Development Of Polyamides Research Articles

Development of polyamide 6‐graphene oxide nanocomposite and direct‐joining with aluminum alloy for lightweight engineering applications

AbstractLightweight polyamide composites and structures have been widely studied and employed in several industrial sectors. In this study, the development of a nanocomposite of polyamide 6 and graphene oxide (PA6‐GO) by melt‐compounding and the joining with aluminum alloy AA6061 through direct‐adhesion injection overmolding are addressed. PA6‐GO nanocomposite exhibited well‐dispersed thin (300 nm) GO platelets distributed within the PA6 matrix, which resulted in an increase of 21% in the tensile modulus and 16% in the yield stress for a filler loading of 0.5 wt%. PA6‐GO/AA6061 hybrid joints showed good mechanical anchorage through the complete filling of the polymer into micro‐scale grooves designed onto the metal surface, which ensured outstanding shear strength of 7.1 ± 1.0 MPa, comparable to other polyamide‐metal hybrid joints reported in the literature. This indicates that the processing routes and materials developed are promising for lightweight engineering applications.Highlights A PA6‐GO nanocomposite with enhanced tensile properties was developed. A joint of PA6‐GO and AA6061 with outstanding shear strength was obtained. Fast and efficient melt‐processing routes were employed. These materials are promising for lightweight engineering applications.

Development of polyamide/polyacrylonitrile thin film composite RO membranes by interfacial polymerization assisted with an aromatic/aliphatic organic solvent mixture

AbstractThe proper control of polymerization is a prerequisite in fabrication of thin film composite reverse osmosis (RO) membranes. But it not trivial when hydrophilic substrates are used. Herein, we report an innovative approach which involves using an aromatic/aliphatic solvent mixture of toluene and n‐hexane as the organic phase for interfacial polymerization. Membranes were tuned by using a customized developed polyacrylonitrile (PAN) substrate and exploring the impacts of organic solvent and curing temperatures on their morphology and performance characteristics. Results revealed that increasing the temperature of organic phase to 20°C improved salt rejection significantly to 98.6% with the flux of 16.1 LMH. However, its further increase to 30°C was not beneficial due to formation of a looser chain packing which led to rejection drop. In addition, raising curing temperature to 90°C was not favorable due to transformation of surface morphology from ridge‐and‐valley to nodular structure, accompanied with defective sites at the selective layer and insufficient degree of crosslinking evidenced by declines in both flux and rejection to 11.1 LMH and 83.4%, respectively. Overall, the findings suggested that an optimal performance could be obtained by using a solvent mixture of toluene/n‐hexane (1,1) and setting organic solvent and curing temperatures to 20 and 70°C, respectively.

Development of Polyamide 6 (PA6)/Polycaprolactone (PCL) Thermoplastic Self-Healing Polymer Blends for Multifunctional Structural Composites

High-performance composites suffer from fatigue crack propagation during service. Traditional repair methods can be expensive and time-consuming. Therefore, research on composites with self-healing capabilities has considerably increased in the past decade. The aim of this work is to develop a polyamide 6 (PA6) matrix with self-healing properties. Polycaprolactone (PCL) was used as healing agent and melt compounded with PA6. PCL caused a decrease of the mechanical properties of PA6, due to its immiscibility and low mechanical properties. Nevertheless, acceptable fracture toughness values in quasi-static mode were obtained. Samples were thermally mended at 80 and 100 °C, and the healing efficiency was assessed by comparing the fracture toughness of virgin and repaired samples both in quasi-static and in impact mode. The blend with a PCL content of 30 wt% showed limited healing efficiency values (up to 6%) in quasi-static mode, while an interesting repair capability (53%) was detected under impact conditions. This discrepancy was explained through microstructural analysis and correlated to a different fracture morphology. In fact, under quasi-static mode, the PA6 matrix was severely plasticized, while under impact a brittle fracture surface was obtained. This morphology favored the flow of PCL during the thermal healing process.

Frictional Losses of Polyamides Mounted on Tensioning Guides in Contact with Chains

The development of polyamides has increased in recent years due to scientific research and the aim of the industry to find materials characterized by good frictional behavior at high temperatures, high loads and high speeds. The wide areas of application of polyamides in the mechanical contacts with relative motions offered new development opportunities for polyamides (PA), such as PA66, PA46 and PTFE mixed PA46. One of the applications of these polyamides in mechanical contacts with relative motions is the contact between the timing chains and the active part of the tensioning guides. For a comparison with a previous study of friction of PA66, PA46 and PTFE mixed PA46, performed on a pin-on-disk tribometer, this study is based on performing tests on the same materials, on the tensioning guide of a silent chain used as a timing chain in combustion engines, with lubricating conditions much closer to the application field. The diagrams comparatively present the variation of the percentage of frictional losses for PTFE mixed PA46, PA46 and PA66 polyamides mounted on tensioning guides in contact with chains. The results clearly show that the PTFE mixed PA46 polyamide has smaller frictional losses than the PA46 and the PA66 polyamides, but the influence of speed and tensioning is also important. A comparison with the previous study is also useful for making a decision on using a polyamide for the guide of a timing chain.

Biocomposites from biobased polyamide 4,10 and waste corn cob based biocarbon

Development of polyamide 4,10 (PA 4,10) from renewable resources is a positive step towards replacement of traditional polyamides. The environmental impact of PA 4,10 is further improved through incorporation of sustainable biocarbon (BioC) filler derived from agro-residues, specifically corn cob. Pyrolysis improved filler stability at high temperatures required for PA 4,10 processing as opposed to raw corn cob, with biocomposites in the present work having an elevated biocontent to 76%. Corn cob BioC pyrolyzed at 350, 500, and 900 °C was characterized to elucidate its interactions with PA 4,10, finding a pyrolysis temperature of 350 °C providing strong interfacial adhesion via particle encapsulation. Biocomposites maintained similar mechanical and thermal properties as compared to neat polymer. Hindrance of crack propagation and rigidity of filler particles led to improvements in tensile modulus and heat deflection temperature by 6 and 12%, respectively. These composites provide a route to diminish reliance on petroleum-based polyamide products.

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 LLDPE-g-MA on the rheological, thermal, mechanical properties and morphological characteristic of PA6/LLDPE blends

The development of polyamide 6 (PA6) and linear low-density polyethylene (LLDPE) blends is of great technological interest, as they have the potential to combine the good mechanical and thermal properties of PA6 with the high impact properties and good processability of the LLDPE. However, these two polymers are chemically and structurally different and therefore immiscible, and in general incompatible. The objective of this study was to evaluate the effect of maleic anhydride-grafted linear low-density polyethylene (LLDPE-g-MA) as compatibilizer agent on rheological, thermal, mechanical and morphological properties of PA6/LLDPE blends. PA6/LLDPE blends with different contents of LLDPE (10, 20, 30, 40 and 50 wt%) and with the addition of LLDPE-g-MA (5 wt%) were prepared in a twin screw extruder and the thermal and mechanical analysis were performed. The addition of LLDPE-g-MA as compatibilizer agent resulted in a better distribution and dispersion of LLDPE in PA6 matrix and a significant improvement in mechanical and thermal properties. The addition of the compatibilizer agent increased 160% the impact strength for the 50/50 (PA6/LLDPE) blend.

Redefining polyamide property profiles via renewable long-chain aliphatic segments: Towards impact resistance and low water absorption

A series of renewable, long-chain, fatty acid-derived polyamides (PA) ranging from PA 6,14 to PA 6,18 were synthesized via polycondensation, yielding very high molecular weights and a remarkable property profile distinct from short-chain commercial grades. Most notably, synthesized polyamides exhibited good impact resistance, excellent stiffness-to-toughness balance and very low water absorption yet high oxygen and water vapour permeability; with this property profile being exemplified by PA 6,18. The increased repeating unit length and reduced number of amide linkages able to participate in interchain hydrogen bonding imparted a strong influence on material properties. The data highlights the benefits and technical advantages of utilising long-chain polyamides, while also significantly expanding the repertoire, knowledge and property profile of the long-chain aliphatic polyamide family, and providing a basis for further development of polyamides from renewable sources.

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.

Solid-Phase Synthesis of Pyrrole-Imidazole Polyamides by Resin

Over the past years, synthesis of pyrrole-imidazole (Py-Im) polyamides has been achieved by solution-phase and solid-phase methods. Comparing with solution-phase synthesis, the solid-phase synthesis has showed great superiority in various aspects. The solid-phase synthesis is a rapid, effective, energy-saving and environment-friendly method, which has been widely used in the synthesis of pyrrole-imidazole polyamides. Many complicated polyamides can be obtained quickly and effectively through this method. By far, the application of the solid-phase synthesis for Py-Im polyamides has made rapid development. Resin as the main carrier, a key substance in solid phase synthesis, consists of two parts: polymer (macromolecular resin) and linking chain (linker). To date, there are many kinds of resins applied in the solid phase synthesis, such as PAM resin, Wang resin, Oxime resin and Clear resin, and so on. In this article, we will focus on the elaboration about the basic principle and application of the four kinds of resins mentioned above in solid-phase synthesis of polyamides. This provides an important reference for development of polyamides.

Development of Polyamide 6/Compound by Recycled Rubber Blends Using Graphitized Polyethylene or Polypropylene with Maleic Anhydride as Compatibilizer Agent

The toughening of polyamide 6 is desirable for many applications and may be obtained by adding a phase to the elastomeric matrix. However, this leads to a loss in its rigidity characteristics. Therefore, this study aimed at developing blends of polyamide 6/compound by recycled rubber (SBR-R), with the addition of compatibilizer graphitized polyethylene and polypropylene with maleic anhydride method by mixing in the molten state in order to obtain a balance between stiffness and toughness. The systems were prepared in several compositions, and their rheological properties and spectroscopy in the Fourier transform infrared were studied by means of rheological curves obtained in an internal mixer of Haake Buchler. The results obtained with the rheological study and Fourier transform infrared showed that mixtures of polyamide 6/graphitized polyethylene with maleic anhydride presented the best results compared to those of polyamide 6/ graphitized polypropylene with maleic anhydride, probably indicating reaction between the components. Thus, it was chosen graphitized polypropylene with maleic anhydride as a compatibilizing agent for carrying out other characterizations. Blends of polyamide 6/compound by recycled rubber/ graphitized polypropylene with maleic anhydride and their properties were analyzed by means of mechanical tests (tensile and impact), dynamic mechanical thermal analysis, differential scanning calorimetry, and scanning electron microscopy. The impact strength and elastic modulus of the blends compatibilized reduced somewhat when compared to polyamide 6. Therefore, these results indicate a good prospect of application of industrial waste, minimizing the negative effect on the environment and adding value to a disposable material.

Novel diamino imidazole and pyrrole-containing polyamides: Synthesis and DNA binding studies of mono- and diamino-phenyl-ImPy*Im polyamides designed to target 5′-ACGCGT-3′

Pyrrole- and imidazole-containing polyamides are widely investigated as DNA sequence selective binding agents that have potential use as gene control agents. The key challenges that must be overcome to realize this goal is the development of polyamides with low molar mass so the molecules can readily diffuse into cells and concentrate in the nucleus. In addition, the molecules must have appreciable water solubility, bind DNA sequence specifically, and with high affinity. It is on this basis that the orthogonally positioned diamino/dicationic polyamide Ph-ImPy*Im 5 was designed to target the sequence 5′-ACGCGT-3′. Py* denotes the pyrrole unit that contains a N-substituted aminopropyl pendant group. The DNA binding properties of diamino polyamide 5 were determined using a number of techniques including CD, ΔTM, DNase I footprinting, SPR and ITC studies. The effects of the second amino moiety in Py* on DNA binding affinity over its monoamino counterpart Ph-ImPyIm 3 were assessed by conducting DNA binding studies of 3 in parallel with 5. The results confirmed the minor groove binding and selectivity of both polyamides for the cognate sequence 5′-ACGCGT-3′. The diamino/dicationic polyamide 5 showed enhanced binding affinity and higher solubility in aqueous media over its monoamino/monocationic counterpart Ph-ImPyIm 3. The binding constant of 5, determined from SPR studies, was found to be 1.5×107M−1, which is ∼3 times higher than that for its monoamino analog 3 (4.8×106M−1). The affinity of 5 is now approaching that of the parent compound f-ImPyIm 1 and its diamino equivalent 4. The advantages of the design of diamino polyamide 5 over 1 and 4 are its sequence specificity and the ease of synthesis compared to the N-terminus pyrrole analog 2.

Development of Polyamide 6 Based Blend Fibers with Surface Roughness for Artificial Hair

Development of Polyamide 6 Based Blend Fibers with Surface Roughness for Artificial Hair

Development of Polyamide 6/Ferrite Composites for Absorbers of Electromagnetic Radiation

Composites consist of a mixture or combination of the two or more, micro or macro constituents that differ in shape and chemical composition and, in essence, are insoluble in one another. The polyamide is a polymer that presents dimensional stability, good resistance to impact without notch and excellent chemical resistance. Already the ferrites are absorbers of electromagnetic radiation and have versatility to be used as a composite of ferrites. The composite of polyamide6/ferrite was obtained by mixing 10 and 30wt.% of ferrite added to polyamide 6 in a Torque Rheometer Haake. The objective of this work was to develop of polyamide6/ferrite composites to be used as absorbers of electromagnetic radiation. The results were very promising and showed that occurs interaction between the ferrite and polyamide6.

The development of polyamide 6.6 nanofibres with a pH-sensitive function by electrospinning

The development of a pH-sensitive nanofibrous sensor could contribute to interesting applications thanks to the combination of the pH-sensitive functionality and the unique characteristics of nanofibres. The effect of the addition of pH-sensitive dyes to the polymer solution is however unknown. Moreover also the halochromic behaviour of the resulting nonwovens can be influenced by this incorporation. Therefore, we studied the production of halochromic nano nonwovens by adding various pH-indicator dyes to a polyamide 6.6 polymer solution prior to electrospinning. Next, the halochromism of two selected dyes (Bromocresol Purple and Brilliant Yellow) was investigated as case studies. Our results show that the pH-indicator addition has no influence on the average fibre diameter. Poorly dissolved dyes cause however instabilities in the process as seen by the droplet formation. The investigated nanofibrous structures showed a clear colour change with a change in pH. This halochromic behaviour was however different from the behaviour of the dye in solution due to dye–fibre interactions. Generally it can be concluded that a nanofibrous pH-sensor can be developed by electrospinning with incorporated pH-indicator dyes.