The SPE Library contains thousands of papers, presentations, journal briefs and recorded webinars from the best minds in the Plastics Industry. Spanning almost two decades, this collection of published research and development work in polymer science and plastics technology is a wealth of knowledge and information for anyone involved in plastics.
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Rheology Optimized Processing Temperature for Preparation of Amorphous Solid Dispersions via Hot Melt Extrusion (HME)
The production of amorphous solid dispersions via hot melt extrusion (HME) relies on elevated temperature, applied mechanical force and prolonged residence time, which can result in potential degradation and decomposition of thermally-sensitive components. In this study, the rheological properties of a physical mixture of polymer/active pharmaceutical ingredient (API) were utilized to guide HME processing temperature. A critical temperature, which is substantially lower (~13°C) than the melting point of crystalline API, was captured during a temperature ramp examination and regarded as the critical point at which the API molecularly dissolves into the polymer. After identification, solid dispersions were prepared by HME processing below, on, or above the recognized critical temperature and characterized by scanning electron microscopy, hot stage microscopy, Xray diffraction, differential scanning calorimetry and rheology. Physicochemical properties of resultant solid dispersions indicated that the obtained critical temperature is sufficient for the polymer/API system to reach a molecular-level mixing, manifested by the transparent and smooth appearance of extrudates, absence of API crystalline diffraction and melting peaks, and dramatically decreased complex viscosity. Once the critical temperature is achieved, further raising temperature only results in limited improvement of the dispersion, reflected by slightly reduced storage modulus and complex viscosity.
A Critical Review of a New Joint Test Proposed in NCHRP Report 190
Pipe joint performance is a critical factor in the overall pipe system success. Design of joints is more complex than the design of the pipe wall. There are many different joint designs manufactured and marketed by the pipe industry for non-pressure pipe designs. The recent National Cooperative Research Program (NCHRP) project report 190 attempts to address the structural performance, largely based on shear failure at the joint. This project did a very good job of analyzing the shear and rotation stresses for concrete, corrugated steel, PVC, and HDPE on a limited number of joints. There are practical issues with the recommended test. This paper focuses only on the thermoplastic pipe designs.
Bonding of Plastics
Many types of polymers are not weldable. For example, thermoset polymers cannot be welded. While thermoplastic polymers are considered weldable as a class, most combinations of dissimilar plastics cannot be welded. Even plastics within the same generic grouping may not weld easily because of high crystallinity or high melting temperature, widely differing melt flow indices, or high melt viscosity.
In this presentation, the basics of adhesive bonding of plastics will be given. This will serve as review for some and introduction for others. General topics include surface preparations and primers, joint design, selection of adhesives, and some specific ideas on bonding of difficult materials such as fluoropolymers and elastomers.
Study of Ketoprofen’S Dissolution in Polyethylene Oxide Formulations Prepared by Hot Melt Extrusion
Solubility parameters have been used as an approach to predict active pharmaceutical ingredients solubility in a polymeric excipient. The solubility is important because it dictates the processing window for hot melt extrusion and the stability of the formulation during storage. Nevertheless, it is challenging and complicated to predict the solubility and there is very few published studies in the field. In this study Film Casting Technique, Differential Scanning Calorimetry, Thermal Gravimetric Analysis, and Hot Melt Extrusion process were used to study and analyze the solubility of ketoprofen in polyethylene oxide (Polyox™ N10). The outcomes from the different method and techniques implemented were consistent and the best results were obtained with the maximum concentration of ketoprofen. The suggested processing temperature was 70°C and 70 rpm for the rotor rotation speed. The stability of the samples were monitored by two months. The methodology used in this study can be applied to analyze and investigate other drug-polymer pairs.
Product Quality Control for Single Screw Extrusion Process
As a major polymer processing technique, single screw polymer extrusion is a continuous process, during which material properties, machine variables, and process variables interact with each other to determine the final product quality. In order to achieve the desired product quality, the industry has been focused primarily on the control of critical process variables such as melt pressure and barrel temperatures. Recently, increasingly stringent customer demand on product quality has forced the machine maker to put more effort on the control performance. This paper first defines the extrusion product quality into two categories: precision and accuracy. The extrusion product precision control can be achieved by good process variables control, while the quality accuracy is a joint effect of the machine variable and process variables. The characteristic of the extrusion product quality shows as multivariable, non-linear, large time delay, hence advanced control algorithm must be employed in the product quality control. The control scheme is implemented experimentally via a self-developed controller on an industrial pilot-scale single screw extrusion process. Some representative results are presented to highlight the advantages and limitations of the control strategy.
Development of Advanced Microlayer Coextruded Films for Optical and Packaging Applications
Advanced optical and packaging films were developed by using microlayer coextrusion process technology with improved flow design and processing control. Combinations of layers and biaxial stretching provided enhanced optical properties. Films with broad band and wavelength-selective reflection were developed. The relationships of layer arrangement and processing control to properties were discussed. The high rate processes led to enhanced iridescent and optical filtering products for decorative packaging, energy control and consumer applications. The layered coextrusion process helped enable films and sheets with improved properties beneficial for packaging and consumer applications.
Development of a Flexible Polymer Joining Center Capable of Performing Multiple Joining Processes Using Different Methods in a Single Cycle
Goal of this research is the implementation of a flexible polymer joining center as a prototype machine integrating different friction welding methods. This prototype joining cell combines (a) flexibility by being capable of performing joining processes in any order in a single flow with (b) modularity by integrating unified interfaces for exchanging joining modules, and (c) scalability by offering a wide range of setups for smaller to larger work pieces. Corresponding interfaces to up- and downstream processes enable implementation in fully automated environments.
This paper will give a brief overview of the introduced technology and its current status, and present results from first welding experiments with non-reinforced PP and 30% glass fiber reinforced PA 66, mainly investigating reproducibility of welding results, and give an indication of overall welding quality potential.
Influence of Filler Dispersion on Electrical and Rheological Properties of Pc/San Blends with Graphite Nanoplates or Expanded Graphite
The effect of Graphite Nanoplates (GnPs) and Expanded Graphite (EG) on electrical and rheological properties was investigated in co-continuous melt-mixed polycarbonate (PC) /poly(styrene-acrylonitrile) = 60/40 wt% prepared using micro-compounder in two steps. Mixing conditions in premixing the fillers into PC were varied. Similar to carbon nanotubes (CNTs), GnPs and EG tend to localize in PC. Improved filler dispersion for samples exposed to higher mixing energy in the premixing step resulted in larger increase of complex viscosity and storage modulus. However, electrical resistivity was lower in samples which experienced lower mixing energy. Comparing EG and GnP, the effects are quite similar. EG showed a slightly better electrical performance.
Increased Throughputs in Blown Film Extrusion by Using a Contact Cooling Sleeve
One of the most important requirements for an efficient blown film extrusion process is the cooling of the film bubble. Conventional blown film lines use air rings to cool the film bubble. A new approach to enhance the cooling power is the use of an additional contact cooling sleeve that is placed on top of the die and which cools the melt via conduction.
The influences of the use of the contact cooling sleeve on the blown film process and the resulting film properties were tested. In order to do so, process settings were varied and the mechanical and optical film properties, as well as the maximum throughput of the blown film line have been determined. These trials showed that the mechanical film properties are not significantly influenced by the use of a contact cooling sleeve. For the optical film properties, the transmission is slightly decreased while the haze of the films is increased by about 10 % absolute. With the use of a contact cooling sleeve, it is possible to increase the throughput of the blown film line especially for smaller blow-up ratios. A simulation of the cooling process of the melt within the cooling sleeve has been performed as a first step to be able to dimension cooling sleeves for different sizes of blown film lines and process conditions.
Improvement of the Extrusion Foaming Properties of Externally Plasticized Cellulose Acetate by Reactive Melt Mixing Using a Multifunctional Reactive Oligomer
Externally plasticized cellulose acetate was modified by reactive melt mixing with a multi-functional oligomer (chain extender). The modified compound was characterized in terms of molecular properties and viscosity. The reactive modification was applied in an extrusion foaming process using 1,3,3,3-tetra-fluoropropene (HFO-1234ze) as blowing agent. The reactive modification in the foam extrusion process can be used to affect the rheology and thereby foaming properties of the cellulose acetate compound to optimize the cell morphology of the resulting foam sheets or boards.
Cycle Time Reduction by Water Spray Cooling in Thermoforming
The cycle time of automated multi-station thermoforming machines is limited by the cooling time. Optimizations of heat dissipation in negative thermoforming are especially focused on the mold-side cooling. However, cooling the inner, non-mold-contact side of formed part also provides potential for increasing the total cooling rate. The injection of water spray on the non-mold-contact side during the forming step is a promising approach to reduce the cooling time in thermoforming due to better heat transfer properties or the evaporation potential. In this paper the influence of an internal water spray cooling on the deforming temperature of thermoformed cups is examined.
During water spray cooling a conflict of aims results between the maximum cooling effect and a water-residuefree cup. The injected volume of water spray significantly affects both the deforming temperature of the formed cup and the water residue. By optimizing the process a maximum injection volume of 6 ml water can be achieved for the examined 400 ml large cup with negligible residual water containing after deforming in the molded part. The results show that already minimal wetting of the partsurface results in effective cooling. To ensure negligible amount of residual water, a superposition of the water spray droplets should be avoided. Otherwise larger water droplets are created, which can not be removed by evaporation or an additional blowing process step. By using water spray, the cooling can be accelerated up to 6 K/s for the cup demonstrator. Thus, the application of water spray cooling reduces the cycle time of multistation thermoforming machines.
Highspeed Tensile Testing of Polymer Materials Considering Force-Oscillations and its Origin
The force-oscillation phenomenon describes a superimposition of force measurements with an oscillating signal which can be monitored in tensile impact testing. These oscillations become predominant with an increase of the haul-off velocity which prohibits a resilient evaluation of the measured force characteristics. Hence force-oscillations present a limiting factor to the maximum haul-off velocities in tensile impact testing and therefore a limitation to material data measurement for crash analysis in general.
The presented research looks at the phenomenon of force-oscillations on viscoelastic materials and gives an elementary investigation on its origin. Furthermore a new approach is outlined to overcome the existing limitations to tensile impact testing which enables a material data measurement basically independent of the considered haul-off velocity.
Atomized Spray as a Process Fluid for Fluid-Assisted Injection Molding
Gas- and water-assisted injection molding (GAIM, WAIM) can be used to produce hollow plastics parts. Previous research showed that the thermal properties of gas and water have a large influence on part properties and the formation of part defects. A new approach is to use atomized spray to adjust the thermal properties of the process fluid to the needs of the process and used material. The study will determine the effect of water percentage on the cooling effect of the atomized spray and the resulting part properties. High speed imaging will show effects of water coagulation on the part cooling.
Analysis of the Process-Induced Microstructure in Injection Molding of Long Glass Fiber-Reinforced Thermoplastics
Over all stages in the injection molding process of long fiber-reinforced thermoplastic (LFT) materials, the configuration of the fibers changes, which ultimately affects the mechanical performance of the finished part. This article presents a full microstructure analysis of an injection molded part made out of polypropylene reinforced with 40% by weight of glass fibers. The analysis takes into account local measurements of fiber orientation, fiber length, and fiber density distributions by applying sophisticated measurement techniques, such as micro-computed tomography.
The results of this work show that the assumption of a uniform fiber length and fiber density throughout the entire part is not valid. The number (weight) average fiber length increases from 0.64 mm (1.63 mm) close to the gate to 1.12 mm (2.81 mm) at the end of the flow path. Similarly, the fiber density varies along the flow path from 37.7 wt% in the gate region to 44.6 wt% at the end of flow. Moreover, the fiber density measurements across the part thickness show a significant fiber agglomeration in the core of the part that consistently suggests almost 30% more fibers in the core layer than in the shell regions.
Micropelletization and Their Application to Manufacture Porous Plastic Parts
A novel micropelletization technique yields micropellets with a controlled morphology and narrow particle size distribution which can be used for sintering applications and additive manufacturing processes such as laser sintering. A polymer melt is extruded through a capillary and the extruded thread is stretched with a hot air stream until flow instabilities cause it to breakup into small droplets. This work focuses on an improved experimental setup with additional temperature control for the production of micropellets. By performing a variety of test series, options for further optimization of the process have been worked out. This is another important step towards an economical, ready-to-use-process that can provide ideally shaped and size-distributed micropellets using a wide range of polymers. Furthermore, sintered parts were produced to demonstrate possible utilization of these micropellets for industrial and commercial applications.
Melt Devolatilization Extruson Process for Brominated Polymeric Flame Retardant
A brominated polymeric flame retardant has a significantly advantaged environmental, health and safety profile compared to small molecule halogenated flame retardants due to reduced molecular mobility and thus no bio-availability. The brominated polymeric flame retardant can be prepared using an innovative indirect bromination reaction, which requires the use of a halogenated solvent. A devolatilization extrusion process has been identified as an economically favorable and technically simplest isolation process among many other isolation technologies assessed. The development of a devolatilization extrusion process for the brominated polymeric flame retardant is presented.
Fiber Surface Treatment as an Approach to Increase Fiber Content in AGAVE-LMDPE Composites Produced by Rotomolding
In this study, Agave fibers (Agave tequilana Weber var. Azul) were surface treated with maleated polyethylene (MAPE) to increase the polymer-fiber compatibility with two main objectives: 1) to improve the mechanical properties of composites produced by rotational molding, and 2) to increase the fiber content in the composite. The rotomolded composites were produced at 0, 10, 20, 30 and 40% wt. of fiber contents (treated or untreated) and characterized in terms of morphology and mechanical properties (impact, tensile and flexural). The results show that the MAPE surface treatment was successful by causing a better fiber distribution and a more uniform composite morphology allowing the possibility to use higher fiber contents in rotational molding. At low fiber contents (10 and 20% wt.), the mechanical properties were improved (up to 52%) in treated fiber composites (TFC) compared to the neat polymer and untreated fiber composites (UFC). Although the mechanical properties of TFC decreased at high fiber contents (30 and 40% wt.), they were substantially higher than UFC (about 160%, 400% and 240% for impact, tensile and flexural properties, respectively).
Study on Extrudate Swell of High-Density Polyethylenes in Slit (Flat) Dies
Extrudate swell of a high molecular weight high density polyethylene (HDPE) in flat/slit dies is studied using both experiments and simulations. The experimental set-up consists of an optical micrometer to measure the extrudate dimensions (both thickness and width) and a pair of radiation heaters to control the extrudate temperature outside the die, attached to the capillary rheometer. The simulation of extrudate swell phenomenon is carried by using the well-known integral K-BKZ model. The effects of die geometrical characteristics, molecular characteristics of polymers and operating parameters on extrudate swell measurements are studied systematically. The experimental data are compared with corresponding two dimensional steady state numerical predictions. The thickness swell is predominant in comparison with width swell due to larger shear rates applied in that direction.
Dynamic Rheological Measurements of Aqueous Polyester Dispersion in Batch Reactor and Twin Screw Extruder
This paper reports on inline measurement techniques for the rheological behavior of aqueous polyester dispersion in batch reactor and twin screw extruder (TSE). Since the preparation of latex without hazardous solvent is a relatively new technique, very little has been reported to understand the kinetic aspects of the process for both batch reactor and TSE. A sudden viscosity drop is observed in a batch reactor whereas the viscosity tends to oscillate in TSE during the addition of water when surface tension is low enough. The viscosity changes during the addition of water are thought to be related to the morphological changes during the process since surfactant must be present else no change occurs. In this paper, different surfactant and NaOH concentrations have been studied for their influence on the viscosity so that emulsification may become a predictable process in a TSE.
Innovative Extrusion Process for Liquid Silicone Rubber: Calculation Versus Experiment
Silicone rubber with its good chemical and physical resistance properties is of major interest for elastic tubing. The breadth of silicone tubings is continuously manufactured by extrusion. The extruded silicone products are cured downstream of exiting the die. Thus the viscosity of the uncured silicones must be high enough for a dimensionally stable extrudate and even with high viscosities, achievable precision and tolerances are limited due to this fact. Therefore an innovative extrusion process, which uses a heated die in order to vulcanize the extrudate inside the die, has been developed.
In this work, a formula for the flow rate is derived for an in-die-curing silicone extrusion in order to mathematically describe this process and to be able to predict the capabilities of this technology. The results of the calculations are being compared to experimental results to determine their validity.
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