The Effect of Microstructure on the Dynamic Equi-Biaxial Fatigue Behaviour of Magnetorheological Elastomers

Dynamic equi-biaxial fatigue behaviour of isotropic and anisotropic magnetorheological elas-tomers (MREs) based on a silicone rubber matrix was investigated using the bubble inflation method. Con-stant engineering stress amplitude was used as the control mode and samples were fatigued over different stress ranges between 0.75MPa and 1.4MPa. S-N (Wöhler) curves showing plots of stress amplitude (σa) ver-sus cycles to failure (N) are presented. Stress-strain behaviour throughout the fatigue process is described. Elastic modulus (E*) was studied for the specific cycles measured. It was found that anisotropic MREs exhi-bited greater fatigue resistance than isotropic MREs for a given magnetic particle content. Stress softening and hysteresis continued throughout the tests though they were most pronounced in the first dozen cycles at the lower stress amplitudes. A limiting value of E*, below which fatigue failure is likely to take place was ob-served in both isotropic and anisotropic MREs, although the initial modulus was higher in anisotropic MREs

The Influence of Particle Content on the Equi-Biaxial Fatigue Behaviour of Magnetorheological Elastomers

The equi-biaxial fatigue behaviour of silicone based magnetorheological elastomers (MREs) with various volume fractions of carbonyl iron particles ranging between 15% and 35% was studied. Wöhler curves for each material were derived by cycling test samples to failure over a range of stress amplitudes. Changes in complex modulus (E*) and dynamic stored energy during the fatigue process were observed. As for other elastic solids, fatigue resistance of MREs with different particle contents was shown to be dependent on the stress amplitudes applied. MREs with low particle content showed the highest fatigue life at high stress amplitudes while MREs with high particle content exhibited the highest fatigue resistance at low stress amplitudes. E* fell with the accumulation of cycles for each material, but the change was dependent on the particle content and stress amplitude applied. However, each material failed in a range suggesting a limiting value of E* for the material between 1.22 MPa and 1.38 MPa regardless of the particle content and the magnitude of the stress amplitude. In keeping with results from previous testing, it was shown that dynamic stored energy can be used to predict the fatigue life of MREs having a wide variation in particle content

The Effect of Process Parameters on the Properties of Elastic Melt Blown Nonwovens: Air pressure and DCD

An elastic masterbatch and elastic melt blown nonwovens are prepared based successively on styrene-ethylene/butylene-styrene (SEBS) and polypropylene (PP) blend. The phase separation morphology, rheological properties and crystal structure of the elastic masterbatch are investigated. The results show that a compatible and stable structure is obtained in molten SEBS and PP blend with excellent mobility in the temperature range of 210–230C. The crystallization of PP slows down resulting in a finer structure due to the restriction of the SEBS network structure with rarely change of crystalline structure. The relationship between process parameters and properties of the elastic nonwoven is also studied in detail. Air pressure and die to collector distance (DCD) have discernible effects on fiber diameter and bonding between fibers, further influencing the performances of nonwovens including porosity, tensile strength and elastic recovery. Elastic recovery is shown to be significantly more affected by DCD than by air pressure

Mesoporous polymer loading heteropolyacid catalysts: one-step strategy to manufacture high value-added cellulose acetate propionate

Cellulose esters are cellulose derivatives with broad application in plastics, films, fibers, coatings, textiles industries, and so forth. Taking cellulose acetate propionate (CAP) as an example, high-viscosity CAP products are widely used in printing inks, hot-melt dip coatings and lacquer coatings, and so forth. However, it was and remains to be a great challenge to manufacture high-viscosity CAP derivatives because of the overuse of sulfuric acid as catalyst that can degrade cellulose and then affect the viscosity and molecular weight of the product. Herein, with use of the copolymer of divinylbenzene with 4-vinylbenzyl chloride (PDVB–VBC) as support, imidazole-containing ionic liquid (IM) as linker, and polyoxometalates (POMs) as catalytic active sites, novel solid acid catalysts of PDVB–VBC–IM–POMs are prepared and fully characterized by Fourier transform infrared, scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, nuclear magnetic resonance, Brunauer–Emmett–Teller, thermogravimetry-differential scanning calorimetry, and X-ray photoelectron spectroscopy. Application of the as-prepared catalysts for CAP shows the following advantages: (1) high viscosity and high molecular weight (Mw) of CAP can be achieved; (2) partially substituted CAP product (degree of substitution, 2.18–2.77) can be obtained without necessity of the hydrolysis step, in which the relatively higher substitution degree of cellulose takes place at the C6 position. This work shows the great potential of new designed solid acid catalyst for high value-added cellulose derivatives

Electromechanical Instability in Silicone-and Acrylate-based Dielectric Elastomers

Electromechanical instability (EMI) is regarded as a significant factor in preventing dielectric elastomers (DEs) fromachieving large voltage-induced deformations. In this study, the strain-stiffening effect was used to control the occurrence of EMI in DEs. The results show that the stretching ratio required to provide a feasible strain-stiffening effect in silicone rubber (SR) was smaller than that needed for a commercial DE material, VHB 4910. The experimental data were compared with currently used models for the simulation of EMI in DEs. We found that EMI could be eliminated in the deformation of these elastomers when pre-stretching was used. Through the application of a prestretching ratio of above 2.0, EMI was suppressed in both the VHB 4910 and SR samples. The findings of this research are of great significance in the maximization of the electromechanical performance of DE materials

Rapid fabrication of silver nanoparticle/polydopamine functionalized polyester fibers

In this paper, silver nanoparticles functionalized poly(ethylene terephthalate) (PET) fibers with antimicrobial activity, electrical conductivity and good coating stability are reported. Firstly, silver plated PET fibers were fabricated by rapid polydopamine (PDA) modification followed by electroless plating. Secondly, the surface morphologies and compositions of PDA modified and silver coated PET fibers were characterized by employing scanning electron microscopy, atomic force microscopy, X-ray diffraction and energy dispersive spectrometry. Finally, the antimicrobial properties and electrical conductivity of the silver plated PET fibers were investigated. The results showed that the silver coated PET fibers exhibited excellent antimicrobial activity to both Escherichia coli and Staphylococcus aureus (with an antimicrobial efficiency of 100 and 99.99%, respectively), and that the antimicrobial activity was well maintained after washing. The silver coated PET fibers showed electrical resistance of 0.76 Ω per 1 cm, indicating good conductivity. It was also demonstrated that the silver layer that formed had good mechanical durability, as indicated by conductivity measurements during tensile loading and observation of the surface morphology of the fibers under various modes of deformation

Isolation of Mycobacterium tuberculosis complex (MTBC) from dairy cows in China

Eleven thousand five hundred and eighty non-blood samples from dairy cows were subjected to mycobacterium culture and genotyping. As a result, a total of 142 isolates of Mycobacterium tuberculosis complex (MBTC) were identified. Among them, 65 were Mycobacterium tuberculosis, while 77 Mycobacterium bovis. The genotype of M. tuberculosis strains was mainly Beijing family. In addition, the isolation rates of MTBC were 33.89% for lung lymph nodes, 2.81% for nasal swabs, and 3.95% for pharyngeal swabs from cattle positive to tuberculin skin test, respectively. This evidence implied that M. tuberculosis infection in cattle is a new risk to public health and should be paid more attention.Key words: Mycobacterium tuberculosis complex, cows, tuberculosis, zoonosis

Study on Spinnability of PP/PU Blends and Preparation of PP/PU Bi-component Melt Blown Nonwovens

Melt blown polymer blends offers a good way to combine two polymers in the same fiber generating nonwovens with new and novel properties. In this study, polypropylene (PP) and polyurethane (PU) were blended to prepare PP/PU bicomponent melt blown nonwovens. The spinnability of PP/PU composites was investigated and PP/PU bi-component nonwovens with compositions of 95/5, 90/10, 80/20 and 70/30 were prepared by using the melt blowing technique. The melt blown fibers exhibited a ‘sea-island’ structure with PP as the continuous phase and PU as the dispersed phase. When the content of PU in the blend was above 40 %, PP/PU melt blown nonwovens could not be produced due to fiber breaking. For PP/PU (90/10) nonwovens, it was found that the average fiber diameter decreased with increasing die to collector (DCD) and elevated hot air pressure

The fabrication and properties of magnetorheological elastomers employing bio-inspired dopamine modified carbonyl iron particles

To obtain magnetorheological elastomers (MREs) with improved mechanical properties and exhibiting an enhanced magnetorheological (MR) effect, bio-inspired dopamine modification has been used to improve the functionality at the surface of carbonyl iron (CI) particles. Various techniques including x-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to confirm that a polydopamine (PDA) layer of about 27.5 nm had been successfully deposited on the surface of the carbonyl iron particles prior to their inclusion in the MRE composites. The magnetic properties of PDA modified CI particles were shown to be almost the same as those for untreated CI particles. With the introduction of a PDA layer to the surfaces of the particles, both the tensile strength and the elongation at break of the MREs were improved. Furthermore, the MRE composites filled with PDA-coated CI particles exhibited lower zero-field storage moduli but higher magnetic field induced storage moduli when magnetization saturation was reached. The absolute and relative MR effect for the MREs reached 0.68 ± 0.002 MPa and 294% respectively, which were higher than those of MREs with pristine CI particles whose absolute and relative MR effect were 0.57 ± 0.02 MPa and 187% respectively. The findings of this work provide insights into enhanced fabrication of MREs with both improved mechanical properties and magneto-induced performance

Carbon Nanotube Coated Fibrous Tubes for Highly Stretchable Strain Sensors Having High Linearity

Strain sensors are currently limited by an inability to operate over large deformations or to exhibit linear responses to strain. Producing strain sensors meeting these criteria remains a particularly difficult challenge. In this work, the fabrication of a highly flexible strain sensor based on electrospun thermoplastic polyurethane (TPU) fibrous tubes comprising wavy and oriented fibers coated with carboxylated multiwall carbon nanotubes (CNTs) is described. By combining spraying and ultrasonic-assisted deposition, the number of CNTs deposited on the electrospun TPU fibrous tube could reach 12 wt%, which can potentially lead to the formation of an excellent conductive network with high conductivity of 0.01 S/cm. The as-prepared strain sensors exhibited a wide strain sensing range of 0–760% and importantly high linearity over the whole sensing range while maintaining high sensitivity with a GF of 57. Moreover, the strain sensors were capable of detecting a low strain (2%) and achieved a fast response time whilst retaining a high level of durability. The TPU/CNTs fibrous tube-based strain sensors were found capable of accurately monitoring both large and small human body motions. Additionally, the strain sensors exhibited rapid response time, (e.g., 45 ms) combined with reliable long-term stability and durability when subjected to 60 min of water washing. The strain sensors developed in this research had the ability to detect large and subtle human motions, (e.g., bending of the finger, wrist, and knee, and swallowing). Consequently, this work provides an effective method for designing and manufacturing high-performance fiber-based wearable strain sensors, which offer wide strain sensing ranges and high linearity over broad working strain ranges