In this study, a series of crosslinked waterborne polyurethane/acrylate copolymer latexes with different compositions were fabricated via emulsion polymerization using oil-soluble initiator (AIBN) ...based on a solvent-/emulsifiers-free method. Using the blend of styrene (St), butyl acrylate (BA) and crosslinkers (pentaerythritol triacrylate (PET3A) and pentaerythritol tetraacrylate (PET4A)) instead of acetone as a diluent and modifier, polyurethane prepolymers terminated with hydroxyethyl acrylate composite emulsions were prepared using polypropylene glycol (PPG), toluene diisocyanate (TDI), 2,2-dihydroxymethylpropionic acid (DMPA) and diethylene glycol (DEG) without other solvents. It was found that for all the emulsion polymerization of waterborne polyurethane and acrylates initiated by AIBN, the monomer conversions exceeded 96% when the concentration of AIBN was in the range of 0.5% to 0.9% (w/w) and the optimal reaction temperature was 75 °C. The introduction of St, BA and crosslinkers would form the polymer network, improving the tensile strength, water absorption of the copolymer latex films. Dynamic light scattering analyses showed that the copolymer latexes exhibited a unimodal distribution and showed no precipitates and unstable aggregates. The average particle size distribution was in the range of 131-154 nm. Transmission electron microscopy studies have confirmed the similar results and the latex particles possessed the core-shell morphology structure.
In order to improve the accuracy and robustness of existing automated crack detection methods, a fully convolutional neural network for pixel-level detection based on densely connected and deeply ...supervised network is proposed. First, the densely connected layers are applied for enhancing the propagation and reuse of crack features. Then, the deeply supervised modules are designed to make network extract more significant features through multi-scale levels. Finally, the feature maps from different scales are fused to achieve complementarity at different levels. In addition, a class-balanced cross-entropy loss function is designed to balance backgrounds and cracks by increasing the weight of crack pixel loss. The proposed method is tested on three public datasets, and the experiments show that our method is superior to state-of-the-art methods in accuracy, speed and robustness.
We develop a singular stochastic control model for pricing variable annuities with the guaranteed minimum withdrawal benefit. This benefit promises to return the entire initial investment, with ...withdrawals spread over the term of the contract, irrespective of the market performance of the underlying asset portfolio. A contractual withdrawal rate is set and no penalty is imposed when the policyholder chooses to withdraw at or below this rate. Subject to a penalty fee, the policyholder is allowed to withdraw at a rate higher than the contractual withdrawal rate or surrender the policy instantaneously. We explore the optimal withdrawal strategy adopted by the rational policyholder that maximizes the expected discounted value of the cash flows generated from holding this variable annuity policy. An efficient finite difference algorithm using the penalty approximation approach is proposed for solving the singular stochastic control model. Optimal withdrawal policies of the holders of the variable annuities with the guaranteed minimum withdrawal benefit are explored. We also construct discrete pricing formulation that models withdrawals on discrete dates. Our numerical tests show that the solution values from the discrete model converge to those of the continuous model.
In order to prepare polyurethane–polysiloxane block copolymers, α,ω-hydroxyalkyl polysiloxanes with methacrylate side chain and α,ω-bis(2-methyl-3-hydroxypropyl)polymethyl(2-methyl-methylpropanoate) ...siloxanes, were synthesized and characterized in this study. The syntheses process included hydroxyl protection, hydrosilylation, deprotection, and ring-opening equilibrium reactions. The intermediates and target products were characterized by Fourier transform infrared spectroscopy and
H nuclear magnetic resonance methods. The characterization results showed that each step was successfully carried out in all the cases. Then the waterborne polyurethane–polysiloxane block copolymers were prepared via step-growth polymerization. The properties of the block copolymer films were characterized by thermal gravimetric analysis, differential scanning calorimetry, and dynamic thermomechanical analysis methods in detail. The experimental results showed that the block introduction of hydroxyalkyl polysiloxane could reduce the water absorption of waterborne polyurethane from 62 to 11%, and significantly improve the water resistance of polyurethane. With the introduction of polysiloxane, the tensile strength decreased and the elongation at break increased. At the same time, with the increase of the polysiloxane content, the glass transition temperature of the soft segment decreased to −56.4°C and the thermal decomposition temperature increased to 300°C. The results revealed that the introduction of polysiloxane could effectively improve the comprehensive performance of polyurethane–polysiloxane block copolymer films.
The composite phase change material was prepared via the impregnation method using diatomaceous as the carrier and stearic acid as the phase change material. The effects of diatomite content, ...temperature, immersion time and pressure on the mass ratio of stearic acid and diatomaceous earth in the composite phase change materials were discussed. The experimental results showed that the optimum conditions for preparing stearic acid/diatomite composite phase change material were immersion temperature of 80℃, socking time of 2 h, diatomite mass fraction of 23.04%, and vacuum degree of 0.03 MPa. Finally, the infrared spectroscopy analysis of stearic acid/diatomite composite phase change energy storage material showed that there is no chemical reaction between stearic acid and diatomite. And they are held together by intermolecular forces.
In this paper, by optimizing synthesis process of α,ω-hydroxyalkyl telechelic polydimethylsiloxane, α,ω-bis(3-(1-methoxy-2-hydroxypropoxy)propyl)polydimethyl siloxane (PMTS), the yield of ...hydrosilylation product, 1,3-bis(glycidoxypropyl) tetramethyldisiloxane exceed 86.5%. By tracing the change of methanol (gravimetry) and measuring the change of molecular weights of polydimethylsiloxanes at different reaction time (titration), the optimum reaction time of methoxylation reaction and ring-opening polymerization was determined as 8 and 12 h. Using α,ω-bis(3-(1-methoxy-2-hydroxypropoxy)propyl)polydimethyl siloxane with different molecular weights, waterborne polyurethane-polydimethylsiloxane block copolymer were prepared. The influences of molecular weights and content of α,ω-hydroxyalkyl telechelic polydimethylsiloxane on the waterborne polyurethane-polydimethylsiloxane block copolymers were investigated in detail. The addition of α,ω-hydroxyalkyl telechelic polydimethylsiloxane could improve the water-resistance property obviously and increase the elongation at break. However, the mechanical property was reduced with increase of content and molecular weight of α,ω-hydroxyalkyl telechelic polydimethylsiloxane.
We synthesized polydimethylsiloxane–polyurethane dispersions modified with graft copolymerization (PDMS-
G
-PUDs) and polydimethylsiloxane–polyurethane dispersions modified with block ...copolymerization (PDMS-
B
-PUDs). We systematically investigated the effects of PDMS’s structure, content, and molecular weight on properties of copolymer including viscosity, particle size, and stability of dispersions as well as the properties of the film formed by dispersions including gloss, contact angle, water resistance, oil resistance, and mechanical properties. The results demonstrated that the viscosity, particle size, water resistance increased but gloss decreased with the increase of PDMS content and molecular weight. In addition, we compared the properties of PDMS-
B
-PUD films and PDMS-
G
-PUD films with the same amount of PDMS and similar molecular weight. PDMS-
G
-PUD films showed higher water and oil resistance, but lower gloss and poorer mechanical properties. Scanning electron microscopy–energy dispersive spectroscopy analysis (SEM–EDS) indicated that the films of PDMS-
G
-PUD had better microphase separation and PDMS surface enrichment.
A novel synthesis path for the monotelechelic polydimethylsiloxane with a diol-end group, α-butyl-omega-{3-2-hydroxy-3-(N-methyl-N-hydroxyethylamino)propoxypropyl}polydimethylsiloxane, is described ...in this article. The preparation included three steps, which were anionic ring-opening polymerization, hydrosilylation, and epoxy addition. The structure and polydispersity index of the products were analyzed and confirmed by FTIR, ¹H NMR, ¹³C NMR, H---H, and C---H. Correlated Spectroscopy and gel permeation chromatography. The results demonstrated that each step was successfully carried out and the targeted products were accessed in all cases.
Airport runway defect detection is indispensable to guarantee the safety of aircraft landing and taking-off, automating the inspection process has been the focus of airport management department. ...Defects such as crack, seam-broken, and corner fracture, which are common to airport runway, are characterized by extremely small sizes, similar shapes, and low contrast with the background, making the automatic detection task challenging. Thus, we propose an algorithm based on bidirectional feature pyramid to perform the automatic detection. The proposed network applies VGG-16 as backbone to extract features, reducing the information loss during down sampling to retain more detailed features of small defects. A bidirectional feature pyramid module is designed to enhance feature fusion, which can balance the feature information of small defects in different scales. The module expands the receptive field on the basis of Feature Pyramid Network (FPN), which can obtain the global semantic information of the target, and achieve better classification and localization performance. Compared with five existing deep learning methods, experimental results show that our proposed algorithm outperforms all counterparts, making the automatic detection and monitoring of airport runway more efficient.
In this study, a fluoro-diol, trifluoroethyl-2-methylpropanoate-β-dihydroxy ethylamine (TFMDA), was successfully synthesized by Michael Addition reaction between trifluoroethyl-2-methacrylate (TFEMA) ...and diethanolamine (DEA). The chemical structures were characterized by FT-IR and
1
H NMR methods. And then by the reaction of dicyclohexylmethylmethane-4,4′- diisocyanate (HMDI), poly(propylene glycol) (PPG), 2,2-dimethylolbutanoic acid (DMBA), diethylene glycol (DEG) and trifluoroethyl-2-methylpropanoate-β-dihydroxyethylamine (TFMDA), fluorinated waterborne polyurethane emulsions with different content of COOH and TFMDA were successfully prepared. It was demonstrated that all the polyurethane emulsions exhibited enhanced storage stability and all the polyurethane films possessed high elongation at break and exceeded 1000%. Addition of organic fluorine obviously improved the water-resistance property of the waterborne polyurethane films.
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