Amorphous Polyamide Research Articles

Performance polyamides built on a sustainable carbohydrate core

Sustainably producing plastics with performance properties across a variety of materials chemistries is a major challenge—especially considering that most performance materials use aromatic precursors that are still difficult to source sustainably. Here we demonstrate catalyst-free, melt polymerization of dimethyl glyoxylate xylose, a stabilized carbohydrate that can be synthesized from agricultural waste with 97% atom efficiency, into amorphous polyamides with performances comparable to fossil-based semi-aromatic alternatives. Despite the presence of a carbohydrate core, these materials retain their thermomechanical properties through multiple rounds of high-shear mechanical recycling and could be chemically recycled. Techno-economic and life-cycle analyses suggest selling prices close to those of nylon 66 with a reduction of global warming potential of up to 75%. This work illustrates the versatility of a carbohydrate moiety to impart performance that can compete with that of semi-aromatic polymers across two important materials chemistries.

Effect of intermolecular hydrogen bonding strength on the dynamic fragility of amorphous polyamides.

Small-molecular-induced intermolecular hydrogen bonding (inter-HB) interactions were reported to increase the glass transition temperature (Tg) while decrease the dynamic fragility (m) of polymers. Herein, enthalpy relaxation parameters heat capacity jump (ΔCp) at Tg and enthalpy hysteresis (ΔHR) were investigated to help clarify the effect of macromolecular-induced inter-HB on Tg and m using amorphous polyamides as model polymers. The inter-HB strength was weakened by random copolymerization with varied chain rigidity, but was enhanced by decreasing steric hindrance. It was found that Tg and m increased after copolymerization due to the increased chain rigidity. Nevertheless, increasing steric hindrance leads to an increased Tg while anomalously reduced m. Further results found that m can be well correlated to Tg·ΔCp/ΔHR. ΔCp increases more significantly than ΔHR in co-polyamides, and thus the entropy change dominates the activation free energy of cooperative rearrangement. By contrast, ΔHR increases more significantly than ΔCp with increasing steric hindrance, and thus it is reasonable that Tg increases while m decreases. Most importantly, ΔCp and ΔHR decrease with increasing inter-HB strength regardless of the variation of Tg. These results indicate that the inter-HB strength may be very strong and insensitive to temperature in polyamides, thus behaving like physical cross-linking.

Calculation of the macroscopic mechanical properties of polyamide 6.6 underwater influence using molecular dynamics simulations, hyperelastic material modeling of the amorphous fraction, and homogenization schemes

AbstractThe macroscopic mechanical properties of water‐influenced polyamide 6.6 is analyzed by combining molecular dynamics simulation and experimental measurements of the media concentration and the degree of crystallization. The mechanical properties of α‐crystalline and amorphous polyamide 6.6 are analyzed separately by using molecular dynamics simulations. The anisotropic linear‐elastic stiffness tensor of the crystalline material is determined by unidirectional tensile and shear stress simulations. The deformations of amorphous simulation cells with different water concentrations are fitted in a compressible hyperelastic Yeoh material model. The media concentration of tensile specimens conditioned in air with 50% relative humidity at 23°C and in water is determined after different conditioning times. The degree of crystallization of the material is determined using Differential Scanning Calorimetry. Both parameters are used to estimate the macroscopic mechanical properties of polyamide 6.6. The homogenization schemes by Reuss and Ahzi are compared to calculate the resulting macroscopic properties. Tensile tests are used to validate the calculated properties: The weakening of the material due to water molecules in the amorphous phase can be shown, but it is underestimated in the methods used.

Molecular dynamics simulation of the relationship between molecular chain morphology and tensile response of amorphous polyamide

Molecular dynamics simulation of the relationship between molecular chain morphology and tensile response of amorphous polyamide

Amorphous polyamide m‐xylylenediamine‐adipic acid‐isophthalic acid copolymer (MXD6I): Evaluation of oxygen barrier property and free volume in high humidity condition

AbstractTo get insights into the excellent gas‐barrier properties of amorphous polyamide m‐xylylenediamine‐adipic acid‐isophthalic acid copolymer (MXD6I), free‐volume hole size and thermophysical properties of MXD6I were evaluated. The results from positron annihilation lifetime spectroscopy (PALS) showed that the free‐volume hole size of MXD6I—which was estimated from the ortho‐positronium (o‐Ps) lifetime and o‐Ps intensity—remained almost unchanged even with a high water‐absorption rate. This indicates that no significant structural changes occurred in MXD6I. In contrast, the free‐volume hole size of the semicrystalline polyamide MXD6 significantly increased due to water absorption. The glass transition temperature (Tg) of MXD6I decreased due to water absorption, but it remained higher than the ambient temperature. The molecular motion of MXD6I is likely to be limited even under high humidity conditions; therefore, nanoscale structural changes such as crystallization are unlikely. We found that the stable gas‐barrier properties of MXD6I can be attributed to its amorphous nature and a high Tg even in a water‐saturated state.

Reprocessing of Covalent Adaptable Polyamide Networks through Internal Catalysis and Ring-Size Effects.

Here, we report the introduction of internally catalyzed amide bonds to obtain covalent adaptable polyamide networks that rely on the dissociation equilibrium between dicarboxamides and imides. While amide bonds are usually considered to be robust and thermally stable, the present study shows that their dynamic character can be activated by a smart choice of available building blocks without the addition of any external catalyst or other additives. Hence, a range of polyamide-based dynamic networks with variable mechanical and viscoelastic properties have been obtained in a systematic study, using a straightforward curing process of dibasic ester and amine compounds. Since the dissociation process involves a cyclic imide formation, the correlation between ring size and the thermomechanical viscosity profile was studied for five- to seven-membered ring intermediates, depending on the chosen dibasic ester monomer. This resulted in a marked temperature response with activation energies in the range of 116-197 kJ mol-1, yielding a sharp transition between elastic and viscous behavior. Moreover, the ease and versatility of this chemistry platform were demonstrated by selecting a variety of amines, resulting in densely cross-linked dynamic networks with Tg values ranging from -20 to 110 °C. With this approach, it is possible to design amorphous polyamide networks with an acute temperature response, allowing for good reprocessability and, simultaneously, high resistance to irreversible deformation at elevated temperatures.

Synthesis and Characterization of Bio-Based Amorphous Polyamide From Dimethyl furan-2,5-dicarboxylate

In this research, bio-based polyamide (bio-PA) was synthesized from dimethyl furan-2,5-dicarboxylate and 1,3-cyclohexanedimethanamine by melt polymerization. The properties of bio-PA were analyzed by Fourier transform infrared spectrometer (FTIR), nuclear magnetic resonance (NMR), differential scanning calorimetry (DSC), X-ray diffraction (XRD), and thermal gravimetric analysis (TGA), respectively. The results show that this bio-PA presents high glass transition temperature (Tg) from 150 °C to 180 °C and poor crystallization due to the asymmetric rigid structure of cyclohexane and furan. Its molecular weight is low, ascribing to the large steric hindrance from cyclohexane and furan, and the side reaction of N-methylation and decarboxylation. Besides, the results of solubility reveal that this bio-PA can be dissolved in DMSO, DMF and DMAC.

Facile Synthesis of Thermoplastic Polyamide Elastomers Based on Amorphous Polyetheramine with Damping Performance.

Novel thermoplastic polyamide elastomers (TPAEs) consisting of long-chain semicrystalline polyamide 1212 (PA1212) and amorphous polyetheramine were synthesized via one-pot melt polycondensation. The method provides accessible routes to prepare TPAEs with a high tolerance of compatibility between polyamide and polyether oligomers compared with the traditional two-step method. These TPAEs with 10 wt % to 76 wt % of soft content were obtained by reaction of dodecanedioic acid, 1,12-dodecanediamine, and poly(propylene glycol) (PPG) diamine. The structure–property relationships of TPAEs were systematically studied. The chemical structure and the morphologic analyses have revealed that microphase separation occurs in the amorphous region. The TPAEs that have long-chain PPG segments consist of a crystalline polyamide domain, amorphous polyamide-rich domain, and amorphous polyetheramine-rich domain, while the ones containing short-chain PPG segments comprise of a crystalline polyamide domain and miscible amorphous polyamide phase and amorphous polyetheramine phase due to the compatibility between short-chain polyetheramine and amorphous polyamide. These novel TPAEs show good damping performance at low temperature, especially the TPAEs that incorporated 76 wt % and 62 wt % of PPG diamine. The TPAEs exhibit high elastic properties and low residual strain at room temperature. They are lightweight with density between 1.01 and 1.03 g/cm3. The long-chain TPAEs have well-balanced properties of low density, high elastic return, and high shock-absorbing ability. This work provides a route to expand TPAEs to damping materials with special application for sports equipment used in extremely cold conditions such as ski boots.

Influence of crystallinity and chain interactions on the electrical properties of polyamides/carbon nanotubes nanocomposites

AbstractThis work evaluates the effects of the crystallinity degree and π–π interactions between nanoparticles and a polymeric matrix on the electrical properties of polyamides and carbon nanotubes (CNT) nanocomposites. Two polymeric matrices were chosen; polyamide (PA) 6.6, a semi‐crystalline polymer, and PA 6I‐6T (here called aPA), a semi‐aromatic and amorphous polyamide. The PA 6.6 crystallinity degree did not significantly change. Both lamellar thicknesses, amorphous (La) and crystalline (Lc), were estimated through Small‐angle X‐ray scattering. La increased significantly when CNTs were added. Both nanocomposites presented almost the same percolation threshold. In aPA nanocomposites, the π–π interaction between aromatic groups of CNTs and aPA is not only responsible for a homogeneous CNT dispersion, but also creates a direct path, parallel to the electrodes, for electron conduction after the percolation limit. In the PA 6.6 nanocomposites, the CNTs preferably disperse in the amorphous regions, forming a conductive network.

Melt Polymerization of Acrylamide Initiated by Nucleophiles: A Route toward Highly Branched and Amorphous Polyamide 3

The melt polymerization of acrylamide initiated by nucleophiles allows for the preparation of polyamide 3 (PA 3) with a branching factor of about 1.5. The high share of branching units imparts a fully amorphous morphology featuring a low glass-transition temperature of 67 °C and renders the polymer water-soluble (430 ± 20 g/L at 25 °C). The disclosed method provides an easy, resource-efficient, and green access to a polymer interesting for applications in biological and biomedical systems. The obtained PA 3 was characterized by several NMR techniques, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, size exclusion chromatography, thermal analyses, and powder-X-ray diffractometry. Preparation and characterization of a 15N-marked polymer complemented the elucidation of the polymer structure. Mechanistically, the polymerization can be considered as an aza-Michael polymerization of acrylamide involving zwitterionic species as the key intermediates being responsible for the high degree of branching that can be controlled by the temperature at which the polymerization is carried out. The highest branching is obtained at 83 °C and decreases upon increasing the temperature.

Investigation of the interphase mechanisms and welding behaviour of fast-curing epoxy based composites with co-cured thermoplastic boundary layers

This study focuses on investigating thermoplastic polymers and their interphase behaviour with the fast-curing epoxy system Araldite LY3585/Aradur 3475. The three compatible thermoplastic polymers poly(methyl methacrylate) (PMMA), amorphous polyamide (PA12TR90), and poly(hydroxy ether) (phenoxy) were chosen to determine their affinity and interphase formation with the epoxy system. The final concept involves the use of a thermoplastic as a boundary layer on top of the epoxy to establish a connection between two joined parts by resistance welding. The thermoplastic boundary layer was generated by co-curing during the curing process. The experiments resulted in a high compatibility between phenoxy and PMMA in the selected epoxy system which leads to excellent mechanical properties after welding. Phenoxy showed the strongest joints, with an average lap shear strength of 25 MPa, demonstrating the high potential of this joining technique for industrial applications in the automotive and wind energy fields.

The Effect of Various Nanoclay Surface Modifications on the Thermal and Mechanical Properties of Amorphous Polyamide Nanocomposites

The addition of nanoclay within polymer matrix is anticipate to enhance the properties of the polymer system. Nonetheless, one of the key elements in property enhancements of a polymer nanocomposites is the surface modifications of the nanoclay. This is due to the affinity between polymer matrix and nanoclay is of important factors should be considered. In this study, amorphous polyamide were melt blended with different nanoclay grades with different surface modifications in order to evaluate the best clay grade for the polymer system. The thermal analysis carried out on the amorphous polyamide nanocomposites were carried out by means of differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) whereas the mechanical properties were investigated using tensile testing. It was observed that there were changes in the glass transition temperature (Tg) of the nanocomposites due to clay additions. Further, the storage modulus was found to increase as a result of nanoclay incorporation. The type of clay grades significantly affects the mechanical properties of the amorphous polyamide nanocomposites.

Study of Damage Mechanisms of Amorphous and Low Semicrystalline Polymers under Tensile Deformation by Ultrasmall-Angle X-ray Scattering

We investigate the damage mechanisms of amorphous and low semicrystalline semiaromatic polyamides, polyphthalamides (PPA), and two other amorphous polymers, polycarbonate (PC) and poly(methyl methacrylate) (PMMA), under tensile deformation. Ultrasmall-angle X-ray scattering (USAXS) experiments allow us to describe the beginning of the damage and the growth of crazes. Interpreting the results allows us to measure the volume fractions of damages, as well as their distribution of sizes at different stages of tensile deformation. Different modes of damage are observed. They are initiated by the nucleation of nanometric crazes around preexisting defects for PC, PMMA, and the amorphous polyamide. Then, the growth of these crazes is blocked by the strain hardening at the local level. By increasing the strain further, the growth of a second family of large crazes is observed for these three polymers before the yielding, which leads to fracture for PC and PMMA far in the macroscopic strain hardening regime, but not for the amorphous polyamide for which damaged is stabilized after the stress softening and in the ensuing necking regime for which strain hardening is also observed. In the case of two low semicrystalline polyamides, no damage is observed at all and deformation takes place by necking without damaging and breaking. We propose interpretations for these different behaviors.

Comparative performance of carbon nanotube and nanoclay on thermal properties and flammability behavior of amorphous polyamide/SEBS blend

AbstractMultiwall carbon nanotubes (CNT) or montmorillonite clay (MMT‐30B) were added to a poly(hexamethylene isophthalamide‐co‐terephthalamine) (an amorphous polyamide ‐ aPA) and styrene‐ethylene/butylene‐styrene graphitized with maleic anhydride (SEBS) blend, in different concentrations, in order to investigate the morphology, thermal properties and flammability behavior. Different nanoparticle localizations in the phase blend were observed through transmission electronic microscopy. CNT nanoparticles are localized in SEBS phase, and MMT‐30B nanoparticles in aPA phase. No significant changes were observed on transition temperatures and thermal stability with both nanoparticle additions. However, a slight increase on storage modulus for clay nanocomposites and a slight reduction for carbon nanotube nanocomposites were observed, due to their different phase localizations. Regarding flammability, CNT nanocomposites showed better performance as a flame retardant when compared to samples with MMT‐30B. Although the MMT‐30B nanocomposites could not be classified according to the UL‐94 criteria, no dripped flaming particles were observed, due to the a char barrier formation on the polymer surface. The CNT nanocomposites were classified according to the UL‐94 criteria as V‐2. The CNT's selective localization on the SEBS phase decreases its heat‐release rate, but no interconnected network structure was formed in the matrix to suppress the dripping flaming particles.

Improved abrasion resistance of textile fabrics due to polymer coatings

Textile fabrics are often subject to abrasion, starting from exposed parts of garments to a variety of technical textiles. Abrasion protection by usual coatings, however, can significantly decrease the water vapor transport through a fabric which is often not desired, especially in the case of garments. In our paper, we report on an approach to combine increased abrasion resistance with sufficient water vapor transport properties. For this, different polymers (poly(methyl methacrylate), acrylonitrile butadiene styrene, or amorphous polyamides) were coated on cotton and polyester woven fabrics. The results of abrasion tests against sandpaper show significantly increased abrasion resistance. The absolute evaporation resistance, measured by a Permetest testing device, was only slightly increased up to values still acceptable for typical garments. Images of all coatings by helium ion microscopy deliver an explanation for the measuring results. Polymer coatings on the polyester fabric resulted in a slight reduction of the hydrophobicity, while coating the cotton fabric severely increased the contact angles of the originally superhydrophilic material.

Simulation of osmotic pressure across an amorphous semipermeable membrane

Molecular simulations were employed to investigate osmosis for systems far from ideal conditions. Osmotic pressure was calculated for of a fluid mixture separated from a pure fluid by a fictitious semipermeable membrane using Gibbs ensemble Monte Carlo (GEMC) and compared with that of the two phases separated by a physical amorphous polyamide membrane using molecular dynamics. The calculated osmotic pressure for these two simulation set-ups was compared with various predictive models for a range of solute concentrations and solution densities. Both equilibrium-based theories, which are mostly limited in their applicability to near-ideal conditions or low solute concentrations, and non-equilibrium theories that extend to more concentrated solution conditions fared well against the GEMC simulation in their expected range, but did not adequately predict the osmotic pressure calculated according to simulations across the physical membrane for finite system size and under the limiting conditions considered. The discrepancies were particularly large for high solute concentrations and low solution densities. The observed differences are discussed in terms of solution inhomogeneities resulting from particle-membrane interactions.

Changing the Supramolecular Structure of Reinforcing Aramid Fibers upon Interaction with Water

Using the methods of sorption of water vapors and relaxation NMR spectroscopy, a comparative study of the features of the supramolecular structure of fibers has been performed based on crystallizing and X-ray amorphous aromatic polyamides. The quantitative ratios of crystalline, amorphous, and mesomorphic regions and their variation under the action of water have been determined.

Effect of the isothermal crystallization method on amorphous block copolymers of aromatic polyamides and their packing behavior in two‐dimensional films for screening of potential crystallization ability

The crystalline packing of polymers with high tendencies to form amorphous materials has been attained by controlling intermolecular interactions. Block copolymers of aromatic polyamides in which hydrogen‐bonding moieties are sparing and mostly substituted easily form amorphous materials because of steric hindrance and weak intermolecular affinities. Block copolymers of aromatic polyamides synthesized from 4‐(N‐methylamino)benzoic acid, terephthalic acid chloride, and poly(propylene glycol)bis(2‐aminopropyl ether) are commonly amorphous, regardless of unit length. Despite these copolymers not having distinct hydrophobic groups along the alkyl chain, aromatic rings in the same plane could be packed by π–π stacking by the method of two‐dimensional interfacial molecular films. The hard segment responsible for the c‐axis length increased the tilted angle depending on the chain length; as a result, the chain length was not dependent on the long spacing value. Actually, the layered period in organized films of aromatic polyamides did not depend on the segment length and always indicated a constant value. Isothermal crystallization was attempted for block copolymers of aromatic polyamides exhibiting potential packing ability by the method of organized molecular films. The analyzed glass transition temperature of the oligomer corresponding only to the block unit was adopted as the crystallization temperature. All amorphous polyamides used in this study crystallized after 24 h. A monoclinic packing structure and interactions between the few remaining hydrogen‐bonding moieties were suggested by a reciprocal lattice analysis. POLYM. ENG. SCI., 58:2019–2030, 2018. © 2017 Society of Plastics Engineers

Effect of water content on the thermal degradation of amorphous polyamide 6,6: A collective variable-driven hyperdynamics study

Thermal degradation under wet conditions is considered as an important aging mechanism in polyamide 6,6 (PA 6,6). The effect of water on thermal degradation of amorphous PA 6,6 is investigated at relatively low temperatures, varying from 1000 to 2000 K, using reactive force field molecular dynamics (MD) and collective variable-driven hyperdynamics simulations. The simulation of the related long-term chemical reactions is made possible thanks to the self-learning accelerated MD concept of hyperdynamics in combination with the corresponding accurate reproduction of the correct dynamics, consistent with unbiased MD simulations. The kinetics of cleavage reactions of the amide bonds in the backbone of the polymer chains, responsible for the thermal degradation of the polymer, is studied, and the influence of water content on the activation energy and pre-exponential factor of the cleavage reactions is explored. The results show that activation energy and pre-exponential factor are in agreement with experimental data. The proposed simulation framework not only estimates kinetic properties of thermal degradation that are consistent with experimental observations but also provides a predictive tool for studying long-term thermal degradation of PA 6,6.

Stable and ordered amide frameworks synthesised under reversible conditions which facilitate error checking

AbstarctCovalent organic frameworks (COFs) are network polymers with long-range positional order whose properties can be tuned using the isoreticular chemistry approach. Making COFs from strong bonds is challenging because irreversible rapid formation of the network produces amorphous materials with locked-in disorder. Reversibility in bond formation is essential to generate ordered networks, as it allows the error-checking that permits the network to crystallise, and so candidate network-forming chemistries such as amide that are irreversible under conventional low temperature bond-forming conditions have been underexplored. Here we show that we can prepare two- and three-dimensional covalent amide frameworks (CAFs) by devitrification of amorphous polyamide network polymers using high-temperature and high-pressure reaction conditions. In this way we have accessed reversible amide bond formation that allows crystalline order to develop. This strategy permits the direct synthesis of practically irreversible ordered amide networks that are stable thermally and under both strong acidic and basic hydrolytic conditions.