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 the 1940's when rotational moulding of plastics was first developed, open flames were used to heat the mould. In the 1950's there was a switch to hot air ovens as a cleaner method to heat biaxially rotating moulds. Today hot air ovens dominate the market due to the convenience that they offer the user, although it is widely recognised that they are relatively inefficient as a means of heating. This paper presents results from an experimental investigation to assess the relative merits of open flame and hot air oven rotational moulding machines. Polyethylene mouldings of varying thickness were produced on both types of machine and cycle times were compared by using ROTOLOG to record mould internal air temperatures. It is shown that significant cost savings are possible using the open flame heating method. These savings arise from both lower energy consumption and reduced cycle times.
Samuel Ding, Craig L. Sandford, Michael T.K. Ling, Atul Khare, Lecon Woo, May 2000
We have studied material degradation and durability in a broad based program in selecting medical materials. In addition, the specific requirement that medical devices and packaging must have specified shelf-lives supported by real time data also prompted for quantitative evaluation. A large number of PP types and samples were studied under diverse conditions. These included high temperature oxidative stability by oxidation induction time (OIT), high oxygen pressure OIT, oven aging, aging and oxidative stability after ionizing radiation and real time ambient storage. The activation energies from the surface embrittlement processes were also found to have a striking similarity to the thermal processes. To overcome the difficulties in generating long term ( greater than 10 years) data, well characterized historic samples of up to 23 years in age were included in this study. When all data were combined, a striking feature was apparen very few data points at higher temperatures could allow a reasonable determination of the shift factor and quite accurate estimates for lower temperature durability. This methodologyt: that for PP, a self-similarity existed among all systems examined. This allows a simple vertical shift of data to construct a master curve" similar to rheological master curves. The implication being if the master curve can be constructed when supported by further studies could lead to broader applications and deeper understandings on polymer degradation"
Sherwin Shang, Tahua Yang, Craing Sandford, Michael T.K. Ling, Lecon Woo, May 2000
Medical devices industry differs from other polymer applications in one major aspect: that the products frequently need to be sterilized. Recently, sterilization by ionizing radiation has become increasingly popular, due to simplicity and cost effectiveness. In particular, the beta or electron beam (E-beam) irradiation has been adopted along with the traditional gamma radiation from radioactive Cobalt or Cesium sources. Of course, the ionizing radiation that disrupts bio-macromolecular structures in bio-burdens can and also frequently do damage polymer chains. We have conducted a study on material degradation due to E-Beam irradiation and compared with treatment with gamma. Similarity of the two processes as well as significant differences will be presented.
The non-linear creep-based models cause numerical instabilities during FEA calculations because of the necessary inversion of stress-strain relations. From this point of view, the relaxation-based models are preferable for use within FEA. On the other hand, engineers avoid such models, due to complicated tests. Therefore, the goal was to develop the non-linear relaxation model, which uses the data of creep-recovery tests. In this way the model would be comparatively inexpensive and unconditionally stable in FE calculations.
Z. Fan, R. Zheng, P. Kennedy, H. Yu, A. Bakharev, May 2000
The requirement to create a shell model on the midplane of the part for warpage analysis is at odds with the trend toward solid modeling. A method is introduced that enables warpage analysis without the midplane model. This ensures that the user interacts only with the solid geometry. In this paper we present results obtained with the new technique and compare them to those obtained on a midplane model.
Chaotic mixing of binary components has been recently used to produce and distribute fibers, multi-layer films, and fragmented sheets in melts. Formation mechanisms and means to promote one type over the other remain uncertain. In this study, in situ film formation and breakup in PS/LDPE blends was examined for differing extents of mixing. Results demonstrate new opportunities to develop distributed multi-layer films during blending processes.
Gale A. Holmes, Donald L. Hunston, Walter G. McDonough, Richard C. Peterson, May 2000
One of the critical factors controlling the long-term performance and durability of composites in structural applications is the interfacial shear strength (IFSS). The single fiber composite (SFC) test has been viewed by many as the best test for determining this parameter. Although the SFC test has been extensively researched, the micro-mechanics models used to obtained IFSS values are based on simplifying assumptions that are not realized under experimental conditions. Thus, results from this test often violate the known strength of the constituent materials. Therefore, a new methodology is presented that utilizes realistic assumptions.
Craig Sandford, Samuel Y. Ding, Michael T.K. Ling, Lecon Woo, May 2000
Medical devices differ from other polymer applications in one major aspect: that the product frequently needs to be sterilized. Due to simplicity and cost effectiveness, sterilization by ionizing radiation has become increasingly popular. Of course, the ionizing radiation that disrupts biological macromolecular structures (bio-burden) can and frequently does damage synthetic polymer chains. We have examined several polypropylenes (PP) subjected to long term ambient storage for up to 18 years after gamma irradiation at different doses. Many of the samples in thin film form have completely disintegrated. However, in many cases the degradation reaction was not homogeneous, with an apparent distinct skin-core structure and very different properties. These results and interpretations with an oxygen diffusion limited degradation reaction model will be presented.
Michael T.K. Ling, Craig Sandford, Adel Sadik, Henk Blom, Samuel Y. Ding, Lecon Woo, May 2000
In the medical packaging and devices industries, products are subjected to numerous converting and other downstream processing steps. For example, a vigorous drying step must be in place to minimize the reverse depolymerizing hydrolysis reaction before melt processing for condensation polymers. Another major downstream process for medical products is the sterilization. For medical devices, ionizing radiation has become increasingly popular. Of course the ionizing radiation which disrupts bio-macromolecular structures in bio-burdens can and frequently does damage polymer chains. In this presentation, we will report on case histories of processing modality and severity and their influence on material degradation and subsequent failures. In addition, situations where control limits can be created on manufacturing procedures can be put in place to prevent (minimize) failures due to processing degradation.
John Viego, Richard P. Theriault, Tim A. Osswald, May 2000
Thick components or sections such as ribs and bosses require a 3-D simulation to fully determine final properties due to the curing reaction and vitrification effects. A finite element simulation has been developed to model curing of thermoset parts, including compensation for diffusion control effects and varying boundary conditions. For diffusion control, the glass transition temperature (Tg) was related to conversion by the DiBenedetto equation. The simulation considers parts molded under realistic industrial processing conditions and has shown that non-uniform curing and thermal gradients occur during processing. These gradients depend on part geometry, cure kinetics, and processing conditions. This paper presents the models used, along with the results of the simulation applied to a sample geometry molded under various conditions.
X. Wang, R.J. Crawford, A.M. Fatnes, E. Harkin-Jones, May 2000
Metallocene grades of polyethylene offer exciting opportunities for the rotational moulding industry. However, as they have only become commercially available in the last few years, their full potential has yet to be exploited. This paper reports on the results of an experimental investigation in which processing conditions are related to the microstructure and mechanical properties of three grades of metallocene polyethylene. The materials have been characterised by dynamic parallel plate rheological tests, NMR spectra and DMTA. The results obtained from equivalent standard grades of polyethylene are used as a basis for comparison. It is shown that the metallocene materials possess many rheological and physical properties that are desirable in rotational moulding. A detailed understanding of the unique nature of these materials is necessary in order to take full advantage of their properties in rotational moulding.
Olga I. Kuvshinnikova, Robert E. Lee, Nick A. Favstritsky, May 2000
The purpose of this paper is to present the data on UV stabilization of flame retarded polypropylene fiber. The evaluation was conducted by exposure in the xenon arc weatherometer @ 63°C under dry conditions. Proprietary additives provided unique physical property retention for flame retarded polypropylene fiber.
Thomas M. Ellison, Stephen P. McCarthy, Arthur K. Delusky, May 2000
Thermoplastic film technology and a new plastic molding process, under development in a joint effort by ValTek and U Mass Lowell, combine to offer reductions in system cost, total emissions and weight for automotive Class A" exterior panels in the new millennium. The recyclable structural panels are fabricated using Class "A" film finishes in one step and targeted for vertical and horizontal automotive panels."
The idea of using an impact tower for 3-point bending for polymer testing has been developed before [1]. In this work the experimental method is refined. The vibrations are reduced by removing the ends of the specimen and by using a smaller span. Results are presented for a polypropylene. The modulus and the yield stress increase with strain rate, as predicted by viscoelastic consideration and by the Eyring theory for the yielding of polymers.
Space Structures that require light-weight materials with sufficiently high strength and environmental endurance have been in increasing demand since the early 1980's. However, the biaxial behavior of these structural materials under pressurized loading, is rarely found in the literature. An experimental investigation was conducted to develop a test method and hardware to characterize the biaxial behavior of a fabric-film laminate intended for use as a structural envelope for large balloons. The material tested is a composite laminate of three layers. The three layers are: polyester-based woven fabric, 6 microns film of polyester (Mylar type A) and 6 microns film of linear low density polyethylene (LLDPE). The laminate structure provides high strength to weight ratio. In this study, a test technique has been developed to measure the biaxial response of the material to known stress ratios. The information gained from the test can be manipulated to estimate Poisson's ratio and the development of a material structural model.
A geometry-based model is developed for determining the fill time in resin transfer molding process. In this model, the preforms are assumed to be thin flat with isotropic and orthotropic permeabilities. The in-plane shape of the preform is arbitrary. The location of the vents, the maximum flow length, and the time required to fill the mold are calculated applying analytical solutions. The variety of preforms and processing conditions are used to verify the model. The mold filling time calculated by the model was in good agreement with those obtained using the C-MOLD filling simulation. Saving in the computational time was the key advantage of this model.
A model is developed for predicting the location of the vents in isotropic RTM molds of various geometries. The preforms may contain holes and/or impermeable inserts. The location of the vents required to avoid trapping air bubbles are determined using neural network and geometric-based solutions. The neural network was trained with data obtained from simulation and actual molding experimentation. For a number of test cases, the performance of the method is compared to the prediction of vent locations obtained using a commercial mold filling simulation. It was found that the proposed method can predict vent locations with a good accuracy as compared to the filling simulation results. Applying the neural networks reduced the amount of computational time in comparison to the simulation methods.
Catherine Jung Hyun Cho, João B.P. Soares, Costas Tzoganakis, May 2000
A single active-site-type catalyst was supported onto silica and used to produce propylene/ a-olefin copolymers with high isotacticity and high molecular weight. The effects of different reaction conditions such as temperature, pressure and hydrogen content on structural properties were investigated. Several comonomers with varying length and bulkiness such as hexene, decene, octene, dodecene, hexadecene, eicosene, and styrene were copolymerized with propylene. With the knowledge of the reactivity ratios and the effect of different reaction parameters on polymer microstructure, copolymers with the same level of comonomer content and similar molecular weight were made with different comonomer types. The produced copolymers were analyzed for their structural and rheological properties using GPC, DSC, CRYSTAF, NMR and RMS. Thus, the isolated effects of comonomer type (length and bulkiness) on structural and rheological properties were studied and correlated.
Minhee Lee, Costas Tzoganakis, Jeong-Min Kim, May 2000
Morphological studies for various ternary polymer blends were performed. The blends were prepared using a Haake batch mixer and analyzed using SEM and TEM. Interfacial tensions and spreading coefficients were used for predicting the blending morphology, and the predicted morphology was compared to the experimental results. The interfacial tensions were calculated from surface tensions at 20°C, and the temperature dependence of the surface tension and a harmonic mean equation were also used. All blending systems chosen in this experimental work were expected to have a minor component (B or C) encapsulated by the second component (C or B) in the matrix (A). It was found that many ternary blends (PC/PMMA/PE, PMMA/SAN/PBT, PBT/SAN/PC, etc) agree with the predicted morphology. However, some blending systems show an opposite encapsulation behavior (SAN/PC/PMMA) or a complex blending behavior (PP/PC/SAN).
Roger Reinicker, Adriano Pangelinan, Imrich Greschler, May 2000
Polytrimethylene terephthalate (PTT) is a recently commercialized polymer with both demonstrated and potential for increasing use in fibers for carpets and textiles. It is both dyeable in the conventional sense but also readily colored in the melt phase with pigments and polymer soluble dyes. This paper explores the methods used to mass color (solution dye) PTT, the pigments and dyes that can be employed, and the color and fastness results obtained with eleven selected colorants.
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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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