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 this study, the effects of polyethylene (PE) and polypropylene (PP) colorant carriers for various levels of loading on the short-term strength of weld lines in homopolymer polypropylene are quantified. Tensile bars (“dog bones”) were molded with an intentional weld line in the gauge length of the bars for a variety of material mixes. When tested at room temperature, the colorants with the polyethylene carrier drastically reduced the tensile elongation of the bars when compared with an unpigmented sample. The reduction was so severe that the PE-carrier specimens broke before yielding, thus exhibiting significant loss of strength. Samples of PP having the colorant with the PP carrier, while breaking at significantly lower elongation than their unpigmented counterparts, showed no reduction in weld-line strength because they yielded. Elevated temperature results are less dramatic, the unpigmented and PP-colorant samples yielded and stretched beyond 450%, while three-fifths of the PE-colorant specimens exhibited a yield. A PP co-polymer with PP-based colorant was also studied. In addition, slow strain-rate data is presented for a few compounds, and the rate / temperature dependence is discussed. Finally, several samples were aged at elevated temperature and subsequently tensile tested at room temperature. The results showed reductions in elongation but not weld-line strength.
A number of metallocene and conventional LLDPEs, with different material properties, were injection moulded over four different mould temperatures. An assessment of the effect of cooling rate and polymer properties on the mechanical performance of the specimens was conducted to establish any significant correlations. Rheological studies of the materials under high shear rates experienced in injection moulding, was performed to determine flow characteristics of the materials. Differential scanning calorimetry (DSC) and dynamic mechanical thermal Analysis (DMTA) were used to study the influence of the comonomer type and degree of branching on the properties of the materials.
This study investigated the effect of nitrogen purging in the material hopper on the melt flow index (MFI), residual oxidative induction time (OIT), color and impact strength of impact modified polypropylene copolymer and polycarbonate during repeated reprocessing through an injection molder. Heat history had the expected effect of increasing MFI, changing color and decreasing impact strength for both resins and decreasing OIT in polypropylene. In polypropylene nitrogen purging significantly reduced the changes in MFI and OIT resulting from repeated reprocessing. However, nitrogen purging did not have a significant effect on the properties of polycarbonate, probably due to its inherent resistance to oxidative degradation.
Injection moulded samples of a commercial propylene-ethylene block copolymer containing 0% - 8% phthalocyanine blue pigment were prepared using a range of mould temperatures (40°C - 80°C). Mechanical and thermal analysis showed progressive increase in tensile modulus, storage modulus (E’) and glass transition temperature (Tg) with increase in pigment loading. However, impact strength of the pigmented copolymer decreased progressively with increase in pigment loading and mould temperature. Thermal analysis of the samples shows that changes in crystalline melting phase ?H, and activation energies Ea for phase relaxations (DMTA) may account for the overall decrease in impact performance of the pigmented copolymer.
Mingjun Yuan, Lih-Sheng Turng, Rick Spindler, Daniel Caulfield, Chris Hunt, May 2004
This study aims to explore the processing benefits and property improvements of combining nanocomposites with microcellular injection molding. The molded parts produced based on the Design of Experiments (DOE) matrices were subjected to tensile testing, impact testing, and Scanning Electron Microscope (SEM), Transmission Electron Microscope (TEM), Dynamic Mechanical Analysis (DMA), and X-ray Diffraction (XRD) analysis. Effects of processing conditions on the mechanical properties and microstructures have been studied. The results show that the supercritical fluid (N2) helps to further exfoliate and uniformly disperse the nano-clays in the matrix during the course of molding process. Compared to the corresponding base polyamide microcellular parts, the microcellular nanocomposites exhibit better cell structures and cell distributions as well as better mechanical properties.
Herman Winata, Lih-Sheng Turng, Daniel F. Caulfield, Tom Kuster, Rick Spindler, Rod Jacobson, May 2004
In this study, a cellulose-fiber-reinforced Polyamide-6 (PA-6) composite, a hybrid composite (PA- 6/cellulose/Wollastonite), and the neat PA-6 resin were injection molded into ASTM test–bar samples with conventional and microcellular injection molding. The impact and tensile strengths of molded samples were measured and the Scanning Electron Microscopy (SEM) images were taken at the fracture surfaces. The effects of filler systems and the introduction of microcellular structure on the impact and tensile strengths were studied. It was found that the cellulose fibers and the cellulose/Wollastonite fillers improve the tensile strength and tensile modulus. In addition, the microcellular injection molded neat resin exhibits a higher impact strength than that of the conventionally molded solid part. However, a reduction in tensile strength was observed with both of the filled composites when molded with microcellular injection molding. This could be attributed to microcells at the interface of cellulose fibers and the polymer matrix.
Kohji Yamada, Kiyotaka Tomari, Toshihiko Harada, Hiroyuki Hamada, May 2004
Fracture toughness of adjacent flow weldline occurring around an obstructive pin was evaluated by single edge notched bend (SENB) method. The fracture toughness near the pin was higher than any other part of the weldline. The fracture toughness decreased drastically along the weldline and then increased gradually toward the end of the specimen. These characteristic features could be explained by flow-induced molecular orientation at the weldline interface. The material flow beside the pin stopped in the middle of the filling process. Molecular orientation parallel to the weldline due to the fountain flow relaxed since no shear stress affected the area, resulting in high molecular entanglement across the weldline. On the contrary, at the downstream side the material kept on flowing during the filling process. This indicated that the molecular orientation could not relax due to flow-induced stress during the process. The magnitude of these two areas was dependent on the position of first collision point (FCP) at which two melt fronts collided first behind the pin. The V-notch depth on the surface of the specimens was also dependent on the distance from FCP.
A novel approach for the numerical simulation of frozen-in birefringence in moldings of semicrystalline polymers was proposed. The approach was based on the calculation of elastic recovery and crystalline orientation function frozen when the stress-induced crystallization occurred. The flow effect on the equilibrium melting temperature elevation due to the entropy reduction between the oriented and unoriented melts was incorporated to model crystallization. To find frozen-in elastic recovery and entropy change, a non-linear viscoelastic constitutive equation was used. The crystalline and amorphous contributions to the overall birefringence were obtained from the crystalline orientation function and the flow birefringence, respectively. The skin layer thickness and birefringence profiles were predicted and measured in moldings of polypropylenes of different molecular weights at various processing conditions.
Most molders are aware of the potential for creating burn marks where air gets trapped in molded parts. What no one seems to consider is blush or splay marks that manifest specifically along knit lines and would otherwise be assumed to be the effect of shear. The only problem is that the shear cannot be accounted for in the tool design. The cause can be traced back to trapped air, predicted with mold filling analysis software (as such), and verified with physical testing. The purpose of this paper is to give proper definition to this defect and distinguish it from burns and short-shots as caused by air entrapment, and thus can be more easily identified and remedied.
Stefan Roth, Ines Kuehnert, Guenter Mennig, May 2004
The focus of attention is kept on weldline behavior in parts of complex geometry, i.e. the upper part of an air intake manifold. By simulating the filling process using simulation software, the fiber orientation and the filling was calculated and compared to experimental studies. Thereby, a rather inhomogeneous filling behavior was found, caused by an unequally balanced runner system that leads to changes of the flow direction within the cavity during the injection process. These circumstances prevent the weldlines zones from spreading throughout the part. Hence, a distinct control of an uneven flow front pattern could help to reduce the weldline area and therefore minimize zones of optical and mechanical weak points in plastic parts.
Injection molded parts with plane surfaces and complex flow are subjected to distortion depending on the mould geometry and general processing conditions. In this study, the effects of several mould and part design solutions were evaluated as well as the operating conditions of the injection molding machine. To examine warpage, the geometry of the plastic parts was defined and a modular mould was designed integrating pressure and temperature sensors. Experimental results, namely pressure, temperature and warpage values, were compared with those obtained from C-MOLD simulations.
Because communication and Internet are so popular, light communication will become an efficient way to send message in the next generation. Optical fiber connector becomes an important component that connects, divorces or reunites the fiber, light source, light sensor and the other fiber ferrule connector. Because of the tiny size of products and the demand of precision, the decrease of manufacturing cost and the increase of demanded precision will be a huge obstacle that has to be overcome.This paper presents the study for the molding of ferrule in MT-RJ fiber connectors. The work includes the design of molding configuration with three different gating locations which are used to study the effects for the critical dimensions and precision of fiber holes. In addition, the 3D CAE software are used to simulate and verify the molding results. Moreover, the Taguchi method is used to find optimal processing conditions for resolving the void problems.
In thermoforming, it is found difficult to process Polypropylene if the heating control is based on measured sheet temperatures. It is shown that monitoring the melting of spherulites provides a better method. Testing is carried out using a novel device transmitting a laser beam through the PP-sheet. The scattering of the beam at spherulites within the sheet is indirectly measured via remaining beam intensity behind the sheet. With translucent Polypropylene, the melting of spherulites can be observed during heating.
C. deGrandpré, N. Nardini, P. Girard, L. Savoni, R. DiRaddo, May 2004
Twin sheet thermoforming has increased in usage over the last ten years, in particular due to its inherent ability to produce hollow parts and consequently challenge blow moulding. Blow moulded automotive fuel tanks are the parts that are the most challenged by twin sheet thermoforming.This work considers the conversion of a fuel tank blow mould for use in twin sheet thermoforming. The added challenge for the project is that the mould needs to maintain a flexibility to return to blow moulding, upon demand. Furthermore, the work includes the use of finite element simulation to reduce the sheet heating times.
P. Girard, V. Thomson, B. Hou, A. Yousefi, R. DiRaddo, May 2004
Some of the main problems to be solved when applying simulation to a process are the discrepancies between the predicted and measured parameters. This can be due to the fact that the actual operating conditions are different from the ones that were input into the simulation due to variations in material properties and errors in the assumptions for the simulation model. This work proposes a technique to tune the results of the simulation to the actual sensor outputs of the machine. The simulation can then be used as a generalized soft sensor for the process: Since the model of the simulation has been fitted to the actual process, the predictions of the simulation for non-readily accessible points will be that much closer to reality. A further advantage is that variations of the process are back-propagated to the input, so that faults that may appear in the system are presented as more easily interpretable variations of the input data.
Bunyong Rungroungdouyboon, John P. Coulter, May 2004
In this paper, the optimized radiative heating of opaque thermoplastic sheet during thermoforming processes has been studied by using a newly developed modeling and optimization approach. The net radiation method has been employed to develop a comprehensive numerical code that can compute the total radiative heat and associated temperature developments locally on the thermoplastic sheet. The resultant simulation model can accommodate full non-symmetric zone heating situations and multi-layered forming materials. A coupled optimization package was then developed to obtain optimized heater pattern solutions that will lead to desired material temperatures during thermoforming processes. This is done by specifying a desired thermoplastic sheet temperature distribution and iteratively solving for the heater setting needed to obtain the desired results
K.Y. Tshai, E.M.A. Harkin-Jones, P.J. Martin, G.H. Menary, May 2004
A non-linear viscoelastic model comprised of two components, a rubber-like hyperelastic component and a viscoelastic time-dependent relaxation spectrum was used to model the behavior of semi-crystalline PP at rates and temperatures close to that found in the thermoforming process. Temperature dependence was introduced through time-temperature-superposition (TTS) using WLF. The hyperelastic constants were identified from equibiaxial tensile experimental tests while the time-dependent relaxation spectrum was characterized through a temperature-frequency sweep analysis from a strain controlled DMTA test. Results show that the developed model is capable of simulating the behavior of semicrystalline PP fairly well.
Bernhard Hegemann, Peter Eyerer, Noel Tessier, Karel Kouba, Tom Bush, May 2004
Plug assist thermoforming is one of the most important process variants for the thermoforming industry. The purpose of the plug assist is to pre-stretch the heated polymer sheet prior to the application of pressure and/or vacuum during the final part formation. Parametric studies performed on simulation models of the thermoforming process have shown friction between the polymer and the plug assist to be critical in predicting material distribution in the thermoformed part.This report presents the results of investigating the friction behaviour of a polymer to plug assist material at thermoforming conditions. A new measurement technique to determine friction coefficients will be shown and explained in detail. This technique allows the characterization of the friction coefficient as a function of temperature and rate and shows the sensitivity respectively.
Sheet Molding Compound (SMC) is a widely utilized material to manufacture automotive exterior body panels. Cycle time, dimensional consistency, and surface finish are among the most important aspects to consider in the production of SMC due to their impact in profit and quality. These performance measures often exhibit conflicting behavior i.e. lowering the cycle time might imply decreasing the part surface quality and/or achieving a lower overall part dimensional consistency. One must exercise especial care in identifying the best compromises between these performance measures (PMs) along with the processing conditions that result in these best compromises. This paper describes an application in SMC processing where the multiple criteria optimization problem is addressed by means of a non-parametric approach known as Data Envelopment Analysis.
The most common commercial processes for manufacturing pre-pregs for electronic boards use solvent-based resin systems. Solvents are environmentally unfriendly and contribute to voids in the pre-preg and laminate. The resin impregnation process is done in an open resin bath. This low-pressure impregnation is conducent to voids in the prepregs. Voids cause product variability, which is a major source of scrap in board shops. To eliminate the above mentioned drawbacks, a solventless process, based on the concept of injection pultrusion, is developed. The impregnation is done in a die under pressure to minimize voids.In previous work, chemo-rheological and kinetic measurements were used to identify a potential epoxy-based resin system. In addition, flow visualization using model fluids was used to establish the basic flow mechanism. Here, we use the previous results to develop a mathematical model for the B-staging process. Based on the mathematical model, three potential alternatives to produce prepreg are developed and analyzed. A prototype B-staging die is built and used to verify the mathematical model. The result shows that the model agrees well with the experimental data for low pulling speed and slightly under predicts the high pulling speed runs.
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