Volume 32, Issue 6-7

One of the most crucial issues in developing a material model to describe the long term behaviour of polymers is to represent adequately the load dependency of the considered material. In many publications, it is shown that the free volume affects the mechanical behavior of polymers. For a further investigation of the dependency of the creep behavior on free volume, different experiments are presented in this paper. In one experiment, the creep behavior under tension and shear are compared, to see how the different hydrostatic pressures in these tests influence mechanical behavior. Furthermore, tensile creep tests under different hydrostatic pressures are conducted experimentally. The experiments are conducted on a polycarbonate, a polypropylene and a polymethyl methacrylate. It is shown that the hydrostatic pressure has a significant influence on the creep behavior of all three materials. This effect is related to the change of free volume.

Increasing requirements which extruded polymeric products should accomplish are imposed to quantitatively characterize the factors which have a considerable effect on extrusion stability. Investigation has been realized by means of a rheological measurement device including a single screw extruder, as well as a rheological die, signal acquisition and analysis system. Due to a specially designed measurement track and modern signal processing technique, the separation of cyclic instabilities from received signals (representing the course of melt pressure) and the definition of the influence on the extrusion process were feasible. This paper demonstrates an example of the application of two new methods which facilitate the detection of sharkskin instability, irrespective of visual observation of the extrudate. Autocorrelation function and frequency analysis based on a fast Fourier transformation (FFT) were used as numeric tools applied to register and control the extrusion process. The flow of molten polymer was studied under various processing conditions, giving an opportunity to split high frequency pressure fluctuations by means of the autocorrelation function and fast Fourier transform, and to create, in the future, a catalogue of data which can be used to define particular distortions in technological investigations.

The tensile stress and strain under small deformation for plastics/elastomer blends were analyzed, based on a geometric model and mechanical element model, and a Young’s modulus equation was derived based on the hypothesis with equal strain and Hooke’s law. The polypropylene (PP)/polyolefin elastomer (POE) blends were prepared by means of a twin screw extruder, and the Young’s modulus was measured at room temperature. It was found that the Young’s modulus decreased nonlinearly with increase in the POE volume fraction. The Young’s modulus of the PP/POE blends was estimated using the equation and was compared with the measured data. There was good agreement between them. Moreover, the Young’s modulus of PP/ethylene propylene diene monomer (EPDM) rubber EPDM blends at room temperature was estimated respectively using this equation and the mingling rule equation, as well as Liang’s equation published in the literature. The results showed that the calculations with this equation were closer to the experimental data reported in reference than those with the other two equations.

In this study, the tribological performance of poly-ether-ketone (PEEK), ultrahigh molecular weight polyethylene (UHMWPE), glass fiber reinforced poly-tetra-fluoro-ethylene (PTFE) and PTFE reinforced poly-ether-imide (PEI) composite materials, under dry and lubricated conditions, were compared and evaluated. Wear tests were carried out on a pin-disc arrangement and under 50, 100 and 150 N applied loads and 0.5 m/s sliding speed conditions. The results show that the coefficient of friction and specific wear rates for these materials decreases with the increase in applied load values. Finally, the wear rates for PEEK, UHMWPE polymers, PTFE+20% glass fiber reinforced (GFR) and PEI+10% PTFE composites under dry and lubricated conditions are in the order of 10 -14 and 10 -15 , respectively. The results suggested that it is convenient to use PTFE+20% GFR composites for machine components with low processing and product costs.

In this work, the effect of the initial and secondary temperature differences on the solidification behaviors of high-density polyethylene (HDPE) during the thin-walled injection molding (TWIM) was intensively investigated. Simulated temperature profiles using the enthalpy transformation methodology were compared with an in situ temperature measurement, and reasonable agreement was achieved between calculations and measurements. Two-dimensional wide-angle X-ray diffraction characterization shows that the formation of oriented crystal structures was considerably affected by the thermal gradient within the injection-molded article. The present study can be practically significant to the optimization of the cooling parameters during the TWIM of crystalline polymers as well as to the further study on the relationship among “processing-structure-property” of polymeric materials.

Weld lines are commonly present within injection-molded plastic components and generally reduce strength. In designing a plastic part, the designer can often vary the wall thicknesses, or move the gate locations to position the weld line, so that its structural loading is minimized. By altering such variables as melt temperature, mold temperature, and packing pressure, slight increases in weld-line integrity can be achieved. These approaches often do not increase the part strength or performance to an acceptable level, resulting in the exclusion of numerous applications for plastic conversion. This study investigated a hot runner system, sequential valve gates, and heat degree, to achieve economical methods for predicting weld-line properties. By calculating melt front temperatures with MoldFlow analysis, we can predict the strength of the weld line according to the definition of “heat degree”, which is the effective cross-sectional area of the melt front multiplied by the temperature gradient. An effective cross-sectional area of the melt front is defined as the area of the temperature above the melting point. In contrast to the test result, when the “sum of heat degree” is lower than 1150 mm 2 °C for PA6 (Mitsubishi 1030J) and 500 mm 2 °C for polypropylene (PP) (FCFC K1012), the molecules cannot bond adequately at the interface of the melt fronts. Therefore, the mechanical property declines significantly.

This investigation highlights the processing of Nylon 66 and the incorporation of nano-silicate into the Nylon 66 polymeric matrix. Further, radiation modification of Nylon 66 and nano-silicate dispersed Nylon 66 was carried out in order to essentially alter the physicochemical properties of the material. A combination of both the above methods of processing and modifying the neat Nylon 66 polymeric matrix provides an interesting aspect for studying the resultant effect on the variation in properties of the composite material over the virgin polymer. There was a significant improvement of physicothermal and physicomechanical properties when Nylon 66-silicate nanocomposites were further modified under gamma radiation, which was confirmed by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), tensile and water absorption studies.

Sticking in microinjection molds is a significant problem in controlling the qualities of molded parts such as replication rate and appearance. To resolve the problem, this study investigates the effect of chromium nitride (Cr-N) and diamond-like carbon that contains zirconium (Zr-DLC) layers deposited on mold inserts on the antisticking properties of molds. The injection-molded flat plate used is 0.4 mm thick and has 5, 10, and 20 μm high v-grooved microfeatures. To evaluate the importance of the major control factors in determining the microinjection molding quality and to obtain the optimal settings of those factors, the Taguchi method and analysis of variance were utilized. The sticking behaviors of the melt plastics on the cavities that were deposited Cr-N/Zr-DLC layers using an unbalanced magnetron sputtering process were studied with scanning electron microscopy. The experimental results indicate that an antistiction coating most strongly affects replication quality and is followed in that respect by the mold temperature and the barrel temperature. As the dimensions of the microfeatures decrease, the effect of the mold temperature on replication rate becomes more significant. In particular, a Zr-DLC coating on the mold surface yields a low coefficient of friction and a low resistance to the flow of polymer during cavity filling, improving the replication of the heights of the microfeatures. Nevertheless, a Cr-N coating provides better antisticking. This improvement follows from the lower stripping force, which results in the lower surface free energy on the Cr-N layers.

The thermal conductivity of polypropylene (PP) composites filled with Al(OH) 3 and Mg(OH) 2 was measured by means of the stable flat measuring instrument at different testing temperatures. The effective thermal conductivity of the composites was estimated by applying the thermal conductivity equation proposed previously, and the estimations were compared with the experimental measured data under the same experimental conditions. The results showed that the calculations and measurements of the effective thermal conductivity were close to each other when the volume fraction of the Al(OH) 3 /Mg(OH) 2 powder was <10.4%. Moreover, the effective thermal conductivity of the composites was estimated using the Russell model and the Maxwell-Eucken model, and the predictions were compared with the experimental data and the estimations of this equation. It was found that the estimations of this equation were closer to the experimental data than those of the Russell model and Maxwell-Eucken model.

The aim of this study was to prepare polyvinyl alcohol/carbon nanotube (PVA/CNT) conductive nanofibers by the electrospinning process. Prior to composite preparation, carbon nanotubes are dispersed homogeneously in N-methyl-2-pyrrolidone (NMP) and mixed with a PVA solution. A series of PVA/CNT films and nanofibers with various CNT compositions are prepared. Electrical conductivity and specific capacitance of spin-coated PVA/CNT films and electrospun PVA/CNT fibers increase with an increase in CNT content. Electrospun PVA/CNT nanofibers with a larger electrode surface result in a higher specific capacitance when compared with spin-coated PVA/CNT films. According to the morphology analysis, homogeneous and highly porous PVA/CNT mats containing 50–300 nm diameter nanofibers are obtained by the electrospinning process.

Copolymerization of 5-norbornene-2-metheneoxy-trimethylsilyl [NB-CH 2 OSi(CH 3 ) 3 ] with norbornene (NB) or methyl 5-norbornene-2-carboxylate (NB-COOCH 3 ) was carried out in toluene by using novel nickel(II) complex catalyst systems, Ni(benzocyclohexan-ketonaphthylimino) 2 /B(C 6 F 5 ) 3 [Ni(bchkni) 2 /B(C 6 F 5 ) 3 ]. The catalyst system showed high activity on the copolymerization of NB-CH 2 OSi(CH 3 ) 3 with NB (2.3–3.3×10 4 g polymer /mol Ni ·h) and NB-CH 2 OSi(CH 3 ) 3 with NB-COOCH 3 (0.5–3.0×10 4 g polymer /mol Ni ·h). However, the solubility of copolymers of NB-CH 2 OSi(CH 3 ) 3 with NB and NB-CH 2 OSi(CH 3 ) 3 with NB-COOCH 3 , which contain 18.7–86.7 mol% of NB-CH 2 OSi(CH 3 ) 3 , was too poor to characterize. The achieved copolymers were confirmed to be vinyl-addition copolymers through the analysis of FTIR, 1 H NMR, and 13 C NMR spectra. The incorporation rate was 8.7–86.7 mol% at a content of 10–90 mol% of the NB-CH 2 OSi(CH 3 ) 3 in the monomer feeds ratios. The obtained ester functionalized NB copolymer containing 8.7–18.7 mol% of NB-CH 2 OSi(CH 3 ) 3 showed a moderate molecular weight (M w =1.6–6.0×10 4 g/mol) and relative narrow molecular weight distribution (M w /M n =1.6–2.2). Thermogravimetry (TGA) analyses results showed that the copolymers exhibited good thermal stability (T d =330–350°C) and were noncrystalline by WAXD analyses results.

In-situ nitroxide mediated polymerization (NMP) of 1,3-butadiene was carried out in the presence of tetraethylenepentamine (TEPA) as a tri-functional nitroxide precursor, which furnished a high degree of hydroxy functionality. The multi-modal molar mass distribution of the product was elucidated by reductive hydrolyzation of the oligomeric product. The new polyfunctional hydroxyl-terminated polybutadiene (PFHTPB) was characterized and used in preparation of an HTPB-based polyurethane (PU). The effects of this new HTPB on mechanical and dynamic-mechanical properties of its corresponding polyurethane elastomer were studied. The mechanical and dynamic-mechanical characterization of the elastomer was evaluated by tensile and dynamic mechanical thermal analysis (DMTA) tests. A significant enhancement in mechanical properties of the elastomeric product with a small increase in the glass transition temperature was achieved using PFHTPB. In addition, there was a significant decrease in loss of the tangent value over the use of PFHTPB, compared to industrial HTPB, due to an efficient increase in crosslink density of the PFHTPB-based PU elastomer. The thermal stability of PFHTPB-based PU was comparable with its corresponding HTPB-based PU elastomer.

Melt blending of polylactide (PLA), poly(ε-caprolactone) (PCL), and wood flour (WF) was performed in an effort to overcome the major drawbacks (brittleness and high price) of PLA. In addition, the acrylic acid (AA)-grafted PLA 70 PCL 30 (PLA 70 PCL 30 -g-AA) was used as the alternative for the preparation of ternary blends to improve the compatibility and the dispersability of WF within the PLA 70 PCL 30 matrix. As expected, PCL improved the elongation at break and the toughness of PLA but decreased the tensile strength and modulus. Because the hydrophilic WF is dispersed physically in the hydrophobic PLA 70 PCL 30 matrix, as the result of Fourier transform infrared analysis, the mechanical properties of PLA 70 PCL 30 became noticeably worse when it was blended with WF. This problem was successfully conquered by using PLA 70 PCL 30 -g-AA to replace PLA 70 PCL 30 due to the formation of an ester carbonyl group between PLA 70 PCL 30 -g-AA and WF. Furthermore, the PLA 70 PCL 30 -g-AA/WF blend provided a plateau tensile strength at break when the WF content was up to 50 wt%. PLA 70 PCL 30 /WF exhibited a tensile strength at break of approximately 3–25 MPa more than PLA 70 PCL 30 -g-AA/WF. By using p -cresol and tyrosinase, the enzymatic biodegradable test showed that PLA 70 PCL 30 -g-AA is somewhat more biodegradable than PLA 70 PCL 30 because the former has better water absorption. After 16 weeks, the weight loss of the PLA 70 PCL 30 /WF (50 wt%) composite was >80%. PLA 70 PCL 30 -g-AA/WF exhibited a weight loss of approximately 1–12 wt% more than PLA 70 PCL 30 -g-AA/WF. It was also found that the addition of WF to PLA 70 PCL 30 or PLA 70 PCL 30 -g-AA decreased the crystallinity of PLA and PCL in PLA 70 PCL 30 or PLA 70 PCL 30 -g-AA and then increased their biodegradable property.

The influence of nanosized filler particles on mechanical properties of composite fibers has some specific features related to the fiber matrix, its preparation and the filler content, as well as the orientation of the fibers at their drawing. This paper discusses the manner of dispersion of chemically unmodified boehmite type nanofiller, Disperal 40 (D40) or Disperal 60 (D60) in polypropylene (iPP) fibers, and the influence of filler and its particle size on the tenacity, modulus and elongation of the iPP fibers. It was found that filler D40 was effective in increasing the tenacity only up to a content of about 1 wt% and in fibers prepared only at higher drawing ratios. Transmission electron microscopy (TEM) pictures of the cut iPP+D40 or iPP+D60 fibers have shown the presence of aggregation of nanosized boehmite particles in all cases. A comparison of the effects of two different particle sized fillers on the mechanical properties of the isotactic PP (iPP) fibers showed that a small difference between the particle sizes of both kinds of filler plays some role regarding the tensile strength of the fibers. The iPP fibers containing a mixture of D40 and D60 showed some deviations from the expected sum of the effects of both fillers on their mechanical properties.

In this study, six polyblended nanofiber mats, composed of poly ε-caprolactone (PCL)-polyethylene glycol (PEG) mixed at different proportions in an electrospinning solution were fabricated, and then utilized alongside commercial polyester microcarriers for the mass cultivation of recombinant Chinese hamster ovary (rCHO) cells. The SEM micrographs showed that the rCHO cells were attached to the nanofiber mats with significant differences in their affinities, which can be related to the chemical structure and hydrophilicity of the nanofiber mats. The cell densities of the rCHO cells grown on the polyblended PCL-PEG nanofiber mat (80:20)14% were much higher when compared with the commercial polyester microcarrier. Moreover, recombinant protein production increased by approximately 20% when cells were grown on the PCL-PEG nanofiber mat (80:20)14%. The results of this research indicated a potential for the replacement of the commercial polyester microcarrier with the PCL-PEG polyblended nanofiber mats, in order to achieve mass cultivation of recombinant animal cells in industrial bioreactors.