Polyamide 4 Research Articles

Microstructure and Crystal Modulus of Polyamide 4 α-form in the Direction Parallel to the Chain Axis

Polyamide 4 (PA4) is a lactam-based aliphatic synthetic polymer with promising properties and admirable biodegradability. In this study, oriented PA4 fibers were fabricated by dry spinning followed by thermal drawing. Elastic modulus (El) of the crystalline regions (crystal modulus) of PA4 fibers in the direction parallel to the chain axis was evaluated from the X-ray diffraction peak shift owing to the tensile stress. The apparent El value of PA4 is 67 GPa for meridional 004 reflection and 119 GPa for 0010 reflection, respectively. The reason for the different El is that the decrease of crystallite size of PA4 by the applied stress brought extra shifts of 004 reflection peak to lower angle based on the Laue factor. In contrast, 0010 reflection peak received less effects from this effect, and the El value of 119 GPa obtained from 0010 reflection was considered to be a reliable value. The observed El value of PA4 is much lower than the calculated values assuming fully extended planar zigzag skeleton for PA4. Thus the low El value is attributed to the highly contraction (-1.9%) from the fully extended conformation as observed for another polyamides.

Kinetic analysis of PA4 thermal degradation: Thermal stability with respect to crystallinity

Polyamide 4 (PA4) has garnered considerable attention due to its fully bio-based origin and biodegradability as a high-performance polyamide. Nevertheless, thermal degradation during the melting process impedes thermal processing, thereby constraining its potential for engineering plastics applications. To clarify the thermal degradation reactions of PA4 amidst intricate physical and chemical transformations, establishing a theoretical foundation for the thermal stability modification, we conducted a comprehensive analysis of PA4 thermal degradation coupled with crystallization, considering kinetics and reaction mechanisms. Calculation of reaction activation energies and mechanism functions revealed that PA4 pyrolysis is a two-stage compound process, with distinct degradation mechanisms attributed to the crystalline and amorphous regions. Additionally, the thermal degradation mechanism of the PA4-CaCl2 composite system at varying crystallinity levels was illustrated. The incorporation of Ca strengthens intermolecular forces in the samples, leading to an increased overall stability. Simultaneously, a notable alteration in the reaction mechanism was observed in the crystalline zone lacking the Ca phase.

Marine bacteria have multiple polyamide 4-degrading enzymes.

Polyamide 4 (PA4) is expected to solve the issue of marine plastic pollution due to its excellent mechanical properties and biodegradability. In this study, to reveal the mechanism of PA4 biodegradation in the marine environment, we isolated 5 strains of PA4-degrading bacteria belonging to Aliiglaciecola, Dasania, and Pseudophaeobacter from a marine environment. The isolated 5 strains are novel PA4-degrading bacteria that are phylogenetically distinct from those isolated in previous studies. In addition, we compared the PA4-degrading activities and structures of the PA4-degrading enzymes secreted by the 5 strains and PA4-degrading strains isolated in our previous study. The PA4-degrading activity in the supernatant of the cultivation solutions differed among the strains. Native-PAGE and zymography using a polyacrylamide gel containing a PA4 emulsion demonstrated that PA4-degrading enzymes are classified into no less than three types of structures. These results suggested that marine PA4-degrading bacteria have multiple PA4-degrading enzymes. Our findings will contribute to a better understanding of the microbial degradation of PA4 in the marine environment.

Crystallization behaviour of polyamide 4 and its effect on melting point

Polyamide 4 (PA4) has received widespread attention as a bio-based polyamide exhibiting biodegradability. However, the melting and degradation processes of PA4 occur simultaneously, making it difficult to perform thermal processing. To expand the difference between the melting point temperature (Tm) and the thermal decomposition temperature (Ttd), the crystallization and melting processes of PA4 were investigated to design strategies for regulating the crystallization. The isothermal crystallization and cold crystallization properties of PA4 were investigated with flash DSC. A special self-nucleation phenomenon which slowed the rate of recrystallization has been discovered. It confirms the significant differences in the morphology of crystals generated at differences temperatures. By controlling the crystallization process, the end-of-melt temperature (T95) was greatly reduced. Nucleation and crystal growth at different temperatures provided a low melting temperature (T95 = 246 °C), which was 20 °C lower than that for isothermal crystallization.

Exploring microbial degradation of polyamide 4 in soils: Unveiling degradation mechanisms, pathways, and the contribution of strain NR4

Evidence for microbial degradation of polyamide 4 (PA4) has previously been reported, but little is available on the specific strains and enzymes. The mechanism responsible for the degradation is still unknown. This study investigated the degradation behaviors of PA4 films in composted, garbage and campus soil. Various characterization methods were used to evaluate the changes in morphology, structure, crystallinity, and thermal properties of PA4 films during the soil biodegradation, to assess its degradation efficiency in four types of soils. The results showed that the highest degradation behavior of soil in composted soil that almost no residual films can be observed in this type of soil after 60 days, compared to those in garbage and campus soil. PA4 degradation resulting occurring in soils can enhance the population of certain beneficial microorganisms in the soil environment, such as Ensifer, Luteimonas, etc., which play a key role in nitrogen fixation, promoting plant growth, and carbon cycling. Moreover, a highly efficient single bacterium for PA4 degradation was isolated from the soil enriched and acclimated by PA4 films, named strain NR4. The complete genome of strain NR4 was sequenced to identify relevant enzyme-coding genes and metabolic pathways associated with PA4 degradation, ultimately leading to the proposal of a mechanism for PA4 biodegradation. The research not only examined how PA4 degrades in different types of soil but also suggested practical recommendations for promoting biodegradation of other products in the nylon family. The results obtained from the current study are essential in addressing environmental issues surrounding the buildup of non-biodegradable nylon items in the ecosystem.

Crystallization and Performance of Polyamide Blends Comprising Polyamide 4, Polyamide 6, and Their Copolymers.

Polyamide 4 (PA4) is a biobased and biodegradable polyamide. The high hydrogen bond density of PA4 bestows it with a high melting point that is close to its thermal decomposition temperature, thereby limiting the melt processing of PA4. In this study, PA4 was blended with polyamide 6 (PA6) and further modified with copolyamide 4/6 (R46). The effects of composition on the crystallization behavior of the blends were studied. The results demonstrated that the binary PA4/PA6 (B46) and ternary PA4/PA6/R46 (B46/R46) blends formed two crystalline phases (PA4- and PA6-rich phases) through crystallization-induced phase separation. With increasing PA6 content, the thermal stability and crystallinity of the B46 blend increased and decreased, respectively, and the contribution of PA6 toward the crystallization of the PA4-rich phase diminished. Molecular dynamics simulations showed the molecular chain orientation of the B46 blends well. The melting points, crystallinities, and grain sizes of the B46/R46 blends were lower than those of the B46 blends. The crystallization of the PA4-rich phase was restrained by the dilution effect of molten-state PA6, and the nucleation and crystallization of the PA6-rich phase were promoted by the presence of crystallized PA4. The B46 blends with 30-40 wt% PA6 had the best mechanical properties.

Marine bacterial enzyme degrades polyamide 4 into gamma-aminobutyric acid oligomers

Polyamide 4 (PA4) is a biobased plastic that has superior mechanical properties. PA4 shows good biodegradability in terrestrial and marine environments; however, the detailed interaction between PA4 and PA4-degrading enzymes from PA4-degrading microorganisms remains unclear. In this study, we isolated 11 novel strains of a PA4-degrading bacterium belonging to Pseudoalteromonas from a marine environment. Pseudoalteromonas sp. Y-5, which showed the highest PA4-degrading activity among the isolates, produced maximum PA4-degrading activity in culture supernatant after 4 days of incubation at 15 °C in Marine Broth 2216 containing 0.5 w/v% PA4 powder. We purified an enzyme that hydrolyzes PA4 at amide bonds into γ-aminobutyric acid oligomers (2–3 mers) from the culture supernatant. Based on a homology search using the amino acid sequence and predicted 3D structure of the enzyme, it was predicted to be composed of a substrate binding domain (SBD), linker domain, and catalytic domain (CD). The enzyme is a homodimer consisting of 75-kDa subunits, and the SBD is digested by autolysis in the absence of Ca2+. Interestingly, enzymatic properties, such as optimum temperature, pH, and NaCl concentration for high activity, differed between the full-size enzyme and autolyzed enzyme. In the predicted 3D structure of the enzyme, the structure of the CD overlapped with that of 6-aminohexanoate-dimer hydrolase, with a root mean square deviation of 1.084 Å. To our knowledge, this is the first report on the enzymatic and structural properties of a marine PA4-degrading enzyme. Our findings contribute to the understanding of the mechanisms of PA4 degradation in the marine environment.

Development of Biodegradable Polyamide 4/Polyvinyl Alcohol/Poly(lactic acid) Multilayer Films with Tunable Water Barrier Property and Superior Oxygen Barrier Property

Poor mechanical and barrier properties of biopolymer-based packaging materials limit their widespread applications. The combination of biopolymers with different nature is considered an effective strategy to obtain complementary properties, but this method is always restricted by the incompatibility between matrices. To combine polyamide 4 (PA4) and poly(lactic acid) (PLA), which present excellent oxygen barrier and water barrier properties, respectively, this study puts forward the use of polyvinyl alcohol (PVA) as a bonding layer to connect them and form the PA4/PVA/PLA multilayer films by the layer-by-layer solution casting method. PA4 and PLA are successfully linked through hydrogen bonding and electrostatic interactions with PVA. The cross-section morphology and peel test results proved the good interlayer adhesion between layers. After combination with PA4, the tensile strength, elongation at break, and oxygen barrier properties of PLA were greatly improved. The oxygen barrier of the PA4/PVA/PLA multilayer film was more than 260 times higher than that of the PLA monolayer. PA4/PVA/PLA films presented better thermal stability, transparency, and water barrier properties compared to the PA4 monolayer. Besides, PA4/PVA/PLA multilayer films presented a one-way water barrier characteristic, which made them effective in avoiding the condensation phenomenon when used as fruit or vegetable packaging. The study improved the poor interfacial compatibility between PA4 and PLA and provided a simple strategy for developing sustainable packaging with excellent performance.

Molecular dynamics simulation and non-isothermal crystallization kinetics of polyamide 4 and different bio-based polyamide blends.

The effects of the structural units and blending ratio on the crystallization behavior of blends of polyamide 4 (PA4) with polyamide 56 (PA56) and polyamide 11 (PA11) were studied using molecular dynamics simulations and non-isothermal crystallization kinetics. The simulation results show that the crystallinity of PA4/PA56 blends (B4/56) with a PA56 content of 30-50% was 3.5-10.8% lower than that of B4/56 with a PA56 content of 20%, and the crystallinity of PA4/PA11 blends (B4/11) decreased by 9.5% as PA11 content increased from 20% to 50%. The experimental results show that both B4/56 and B4/11 form PA4- and PA56-rich (PA11-rich) phases through crystallization-induced phase separation. The interplanar spacing of the PA4-rich phase of B4/56 changed relative to that of PA4, indicating that some PA56 entered the PA4-rich phase unit cell. As the PA56 content increased from 20% to 50%, the crystallinity of B4/56 decreased by 11.2%, and the crystallization-induced phase separation grew distinct. The B4/56 with a higher PA4 content crystallized more easily. As the PA11 content increased from 20% to 50%, the crystallinity of B4/11 decreased by 12.5%, and PA11 barely participated in the crystallization of the PA4-rich phase. The blending ratio had no significant effect on the crystallization rate and crystal-growth degree of B4/11, and the non-isothermal crystallization activation energy of B4/11 was significantly higher than that of B4/56, indicating that the crystallization ability of the B4/11 blend system is worse. This study provides a theoretical basis for the design and performance regulation of PA4-based polyamide blends.

Characterization of biodegradable food packaging films prepared with polyamide 4: Influence of molecular weight and environmental humidity

AbstractThe development of biodegradable packaging materials focuses on their barrier properties and mechanical properties, which are critical parameters for food protection. Synthetic biodegradable material polyamide 4 (PA4) may offer outstanding capacities for packaging due to its rigid molecular structure. The current study originally reveals the various physical properties of PA4 films and explores the influence of its internal structure, molecular weight, and external environment, environmental humidity, on its performance to provide further guidance for PA4 application. PA4 (Mη = 18,000 g/mol) films showed tensile strength (TS) of 47.5 ± 1.3 MPa, elongation at break (EB) of 228% ± 30%, oxygen permeability of 7.83 ± 3.32 × 10−17 cm3 m−1 s−1 Pa−1, and water vapor permeability of 4.34 ± 0.06 × 10−11g m−1 s−1 Pa−1. The TS and EB of PA4 improved slightly with increasing molecular weight, while the barrier characteristic remained unchanged. The moisture adsorption capabilities of PA4 films were similar to natural hydrophilic polymers. The mechanical characteristic of PA4 changed from brittle to ductile with the increase in relative humidity. Overall, PA4 can be considered to be a promising food packaging material since it presented better mechanical and oxygen barrier properties than those of commercial food packaging polymers.

Water-Induced Crystal Transition and Accelerated Relaxation Process of Polyamide 4 Chains in Microfibers

Microplastics have recently been identified as one of the major contributors to environmental pollution. To design and control the biodegradability of polymer materials, it is crucial to obtain a better understanding of the aggregation states and thermal molecular motion of polymer chains in aqueous environments. Here, we focus on melt-spun microfibers of a promising biodegradable plastic, polyamide 4 (PA4), with a relatively greater number density of hydrolyzable amide groups, which is regarded as an alternative to polyamide 6. Aggregation states and thermal molecular motion of PA4 microfibers without/with a post-heating drawing treatment under dry and wet conditions were examined by attenuated total reflectance-Fourier transform infrared spectroscopy and wide-angle X-ray diffraction analysis in conjunction with dynamic mechanical analysis. Sorbed water molecules in the microfibers induced the crystal transition from a meta-stable γ-form to a thermodynamically stable α-form via activation of the molecular motion of PA4 chains. Also, the post-drawing treatment caused a partial structural change of PA4 chains, from an amorphous phase to a crystalline phase. These findings should be useful for designing PA4-based structural materials applicable for use in marine environments.

Purification and characterization of an enzyme that degrades polyamide 4 into gamma-aminobutyric acid oligomers from Pseudoxanthomonas sp. TN-N1

Polyamide4 (PA4) is a bioplastic with superior properties and high biodegradability. Although some PA4-degrading microorganisms have been isolated from various environments, enzymes that play a role in PA4 degradation are yet to be identified. In this study, we isolated a novel PA4-degrading microorganism, Pseudoxanthomonas sp. TN-N1. This strain showed a clear zone surrounding the colony on an agar plate with the medium containing PA4 powder. The PA4-degrading activity using the supernatant of the culture medium was maximum when the strain was cultured in an appropriate medium containing 0.5% (w/v) PA4 at pH 7.0, and 30 °C for 3 days. Furthermore, we purified an enzyme that hydrolyzes the amide bonds of PA4 into γ-aminobutyric acid oligomers (2–4 mers) from the supernatant of the culture medium using anion exchange and gel permeation column chromatography. However, the enzyme exhibited no protease activity for casein, and it consisted of monomers or dimers with a molecular mass of 90 kDa. The PA4-degrading activity was optimum at pH 7.5 and 35 °C, and more than 80% of the enzyme activity was retained in the pH range of 6.0– 7.0 and temperature below 35 °C. In addition, PA4-degrading activity was significantly inhibited by ethylenediaminetetraacetic acid treatment. In our opinion, this is the first report of an enzyme exhibiting PA4-degrading activity. Our findings will contribute to a better understanding of the mechanism of PA4 degradation by microorganisms.

Polymer-Assisted Biocatalysis: Polyamide 4 Microparticles as Promising Carriers of Enzymatic Function

This study reports a new strategy for enzyme immobilization based on passive immobilization in neat and magnetically responsive polyamide 4 (PA4) highly porous particles. The microsized particulate supports were synthesized by low-temperature activated anionic ring-opening polymerization. The enzyme of choice was laccase from Trametes versicolor and was immobilized by either adsorption on prefabricated PA4 microparticles (PA4@iL) or by physical in situ entrapment during the PA4 synthesis (PA4@eL). The surface topography of all PA4 particulate supports and laccase conjugates, as well as their chemical and physical structure, were studied by microscopic, spectral, thermal, and synchrotron WAXS/SAXS methods. The laccase content and activity in each conjugate were determined by complementary spectral and enzyme activity measurements. PA4@eL samples displayed >93% enzyme retention after five incubation cycles in an aqueous medium, and the PA4@iL series retained ca. 60% of the laccase. The newly synthesized PA4-laccase complexes were successfully used in dyestuff decolorization aiming at potential applications in effluent remediation. All of them displayed excellent decolorization of positively charged dyestuffs reaching ~100% in 15 min. With negative dyes after 24 h the decolorization reached 55% for PA4@iL and 85% for PA4@eL. A second consecutive decolorization test revealed only a 5–10% decrease in effectiveness indicating the reusability potential of the laccase-PA4 conjugates.

Synthesis, Properties, and Biodegradation of Sequential Poly(Ester Amide)s Containing γ-Aminobutyric Acid.

Poly(ester amide)s are attracting attention because they potentially have excellent thermal and mechanical properties as well as biodegradability. In this study, we synthesized a series of novel poly(ester amide)s by introducing γ-aminobutyric acid (GABA) regularly into polyesters, and investigated their properties and biodegradabilities. GABA is the monomer unit of biodegradable polyamide 4 (PA4). The new poly(ester amide)s were synthesized from the reaction of ammonium tosylate derivatives of alkylene bis(γ-aminobutylate) and p-nitrophenyl esters of dicarboxylic acids. All the obtained polymers showed relatively high melting temperatures (Tm). Their thermal decomposition temperatures were improved in comparison with that of PA4 and higher enough than their Tm. The poly(ester amide)s exhibited higher biodegradability in seawater than the corresponding homopolyesters. Their biodegradabilities in activated sludge were also studied.

Bio-based and Biodegradable Electrospun Fibers Composed of Poly(L-lactide) and Polyamide 4

Novel bio-based and biodegradable block copolymers were synthesized by “click” reaction between poly(L-lactide) (PLLA) and polyamide 4 (PA4). Upon tuning the molar mass of PLLA block, the properties of copolymers and electrospun ultrafine fibers were investigated and compared with those of PLLA and PA4 blends. PLLA and PA4 were found incompatible and formed individual crystalline regions, along with reciprocal inhibition in crystallization. Electrospun fibers were highly hydrophobic, even if hydrophilic PA4 was the rich component. The crystallinity of either PLLA or PA4 decreased after electrospinning and PLLA-rich as-spun fibers were almost amorphous. Immersion tests proved that fibers of block copolymers were relatively homogeneous with micro-phase separation between PLLA and PA4. The fibrous structures of copolymers were different from those of the fibers electrospun from blends, for which sheath-core structure induced by macro-phase separation between homopolymers of PLLA and PA4 was confirmed by TEM, EDS, and XPS.

Biodegradation control of a polyamide 4–visible-light-sensitive TiO2 composite by a fluorescent light irradiation

A biodegradable polymer–titanium dioxide (TiO2) nanocomposite with antimicrobial activity by photooxidation of the composited TiO2 under fluorescent light irradiation was investigated. Polyamide 4 (PA4)–visible-light-sensitive TiO2 nanocomposite films were prepared. The nanocomposite films exhibited antibacterial activity slightly in the dark, whereas antibacterial activity against Escherichia coli was enhanced according to the increase of TiO2 concentration under fluorescent light irradiation for 1 h at 4000 lx. As the increase of the illumination intensity and irradiation time, nanocomposite films exhibited high antibacterial activity. The cell count on nanocomposite films with 1 wt% TiO2 decreased three orders of magnitude comparing to that of films without TiO2 under irradiation for 6 h at 3000 lx. Staphylococcus aureus was resistant to PA4-TiO2 nanocomposites in contrast to E. coli. In contrast, a PA4-degrading bacteria (ND-11) was sensitive to PA4-TiO2 nanocomposites comparing E. coli. In addition, the PA4-degrading bacteria was sensitive to the copper containing in TiO2. Therefore, the biodegradability was reduced according to the increase the TiO2 (copper) concentration in PA4-TiO2 nanocomposites in the dark. It was suggested that the effects of TiO2 against microbial differ from every biodegradable polymer. In this study, we were able to impart a biodegradation control function, in which biodegradation is suppressed by fluorescent light irradiation and progressed in the dark, to PA4 by compositing visible-light-sensitive TiO2.

Biodegradation of polyamide 4 in seawater

Herein, we report on the aquatic degradation of polyamide (nylon) 4. Polyamide 4 (PA4) has previously been shown to degrade in natural environments such as activated sludge and soil, as well as in vivo (when subcutaneously implanted in the backs of rats). In laboratory biodegradation tests of PA4, polyhydroxybutyrate (PHB), and polycaprolactone (PCL) in sampled seawater, the amount of oxygen absorption increased over time. PA4 degraded by about 30% in 4 weeks, which is comparable to that of PCL (30%) but less than that of PHB (60%). PA4 films were immersed in the sea and recovered at adequate intervals and weighed. The weight of the films decreased by 10–70% in 6 weeks, showing that PA4 is degraded in actual aquatic (sea) environments. We isolated PA4-degrading bacteria, strain MND-1, from the seawater used in the laboratory degradation tests. MND-1 is thought to belong to the family Alteromonadaceae from the DNA sequence of 16S rDNA. Gamma-aminobutyric acid (GABA) and GABA oligomers were detected in the PA4 degradation products. This indicates that the strain MND-1 hydrolyzes the amide bonds of PA4 into GABA oligomers and GABA.

One-pot low temperature synthesis and characterization of hybrid poly(2-pyrrolidone) microparticles suitable for protein immobilization

Neat and hybrid poly(2-pyrrolidone), i.e. polyamide 4 (PA4) microparticles containing magnetic or conductive metal, metal oxide, or carbon nanotube fillers were prepared via environmentally-friendly solventless activated ring-opening polymerization of 2-pyrrolidone at 40 °C. The method produces high porosity microparticles with diameters of 5–12 μm and conversion to PA4 of 56–65%. Their structure and properties were characterized by light- and electron microscopy, thermal, spectral and X-ray diffraction techniques. Two crystalline polymorphs, namely α− and β−PΑ4, were found to coexist at room temperature by X-ray diffraction. The assessment of the adsorption capacity of the PA4 hybrid microparticles toward model protein showed up to 60% efficiency only after 1 h of incubation without any preliminary activation or functionalization.

Biodegradation of polyamide 4 in vivo

We determined that polyamide 4 (PA4), which is easily degraded in the environment, is also degraded in vivo. We previously reported that PA4 was degraded by activated sludge. However, the potential biodegradability of PA4 in vivo has not been evaluated. In the present study, we subcutaneously implanted various PA4 samples in the backs of rats, including non-woven fabric as well as film and mold. The weights of implanted and recovered non-woven cloth composed of the PA4 polymer started to decrease at 3 months. At 8.5 months, weights decreased by 90%. For the non-woven PA4 cloth with a fine structure, there was no significant decrease in weight until 8.5 months. These results showed that PA4 was degraded in vivo and that polymer structure was important in determining the degradation rates. Copolymers composed of PA4 and polycaprolactone were also degraded in vivo. Homopolymers of PA4 were not hydrolyzed in phosphate buffer at 37 °C after one year. These results suggested the possibility that biochemical reactions were implicated in the degradation of PA4 in vivo. Based on tissue sample observations, implanted PA4 did not modify surrounding tissues. Safety evaluation, mutagenicity testing using bacteria (Ames test), and in vitro cytotoxicity testing using Chinese hamster V79 cells suggested that PA4 had no mutagenicity or cytotoxicity. Our study demonstrates that PA4 has potential as a bioabsorbable polymer material for biomedical applications.

Polyamide4‐block‐poly(vinyl acetate) via a polyamide4 azo macromolecular initiator: Thermal and mechanical behavior, biodegradation, and morphology

ABSTRACTA series of polyamide4‐block‐poly(vinyl acetate)s were synthesized by the radical polymerization of vinyl acetate (VAc) using an azo macromolecular initiator composed of polyamide4 (PA4). The block copolymers were investigated by examining their molecular weight, structure, thermal and mechanical properties, biodegradation, and the morphology of the film surface. The compositions and molecular weights (Mw) ranging from 46,800 to 163,700 g mol−1 of the block copolymers varied linearly with increasing molar ratio of VAc to azo‐PA4. The block copolymers have high melting points of 248.2–262.5°C owing to PA4 blocks and heats of fusion, which were linearly dependent on the PA4 content. The mechanical properties of the block copolymers were monotonically dependent on the composition, i.e., increasing the PA4 content increased the tensile strength, whereas increasing the poly(vinyl acetate) content increased the elongation at break. The morphology of the block copolymers suggested the appearance of microphase separation. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42466.