6) blends through different sample preparation methods. The mechanical measurements demonstrate that, when the nanocomposite is prepared from the HDPE master batch, the sample exhibits excellent tensile strength and toughness simultaneously. For all the nanocomposites, FMWCNTs tend to migrate and/or maintain in PA6 particles, leading to the variation of the crystallization behavior in PA6 phase. Further results based on morphologies characterization indicate that the intensified interfacial adhesion between HDPE and PA6, which is realized by the nano‐bridge effect of FMWCNTs in the interfaces, is the main reason for the largely improved ductility. Copyright © 2010 John Wiley & Sons, Ltd.     

Anti‐static Agent Containing Zinc Oxide and its Modification for PA6 Fiber

A new anti‐static agent was synthesized from zinc oxide‐adipic acid‐polyethylene glycol and caprolactam by three‐step reactions. The antistatic agent (called poly(ether ester amide zinc oxide) or PEEAZ) was analyzed by IR and DSC. The results showed that zinc oxide existed in the main chain of PEEAZ. The glass temperature and melt temperature of poly(ether ester amide zinc oxide) (referred to as PEEAZ in the following) decreased with increasing poly(ether ester zinc oxide) increasing in PEEAZ. Antistatic PA6 fiber was obtained by adding PEEAZ 2–8% (wt/wt) to PA6 during blend spinning. The specific resistance and the static half‐value period of PA6 fiber was less than 10⁹Ω · cm and 60 sec, respectively. Excellent antistatic property remained after being washed 30 times.     

Does nanoclay addition always lead to amelioration? Dual effects of the nanoclay on the PA‐6/EVOH/SEBS ternary blends

This work presents the investigation of properties of polyamide‐6 (PA‐6)/ethylene vinyl alcohol (EVOH)/styrene‐ethylene‐butylene‐styrene (SEBS) ternary blends and related nanocomposites with nanoclays. In this way, the effect of the mixing protocol and nanoclay type on the morphology, mechanical, and rheological properties of the blends was comprehensively studied. Scanning electron microscopy (SEM) observation revealed that, for the neat ternary blends, core‐shell droplets were formed in which SEBS droplets were encapsulated by EVOH phase in the PA‐6 matrix. In this regard, experimental observations were compared and discussed with the predictions of phenomenological models. According to the X‐ray diffraction analysis, the distribution and degree of dispersion of the nanoclays were significantly influenced by mixing protocol. It was demonstrated that competition between the intrinsic effect of the nanoclay on the physical properties and its inhibiting effect on the interactions between PA‐6 and EVOH phases led to some interesting observations for the rheological and mechanical properties of the ternary blends. The results revealed that optimum properties could be obtained by selecting appropriate nanoclay and mixing protocol.     

Synthesis of intrinsically flame‐retardant copolyamides and their employment in PA6‐fibers

Flame‐retarded polyamide 6.6 (FR‐PA6.6) was prepared by the cocondensation of hexamethylene diammonium adipate (AH‐salt) with the corresponding salts of hexamethylene diamine and two different organophosphorus compounds, namely, 3‐hydroxyphenylphosphinylpropanoic acid (3‐HPP, 1) and 9,10‐dihydro‐10‐[2,3‐di (hydroxycarbonylpropyl]‐10‐phosphaphenanthrene‐10‐oxide (DDP, 2). The incorporation of the phosphorus comonomers and the thermal and physical properties of the resulting copolyamides have been studied. The phosphorus‐modified FR‐PA6.6 possesses high relative viscosities of 2.0 to 2.4, good thermal stability, and was used for the production of polyamide blends by merging FR‐PA6.6 with commercial PA6. This offered access to flame‐retarded PA6 multifilaments, which possess tensile strengths up to 0.7 GPa and elastic moduli up to 6.2 GPa. Knitted fabrics of FR‐PA6 exhibit high limiting oxygen index (LOI) values between 36 and 38 and executed burning tests demonstrate that the incorporation of phosphorus‐based comonomers improve flame retardancy significantly. The approach presented here offers a straightforward access to effective flame retardancy in nylon 6.