Volume 32, Issue 3

Undesirable features of polymeric materials include insufficient thermal stability under specified exploitation conditions and too high flammability. These features depend on the chemical structure of polymer macromolecules, and composition of polymeric composites. Polymeric materials with increased thermal stability and improved resistance to the action of fire are produced with the use of various types of fillers with nanometric dimensions. Among numerous nanofillers, carbon-based nanofillers such as graphite nanoplatelets, carbon nanotubes and graphenes (graphene oxide, reduced graphene oxide and modified graphene) play an essential role. The aim of this report is to highlight the latest findings concerning the effect of carbon fillers, mainly graphene and carbon nanotubes on the thermal properties and flammability of polymer nanocomposites.

To understand the flow behavior of a melted polymer during injection molding with ultrasonic vibration, a new visualization device was developed and a method was proposed to analyze the filling velocity field during the injection molding process. Using the device and method, both the influence of ultrasonic vibration on the velocity of the filling front and the velocity distribution of a polypropylene melt within a cavity are discussed. The results showed that the filling front velocity of the melt was improved by ultrasonic vibration (the filling front velocity was improved by up to 27% when 200 W of ultrasonic power was applied). In addition, it was shown that the velocity gradient of the melt within the cavity decreased, and that the velocity distribution became more uniform during ultrasonic vibration.

Flexural fatigue performance of newly developed step-wise functionally graded (FG) composites has been investigated experimentally. Two unidirectional glass fiber (UGF)/epoxy FG composites with overall fiber volume fraction of 39.9 ± 0.3% and thickness of 6.0 ± 0.1 mm were fabricated using hand lay-up technique. The fabrication proposed technique depends on the variation of the composite structure achieved by three different templates. A non-functionally graded (NFG) composite laminate with the same overall fiber volume fraction and thickness was also fabricated using a fourth template for comparison. Each of the FG and NFG composites is made of six plies. Each ply has a thickness of 1.0 mm. This occurs by controlling the amount of matrix in each ply (constant matrix amount for all plies). Fatigue tests were performed at zero mean stress. A 20% reduction of the initial flexural stiffness was taken as a failure criterion. The S–N curves for the fabricated FG and NFG composites have been constructed as design curves. For FG composites, the effects of the spatial gradient of fiber content and plies stacking sequence on both S–N relationships and the specimens’ surface temperature rise were studied. Two-parameter Weibull distribution function was used to statistically analyze the fatigue life results.

With the growing apprehension about ecology and economics, the composite materials based on low-cost lignocellulosic biomass have generated a great interest of research. In this paper, a polymer composite has been developed using specific grade epoxy matrix and “particular micron size” bamboo filler and its different mechanical properties have been investigated. The mechanical properties were determined with a variation in different constraints like filler content, strain rate, temperature and chemical treatment to establish the applicability of the developed composite. From the results, it has been found that the static and dynamic mechanical properties of the developed composite are significantly influenced by the different parameters. The scanning electron micrographs demonstrated the even dispersion of particulate fillers in the matrix, agglomeration at higher filler loading and better adhesion due to alkali treatment. Also, the properties are comparable with the existing different bamboo based composite.

In the present study, Polypropylene composites were fabricated by varying different weight percentages (0 to 20%) of alumina powder by using Injection Molding Technique. Then the fabricated composites were characterized by physical characterization such as void content test, chemical characterization such as Fourier-transform infrared spectroscopy, mechanical characterization such as Shore hardness test, flexural test, compressive strength, Izod impact test, thermo-mechanical characterizations such as Dynamic Mechanical Analysis, Thermo-gravimetric analysis and morphological characterizations such as Scanning Electron Microscopy (SEM) and Atomic force Microscopy (AFM). The results indicate that the shore hardness values increase up to 25% with the increase in alumina filler up to 20%. The highest flexural strength and flexural modulus achieved are 59.26 MPa and 2126 MPa respectively with 20% filler loading. Further, it was also revealed that the storage modulus of the composites was found to be higher than that of the virgin PP because filler increases the stiffness of the composites. Thermo-gravimetric analysis (TGA) measurements indicate that both the initial degradation temperature and end degradation temperature increase with increasing filler content. SEM exhibits that alumina particles were uniformly and finely dispersed though some aggregates and agglomerates are identifiable. AFM results indicate that morphology of alumina in the PP matrix is characterized by a chainlike branched structure.

Novel blends of polyurethane and acrylonitrile butadiene styrene, in both forms, compatibilized and uncompatibilized, were developed by melt reactive extrusion technique in a twin-screw extruder. This technique involved acrylonitrile butadiene styrene grafted maleic anhydride (ABS-g-MAH) as the compatibilizer. The objective of this study was to enhance the rigidity characteristics of polyurethane by melt blending acrylonitrile butadiene styrene into polyurethane using a compatibilizer. The blends were analyzed using different techniques to confirm the occurrence of compatibilization reaction between the parent polymers and the compatibilizer. It is observed that addition of the compatibilizer has improved the mechanical properties of the resultant blends.

In this investigation, a high-consistency rubber (HCR) was mixed with five different, typically used crosslinking agents that are based on organic peroxide. Furthermore, the amount of crosslinking agent was varied in order to quantify the effect on the mechanical properties. All materials were processed in a hot pressing process, and, subsequently, post-cured. The properties were characterized by the measurement of the swelling ratio, shore A-hardness, rebound resilience and tensile test. We successfully proved that the swelling ratio is a suitable indicator for the evaluation of the crosslinking density of silicone rubber. The results show that the crosslinking density increases as the amount of crosslinking agent increases. The hardness, rebound resilience, and stress at 100% elongation increase as the crosslinking agent does. In contrast, the ultimate elongation decreases as the crosslinking density rises. The absolute values depend on the type of crosslinking agent used. The most commonly used crosslinking agent for high-consistency rubber is Di(2.4-dichlorobenzoyl) peroxide. We were able to verify that there are more possible curing agents based on organic peroxides on the market. Depending on the required properties, customized silicone elastomers could be easily produced.

Among several operational parameters such as rotor speed, fill factor and ram pressure, the orientation of the mixing rotors with respect to each other plays a significant role in the mixing performance. An understanding of the flow field and mixing characteristics associated with the orientations of the rotors will help in obtaining a final product with a better quality. For that purpose three phase angle orientations: 45°, 90° and 180° are investigated here in a 75% filled chamber with two rotors counter-rotating at an even speed of 20 min –1 . Two dimensional, transient, isothermal, incompressible simulations are carried out using a CFD code. While an Eulerian multiphase method was used to solve for the transport variables in the two phases: rubber and air, the volume of fluid (VOF) method was used to solve for the interface between the two phases. A non-Newtonian Carreau-Yasuda model was used to characterize rubber. Massless particles were injected in the domain to calculate statistical quantities in order to assess dispersive and distributive mixing characteristics associated with rotor orientations. The flow field is analyzed via pressure and velocity contours. Dispersive mixing was analyzed through histograms of mixing index and cumulative probability distribution functions of maximum shear stress experienced by the particles. Distributive mixing was quantified statistically using cluster distribution index and interchamber material transfer. The phase angle of 180° was found to perform the best in terms of both dispersive and distributive mixing characteristics.

Porous polymer sheets created by the “solid state microcellular foaming process” possess an impermeable solid skin on the boundary. In order to experimentally determine the internal structure's fluid permeability, the skin is removed by machining a pattern of holes or channels so that fluid flow can be established when applying a pressure difference across the faces. In this work, a fluid flow model for this particular geometry assuming a Newtonian fluid and isotropic internal porous structure is established. This yields formulae used to compute the structure's Darcy permeability from experimental flow data. Experimental verification of the model is provided for a sample of Polyetherimide (PEI) nanoporous polymer sheet whose skin was drilled in various hole patterns, thus establishing the mathematical foundation for future work in investigating this class of porous materials.

Immiscible PLA/PA11 of 80/20 and 50/50 wt% were compatibilized through addition of p-toluenesulfonic acid (TsOH) catalyst in reactive ultra-high speed twin-screw extrusion. Two mixing screw designs were compared for their ability to disperse the PA11 droplets in the PLA matrix as a function of screw speed up to 2000 rpm. The size and polydispersity of droplets of dispersed PA11 decreased when a high shear (HS) screw was used, whereas broad droplet size distribution was produced in the low shear (LS) screw. Two models predicting the droplet size dependence on shear rate, viscosity ratio and interfacial tension were fit to the experimental data. The Serpe model including volume fraction effects produced a better fit compared to the Wu model, which does not include volume fraction effects. Mechanical testing indicated that the compatibility of PLA/PA11 blends was improved through addition of TsOH catalyst for 50/50 wt% blends due to ester – amide exchange reactions at the interfaces in the immiscible PLA and PA11 phases. The enhancement of ductility was greater after processing with the LS screw configuration than the HS screw configuration. The inferior properties after high shear mixing were likely due to molecular weight degradation during processing. While the aggressive shear in the HS screw design resulted in fine dispersion, care should be taken to minimize degradation, especially for shear sensitive polymers.

Determining the operational settings for the heating equipment in thermoforming is still mainly done by trial and error as well as personal experience. Depending on the type of IR heating equipment, these settings can be the consumed electrical power or the desired temperature of the heating elements. In this study, a workflow is developed, applied and validated to characterize the IR heating equipment and to determine the optimal heating strategy. The workflow starts with an on-site equipment/machine characterization, which takes all machine and environment parameters into account. This approach results in the optimal heater setting and heating duration in order to obtain a through thickness temperature distribution which lies within a predefined forming range. The proposed methodology is universally applicable as it can deal with different types of sheet material and thicknesses. Moreover it can be applied to any type of IR heating element (halogen, metal foil, ceramic or quartz). Moreover, the methodology can easily be implemented in an industrial environment. Additionally, an estimate for the thermal efficiency of halogen heater equipment can be determined.

We present a semi-numerical modeling approach to analyzing the role of surface renewal during bubble-free devolatilization in vented single-screw extruders. To demonstrate the significance of surface renewal in the mass transport of volatiles, we derived approximate analytical solutions for the two-dimensional circulatory flow in a partially filled screw channel, placing special emphasis on the melt pool that forms in front of the active flight. By applying the resulting velocity field to the governing conservation equation for the volatile concentration in the polymeric phase, the convective influence of the polymer flow on mass transport is taken into account. The resulting convection-diffusion equation, which is solved numerically using the finite-volume method, provides both qualitative and quantitative insights into how volatile depletion in the melt pool is related to the flow field developed. Thus, we clearly demonstrate that surface renewal improves mass transport efficiency considerably, even at very low screw speeds.

The thermal bonding method is an advanced processing technology, which can bond a variety of polymer sheets on request. This work aims to analyze the effect of applied loading, heating temperature and duration on the depth loss of the PMMA microfluidic chip after bonding. Several experiments were designed by us and the results were analyzed by orthogonal experimental method. Finally optimal applied loading, heating temperature and duration were obtained and in the optimal case, the bonded microfluidic chip has small depth loss and enough strength.