Volume 37, Issue 5

Acrylonitrile-butadiene-styrene copolymer (ABS) was introduced to modify the epoxy resin (EP) by the solution mixing method. The results showed that the modulus was decreased with the addition of ABS. Short carbon fibers (SCF) were chosen as the reinforcement agent to prepare high-performance EP/ABS/SCF composites. Meanwhile, a self-made conical mixer was applied to improve the dispersion behavior of the SCF in EP. The properties of both EP/ABS matrix and EP/ABS/SCF composites were investigated and discussed. The results showed that the tensile strength and impact strength of EP/ABS matrix are remarkably improved in the presence of 4,4-diaminodiphenyl methane (DDM), which reached the maximum value at 4 wt% ABS. The introduction of ABS and SCF eventually can maintain the excellent original properties of EP and greatly improve the tensile modulus of EP/ABS/SCF composites with the specialized self-made conical mixer.

The novel poly (amide-ester-imide) (PAEI)/Na + -MMT (montmorillonite) nanocomposites were synthesized by ultrasound-assisted technique successfully. PAEI/Na + -MMT nanocomposites with various content of Na + -MMT were applied to enhance the dispersion of the clay layers with polymer matrix. Water-soluble PAEI containing poly (ethylene glycol) (PEG-6000) was prepared, and nanocomposites with various content of Na + -MMT (5, 10, 15, and 20 mass %) were fabricated by ultrasonic method to produce nano-scale composites. The effects of Na + -MMT on the nanocomposites were investigated by Fourier transform infrared, X-ray diffraction (XRD), transmission electron microscopy (TEM), and scanning electron microscopy (SEM) and for thermal properties. XRD approved the structure information of the synthesized nanomaterials, and it was shown that the interlayer spacing increased with clay loading. The magnitude of dispersion of the clay in the nanocomposite matrix was investigated by TEM and SEM images. The results indicated that the lateral dimension of Na + -MMT particles in composites was approximately 100 nm, and the nanomaterials are well dispersed in the polymer matrix to produce exfoliated structure in polymer/nanocomposite. Thermogravimetric analysis confirms that PAEI/Na + -MMT nanocomposites show superior thermal stability with respect to the pure PAEIs.

Polyurethane (PU) membrane has great potential in pervaporation recovery of phenol from water. In order to improve the permeability of the membrane, cyclodextrin was attached onto carboxylic and hydroxylate carbon nanotubes (CNTs) by physical and chemical methods, with which modified CNTs/PU membranes were prepared. The results showed that the addition of modified CNTs greatly increases the permeability and comprehensive performance of PU membranes in the pervaporation separation of a phenol/water mixture. With 0.5% phenol content in feed at 80°C, the flux and pervaporation separation index of blank PU are 6.10 and 324 kg·μm·m −2 ·h −1 , while those of chemically modified carboxylic CNTs/PU membranes are 156.1 and 655.8 kg·μm·m −2 ·h −1 , respectively.

Chitosan (CS) is an excellent biocompatible natural antibacterial material that has attracted researchers to study its biological applications as artificial tissue scaffolds and wound-healing materials. In this research, CS has been mixed with polyethylene oxide (PEO) and mica at various weight ratios to prepare nanofibers; however, it is found to be a difficult task to prepare the nanofiber using pure CS. The composite in form of nanofibrous mat was prepared with CS/PEO solution and CS/PEO/mica solution using electrospinning. Processing conditions were adjusted to a flow rate of 6 ml/min, with an applied voltage of 27 kV. The distance of capillary tip to target was kept about 10 cm at 25°C with a collector having a speed of 200 rpm. The spinnability of solutions was also evaluated by using both plate and cylinder collectors. The composite mats were analyzed in detail using scanning electron microscopy (SEM), Fourier transform infrared (FTIR), thermogravimetric analysis, and X-ray diffractogram (XRD). SEM photomicrograms indicated that the morphology and diameter of the nanofibers were affected by weight ratio of CS/PEO, concentration of mica, and types of collector. Furthermore, mica was incorporated in the CS/PEO matrix to enhance the specific surface area. Molecular interactions between CS/PEO and mica were investigated using FTIR and XRD.

An investigation on the cooling-induced crystallization in three thermoplastic polyurethanes based on MDI, PTMG, and 1.4-BD as chain extender with different hard segment content is reported. Thermal transitions were determined using differential scanning calorimetry (DSC) measurements at different cooling rates, and thermal stability was studied by thermogravimetric analysis. Changes in Raman spectra were useful to correlate the thermal transitions with changes in the morphology of the polymers. The dissimilarity in the composition gave different rheological behavior in the molten state, indicated by the temperature dependence of the viscosity. The mechanical properties and the crystallinity was influenced not only by the cooling rate but also by the hard segment content. Thermoplastic polyurethanes with more hard segment content formed more crystalline hard domains as evidenced by the DSC and atomic force microscopy results.

Nanocolloidal polypyrrole/poly(styrene sulfonate) PPy:PSS composites were prepared by dispersion polymerization of pyrrole with 0.5 wt%, 1 wt%, 2.5 wt%, 5 wt%, 10 wt% and 15 wt% of PSS. Higher doping level of PPy was confirmed with increased S/N value of elemental analysis. Morphological variations of PPy composite matrix based on PSS were analyzed in which spherical shaped PPy particles of 20–40 nm were obtained for 1:1 wt% of PPy:PSS. Presence of higher concentration of PSS within the PPy matrix substantially improved its thermal stability. Dielectric properties were investigated using complex impedance analyzer as a function of frequency (50 Hz–5 MHz) and temperature between 30°C and 120°C. PPy, with improved dispersion, showed higher dielectric constant values up to 15 wt% of anionic polyelectrolyte PSS and the dielectric loss varied between 4.7 and 7.9 for different wt% of PSS. AC conductivity (σ ac ) enhanced up to 1:1 wt% of PPy:PSS composite, which is found to be the optimum wt% in this study. DC conductivity was found to decrease after 1:1 wt% of PPy:PSS composite, which is due to excess oxidation, leading to reduced π conjugation of PPy chains. Higher dielectric constant values of composite, with relatively low dielectric loss values, indicate their potential usage in the electric and electronic industry.

A novel method for the chemical manufacturing UV-curing assisted injection molding was proposed in this paper. A prototype of UV-curing injection molding apparatus has been manufactured. By using the prototype, we have successfully fabricated microfluidic chips, which can be practically applied in micro mixing experiments. Similar to the thermoplastic parts molded by traditional injection molding, the appearance defects such as bubbles also occurred on products fabricated by UV-curing injection molding. The generation process of bubble defect has been observed and captured through the visualization device. Because there is no gas produced in the polymerization chemical reaction, the shrinkage was considered to be the essential reason of bubble defect. In this paper, the solution of bubble defect was studied by employing single factor control variable method from the aspects of process parameters, materials, and mode of irradiation. It was noted that the bubble defect could be improved by increasing holding pressure, reducing irradiation intensity, and improving viscosity. Nevertheless, the achievement of process parameters was limited. On equal experimental conditions of process, equipment, and material, results revealed that the dynamic irradiation pattern can improve the feeding capacity significantly in UV-curing injection molding. It is further demonstrated that the bubble defect is caused by the polymerization shrinkage. Eventually, we obtained the microfluidic chips with good surface quality, high dimensional accuracy, and high transparency by UV-curing injection molding. Moreover, it provides a feasible high efficiency and low cost manufacture technology for microfluidic chips in the future.

Plastic products are common in contemporary daily lives. In the plastics industry, the injection molding process is advantageous for features such as mass production and stable quality. The problem, however, is that the melt will be affected by the residual stress and shrinkage generated in the process of filling and cooling; hence, defects such as warping, deformation, and sink marks will occur. In order to reduce product deformation and shrinkage during the process of molding, the screw of the injection molding machine will start the packing stage when filling is completed, which continuously pushes the melt into the cavity, thus making up for product shrinkage and improving their appearance, quality, and strength. If the packing pressure is too high, however, the internal residual stress will increase accordingly. This study set out to apply gas counter pressure (GCP) in the injection molding process. By importing gas through the ends of the cavity, the melt was exposed to a melt front pressure, which, together with the packing pressure from the screw, is supposed to reduce product shrinkage. The aim was to investigate the impacts of GCP on the process parameters via the changes in machine feedback data, such as pressure and the remaining injection resin. This study also used a relatively thin plate-shaped product and measurements, such as the photoelastic effect and luminance meter, to probe into the impacts of GCP on product residual stress, while a relatively thick paper-clip-shaped product was used to see the impacts of GCP on shrinkage in thick parts. According to the experimental results, the addition of GCP resulted in increased filling volume, improvement of product weight and stability, and effective reduction of section shrinkage, which was most obvious at the point closest to the gas entrance. The shrinkage of the sections parallel and vertical to the flow direction was proved to be reduced by 32% and 16%, respectively. Moreover, observations made via the polarizing stress viewer and luminance meter showed that the internal residual stress of a product could be effectively reduced by a proper amount of GCP.

In this study, heat vulcanizing silicone rubber (HVSR) composites were prepared and the impact of the addition of carbon fibers (CFs) on the mechanical and ablation properties of the composite was demonstrated. It was found that with increasing content of CFs, the tensile property and the hardness of the composite increased significantly. The back-face temperature, the ablation rate and the ablation mechanism of the composite were discussed based on the data derived from several characterization methods, including oxygen-acetylene ablation device, scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier transform infrared (FTIR). Along with the increasing of the content of CFs, the mass and linear ablation rates both decreased, but the back-face temperature increased. The interaction between ablation layer and the composite became intense due to the addition of the CFs, which led to the difficult peel-off of the ablation layer. Four layers can be formed after the oxygen-acetylene ablation of the composite including the surface layer, the carbonization layer, the pyrolysis layer and the matrix layer. The ablation mechanism was also proposed. It mainly involves the carbonization of the composite, the ceramization of SiC and the shielding effect of the ablated layer.

Ultra-high pressure water jet is proposed for recycling of vulcanized waste rubber, and cavitation desulfurization in the recycling process is analyzed. The chemical effects of mechanical shearing, pyrolysis, free radical oxidation, and supercritical oxidation produced by bubble collapse are considered the main causes of desulfurization. Scanning electron microscopy, Fourier transform infrared spectrometry, differential scanning calorimetry, nuclear magnetic resonance test, and X-ray photoelectron spectroscopy are used to determine the performance of rubber powder. Gel fraction of rubber powder is measured to analyze the effect of jet pressure on desulfurization. Results indicate that the vulcanized rubber could achieve partial desulfurization. The glass transition temperature of the rubber powder slightly increases after crushing. With the increase of jet pressure, the gel fraction of rubber powder initially decreases and then increases, as well as achieves a minimum value at the jet pressure of nearly 220 MPa, which is ideal for desulfurization.