We used a temperature-sensitive fluorescent dye, perylene, to monitor the true resin temperature during extrusion of polycarbonate. The measurement involved doping polycarbonate with perylene and detecting fluorescence with an optical sensor that accesses a standard instrumentation port on a barrel of a single-screw extruder. The sensor's confocal optics design permits fluorescence intensity measurements as a furiction of position. Using a previously established calibration function, temperature and temperature gnadients were obtained from the measured fluorescence. Because the origin of the measurement is the fluorescent dye molecule that is soluble in the resin, this method allows temperature measurement of the polymer without interference from the surrounding metal parts. With the sensor looking over the screw, temperature profiles from the barrel wall to the core of the screw were obtained as a function of screw speed, screw design and resin melt flow rate. (C) 2004 Society of Plastics Engineers.(dagger).

A competitive global economy requires processors to consider every available option to reduce their costs. One popular approach is to convert to in-house coloring, the blending of natural resin with color concentrate at the injection molding machine. With this approach, the greatest cost savings can be realized by using the highest letdown ratio of color concentrate possible. However, to successfully realize this cost savings, good mixing performance in the barrel is essential. This study will show that a mixing screw provides better mixing than a conventional screw and that a sleeve mixer non-return valve significantly improves mixing when it is used with either screw. Thus, the improved productivity of in-house coloring can be realized by applying this technology.

Flow surging in single-screw, plasticating extruders is the variation of the machine's rate with time, and it generally leads to higher production costs, lost production, and often higher scrap rates. Flow surging can originate from many different sources including machine controls, resin feedstock variation, screw geometry, and machine temperature. This paper will focus on flow surging that originates from improper solids conveying, and it will present experimental data and corrective action to eliminate or minimize surging.

An investigation of the extrusion performance of ethylene/styrene Interpolymers was performed. These Interpolymers are pseudo-random copolymers of ethylene and styrene synthesized via INSITE* Technology, Dow's proprietary, single-site, constrained-geometry catalyst technology (1,2). Extrusion characteristics such as output rate, specific energy consumption, and extrudate temperature were measured as a function of screw design and processing conditions.

The results of extrusion trials on several single and barrier-flighted screws which highlight the importance of proper screw design for engineering thermoplastic polyurethanes are presented. Fundamental properties of the resins, including solid bulk density, coefficients of dynamic friction, melting rates and thermal properties are included to demonstrate their use in screw design.

Experiments were performed to determine the performance of three floating ring mixing devices. The mixers studied were 1) a Twente mixing ring, 2) a Barr sleeve mixer, and 3) a Parr ring mixer. Performance was measured using extrudate sampling, extruder performance, and extrusion solidification experiments.

The size of flight radii on the screw channel is important for the proper performance of a single-screw extruder. SPI guidelines state that the root radii should not be less than half the depth of the channel. Improper design or fabrication, however, often results in radii that are less than half that for the metering and transition sections, leading to regions with long residence time and material degradation. For optimal solids conveying, however, the effect of flight radii is considerably more complicated. This paper will present experimental and numerical data that indicate how to specify the flight radii for all sections of the screw.

A rheology model has been developed which brings together Graessley's concept of treating entanglements as couples (1), the framework of molecular network theory developed by Lodge (2), and the concept of reptational pathways first introduced by deGennes (3) and subsequently developed by Doi and Edwards (4). The model to be presented herein predicts the following relationship between zero shear viscosity and molecular weight in the entanglement regime: eta(o) similar to M-3.5. This prediction is closer in agreement with what has been seen experimentally (eta(o) similar to M-3.4) than that predicted by the classic reptation model (eta(o) similar to M-3.0) This paper will first describe the Forced Reptation Model and then a presentation of various rheological predictions that arise from this model will be given.

Solids conveying is the least understood operation for single-screw, plasticating extruders, yet it can be the source of many problems such as flow surging, low rates, high discharge temperatures, and material degradation. A lack of solids conveying devices and adequate physical property data for resins has contributed to this poor understanding of the section. For this paper, experimental solids conveying rate data will be presented for a low density polyethylene (LDPE) resin at several different process conditions for two screws with either a smooth or grooved barrel.

Experiments were performed on a mixing screw to assess its melting, pumping, and mixing characteristics. This was done by extrusion trials, extrudate sampling, extrusion solidification experiments, and comparison to results for a screw without a mixing section. Comparisons were made as a function of screw speed and color concentrate letdown ratio.

During the extrusion process, polymer solids are conveyed forward, heated, and compacted under pressure. For some powder resins, the compaction process can increase the density of the solids by a factor of between 2 to 3. For all extrusion solids conveying models, this pressure (or stress) is assumed to be isotropic in the plane perpendicular to the flight. The data presented here, however, indicate that stresses in the solid bed are anisotropic. This anisotropy will affect the solids conveying forces at the metal surfaces of the extruder and hence affect the accuracy of the current published models. A new compaction cell was developed to measure the bulk density, coefficient of storage friction, the lateral stress ratio, and the coefficient of static friction at the wall. The lateral stress ratio is defined as the stress in the secondary direction divided by the stress in the primary direction.

Solids conveying in single-screw extruders is the result of both frictional and viscous forces acting on the solid bed. Viscous forces, however, are often neglected or simply viewed as being frictional in nature. This paper shows experimental data and then relates these forces to shear stresses for solids conveying. Melting rates and specific energy consumption for an extruder were also measured and presented.

Syndiotactic polystyrene (sPS) is a semi-crystalline polymer polymerized from styrene monomer via a novel catalyst. The crystalline melting point of 270 degrees C sets it apart from atactic polystyrene (PS) which begins to soften above 100 degrees C.The design of an extrusion process for sPS presents several challenges beyond the normal. Far example, the temperature of the pellets must be rapidly increased to soften them, yet compaction must occur slowly enough to effectively remove inter-pellet air while the pellets compact to form the solids bed. Additionally, the polymer temperature must be increased from ambient temperature to above the melting point, requiring an energy input of almost 500 J/g.The work presented here will show data which will be used to determine the best extruder screw design and operating conditions for sPS.

Solids conveying is the least understood operation for single-screw, plasticating extruders, yet it can be the source of many problems such as flow surging, low rates, high discharge temperatures, and material degradation. This lack of understanding has led to poor solids conveying models that do not describe conveying behavior. A new conveying model, however, has been developed that describes the pressure generation and thermal effects utilizing realistic physical property data. The model is compared to experimental solids conveying rate data for a low density polyethylene (LDPE) resin at several different process conditions and for two screws.

Debugging and optimization of extruder performances are often complicated by the lack of transient process data. Most production extruders have excellent process controllers, but they generally lack data acquisition systems. Because of these equipment limitations, all transient, unsteady-state data for a process are unavailable for analysis. Highlighted in this article are four case studies where transient data were collected and used (1) for the diagnosis and elimination of extrusion instabilities; (2) to show differences between competing resin processability; and (3) in extrusion research. In all cases, a portable data acquisition system was temporarily connected to the extruder control panel and was used to collect transient process data. For extruder instability problems, the data collected were used to help diagnose and eliminate the problems quickly, bringing the extrusion lines up to standard production in the shortest possible time, minimizing costly recycle, and maximizing the profits for the processors. © 1996 John Wiley & Sons, Inc.

Solids conveying is the least understood process for single-screw extruders. This lack of understanding was caused by the unavailability of solids conveying rate data. A new device has been developed to measure solids conveying rates as a function of barrel and screw temperatures, screw speed, and discharge pressure. These data along with friction and bulk density data will be used to determine the accuracy of several solids conveying models.

Previous research and this research indicate that the mechanical melting for poly(vinylidene chloride) copolymers (PVDC) is complex. Mechanical melting is defined as the melting (or devitrification) of a polymer when a significant portion of the thermal energy originates from a mechanical energy dissipative process. PVDC mechanically melted on a moving metal surface at temperatures of the test instrument that were considerably lower than the differential scanning calorimetry (DSC) onset melting temperature. PVDC formulated with low levels of high density polyethylene (HDPE), however, melted at metal temperatures near the DSC onset melting temperature. Two different mechanical melting mechanisms are proposed to explain the data, and the frictional data are discussed with respect to solids conveying in a single-screw, plasticating extruder.

The coefficient of dynamic friction is often the controlling factor for solids conveying, pressure generation, and thermal decomposition of a resin in the feed section of a single-screw plasticating extruder. The coefficients of friction are, however, very poorly understood, and the interpretation of the measurements are complicated by the dissipation of frictional energy at the sliding interface. A new instrument was recently built to help understand dynamic friction, and a numerical technique was developed to estimate the interface temperature. Coefficients of dynamic friction for several polyethylene resins are presented in this paper as a function of the surface temperature, pressure, and velocity. The relationship of the data with respect to the extrusion process is discussed.