An experimental study of polymer-polymer interdiffusion under co-extrusion processing conditions

This work aims to investigate the growth and structural evolution of a diffuse interphase generated in a flow field and to highlight its importance on controlling the final properties of compatible multilayer materials. The model polymers chosen are poly(methyl methacrylate) (PMMA) and poly(vinylidene fluoride) (PVDF). Interdiffusion kinetics, geometrical, and rheological properties of the interphase decoupled and coupled to flow have been probed and quantified under fundamental conditions of rheological measurement and under real practical conditions of processing, respectively. Polymer chain orientation is shown to decelerate the interdiffusion coefficient. This phenomenon is demonstrated to be balanced by intermixing (i.e. flow effect) at the vicinity of the interface triggered from excess interfacial shear stress, thus favors development of the interphase. The diffuse interphase generated therein during the processing has been well characterized via scanning electron microscopy coupled with energy dispersive X‐ray analysis (SEM‐EDX) and transmission electron microscopy (TEM). Results indicate that the interphase is robust with a geometrical property of tens microns depending on processing conditions and the interfacial structure is shown to be smooth with continuous amorphous‐crystallization transition between neighboring layers without causing any interfacial disturbances. Finally, experimental studies concerning the interfacial flow instability and encapsulation in coextrusion process have been performed, taking into account some key classical decisive parameters such as viscosity ratio, thickness ratio and elasticity ratio, etc. Different from severe flow instability observed in incompatible multilayer systems, presence of the interphase at PMMA/PVDF multilayers plays a vital role in weakening (or even eliminating) the viscous instabilities and elastic instabilities despite of the very high rheological contrast. POLYM. ENG. SCI., 55:771–791, 2015. © 2014 Society of Plastics Engineers

Polymer melts experience complex, time variant, stress and deformation fields on their passage through fixed geometries in many conversion operations. Flow complexity is further increased in operations involving the co‐joining of two or more melt streams where one confining boundary is moving and viscoelastic. Such a complex situation arises in coextrusion processes. This work covers experimental studies on polyethylene melt flows in complex coextrusion geometries with a view to understanding the stress fields involved and their effects on flow stability.A 30° coextrusion geometry is studied using two extrusion arrangements. In one arrangement a single extruder is used to feed a ’bifurcated’ die design wherein the melt stream is split prior to, and rejoined after, a divider plate in the die. In the other design melt streams are delivered to, and converged at 30°, using two independent extruders. In a second die melt streams are brought together at 90°. In each die arrangement melt flow in the confluent region and die land to the die exit was observed through side windows of a visualisation cell. Velocity ratios of the two melt streams were varied and layer thickness ratios producing instability are determined for each melt for a variety of flow conditions. Stress and velocity fields in the coextrusion arrangements were quantified using stress birefringence and particle image velocimetry techniques.The study demonstrates conclusively that wave type interfacial instability occurred in the coextrusion geometries when the same low density polyethylene melt is used in each stream. This observation occurred at specific, repeatable, stream layer ratios in each die arrangement. The complex flows were numerical modelled using a modified Leonov model and Flow 2000™ software. There was reasonable agreement between modelled at experimentally determined stress fields. Modelling however provided far more detailed stress gradient information than could be resolved from the optical techniques. A total normal stress difference (TNSD) sign criterion was used to predict the critical layer ratio for the onset of the interfacial instability in one die arrangement and good agreement between theory and experiment has been obtained.The study conclusively demonstrates wave type interfacial instability in the coextrusion process is not caused by process perturbations potentially introduced by extruder screw rotation but is associated with process‐history dependant differences in melt elasticity.

Experimental and numerical studies of slurry-based coextrusion deposition of continuous carbon fiber micro-batteries to additively manufacture 3D structural battery composites

Imaging and analysis of wave type interfacial instability in the coextrusion of low-density polyethylene melts

in this research, an experimental apparatus has been developed for observing interfacial stability and deformation of multilayer pressure driven channel flows. The interface instability of the co-extrusion flow of polyethylene and polypropylene is studied experimentally in a slit geometry. This is done by introducing disturbances of controlled wave length and amplitude on three-layer symmetric (A-B-A) polymer melts as well as performing a series of extrudate mechanical testing. In this study variations of the mechanical properties as well as wave interlocking have been related to the conformation of the interfacial waves (IW). By investigating the growing (IW) and tensile stress of extrudate samples a relationship between interfacial instability (II) and mechanical properties of polypropylene (PP) and high density polyethylene (HDPE) has been established. It has been shown that instabilities are associated with IW, and it turns out that IW amplitude is known as a mechanism for controlling the strength of three layer polymer products. It is shown that the mechanism of interfacial strength is related to interfacial instabilities as well as the interfacial strength. By considering that the instability is controlled by its dominant mode. It is shown that there is ability to forecast the quality of final products in co-extrusion process.

It is detected, that the main ignition regularities of dispersed wood possible on the basis of experimental studies in terms of the real modes of ignition. The aim of this article is the experimental study of the conditions and characteristics of the single ignition fragments wood the made of dry pine during heating energy intensive metal plate with a constant temperature. The experiments were carried out with particles of wood characteristic sizes. As a result the experimental studies were identified, typical ranges of sample sizes with maximum temperatures of ignition. The results of our experimental studies are the basis for selection of a specific optimization parameters (the temperature of the steel plate and the ignition delay time) when selecting a pulse pyrolysis technologies. Established in experiments regularities allow us to determine fireproof conditions of pyrolytic processes of wood processing in the mode heating pulse for the purpose of biofuel production.

Effect of powders and binders on material properties and molding parameters in iron and stainless steel powder injection molding process

The present paper describes the results of high speed photography, acoustic emission (AE) detection and plasma light emission (LE) measurement during CO₂ laser welding of 304 stainless steel in different processing conditions. Video images with high spatial and temporal resolution allowed to observe the melt dynamics and keyhole evolution. The existence of keyhole was confirmed by the slag motion on the weld pool. The characteristic frequencies of flow instability and keyhole fluctuations at different welding speed were measured and compared with the results of Fourier analyses of temporal AE and LE spectra. The experimental results were compared with the newly developed numerical model of keyhole dynamics. The model is based on the assumption that the propagation of front part of keyhole into material is due to the melt ejection driven by laser induced surface evaporation. The calculations predict that a high speed melt flow is induced at the front part of keyhole when the sample travel speed exceeds several 10 ㎜/s. The numerical analysis also shows the hump formation on the front keyhole wall surface. Experimentally observed melt behavior and transformation of the AE and LE spectra with variation of welding speed are qualitatively in good agreement with the model predictions.

This paper discusses the use of variable speed cutting for vibration control in the face milling process. Both simulation and experimental results show that the self-excited vibrations that can occur during constant speed cutting, and hence put limitation on the possible size of cut, can be suppressed by continuously varying the spindle speed. Through both analytical and experimental studies, the shape of variable speed trajectory has been examined, in terms of both the trackability by the spindle servo system and performance in terms of vibration suppression. It was found that a sinusoidal wave because of its acceleration and jerk characteristics can be tracked more precisely than some other periodic waves. The dynamic face milling force model was used to study the effects of speed trajectory parameters, namely, the frequency and amplitude. The results, in general, show the method to be fairly robust to the specific nature of the machining situation in terms of both processing conditions and system dynamics. Speed trajectory design was, however, shown to be somewhat dependent upon the nominal cutting speed and dominant frequencies of the system.

The objective of this work is to investigate the effects of different chemical blowing agents (CBAs) and processing conditions on the cellular structure of foamed metallocene polyethylene and characterize an appropriate blowing agent. An experimental study was conducted to produce metallocene polyethylene foams in dry-blending-based rotational foam molding. The critical processing parameters that optimize the foam structure have been identified through modifications of the molding conditions. The physical properties and cellular structure of the final foamed parts were also examined. The foaming performance of exothermic and endothermic CBAs was studied. It was revealed that selecting a suitable CBA is crucial as the foam structure depends significantly on the properties of the blowing agent. Exothermic blowing agents resulted in greater foam density reduction and exhibited a wider processing window compared to endothermic blowing agents. It was found that a balance between different properties of the blowing agent is required to achieve control over the foam structure.

Rotational molding is one of the most important methods for the manufacture of hollow plastic products. However, there are several unsolved problems that confound the overall success of this technique. Part warpage caused by inappropriate mold design and processing conditions is one of them. An experimental study is reported on the effect of different processing factors on the warpage of rotationally molded parts, including part thickness, oven temperature, cooling condition, mold material, mold release, colorant, fiber reinforcement, foaming and mold pressurization. Experiments were carried out on a lab-scale rotational molding unit. After molding, the part warpage was measured by a profile-meter. It is shown that the mechanisms of warpage formation and removal can be explained and, this being done, steps can be taken to ensure that the warpage is minimized. This provides significant advantages in terms of reduced cycle time and improved product quality. © 1999 John Wiley & Sons, Inc. Adv Polym Techn 18: 201–207, 1999

A coupled experimental and theoretical investigation on joining of aluminium and galvanized sheets in lap joint geometry using an advanced pulsed current gas metal arc based process is presented. The experimental study was focussed on finding suitable processing conditions to restrict the heat input, and minimize the growth of the phase layer thickness and the formation of Fe-Al intermetallic compounds along the joint interface. The theoretical study included the development of a three-dimensional heat conduction model to compute the temperature field and thermal cycles, and estimate the final joint bead profiles and phase layer thickness as a function of processing conditions. The estimated results are tested extensively for a wide range of experimental conditions. The experimentally measured and the corresponding computed results show that the dissimilar material combinations of aluminium and galvanized steel can be joined successfully by pulsed current gas metal arc with a precise control of processing conditions and heat input.

The paper presents one aspect of the analysis of energy consumption and productivity of the manufacturing operation. As an example of the operation, the operation of turning with a single-blade tool was taken. Sustainable development in its general concept implies sustainable materials, sustainable design, and sustainable manufacturing. This paper presents an analysis of one important part of sustainable manufacturing, and that is energy saving. The experimental study was conducted as follows. In laboratory conditions, an experimental-mathematical regression model of the relationship between cutting force and processing conditions was defined. Machining experiments were performed under ECO-friendly conditions with technology known as MQCL (Minimum Quantity Cooling Lubrication) machining. The obtained mathematical model was used to calculate the energy consumption and the workpiece material removal rate (MRR, productivity). The results of the analysis showed that there is a lot of space for optimization of machining conditions from the aspect of power consumption, with mandatory calculation and other machining costs, above all, the cost of tools and machine tools. In this regard, recommendations for analysis with the aim of power saving are given.

BACKGROUND: Corrosion damage to structural steels, especially in welded joints of agricultural machinery, leads to significant economic losses (3-5% of GDP). In addition to the main conventional methods of corrosion protection (painting, galvanizing), the technology of manufacturing (hardening) of parts has a significant impact on corrosion resistance. The effect of surface plastic deformation (SPD) on corrosion resistance remains insufficiently studied, especially for welded joints of steels of the agricultural industry. AIM: Definition of quantitative patterns of the influence of wave strain hardening (WSH) parameters on the corrosion resistance, microstructure and microhardness of structural steels (09G2S, 30KhGSA, 40Kh, 45, 10HSND) and their welded joints for the development of optimal processing conditions. METHODS: Five grades of agriculture-purposed structural steels (09G2S, 30KhGSA, 40Kh, 45, 10KhSND) and their welded joints were studied. The samples were subjected to wave strain hardening (WSH) with variable processing parameters. Corrosion resistance was assessed by weight loss after salt fog tests. The microstructure (grain size, defects) was analyzed using optical microscopy. RESULTS: Experimental studies have revealed the dependence of the effect of wave strain hardening on corrosion resistance depending on the steel grade. For alloy steels (30KhGSA, 40Kh, 10HSND, 09G2S), WSH can both increase and decrease resistance depending on the processing conditions and the type of sample (base metal or welded joint). The maximum improvement in corrosion resistance reached 42%. On the contrary, for carbon steel 45, the use of WSH led to a decrease in corrosion resistance by 26–35%. CONCLUSION: WSH effectively increases the corrosion resistance of alloy steels (up to 42%), but requires individual selection of processing modes (including the overlap coefficient) for each material and type of joint. The use of WSH on carbon steel 45 is not recommended due to a decrease in corrosion resistance.

Non-uniform temperature distribution within solid food is a major problem associated with microwave heating, which limits industrial applications. Therefore, an experimentally validated 3D model was proposed to study the effect of microwave applicator geometry on the electromagnetic field distribution and heating pattern of shrimp under different processing conditions. Simulation results were compared with physical experiments, in which a cooked peeled shrimp sample was heated using two different laboratory-scale microwave applicators (rectangular and cylindrical cavities). For the rectangular applicator, the temperature distribution within the shrimp, when examined in cross-section, was more homogeneous compared to that of the cylindrical applicator. The results showed the influence of the complex shape of the food on the temperature distribution during microwave heating, as well as of process parameters (input power and geometry cavity). Moreover, this modelling method could provide a better understanding of the microwave heating process and assist manufacturing companies to evaluate a suitable microwave applicator according to their specific purpose.