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The co-rotating fully intermeshing twin-screw extruder has evolved significantly in the 60 years since it was commercialized in 1957. While this equipment might be considered a “mature” technology, it has not experienced a decline in new developments as might be expected, but rather a significant number of advancements. The technology continues to evolve. For example in the last 20 years several significant developments have been introduced. These include a) the implementation of high torque (power) designs, b) the use of increased screw rpm in conjunction with high torque for improved operating flexibility and productivity, and c) a breakthrough technology for feeding difficult to handle low bulk density materials. However, one area of twin-screw technology that has not evolved as much is screw elements geometry. Conveying elements and kneading blocks have remained essentially the same since the original Erdmenger design patents filed in the late 1940’s and early 1950’s. However, to take advantage of increased torque and power transmission capacity introduced in the newest generation of twin-screw compounding extruders, solids feed conveying and melt/mixing capacity in, for example, some highly filled compounds, had to be improved. Coperion has developed special involute screw and kneading elements with a new (Patent: EP 2 483 051 B1) cross section design to help achieve this objective. This paper will focus on the comparison of standard kneading blocks vs new involute kneading elements, specifically looking at some significant aspects related to performance.
The application of micro-structures enables the integration of new functionalities on product surfaces. Though some applications have successfully been introduced on the market, widespread use of the full potential is depending on efficient and economical production processes. For plastics films the variothermal extrusion embossing process enables a quick and cost efficient replication of micro-structures on large areas.To achieve high quality replication, the process has to be finely tuned to the desired geometry. In this paper, the effects of the processing parameters on the replication quality inside previously established processing windows are investigated for two polycarbonate materials. The replication quality is evaluated for three different micro-structures.The experiments confirm strong interdependencies between the processing parameters, the material behavior and the geometric features of the micro-structures. These lead to partly contrary effects on the replication quality for different micro-structures and make the prediction of the optimal processing parameters for any given geometry very difficult.
Filling ratio, resin pressure and resin temperature are important process parameters related to the residence time distribution and thermal history of resin in a twin-screw extruder. This study presents a series of experimental results of these parameters and compares them with the values obtained from the 2.5D Hele-Shaw model calculation developed in our group recently for a twin screw extruder. Homo polypropylene with melt flow rate of 7.0 g/10-min was feed to a ϕ 26 mm co-rotating twin screw extruder. Temperature and pressure of resin were measured using sheathed temperature sensor and pressure transducer contacting to molten resin. Fill ratio distribution was measured by our laser light section method. The experimental results of resin pressure, temperature and fill ratio agreed well with the simulation results. It was validated that the Hele-Shaw model is valid for co-rotating twin screw extruder.
Loss of molecular weight due to shear and hydrolytic degradation resulting in lower Intrinsic Viscosity (IV) is a matter of importance while working with PET resin. In applications that demand high levels of dispersion, for instance, addition of Carbon Black, drop in IV has been an unfortunate compromise to achieve the necessary dispersion, which is measured using a Filter Pressure Value (FPV). This study uses an advanced screw design to compare viscosity retention and effective dispersion of carbon black in Poly(ethylene terephthalate) (PET) resin against a screw design used for many years as an industry standard. The advanced screw design attempts to eliminate the presence of peak shear, which is considered as the leading factor for the degradation of PET and the resultant reduction in IV. PET was blended with carbon black and dispersed in the extruder at a barrel temperature of 220°C to 260°C with screw speeds of 200, 250 and300 rpm. The screw configuration resulting in reduced degradation of PET and the retention of molecular weight was evaluated along with the dispersionpotential. These observations were evidenced from IV measurements on a Ubbelohde viscometers and Filter pressure value (FPV) for dispersion rating on a Collins FPV tester. Melt transducers were used to track melt temperature and pressure.Specific Mechanical Energy (SME) and extruder screw speed were also recorded from the extruder.
We present a systematic approach based on networks that uses tensor algebra and numerical methods to model and calculate selected double wave screw geometries in terms of pressure-throughput behavior. Due to the extreme diversity of their geometries, describing the flow behavior is difficult and rarely done in practice. Three-dimensional CFD methods (finite-element or finite-volume) are well capable of calculating the flow behavior in complicated geometries, but they require vast computational power, large quantities of memory, and consume considerable time to create a geometric model created by computer-aided design (CAD). Consequently, a modified 2.5-dimensional finite-volume method, termed Network Simulation Method (NSM) is preferable.The main goal of this study was to compare the results of the NSM with CFD. The results for isothermal melt-dominant flow correlated well. With recently developed pressure-/throughput models for two- and three-dimensional flow of shear-thinning fluids the accuracy of NSM could be further improved. This makes network analysis a valid and easy-to-use tool for screw calculations in practice.
Water-assisted mixing extrusion was used to prepare thermal conductive poly(vinylidene fluoride)/graphene oxide (PVDF/GO) nanocomposites. The injected water not only improves the GO dispersion in the PVDF matrix, but also promotes in situ thermal reduction of the GO. As a result, the intrinsic thermal conductivity of the GO is significantly increased. The interfacial interaction between the GO and PVDF facilitates the nucleation of crystallites at the PVDF-GO interfaces, leading to reduced interfacial thermal resistivity. The thermal conductivity of PVDF/GO nanocomposites prepared with water injection is significantly improved. The nanocomposite with 1.0 wt% GO exhibits a thermal conductivity of 0.475 W/mK, which is much higher than those of the PVDF (0.206 W/mK) and the nanocomposite prepared without water injection (0.335 W/mK).
The image analysis of the investigation of the melting process, as Maddock has already done in 1959, is further developed by means of modern image analysis. The experiments are carried out on the two most common screw types in the plastics industry: the general-purpose screw and barrier screw. Control of the residence time is essential for the production of high-quality products and is also important for biodegradable and other time-sensitive polymers. The results indicate that both the general- purpose screw and the barrier screw have significant stagnation zones and broad residence time distribution.
A new extensional mixing element (EME) for twin-screw extrusion was applied to compound polypropylene (PP)/glass fibers (GF), polypropylene (PP)/carbon fibers (CF), and polyethylene oxide (PEO)/polyethylene terephthalate fibers (PET-F) composites, and the effects of EME on fiber length distribution have been studied compared to two kinds of shear flow dominated Kneading Blocks (KB) screw configurations. Composites structures were characterized, and good dispersion of the fiber fillers in the systems has been achieved. It was concluded that EME can reduce the breakage of the stiff glass fibers and carbon fibers in the mixing zone compared with the KB, resulting in longer fibers remained after passing through the EME than the KB based on optical fiber length distribution measurements. Although flexible polyethylene terephthalate (PET) fibers are hard to cut by conventional KB, EME can easily break them into small pieces by very high pressure generated.
Polyolefin production requires ~8% of global oil and natural gas production for monomer supply and the energy required for polymerization; often these polyolefins are used in short term applications such as packaging. While researchers work toward long term solutions involving sustainable polymers, the short term focus on how to better recycle polyolefins currently in the production/consumption cycle must be addressed. Given their chemical similarity and similar density, recycled polyolefins are difficult to separate from recycle streams often resulting in mixed stream recycle feeds. Previously we presented the role of residual oligomer after Ziegler-Natta polymerization of polyethylene (PE) and isotactic polypropylene (iPP) in preventing cross interfacial crystallization of immiscible PE-iPP bilayers which resulted in weak interfacial adhesion. We also presented strategies for promoting cross interfacial crystallization via processing (rapid interfacial quenching) and materials selection (thickened interfaces) in PE-iPP bilayers. Here we investigate the role of interfacial adhesive strength between three PE-iPP blends in the absence of applied shear during processing. With poor interfacial adhesion between PE/iPP, brittle failure of each blend was observed, as expected with immiscible polymer pairs. When interfacial adhesion strength exceeded that of the strength of component homopolymer, exciting synergism was observed between PE/iPP blends. Processing in the presence of applied shear flows (injection molding and film extrusion) will also be discussed. This finding highlights the importance of considering interfacial strength when designing mixed polyolefin recycle streams.
Extensional Mixing Elements (EMEs) have been developed to impart extension dominated flow in twin screw extruders (TSE) through hyperbolic contraction channels. In this manuscript, EMEs for TSE have been made more aggressive by incorporating double hyperbolic contraction (contraction in horizontal as well as vertical direction) and were also successful in designing novel modular screw design for single screw extruder (SSE) to have dispersive and distributive mixing simultaneously. The design geometry of EMEs have also been optimized for both TSE and SSE using computational simulations.
The power consumption of a melt spinning extrusion module with mono and bi-component capability was under consideration, especially when analyzing the effects of process settings and downstream equipment on the total power consumption of the extrusion line. Experiments were conducted to quantify in real-time the effects of barrel temperature profiles, godet roll temperatures and godet roll speeds on the total power consumption when the extrusion line was operated to produce both mono and bi-component fibers. Between the effective use of extrusion processing conditions and optimization of the downstream equipment, the results have shown that there is a significant opportunity to save energy for the total power consumption. In bi-component mode, the downstream equipment was found to cause the highest effect on the total energy consumption. In mono-component mode, an optimal combination between metering pump and extruder motor appeared to be crucial for the optimization of the melt spinning system. Specific energy consumption was more favorable when the metering pumps were operated at higher speeds.
Extrusion scale up is the procedure of replicating a plastic extrusion process in order to predict the performance of large production size extruders on the basis of geometrically similar small extruders. Extrusion processes are often developed on small extruders, so the effective scale up of these extrusion processes is very desirable as a means of increasing production rates. Although, studies on scale up procedures have been performed for several decades, no further studies have been undertaken to examine the influence of screw geometry on extrusion performance and energy consumption. In this work, in-process monitoring techniques incorporating thermocouple grid sensors and an energy meter have enabled real time examination of the extruder scale up by comparing the thermal and energy characteristics of a 38 mm diameter single screw extruder to that of a similar extruder with 63.5 mm screw diameter. Experiments, employing identical screw geometries, extruder set temperatures and range of screw speeds, were carried out on both machines with LDPE to quantify the effect of extruder scale on the measured throughputs, melt temperature homogeneity, die pressure and energy consumption.
Capsule breakup percentage in a co-rotating twin screw extruder is studied for the purpose of producing extrinsically self-healing polymers. A method of real-time characterization of stresses using calibrated stress beads and an optical probe was devised for this research. Three different strengths of stress beads are used to represent poly(urea-formaldehyde) (PUF) encapsulated healing agents. Stress bead breakup percentage was depicted over a selected range of statistically significant operating conditions: screw speed (N) and specific throughput (Q/N). Central composite design grids were created to analyze experimental results and generate a set of predictive equations for stress bead percent breakup. This paper examines the relationship between co-rotating twin screw extrusion operating conditions and breakup of PUF encapsulated extrinsic healing agents. It also marks the first step in understanding extrusion of efficient self-healing polymer composites.
A birefringence scanner was used in this study to measure the distribution of birefringence in blown films. The objective of this study was to evaluate the birefringence scanner as a new tool for blown film research. Seven films were made on a small-scale research line at various process conditions (i.e., thickness, blow up ratio (BUR), rate and frost line height (FLH)). Clear in-plane birefringence variations were found in all films. More significant birefringence variation was found in the cross machine direction (CD) of the film and less variation in the machine direction (MD). The birefringence variation on the CD direction could be caused by uneven flow and cooling in the die and air ring. There were no clear relationships found among mechanical properties of films, process conditions and average in-plane birefringence in the films studied. This demonstrates that birefringence scan of film is a very useful tool for studying the fundamentals of blown film process.
A novel and upgraded strategic decision methodology to increase energy efficiency in industrial processes, the Energy Gap Method (EGM), is presented. For this methodology, six different specific energy consumption levels are proposed. Five gaps or differences between specific energy consumptions can be calculated: production, quality, process, technological, and R&D gaps. Three industrial successful case studies enhancing the energy efficiency, two in extrusion blow molding and one in sheet extrusion are presented, obtaining specific energy consumption (SEC) reductions between 14 and 65%.
For a proper selection of materials for solar-thermal applications, the failure behavior of various polypropylene (PP) grades was investigated by fatigue crack growth (FCG) experiments. The four tested material grades differed in their stabilizer system. To determine the effect of environmental media (chlorinated water with a chlorine content of 5 ppm, air and deionized water) and elevated temperatures (95°C and 80°C), cracked round bar specimens were tested on an electro-dynamic testing machine equipped with a special desigend media containment.Tests at all environmental conditions revealed a significant influence of the stabilizer systems on the FCG resistance. While at all conditions the stabilization with a hindered amine light stabilizer resulted in the best FCG behavior, depending on the environmental loading different PP grades showed the worst FCG resistance. In terms of media dependence of the crack growth behavior, for all PP grades, the best and worst FCG behavior were obtained in deionized water and chlorinated water, respectively. Results received from tests under two different temperatures showed that the FCG resistance decreased with increasing temperature in all tested environments and for all PP grades.
Dynamic mechanical analysis (DMA) has been a useful technique for characterizing polymeric materials for over fifty years. Often material comparisons focus on elastic modulus since it is a property similar to something we are familiar with from published data sheets. But a less well known property that arises from DMA, tan delta, provides immense insight into a wide range of behaviors in polymers. This paper will review the definition of this property and illustrate some examples of how it can be used to assess the relative performance of polymeric materials for short-term and long-term use.
In recent decades, the engineering industry has seen a stronger emphasis on cost- and energy-efficient materials. As a result, polymers have increasingly been adopted in load-bearing applications, replacing traditional “engineering materials” such as metals and ceramics in multiple industries, from aerospace vehicles to medical devices. With this transition comes an increased need for understanding how such load-bearing polymers inevitably fail, especially with respect to cracking and fracture. Fractography – the science and art of “reading” fracture surfaces – is a powerful failure analysis tool for dealing with fractured plastic components. Fracture surface features can tell a story regarding the stress state and environment a polymer experienced during fracture, potentially eliminating hours of exploratory testing to replicate the exact failure mechanism. This tutorial will provide an overview of fracture features commonly observed for various plastics, and how those features can be related to the exact mechanism of failure. The various tools of fractography will be explored, highlighting the importance of both low and high magnification in identifying where a crack initiated and how it may have propagated. Traditional brittle and ductile fracture features will be covered, as well as more nuanced failure mechanisms such as environmental stress cracking (ESC). A deeper dive into the fractography of three commonly used commodity plastics will demonstrate the influence of composition and stress state on fracture features, as well as exhibit the value of recreation testing under controlled loading and environmental conditions.
Bottle Internal Pressure Analysis and Test for Hot Fill (BIPATH) is a container, closure, and process design and optimization program for packages that experience pressure or vacuum during any part of the supply chain. It was originally developed for the hot fill PET bottle design at Stress Engineering Services, Inc. (SES) in 2006. Over the years, BIPATH has evolved and expanded to encompass a wide range of container types and pressure/vacuum-prone filling, processing and distribution systems. The container types include injection/extrusion blow-molded plastic bottles and cans, injection-molded or thermoformed tubs and cups, and aluminum and steel cans. The pressure/vacuum-prone filling, processing and distribution systems include hot fill, retort, high pressure process (HPP), carbonation, nitrogen dosing, steam flushing, altitude and temperature change in distribution, air-shipping, product out-gas or oxygen consumption, oxygen/CO2 ingress or egress and plastic creep deformation over time. BIPATH calculates the package pressure allowable, which is the pressure or vacuum that the package can sustain without any unacceptable deformations or distortions, and the package pressure residual, which is the pressure or vacuum generated inside the package. The ratio of the pressure allowable and pressure residual, known as package pressure safety factor, offers bottle suppliers and brand owners a simplistic way to measure how well (or bad) the package would perform at the early stage of the package and product development process since no physical bottle or finished good samples are required for the BIPATH program. The pressure or vacuum can be better managed and optimized using BIPATH through changes in container and closure design, product content, process conditions (pressure, temperature and duration profiles), and shelf life commitment. The validity and versatility of BIPATH program in managing the pressure or vacuum has been demonstrated in real world packaging and process design and optimization since 2006. The theoretical foundation of the program and a case study are presented in this paper.
The fatigue crack growth and failure behavior of five different short glass fiber reinforced polyamide (PA) grades was investigated on specimen level using compact type (CT) specimens. By using a testing device enabling superimposed mechanical and environmental loading, the effect of environmental conditions (23°C in air and 80°C in water), matrix material (polyamide 66 and polyamide 6T/6I) and glass fiber content (30 w%, 40 w% and 50 w%) on the fatigue crack growth kinetics was determined. Tests at 80°C in water exhibited an inferior fatigue crack growth resistance. Furthermore, for PA grades with a similar glass fiber content, an influence of the matrix material was revealed. PA grades with a higher glass fiber content indicate a better fatigue crack growth and failure behavior.
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Any article that is cited in another manuscript or other work is required to use the correct reference style. Below is an example of the reference style for SPE articles:
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