Aliphatic Nylons Research Articles

Marine sponges as bioindicators of pollution by synthetic microfibers in Antarctica

Different marine sponge species from Tethys Bay, Antarctica, were analyzed for contamination by polyester and polyamide microplastics (MPs). The PISA (Polymer Identification and Specific Analysis) procedure was adopted as it provides, through depolymerization and HPLC analysis, highly sensitive mass-based quantitative data. The study focused on three analytes resulting from the hydrolytic depolymerization of polyesters and polyamides: terephthalic acid (TPA), 6-aminohexanoic acid (AHA), and 1–6-hexanediamine (HMDA). TPA is a comonomer found in the polyesters poly(ethylene terephthalate) (PET) and poly(butylene adipate co terephthalate) (PBAT), and in polyamides such as poly(1,4-p-phenylene terephthalamide) (Kevlar™ and Twaron™ fibers) and poly(hexamethylene terephthalamide) (nylon 6 T). AHA is the monomer of nylon 6. HMDA is a comonomer of the aliphatic nylon 6,6 (HMDA-co-adipic acid) and of semi-aromatic polyamides such as, again, nylon 6 T (HMDA-co-TPA). Except for the biodegradable PBAT, these polymers exhibit high to extreme mechanical, thermal and chemical resistance. Indeed, they are used as technofibers in protective clothing able to withstand extreme conditions as those typical of Antarctica. Of the two amine monomers, only HMDA was found above the limit of quantification, and only in specimens of Haliclona (Rhizoniera) scotti, at a concentration equivalent to 27 μg/kg of nylon 6,6 in the fresh sponge. Comparatively higher concentrations, corresponding to 2.5–4.1 mg/kg of either PBAT or PPTA, were calculated from the concentration of TPA detected in all sponge species. Unexpectedly, TPA did not originate from PET (the most common textile fiber) as it was detected in the acid hydrolysate, whereas the PISA procedure results in effective PET depolymerization only under alkaline conditions. The obtained results showed that sponges, by capturing and concentrating MPs from large volumes of filtered marine waters, may be considered as effective indicators of the level and type of pollution by MPs and provide early warnings of increasing levels of pollution even in remote areas.

X-ray crystallographic and mutational analysis of the NylC precursor: catalytic mechanism of autocleavage and substrate hydrolysis of nylon hydrolase.

Nylon hydrolase (NylC), a member of the N-terminal nucleophile (Ntn) hydrolase superfamily, is responsible for the degradation of various aliphatic nylons, including nylon-6 and nylon-66. NylC is initially expressed as an inactive precursor (36 kDa), but the precursor is autocatalytically cleaved at Asn266/Thr267 to generate an active enzyme composed of 27 and 9 kDa subunits. We isolated various mutants with amino acid changes at the catalytic centre. X-ray crystallographic analysis revealed that the NylC precursor forms a doughnut-shaped quaternary structure composed of four monomers (molecules A-D) with D2 symmetry. Catalytic residues in the precursor are covered by loop regions at the A/B interface (equivalent to the C/D interface). However, the catalytic residues are exposed to the solvent environment through autocleavage followed by movements of the loop regions. T267A, D306A and D308A mutations resulted in a complete loss of autocleavage. By contrast, in the T267S mutant, autocleavage proceeded slowly at a constant reaction rate (k=2.8 × 10-5 s-1 ) until complete conversion, but the reaction was inhibited by K189A and N219A mutations. Based on the crystallographic and molecular dynamic simulation analyses, we concluded that the Asp308-Asp306-Thr267 triad, resembling the Glu-Ser-Ser triad conserved in Ntn-hydrolase family enzymes, is responsible for autocleavage and that hydrogen-bonding networks connecting Thr267 with Lys189 and Asn219 are required for increasing the nucleophilicity of Thr267-OH in both the water accessible and water inaccessible systems. Furthermore, we determined that NylC employs the Asp308-Asp306-Thr267 triad as catalytic residues for substrate hydrolysis, but the reaction requires Lys189 and Tyr146 as additional catalytic/substrate-binding residues specific for nylon hydrolysis.

New Aspects on the Direct Solid State Polycondensation (DSSP) of Aliphatic Nylon Salts: The Case of Hexamethylene Diammonium Dodecanoate.

The direct solid state polymerization (DSSP) of hexamethylene diammonium dodecanoate (PA 612 salt) was investigated for two different salt grades, fossil-based and bio-based. Aliphatic polyamide salts (such as PA 612 salt) are highly susceptible to solid melt transition (SMT) phenomena, which restrain the industrial application of DSSP. To that end, emphasis was given on reactor design, being the critical parameter influencing byproduct diffusion, amine loss and inherent DSSP kinetics. Experiments took place both at the microscale and the laboratory scale, in which two different reactors were tested in terms of bypassing SMT phenomena. The new reactor designed here proved quite successful in maintaining the solid state during the reaction. Scouting experiments were conducted in order to assess the effect of critical parameters and determine appropriate reaction conditions. Fossil-based PA 612 products proved to have a better end-group imbalance in comparison to bio-based ones, which is critical in terms of achieving high molecular weight. Finally, a real DSSP process was demonstrated, starting from PA 612 salt crystals and ending with PA 612 particles.

Structural Evolution Mechanism of Crystalline Polymers in the Isothermal Melt-Crystallization Process: A Proposition Based on Simultaneous WAXD/SAXS/FTIR Measurements.

Time-resolved simultaneous measurements of wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS) (and FTIR spectra) were performed for various kinds of crystalline polymers in isothermal melt-crystallization processes, from which the common features of the structural evolution process as well as the different behaviors intrinsic to the individual polymer species were extracted. The polymers targeted here were polyethylene, isotactic polypropylene, polyoxymethylene, aliphatic nylon, vinylidene fluoride copolymer, trans-polyisoprene, and poly(alkylene terephthalate). A universal concept of the microscopically viewed structural evolution process in isothermal crystallization may be described as follows: (i) the small domains composed of locally regular but more or less disordered helical chain segments are created in the melt (this important information was obtained by the IR spectral data analysis); (ii) these domains grow larger as the length and number of more regular helical segments increase with time; (iii) the correlation among the domains becomes stronger and they approach each other; and (iv) they merge into the stacked lamellar structure consisting of the regularly arranged crystalline lattices. The inner structure of the domains is different depending on the polymer species, as known from the IR spectral data.

Synthesis and characterization of copolyamides derived from novel aliphatic bio‐based diamine

ABSTRACTNovel aliphatic nylon 6 (PA6) copolyamides were produced by melt polymerization reaction of our newly synthesized aliphatic bio‐based diamine monomer: N1, N6‐bis (4‐aminobutyl) adipamide (BABA). The pertinent long‐chain polyamide salt (BABA/SA) monomer was isolated as white solid, utterly characterized for the first time. The chemical structure of BABA, BABA/SA salt, and copolyamides (PA6‐BABA/SA) were investigated by 1H NMR and FTIR spectroscopy. Depending on the chemical compositions, the viscosity and molecular weight of the copolyamides were in the range of 20 275–12 652 and 2.81–2.12 dL/g. With increasing BABA/SA salt weight content in the synthesized copolyamides, their melting temperatures (Tm) and glass transition temperatures (Tg) decreased from 211.0 to 164.0 °C and 66.6 to 43.5 °C. In addition XRD results were investigated revealing all the copolyamides transferred from α‐form to γ‐form. Interestingly, the as‐synthesized all copolyamides possess nearly similar thermal stability (Td = 452.2–449.5 °C) as neat PA6. Mechanical testing data revealed that with increasing BABA/SA salt content, the elongation at break of copolyamides are increased (726.19–429.34%), while the tensile strength are decreased. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46878.

Difference in the micro-dynamics mechanism between aromatic nylon and aliphatic nylon during water absorption: spectroscopic evidence.

The difference in the micro-dynamics mechanism between aromatic nylon and aliphatic nylon during water absorption was studied to explore the reason for the significantly smaller decline of barrier performance of poly(m-xylene adipamide) (MXD6) film than that of polyamide 6 (PA6) film under high humidity. Attenuated total reflection (ATR) FTIR, combined with scaling moving-window 2D correlation spectroscopy (scaling-MW2D) and generalized 2D correlation analysis, was used. The scaling-MW2D confirmed that the water absorption of MXD6 comprises two processes, designated process I (2.0-12.0 min) and process II (12.0-27.0 min). According to the sequential order of the functional groups' movement obtained from the generalized 2D correlation analysis, processes I and II undergo three and two steps, respectively. Process I is the process of water plasticizing MXD6, which primarily consists of hydrophilic groups forming hydrogen bonds with water molecules and the hydration of hydrophobic groups. Process II is the strong crystallization of MXD6 induced by water molecules, entailing the generation of the double hydrogen bond and the rearrangement of hydrophilic groups into the crystal lattice. However, for PA6, the results confirmed that its water absorption only had a single process with two steps, which was actually the plasticization of PA6 macromolecular chains by water molecules. Therefore, the reason for the barrier performance decline of the MXD6 film being significantly smaller than that of the PA6 film is that water molecules induced a large amount of new crystalline regions in the MXD6 matrix during plasticization.

Effect of adding a reactive plasticizer on the mechanical, thermal, and morphology properties of nylon toughened wheat gluten materials

ABSTRACTBlends of wheat gluten (WG) with up to 30% aliphatic nylon were prepared by mixing in 70% aqueous ethanol solution at 110 °C in a sealed reactor. After solvent removal and mechanical milling, rigid plaques were compression molded from the powdered blends. The microstructure of the molded plaques was studied via scanning electron microscopy. All compositions showed a phase separated morphology with seemingly poor compatibility between the two components. Up to 10% addition, the nylon was dispersed within the gluten matrix as discrete particles with an average diameter >10 μm. At higher nylon volume fractions there was evidence for the presence of gluten sub‐inclusions within the nylon phases. The dispersion of particles in a blend containing 10% nylon was improved and the particle size was decreased to roughly 5 μm by addition of an epoxy functionalized ethylene glycol oligomer. The additive simultaneously lowered the modulus of the WG matrix and appeared to improve the interfacial bonding between the gluten and the nylon. In cross‐sections of the ternary blends, fine filaments were observed spanning the gluten/nylon phases at the phase boundary. The compression molded plaques continued to exhibit brittle failure in mechanical bending tests characteristic of glassy gluten materials, however, the mechanical toughness was boosted to almost three times that of reference gluten plaques by the combined addition of the nylon and reactive plasticizer. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45931.

Study of Phase Transition by FTIR/SAXS/WAXD Simultaneous Measurement System

FTIR/SAXS/WAXD simultaneous measurement system has been developed for the study of the structural phase transition behaviors of soft materials including crystalline polymers. The system consists of a transmission-type miniature FTIR spectrometer set around the sample stage and the 2-dimensional detectors for WAXD and SAXS measurements in a synchronized mode, as shown in Figure. The infrared and X-ray beams can pass through the same position of a sample, which is set on the various types of equipments such as a stretcher, a heater, a temperature-jump cell for isothermal crystallization, etc. The system has been successfully applied to the studies of the structural evolution processes of crystalline polymers. For example, an intimate relationship has been clarified between the structural change in the crystal lattice and the change in lamellar stacking mode during the stress-induced phase transition of poly(tetramethylene terephthalate). Another example is the study of phase transition of aliphatic nylons in the heating and cooling processes. So far the aliphatic nylons were considered to show the phase transition at a so-called Brill transition point, but the simultaneous measurement revealed another phase transition occurring in a temperature region immediately below the melting point. The structural evolution has been also studied for the isothermal crystallization process of crystalline polymer from the melt, as seen in the case studies of polyethylene, nylon, polyester, and so on. The concrete description was made for the regularization process viewed from the various hierarchical levels of molecular chain conformation, chain packing mode, and lamellar stacking mode or higher-order structure.

Enzymatic hydrolysis of nylons: quantification of the reaction rate of nylon hydrolase for thin-layered nylons.

Nylon hydrolase degrades various aliphatic nylons, including nylon-6 and nylon-66. We synthesized a nylon-66 copolymer (M w = 22,900, M n = 7,400), in which a part of an adipoyl unit (32 % molar ratio) of nylon-66 was replaced with a succinyl unit by interfacial polymerization. To quantify the reaction rate of the enzymatic hydrolysis of nylons at the surface of solid polymers, we prepared a thin layer of nylons on the bottom surface of each well in a polystyrene-based micro-assay plate. The thickness of the nylon layer was monitored by imaging analysis of the photographic data. More than 99 % of the copolymer with thicknesses of 260 nm (approximately 600 layers of polymer strands) were converted to water-soluble oligomers by nylon hydrolase (3 mg enzyme ml(-1)) at 30 °C within 60 h. These results were further confirmed by TLC analysis of the reaction products and by assay of liberated amino groups in the soluble fractions. The degradation rate of the thin-layered nylon-6 was similarly analyzed. We demonstrate that this assay enables a quantitative evaluation of the reaction rate of hydrolysis at the interface between the solid and aqueous phases and a quantitative comparison of the degradability for various polyamides.

Properties of co-extruded nanoclay-filled aliphatic nylon (PA6)/linear low-density polyethylene and aromatic nylon (MXD6)/ linear low-density polyethylene multilayer films

In this study, coextruded multilayer films with aliphatic (polyamide 6) and aromatic (poly (m-xylene adipamide)) nylons as well as their in-situ polymerized nanocomposites with 4 wt% nanoclay, as an oxygen barrier layer (core), and a linear low-density polyethylene, as a moisture barrier layer (skin), were produced and characterized. Five-layer films were prepared by cast coextrusion and rapidly cooled using an air knife. Dynamic rheological measurements showed that the selected materials can be coextruded with a minimum interfacial instability between the melt flows in the feed block. Type of crystals, crystallinity and thermal transitions of layers were investigated using differential scanning calorimetry and modulated differential scanning calorimetry. The mechanical, optical, oxygen and water vapor barrier properties of the coextruded multilayer films were measured and discussed. Although the crystallinity of the poly (m-xylene adipamide) layer in the multilayer films was lower compared to the polyamide 6 layer, the impermeability to oxygen and water vapor was much better for the former multilayer films. In addition, substituting the neat polyamide 6 and poly (m-xylene adipamide) by their nanocomposites improved the oxygen barrier of the multilayer films by more than 50%. The series resistance model was not able to predict the barrier properties of the multilayer films due to the difference in polymer behavior for the single layer and multilayer, and boundary adjacent layer effects. The coextruded polyamide linear low-density polyethylene multilayer films showed higher toughness, tear and flex crack resistance compared to the poly (m-xylene adipamide)/linear low-density polyethylene samples. The pristine poly (m-xylene adipamide)-based multilayer film showed a lower haze compared to the polyamide 6 films due to very little crystallinity in the former.

Anionic Aliphatic Polyesteramide Copolymers: Evaluation of Dielectric Properties

This study looks at the effects on the dielectric behavior as result of the incorporation of ester sequences along the nylon 6 chains. The aliphatic polyesteramide copolymers and nylon 6 homopolymer were synthesized via anionic ring-opening copolymerization using the rotational molding technique by varying the ratio of the e-caprolactam (CLA) and e-caprolactone (CLO) comonomers. The ester units are correlated with biodegradable potential of polymers and the polar amide groups are able both to confer the polymer semicrystalline character and to be sensitive to the electric stimulus. The dielectric properties of the anionic nylon 6 and polyesteramides have been carried out as a function of frequency (100 Hz-106 Hz), at ambient temperature. Regarding to dielectric permittivity, e*(f), it was observed that the samples exhibit same behavior at increasing of the frequency. Experimental data revealed that the real part of electric modulus, M'(f) of the copolymers are many lower than those corresponding of the homopolymer. The presence of a single arc in the complex impedance plane plots confirms that, within the studied frequency range, the samples have a highly capacitive behavior. The results related to dielectric, crystalline and thermal properties of copolymers were compared with those obtained for homopolymer.

Morphology and mechanical properties of a novel amorphous polyamide/nanoclay nanocomposite

AbstractA novel amorphous polyamide/montmorillonite nanocomposite based on poly(hexamethylene isophthalamide) was successfully prepared by melt intercalation. Wide angle X‐ray diffraction and transmission electron microscopy showed that organoclay containing quaternary amine surfactants with phenyl and hydroxyl groups was delaminated in the polymer matrix resulting in well‐exfoliated morphologies even at high montmorillonite content. Differential scanning calorimetry results indicated that clay platelets did not induce the formation of a crystalline phase in this amorphous polymer. Tensile tests demonstrated that the addition of nanoclay caused a dramatic increase in Young's modulus (almost twofold) and yield strength of the nanocomposites compared with the homopolymer. The nanocomposites exhibited ductile behavior up to 5 wt % of nanoclay. The improvement in Young's modulus is comparable with semicrystalline aliphatic nylon 6 nanocomposites. Both the main chain amide groups and the amorphous nature of the polyamide are responsible for enhancing the dispersion of the nanofillers, thereby, leading to improved properties of the nanocomposites. The structure‐property relationship for these nanocomposites was also explored. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2605–2617, 2008

Thermal properties of aliphatic nylons and their link to crystal structure and molecular motion

The phase behavior of semicrystalline, aliphatic nylons is analyzed on the basis of differential scanning calorimetry, DSC, and quasi-isothermal, temperature-modulated DSC, TMDSC. The data of main interest are the apparent heat capacities, Cp, in the temperature range from below the glass transitions to above the isotropization. Based on the contributions of the vibrational motion to Cp, as is available from measurements in our laboratory, the ATHAS Data Bank, and multifaceted new TMDSC results, as well as on information on the crystal structures, NMR, molecular dynamics simulation of paraffin crystals, and quasi-elastic neutron scattering, the following observations are made: (a) In semicrystalline nylons the glass transition of the mobile-amorphous phase is broadened to higher temperature. The additionally present rigid-amorphous phase, RAF, undergoes a separate, broad glass transition at somewhat higher temperature. (b) The transition of the RAF, in turn, overlaps usually with an increase in large-amplitude motion of the CH2-groups within the crystals and latent heat effects due to melting, recrystallization, and crystal annealing. (c) Above the glass transitions of the two non-crystalline phases, Cp of the crystals approaches and exceeds that of the melt. This effect is due to additional entropy contributions (disordering) within the crystals, which may for some nylons lead to a mesophase. In case a mesophase is formed, the Cp drops to the level of the melt as is common for mesophases. (d) Some locally reversible melting is present on the crystal surfaces, but seems to be minimal for the mesophase. (e) The increasing amount of large-amplitude motion in the crystals is described as a third glass transition, occurring over a broad temperature range below the melting or disordering transition from crystal to mesophase.

Structural Phase Transitions of Aliphatic Nylons Viewed from the Simultaneous Measurements of WAXD and SAXS

AbstractStructural changes occurring in the high temperature region of doubly‐oriented nylon 10/10 sample have been investigated through the temperature‐dependent simultaneous measurements of wide‐angle and small‐angle X‐ray scatterings, and the results were compared with the infrared spectral data as well as the molecular dynamics simulation results. In the Brill transition region of 150–180 °C the methylene segments are conformationally disordered with keeping the intermolecular hydrogen bonds. During this phase transition the stacked lamellar structure did not change very much: the lamellae are tilted by ca. 34° from the draw axis and the long period is almost 160 Å. In the temperature region immediately below the melting point the molecular chains were found to be contracted by ca. 10% the original repeating period and the intermolecular hydrogen bonds were almost broken, causing the violent rotational and translational motions of the chains around the chain axis. At the same time the long period increased remarkably from 160 Å to 410 Å and the originally tilted lamellae stood up in parallel to the draw axis.

The glass transition of polymer crystals

The statement: “A solid is a condensed phase at a temperature below its glass transition”, is an operational definition. It leads to the corollary that for crystals to be solid, they must be below their glass transition. In this paper evidence for the usefulness of this definition is presented. It is based on the measurement of the glass transition of crystals in the presence of melting and crystallization. The experimental tool is temperature-modulated differential scanning calorimetry, TMDSC, which enables the measurement of heat capacity in the presence of irreversible latent heat of melting and crystallization. Not only is the expected change of the heat capacity during the first-order phase transition identified, but it was also discovered that in some flexible polymer crystals the glass transition of the crystal can occur at a lower temperature than the order/disorder process without a change in crystal structure. Typical examples for such behavior are seen in poly(oxyethylene), poly(oxytetramethylene), aliphatic nylons, and most likely also in polyesters, polyurethanes, and polymers with other functional groups, separated by longer CH 2-sequences. Such order/disorder transitions above the vitrification to a solid are well-known for the mesophases described as liquid crystals, plastic crystals, and condis crystals of small and large molecules, attesting for the universality of the operational definition.

Molecular dynamics simulation of the structural and mechanical property changes in the Brill transition of nylon 10/10 crystal

In order to confirm the structural features in the Brill transition of aliphatic nylons, molecular dynamics calculation has been performed at the various temperatures for nylon 10/10 crystal as a model. With an increase in temperature, the torsional motions around the methylene–amide and methylene–methylene bonds were activated. These motions became more remarkable above 420 K and the interconversion between trans and gauche forms occurred frequently, resulting in the disordered conformation of the methylene sequences and the pseudo-hexagonal packing of these parts. During such a drastic structural disordering, however, the hydrogen bonds were kept alive although the bond strength became weaker. These calculations were found to be consistent with the experimental results by the temperature-dependent X-ray diffraction and infrared spectral measurements. The Young's modulus along the chain axis was also calculated as a function of temperature: it decreased remarkably from 250 GPa at 0 K to 180 GPa at 300 K due to a small contraction of the skeletal chain by only about 0.2–0.5% through the torsional motion of the skeletal chains, and the modulus decreased furthermore to 80 GPa at 550 K because of the larger conformational disordering of the skeletal chains. The Young's modulus in the direction perpendicular to the chain axis was also found to decrease remarkably in parallel to the change of the chain packing mode.

Polymer concepts in microscopically‐viewed phase transition behavior of crystalline polymers

AbstractStructural evolution process in crystalline phase transition, isothermal crystallization from melt and solvent‐induced crystallization has been investigated for crystalline polymers on the basis of the time and/or temperature dependence of small‐angle X‐ray scattering (SAXS), wide‐angle X‐ray scattering (WAXS) and infrared/Raman spectra. As examples of isothermal crystallization study, polyethylene and polyoxymethylene were investigated. As for polyoxymethylene, the time‐resolved infrared spectral measurement clarified the appearance of infrared bands characteristic of folded chain crystal (FCC) in the early stage of crystallization process, followed by the detection of infrared bands characteristic of extended chain crystal (ECC) in a later stage. From the time‐resolved SAXS measurement, the stacked lamellar structure of ca. 14 nm long period was detected at first and it was followed by an appearance of the new lamellae in the amorphous region sandwiched between the original lamellae, resulting in the tightly stacked lamellar structure of 7 nm long period. The timing of detecting the SAXS 14 nm peak was almost the same with the observation of infrared FCC bands and the SAXS 7 nm peak with the infrared ECC band. This correspondency allowed us to speculate that some chains bridging several lamellae became fully extended when the new lamellae were formed in the amorphous region sandwiched between the original lamellae. As a result the ECC‐like structural parts were formed, giving the ECC infrared bands. As other examples, the Brill transition of aliphatic nylons and the solvent‐induced crystallization of syndiotactic polystyrene have been reviewed.

Structural Changes in Phase Transitions of Nylon Model Compounds. 1. Transition Behavior of Model Compounds of R-NHCO-R‘ Type

To clarify the essential features of Brill transition of aliphatic nylons, structural changes have been investigated by X-ray diffraction and infrared spectroscopic methods for the compounds CH3(CH2)10NHCO(CH2)9CH3 (designated as N11) and CH3(CH2)9NHCO(CH2)8CH3 (N10) which were assumed to be the simplest models of nylons 11/11 and 10/10, respectively. Depending on the preparation conditions, N11 crystallized to the α and γ forms and N10 to the α form at room temperature. Infrared and X-ray diffraction data clarified that the α form took essentially the same chain packing structure as that of the α form of parent nylons, in which the all-trans methylene segments were packed in a triclinic subcell and the amide groups were connected by intermolecular hydrogen bonds to form a sheet structure and these sheets were stacked by a weak van der Waals force. In the DSC thermograms, the α form of N10 and N11 showed two main endothermic peaks in the Brill transition (ca. 50 °C) and melting regions. The temperature re...

Structural change in the Brill transition of Nylon m/ n (2) conformational disordering as viewed from the temperature-dependent infrared spectral measurements

The structural changes in the Brill transition of aliphatic Nylons m/ n have been investigated by carrying out the temperature-dependent infrared spectral measurement for Nylon 6/10 –[–NH–(CH 2) 6–NHCO–(CH 2) 8–CO–] n –, Nylon 6/12 –[–NH–(CH 2) 6–NHCO–(CH 2) 10–CO–] n – and Nylon 10/10 –[–NH–(CH 2) 10–NHCO–(CH 2) 8–CO–] n –. They took the crystal structure of α-form at room temperature. By heating the samples up to the Brill transition temperature region, the conformation of the methylene segments was found to change remarkably from the all trans-zigzag form to the disordered conformation constructed by shorter trans-zigzag segments combined with some gauche bonds. At the same time, the twisting motion was found to occur around the CH 2–amide bonds. During this order-to-disorder transition of molecular conformation, the intermolecular hydrogen bonds were kept alive although they were weaker gradually with increasing temperature. The methylene segments sandwiched by NH groups [NH(CH 2) m NH] were found to be disordered more remarkably than those of CO(CH 2) n CO sequence due to the difference in torsional energy barriers around the CH 2–NH and CH 2–CO bonds.

Effect of thermal ageing on Nylon 6,6 fibres

The residual effects of thermal ageing at various temperatures on fibres of the aliphatic polyamide Nylon 6,6 have been studied. Both crystal and macro structural characteristics manifest the residual effects. The former category includes changes in intensity, 2θ values and half width. The macro changes include introduction of surface damages in the form of holes, material deposits etc. The fibre also undergoes reduction in weight. The structural changes suggest deterioration in the initial tensile characteristics which has been verified experimentally. A direct correlation between the tensile strength and the angular separation of the equatorial reflections has also been observed.