Volume 34, Issue 5

This review paper is devoted to the preparation of clay-based thermoplastic nanocomposites by melt blending in a twin-screw extruder. The influence of the main processing parameters (screw speed, feed rate, barrel temperature, screw profile) on the state of the clay dispersion at the micro- and nanoscale is characterized. The change of dispersion state along the screws and the corresponding mechanisms are presented. The interest of process modelling to predict the state of dispersion is evaluated and, finally, the main modifications of the twin-screw extrusion process to improve the clay dispersion are reviewed.

Many surfaces in nature such as the lotus leaf, cicada wings, water spider legs and gecko feet have attracted attention due to their inherent superhydrophobicity and self-cleaning properties. These surfaces are characterized by water contact angles greater than 150° and contact angle hysteresis < 10°. In this work, a continuous fabrication methodology for production of such superhydrophobic surfaces consisting of well-ordered micro-pillar structures (aspect ratio greater than 1 (1.3)) on a large area polyamide film using roll-to-roll hot embossing process was demonstrated. It was found that the temperature played a significant role in replication. Incomplete replication was observed in regime 1 (150 to 155 °C) and the height of replication was influenced by nip pressure and roll speed due to viscosity variations. In contrast, complete replication was seen in regime 2 (190 to 195 °C) and the height of replication was insensitive to nip pressure and roll speed due to a fairly constant viscosity value. The embossed polyamide surface, once coated with a low surface energy 1H, 1H, 2H, 2H-perfluorooctyltrichlorosilane (PFTS) monolayer, showed super-repellant characteristics with respect to water and demonstrated a successful manufacturing approach to fabricate superhydrophobic surfaces.

The broad objective of this work was to demonstrate a modelling and simulation framework for foam blow molding using commercially available simulation software. The simulation framework would have to account for the initial morphology of the foam, the relationship between the morphology and the rheological and deformation characteristics of the foam at high temperatures and high strains that are typically encountered during blow molding, and correlate the strains developed during blow molding to the morphological aspects in the resulting blow molded part. These aspects are addressed in this paper using simulations of uniaxial tensile deformation of a virtual representative volume element of a foam microstructure (rendered in DIGIMAT-FE) to derive the nonlinear tensile response of the foam at high temperatures (using ABAQUS). The resulting simulated stress-strain curve is employed to parameterize a nonlinear rheological constitutive equation. These parameters are then employed for the homogenized representation of the foam in the blow molding simulation carried out in B-SIM, a commercially available simulation software for blow molding. The regions where the simulated parison has undergone primarily uniaxial elongation are then mapped back to the expected local foam morphology using the transfer functions derived from the RVE simulations. These steps result in a preliminary and simple demonstration of the simulation framework, and offer a template that can be detailed further with experimental rheological information on actual foamed parisons, and more detailed post-processing algorithms to correlate multiaxial elongations with microstructure.

The mechanical properties of self-reinforced composites (SRCs) produced in a hot compaction process significantly depend on the process parameters. Only a little deviation of the process temperature or pressure causes the component to act differently under mechanical load. This is a chance and a challenge at the same time, since this process is difficult to handle but by properly controlling the process parameters, the mechanical properties can be adjusted, even locally for one component. In this research SRC are manufactured in a hot compaction process. A correlation between process parameters and density is found. Density increased from 0,8 to 0,91 g/cm³ by increasing temperature and pressure in the hot compaction process. The different thermal properties in the direction of orientation (IP) and transverse to orientation (TP) are measured with a laser flash device. It was found that, due to a change in density and molecular orientation, diffusivity and conductivity are influenced in different degrees in IP and TP directions. For interpretation of thermal measurement results, microstructures are analysed with a confocal laser scanning microscope after preparing the specimen with a permanganate etching. A schematic model of conductive path is worked out and discussed. With measurement data the anisotropy of IP and TP diffusivity is calculated, and a model is built to describe relative density related to anisotropy. The highest anisotropy between IP and TP diffusivity was calculated with a ratio of 6 at a relative density of approximately 0,82 g/cm³. Since mechanical properties in correlation to process parameters have already been investigated, results of this investigation, in combination with previous research on mechanical properties, will enable the development of a non-destructive testing method for SRCs by measuring the thermal diffusivity.

This research aimed to study the effects of fire combustion on materials coated with ethylene vinyl acetate and polyvinyl acetate copolymer emulsion resins with differing foam producing substance to dehydrating agent ratios. The flame retardancy of these materials was assessed by evaluating their heat release, CO and CO 2 emissions. Experimental results indicate that intumescent paint formulations significantly enhance the flame retardancy of painted plywood, thus reducing peak heat release rate and extending the time to reach peak heat release rate. Moreover, a low amount of foam producing substance enhances the fire retardancy of plywood panels. Furthermore, binder resin containing vinyl acetate monomer in intumescent coatings can enhance fire performance. In addition, low foam producing substance content can form an ideal char layer, which significantly reduces CO and CO 2 emissions. The mechanism to achieve more favorable fire performance was verified by carrying out thermogravimetric analysis, which demonstrated lower weight loss. The results of this study provide an improved understanding of the effects of intumescent coatings.

A functional lignin-modified polyvinyl alcohol material was prepared by in-situ copolymerization and alcoholysis of vinyl acetate and functional lignin. We then investigated the molecular functional groups, mechanical properties, thermal properties and flame retardancy of the materials by using Fourier-transform infrared spectrometer, universal testing machine, differential scanning calorimeter, thermal gravimetric analyzer, scanning electron microscope, limiting oxygen indexer and horizontal vertical burning tester. The results show that with increase in functional lignin content, the limiting oxygen index, combustion grade and glass transition temperature of the functional lignin-modified polyvinyl alcohol film increased. Both tensile strength and elongation at break increased first and then decreased with increasing functional lignin content. When the functional lignin content was 15 %, these two indices reached their maximum values. As the functional lignin content increased, the melting temperature of the material gradually rose after a sudden drop. When the functional lignin content was 5 %, the melting temperature was the lowest.

This paper is concerned with the feasibility of melt spinning of polyacrylonitrile (PAN) copolymer (acrylonitrile/methylacrylate 95.6/4.4 mol% ratio) plasticized with water-ethanol (EtOH) mixtures. The melting point and rheological and stability behaviors of PAN/water/ethanol mixture are reported. The objective is to determine whether this mixture is appropriate for allowing the PAN to be melt spun. The melting point results from differential scanning calorimetry show the T m of PAN/water/ethanol (70/15/15 wt%) mixture can be reduced to 150 °C from 300 °C. The time-dependent viscosity results showed that this mixture can be processed at 170 °C for more than 100 min without degradation. The steady-shear viscosity results indicated the shear-thinning behavior is observed for this mixture at a temperature ranging from 170 °C to 190 °C. These rheological data are also highly similar to the reference condition and other potential conditions reported in our previous paper, which indicates PAN/water/ethanol (70/15/15 wt%) at 170 °C is a potential condition for PAN melt spinning. The scanning electron microscopy diagrams show the copolymer strand melt extruded from PAN/water (70/30 wt%) mixture contains many more voids and bubbles than the PAN/water/ethanol (70/15/15 wt%) system. In conclusion, PAN/water/ethanol (70/15/15 wt%) at 170 °C is the most benign set condition (i. e. the composition and temperature) for carrying out the PAN melt spinning process.

The velocity/pressure (V/P) switching time, the transition from the filling phase to the holding phase during the injection molding cycle, plays a crucial role in ensuring the quality of the injection molding. Improper settings can lead to a variety of defects, including oversize/undersize, excessive residual stress, flash, warpage, and the like. There are currently many V/P switching methods to choose from. For example, when the injection time or the screw position reaches a prescribed value, that is, when a specified percentage of the cavity is filled with the molten resin, the switching time can be started. These traditional V/P switching methods should work well using precision injection molding machines to ensure accurate and repeatable motion control. However, the quality of shot-to-shot injection molding still varies with environmental changes, such as varying mold/melt temperatures. In this study, we propose a V/P switching adjustment method involving part weight or maximum clamping force increments. It was found that the weight of the injection molded part was highly correlated with the maximum clamping force increment and the V/P switching time. Experimental verification by considering various settings such as V/P switching time, injection speed and holding pressure show that the adjustment method is a feasible means of assuring quality consistency.

This research presents the investigation of mechanical and thermal characteristics as well as fracture toughness of Polypropylene (PP) based functionally graded materials (FGMs) and compares them vis-a-vis PP based homogeneous composites and neat PP. FGMs and homogeneous composites are fabricated with 15 wt.% and 30 wt.% glass fiber-reinforced PP. The gradient of fiber distribution in functionally graded materials is verified by scanning electron microscope analysis and ignition loss test. Findings of this work reveal that FGMs outperform neat PP and homogeneous composites. Tensile, flexural and compression strength of FGMs are found to be better as compared to neat PP and homogeneous composites. Fracture toughness and thermal conductivity are also found higher for FGMs. The performance of fabricated composites is optimized by using the VlseKriterijuska Optimizacija I Komoromisno Resenje (VIKOR) method.