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1.
Shape memory polyurethanes (SMPUs) have generated great attention because of their unique properties. These properties are result of a particular molecular structure consisting of flexible molecular chains with low glass transition temperatures alternating with hard urethane segments. In this field, bisphenol A (BA) has been used for a long time as chain extender due to the good properties of the obtained SPMU materials. Nevertheless, the high toxicity of this compound has caused a high decrease on its use. For this reason, it has been selected a lower toxicity compound, bisphenol A ethoxylate (BAE). In this work, it is described a new SMPUs based on BAE and the influence of the hard segment on the thermo-mechanical properties and shape memory capacity. For that, both the proportion of the components and the diisocyanate employed (2,4-toluene diisocyanate (TDI), 4,4′-methylene bis(phenylisocyanate) (MDI) or a TDI/MDI mixture) have been modified. Then, depending on the molecular architecture achieved, the polyurethanes present different properties, which were studied by different techniques, such as thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and dynamic-mechanical thermal analysis (DMTA). It has been observed that glass transition temperature (Tg) increases as the hard phase content in the PU samples increases. In addition, Tg-MDI > Tg-MDI-TDI > Tg-TDI, so it is possible to control the Tg of the material, that is, shape memory transition temperature varying the diisocyanate. Finally, the shape memory capacity of the PUs was evaluated by thermo-mechanical analysis (TMA). All the synthesized PUs have shown good shape memory effect with fixation ratios up to 80% and recovery ratios close to 100%.  相似文献   
2.
Up to now, it is a major challenge to protect leading edge of the blades from solid particle erosion. Herein, we propose a structure optimization strategy to fabricate non-woven (NW) enhanced thermoplastic polyurethane nanocomposite films (thermoplastic polyurethane [TPU] - NW@G/Cx) with “sandwich - like” structure by hot pressing technology. TPU NW/graphene nanoplates/carbon nanotube (NW@G/Cx) interlayer film were first fabricated by spraying method. Then the interlayer film was laminated between TPU films to fabricate nanocomposite films. Such prepared TPU - NW@G/Cx film shows excellent solid particle erosion resistance and high-tensile strength. For example, the “steel-and-mortar” structure of NW fabric in TPU film results in high-tensile strength of 45 MPa and storage modulus of 21.2 MPa for TPU - NW@G/C1.0, increasing by 25% and 171% compared with original TPU film (35 MPa, 8 MPa), respectively. In addition, compared with pure TPU film, the “sandwich - like” structure endows TPU - NW@G/C1.2 with excellent solid particle erosion resistance and the thermal conductivity (0.251 W/m·K). These superior properties extends application of the TPU - NW@G/Cx film on wind turbine blades.  相似文献   
3.
以聚乳酸(PLA)为基体,添加不同含量聚氨酯(TPU)熔融共混制备具有不同相形态的PLA/TPU共混物,基于超临界二氧化碳(scCO2)微孔发泡工艺,研究不同发泡温度下PLA/TPU复合多孔材料泡孔结构、发泡倍率和开孔率对样品吸油性能的影响。结果表明,随着TPU含量从10 %(质量分数,下同)增加到50 %,共混物从典型的“海?岛”相形态转变为部分共连续相形态,PLA基体黏弹性提升,结晶能力下降;PLA70组分发泡后泡孔结构更为均匀,随着发泡温度的增加,泡孔尺寸和发泡倍率先增大后减小,在94 ℃发泡温度下发泡样品发泡倍率达到29.1倍,最大开孔率75 %;TPU的加入显著增加了PLA基体的弹性回复能力,94 ℃发泡温度下的发泡样品具有最大的抗压强度,永久形变量最小;针对硅油和环己烷的吸油测试发现对硅油的吸油量大于环己烷,发泡材料的吸油量与发泡倍率和开孔率的乘积成正比,针对硅油单次最大吸油量为10.4 g/g。  相似文献   
4.
刘志仁 《煤气与热力》2021,(2):10011-10014,10045
介绍水运行业推广LNG应用的现状、政策及规划。从市场、管理、油品、引导4个方面分析存在的挑战,提出建议。  相似文献   
5.
All-solid-state lithium batteries(ASSLB) are promising candidates for next-generation energy storage devices.Nevertheless,the large-scale commercial application of high energy density AS S LB with the polymer electrolyte still faces challenges.In this study,a thin solid polymer composite electrolyte(SPCE) is prepared through a facile and cost-effective strategy with an infiltration of thermoplastic polyurethane(TPU),lithium salt(LiTFSI or LiFSI),and halloysite nanotubes(HNTs) in a porous framework of polyethylene separator(PE)(TPU-HNTs-LiTFSI-PE or TPU-HNTs-LiFSI-PE).The composition,electrochemical performance,and especially the effect of anions(TFSI~-and FSI~-) on cycling performance are investigated.The results reveal that the flexible TPU-HNTs-LiTFSI-PE and TPU-HNTs-LiFSI-PE with a thickness of 34 μm exhibit wide electrochemical windows of 4.9 and 5.1 V(vs.Li+/Li) at 60℃,respectively.Reduction in FSI~-tends to form more LiF and sulfur compounds at the interface between TPU-HNTs-LiFSI-PE and Li metal anode,thus enhancing the interfacial stability.As a result,cell composed of TPU-HNTs-LiFSI-PE exhibits a smaller increase in interfacial resistance of solid electrolyte interphase(SEI) with a distinct decrease in charge-transfer resistance during cycling.Li|Li symmetric cell with TPU-HNTs-LiFSI-PE could keep its stable overpotential profile for nearly 1300 h with a low hysteresis of approximately39 mV at a current density of 0.1 mA cm~(-2),while a sudden voltage rise with internal cell impedance-surge signals was observed within 600 h for cell composed of TPU-HNTs-LiTFSI-PE.The initial capacities of NCMITPU-HNTs-LiTFSIPEILi and NCMITPU-HNTs-LiFSI-PEILi cells were 149 and 114 mAh g~(-1),with capacity retention rates of 83.52% and89.99% after 300 cycles at 0.5 C,respectively.This study provides a valuable guideline for designing flexible SPCE,which shows great application prospect in the practice of ASSLB.  相似文献   
6.
Two kinds of bio-based polyurethane coatings for controlled-release urea were prepared by in-situ polymerization used castor oil and liquefied starch as raw materials, respectively. Scanning electron microscopy (SEM) showed that the section morphology of castor oil based polyurethane (Castor-PU) coating was uniform and dense, and that of liquefied starch based polyurethane (Starch-PU) coating had certain proportion of microporous. Infrared spectroscopy (IR) showed that the two coatings had typical urethane characteristic structure, but the difference was that the Starch-PU had obvious unreacted isocyanate structure. Differential scanning calorimetry (DSC) showed that the glass transition temperature of the two coatings was around 58°C, but the Castor-PU had a crystallization domain with obvious crystallization melting peak at 130°C. Thermogravimetric analysis (TG) showed that the thermal stability of Castor-PU was significantly higher than that of Starch-PU. The controlled-release property test showed that when the coating ratio was 2.8%, the nutrient release longevity of urea coated with Castor-PU was 49 days and that of urea coated with Starch-PU was 14 days. The reasons for the poor controlled-release performance of Starch-PU were analyzed, which probably caused by concentrated sulfuric acid and hydrophilic dispersant added in the liquefied starch.  相似文献   
7.
Nanocomposites of thermoplastic polyurethane (TPU) with cellulose nanocrystals (CNC) without and with surface treatment are obtained by melt processing. Nanocomposites are obtained with nanofiller weight content near of the theoretical percolation threshold (3.9 wt%). Visual observation of CNC agglomerates is sufficient to prove the inefficiency of the mixing in systems with untreated CNC. The crystallization kinetics of the TPU changes with the addition of CNC and this is confirmed by differential scanning calorimetry analysis. Thermogravimetric analysis prove that the addition of CNC increases the thermal stability of the TPU. From the rheological analysis it is possible to verify the absence of percolation and an intermediate state of sol–gel transition in the nanocomposites. CNC/TPU nanocomposites with 5 wt% of treated CNC present better mechanical performance than de neat TPU and the other processed nanocomposites and display around 130% increase in Young's modulus while retaining significant values of toughness, tensile strength and elongation at break.  相似文献   
8.
Currently, the fabrication of microcell and bimodal cell structures (BCS) in polymer foams by using supercritical fluids has become a hot as well as a challenging research area worldwide. In this work, an environmentally friendly, effective, facile, and CO2-based foaming technique was presented to fabricate microcellular polypropylene (PP) foams with BCS via blending with thermoplastic polyurethane (TPU). The toughness, thermal properties, rheological properties, and foamability of PP were systematically investigated with gradual incorporation of TPU. Representative sea-island structure was observed in the scanning electron microscopy (SEM) images for the fracture surface of various PP/TPU samples. Rheological measurement results demonstrated that the viscoelasticity of various PP/TPU samples was improved remarkably compared with that of pure PP and pure TPU. The impact strength of various PP/TPU samples possessed the highest value as 12.4 kJ/m2 with the TPU content of 15 wt%. After the addition of TPU, an ameliorative cellular morphology was observed in the SEM micrographs of various PP/TPU samples and their volume expansion ratio was enhanced significantly thanks to their improved melt elasticity. Moreover, it is worth noting that BCS appeared in various PP/TPU foams when the TPU content exceeded 5 wt%.  相似文献   
9.
Polymer blends based on Tecoflex™ and an experimental aliphatic polyurethane (HMDI-PCL-arginine stands for 4,4 (metylene-biscyclohexyl) isocyanate - poly (ε caprolactone) diol, SPUUR stands for segmented poly(urea)urethanes using amino acid of L-Arginine as chain extender) were obtained by solvent casting, and further studied by fourier transform infrared (FTIR) and Raman spectroscopy, differential scanning calorimetry (DSC), thermogravimetric analysis, and X-ray diffraction (XRD). Their biological performances were assessed in terms of hemocompatibility and Human umbilical vein endothelial cell (HUVEC) cytotoxicity. Tensile properties of dumbbell specimens were compared to longitudinal and circumferential tensile properties of tubular vascular graft. FTIR showed that as the SPUUR content increased in the blend, absorptions at 2860 cm−1 increased, carbonyl absorptions at 1724 cm−1 broaden and the small peak at 2796 cm−1, typical of Tecoflex™ disappeared. Raman spectroscopy showed that the low intensity carbonyl absorption at 1724 cm−1 also increased with SPUUR content. DSC allowed detection of PCL soft segment melting (Tm = 50°C) in agreement with X-ray reflections at 21.3° and 23.6°, assigned to SPUUR. However, no improvements in thermal stability were detected by TGA by blending. The addition of SPUUR to Tecoflex™ improved hemocompatibility and HUVEC cytotoxicity. The vascular grafts performance showed that 40% SPUUR blends exhibited the highest force in the longitudinal test whereas 50% SPUUR blends showed the highest circumferential force. Pressure burst strength was higher than 1000 mmHg for all blends. Overall, these blends can be used for high caliber vascular grafts.  相似文献   
10.
This article reports an aramid pulp (AP) treated with two ionic liquids (IL), namely 1-n-butyl-3-methylimidazolium chloride (C4.Cl) and 1-carboxymethyl-3-methylimidazolium chloride (HO2C), and its use as a filler in reinforced rigid polyurethane foams (RPUF). The RPUF were incorporated with the treated AP at three weight fractions (c.a. 0.1, 0.5, and 1.0 wt%) and were produced by the free rising method. The results showed that the studied IL promoted a better interaction between the AP and the RPUF system, which increased the overall reactivity, imparting a higher cell anisotropy. This also yielded a positive effect in mechanical properties and thermal stability of the RPUF. Compared to the neat RPUF, outstanding increases of approximately 50 and 20% were achieved in compressive modulus and strength, respectively. In all, the use of IL promoted increased compatibility between matrix and reinforcement, especially that HO2C IL.  相似文献   
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