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

Prediction of Degradation of Polyethylene during Rotational Molding
M.C. Cramez, M.J. Oliveira, R.J. Crawford, May 2000

During rotational molding the plastic is subjected to relatively high temperatures for long periods of time. This often causes degradation of the polymer at the inner surface of the molded article. The resulting degraded layer is responsible for the deterioration of the mechanical properties of the part. In practice, the optimum processing temperature and/or heating time must be obtained by means of an extensive molding and testing program. Moreover, as the degradability of polyethylene depends on many factors, such as the molecular structure of the material, the type and concentration of stabilizers and the thermal history experienced during processing, an optimization program that takes into account all these variables is very expensive and time consuming. In this work the degradation of polyethylene is studied using a technique widely used in the assessment of degradation resistance in the pipe industry - Oxygen Induction Time (OIT). The method enables the onset temperature of degradation to be identified using only a few milligrams of material. The data obtained from simple and quick experiments was used to produce an empirical model to predict the optimum inner air temperature for rotational molding of the materials. It is shown that whilst the maximum internal air temperature experienced during rotational molding is a good quality control parameter, there are many other important factors, such as the heating rate of the mold, the thickness of the mold material, etc.

Mixing Characteristics and Mechanical Properties of Polypropylene-Clay Composites
Kyu-Nam Kim, Hyung-Su Kim, Jae-Wook Lee, May 2000

Polypropylene(PP)-clay composites were prepared by melt mixing in an intensive mixer. Three grades of PP's having different melt viscosities were employed to investigate the mixing characteristics of the composites with various clays which belong to organically modified montmorillonite(org-MMT). Depending on the matrix viscosity and nature of the organic layer in MMT, significant variations in the phase structure of the composites were found. In addition to the simple combination of PP and clay, modified PP's having various content of maleic anhydride were also incorporated. Major interest was focused on the effect of varying thermodynamic affinity between the components on the phase evolution and mechanical properties of the composites. Requirements for the effective dispersion of clay in the PP matrix are discussed in terms of both rheological effect and thermodynamic interaction.

Virtual Instruments for Polymer Characterization and Processing
Ian R. Harrison, May 2000

It's expensive in terms of time and equipment to give students the necessary exposure to a wide variety of polymer behavior in different areas of characterization and processing. 'Virtual instruments' (VIs) consist of interactive software that simulates the response of a particular characterization instrument or a process. A characterization 'suite' contains many thermal instruments; other instruments are under development. A blown film process line has also been assembled relating film properties to operational parameters.

Predicting How the Cooling and Resulting Shrinkage of Plastics Affect the Shape and Straightness of Extruded Profiles
Randy J. Brown, May 2000

During the extrusion of complex plastic profiles, the parts often distort and bow during the cooling phase of the process. The traditional methods of dealing with this are to use heat lamps to re-warm certain sections to remove the bow or to apply jigs to distort the part in the opposite direction so that when it cools, it comes back into the proper shape. A method to look at the cooling requirements of a particular profile is proposed along with a method to calculate how the part should be cooled in order to avoid distortion and bow.

Clear and High Heat Resistant TPEs
Y. Martin Lu, Joe Kutka, May 2000

There is a market need for soft (35 - 70 Shore A) clear TPEs with heat resistance high enough for repeated boilable applications. Flexible PVC meets most of the requirements, but it is out of the scope of this work. Styrenic Block Copolymer based compounds have been developed to fill this need. Important parameters, such as molecular weight of the base polymer, surface quality of the molded part and rheology of the material, have been correlated with clarity and heat resistance. Some of the myths about the clarity of SBC compounds will also be discussed.

Orientation Measurements Online
Abdellah Ajj, May 2000

Orientation of polymers enhances many of their properties, particularly mechanical, impact, barrier and optical etc.. Orientation processes all involve extrusion prior to deformation and can generally be classified into three categories: fibers, films, and parts (sheets, bottles, rods, ...). The knowledge of the polymer orientation produced by the different processes is critical for establishing the process conditions and the final properties of the oriented polymer. There is a long history of investigations of orientation in polymers, mainly from off-line measurements, involving techniques such as birefringence, infrared spectroscopy, X-ray scattering, Raman, NMR, fluorescence, ultrasonic etc. In this presentation, we will focus on techniques which are or could be used for on-line monitoring of orientation processes. These include birefringence, spectroscopy, fluorescence and ultrasonic.

Dynamic Vulcanization of Elastomers in Polypropylene Blends
Miguel A. López, José M. Kenny, May 2000

The use of innovative crosslinking agents for the preparation of thermoplastic vulcanizates (TPVs) is investigated. In this preliminary study, the most common TPVs systems, based on polypropylene (iPP) and rubber ethylene-propylene-diene terpolymer (EPDM) blends, are studied. Typical vulcanization agents, such as sulfur, phenolic resins and peroxides do not permit to crosslink saturated elastomers and, furthermore, give rise to dynamic vulcanization of the polyolefins. For this reason, the main goal of the present study is to investigate a new vulcanization agent for elastomeric matrices. This agent is based on azide derivative, 1,3-bis sulphonyl azide benzene that, for the specific behavior of the sulphonyl azide group, allows its interaction with the C-H bonds of the elastomeric phase and of the polyolefin. The study includes the dynamic vulcanization of PP-EPDM blends and their rheological, mechanical and thermal characterization. A comparison with traditional blends prepared with sulfur as vulcanization agent is also presented.

Effects of Fibers on the Crystallization of Polypropylene in Binary and Ternary Composites
Miguel A. López, Jerico Biagiotti, Luigi Torre, José M. Kenny, May 2000

The simultaneous effects of the incorporation of different types of fibers and of the presence of EPDM on the crystallization kinetics and thermodynamics of isotactic polypropylene are presented. The study is applied to the behavior of polypropylene matrix composites reinforced with glass, PET, aramidic and sisal fibers. The results obtained show that in all cases, either the fibers and the EPDM rubber behave as effective nucleant agents for the crystallization of polypropylene. A dramatic decrease of the half time of crystallization, t1/2, and an increase of the overall crystallization rate, Kn, are observed being the aramidic fibers the most effective. It is also reported that transcrystallinity takes places in all fibers being more evident with aramidic fibers in the neat PP matrix. Only a slight transcristallinity effect is detected when fibers were incorporated in the PP-EPDM matrix.

Solid State Shear Orientation of Polymers via Equal Channel Angular Extrusion
Zhiyong Xia, Chris K.-Y. Li, Hung-Jue Sue, Alex J. Hsieh, Jack Chu, May 2000

The effect of large strain, simple shear deformation induced by the Equal Channel Angular Extrusion (ECAE) process on semi-crystalline poly(ethylene terephthalate) (PET) and amorphous polycarbonate (PC) has been investigated. A through-thickness shear strain of approximately 190% after one ECAE pass is induced in the extrudates. Mechanical tests revealed that the extrudates are anisotropic, indicating that the process is capable of generating highly oriented microstructures. Improved fracture toughness can also be achieved via the ECAE process.

Best Practices: Looking beyond Benchmarking to Develop Your Business Strategy
Margaret Baumann, May 2000

Real breakthroughs in strategy and business development come from looking beyond your in-kind competitors for a process view of customer-focused solutions. A company's basic operations are first level processes and cross over industry type. Best practices is the study of identifying the companies which have developed superior processes in product development, manufacturing, customer service and market segmentation regardless of the industry they are in. This paper discusses the benefits of the study of Best Practices in addition to competitive intelligence and benchmarking in business planning. Examples of companies in the plastic industry who have distinguished themselves by their best practices will be presented.

The Impossible Part-On the Verge of Failure?
Jerry Golmanavich, Barry Hofmaster, May 2000

There have been several occasions in the past where part designs have been proposed which require non-traditional approaches to manufacturing. Even with run-of-the-mill designs it seems prudent to do computer flow simulations to verify that a part is manufacturable. The case history described below details how a product was deemed impossible"; the flow simulation verified that it was "impossible" and yet the project was pursued and has now passed the prototyping stage. This paper describes a project where some risk was taken and may provide the drive to explore new limits."

Studies on the Rotomolding of Liquid Crystalline Polymers
P. Rangarajan, J. Huang, D. Baird, May 2000

This paper is concerned with the rotomolding of thermotropic liquid crystalline polymers (TLCPs) for the purpose of generating tank liners with excellent barrier to oxygen. The major issues involved include whether the TLCPs can be ground to provide resins suitable for rotomolding (~40 mesh size powder) and their ability to fuse together to provide adequate strength and barrier properties. With the use of appropriate grinding techniques, the TLCPs were found to fuse well to provide strength and stiffness significantly greater than that of HDPE.

Critical Conditions for the Onset of Unstable Flows of Molten Polymers
Kolapo P. Adewale, Arkadii I. Leonov, May 2000

A simple method to predict the critical shear stress and the critical shear rate for the onset of melt flow instabilities in capillary flow is presented. The method, earlier reported for polyisoprene, employed a bulk stable viscoelastic constitutive equation that contains a hardening parameter ?. The parameter ? is solely determined by the molecular characteristics of the polymer. Below we compare predictions of the critical shear stress with experimental data for some common polymers.

Effects of Twin Screw Compounding Conditions on the Mechanical Properties of Nylon-6/Glass Fiber Composites
Murat Cansever, Ulku Yilmazer, May 2000

The effect of processing conditions on fiber length degradation was investigated in order to produce higher performance composites. For this aim, Nylon-6 was compounded with glass fibers in a twin screw extruder for various combinations of screw speed and feed rate. Collected samples were injection molded and izod impact and tensile strength tests were performed in order to observe the effects of fiber length on mechanical properties. Also, by using the extruded and injection molded samples, fiber length distribution curves for all experimental runs were obtained. Results show that when the shear rate is increased through the alteration of screw speed and feed rate the average fiber length decreases.

Polymer Raw Material, Process and Production Fingerprints in Injection Moulding
A.J. Dawson, A. Key, P.D. Coates, May 2000

In-process monitoring of polymer melts is found to provide a fingerprint of the: • polymer (process-relevant polymer rheometry); • the process (injection pressure-time curves which reflect the material-machine-mould combination, including polymer batch to batch variation and machine dynamic repeatability); and • production trends, with 'process indices' offering an efficient basis for 100% automatic inspection, Statistical Process Control, and even insight into factory housekeeping. Specific pressure indices in an indentified low noise region of the primary injection stage of injection moulding have been found to provide a sensitive indicator of changes in a polymer, including batch to batch changes and process-induced changes, as such measurements are closely related to the rheology of the polymer melt. The same information has also been found to provide sensitive indications of variation in the processing operation for a given polymer-mould combination, and also consequently to allow meaningful statistical analysis of trends in the injection moulding process. Laboratory and factory data for raw material, process and production trend analysis (the latter involving data from substantial production runs) are presented.

Novel Small and Large Scale Flow Visualisation of Polymer Melts
P.D. Coates, M.T. Martyn, M. Kamala, C. Parminter, May 2000

A novel small scale (<30g of polymer) recirculating flow visualisation cell has been designed and built. The unit comprises a single screw extruder, gear pump and variable geometry inserts making a flow recirculation loop. The recirculation flow cell is capable of being used with a range of entry geometries, including abrupt entry and hyperbolic, with a polariscope for stress birefringence, and a CCD camera and image processing system for particle streak velocimetry. This new facility complements existing larger scale flow visualisation cells in our laboratory, fitted to a single screw extruder. Information from flows in both scales of flow cell are presented for an LDPE melt.

Viscoleastic Properties of Reactive and Non-Reactive Styrene-Maleic Anhydride / Olefinic Blends
G. Bayram, U. Yilmazer, M. Xanthos, May 2000

Reactive blends of styrene-maleic anhydride (SMAH) with polyethylene/methyl acrylate/glycidyl methacrylate (PE-F) and non-reactive blends of SMAH with polyethylene/methyl acrylate (PE-NF) were produced and characterized in terms of morphology and viscoelastic properties in order to understand the reaction characteristics between anhydride/epoxy functional groups. Storage modulus, G', loss modulus, G and complex viscosity ?* of reactive blends at 25 % and 50 % PE-F were higher than those of non-reactive ones. At 25 % PE-F a maximum in complex viscosity was obtained for the reactive blends. In morphological analysis the reactive blends showed finer morphology than the non-reactive ones."

Simultaneous Measurement of Torque, Axial Normal Force and Volume Change in the NIST Torsional Dilatometer-Experiments and Analysis
Carl R. Schultheisz, Gregory B. McKenna, May 2000

The NIST Torsional Dilatometer measures simultaneously the torque, axial normal force and volume change in response to a torsional deformation. While the torque is a linear function of the angle of twist per unit of length, the normal force and volume change are effects of geometrical nonlinearities. In stress-relaxation experiments with an epoxy cylinder near its glass transition temperature, the torque and normal force decay monotonically, but the volume change associated with the torsion shows a significant non-monotonic decay at lower temperatures. The measurements are investigated with a series solution for torsion of an elastic, compressible material [Murnaghan, F.D. (1951) Finite Deformation of an Elastic Solid. Wiley, New York.].

A Unique Benzoate Plasticizer for Reducing Viscosity and Fusion Temperature
T. Bohnert, B. Stanhope, K. Gruszecki, S. Pitman, V. Elsworth, May 2000

Plastisol viscosity reduction and control is an important property specification in many vinyl plastisol formulations. A unique benzoate plasticizer is under development that functions as a viscosity reducer. It also is a high solvating plasticizer in standard plastisol systems. Data will be presented on the effect of the new benzoate plasticizer on phthalate and benzoate containing plastisols and vinyl sheet properties.

Using Branched Polypropylene as a Melt Strength Modifier-Improvement in Sheet Sag Resistance
V.V. DeMaio, D. Dong, A. Gupta, May 2000

Blends of conventional polypropylene (PP) and branched PP (bPP) enable PP to perform well in applications where extensional flow dominates, such as blow molding, thermoforming and foaming. Sag resistance tests shows a significant improvement in sag time of extruded sheet as the content of bPP increases, up to 30-wt.%. These blends (PP/bPP) show synergistic increases in melt tension while providing excellent processability by maintaining low viscosity.

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