SPE Library

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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Conference Proceedings

Effect of Different Nucleating Agents on the Degassing Conditions as Measured by Ultrasonic Sensors

Jacques Tatibouët, Abdelhadi Sahnoune, André Hamel, Richard Gendron, May 2001

Ultra sonic sensors have proven to provide valuable information on the thermoplastic foaming process in polymers. Measurement of the attenuation of the ultrasonic signal can be easily related to the nucleation process, i.e. the onset of bubble formation in the foam matrix. The ultrasonic sensors can be installed in-line, on the extrusion line, and thus allow direct access to the prevailing processing conditions. In this work, the degassing conditions (pressure and temperature) of a mixture of polystyrene and a physical blowing agent, HCFC 142b, are determined for two different nucleating agents. The resulting cellular structure of the extruded foams is correlated to the degassing conditions determined by the ultrasounds. The results are discussed in light of other observations on the nucleation process.

Falling Weight Impact Testing Analysis of Rotationally Moulded Polyethylene

J. Kissick, X. Wang, E. Harkin-Jones, R.J. Crawford, May 2001

The falling weight impact test is a common method to evaluate mechanical properties of rotomoulded parts. This is because the resistance to impact of rotationally moulded articles is very sensitive to variations in resin, processing conditions, etc. More information could be obtained from an instrumented falling weight impact test, such as impact force/time and failure mode variation. In this work, these relationships are studied. Also, the effects of material properties, processing parameters, such as temperature and introducing pressure, are discussed.

Investigations for the Numerical Determination of the TTT-Diagram for Unsaturated Polyester Resin Systems

Marco Wacker, Gottfried W. Ehrenstein, May 2001

During cure of a thermoset resin, the material exhibits three distinct phases: liquid, gel, and solid. Each of these material states is marked by dramatic changes in the thermomechanical properties of the resin. The glass transition temperature and the elastic modulus of the thermoset materials are two examples of the material properties that are of great interest to processors in the thermoset resin industry. The ability to predict the progression can give insight into the performance and optimisation of processing methods for thermoset resins.

Prediction of the Impact Behavior of Injection Molded Plates

J.C. Viana, A.M. Cunha, N. Billon, May 2001

The falling-weight impact test in injection-molded plates is simulated in a finite element based computer code (FORGE2®). The effect of processing is introduced on the material constitutive model through the dependence of its coefficients upon the thermomechanical indices computed from mold filling simulations. Two plate-like moldings (a box and lateral gated disk) were injected with arbitrary sets of processing conditions. In the impact simulations, two extreme conditions of contact between the impactor and the plates are considered: frictionless and adhesive contacts. The simulated force-deflection curves are compared with the experimental ones. Good agreements are obtained providing the different strain-rate sensitivities of the microstructural parameters are taken into account The results also evidence the role of the viscoelastic coefficient on the initial deformation stages. Moreover, the contact conditions have a strong effect on the mode of rupture of the plates and consequently on the maximum sustained strength levels.

Effect of Compounding Conditions on the Wood Flour/Polyethylene Composites in Twin-Screw Extruders

Yeh Wang, Hsun-C. Chan, Sun-M. Lai, Hsiao-F. Shen, Yao-K. Hsiao, May 2001

The compounding of wood flour filled polyethylene is discussed with reference to co-rotating twin-screw extruders from two manufacturers. An acrylic acid-grafted polyethylene copolymer was used as the compatibilizer in high-density polyethylene-wood flour composite system. Special consideration was given to the compounding of the heat- and shear-sensitive wood flour. The relevant screw configuration was found to consist of short mixing elements with low intensity of shearing. A suitable combination of processing variables, including screw rotation speed, throughput rate, and barrel temperatures, was necessary for limiting the thermal degradation and the darkening of the wood filler. However, tensile properties of the composites were not affected much.

Effectiveness of Functionalized Polyolefins as Compatibilizers for Polyethylene/Wood Flour Composites

Sun-M. Lai, Feng-C. Yeh, Yeh Wang, Hsun-C. Chan, Hsiao-F. Shen, Yao-K. Hsiao, May 2001

The effects of various types of compatibilizers on the mechanical properties of high-density polyethylene/wood flour (HDPE/WF) composite were investigated. Functionalized polyolefins such as maleated linear low-density polyethylene, polypropylene, and styrene-ethylene/butylene-styrene copolymer were incorporated to reduce the interfacial tension between polyethylene matrix and wood filler. It was found that LLDPE-g-MA gave maximum tensile and impact strength of the composite presumably due to better compatibility. Similar but less enhanced improvements in the mechanical properties, depending on the compatibilizer loading, were seen for SEBS-g-MA system. Whereas, notched impact strength decreased with increasing loadings of PP-g-MA. A scanning electron microscopy study was employed to reveal the interfacial region and confirm these findings.

Separability Criteria for Entangled Polystyrene Solutions Using Flow Birefringence

M.T. Islam, L.A. Archer, May 2001

Step shear strain experiments were performed using several entangled polystyrene (PS) solutions to investigate factorability requirements of the non-linear relaxation modulus, G(t,?) [? ?12(t,?)/?]. A phase modulated flow birefringence apparatus was used to measure optical equivalents of shear stress (n12) and first normal stress difference (n11-n22) in a plane-Couette shear flow geometry. For all polymers studied, a separability time ?k was identified beyond which the optical equivalent of G(t,?) [B(t,?) ? n12/? ? G(t,?)×C] could be factorized into separate strain and time dependent functions. In every case, ?k exceeded longest Rouse relaxation time ?R and found to be of the order of terminal relaxation time ?d0. These findings could help explain previous experimental observations of delayed factorability and non-factorable relaxation moduli in well entangled polymer solutions and melts.

Simulating the Cohesive Properties of Ultem and Related Molecules

B.E. Eichinger, David Rigby, Judith Stein, May 2001

The cohesive properties of many engineering plastics are difficult to determine experimentally, as the polymers are frequently insoluble, have high Tg's, and are sometimes poorly characterized. Molecular modeling can provide useful information of higher quality than might be obtained by other methods for these difficult polymers. A series of simulations on Ultem® and related molecules have been performed to evaluate the cohesive energy density of the polymer and determine interfacial interactions with small molecules. These methods yield a value near 22.0(MPa)½ for the solubility parameter of the polymer, and it is shown that benzyl alcohol has the most favorable interactions.

Modeling the Melting Process of Polymer Pellets Caused by Friction

K.L. Yung, Yan Xu, Francis Lau, May 2001

The melting of polymer caused by friction before the solid plug is formed is an important phenomenon in the plastic injection process. To analyze the melting process caused by solid particles sliding against the bellow, an analytical method that can simulate behavior of each particle during the calculation should be used. Particle element numerical method is hence adopted in the analysis for this research to take into consideration the behavior of each particle. In the review of literatures in this area, no publication has reported success in the analysis of the transient close-contact melting process caused by friction. In this paper an analytical expression for the transient melting process is derived by assuming friction against flight and screw as friction against adiabatic walls.

Modelling of the Effect of Slip in Plug-Assisted Thermoforming

D. Laroche, P. Collins, P. Martin, May 2001

In plug-assisted thermoforming, the interaction between the sheet and the plug strongly affects the final part thickness distribution due to sheet cooling and slippage on the plug surface. The type of plug material and surface finish has to be carefully selected. The amount of slip on the plug surface depends on the rheology of the polymer sheet and on the friction coefficient. Both properties are temperature dependent. In this work a non-isothermal friction coefficient model is evaluated for its potential in predicting the amount of slip in plug-assisted thermoforming. The model has been implemented in a finite element analysis software for predicting the consecutive steps of the thermoforming process. The model has been applied to simulate industrial scale plug-assisted thermoforming and the predictions are compared to experimental measurements.

Polyurethane Coatings Based on Soybean Oil Prepolymers and Crosslinkers

I. Javni, V. Karajkov, Z. Petrovic, May 2001

Four series of coatings were prepared by using a soybean oil based isocyanate prepolymer and two types of the soybean oil based polyols as the crosslinkers. Water (humidity from the air ) was also used as a co-crosslinker. The isocyanate prepolymer and the polyols were prepared according to the original, proprietary methods. Varying the hydroxyl number of the polyol and polyol/ water ratio in the crosslinker varied the structure and properties of the coatings. The coatings were tested for hardness, elasticity (bending test), scratch resistance and adhesion. DSC, TGA, TMA, tensile strength and swelling were used to assess the glass transition and crosslinking density of the films.

Generation of Thermotropic Liquid Crystalline Polymer/Thermoplastic Polymer Strands for Producing Wholly Thermoplastic Composite Materials

Jianhua Huang, Donald G. Baird, Wei Huang, May 2001

Thermotropic liquid crystalline polymer (TLCP) reinforced thermoplastic polymer (TP) strands were spun and used in injection molding to form wholly thermoplastic composite materials. While keeping the strand size suitable for injection molding, effort was made to increase the orientation and aspect ratio of the TLCP fibril that would remain in the final product as reinforcement. The pelletized strand can be injection molded without disturbing the TLCP reinforcing fibrils. The samples have similar mechanical properties, lower density and smoother surfaces compared with glass fiber reinforced samples.

Rheology beyond One Million Reciprocal Seconds

David W. Riley, May 2001

In the wire and cable industry the speed of the insulated copper wire through the die is very fast. In 1963 a 24 gage wire was coated with plastic with a clearance in the die of only 5 mils (1 mm = 40 mils, i.e., 5 mils = 0.125 mm) at a speed that exceeded 2500 feet/min (almost 1 kilometer/minute). The shear rate calculates to be in excess of one million reciprocal seconds (actually this is 4 x 106 sec-1). Drastic changes were discovered in the molecular structure of the plastic. Shearing the polymer chain causes changes in the molecular structure that can be advantageous or severely detrimental. These running conditions and the effect on the PVC is the concern of this paper.

Re-Inventing the Wheel: Breaking New Ground with Rotary Shuttle Technology

Brian L. Dowler, Rolf Weingardt, May 2001

Long-stroke shuttle machines have developed a well-defined role in the extrusion blow molding of calibrated neck bottles. However, these machines have limitations due to factors such as the long axial length of the stroke and the need for large multiples of tooling, knives, dies, punches and In-Mold Labeling (IML) tooling sets per the number of mold sets. Many of these limitations have been overcome through the incorporation of an indexing rotary motion. The end result is a technologically advanced, small footprint machine that can produce IML bottles with very little cycle time penalty. Further, the multi-layer containers are de-flashed before exiting the machine with positive bottle transfer between stations with a true single-point product discharge. All of this is accomplished using fewer die pins, bushing sets, cut-off knives, trim dies, punches, and IML deployment heads than typically required. This paper discusses the technical hurdles that were overcome to re-invent" the shuttle machine and open up new possibilities in extrusion blow molding."

Effects of Chain Extension/Branching on the Viscoelastic Behavior of Styrene-Maleic Anhydride/Polyol Blends

Goknur Bayram, Ulku Yilmazer, Marino Xanthos, May 2001

Styrene Maleic Anhydride (SMAH) / Polytetramethylene Ether Glycol (PTMEG) blends were produced in a batch mixer in the presence or absence of hydrated zinc acetate catalyst. The oscillatory shear properties in the melt state and the Fourier Transform Infrared Spectra (FTIR) of the blends were studied. The SMAH/PTMEG/zinc acetate blend had higher storage modulus, G', loss modulus, G and complex viscosity ?* than the blend without the catalyst. The distribution of relaxation times was calculated by using the oscillatory shear data and a generalized Maxwell Model. In comparison to pure SMAH for all the blends higher relaxation strengths at longer relaxation times were obtained due to chain extension and branching. The FTIR spectra of the SMAH/PTMEG blend indicated ester formation confirming the existence of chain extension / branching reactions in batch mixing."

The Selection of Mould Design Variables in Direct Stereolithography Injection Mould Tooling

R.A. Harris, P.M. Dickens, May 2001

Models produced by rapid prototyping (RP) allow the validation of a parts design with respect to its geometry. Beyond this, the rapid prototyping technique Stereolithography (SL); when used to manufacture moulding cavities, has shown itself to be capable of rapidly and economically producing low volumes of plastic injection moulded parts prior to commitment to hard tooling. These parts are more complete prototypes, they imitate parts that would be produced by a hard tooling manner with respect to their material, geometry and production process. A major drawback of the SL injection moulding process is that the tools are susceptible to producing only a small number of parts before failure. SL tools may break under the force exerted by part ejection when the friction between a moulding and a core is greater than the tensile strength of the core resulting in tensile failure. Very few justified recommendations exist concerning the choice of mould design variables that can lower the part ejection force experienced and reduce the risk of SL tool failure. This research investigates the ejection forces resulting from injection moulding polypropylene (PP), acrylonitrile-butadiene-styrene (ABS) and polyamide 66 (PA66) parts from SL tools which are identical in all respects except for their build layer thickness (a process variable when generating the SL tooling cavities) and incorporated draft angles (a tooling design variable). This work attempts to identify appropriate evidence for recommendations with respect to these variables and SL injection moulding. The results show that linear adjustment of draft angle results in a fairly minor linear change of part ejection force according to the moulding material. A linear adjustment of the build layer thickness results in a greater change in part ejection force as a more non-linear relationship. In both cases greater ejection forces were experienced by PA66, then ABS and then PP parts, respectively. The results also show that the s

Modeling of Fluted Mixing Elements

Petra Samsonkova, Jiri Vlcek, May 2001

3D simulation helps to have a better understanding of material behavior in complicated flow geometries such as extrusion dies or mixing elements where a 2D simplification fails. In our study, we will simulate the material behavior in a fluted mixing element. The fluted mixing element is one of many used mixing elements. Its specific geometry influences a good or bad mixing performance as well as local heat generation because of the shear dissipation. The study is focused on parametrical study of the influence of mixing element dimensions on the material behavior (generated pressure drop, mixing quality etc.). It is also focused on the determination where and under which conditions the heat generation is occurring, what is the related temperature rise and how this high heating can be prevented.

Blends of Various Proteins with Poly(Hydroxy Ester Ether)

C. Wang, C.J. Carriere, J.L. Willett, May 2001

Blends of poly (hydroxy ester ether) (PHEE), a recently developed bisphenol A ether-based synthetic biodegradable thermoplastic polymer, with a soybean protein isolate and two hydrolyzed wheat glutens were studied. Blends of the proteins with PHEE were produced from 20-70% by weight of protein content. The Young's moduli of the protein/PHEE blends falls in the range of 0.8 - 1.5 GPa with the tensile strengths ranging from 10-30 MPa. Fracture strengths of the blends ranged from 9-2 MPa-m1/2 depending on the amount of protein added. Morphological analysis indicated acceptable adhesion between the protein and PHEE phases in the blends. In general, as the protein content was increased the materials lost ductility and failed in a brittle manner; however, the mechanical properties of several compositions were comparable to current commercial thermoplastics such as polystyrene.

The Shelf Life of Filled Polymeric Material for Medical Device: Accelerated Thermal Aging Experiment and Kinetic Prediction

Xiaoping Guo, Richard E. Stehr, May 2001

In the present study, a kinetic method is suggested to determine the shelf life of a filled polymer material prepared for making medical device, including barium sulfate-filled polyethylene and poly(ether block amide), by using an well-designed accelerated thermal aging experiment. Accordingly, the effects of aging time and elevated temperature on mechanical performance of the material are mathematically defined by thermal aging index, namely the ratio of the elongation-at-break after to that before a period of thermal aging. A general m-order rate kinetics with Arrhenius-type temperature dependence is utilized to describe the deterioration of the mechanical properties during aging. An accelerated thermal aging experiment is performed to statistically measure various aging indices for the samples aged at various elevated temperatures within different short-term aging times. Kinetic parameters are acquired using nonlinear regression to the experiment. By assigning a permissible aging index, the shelf life of the material (or medical device) is kinetically predicted at storage temperature.

Robust Simulation for the Heating Stage in Thermoforming

A. Yousefi, A. Bendada, R. DiRaddo, May 2001

Process simulation traditionally relies on the exact knowledge of parameter inputs, such as material properties, process conditions and heat transfer properties. However, these parameters are never known exactly and a degree of uncertainty exists. This level of uncertainty affects the confidence in the results obtained. One therefore has two options, reduce the level of uncertainty or account for it in the simulation through appropriate sensitivity trials. This work reduces the level of uncertainty through accurate evaluation of the input parameters. Accordingly, the accuracy of the predictions is significantly improved.