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The effect of structure and properties of polyacrylonitrile (PAN) fibers during thermal oxidative stabilization (TOS) stage (especially high‐temperature TOS stage at 270–300°C) on the skin‐core structure of carbonized fibers was studied. The work clarified the reasons for selecting the highest TOS temperature, and also determined the optimal TOS temperature range of obtaining structurally stable carbonized fibers. The changes of chemical groups were quantitatively calculated by a combination of peak‐fitting and second‐order derivative methods. The results showed that the cyclization was dominant in the early TOS stage, oxidation reaction mainly occurred in the post‐TOS stage, and crosslinking structure significantly increased after 250°C. In the high‐temperature TOS stage, cyclization reaction was basically completed, the growth rate of oxygen content slowed down, and dehydrogenation index continued to increase. The microstructure observation found that the grooves on the fiber surface were gradually smooth after low‐temperature and high‐temperature carbonization. The radial structure of A285‐1350 and A300‐1350 fibers have obvious heterogeneity, and diameter dropped below 5 μm. Therefore, carbonized fibers have obvious structural defects when the TOS temperature is above 285°C. The TOS temperature between 200 and 285°C is more conducive to obtain structurally stable carbonized fibers. [ABSTRACT FROM AUTHOR]

Damping coatings can convert kinetic energy into other forms of energy for consumption and have been widely used for vibration and noise reduction in rail trains, aerospace, automobile industry, and other fields. However, many aspects of damping coating such as, damping, water resistance, heat resistance, mechanical properties and antistatic properties require further improvement. In this study, a low‐cost conductive polyaniline (PANI) with a simple preparation method was dispersed in N‐methyl pyrrolidone and added to waterborne polyurethane‐acrylate (WPUA) hybrid latexes. The interfacial hydrogen bonding increases the interaction force between molecular chains, effectively improve the water resistance, heat resistance, damping, and mechanical properties of WPUA, and endowed WPUA with antistatic properties. Among them, PANI was used as an antistatic medium to be synthesized by chemical oxidation and doped with dodecylbenzene sulfonic acid, and the matrix polymer WPUA was the used of hydroxyethyl methacrylate (HEMA) to combine polyacrylate with waterborne polyurethane (WPU) by chemical bonds. The waterborne polyurethane‐acrylate‐polyaniline (WPUA‐PANI) films were investigated using dynamic light scattering , contact angle measurements , dynamic mechanical analysis, Fourier‐transform infrared spectroscopy (FTIR), digital highresistance meter and other characterization methods. It was concluded that the base latex has good stability, and when the PANI dispersion content was 35%, the comprehensive performance of the WPUA‐PANI films were the best, in which the maximum water contact angle was 106.8°, the tensile strength was increased from 0.7 MPa to 2.3 MPa, the effective damping temperature range (Tanδ ≥ 0.3) was increased from 50 °C to 87 °C, and the resistivity was reduced from 6.41E + 7 Ω·cm to 1.38E + 4 Ω·cm, which had better antistatic properties. This study will promote the development and application of damping coatings. [ABSTRACT FROM AUTHOR]

Polyacrylonitrile precursor was pretreated under nitrogen to study the effect of the extent of cyclization of pretreated fibers on the chemical structure, crystal structure and skin‐core structure of thermal oxidative stabilization (TOS) fibers. Based on the FTIR spectra, the cyclization degree of pretreated fibers was quantitatively calculated by a combination of peak‐fitting and second‐derivative operations. Combining the results of wide‐angle X‐ray diffraction, Raman spectroscopy and scanning electron microscope analysis, pretreatment was beneficial to increase the cyclized structure of TOS fibers, but inhibited the oxidation reactions in the TOS process. As the increase of cyclization degree of pretreated fibers, the oxygen content and crystal size of TOS fibers decreased and the crystal interplanar spacing increased; in the skin layer of TOS fibers, the ID/IG ratio increased and brittle fracture area decreased. When the cyclization degree of pretreated fibers was in the range of 10%–35%, the skin‐core structure of TOS fibers was weakened, which demonstrated that proper pretreatment before TOS process can improve the skin‐core structure. [ABSTRACT FROM AUTHOR]

A new kinds of waterborne polyurethane acrylate (WPUA) dispersions were synthesized based on isophorone diisocyanate (IPDI), hydroxyl‐terminated polybutadiene (HTPB), 1, 4‐butanediol (1, 4‐BDO), polytetramethylene ether glycol (PTMG), dimethylolpropionic acid (DMPA), 2‐ethylhexyl acrylate (EHA), and methyl methacrylate (MMA) as main raw materials. The influence of the HTPB content on the particle size, storage stability of the WPUA dispersions and the damping property of cured films were studied by using dynamic light scattering (DLS), dynamic mechanical analysis (DMA), respectively. It can be found the WPUA dispersions have a good stability and the damping temperature range of loss tangent (tan δ) >0.3 reaches a maximum (−26.6–79.14°C) when the content of HTPB is 20%. The HTPB based WPUA could be applied to damping material. [ABSTRACT FROM AUTHOR]

ABSTRACT Acrylic impact modifier (ACR), one kind of methyl methacrylate-butyl acrylate copolymer with a core-shell structure, was prepared by seed emulsion polymerization. The weight ratio of core-shell ranges from 85.5/14.5 to 71.9/28.1. Then PLA/ACR blends were prepared with a constant ratio of 80/20. The effect of core-shell ratio of ACR on toughening PLA was investigated. Torque analysis revealed that the torque values of PLA/ACR blends increased with increasing shell content of ACR. The impact strength of PLA/ACR blends reached the highest value of 77.1 kJ m−2 when the core-shell ratio of ACR was 79.2/20.8. Transmission electron microscope (TEM) photographs revealed that ACR was dispersed uniformly in the PLA matrix. Scanning electron microscopy (SEM) suggested that the plastic deformation and cavitations were the major toughening mechanism for the PLA/ACR blends. The shell partition PMMA of ACR was partially miscible with PLA from dynamic mechanical analysis. [ABSTRACT FROM AUTHOR]

The present work provided some in-depth understanding on the role of itaconic acid (IA) in the structural evolution of poly(acrylonitrile-co-itaconic acid) (PAI) polymers and the formed cyclic structures during thermal treatment. As the increasing content of IA, the cyclization initiated by the ionic mechanism increased with the less β-amino nitrile formed and the higher extent of cyclization. The IA comonomer initiated multiple cyclization reactions, namely, the first ionic cyclization and the second ionic cyclization, by the jump transportation of activation species between different PAI chains during thermal treatment. The times of the jump transportation of activation species was about two or three at 250°C. The presence of IA comonomer promoted the formation of long sequence cyclic structures rather than isolated cyclic structure under non-oxidative condition. The thermal stability of PAI was improved by the more and better cyclic structures and the crosslinking structures caused by the jump transportation of activation species, which reasonably resulted in a better graphitic lattice during the carbonization. Copyright © 2017 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

ABSTRACT This article was to provide some new insights into the influences of itaconic acid (IA) content in polyacrylonitrile (PAN) copolymers on polymerization, structural evolution, thermal behaviors and carbon yield relatively comprehensively. High IA containing poly(acrylonitrile- co-itaconic acid) (PAI) oligomers were successfully extracted from PAI copolymers with 2.0 and 3.0 mol % IA. PAI copolymers with 0.5 mol % and 1.0 mol % IA possessed more cyclized structures, conjugated carbonyl group, conjugated nitrile group, and less β-amino nitrile group as well as faster structural evolution rate than those of the other three PAI copolymers. Kinetic parameters indicated that excessive IA content in PAI copolymer did not have advantages in promoting cyclization reaction. The PAI copolymers with 0.5 wt % to 1.0 mol % IA possessed better crystalline parameters as well as higher carbon yield than those of the other two PAI copolymers after carbonization at 1350 ºC. In summary, PAI copolymers with 0.5 mol % to 1.0 mol % IA will be more suitable for fabricating of high performance PAN-based carbon fibers. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43919. [ABSTRACT FROM AUTHOR]

The structural evolution of poly(acrylonitrile-co-dimethyl itaconate) [P(AN-DMI)] copolymer was investigated by Fourier transform infrared spectroscopy (FTIR) in detail and compared with the polyacrylonitrile (PAN) homopolymer. The extent of cyclization reactions was calculated from the FTIR data. It was found that DMI comonomer had the ability to promote the cyclization reactions significantly at the temperature of 240°C, compared to the PAN homopolymer. The results of quantitative FTIR analysis in the range of 1000-1800 cm−1 showed that the DMI comonomer not only promoted the cyclization reactions, but also facilitated the oxygen uptake reactions, especially the conjugated carbonyl group in an acridone ring in the ladder polymer chains, which proved that DMI comonomer had the potential ability to make successful thermal oxidative stabilization (TOS) process. The positive effects of DMI comonomer on TOS reactions and carbon yield were further confirmed by the dynamic thermogravimetry (TG) analysis. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

A series of submicrometer-sized polybutadiene(PB) rubber particles with different diameters ranging from 100 to450 nm were prepared via an emulsion polymerization. Subsequently,core–shell polybutadiene-graft-polystyrene(PB-g-PS) particles were synthesized using a redoxinitiator system (cumene hydroperoxide and ferrous sulfate) by anemulsion grafting polymerization. Then the submicrometer sized PB-g-PS impact modifiers were utilized to toughen polystyrene(PS) by blending PS and high-impact polystyrene. From measuring mechanicalproperties, it was found that the notched impact strength of toughenedPS was significantly influenced by core–shell PB-g-PS particle size. When the rubber particle size was above 300 nm,the notched impact strength was 208 J/m, nearly 2 times than thatof toughened PS with particle size 100 nm. Moreover, the stress whiteningzones were observed by transmission electron microscopy, and the resultshowed that multiple crazing is its dominative toughening mechanism. [ABSTRACT FROM AUTHOR]

Maleic anhydride (MAH) functionalized acrylate-styrene-acrylonitrile(ASA) copolymers (F-ASA) were prepared via an emulsion polymerizationprocess. The F-ASA particles were used to toughen Polyamide-6 (PA-6).Molau tests showed the compatibilization reactions between PA-6 andF-ASA. The notched impact strength of PA-6 was effectively improvedby the use of F-ASA. At a rubber content of 20% by weight in PA-6/F-ASAblends, it was found that the impact strength increased with the MAHcontent. When the MAH content was 8% in F-ASA, the impact strengthwas 1008 J/m. The influence of rubber content on the properties ofPA-6/F-ASA8 blends was investigated. The results showed that brittle-ductiletransition took place when the rubber content was 20%. Moreover, increasingthe MAH content of the blends reduced the brittle-ductile temperatureof the F-ASA/PA-6 blends from 50 °C to about 0 °C. Scanningelectron microscopy (SEM) results showed that cavitation of rubberparticles and shear yielding of the PA-6 matrix were the major tougheningmechanisms. [ABSTRACT FROM AUTHOR]

A series of hyperbranched waterborne polyurethane–acrylate (HWPUA) hybrid emulsions were prepared with isocyanate‐terminated PU prepolymers, hyperbranched polyol (HP), and acrylate monomers. The HP as crosslinker was synthesized with isophorone diisocyanate, dimethylol propionic acid, and diethanol amine. The influence of the HP content on the chemical structure, particle size, morphology, damping properties, and thermal stability of the HWPUA hybrid emulsions and films were investigated by Fourier transform infrared spectroscopy, dynamic light scattering, transmission electron microscopy, dynamic mechanical analysis (DMA), and thermogravimetric analysis, respectively. The results show that the addition of HP obviously improved the damping and thermal properties of the HWPUA films. However, the addition of excessive HP had a detrimental impact on the performance of films. The DMA curves indicated that when the HP content was 1%, tan δ was 0.3 or greater and spanned the broadest temperature range, with a maximum value of 0.65. The HWPUA hybrid emulsions could be used as damping coatings. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47733. [ABSTRACT FROM AUTHOR]

Background: In the series of improved versions of U-Net, while the segmentation accuracy continues to improve, the number of parameters does not change, which makes the hardware required for training expensive, thus affecting the speed of training convergence., Objective: The objective of this study is to propose a lightweight U-Net to balance the relationship between the parameters and the segmentation accuracy., Methods: A lightweight U-Net with full skip connections and deep supervision (LFU-Net) was proposed. The full skip connections include skip connections from shallow encoders, deep decoders, and sub-networks, while the deep supervision learns hierarchical representations from full-resolution feature representations in outputs of sub-networks. The key lightweight design is that the number of output channels is based on 8 rather than 64 or 32. Its pruning scheme was designed to further reduce parameters. The code is available at: https://github.com/dengdy22/U-Nets., Results: For the ISBI LiTS 2017 Challenge validation dataset, the LFU-Net with no pruning received a Dice value of 0.9699, which achieved equal or better performance with a mere about 1% of the parameters of existing networks. For the BraTS 2018 validation dataset, its Dice values were 0.8726, 0.9363, 0.8699 and 0.8116 on average, WT, TC and ET, respectively, and its Hausdorff95 distances values were 3.9514, 4.3960, 3.0607 and 4.3975, respectively, which was not inferior to the existing networks and showed that it can achieve balanced recognition of each region., Conclusion: LFU-Net can be used as a lightweight and effective method in the segmentation tasks of two and multiple classification medical imaging datasets., (Copyright© Bentham Science Publishers; For any queries, please email at epub@benthamscience.net.)