Polyamide Hydrolysis Research Articles

The catalytic mechanism and limiting factor of polyamide hydrolysis for chemical recycling: the classic hydrolysis of polyamide 4

The catalytic mechanism and limiting factor of polyamide hydrolysis for chemical recycling: the classic hydrolysis of polyamide 4

Revisiting the alkali hydrolysis of polyamide nanofiltration membranes

High flux membranes are required for energy-efficient separation processes. Chemical treatments of conventionally prepared polyamide thin film composite (TFC) membranes, including alkali hydrolysis of polyamide, have been found suitable for achieving higher membrane permeance without significant loss in solute rejection. However, polyamide-based membranes are known to be stable in alkaline conditions during chemical cleaning. Hence, we revisited the possibility of alkali hydrolysis post-treatment of the polyamide layer of a commercial nanofiltration membrane upon short-term exposures at a wide range of pH exceeding the recommended value (up to pH 13). We optimized the post-treatment parameters using the Box Behnken design (BBD) of Response Surface Methodology (RSM) to achieve maximum pure water permeance. We observed that the pure water permeance (PWP) of the post-treated (optimum) membrane increased to 21.1 ± 0.4 LMH/bar from 12.3 ± 0.4 LMH/bar of the pristine membrane while retaining the same salt rejection. However, the chemical composition, thickness, surface charge, and pore size of the polyamide layer in the pristine and post-treated membranes were found identical. Hence, it was concluded that the increase in PWP might be attributed to the physical restructuring of the polyamide layer or restructuring of the support layer and interface, making the membrane more permeable, rather than hydrolysis of the polyamide layer.

Release mechanisms for PA6 nanocomposites under weathering conditions simulating their outdoor uses

The increased use of polymer nanocomposites in different applications could lead to potential nanofiller release into different human and environmental compartments and consequently, increase the exposure of human and environmental species to nanomaterials. This study aims at determining how the inclusion of nanofillers with diverse chemical nature (SiO2, TiO2, ZnO, multiwalled carbon nanotubes and two nano-organoclays) in polyamide 6 composites influences the nanomaterial release during the use of these products. The different nanocomposites were exposed to accelerated ageing processes, simulating outdoor conditions, through irradiation with UV light under a combination of dry-wet cycles. Release monitoring consisted of nanocomposites characterisation, run-off waters collection and released materials quantification and characterisation. The study confirmed that the chemical surface nature of the nanofiller strongly impacts on polymer degradation, in some cases enhancing its protection and in others promoting polyamide hydrolysis and/or photo-degradation processes. Polymer degradation and nanomaterial-polymer compatibility are the main determinants for the release and consequent exposure to nanofillers.

Quantitative assessment of the iron-catalyzed degradation of a polyamide nanofiltration membrane by hydrogen peroxide

Peracetic acid (PAA)/hydrogen peroxide (H2O2) is of interest as a substitute disinfectant and antifouling agent for chlorine in water treatment systems using reverse osmosis (RO) and nanofiltration (NF). To maximize disinfection while minimizing damage to membranes, it is necessary to understand the factors that govern the oxidation of the polyamide (PA) separation layer by peroxides. This study evaluated the tolerance of a NF membrane to H2O2 exposure and quantified the catalytic effect of different forms of iron on membrane oxidation and the inhibitory effect of radical quenching by methanol (MeOH) and tert-butanol (t-BuOH). The experimental approach involved exposing a swath of a nanofiltration membrane (NF90, Dow) to high concentrations of H2O2 (up to 102 g/L) without and with the presence of goethite and ferric oxide and colloidal iron. Membranes were tested by quantifying flux and rejection in a gas-pressured, non-metallic, 50 mL-stirred ultrafiltration cell (Amicon). Membranes oxidation was studied using X-ray photoelectron (XPS) and Fourier Transformed Infrared Spectroscopy (FTIR). In pure water without iron oxides, the membrane tolerated H2O2 concentrations of 3000 mM (102,000 mg/L) for more than 168 h (CTmax > 1.7 × 107 mgˑh/L (ppm-h)). All forms of iron accelerated membrane oxidation causing PA hydrolysis and membrane failure. In the presence of 90 mg goethite (6.72 mg/cm2) at an exposure of 2 mM initial H2O2, goethite decreased the rejection of NaCl to 70% and ACE to 85% in 24 h. Rejection loss accelerated with increasing H2O2 concentration and goethite loading. If MeOH and t-BuOH concentration were two times that of the H2O2 concentration, membrane degradation was significantly inhibited apparently because the alcohols acted as a sink for •OH and other reactive species. Findings are in agreement with studies that indicated activation of H2O2 by iron oxides via a Fenton-like mechanism.

MEG Effects on Hydrolysis of Polyamide 66/Glass Fiber Composites and Mechanical Property Changes.

Polyamide66 (PA66) hydrolysis affects the mechanical properties of Polyamide66/glass fiber (PA66/GF) composites. We investigated the effects of monoethylene glycol (MEG) on the degree of hydrolysis and mechanical properties of four different commercial PA66/glass fiber composites. Using pyrolysis-gas chromatography/mass spectrometry (py-GC/MS), we identified the byproducts of PA66 composite hydrolysis: carboxylic acid and alkylamine substances. The degree of hydrolysis increased as the immersion time in MEG increased. However, the tensile and flexural properties decreased due to hydrolysis. The tensile strength decreased by 42–45%; however, elongation increased by 23–63%. When PA66 absorbs MEG at 130 °C, the materials molecular chains’ bonding force decreased, resulting in increased elongation.

Effect of enzymatic hydrolysis on developing support of polyamide woven fabric for enzyme immobilization

Polyamide fiber has been considered as a suitable support for enzyme immobilization because of its low cost, chemical and mechanical properties and ready availability in a number of different forms. In particular, polyamide fabric has highly specific surface and good elasticity. The present study aims to develop an immobilization support from polyamide fabric and to establish the optimum immobilization conditions for laccase. For this, the enzymatic hydrolysis process was introduced to the hydrolysis of polyamide, creating amino groups that immobilize enzyme molecules. When polyamide fabric was hydrolyzed by bromelain during enzymatic hydrolysis, the highest immobilization yield (68 ± 0.7%) and relative activity (95 ± 0.52%) of immobilized laccase were obtained. For successful enzyme immobilization, the optimal glutaraldehyde crosslinking conditions were pH of 9.0 with 10% (v/v) of glutaraldehyde concentration for 240 min at 45℃. The most favorable immobilization conditions were as follows: pH of 6.0 with 35% (owf) of laccase concentration for 600 min at 4℃. Under the optimum treatment conditions, the pH and thermal stability of immobilized laccase were improved. After 20 days of storage, the immobilized laccase on enzymatic hydrolyzed polyamide fabric retained approximately 30% of its initial activity. Furthermore, the immobilized laccase indicated potential reuse over 10 use cycles. The structural changes of polyamide fabric according to treatment processes were demonstrated by Fourier transform infrared spectroscopy. The changes of surface morphology were measured by scanning electron microscopy according to the multi treatment steps.

Enhanced hydrothermal conversion of caprolactam from waste monomer casting polyamide over H-Beta zeolite and its mechanism

The exploration of reaction process plays an important role in the mechanism study of plastic hydrothermal recovery. This work investigated the procedure of the efficient heterogeneous catalytic hydrolysis of waste monomer casting polyamide in subcritical water and then proposed the depolymerization mechanism. The solid products obtained before the complete hydrolysis became less thermodynamically stable than raw polyamide material as the degree of hydrolysis increased. According to the characterization of liquid phase products, the monomer casting polyamide was depolymerized to cyclic and linear oligomers, which were further converted to the target monomer ε-caprolactam by gradual chain scission. As firstly applied in the waste polyamide hydrolysis, the zeolite H-Beta was proved a promising solid catalyst which increased the degree of hydrolysis from 31% to more than 60% (300°C, 50min) and facilitated to produce the intermediates with specific structure due to the microporous topology. The kinetic analyses showed that compared to the formation step of oligomers, the hydrolysis of oligomers into the monomer was the critical step which could be accelerated by the zeolite H-Beta catalyst.

Polyamide hydrolysis accelerated by small weak organic acids

It is well known that acidity, pH, of a solution accelerates the hydrolysis of soluble amides. Here we describe the unexpected result that weak small organic acids at low concentrations hydrolyze a polyamide at rates approximately twice that of a water HCl solution of the same pH. The effect of three small organic acids in dilute solutions, acetic, propanoic, and butanoic was studied. It is observed that the effect on the hydrolysis rate increases as the organic acid gets weaker. Butanoic, the weakest acid, has the strongest effect on increasing the hydrolysis rate. Measurements on the concentration of these acids in the polyamide reveal that there is a selective desire for these weak organic acids to diffuse into the polyamide. The concentration of these acids in the polyamide is found to be several multiples of the concentration in the water environment. And the acid concentration is highest for butanoic. The hydrolysis rate is shown to be governed by solubility, not pH of the water environment. The longer hydrocarbon tail on the carboxylic group increases its compatibility with the polyamide's monomer structure. Results are reported on the hydrolysis of polyamide-11 polymerized from aminoundecanoic acid, both neat and a commercial plasticized composition, placed in water at 100 °C and 120 °C under anaerobic conditions in high pressure glass tubes.

Effects of hypochlorous acid exposure on the rejection of salt, polyethylene glycols, boron and arsenic(V) by nanofiltration and reverse osmosis membranes

The separation layer of polyamide-based (PA) thin film composite (TFC) membranes can be modified by active chlorine species. The PA-TFC membranes, NF90, BW30 and NF270, were exposed to different concentrations of sodium hypochlorite (NaOCl) at pH 5 for 24 h. Elemental composition obtained from X-ray Photoelectron Spectroscopy (XPS) showed that the chlorine content in the PA layer increased with the chlorine concentrations. Treatment of membranes with 10 ppm Cl increased the membrane hydrophilicity. By contrast, when treated with 1000 ppm Cl or more, the membranes became less hydrophilic. Water permeability values for all 3 membrane types declined with increased chlorine concentrations. Filtration of polyethylene glycols (PEGs) with molecular weights of 200, 400 and 600 Daltons (Da) was performed to investigate the influence of chlorine treatment on membrane molecular weight cut off (MWCO) and rejection by size exclusion. Treatment with 10 and 100 ppm Cl lowered the MWCO while treatment with higher concentrations increased the MWCO. All chlorinated membranes experienced higher NaCl rejection compared to virgin ones. The performance of NF90 was tested with respect to the rejection of inorganic contaminants including boron (H3BO3) and arsenic (H2AsO4−). The boron rejection results paralleled PEG rejection whereas those for arsenic followed NaCl rejection patterns. The changes in membrane performance due to chlorine treatment were explained in terms of competing mechanisms: membrane tightening, bond cleavage by N-chlorination and chlorination promoted polyamide hydrolysis.

Degradation of Poly(glycoamidoamine) DNA Delivery Vehicles: Polyamide Hydrolysis at Physiological Conditions Promotes DNA Release

Poly(glycoamidoamine)s (PGAAs) are a group of efficient and degradable gene delivery vehicles that consist of three main functionalities: carbohydrate groups, secondary amines, and amide bonds. Herein, we have created nonhydroxylated models to these structures by polymerizing oxylate, succinate, or adipate groups with pentaethylenehexamine. The resulting polymers (named O4, S4, and A4, respectively) were created to understand how the absence of hydroxyl groups and changes in the amide bond spacing affect polymer degradation, plasmid DNA (pDNA) complexation, toxicity, and transfection efficiency in vitro. An additional model was also created that retains a galactaramide unit, but we have replaced the secondary amines with ethyleneoxide units (GO2) to understand the effects of the amine groups on polymer degradation. We have found that the secondary amines and hydroxyls are necessary to facilitate rapid degradation of these polymers, and analogues lacking hydroxyls or amines did not degrade over the time course of the study. Through electron-withdrawing and hydrogen bonding, the hydroxyls appear to activate the carbonyls of the amide bond to hydrolysis via an inductive electron withdrawing effect. Through titration experiments, PGAA degradation appears not to affect the polymer buffering capacity. Furthermore, we have found that PGAA degradation may enhance gene expression by releasing pDNA from polyplexes (polymer-pDNA complexes) and, thus, exposing it to undergo transcription and translation. The difference in the optimal pH that promotes degradation of the PGAAs and the hydroxyl-free analogues may prove to be a useful means to achieve pH-regulated DNA release from polyplexes by specifically modulating the chemical structures.

マイクロ波照射を利用した環境適合型ポリアミド系高分子の合成と加水分解

マイクロ波照射を利用した環境適合型ポリアミド系高分子の合成と加水分解

A novel aryl acylamidase from Nocardia farcinica hydrolyses polyamide

An alkali stable polyamidase was isolated from a new strain of Nocardia farcinica. The enzyme consists of four subunits with a total molecular weight of 190 kDa. The polyamidase cleaved amide and ester bonds of water insoluble model substrates like adipic acid bishexylamide and bis(benzoyloxyethyl)terephthalate and hydrolyzed different soluble amides to the corresponding acid. Treatment of polyamide 6 with this amidase led to an increased hydrophilicity based on rising height and tensiometry measurements and evidence of surface hydrolysis of polyamide 6 is shown. In addition to amidase activity, the enzyme showed activity on p-nitrophenylbutyrate. On hexanoamide the amidase exhibited a K(m) value of 5.5 mM compared to 0.07 mM for p-nitroacetanilide. The polyamidase belongs to the amidase signature family and is closely related to aryl acylamidases from different strains/species of Nocardia and to the 6-aminohexanoate-cyclic dimer hydrolase (EI) from Arthrobacter sp. KI72.

Surface hydrolysis of polyamide with a new polyamidase from Beauveria brongniartii

Twelve fungi were screened for the potential of their extracellular enzymes to increase the hydrophilicity of polyamide (PA) materials. The most pronounced increase in hydrophilicity was found for enzymes from Beauveria brongniartii and B. bassiana. The 55 kDa polyamidase from B. brongniartii was purified using ultrafiltration, anion exchange chromatography and size exclusion chromatography. This polyamidase was able to hydrolyse adipic acid bishexylamide and various typical amidase substrates, but did not show protease activity. In contrast, the 27 kDa protease from B. brongniartii did not show activity on PA. The improvement of hydrophilicity due to hydrolysis with the 55 kDa polyamidase from B. brongniartii based on rising height was 11 cm for PA 6 Perlon fibres and 5 cm for PA 6.6 Nylon. The drop dissipation measurement corroborated the improvement of the hydrophilicity giving 7 s and less than 1 s for the two enzyme treated materials, respectively. The surface tension s of Perlon increased from 46.1 to 67.4 mNm after enzyme treatment.

Laser reflectometry to investigate adsorption–desorption of poly(styrene sulfonate) onto polyamide 6.6

The adsorption of poly(styrene sulfonate) (PSS) on polyamide 6-6 was investigated using fixed angle laser reflectometry. The appropriate polyamide film thickness for an accurate analysis was first determined theoretically. Polyamide films were further prepared at controlled thickness using dip-coating processes and characterized. The adsorption of PSS was measured at pH 3 on dip-coated films as a function of time and polymer concentration. The adsorption rate at very low polymer coverage revealed diffusion limited adsorption. At and above pH 10, the PSS adsorption/desorption was difficult to evaluate. At and above pH 11.5, the hydrolysis of polyamide produced artifacts that prevent any meaningful measurements. This work showed that reflectometry is an interesting analytical tool in the in situ study of the functionalization of organic materials and to investigate the stability of the films produced.

Molecular weight distribution and mass changes during polyamide hydrolysis

Samples of polyamide 6, 11 and 12 have been hydrolysed at various temperatures ranging from 80 to 120°C in water baths of pH ranging from 0 to 4. The polymer degradation was monitored by steric exclusion chromatography (SEC), viscometry and gravimetry. SEC data indicate that the polydispersity of the polyamides tested does not increase during ageing. This can be considered as proof of the homogeneity of the reaction. Average molecular weight data from SEC or viscometry appear to be consistent with a random chain scission process, however gravimetry (at least in the case of relatively soft conditions, for instance pH ≥ 4) indicates a high monomer yield. These apparently contradictory results are tentatively explained by the equilibrated character of hydrolysis. Acid—amine pairs resulting from hydrolysis events would recombine easily when both belong to macromolecular fragments. When one fragment is the monomer or a low oligomer, it can escape easily from the cage and the corresponding recombination yield is decreased. The monomer extraction by water complicates the gravimetric behaviour, especially in the most severe hydrolysis conditions.

Amine/anhydride reaction versus amide/anhydride reaction in polyamide/anhydride carriers

AbstractPolyamide 6 (PA6) and poly(metaxylene adipamide) (PAmXD6) were blended in a batch mixer with anhydrides such as phthalic anhydride, n‐octadecyl succinic anhydride, and anhydride‐grafted ethylene propylene rubber. The melt viscosity, the solution viscosity, and chain end concentration were studied during the mixing. PA was first mixed 5 min to get an homogeneous melt prior to the anhydride addition. The introduction of the anhydride to the molten polyamide resulted in large decreases of melt and solution viscosities and of amine chain end concentrations. The anhydride units react with amine chain ends to form imide groups. The resulting low amine chain end concentration causes hydrolysis reaction to maintain the condensation equilibrium. As a consequence an increased carboxylic chain end concentration is observed. The imide concentration was studied by IR. It was shown that when most of the amine chain ends are consumed, the remaining anhydride reacts with amino groups formed by polyamide hydrolysis. © 1995 John Wiley & Sons, Inc.

Quantum-Chemical Calculation of the Effect of Stress upon Reactions in Polymers

Abstract The change of energy barrier of stretched model molecules is calculated using semi-empirical quantum-chemical method MNDO. The reactions studied include hydrogen abstraction from polyolefin chains and hydrolysis of polyamide and polyester molecules. Susceptibility of reactions to strain is evaluated. Comparison of calculated results with published experimental data on reactivity of stressed polymers shows that semi-empirical calculations provide reasonable evaluation of stress influence on kinetics of polymer reactions.

Hydrolysis and other phenomena affecting structure and performance of polyamide 6 membrane

The rate of hydrolysis of polyamide 6 in membrane casting solution containing strong mineral acid has been studied by determining changes in molecular weight, as estimated from dilute solution viscometry measurements. Hydrolysis is shown to be first order with a long half-life of about 250 days. A two-step dissolution process for polyamide 6 is proposed. The effect of extended dope maturation time upon polyamide 6 membrane preparation and performance has been examined. At short maturation times where protonation of polymer chain is occurring, flux is relatively low. A major increase in flux occurs after about 10 h, when protonation appear complete and hydrolysis has begun. Hydrolysis reduces polymer chain entanglement, and so quite different mechanisms for membrane formation exist as dope maturation time proceeds. With chains less than the critical entanglement length, nodular top layer membranes and alveolar walls lead to high water flux. However, such membranes are quite fragile.

Kinetic study of hydrolysis of butadiene-nitrile rubber in alkaline medium

A kinetic study was made of the interaction of butadiene-nitrile rubber dissolved with alkali in o-xylene. It was found that, in the complex process of hydrolysis of polyaer molecules, hydrolysis of the polyamide obtained is the decisive stage. The activation energy of hydrolysis of polyamide was determined at temperatures of 125 to 145°.