抗静电PET/ATO纤维的制备及材料的性能

采用原位聚合的方法制备了抗静电涤纶(PET)/锑掺杂二氧化锡(ATO)纳米复合材料。结果显示,ATO在PET中分散良好,团聚体尺寸小于200 nm;加入ATO没有影响PET的流动曲线类型,随着ATO含量的增加,在相同的剪切频率下,熔体黏度均呈先增加后减小的趋势;加入ATO提高了材料的热性能,利于熔融纺丝。采用熔融纺丝法制备了抗静电纳米复合纤维。ATO含量为1.0%(质量分数,下同)时纤维的比电阻由2.7×1013Ω.cm下降到4.9×108Ω.cm。抗静电纤维的渗滤阈值为1.05%,低于传统抗静电填料。     

Characterization of attenuated total reflection infrared spectral intensity variations of immature and mature cotton fibers by two-dimensional correlation analysis

Two-dimensional (2D) correlation analysis was applied to characterize the attenuated total reflection (ATR) spectral intensity fluctuations of immature and mature cotton fibers. Prior to 2D analysis, the spectra were leveled to zero at the peak intensity of 1800 cm(-1) and then were normalized at the peak intensity of 660 cm(-1) to subjectively correct the variations resulting from ATR sampling. Next, normalized spectra were subjected to principal component analysis (PCA), and two clusters of immature and mature fibers were confirmed on the basis of the first principal component (PC1) negative and positive scores, respectively. The normalized spectra clearly demonstrated the intensity increase or decrease of the bands ascribed to different C-O confirmations of primary alcohols in the 1050-950 cm(-1) region, which was not apparent from raw ATR spectra. The PC1 increasing-induced 2D correlation analysis revealed remarkable differences between the immature and mature fibers. Of interest were that: (1) Both intensity increase of two bands at 968 and 956 cm(-1) and the shifting of 968 cm(-1) in immature fibers to 956 cm(-1) in mature fibers, together with the intensity decreasing and shifting of the 1048 and 1042 cm(-1) bands, are the characteristics of cotton fiber development and maturation. (2) Intensities of most bands in the 1800-1200 cm(-1) region decreased with the fiber growth, suggesting they are from either noncellulosic components or CH and OH fractions in amorphous celluloses. (3) The reverse sequence of intensity variations of the bands in the 1100-1000 cm(-1) and 1000-900 cm(-1) region of asynchronous spectra indicated a different mechanism of compositional and structural changes in developing cotton fibers at different growth stages.     

Two-dimensional attenuated total reflection infrared correlation spectroscopy study of the desorption process of water-soaked cotton fibers

Two-dimensional (2D) correlation analysis was applied to characterize the attenuated total reflection (ATR) spectral intensity fluctuations of native cotton fibers with various water contents. Prior to 2D analysis, the spectra were leveled to zero at the peak intensity of 1800 cm(-1) and then were normalized at the peak intensity of 660 cm(-1) to subjectively correct the changes resulting from water diffusion in fibers and resultant density dilution. Next, a new spectral set was subjected to principal component analysis (PCA) and two clusters of hydrated (≥13.3%) and dehydrated (<13.3%) fibers were obtained. Synchronous and asynchronous 2D correlation spectra from individual ATR spectral sets enhanced spectral resolution and provided insights about water-content-dependent intensity variations not readily accessible from one-dimensional ATR spectra. The 2D results revealed remarkable differences corresponding to water loss between the hydrated and dehydrated fibers. Of interest were that: (1) the intensity of the 1640 cm(-1) water band remains in a steady state for hydrated fibers but decreases for dehydrated fibers; (2) during the desorption process of adsorbed water, small and water-soluble carbonyl species (i.e., esters, acids, carboxylates, and proteins) begin to accumulate on the cotton surface, resulting in possible changes in the coloration and surface chemistry of native cotton fibers that were rained on prior to harvesting; (3) intensities of bands in the 1200 to 950 cm(-1) region exhibit a more apparent intensity increase than those in the 1500 to 1200 cm(-1) region, indicating the sensitivity of the 1200 to 950 cm(-1) infrared (IR) region to intra- and inter-molecular hydrogen bonding in fiber celluloses; and (4) the 750 cm(-1) band, ascribed to the unstable I(α) phase in amorphous regions, might originate from the cellulose-water complex through hydrogen bonding.     

Vibrational spectroscopic study on the origin of stress oscillation during step-wise stretching in poly(ethylene terephthalate)

The origin of the phenomenon of stress oscillation during step-wise stretching at room temperature for amorphous poly(ethylene terephthalate) (PET) was investigated using vibrational spectroscopy. For the first time, transmission Fourier transform infrared (FT-IR), attenuated total reflection (ATR) FT-IR, and micro-Raman spectroscopies were used in order to investigate the correlation of the orientation of the molecular chains, their conformational transformations, and the appearance of stress-induced crystallization to the phenomenon of stress oscillation during the step-wise stretching procedure. The phenomenon of stress oscillation occurs when amorphous PET is exposed to mechanical stress during which the extension rate is increased in a step-wise manner. This phenomenon leads to the formation of a pattern of opaque and transparent stripes ('striated' or oscillating region), clearly distinguished from the unstretched ('bulk') and the 'necking' regions. Both infrared and Raman spectroscopic investigations revealed that the main conformational transformations and a significant increase of the crystallinity occur simultaneously in the 'striated' region. Polarized infrared experiments showed the presence of increased molecular orientation, which is more profound for the 'intense striated' region. Finally, micro-Raman spectroscopy allowed the study of opaque and transparent stripes individually and showed that the opaque stripes are more crystalline. Thus, our findings provide conclusive experimental support for the theory, which directly correlates the appearance of the stress-oscillation phenomenon with the induction of crystallinity and heat release and is based on Barenblatt's model. Our study also provides new conformational assignments for the infrared bands in PET for the high-frequency region from 3200 to 3800 cm(-1). Specifically, the bands at 3336 cm(-1) and at 3298 cm(-1) have been attributed to the trans and gauche conformations, respectively.     

ABS/PET复合材料的制备及界面相容性

采用醇化聚对苯二甲酸乙二醇酯(PETG)和乙烯-正丁基丙烯酸酯-甲基丙烯酸缩水甘油酯共聚物(PTW)对聚对苯二甲酸乙二醇酯(PET)进行改性,再与丙烯腈-苯乙烯-丁二烯共聚物树脂(ABS)制成复合材料。扫描电镜(SEM)表明,改性后的PET相在ABS基体中分散均匀,形成的分散相区尺寸小,相容性好。红外光谱分析发现,界面经冷热循环后,PET分子中乙二醇链段从左右式构象转变为反式构象,当复合材料在经受高低温试验的过程中,PET和ABS因具有不同膨胀系数而在界面处产生应力。采用改性PET可使ABS/PET复合材料的拉伸强度、弯曲强度和缺口冲击强度分别提高10.8%、13.3%和150%。     

导电聚苯胺纤维的制备与性能表征

以一种新型的双子表面活性剂6,6′-(丁基-1,4-二基双氧)双(3-壬基苯磺酸)(9BA-4-9BA)作为掺杂剂制备聚苯胺导电纤维,并与用2-丙烯酰胺基-2-甲基丙磺酸(AMPSA)掺杂的聚苯胺纤维的性能进行比较,探讨了聚苯胺分子量、纺丝原液的浓度、掺杂剂种类、凝固浴、牵伸工艺对纤维形貌和导电性能的影响。研究表明,质量分数为14%的AMPSA掺杂聚苯胺的二氯乙酸溶液在丙酮凝固浴中得到的初生纤维的电导率达到1.77S/cm,而质量分数为14%9BA-4-9BA掺杂聚苯胺的二氯乙酸溶液在9BA-4-9BA/丙酮凝固浴中得到的初生纤维及1倍牵伸纤维的表面形貌光滑规整,电导率分别为0.39 S/cm和1.14 S/cm。     

Crystalline phase transition with a large conformational change in a thiodicarboxylic acid

A large conformational transition in a crystal of thiodipropionic acid is investigated by differential scanning calorimetry (DSC), X-ray diffraction, optical microscopy, and computer modeling. The room temperature phase (A-phase) was already known to be orthorhombic where the chains have largely zigzagged conformation with both S–C bonds in gauche conformation. A high temperature phase (C-phase) above 105°C is found by DSC. By X-ray analysis, the crystal structure of the C-phase is found to be monoclinic with molecules having nearly extended conformation. Nucleation and growth of the C-phase are clearly observed by polarizing microscope. It is found that each C-phase domain grows very fast in a preferred direction which is nearly parallel to the {110} planes of the C-phase. Molecular dynamics simulation of the transition reveals that the largely zigzagged molecules in the A-phase readily transforms to the extended all trans form at higher temperatures.     

Processing of polyethylene terephthalate fiber reinforcement to improve compatibility with constituents of GFRP nanocomposites

The aim of the present research was to improve the impact strength of epoxy-based glass fiber-reinforced nanocomposites by the addition of polyethylene terephthalate (PET) fibers as reinforcement along with nanoclay. Hybrid nanocomposites containing clay as nano-filler and PET fibers as micro-reinforcement were fabricated. Nanocomposites with 1?phr clay and varying concentrations of PET fibers (1–3?phr) were processed using a vacuum-assisted hand layup. Addition of untreated PET fibers did not improve the impact strength of nanocomposites due to the lack of interaction between the inert PET fibers and other constituents. To improve the interfacial interaction, two different compatibilization procedures for the surface modification of PET fibers were used. In the first procedure, silane treatment of fibers was performed using two separate silane agents. In the second method, maleic anhydride (MAH) grafting was performed in the presence of ultraviolet radiations. Compatibilization of fibers was confirmed with scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) and Fourier transform infrared spectroscopy (FTIR). The results of impact and tensile testing showed an improvement of 19% in the impact strength of nanocomposites at 2?phr silane-treated PET fiber loading without significant loss in tensile strength. Finally, scanning electron micrographs of various nanocomposites were analyzed to correlate with the improved impact strength.     

Material and structural performance evaluation of recycled PET fiber reinforced concrete

Most PET bottles used as beverage containers become waste after their usage, causing environmental problems. To address this issue, a method to recycle wasted PET bottles is presented, in which short fibers made from recycled PET are used within structural concrete. To verify the performance capacity of recycled PET fiber reinforced concrete, it was compared with that of polypropylene (PP) fiber reinforced concrete for fiber volume fractions of 0.5%, 0.75%, and 1.0%. Appropriate tests were performed to measure material properties such as compressive strength, elastic modulus, and restrained drying shrinkage strain. Flexural tests were performed to measure the strength and ductility capacities of reinforced concrete (RC) members cast with recycled PET fiber reinforced concrete. The results show that compressive strength and elastic modulus both decreased as fiber volume fraction increased. Cracking due to drying shrinkage was delayed in the PET fiber reinforced concrete specimens, compared to such cracking in non-reinforced specimens without fiber reinforcement (NF), which indicates crack controlling and bridging characteristics of the recycled PET fibers. Regarding structural member performance, ultimate strength and relative ductility of PET fiber reinforced RC beams are significantly larger than those of companion specimens without fiber reinforcement.     

Adsorption characteristics of acetone, chloroform and acetonitrile on sludge-derived adsorbent, commercial granular activated carbon and activated carbon fibers

The adsorption characteristics of chloroform, acetone, and acetonitrile on commercial activated carbon (C1), two types of activated carbon fibers (F1 and F2), and sludge adsorbent (S1) was investigated. The chloroform influent concentration ranged from 90 to 7800 ppm and the acetone concentration from 80 to 6900 ppm; the sequence of the adsorption capacity of chloroform and acetone on adsorbents was F2>F1 approximately C1 approximately S1. The adsorption capacity of acetonitrile ranged from 4 to 100 mg/g, corresponding to the influent range from 43 to 2700 ppm for C1, S1, and F1. The acetonitrile adsorption capacity of F2 was approximately 20% higher than that of the other adsorbents at temperatures<30 degrees C. The Freundlich equation fit the data better than the Langmuir and Dubinin-Radushkevich (D-R) equations. The adsorption rate of carbon fibers is higher than that of the other adsorbents due to their smaller fiber diameter and higher surface area. The micropore diffusion coefficient of VOC on activated carbon and sludge adsorbent was approximately 10(-4) cm2 s(-1). The diffusion coefficient of VOC on carbon fibers ranged from 10(-8) to 10(-7) cm2 s(-1). The small carbon fiber pore size corresponds to a smaller diffusion coefficient.     

Mechanical characterization of melt spun fibers from recycled and virgin PET blends

In this study two Poly (Ethylene Terephthalate) (PET) polymers obtained from mineral water bottles and a virgin fiber grade PET polymer were investigated. In order to improve their properties when reprocessed at high temperatures, recycled polymers were blended with virgin one. Thermal and rheological properties of extruded recycled/virgin (PET-V/R) blends showed a good microstructural stability compared to extruded pure recycled polymers. Mechanical behaviour of melt spun fibers obtained from recycled/virgin blends were investigated in static (tensile) and dynamic (DMA) modes and gave interesting properties. Fatigue failure of fibers was also studied and resulting fracture morphologies were analysed by Scanning Electron microscopy (SEM).     

聚对苯二甲酸乙二醇酯/锡氟磷酸盐玻璃复合材料原位成纤对聚丙烯的增强效果

采用低玻璃化转变温度的锡氟磷酸盐玻璃(Pglass)改性聚对苯二甲酸乙二醇酯(PET),制备低黏度高模量的PET基复合材料(PET/Pglass);以PET/Pglass或PET为成纤相,聚丙烯为基体,利用实验室自主设计的多级拉伸挤出装置,制得原位成纤增强聚丙烯复合材料,并研究成纤相形态及其对复合材料力学性能的影响。结果表明,与PET相比,PET/Pglass在多级拉伸挤出过程中原位成纤更容易,纤维长径比更大,分散更均匀,从而进一步提高聚丙烯的拉伸强度和模量,而且能保持聚丙烯较高的断裂伸长率,表明具有低黏高模的PET/Pglass对聚丙烯的原位成纤增强效果更显著。     

Effect of the addition of milled carbon fiber as a secondary filler on the electrical conductivity of graphite/epoxy composites for electrical conductive material

In this work, carbon composite bipolar plates consisting of synthetic graphite and milled carbon fibers as a conductive filler and epoxy as a polymer matrix developed using compression molding is described. The highest electrical conductivity obtained from the described material is 69.8 S/cm for the in-plane conductivity and 50.34 S/cm for the through-plane conductivity for the composite containing 2 wt.% carbon fiber (CF) with 80 wt.% filler loading. This value is 30% greater than the electrical conductivity of a typical graphite/epoxy composite with 80 wt.% filler loading, which is 53 S/cm for the in-plane conductivity and 40 S/cm for the through-plane conductivity. The flexural strength is increased to 36.28 MPa compared to a single filler system, which is approximately 25.22 MPa. This study also found that the General Effective Media (GEM) model was able to predict the in-plane and through-plane electrical conductivities for single filler and multiple filler composites.     

Determination of mechanical strength properties of hemp fibers using near-infrared fourier transform Raman microspectroscopy

Fourier transform near-infrared (FT-NIR) Raman microspectroscopy was adopted for analyzing the micro mechanical tensile deformation behavior of cellulosic plant fibers. Mechanical strength parameters such as tensile strength, failure strain, and Young's modulus of diversified hemp fibers were determined within the range of single fiber cells and fiber filaments. The analysis of fiber deformation at the molecular level was followed by the response of a characteristic Raman signal of fiber cellulose that is sensitive to the tensile load applied. The frequency shift of the Raman signal at 1095 cm(-1) to lower wavenumbers was observed when the fibers were subjected to tensile strain. Microstructural investigations using electron microscopy under environmental conditions supported the discussion of mechanical properties of hemp fibers in relation to several fiber variabilities. Generally, mechanical strength properties of diversified hemp fibers were discussed at the molecular, microstructural, and macroscale level. It was observed that mechanical strength properties of the fibers can be controlled in a broad range by appropriate mercerization parameters such as alkali concentration, fiber shrinkage, and tensile stress applied to the fibers during the alkaline treatments.     

Development of recycled PET fiber and its application as concrete-reinforcing fiber

We describe a method that can be used to produce concrete-reinforcing PET fiber from used PET bottles. Using this method, the concrete and PET fibers are easily mixed at a fiber contents as high as 3%. The primary characteristic of the PET fiber is that it is easy to handle. The issue of concern in the development of PET fiber is its alkali resistance; however, we encountered no problems when using the fiber in normal concrete. The wetting tension of PET was found to be lower than that of PVA but higher than that of PP. No toxic gas was generated during a combustion test of the PET fiber. We describe two example applications: a gateway support at Hishikari Mine, Japan, and the pavement of bush roads.     

Structural changes of carotenoid astaxanthin in a single algal cell monitored in situ by Raman spectroscopy

The changes of structure of astaxanthin (AXT), a superpotent antioxidant, upon thermal stress were investigated in unicellular microalgae Haematococcus pluvialis by measuring Raman spectra in situ and analyzing obtained results with DFT calculations. Although no visual changes are observed in the Haematococcus cells upon heating, discernible changes in Raman spectra occur from -100 °C systematically up to 150 °C. The exponential increase of the Raman shift of the ν C═C band at ca. 1520 cm(-1) along with the change of the intensity ratio of bands at 1190 and 1160 cm(-1) is observed, that correlates with the changes predicted by calculations for astaxanthin conformers ordered by decreasing energy. It is assumed that AXT molecules, initially in the form of H-aggregates with the trans conformations of the end-rings, interconvert toward more stable gauche forms upon thermal stress of the algae. The applied approach enables one to follow structural changes of the carotenoid upon temperature stress both in a single algal cell and in a multicellular sample in situ. Obtained information might be of use to improve the industrial process of extraction of AXT in its most bioavailable form.     

3D nanometer images of biological fibers by directed motion of gold nanoparticles

Using near-infrared femtosecond pulses, we move single gold nanoparticles (AuNPs) along biological fibers, such as collagen and actin filaments. While the AuNP is sliding on the fiber, its trajectory is measured in three dimensions (3D) with nanometer resolution providing a high-resolution image of the fiber. Here, we systematically moved a single AuNP along nanometer-size collagen fibers and actin filament inside chinese hamster ovary K1 living cells, mapping their 3D topography with high fidelity.     

From random chopped to oriented continuous SiC fibers–ZrB2 composites

ZrB₂–continuous SiC fiber composites were prepared by vacuum-bag infiltration and hot pressing, using homemade 1D fabric preforms of Tyranno SA3 SiC fibers. Sintering behavior and microstructural features such as secondary phases and matrix/fiber interface were compared to those of chopped SiC fibers-reinforced composites. The infiltration process allowed the overall fiber content to be increased up to 40 vol%, because of the ordered arrangement of fibers. When the fiber preforms were properly infiltrated, the composites were nearly fully dense and the densification mechanisms were the same as those of unreinforced matrices. Different from composites containing short discontinuous fibers, the degree of chemical interaction at the fiber/matrix interface was very limited and this resulted in an easier pull out in the fractured surfaces, even in absence of fiber protective coating.     

Effects of carbon nanotube functionalization and annealing on crystallization and mechanical properties of melt-spun carbon nanotubes/poly(ethylene terephthalate) fibers

To generate poly(ethylene terephthalate) (PET) fibers with enhanced mechanical properties, we prepared melt-spun PET fibers that incorporated pristine, acid-treated, and functionalized multi-walled carbon nanotubes (MWNTs) with 2-phenylethyl alcohol and 4-phenyl-1-butanol. The incorporation of MWNTs into the melt-spun fibers resulted in increased crystallization of PET but lower breaking stress than that of pure PET fibers, even in those containing well-dispersed functionalized MWNTs. The breaking stress of drawn composite fibers was also lower than that of pure PET fibers prepared at the same draw ratio. However, the annealing of melt-spun fibers enhanced the mechanical properties and crystallization, and the annealing effect was more dominant for composite fibers with functionalized MWNTs. These findings indicate that the presence of well-dispersed MWNTs disturbs the crystallization and orientation of PET molecules in highly stressed fibers, which differs from MWNT-induced crystallization of PET molecules in relaxed fibers.     

Effects of Temperature,Oxidation and Fiber Preforms on Fatigue Life of Carbon Fiber-Reinforced Ceramic-Matrix Composites

In this paper, the effects of temperature, oxidation and fiber preforms on the fatigue life of carbon fiber-reinforced silicon carbide ceramic-matrix composites (C/SiC CMCs) have been investigated. An effective coefficient of the fiber volume fraction along the loading direction (ECFL) was introduced to describe the fiber architecture of preforms. Under cyclic fatigue loading, the fibers broken fraction was determined by combining the interface wear model and fibers statistical failure model at room temperature, and interface/fibers oxidation model, interface wear model and fibers statistical failure model at elevated temperatures in the oxidative environments. When the broken fibers fraction approaches to the critical value, the composites fatigue fracture. The fatigue life S–N curves and fatigue limits of unidirectional, cross-ply, 2D, 2.5D and 3D C/SiC composites at room temperature, 800 °C in air, 1100, 1300 and 1500 °C in vacuum conditions have been predicted.