A novel shape-stabilized PCM: Electrospun ultrafine fibers based on lauric acid/polyethylene terephthalate composite

Recently, ultrafine fibers of PCM/polymer composites have been developed as a novel shape-stabilized polymer-matrix phase change material (PCM) via electrospinning technique. In this study, ultrafine fibers of lauric acid/polyethylene terephthalate (LA/PET) composite (1:1, w/w) were successfully prepared and characterized by field-emission scanning electron microscopy (FE-SEM), differential scanning calorimetry (DSC) and tensile testing. The results indicated that the electrospun fibers showed smooth surfaces and cylindrical shape with diameters ranging from several tens to several hundreds nanometer, and the latent heat of fusion of the fibers is about 70.76 J/g. Although the tensile properties of the electrospun composite fibers were lower than that of the electrospun pure PET fibers, they showed suitable and competent tensile strength for the potential applications in solar energy storage and thermo-regulating textile.     

MWCNT reinforced Polyamide-6,6 films: preparation,characterization and properties

Composite films of Polyamide-6,6 (PA66) and multi-walled carbon nanotubes (MWCNTs) were prepared by a combination of solution casting followed by compression molding techniques. Both unfunctionalized (u-MWCNTs) and functionalized nanotubes (f-MWCNTs) were used in this study. The functionalization involved direct solvent-free amination of MWCNTs with hexamethylenediamine. Thermogravimetric analysis was used to observe the changes in the nanotubes upon functionalization and morphological features of the resulting composite films were studied using scanning electron microscopy, transmission electron microscopy, and atomic force microscopy. The crystallinity changes by incorporation of the u-MWCNTs and f-MWCNTs in the PA66 matrix were studied by wide angle X-ray scattering and differential scanning calorimetry. The f-MWCNT/PA66 film showed an improvement of ∼43% in maximum tensile stress (MTS) and ∼32% in Young’s modulus over pristine PA66 film, while at a similar loading of 0.5 wt%, the f-MWCNT/PA66 film showed ∼15% increase in MTS and ∼16% increase in modulus over the u-MWCNT/PA66 film. Dynamic mechanical analysis indicated significant difference in the small-strain mechanical properties between the MWCNT-filled and unfilled PA66 at the very low MWNT loadings that were tested and supported the tensile results. The water absorption trend of the composite films showed dramatic improvement over the neat film.     

多壁碳纳米管/聚己内酯超细复合纤维的制备及性能

通过静电纺丝法制备出多壁碳纳米管(MWCNTs)增强聚己内酯(PCL)超细复合纤维膜。用扫描电镜(SEM)、透射电镜(TEM)、拉曼光谱仪、差示扫描量热仪(DSC)和X射线衍射仪(XRD)对MWCNTs/PCL超细复合纤维进行表征,并进行了拉伸测试。结果表明,MWCNTs分散于PCL纤维中,MWCNTs的加入降低了PCL的结晶度。当PCL中MWCNTs的含量为0.5 wt%时,其结晶度最低,但此时MWCNTs/PCL超细复合纤维具有最好的力学性能。     

Uniaxially aligned electrospun fibers for advanced nanocomposites based on a model PVOH-epoxy system

This work demonstrates the potential of aligned electrospun fibers as the sole reinforcement in nanocomposite materials. Poly(vinyl alcohol) and epoxy resin were selected as a model system and the effect of electrospun fiber loading on polymer properties was examined in conjunction with two manufacturing methods. A proprietary electrospinning technology for production of uniaxially aligned electrospun fiber arrays was used. A conventional wet lay-up fabrication method is compared against a novel, hybrid electrospinning–electrospraying approach. The structure and thermomechanical properties of resulting composite materials were examined using scanning electron microscopy, dynamic mechanical analysis, thermogravimetric analysis, differential scanning calorimetry, Fourier transform infrared spectroscopy, and tensile testing. The results demonstrate that using aligned electrospun fibers significantly enhances material properties compared to unreinforced resin, especially when manufactured using the hybrid electrospinning–electrospraying method. For example, tensile strength of such a material containing only 0.13 vol% of fiber was increased by ∼700%, and Young’s modulus by ∼250%, with concomitant increase in ductility.     

Study of rheological properties of polypropylene/organoclay hybrid materials

Polypropylene nanocomposites reinforced with organic modified montmorillonite clay have been fabricated by melt compounding using extrusion. The morphology of the composites is studied with transmission electron microscopy and X-ray diffraction. The melt-state rheological properties of the nanocomposites have been investigated as a function of temperature and organoclay loading. It is found that the organoclays are intercalated and dispersed evenly in the matrix. The storage and loss moduli of the hybrid composites decrease with temperature and increase with organoclay concentration. Both polypropylene and its composites demonstrate a melt-like rheological behavior, indicating the low degree of exfoliation of the organoclay. A shear thinning behavior is found for both polypropylene and its composites, but the onset of shear thinning for organoclay composites occurs at lower shear rates.     

Polyurethane–silver fibers prepared by infiltration and reduction of silver nitrate

Silver-incorporating polyurethane fibers were prepared by infiltration of silver nitrate on electrospun polyurethane fibers and reduction with sodium borohydride. They were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and energy-dispersive X-ray system. The Ag nanoparticles prepared by reduction of silver nitrate showed nano-sized crystals of 4–10 nm in diameter. However, larger aggregated Ag particles of 50–200 nm were also found to be dispersed in the polyurethane matrix when Ag particles were formed in electrospun fibers by the infiltration–reduction process of silver nitrate. As a result, infiltration method of silver nitrate into the electrospun fibers was significantly effective to produce silver-incorporating fibers due to a high specific surface area of fibers.     

Effect of organoclay with various organic modifiers on the morphological,mechanical, and gas barrier properties of thermoplastic polyurethane/organoclay nanocomposites

Thermoplastic polyurethane (TPU)/organoclay nanocomposites are prepared through a melt extrusion process. The TPU is combined with four differently modified organoclays, namely, I.28E, I.30P, I.34TCN, and I.44P. Wide-angle X-ray diffraction and transmission electron microscopy results show that the addition of I.34TCN and I.30P to TPU/organoclay nanocomposites results in the nearly exfoliated structures of the nanocomposites. Addition of I.28E leads to partially intercalated nanocomposites, whereas I.44P cannot disperse effectively in the nanocomposites. Organoclay can enhance the mechanical and gas barrier properties of TPU. The enhancement follows the order TPU/I.34TCN ≥ TPU/I.30P > TPU/I.28E > TPU/I.44P, which is consistent with the degree of dispersion and exfoliation of silicate layers. In addition, Fourier transform infrared absorption spectra show that more hydrogen bonding sites are introduced between the clay modifiers and TPU chains in the TPU/I.34TCN and TPU/I.30P nanocomposites; this has a positive impact on the dispersion of the organoclay and, consequently, the mechanical and gas barrier properties of the nanocomposites.     

玻璃纤维增强PA66复合材料与Al2O3陶瓷的摩擦磨损行为

研究了25%(质量分数)玻璃纤维增强PA66复合材料(25%GF/PA66)在干摩擦和水润滑条件下与Al₂O₃陶瓷之间的摩擦磨损行为。采用激光共聚焦扫描显微镜、 扫描电子显微镜、 傅里叶变换红外光谱仪和X射线光电子能谱分析仪对25%GF/PA66的组织、 磨损形貌和磨损表面的化学结构变化进行分析。结果表明: 相同实验载荷时,润滑条件下25%GF/PA66的摩擦系数小于干摩擦条件下的摩擦系数,但磨损体积却远远大于干摩擦条件下的磨损体积。在有水存在的条件下,机械微切削作用持续发生,温度的升高使25%GF/PA66试样变形,同时引起酰胺基团发生水解,C—C键大量断裂,导致磨损体积增加。采用扩展表面一般导热模型计算本实验所用材料的热软化温度为105.9℃。     

丝胶组分和高湿后处理对静电纺丝素纤维结构与性能的影响

利用静电纺丝法制备了再生丝素和再生丝素/丝胶蛋白纤维,并对所得纤维进行了高湿后处理。采用扫描电镜分析了丝胶蛋白和高湿后处理对静电纺再生丝素蛋白纤维形貌的影响,采用拉曼光谱、X射线衍射和热失重分析研究了所得纤维微细结构及热性能。研究结果表明,添加丝胶蛋白有利于降低静电纺再生丝素蛋白纤维的直径及其分布,而高湿后处理对纤维的形貌没有明显影响;添加丝胶蛋白和/或高湿后处理有利于促进丝素发生向β-折叠构象的转变,并使纤维的结晶结构得到改善,从而进一步提高纤维的热稳定性。     

Structures,thermal stability,and crystalline properties of polyamide6/organic-modified Fe-montmorillonite composite nanofibers by electrospinning

In the present work, Fe-montmorillonite (Fe-MMT) was synthesized by hydrothermal method, and then was modified by cetyltrimethyl ammonium bromide (CTAB). The polyamide6 (PA6)/organic-modified Fe-montmorillonite (Fe-OMT) composite nanofibers were prepared by facile compounding and electrospinning. Fe-OMT was first dispersed in N, N-dimethyl formamide and then compounded with PA6 which was dissolved in formic acid. The composite solutions were electrospun to form PA6/Fe-OMT composite nanofibers. The structure, morphology, thermal stability, and crystalline properties of the composite nanofibers were characterized by Fourier transfer infrared (FTIR) spectra, Energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), High-resolution electron microscopy (HREM), Scanning electron microscopy (SEM), and Thermogravimetric analyses (TGA), respectively. It was found that the silicate clay layers were well exfoliated within the composite nanofibers and were oriented along the fiber axis. The SEM images indicated that the loading of Fe-OMT decreased the diameters of composite nanofibers. TGA analyses revealed that the thermal stability was notably improved in the presence of silicate clay. It was also observed from wide-angle XRD analyses that the presence of nanoclays improved the γ-form crystals and induced the formations of α-form crystals of the PA6, attributed to effective nucleating effects of silicate clay platelets.     

Determination of molecular orientation of uniaxially stretched polyamide fibers by polarized infrared spectroscopy: comparison of X-ray diffraction and birefringence methods

Polarized infrared (IR) spectroscopy has been used to determine the crystalline and amorphous orientation of polyamide fibers. The transition moment angle of the band at 936 cm-1 of PA66 was determined to be 48 degrees using IR spectroscopy and birefringence measurement. The crystalline orientation of PA66 fibers was estimated from the band at 936 cm-1 while the amorphous orientation of PA66 fibers was obtained by an indirect method. The alpha crystalline orientation of PA6 has been obtained using the band at 930 cm-1 and the amorphous orientation of PA6 has been determined using the band at 1124 cm-1. Crystalline orientation increased rapidly at low draw ratios (DR<3) and increased slowly at higher draw ratios (DR>3) for both PA66 and PA6 fibers, while the amorphous orientation increased slowly throughout the whole extension range for PA66 fibers. A good correlation was found between the crystalline orientation values obtained by infrared spectroscopy and other methods such as X-ray diffraction for PA66 and PA6 fibers. On the basis of this observation, it has been concluded that polarized infrared spectroscopy can be used reliably to measure the orientation of polyamide fibers without combining with other techniques.     

Creep behaviour of injection moulded polyamide 6/organoclay nanocomposites by nanoindentation and cantilever-bending

The creep behaviour of injection moulded PA 6/organoclay nanocomposites was studied by depth-sensing nanoindentation and DMA cantilever-bending. The glass transitions of PA 6 and its nanocomposites were decreased below room temperature upon saturation with water so that the materials could be tested in the rubbery regime. For nanoindentation creep on the skin and core regions of injection moulded samples, whilst organoclay improves the creep resistance of PA 6, the enhancement is due to the decrease of the initial compliance at zero time but the time-dependent creep is actually increased. In contrast, for cantilever-bending creep, organoclay reduces the creep compliance and the time-dependent creep in PA 6. It is suggested that the organoclay imparts a constraint effect on the PA 6 molecular chains, restricting their mobility in the bulk compared to the surface and hence improving their resistance to creep. A modified Halpin-Tsai equation was used to model their creep behaviour under these two loading configurations and compared to experimental data.     

Electrospun fibers for tissue engineering, drug delivery, and wound dressing

Electrospinning, a technique well known for fabricating nanoscale fibers, has recently been studied extensively due to its various advantages such as high surface-to-volume ratio, tunable porosity, and ease of surface functionalization. The resulting fibers are extremely useful for applications in the fields of tissue engineering, drug delivery, and wound dressing. Since electrospun fiber mimic extracellular matrix of tissue in terms of scale and morphology, its potential to be used as scaffold is continuously explored by researchers, especially in the field of vascular, nerve, bone, and tendon/ligament tissue engineering. Besides morphology, physical, and chemical properties, electrospun scaffolds are often evaluated through various cell studies. Researchers have adopted approaches such as surface modification and drug loading to enhance the property and function of scaffold. This review gives an overview of some current aspects of various applications of electrospun fibers, particularly in biomedical fields, how researchers have enhanced electrospun fibers with different methods and attempted to overcome the inherent limitation of electrospinning by using novel techniques.     

Preparation and characterization of electrospun core sheath nanofibers from multi-walled carbon nanotubes and poly(vinyl pyrrolidone)

Electrospinning is a versatile technique to prepare polymer fibers in nano to micrometer size ranges using very high electrostatic fields. Electrospun nanofibers with tunable porosity and high specific surface area have various applications, including chromatographic supports for protein separation, biomedical devices, tissue engineering and drug delivery matrices, and as key components in solar cells and supercapacitors. Unspinnable materials such as nanoparticles, nanorods, nanotubes or rigid conducting polymers can also be electrospun into fibers through co-axial electrospinning. In this study, we have prepared core-sheath nanofibers utilizing co-axial electrospinning. The core portion of these electrospun fibers consists of multi-walled carbon nanotubes and the sheath portion is poly(vinyl pyrrolidone) (PVP). Various morphologies were obtained by changing both core and sheath solution concentrations. The core-sheath nanofibers were characterized by scanning electron microscopy and transmission electron microscopy, to confirm core-sheath morphology, thermogravimetric analysis, and mechanical strength testing. The electrical conductivity of the surfaces of poly(vinyl pyrrolidone) fibers and poly(vinyl pyrrolidone)-multi-walled nanotube fibers were both 10(-15) S/m. The highest bulk conductivity observed for the poly(vinyl pyrrolidone)-multi-walled nanotube fibers was 1.2 x 10(-3) S/m.     

有机黏土对碳纤维/聚醚砜-环氧复合材料层间断裂韧性的影响

采用溶剂法和热熔法制备了不同有机黏土质量分数的有机黏土/聚醚砜（PES）-环氧复合材料,通过对其微观形态和力学性能的研究,揭示了复合材料的增韧机制。在有机黏土/PES-环氧复合材料中添加T800H（12K）碳纤维,制备了T800H-有机黏土/PES-环氧复合材料预浸料单向带,采用热压罐工艺制备了复合材料单向板,对其I型、II型层间断裂韧性进行了研究。结果表明:T800H-有机黏土/PES-环氧复合材料的层间断裂韧性随有机黏土质量分数变化趋势与有机黏土/PES-环氧复合材料的断裂韧性趋势一致,证明了增韧机制的正确性。      

Role of micro/nano fillers on mechanical and tribological properties of polyamide66/polypropylene composites

The objectives of this research article is to evaluate the mechanical and tribological properties of polyamide66/polypropylene (PA66/PP) blend, graphite (Gr) filled PA66/PP, nanoclay (NC) filled PA66/PP and NC plus short carbon fiber (NC + SCF) filled PA66/PP composites. All composites were fabricated using a twin screw extruder followed by injection molding. The mechanical properties such as tensile, flexure, and impact strengths were investigated in accordance with ASTM standards. The friction and sliding wear behaviour was studied under dry sliding conditions against hard steel on a pin-on-disc apparatus. Scanning electron micrographs were used to analyze the fracture morphologies. From the experimental investigation, it was found that the presence of NC and SCF fillers improved the hardness of PA66/PP blend. Further, the study reveals that the tensile and flexural strength of NC + SCF filled PA66/PP was higher than that of PA66/PP blend. Inclusion of micro and nanofillers reduced the wear rate of PA66/PP blend. The wear loss of the composites increased with increasing sliding velocity. The lowest wear rate was observed for the blend with nanoclay and SCF fillers. The wear rates of the blends with micro/nanofillers vary from 30–81% and lower than that of PA66/PP blend. The wear resistance of the PA66/PP composites was found to be related to the stability of the transfer film on the counterface. The results have been supplemented with scanning electron micrographs to help understand the possible wear mechanisms.     

Morphology development in nanoclay filled rubber compounds and rubber blends detected by online measured electrical conductance

The online measured electrical conductance (OMEC) during the rubber mixing process has been used as a novel method to characterize the dispersion of organoclay in rubber compounds and blends. This method was also used for the investigation of morphology development and kinetics of organoclay distribution in carboxylated hydrogenated nitrile butadiene rubber (XHNBR) and hydrogenated nitrile butadiene rubber (HNBR) as well as blends of HNBR with natural rubber (NR). The synchronized increase of the OMEC measured directly in the mixing chamber of the internal mixer along with dispersion of organoclay in the rubber matrix has been observed. The conductivity signal is sensitive to the intercalation/exfoliation process of organoclay in rubber compounds. The correlation between the OMEC and intercalation/exfoliation of organoclay has been determined by various offline experimental techniques like atomic force microscopy (AFM), transmission electron microscopy (TEM), and small angle X-ray scattering (SAXS). In heterogeneous blends the organoclay not only has the tendency to localize in one specific phase, but also strongly influence the development of the blend morphology, which has been nicely correlated with the OMEC chart of HNBR/(NR–clay) blends. A deeper insight into the mixing kinetics, clay transfer as well as development of the blend morphology was achieved on the basis of OMEC chart.     

静电纺制备的PLLA/PCL复合支架性能及细胞相容性

利用静电纺丝技术制备了一系列不同比例的左旋聚乳酸/聚己内酯(PLLA/PCL)复合纳米纤维支架。通过扫描电镜、差热分析、宽角X射线衍射和接触角测试手段对支架结构与形态、结晶性能及亲水性进行了表征;采用在缓冲溶液中加酶的方式,研究了复合材料的降解性能;将体外培养的真皮成纤细胞接种至材料表面,用扫描电镜观察了成纤细胞在材料表面的生长情况。研究结果表明,电纺丝得到的复合支架纤维直径均一,且呈相互连通的多孔网状结构;脂肪酶的存在加速了支架材料的降解速度;成纤细胞在复合支架上具有良好的生长状态。     

壳-芯电纺超细纤维作为药物释放载体的研究

应用同轴共纺技术制备了以L-型聚乳酸为壳层材料,盐酸四环素为主要芯质材料的壳-芯超细纤维膜,研究了这种超细纤维膜的微观结构、力学性能与药物释放特性.结果表明,药物能够包覆在一层很薄的可降解聚合物壳层中,形成一种储库型药物释放系统.纤维的直径大小对纤维膜的各项理化性能有较大影响.随壳层聚合物浓度升高,纤维的平均直径增大,力学强度降低.药物能够从纤维膜中持续释放出来.这种壳-芯超细纤维有望用于药物释放、载药缝合线和医用敷料等生物医学领域.     

Fabrication and Fibroblast Attachment Property of Regenerated Silk Fibroin/Tetramethoxysilane Nanofibrous Biocomposites

In this study, regenerated silk fibroin (RSF)/tetramethoxysilane (TMOS) composite electrospun fibers with improved hydrophilicity were successfully prepared by electrospinning method, which was superior for fibroblast attachment. The electrospinning process caused adjacent fibers to “weld” at contact points, as confirmed by scanning electron microscope (SEM) analysis. Fourier transform infrared spectroscopy (FTIR) showed that TMOS has been well incorporated into the silk fibroin electrospun fibers. Thermogravimetric analysis (TGA) was carried out to quantify the water content in RSF/TMOS composite electrospun fibers. The cytotoxicity and L929 adhesion of three‐dimensional RSF/TMOS fibrous biocompoaites were investigated and compared to pure RSF membrane. The water contact angle of RSF/TMOS nanofibrous composites showed a sharp decrease compared to the pure RSF electrospun fibers, which has a great effect on the early stage of cell attachment behavior due to an relatively enhanced hydrophilicity.