Polymer Engineering and Science

Polymer molecular weight heterogeneity affects the rheological properties of polymer melts such as melt viscosity, fracture and die swell. These rheological properties affect the conversion of the polymer from the bulk resin state to its final usable form. In this particular study, the effect of molecular weight distribution on polyethylene blown film characteristics was studied. The effect of the molecular weight heterogeneity on the rheological characteristics of the polymer in the molten state and its effect on the film properties is presented.

The properties studied included film gloss, haze, tear resistance and film impact strength.

This study shows that broadening the molecular weight distribution increases haze and reduces film gloss. Further, it was shown that a linear relationship exists between film gloss and external haze. Both values are measures of surface irregularities in the film which are affected by the drawing characteristics of the polymer.

A broader molecular weight distribution results in increased impact strength as measured by the Dart Drop Impact Test. This is, it is believed, a result of the increase in long chain branching of the higher molecular weight fractions of the polymer which cause a higher degree of molecular weight entanglement at the branch sites. In contrast the tear strength is reduced as the molecular weight distribution broadens because of the low molecular weight fraction in the broad spectrum material which tend to decrease resistance to tear.

The activation energy for sintering of poly(methyl methacrylate) particle pairs is shown to be similar to their activation energy for Newtonian flow. Sintering progress with time is in good agreement with the Frenkel's coalescence theory. Typical sintering shear rates are shown to be very low and potential energy change (two particles) is small in comparison with the surface energy change. These results lead to the conclusion that the coalescence sintering mechanism of amorphous polymers above their glass transition temperature is essentially a Newtonian viscous flow mechanism where surface tension is the major driving force. A periodical phenomenon associated with sintering progress with time is reported and a supporting mechanism is proposed.

Four processing parameters, layer thickness, printing speed, raster angle, and building orientation were investigated in terms of their effects on mechanical properties, surface quality, and microstructure of acrylonitrile‐butadiene‐styrene (ABS) samples in fused deposition modeling (FDM) by orthogonal experiments. The results show that both the building orientation and the printing layer thickness have a great influence on the mechanical properties of ABS specimens. When the layer thickness is 0.1 mm, samples printed in horizontal direction have the best mechanical performance. The vertical‐direction‐built parts generally have the worst tensile strength and impact resistance. Moreover, the layer surface quality of the products becomes worse with the increasing of layer thickness and printing speed. The influence of layer thickness on the roughness of FDM samples is still very significant. These researches are of great significance to explore the FDM molding mechanism and optimize processing parameters to meet the performance demands. POLYM. ENG. SCI., 59:120–128, 2019. © 2018 Society of Plastics Engineers

The composites discussed in this review are prepared using techniques similar to those used in the new sol‐gel approach to ceramics. Organometallis such as silicates, titanates, and aluminates are hydrolyzed in the presence of polymer chains (for example polysiloxanes and polyimides) that typically contain hydroxyl or amino groups. The functional groups are used to bond the polymer chains onto the silica, titania, or alumina being formed in the hydrolysis, thus forming organic‐inorganic composites. When the polymer chains are present in excess, they constitute the continuous phase, with the ceramic‐type material appearing as reinforcing particles. When present in smaller amounts, the polymer is dispersed in the continuous ceramic phase, to give a polymer‐modified ceramic. Under some conditions, bicontinuous systems are obtained. The composites thus prepared are characterized by electron microscopy, X ray, and neutron scattering intensities, density determinations, and stress‐strain and impact‐strength measurements.

A method of analysis is given by which the critical strain energy release rate G_c for impact tests may be deduced for both Charpy and Izod tests from normal energy measurements. Suitable calibration factors are determined and the method is applied to a range of polymers. Very close agreement is achieved between the Charpy and Izod results except for highly ductile materials for which it was necessary to use a fully plastic analysis. The method is extended to blunt notches and it is shown that the use of a strain energy per unit volume to yielding, together with a blunt notch stress analysis, gives a good description of the results.

In this article, continuous PA6/single‐wall nanotubes (SWNTs) nanofiber yarns were obtained by a special electrospinning method; the mechanical and electrical properties and the electric resistance‐tensile strain sensitivity of the as‐spun yarns were specially studied. The main parameters in the spinning process were systematically studied. Scanning electron microscope images and mechanical tests indicated that the optimum parameters for the electrospinning process were operation voltage = 20 kV, spinning flow rate = 0.09 ml/h, and winding speed = 150 rpm. Transmission electron microscopy images showed that the SWNTs have aligned along the axis of the nanofibers and thus formed a continuous conductive network which greatly improved the electrical conductivity of the PA6 nanofiber yarn and the percolation threshold was about 0.8 wt%. The electric conductivities of the yarns at different stretching ratios were also measured with a custom‐made fixture attached to the high‐resistance meter, and for a given carbon nanotube concentration, the conductivity changes almost linearly with the tensile strain applied on the yarns. POLYM. ENG. SCI., 54:1618–1624, 2014. © 2013 Society of Plastics Engineers

The thermo‐mechanical history of thermosetting compounds in injection molding cavities influences the ultimate properties of molded articles and affects both moldability and the productivity of the process. Mathematical modeling is an attractive approach for obtaining information regarding the thermo‐mechanical history of the compound in the cavity. In order to obtain useful mathematical models of the thermoset injection molding process, it is necessary to have information regarding the kinetics and heats of reaction during cure; the rheological, thermal, and PVT properties of the thermosetting compound; and the variation of these properties with operating variables and the degree of cure. The paper outlines a model of the thermoset injection molding process in simple rectangular or semi‐circular cavities. Methods are described for the experimental determination of the various physical and chemical properties of thermosets, which are required for modeling purposes. The results obtained in conjunction with the characterization of an epoxy system are illustrated. Finally, the paper demonstrates the results of mathematical modeling of the injection molding process for a commercial epoxy molding compound in a semi‐circular cavity, and shows that reasonable agreement is obtained between model predictions and experimental data.

Analysis of the nonisothermal melt and cold crystallization kinetics of poly(aryl ether ether ketone ketone) (PEEKK) was performed by using differential scanning calorimetry (DSC). The Avrami equation modified by Jeziorny could describe only the primary stage of nonisothermal crystallization of PEEKK. And, the Ozawa analysis, when applied to this polymer system, failed to describe its nonisothermal crystallization behavior. A new and convenient approach for the nonisothermal crystallization was proposed by combining the Avrami equation with the Ozawa equation. By evaluating the kinetic parameters in this approach, the crystallization behavior of PEEKK was analyzed. According to the Kissinger method, the activation energies were determined to be 189 and 328 kJ/mol for nonisothermal melt and cold crystallization, respectively.

Blends of poly(vinylidene fluoride) PVF₂, with poly(vinyl acetate), PVAc; with poly(vinyl propionate), PVPr; and with poly(vinyl butyrate), PVBu, were prepared by solution blending. Solutions containing PVF₂ with either PVPr or PVBu exhibited phase separation, and it was concluded that neither of these polymers are miscible with PVF₂. Phase separation did not occur with solutions containing PVF₂ and PVAc. Dried samples of this blend system were subjected to differential thermal analysis, dynamical mechanical testing, and visual observations of their melts. From these results, it was concluded that PVF₂ and PVAc are miscible. The detailed results and the structural implications of these observations are discussed.

The transitional behavior of poly(vinylidene fluoride) (PVF₂) blends with poly(methyl acrylate) and with poly(ethyl acrylate) was examined by differential thermal analysis and dynamic mechanical testing. Both blend systems were judged to be miscible on the bases of the presence of single, composition dependent glass transitions and of the strong melting point depression of the PVF₂ component, Blends of poly(isopropyl acrylate) with poly(vinylidene fluoride) were found to be immiscible. These results suggest that miscibility of the acrylate series depends on a specific attractive interaction between the PVF₂ and oxygen within the acrylate and the effect of this interaction is diminished as the hydrocarbon content of the ester is increased.