Types Of Polyamides Research Articles

Synthesis and characterization of high thermal resistance acetal-containing heterocyclic polyamides

This study synthesized a heterocyclic acetal-containing monomer, 7a,14c-dihydronaphtho[2,1-b] naphtho [1′,2′:4,5] furo[3,2-d] furan (DHNF) with a melting point of 230 °C, through the acidic reaction of 2-naphthol and glyoxal. Two types of heterocyclic polyamides were produced via condensation polymerization of DHNF Diamine with terephthalic acid (aromatic diacid) and sebacic acid (aliphatic diacid), achieving melting points exceeding 400 °C. Spectroscopic methods, including Fourier-transform infrared spectroscopy (FT-IR) and nuclear magnetic resonance spectroscopy (1HNMR), were used to identify the synthesized compounds. Thermal analysis, including Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), demonstrated the thermal stability of the polyamides with acetal functional groups, showing a 10 % weight loss at 193.6 ℃ for PA-1 and 420 ℃ for PA-2, with crystallization temperatures of 155 °C and 180 °C for Types 1 and 2, respectively. The results indicate that the acetal functional group enhances polyamide solubility and processability. Viscometry revealed higher inherent viscosity for PA-2, attributed to its higher molecular weight.

Pure Hydrolysis of Polyamides: A Comparative Study

Polyamides (PAs) undergo local environmental degradation, leading to a decline in their mechanical properties over time. PAs can experience various forms of degradation, such as thermal degradation, oxidation, hydrothermal oxidation, UV oxidation, and hydrolysis. In order to better comprehend the degradation process of PAs, it is crucial to understand each of these degradation mechanisms individually. While this review focuses on hydrolysis, the data from degrading similar PAs under pure thermal oxidation and/or hydrothermal oxidation are also collected to grasp more perspective. This review analyzes the available characterization data and evaluates the changes in molecular weight, crystallinity, chemical structure, and mechanical properties of PAs that have aged in oxygen-free water at high temperatures. The molecular weight and mechanical strength decrease as the crystallinity ratio rises over aging time. This development is occurring at a slower rate than degradation in pure thermal oxidation. By combining the data for the changes in mechanical properties with the ones for molecular weight and crystallinity, the point of embrittlement can be not only predicted, but also modeled. This prediction is also shown to be dependent on the fibers, additives, types of PA, pH, and more.

Investigation of Wear Resistance of Polyamide PA6 Based Composite Materials for Metal - Polymer Plain Bearings and Gears

Metal-polymer plain bearings and gears are becoming increasingly used in many areas of human activity. The wear resistance of one group of such materials - unreinforced polyamides PA6, PA66, and composites with fillers РА6+30GF, РА6+30CF, РА6+MoS2, РА6+Оil was studied. To determine their wear resistance indicators the author's method of model triboexperimental research according to the scheme of end friction at dry sliding friction paired with carbon steel (0.45%C) is used. According to the determined wear resistance indicators, are calculated as the basic parameters of the author's mathematical model of materials’ wear kinetics at sliding friction and the analytical method of the research of specified friction units. Based to the research, polymeric materials’ wear resistance diagrams are plotted as graphical indicators of wear resistance in the accepted range of specific friction forces. The qualitative and quantitative influence of the type and structure of the fillers on the wear resistance has been established. Qualitatively, the nature of the change in wear resistance of the indicated types of polyamides is similar, quantitatively the difference is significantly differentiated. It was found that PA6+Oil has the highest wear resistance compared to the РA6. It consistently increases in the following sequence: PA66, РA6+30GF, РA6+MoS2, РA6+30CF, РA6+Oil.

VAR Fabric Modification: Inducing Antibacterial Properties, Altering Wettability/Water Repellence, and Understanding Reactivity at the Molecular Level.

The present work focuses on the surface coating of VAR technical fibers, consisting of 64% viscose (cellulose), 24% Kevlar, 10% other types of polyamides, and 2% antistatic polymers. Kevlar is an aramid material exhibiting excellent mechanical properties, while cellulose is a natural linear polymer composed of repeating β-d-glucose units, having several applications in the materials industry. Herein, we synthesized novel, tailor-designed organic molecules possessing functional groups able to anchor on VAR fabrics and cellulose materials, thus altering their properties on demand. To this end, we utilized methyl-α-d-glucopyranose as a model compound, both to optimize the reaction conditions, before applying them to the material and to understand the chemical behavior of the material at the molecular level. The efficient coating of the VAR fabric with the tailor-made compounds was then implemented. Thorough characterization studies using Raman and IR spectroscopies as well as SEM imaging and thermogravimetric analysis were also carried out. The wettability and water repellency and antibacterial properties of the modified VAR fabrics were also investigated in detail. To the best of our knowledge, such an approach has not been previously explored, among other factors regarding the understanding of the anchoring mechanism at the molecular level. The proposed modification protocol holds the potential to improve the properties of various cellulose-based materials beyond VAR fabrics.

High-entropy polymer blends utilizing in situ exchange reaction

High-entropy metal alloys comprising near-equimolar multiple elements have attracted considerable attention, and high configurational entropy is the main reason behind their outstanding performance. Analogical material design is expected to be applied for polymer blending; however, high-entropy polymer blends are still an undeveloped field owing to their long-chain structure. Increasing configurational entropy is essential for preparing high-entropy polymer blends, and to realize monomer unit dispersion beyond molecular chains, multi-component blending, utilizing an in situ exchange reaction, was investigated. Four types of aliphatic polyamides were employed as component polymers, and binary-to-quaternary blends were fabricated. Ternary and quaternary blends exhibited restricted crystallization behavior and high elongation at break. These characteristic behaviors were not observed in the reacted binary blends or unreacted quaternary blends. Numerical assessment revealed that the randomness of the molecular sequence in the reactive quaternary blend rapidly increased during melt mixing.

Effect of hydrogen–deuterium exchange in amide linkages on properties of electrospun polyamide nanofibers

The effect of deuteration of polymeric nanofibers (NFs) on their structure and thermal and mechanical properties was investigated. Three types of polyamides (PA; PA66, PA6, and PA11) NFs were prepared by electrospinning from solutions with non-deuterated or deuterated solvents and subsequently characterized. In the NFs prepared with deuterated solvents, partial hydrogen–deuterium (H–D) exchange occurred in the amide linkages of the polymers, leading to improved thermal and mechanical properties. Further, partial deuteration of amide linkages in all the PAs slightly increased the NF melting and glass transition points and substantially improved the Young's moduli and tensile strengths of the NF sheets by 1.2–1.3 times. Additionally, the degree of crystallinity improved due to the deuteration effect. The results clearly indicate that this facile, solution processing approach based on H–D exchange in the amide linkages is promising for improving the properties of polymer NFs.

Differentiation of Polyamide 6, 6.6, and 12 Contaminations in Polyolefin-Recyclates Using HPLC Coupled to Drift-Tube Ion-Mobility Quadrupole Time-of-Flight Mass Spectrometry.

Recycling is a current hot topic with a focus especially on plastics. The quality of such plastic recyclates is of utmost importance for further processing because impurities lead to a reduction thereof. Contaminations originating from other polymers are highly problematic due to their immiscibility with the recyclate, leading to possible product failures. Therefore, methods for the determination of polymer impurities in recyclates should be investigated. In this paper, an approach for the identification of three different polyamide grades (polyamide 6, 6.6, and 12) is presented, applicable for the analysis of polyolefin-recyclates. An HPLC equipped with a drift-tube ion-mobility QTOF-MS was used for the identification and differentiation of compounds originating from the polyamides, which were then used as markers. These marker compounds are specific for each type and can be identified by their corresponding value of the collision cross section (CCS). After a simple sample preparation, all three types of polyamides were identified within one measurement. In particular, the problematic differentiation of polyamide 6 and 6.6 was easily made possible.

Morphology and Mechanical Properties of the Polyketone/Polycarbonate Blends Compatibilized with Polyamides

To enhance impact strength of polyketone (PK) without loss of stiffness, PK was blended with polycarbonate (PC) via melt mixing. Three types of polyamides (PAs) with varying structures, — polyamide 6 (PA6), polyamide 612 (PA612), polyamide 12 (PA12) — were employed as polymeric compatibilizers. To elucidate the effect of the structure of PAs on the compatibilization, morphology, mechanical properties, and fracture behavior of the blends were investigated. The addition of PA6 and PA612 reduced the size of dispersed particles by encapsulating the PC phase, while PA12 was found not to affect the morphology of the PK/PC blend. The change in particle size, glass transition temperature (Tg), and elongation at break exhibited that PA6 was the most effective compatibilizer for the PK/PC blends of this study. These results were interpreted with the change in interfacial tension between PK and PA due to the difference in polarity of the PAs. It was found that the impact strength was not highest in the blend with the smallest particle size. The observation of sub-surface damage zone also indicated that effective toughening by intensive crazing in polymer blends requires dispersed particles of optimum size.

Hydroxypropyl-modified and organosolv lignin/bio-based polyamide blend filaments as carbon fibre precursors’

Hydroxypropyl-modified lignin (TcC) and organosolv lignin (TcA) were melt blended with two types of bio-based polyamides (PA) (PA1010 and PA1012) before being melt spun into filaments. With a lignin/bio-PA ratio 50/50 wt%, the filaments could be continuously produced and spooled having tensile strengths ≥ 20 MPa and moduli ≥ 500 MPa. The influence of each polyamide blended with each lignin on structural (FTIR), thermal (DSC, TGA, DMA), mechanical, rheological and morphological properties of the resultant extrudates and/or filaments was studied. The melting point of each polyamide was reduced in the presence of TcA and TcC lignin, and shifts in the glass transition temperature (Tg) and FTIR characteristic peaks occurred, which suggests that the selected polyamides and lignins are compatible with each other. The improved lignin/polyamide compatibilities were further supported by Pukanszky interfacial adhesion modelling. Despite the evidence for strong interactions, heterogeneous morphologies were observed in the resulting blends and scanning electron microscopy was used to determine dispersed lignin domain sizes which decreased when stronger lignin/polyamide interactions resulted. As a possible indicator of carbonization efficiencies, blends were subjected to a simulated stabilization/cross-linking process and subsequent TGA char residues were higher than those theoretically calculated at 880 °C, indicating that the bio-polyamide acted as a char-promoting agent for the lignin besides being a good blending partner. Overall, this study has indicated that the developed lignin/bio-polyamide filaments have potential as melt-extrudable precursors for carbon fibre production.

The methylene infrared vibration and dielectric behavior monitored by amide group arrangement for long chain polyamides

The effect of arrangement of amide groups on the dielectric behaviors and the methylene infrared vibration for Long chain polyamide (LCPA) were investigated by comparative study on PA11 and PA1012, which are endowed with similar chain structures. Combining with variable temperature Fourier transformation infrared spectroscopy (FTIR) method, the impact of hydrogen bond on the dielectric behaviors was studied. The interrelationship between amide group density and dielectric property was established by extending the research ranges towards PA12 and PA1212. It was found that AB type LCPAs have stronger molecular polarity and amide group density is positive correlation with the polarity, while the hydrogen bonding will weak the dipole polarity. Meanwhile, the IR characteristic fingerprint region about the methylene infrared vibration monitored by amide group arrangement and the corresponding assignments of each absorption peak were concluded. The two methods also can be employed for quickly and accurately identify the AB and AABB types of polyamides.

A unified expression to estimate the stress-strain curve of polyamides at different temperatures

The present paper proposes a unified expression to estimate the mechanical behaviour of polyamides in tensile tests at different temperatures. The goal is to present an algebraic equation able to describe the stress-strain curves that would be obtained using the ASTM D638-14 standard for a wide range of temperatures (roughly from −30 °C to 90 °C, even above the Glass Transition Temperature). This expression is valid for different kinds of polyamides. It is shown that with a minimum of three tests performed at different temperatures, it is possible to obtain a reasonable approximation of the stress-strain curve for this range of temperatures. Examples are presented considering different types of polyamides–PA11, PA12 and PA66-GF30 (PA66 reinforced with 30 wt% of short glass fibres). Although the mechanical behaviour is strongly affected by temperature variation, the estimates of the material behaviour are in good agreement with experiments in all cases studied in this paper. Such a procedure can be a practical tool for designers, used to obtain a reasonable approximation of tensile tests and thus reducing the need of performing many complex experiments.

Structure of Negative Spherulites of Even–Even Polyamides. Introducing a Complex Multicomponent Spherulite Architecture

Even–even polyamides are known to grow as positive spherulites, which implies that the radial, fastest growth direction is parallel to the a-axis and hydrogen bond direction. However, after annealing/self-seeding close to Tm, crystallization in a limited Tc window (down to ≈20 °C below Tm) yields profuse negative spherulites and, frequently stemming from the latter, less frequent and ill-defined entities named “spherulitic aggregates”. The detailed structure and origin of these two entities, and especially of the negative spherulites, are still not clearly established although they were first observed some 70 years ago. The recent recognition that polymer spherulites (specifically, spherulites of PVDF in its γ phase) are made of scrolled, radiating lamellae and the observation and analysis of solution grown, scrolled nylon-66 single crystals provide useful guidelines for a renewed analysis of this structural puzzle. The present analysis relies heavily on the approach and on the detailed diffraction data obtained by Lovinger in the late 1970s. It strongly supports the contention that negative spherulites of even–even polyamides are made of scrolled lamellae. The hydrogen bonds are oblique to the spherulite radius. Twinning parallel to the hydrogen-bonded sheets generates two different orientations of the unit cell that helically wind around the scroll axis. These two cell orientations plus a contribution of aggregate-like lamellae that grow inside the radial scrolls account for the apparent lack of orientation of the unit cell in these negative spherulites. This model explains also the birefringence variation of negative spherulites with Tc and their melting point identical to that of aggregates. Negative even–even PA spherulites thus illustrate an original spherulite architecture in which one population of lamellae generates a scaffold within which a second population develops in a confined but oriented frame. It appears to be applicable, perhaps with variants, to the spherulite structure of other types of polyamides.

EFFECT OF VARIOUS PULLING SPEEDS ON THE MECHANICAL PROPERTIES OF VARIOUS FIBER MIXTURE COMBINATIONS OF POLYAMIDE 6 AND 6.6 MATERIALS

Nowadays, thermoplastic composites have increasingly wide application areas due to their high stiffness and impact strength properties, superior fracture toughness, long duration of raw material shelf life and ease of production processes. Besides, they provide safer work environment. In this study, it has been examined that how the pulling speeds effects mechanical properties of thermoplastic composites. Non-reinforced, 15 percent reinforced and 30 percent reinforced polyamide 6 and polyamide 6.6 samples are produced with using plastic injection molding method and they are subjected to tensile testing at five different pulling speeds using the Tensile Testing Device. The results obtained from testing and those gathered from the plastics manufacturer company are compared with data obtained from the literature to check mechanical properties of thermoplastic composites which have been used in pulling speed test. It is observed that the experimental results were highly consistent with those in literature. According to these results, the positive effect of higher pulling speeds is observed. In this way, the different types of unreinforced and fiber glass reinforced polyamide 6 / polyamide 6.6 samples behavior under different pulling speeds have been determined. The results are in similar behavior with all types of polyamides. In order to gain an understanding of the effect of the overall testing procedure for all speeds, stress–strain graphics are constructed. Article DOI: https://dx.doi.org/10.20319/mijst.2018.41.162179 This work is licensed under the Creative Commons Attribution-Non-commercial 4.0 International License. To view a copy of this license, visit http://creativecommons.org/licenses/by-nc/4.0/ or send a letter to Creative Commons, PO Box 1866, Mountain View, CA 94042, USA.

The comparative study of the static friction coefficient between chain link and different types of polyamides

The comparative study of the static friction coefficient between chain link and different types of polyamides

The comparative study of the static friction coefficient between chain link and different types of polyamides

This paper has as scope the comparative analysis of the experimental study of the static friction coefficients between the chain links and two guide types (segments cut from the tensioning guide of the transmission chain used in combustion engines). Basically, this study will be performed for the contact between steel and different types of polyamides PA46 and PA66, using two tribometers. In the first stage there will be presented the tribometers, devices and work methods followed by the tests results. The next stage presents with the help of finite element analysis the contact pressure variation and displacements distribution. At the end of the paper there are presented the conclusions of the tests performed on the two tribometers.

Tribological tests of steel on polyamide 66, polyamide 46 type surface contacts

Improving the efficiency of mechanical transmissions is made, mostly, by finding new materials characterized through antifriction properties, specific reduced mass, wear resistance and by keeping the mechanical properties at high working temperatures (until 220 C). The paper presents the experimental tests for the surface type contacts between a steel made pin and different types of polyamides; finally there are presented the processing of the experimental data.

Study on the friction in steel/polyamide ball on disk type contacts

The paper presents the experimental study of the friction in the case of steel/polyamide ball on disk type contacts by considering as testing parameters the temperature, the load and the rotational speed. The tests are performed, for two types of polyamides, on a tribometer which allows rotational motions at small and high speeds, with controlled normal loads and temperatures. The tests begin with a one hour running-in at 500 rpm, at ambient temperature. After the running-in process there are made tests, for two types of polyamides at 90°C and 120°C, at loads of 3 N, 5 N, 7 N and at rotational speeds of 5 rpm, 1500 rpm and 3000 rpm. The results are indicating the polyamides behaviour at high temperatures with different loadings, at small and high rotational speeds. The conclusions of the paper offer recommendations regarding the applications of the tested polyamide materials according to temperature, loading and rotational speeds, in the case of ball on disk type contacts.

Effect of ultraviolet light irradiation and sandblasting treatment on bond strengths between polyamide and chemical-cured resin

The aim of this study was to evaluate the effects of ultraviolet light (UV) irradiation and sandblasting treatment on the shear bond strength between polyamide and chemical-cured resin. Three types of commercial polyamides were treated using UV irradiation, sandblasting treatment, and a combining sandblasting and UV irradiation. The shear bond strength was measured and analyzed using the Kruskal-Wallis test (α=0.05). Comparing shear bond strengths without surface treatment, from 4.1 to 5.7 MPa, the UV irradiation significantly increased the shear bond strengths except for Valplast, whose shear bond strengths ranged from 5.2 to 9.3 MPa. The sandblasting treatment also significantly increased the shear bond strengths (8.0 to 11.4 MPa). The combining sandblasting and UV irradiation significantly increased the shear bond strengths (15.2 to 18.3 MPa) comparing without surface treatment. This combined treatment was considered the most effective at improving the shear bond strength between polyamide and chemical-cured resin.

Sequence‐Specific DNA Recognition by Cyclic Pyrrole–Imidazole Cysteine‐Derived Polyamide Dimers

Pyrrole-imidazole (PI) polyamides bind to the minor groove of the DNA duplex in a sequence-specific manner and thus have the potential to regulate gene expression. To date, various types of PI polyamides have been designed as sequence-specific DNA binding ligands. One of these, cysteine cyclic PI polyamides containing two β-alanine molecules, were designed to recognize a 7 bp DNA sequence with high binding affinity. In this study, an efficient cyclization reaction between a cysteine and a chloroacetyl residue was used for dimerization in the synthesis of a unit that recognizes symmetrical DNA sequences. To evaluate specific DNA binding properties, dimeric PI polyamide binding was measured by using a surface plasmon resonance (SPR) method. Extending this molecular design, we synthesized a large dimeric PI polyamide that can recognize a 14 bp region in duplex DNA.

Thermal oxidation kinetics of additive free polyamide 6-6

Thermal aging of an additive free PA 6-6 has been elucidated at 90, 100, 120, 140, 150 and 160 °C in air-ventiled ovens by Fourier transform infrared spectrophotometry, viscosimetry in molten state and uniaxial tensile testing. Oxidation of methylene groups starts after a considerably shorter induction period but reaches a lower maximal rate than in additive free PE. Cleavage of C–N bonds constitutes the main source of chain scissions. It leads to the formation of aldehyde chain-ends and a catastrophic decrease in molar mass. Embrittlement occurs at a very low conversion ratio of the oxidation process, in particular when the concentration of aldehyde chain-ends reaches a critical value of [PH=O]F ≈ 5.6 10−3 mol l−1, corresponding to a critical value of the number average molar mass of MnF ≈ 17 kg mol−1. At this stage, the entanglement network in the amorphous phase is deeply damaged.A non-empirical kinetic model has been derived from the oxidation mechanistic scheme previously established for PE, but improved by adding elementary reactions specific to polyamides such as the rapid decomposition of unstable hydroxylated amide groups. This model describes satisfyingly the main features of the thermal oxidation kinetics of PA 6-6, but also of other types of aliphatic polyamides studied previously in the literature such as: PA 6, PA 12 and PA 4-6, as long as it is not controlled by oxygen diffusion. At the same time, it confirms the existence of an universal character for the thermal oxidation kinetics of aliphatic polyamides whatever their origin, i.e. their initial molar mass, crystallinity ratio, concentration of impurities, structural irregularities, etc.