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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In-line monitoring of the location of the interface inside a co-extrusion die on an accumulator blow moulding machine is performed using ultrasound. Ultrasonic waveguides similar to a pressure transducer are inserted into the wall of the co-extrusion die at different locations along the extrusion direction. One end of each waveguide is flushed with the inner surface of the die and the other end is air cooled to accomodate one ultrasonic transducer (UT). The thickness of each layer is determined by the detection of an interface echo which is enhanced by signal processing techniques. The waveguide has also been modified to measure the temperature and heat flux at the die wall. The results were compared with those obtained from a conventional thermocouple.
The demands on injection molded products have constantly increased over the past few years. This relates not only to the quality of the produced parts but also to the economy of production in which plasticizing plays a vital role. Modern plasticizing by injection molding machines must thereby fulfill the individual demands in the processing of divers materials. This universality, which to this point was attained by the insertion of a single standard screw, reaches its limits with many materials. The insertion of special screws provides a remedy in this area. Based on trails with technical thermoplastic material as well as with polyolefins, the advantages and disadvantages of the various screw geometries, such as 3 zone screws, barrier screws, and low compression screws, are compared.
The orientation of organic thin films of natural polymers of microbial origin was studied with the aid of LangmuirBlodgett films and x-ray reflectivity. The polymer system studied included a number of polyhydroxyalkanoates, a family of microbial polyesters which include both thermoplastic and elastomeric materials and which have previously been shown to form stable monolayers at the air-water interface. The spreading behavior of each polymer was studied and the orientation of the polymer following transfer to a substrate was determined using x-ray reflectivity.
This paper presents experimental results on processing of the novel metallocene polyethylenes. The experiments were performed in a 45 mm- conventional single screw extruder with a barrier screw. The evaluation of the mechanical properties, screw characteristic curves, energy balance, pressure consumption and melt temperature profile experiments were completed for the different blends of metallocene material (mPE), linear low density polyethylene (LLDPE) as the masterbatch (MB) carrier and titanium dioxide as the filler. The results for the metallocene resin show a wider operating window, higher energy dissipation, and higher torque consumption compared to the conventional low density polyethylene. Adding fillers to these materials increased the operating window and the mechanical properties, while the energy dissipation and torque consumption vary according to the filler content and processing conditions.
Dielectric spectroscopy was applied in the present work for the first time to polymeric composite materials containing transcrystallinity, wherein the dielectric properties of pure nylon 66 and of aramid fibre-reinforced nylon 66 microcomposites were examined over wide frequency and temperature ranges. The dielectric response was found to be sensitive to the presence of transcrystallinity in the microcomposites. It was found that the activation energy of the ?, ?, and ? relaxations exhibits typical variations in the presence of reinforcement and transcrystallinity. The specific values of the dielectric loss and dielectric loss tangent at 1MHz as a function of temperature for the transcrystalline layer were retrieved from the composites data using the rule-of-mixtures. A comparison was conducted between the values of the transcrystalline layer and those of the bulk matrix to determine the effect of the transcrystalline layer on the dielectric properties.
The most readily synthesized forms of methyl ethyl ketone peroxide (MEKP) are its monomeric (2,2- dihydroperoxybutane) and dimeric (2-hydroperoxy-2-[1- hydroperoxy-1-methylpropylperoxy]butane) oligomers. Methyl ethyl ketone peroxides are used to initiate cures at ambient temperatures, and are popular for processes that include resin transfer molding, filament winding and casting. Analytical methods have been used to quantify the amounts of residual hydrogen peroxide, MEKP monomer, and MEKP dimer in commercial formulations. This paper will discuss the effect of methyl ethyl ketone peroxide monomer and dimer, and hydrogen peroxide in the cure of orthophthalic, isophthalic, and vinyl ester resins. It will show how variations in these MEKP components affect the overall cure performance of resin systems.
The cast film process, unlike the blown process, is one that quenches the molten extrudate on a chilled steel roller after it exits the die. This paper discusses the process and physical variables and how they affect film properties and quality. Most polyfin films are made by either the cast or blown process. The major differences are the basic resins and the method of cooling the extrudate once it leaves the forming die. The blown film process extrudes the molten poly from a annular die, chills the tube with air, usually chilled, and forms a bubble, with a pair of nip rolls holding the bubble pressure as cooling occurs. In the cast film process, the other popular method of thin film manufacture, the polymer is forced through a slot die and chilled on a chilled roller, solidifying the molten plastic and forming a sheet of film. Fig. 1 shows a diagram of this process. Fig. 2 shows some of the variables. The two different processes requires resins that have properties that support the process and give different properties to the finished film. This paper will discuss the cast film process, how the film is made, properties of the film and how varying the process effects the film properties. The extruder, a major player in cast film has been discussed and the output of the extruder is the feed for the cast film process. Most cast film lines manufactured today are coextrusion lines and as many of seven extruders may feed product to a common die by means of a coextrusion adapter. This adapter aligns the various polymers in a form required for the finished sheet and supplies a “plug” of polymer, correctly proportioned to the entrance of the die. The output of the multiple extruders, the combining adapter and the die determine the layer distribution of the coextruded film. In this discussion we will assume the extrusion line to be coextrusion, however, if the line is mono, the same principles apply except for layer distribution.
The handling of plastic films in continuous web form both in transport through process equipment and particularly in winding is complicated by the fact that these materials are usually characterized as being nonporous and having very low surface roughness. These properties lead to the significant entrainment of air between the web and roller surfaces, or between the layers in a winding roll, such that a very limited state of traction may exist between the surfaces leading to difficulties with the transport of the web through process equipment or in winding without dishing or telescoping and/or poor wound roll integrity. This tutorial reviews the current state of the art in understanding the factors relevant to air entrainment and techniques to deal with it in film handling and winding.
Film fabrication is an important commercial process for plastics. Many of our essential products in our culture use films to package and protect items such as foods and durable goods. The blown film process represents one of the most common commercial technologies used to fabricate polymers into films. The blown film process at first inspection appears to be a relativity simple process which is comparatively easy to operate, but it is in fact a process characterized by it's versatility to produce films suitable for use in widely differing application with specific performance requirements. How are the basic components of the blown film process sized to assure proper operation? What are the critical parameters of the blown film process? How does the selection of process parameters allow similar film properties to be obtained on different blown film lines? What is the interaction of the process and polymer to produce specific performance properties? How do the components of the components of the blown film process work? How are measurements on the process made to assure consistent performance on different lines? What are some troubleshooting guidelines that have been found to be useful for operation of the blown film process? These are some of the questions that this tutorial will address.
Biaxially oriented films of polypropylene (PP), polyester (PET) and high density polyethylene (HDPE) can be made in several different processes. The tenter process will first be shown in overview to describe the function of each of the primary manufacturing steps (coextrusion, casting, machine direction stretching, transverse direction stretching, surface treatment and winding). Next the primary stretching steps and equipment configurations will be defined and characterized in terms of process and material variables and the film properties produced. From a processing focus, the primary process steps may be considered and evaluated as some form of rheometer, either for melt or solid, and these ideas will be introduced and evaluated as a means of understanding the process / film property interactions.
A set of experimental data is carried out on short fiber suspensions in viscoelastic fluids. Parameters such as fiber volume fraction, fiber length and pre-shearing are studied. Transient tests on pre-sheared samples showed that fiber orientation depends on both the strain and the rate-of-strain tensors. Increasing fiber concentration and aspect ratio increases rheological material functions in the low shear rate region. In the high shear rate region, the effect is less pronounced. The experimental data are compared to a rheological model based on the modified Jeffrey equation. The theoretical results are found to be in good agreement with most experimental data. Further changes to the original model were necessary to be able to predict the rate-of-strain-dependent fiber orientation and the observed behavior of the considered material functions.
Impact property development in RPVC construction products is highly dependent on the type of impact modifier used and its contribution to processing. With increasing attention being paid to all aspects of production, particularly machine utilization and cost effectiveness of raw materials, maintaining performance properties remains critical. This study discusses how impact modifier selection can influence processing and the levels of other ingredients, and through these effects, influence the performance properties of articles like siding and window profile.
The phenomena of extrudate swell and associated instabilities have received substantial attention, yet they are still the cause of considerable debate1-9. Laser micrometers are used routinely to measure extrudate swell in capillary rheometers as well as critical profiles like catheter tubing. The speed of typical laser devices was on the order of 200 samples per second. The commercial availability of newer laser technology allows measurement on the order of 700+ samples per second with accuracy’s in the 2.75 micron range. Using these high speed laser micrometers it seemed feasible that the analysis of various types of gross melt fracture and sharkskin might become more quantitative if viewed in the frequency domain i.e. amplitude of diameter variation as a function of frequency in time. Similarly the frequency of the diameter variation can also be viewed as a function of linear distance on the extrudate. The finger print of the amplitude spectrum rather than still photography or nebulous descriptive terminology might be used to characterize the phenomena and, perhaps, give some insight into it’s origin. This paper is our scouting work on this idea.
The objective of this research is to find ecologically and economically acceptable routes to utilize excess xerographic toner from manufacturing and returned toner cartridges. This black toner is a polymer composite comprised of a styrene-based copolymer, carbon black and other additives. The mechanical properties of toners are specifically designed to allow attrition to 10-20 µm particles. Thus the bulk mechanical properties are not desirable for load bearing applications typical of consumer plastics. Reactive and non-reactive blending of toner with other polymers have been used to enhance the mechanical properties. The blends and alloys produced exhibit a transition from brittle to ductile behavior as exhibited by impact energy data. Thus a family of polymeric systems of variable properties versus cost compromise can be created.
The effect of grafting monomer on the performance of thermoplastic vulcanizates (TPVs) of polypropylene (PP) / styrene-ethylene-propylene-styrene copolymer (SEPS) / polyester thermoplastic elastomer (TPEE) has been studied. Glycidyl methacrylate (GMA) and maleic anhydride (MAH) were selected as grafting monomer. MAH grafted sample was observed to give excellent mechanical properties and have higher gel ratio which was determined as insoluble portion after extracted in 60°C acetone and subsequently in 65°C chloroform.
Polyethylene (PE) injection molded rigid containers are widely used for food packaging and promotional drink cups. Molders of these containers have well-defined processing needs and molded part requirements. Likewise, the polymer manufacturer has well-defined manufacturing and analytical methods for characterizing resin properties. This paper presents a unique method of translating the molder's needs back to polymer melt index and molecular weight distribution. The introduction of an Isometric Spiral Flow Chart" provides the basis for this new approach. A nomogram for optimizing injection melt temperatures when transitioning from lot-to-lot is also presented. Utilizing this information injection molders can maximize their production."
Multi-layer high-density polyethylene (HDPE) films are used for numerous food-packaging applications because of their superior water vapor transmission rate (WVTR). Economic factors have caused film converters to produce thinner-gauge films to reduce raw material costs. At thinner gauges, WVTR's can increase faster than the expected inverse relationship with thickness. This paper presents laboratory data that expand on an ineffective film thickness concept first discussed by Talwar . Correlation's showing the effect of resin properties on this ineffective film thickness are presented. Utilizing this information, the barrier performance of multi-layer film structures can be maximized.
This paper documents the development of a novel injection molding machine, the Twin-screw Injection Molding Extruder (TIME). A reduction of capital equipment and thermal degradation is achieved by combining the compounding ability of a Twin Screw Extruder (TSE) with the final part fabrication techniques of an injection molding machine. Tests conducted on a bench-scale model of the machine have shown that an entirely new set of process parameters comes into prominence due to the combination of compounding and injection molding processes. The main control objectives also differ from a traditional injection molding process.
This paper presents and experimentally validates a physically motivated model for predicting the mean residence time in twin screw extruders. Accurate estimation of the mean residence time and the propagation delay through a plasticating extruder is critical for implementing feedback control schemes employing sensors mounted along the extruder. Experiments were carried out on a 30 mm Krupp Werner and Pfleiderer Co-rotating twin screw extruder equipped with reflectance optical probes over the melting section, mixing section and at the die. The residence time distributions for twelve operating conditions and two screw geometries are supplied. The mean residence times predicted by our model are in good agreement with the experimentally measured mean residence times.
In this paper we proposed a viscoplastic material model for PET, which was based on the uniaxial material tests conducted on the newest type of Meissner rheometer. The tests have been performed with the constant strain rates varying from 0.01 to 1 (1/s), at the temperatures ranging from 90°C to 150°C. The proposed model could precisely take into account the effects of strain hardening, strain rate sensitivity, variation of the hardening index, and temperature changes. This model has been implemented into our nonlinear finite element code. Very good agreement has been verified through the comparison between the blow molding simulation result and the measurement.
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