Band 33, Heft 1

Calcium sodium aluminosilicate (CaNaAlSi 2 O 7 ) ceramic powder was prepared from eggshells as a raw material via the sol-gel process at room temperature. The CaNaAlSi 2 O 7 ceramic particles were embedded as a dispersed phase in the polyurethane (PU) foam matrix via a direct foaming process. The calcium sodium aluminosilicate (CaNaAlSi 2 O 7 ) ceramic powder had a high specific surface area of 38.89 m 2  g −1 , and a fine average particle size of 13.27 μm, whereas the PU foam had a low specific surface area of 1.00 m 2  g −1 , and of light weight. After adding 10 vol% CaNaAlSi 2 O 7 to the PU, the composite foams possessed a high specific surface area of 6.0 m 2  g −1 , a bulk density of 0.213 ± 0.012 g cm −3 , a high decomposition temperature of 790 °C, and a high compressive Young's modulus of 346.0 ± 76.5 kPa. The CaNaAlSi 2 O 7 /PU composite foams provided good thermal conductivity, uniform pore size and particle size distribution, good bridge bonding, and with microcellular interconnecting cells. The CaNaAlSi 2 O 7 / PU semi-rigid composite foams are potential candidate materials for a variety of products such as construction materials, catalysts, insulation materials, and adsorbent materials. There are several advantages of the semi-rigid composite foams: light weight, high specific surface area, and high thermal decomposition temperature.

A series of polypropylene hollow fiber membranes was fabricated by melt-spinning and stretching. The crystalline behavior and hard elasticity of precursor hollow fibers were studied by differential scanning calorimetry (DSC), elastic recovery and strain-stress curves. The structure and properties of membranes were investigated in detail by scanning electron microscopy (SEM), optical microscopy, pure water flux, and so on. The results showed that membranes with excellent structure and properties can be obtained at a spin-draw rate of 350 m/min and a stretching ratio of 200 %. The evolution of crystal structure was explored during the annealing and stretching processes by two-dimensional small-angle X-ray scattering (2D-SAXS). Shish-kebab structure was obtained during annealing for hollow fibers at a spin-draw rate of 350 m/min. The crystalline lamellae were destroyed and micropores were formed during the fabrication of membranes by stretching.

Polytetrafluoroethylene (PTFE) micro-porous membranes were prepared from PTFE fine powder through extruding, rolling, and uniaxial longitudinally stretching. In contrast to conventional planar transverse stretching, a novel 3D mold design of non-planar transverse stretching process was employed in this study to produce micro-porous structure. The morphology, membrane thickness, mean pore size, and porosity of the PTFE membrane were investigated. The results show that the non-planar transverse stretched membranes exhibit more uniform average pore diameter with thinner membrane thickness. Morphological changes induced by planar and non-planar transverse stretching for pore characteristics were investigated. The stretching conditions, stretching temperature and rate, affect the stretched membrane. Increasing temperature facilitated the uniformity of pore size and uniformity of membrane thickness. Moreover, increase in stretching rate resulted in finer pore size and thinner membrane.

The surface modification of titanium dioxide (TiO 2 ), which can be easily attained by a simple addition of ascorbic acid (AA) to aqueous TiO 2 suspensions, affects the photodegradation. Surface modification results in the formation of a colored surface complex that causes red shift in the absorption threshold of TiO 2 . Photodegradable polypropylene (PP) composite films were prepared by embedding AA modified nano TiO 2 into the PP matrix (PP/(AA/TiO 2 )). The photocatalytic degradation behavior of PP/(AA/TiO 2 ) composite film under UV light irradiation as investigated and compared with those of the PP/TiO 2 and neat PP films, with the aid of UV-Vis spectroscopy, Fourier Transform Infrared spectroscopy, weight loss monitoring, tensile test and scanning electron microscopy. The degradation rate of the PP/(AA/TiO 2 ) composite films is three times higher than that of PP/TiO 2 film and six times higher than that of neat PP film. In addition, the FTIR spectra show that the intensity of the peak of carbonyl group for neat PP is much lower than that of the composite film.

The effects of graphene nano-platelets (GNPs) content on melt flow behavior and flexural properties of reinforced polypropylene (PP) composites were investigated. The results showed that both the flexural modulus and strength at room temperature increased when GNPs weight fraction was lower than 0.4 wt.%, and then decreased with increasing GNPs weight fraction. During the melt flow of the PP composites in capillary extrusion within temperatures ranging from 180 to 230 °C and in apparent shear rates varying from 100 to 4 000 s −1 , the melt shear flow followed the power law relationship, and the dependence of the melt shear viscosity on temperature obeyed the Arrhenius equation. The correlation between the melt shear viscosity and GNPs weight fraction was approximately linear under the given test conditions.

Elastomeric foams based on 60/40 EVA/NR blend nanocomposite were prepared by melt mixing EVA, NR and clay (5 phr) in an internal mixer, and later foamed with azodicarbonamide through compression molding. Epoxidized natural rubber (ENR) with epoxide content of 25 mole% was used as a compatibilizer to improve interfacial adhesion between EVA and NR. The addition effect of ENR concentration on the blending and properties of EVA/NR blend nanocomposite foams was studied. XRD and TEM results showed that the clay in the EVA/NR blends was intercalated and locally existed in the NR phase as well as at the interface between EVA and NR. The EVA/NR blend nanocomposites showed dispersed NR domains in continuous EVA phase. The addition of ENR into EVA/NR blend nanocomposites reduced the size of the dispersed NR phase, indicating that the blend miscibility was improved. Mechanistic model was proposed for the miscibility improvement of a two-phase structure of EVA/NR blend nanocomposite in the presence of ENR and clay dispersion. However, the improved blend morphology did not significantly affect the cell structure of EVA/NR blend nanocomposites. The observation of cell structure of EVA/NR blend nanocomposites suggested that the increased addition of ENR caused a little increase in cell density, and had no influence on cell size. Furthermore, with increasing addition level of ENR in the blend nanocomposite foams, the foam density slowly decreased, whereas the specific tensile strength slightly increased. The elastomeric recovery of blend nanocomposite foams decreased with increasing ENR content. The thermal conductivity of EVA/NR blend nanocomposite foams also decreased with more addition of ENR, which had beneficial result in improving thermal insulation property.

Previous studies have shown that enhancing injection pressure can help improve the precision and mechanical properties of molding products, and reduce their shrinkage. But for now the ordinary hydraulic injection molding machine cannot generally meet the requirements of high pressure injection. To improve the injection pressure, the pressurizing module and the hydraulic circuit were designed, and their influence on the product quality was explored via molding experiments. The relationship between the system pressure of injection molding machine and the injection pressure was demonstrated. The experimental results showed that the maximum injection pressure of the injection molding machine with the pressurizing module was improved from 204 MPa to 320 MPa, up 56.86 %. The lack of materials, bubbles, sags of products were gradually weakened until finally disappeared with increasing the injection pressure. The pressurizing module was convenient to be assembled into or removed from the injection molding machine without damaging the original structure, and the state of pressurizing or no pressurizing could be transformed easily during the injection molding process. These results indicated that this technology was easy to be popularized and applied.

The melt spinning behavior of electron-irradiated polypropylene (PP) and PP/ethylene-octene-copolymer (EOC) blends was studied. The low ability to fiber formation of the impact enhanced PP/EOC blends with 2.5 mass percent of high viscous and non-spinnable EOC rubber was enhanced to a large extent by applying a dose of 6 kGy using a continuous electron induced reactive processing (CEIReP). The influence of structure alteration during CEIReP on the fiber formation as well as the textile physical properties of as-spun blend fiber were explored. A remarkable enhancement of the initial modulus as well as the linear elastic region of CEIReP modified PP/EOC blend fiber were achieved.

Before injection molding, wood polymer composites (WPC) normally have to be dried to achieve optimal quality of the injected parts as well as to avoid corrosion of the mold. Based on a literature study, there are currently no published investigations dealing with the dependency of WPC properties on the initial moisture content of the compound's pellets. Further, it is known that water and wood in combination with high temperatures can lead to corrosion of steel parts, but a systematic analysis of the impact of WPC injection molding on tool corrosion has not been found in the literature. For the present study, a compound with 68 wt% (weight percent) polypropylene, 30 wt% wood flour and 2 wt% coupling agent was produced and tested in injection molding trials. Specimens according to ISO 527-2 were produced from WPC with defined moisture contents, respectively. Compound moisture, already at very low contents, had significant negative effects on the tested mechanical properties, namely tensile modulus and strength, unnotched and notched Charpy impact strength and heat deflection temperature. Corrosion trials were performed for different tool steel qualities. The severity of corrosion correlates with the amount of chromium (Cr) in the alloys tested.

This paper presents a series of simulation approaches to model the mechanisms associated with the flow and breakup of a polymer melt in a new micropelletization technique. This has proven to be an alternative way of producing micropellets and powders with physical properties demanded in polymer processes such as sintering, rotomolding, injection molding, and extrusion. The new technique involves extruding a polymer melt strand through a capillary and stretching it with a stream of hot air, causing the formation of Rayleigh disturbances that lead to breakup of the strand into small particles. Experimental work has demonstrated that the viscoelastic response of the extruded thread influences the breakup process, affecting the final shape and size distribution of the particles. This work presents simulation results for the melt flow behavior that reproduces what has been observed experimentally during the breakup stage. A free surface viscoelastic solver, implemented in the OpenFOAM computational fluid dynamics software, allows visualization of viscoelastic effects on the melt as it leaves the extrusion die and meets the stream of air. Modeling of the viscoelastic fluid flow in this process is intended to serve as a tool for process control and understanding of influential factors in the development of micropellets, for a range of materials and process conditions.

The majority of native starch is used in the food sector and in the paper industry. Only a small amount is used in polymer engineering. One reason for the reluctance of the plastics processing industry to use starch as a filling material in polymer blends is the unsatisfactory mechanical behavior of starch when combined with thermoplastics. Another reason is the hydrophilicity of starch. In order to make these materials capable of competing, an amelioration of the mechanical properties is compulsory. By means of modifying the native starch and optimizing the compounding process, it is possible to improve the performance of starch blends, and, thus, increase the number of application areas of these materials. For this reason, native starch was modified with a cross-linking agent using a laboratory mixer. Subsequently, the modified starch and poly(lactic acid) were compounded using a co-rotating twin screw extruder. Cross-linking of the native starch in the laboratory mixer resulted in an increase in the mechanical strength of the starch blends. In addition, the blends with cross-linked starch displayed lower moisture absorption levels than blends with native starch as a filling material.

Fiber composites are the pinnacle of lightweight materials in the automotive industry. The orientation of the reinforcing fibers strongly affects the mechanical performance of the finished part. However, fiber orientation prediction with high accuracy is difficult for a complex flow field in practical injection molding. Recently, an objective model, iARD-RPR (Improved Anisotropic Rotary Diffusion and Retarding Principal Rate), has been significant to provide anisotropic distribution of fiber orientation, such as the well-known skin-shell-core structure. Micro-computed tomography (micro-CT) scan is a state-of-the-art technique for measuring a very high 3D resolution of a specimen's fiber orientation data. According to the micro-CT experiments and injection molding simulations with the iARD-RPR computation, we investigate changes in fiber orientation distributions at different concentrations in a rectangle plate, while the alignment of fibers found in weld line is revealed for tensile bar. Comparisons of the fiber orientation predictions with the validated experimental data are also presented herein.

CO 2 laser machining technology is a wide and low-cost method for fabrication of microfluidic chips on polyethylene terephthalate (PET). In this paper, the influence of CO 2 laser parameters including laser power and laser moving velocity on the depth and width of PET microchannel are studied. Laser power is set from 4 W to 20 W and laser moving velocity is set from 5 mm/s to 25 mm/s in the experiment. Compared with experimental results, some rules for the depth and width on laser parameters are obtained. The depth and width of the microchannel increase with the increase of laser power at the same laser moving velocity. However, the depth and width of the microchannel first increase and then decrease with the increase of laser moving velocity at the same laser power. The PET microfluidic chip is fabricated by a hot bonding machine.

For injection molding, a controlled heat removal is important to produce dimensional accurate parts efficiently. The following article introduces a new concept called inverse thermal mold design. Using this method, a proper cooling channel system for the injection mold can be produced to achieve minimal part warpage. Based on the postulate of a homogeneous material density distribution within the plastic part to achieve homogenous shrinkage, the method calculates the local cooling demand of the part to derive the cooling channel layout of the mold.

In this research, the individual influence and synergistic behavior between titanium dioxide modified expendable graphite and ammonium polyphosphate on combustion behavior and physicomechanical properties of rigid polyurethane foam (RPUF) were investigated. Combustion behavior was evaluated by limiting oxygen index, and vertical-combustion tests. Thermal stability was studied via thermogravimetric/differential thermal gravimetric (TG/DTG) analysis. Results showed that the modified expendable graphite presented better thermal stability and flame retardancy for RPUF than the normal expandable graphite. Furthermore, the combination of the modified expendable graphite and ammonium polyphosphate with the mass ratio of 1 : 1 caused the RPUF to exhibit better flame retardancy, compression strength and high temperature thermal stability. Especially, the compression strength of this polymer composite sharply increased by 52.4 % over RPUF.

Commercial poly(l-lactic acid) (PLLA) was blended with different contents of graphene oxide-graft-poly(d-lactic acid) (GO-g-PDLA), which was synthesized via ring-opening polymerization using modified GO as initiator. PLLA and PLLA/GO-g-PDLA blend foams were prepared in a batch process via varying-temperature mode using supercritical carbon dioxide as physical foaming agent. The results showed that the addition of GO-g-PDLA in PLLA leads to the formation of stereocomplex (sc)-crystallites. Increase in the GO-g-PDLA content enhances the IR absorption, diffraction peak and melting peak corresponding to the sc-crystallites. The addition of GO-g-PDLA to PLLA leads to the decrease of the cell diameter, increase of the cell density and to a little change in expansion ratio, which is attributed to the fact that the enhancement of PLLA crystallization restricts cell growth and GO-g-PDLA acts as nucleation point.

In this study, polydimethylsiloxane and graphene were used to fabricate surface electrodes for electrocardiographic (ECG) sensing. A simple and inexpensive method was developed to fabricate graphene-based polymer films. In this method, graphene was inlaid in polydimethylsiloxane by polymer infiltration. The polymer films were successfully used in ECG measurements and performed as well as conventional silver/silver chloride wet electrodes. Few motion artifacts were observed with the graphene films when body postures were changed and during walking. The presented approach is low-cost and suitable for mass production, holding great promise in fabricating polymer electrodes for medical monitoring.