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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

Real Time Temperature Measurement of Nylon 66 Butt-Joints during Vibration Welding
X.P. Zou, G. Park, V. Sidiropoulos, M. Kontopoulou, P.J. Bates, May 2004

Modeling the vibration welding process requires accurate knowledge of the melt temperature at the interface. Due to technical difficulties related to the very small molten film thickness, little work has been done to date on measuring the weld temperature under real time conditions. This paper presents a novel technique for measuring the weld temperature in real time. It involves inserting a 25 ?m thermocouple into one of the welding parts in close proximity to the weld zone. During vibration welding, the thermocouple works its way to the weld interface and records the melt temperature. The experimental data from vibration welding nylon 66 butt joints indicate that the melt temperature at the weld interface is within 15°C of the onset of polymer melting. The temperatures measured in the solid phase prior to entering the melt film are consistent with theoretical models for heat conduction into solid plates.

Heated Tool Welding of Thermoplastic Polyolefin (TPO)
Chung-Yuan Wu, Abbass Mokhtarzadeh, Moonyeong Rhew, Avraham Benatar, May 2004

This study focused on the weldability of two specific thermoplastic polyolefins (TPO-A and TPO-B) using heated tool welding. A three-factor (heating temperature, heating time, and welding pressure) and three-level design matrix was used to perform the welding. Two statistical methods, three-factor two-level design of experiments (DOE) and Box Behnken method, were used to analyze the weld results. In addition, vibration welding of these TPOs was also used to compare the weldability. For heated tool welding, the maximum joint strength was 88% of the bulk strength for TPO-A and 76% of the bulk strength for TPOB. For vibration welding, the maximum joint strength was 65% for TPO-A and 56% for TPO-B. While heated tool welding provided stronger joints compared to vibration welding, it had a longer cycle time. The two statistical methods provided similar results indicating that the simple three-factor two-level design of experiments was a valid screening method for heated tool welding of TPO.

The Effects of Weld Geometry and Glass-Fiber Orientation on the Mechanical Performance of Joints – Part II: Kinetics of Glass-Fiber Orientation and Mechanical Performance
Val A. Kagan, Christopher Roth, May 2004

The mechanical performance of injection molded short glass-fiber reinforced thermoplastic components is anisotropic and is highly dependent on the fiber orientation and distribution. Similarly, the bulk and short and long-term mechanical performance at the weld is influenced by these fibers and the specific welding technology used as related to melt-pool formation.The purpose of this analysis is to show:the short-fiber orientation (analytical and simulation data) and distribution at the pre-welded bead, ribs and wall areas;advantages of SigmaSoft injection molding simulation software, which utilizes full three dimensional fiber representation of any molded part;the mechanical performance of welds with optimized geometry (US Patent 6,447,866).Findings on the mechanical performance of butt-joints with different designs and localized geometry will help designers and technicians with plastic part design optimization. In a previous ANTEC paper (Part I), we related these findings to the kinetics of welds and part design issues for straight and T-type butt-joints.

Feasibility of Selected Methods for Embossing Micro-Features in Thermoplastics
David Grewell, Abbass Mokhtarzadeh, Avraham Benatar, Chunmeng Lu, L. James Lee, May 2004

During the last few decades the use of MEMS (Micro-Electro-Mechanical-Systems) has been steadily increasing in a number of industries, and especially in the medical industry. One application for MEMS is in micro-fluidic devices that rely on micro-channels (10 to 200 ?m wide and deep) to direct and analyze fluids for medical diagnostics. Current methods for producing these features, including hot embossing and micro-injection molding, can be slow (1 to 10 minutes cycle time), are only amendable to batch processing and expensive. Fast surface heating embossing methods have the potential of producing micro-channels rapidly and inexpensively. Three embossing methods were studied: ultrasonic, infrared radiation (IR) heating and hot gas heating. For IR and hot gas heating, a cold tool with the micro-features was pressed onto the surface immediately following heating. Similarly, for ultrasonic embossing the micro-features were machined on the surface of the horn. It was found that cycle times as short as a few seconds were achieved and the quality of the features was similar to those seen in injection molding. In addition FEA studies were conducted to simulate polymer flow during embossing.

3D-Laser Transmission Welding
E. Haberstroh, R. Luetzeler, May 2004

Contour welding is a variant of the laser transmission welding that offers the highest flexibility relative to the weld geometry. In this process the laser beam is translated along the weld line using a robot. This paper reviews the results of welding experiments using a proprietary box geometry with a three-dimensional weld line. It was found that low leakages and high burst pressures can be achieved with optimized process parameters for Polyamide or Polyacetale. In addition, short welding times (a few seconds) were demonstrated. Thus, this process is well suited for mass production of complex plastics parts. It was also seen that the process is relatively robust and weld quality is relatively independent of parameter settings (over the ranges evaluated).

Through Transmission Laser Welding of Polycarbonate and High-Density Polyethylene
Moonyeong Rhew, Abbass Mokhtarzadeh, Avraham Benatar, May 2004

Through Transmission Laser Welding (TTLW) of thermoplastics is a relatively new joining process with many advantages for design and manufacturing of various components in electronic, medical and automotive industries. The use of high power diode laser systems has made TTLW a cost effective process in welding of many amorphous and semicrystalline polymers. In this work, a laser welding system, comprised of a power supply and a diode laser with a Branson proprietary fiber bundle, was used to experimentally study TTLW of polycarbonate (PC) and high-density polyethylene (HDPE). The effects of welding power (measured laser power at the interface), heating time, and welding pressure on joint strength were studied. Maximum weld strength of about 95% the bulk strength of PC and HDPE were achieved.

Overlap Welding of Thermoplastic Parts without Causing Surface Thermal Damage by Using a CO2 Laser
Yasuo Kurosaki, Tomoya Matayoshi, Kimitoshi Sato, May 2004

This paper deals with the principle and applications of a novel infrared laser welding procedure for overlapped thermoplastic parts. Features of experiment, using a CO2 laser as a radiation heat source and numerical simulation of heat transfer phenomena combined with radiation and conduction in the welding process, are demonstrated. Not only high weld strength but also excellent surface quality of welded regions is essential for overlap welding of plastics in industrial applications.The current welding procedure was developed using a combination of penetration infrared radiation heating process and thermal diffusion cooling process by a solid material which is transparent to infrared radiation as a heatsink. The solid heatsink placed in contact with an irradiated surface of overlapped thermoplastic parts during radiation heating. This welding procedure is able to achieve both high weld strength and excellent surface appearance without causing surface thermal damage, as is often suffered in conventional direct infrared radiation welding process without a solid heatsink. In addition, the pigmentation of the welding material to increase absorption of radiation is unnecessary for this procedure.

Technical Review of the Four Major Thermal Press Applications: Staking/Swaging, Inserting, Degating, Part Marking
Thomas R. Kirkland, May 2004

Thermal presses are used primarily in four applications with regard to assembly (decorating) of thermoplastic parts: staking/swaging, inserting, degating and part marking. Thermal staking/swaging and inserting are generally thought of as competitor processes to ultrasonic, while degating operations with heated tooling are thought of as an augmentation to degating by force alone. Part marking such as date- or lot-coding and serializing is another area where these machines can be applied. This paper discusses these four applications areas and references competing processes to highlight the strengths and weaknesses of utilizing modern thermal presses for these applications.

Optical Correction for Heat Buildup in the Center of TTIr Plastics Welds
Scott Caldwell, David Grewell, May 2004

Through Transmission Infrared (TTIr) laser welding of plastics often results in voids forming in the center of the weld. These voids can lead to weak and unattractive welds. Their formation is due to non-uniform temperature distributions within the weld zone and out gassing of volatiles (such as moisture). This non-uniform temperature distribution has been demonstrated not only by a Gaussian laser light distribution but also by an even light distribution depending on the joint/part design. This paper reviews the development of tailored optics that re-shape the distribution of typical light/laser sources in order to promote uniform temperature distributions. It was seen in FEA models that by using uniform heat distributions, uniform temperature fields were produced in butt joint configurations. In addition it was seen that a distribution with high heat input on the outer edges produced uniform heating in lap shear joint configurations. Laboratory experiments verified these FEA predictions, and strong and attractive welds were generated.

Laser Welding of Polypropylene to Thermoplastic Polyolefins
Chung-Yuan Wu, Michael Cherdron, Mark Douglass, May 2004

Polypropylene (PP) and thermoplastic polyolefin (TPO) are currently used in many automotive applications. However, the weldability of these two materials using through transmission scanning laser welding has not yet been reported. This study focused on the effects of color and welding parameters on lap shear joint strength. Three colors, black, blue and tan, as well as three welding parameters, laser power, weld time and scanning speed, were used to evaluate the weldability. The samples were welded using a 200 W flashlamp-pumped Nd:YAG laser. For the 1.06 ?m wavelength, it was found that 3.2 mm thick natural PP has a transmission rate of 29%. It was also found that the black TPO had the most laser absorption, followed by the blue TPO and then the tan TPO. Therefore, the black TPO required the least amount of welding time to reach the maximum joint strength. In addition, as the scanning speed was reduced, the time required to reach maximum joint strength was also reduced.

Modeling the Bond Formation Development between Polymer Filaments in FDM Prototypes
C.T. Bellehumeur, L. Li, Q. Sun, P. Gu, May 2004

Fused Deposition Modeling (FDM) processes have the capability to fabricate parts with locally controlled properties by changing deposition density and deposition orientation. The integrity and mechanical properties of parts are largely determined by the bonding quality realized among polymer filaments. This paper reports a theoretical study of the mechanical properties of FDM prototypes, heat transfer analysis of the FDM process and modeling of the bond formation among ABS filaments. Thermal analysis of the FDM process resulted in an estimation of cooling profile of the extruded filaments. Quantitative predictions of the degree of bonding achieved during the filament deposition process were made. The model was used to estimate the effects of different manufacturing parameters in the FDM process.

Cracking of Resin Rich Layer Joined to Tank Wall Due to Fluctuating Liquid Level
Jack E. Helms, Michael W. Guillot, May 2004

Composite laminate tanks are used in corrosive services in chemical process plants. The inner surface of tanks usually consist of a glass reinforced layer that is mostly resin and is joined to the tank structure to form a corrosion barrier. A large diameter, open top, composite laminate tank containing a hot brine solution suffered vertical cracking in the corrosion barrier during normal process operations. The process involved relatively rapid changes in the liquid level at different times during each day. Vertical cracks were discovered in the corrosion barrier by plant inspectors during a routine plant turnaround. Finite element modeling was used to demonstrate that the cracking was due to transient thermal stresses near the liquid vapor interface that resulted from the fluctuating liquid level and natural convection from the tank wall in cooler weather. In this research, the effects of the amount of glass reinforcement in the resin rich corrosion barrier were also studied. The outer surface of the tank was insulated, but the insulation does not appear to have been a factor in the cracking.

Fast Joining of Composite Pipes Using UV Curing FRP Composites
Su-Seng Pang, Guoqiang Li, H. Dwayne Jerro, Jerry A. Peck, Michael A. Stubblefield, Saleem Hasan, May 2004

For this paper, twelve composite pipe joints were prepared. Among them, six were prepared using ultraviolet (UV) curing E-glass fiber reinforced vinyl ester composites and six were prepared using ambient environment curing E-glass fiber reinforced vinyl ester composites as control. Filament wound E-glass fiber reinforced vinyl ester composite pipes were used. Each section of pipe was 304.8 mm long with a 101.6 mm inner diameter. The wet lay-up technique was used to prepare the test samples. The curing time for the UV cured samples was 40 minutes, while the curing time was 24 hours for the control samples. Both internal pressure tests and four-point bending tests were conducted on the UV cured and control samples. The test results show that the UV cured FRP wrapped composite pipe joints achieved nearly the same bending strength as the control samples. However, the internal pressure rating achieved by the UV cured FRP coupled joints were lower than those achieved by the control samples. Based on the test results, the UV curing FRP can be used in joining composite truss structures and composite frame structures. Further investigation is required in order for the UV cured FRP joined pipes to be used to transport liquids or gases under pressure.

Surface Treatment of Polymers and Composites with UV Light in Air to Improve Adhesion
Alekh S. Bhurke, Lawrence T. Drzal, May 2004

Ultraviolet (UV) surface treatment of polymers in air has been used to successfully modify polymer surfaces in order to enhance adhesive performance and wettability in a cost efficient manner. A wide variety of polymers including thermoplastics (TPO, PP, PC, PMMA), thermosets (Epoxy, Vinyl Ester), rubbers and composites have been successfully modified with this UV treatment. Improvements in adhesive bond strengths from 100-600% can be realized for hydrophobic polymers such as TPO and PP with treatment times on the order of 30-120 seconds. Several key process parameters for UV treatment have been identified. UV radiation in the 180nm-300nm was found to be necessary for surface modification of polymers. The extent of surface modification was found to be strongly dependent on the ozone concentration. The surface temperature during treatment was also found to be a controlling factor for some polymers and preliminary evidence points to a relationship between the optimum treatment temperature and the glass transition temperature (Tg) of the polymer substrate.

Development of Methods for Assessing the Chemical Compatibility of Thread Sealants Used with Plastic Fittings
J.R. Paschal, J. Bian, May 2004

Thread sealants have been used to help ensure a leak-tight joint and reduce friction during installation between threaded metal pipe and fittings for over 100 years. Thermoplastic fittings using the same taper thread cannot be assembled as if they were metal due to chemical compatibility and maximum material stress. However these same sealants are often used on a plastic fitting joint. This may be done either because the installer has been trained to use the same sealants on all threaded joints, or because the plastic parts are not fitted properly and are leaking under pressure. Unfortunately, sealants that work well and are compatible with metal pipe threads may contain stress-cracking agents that will cause failure in plastic fitting joints. Because it is unlikely that the industry practice of using thread sealants will change in the foreseeable future, a method is needed to evaluate these products to determine compatibility with existing fittings materials and designs. The current work develops three categories of testing using tensile, flexural, and threaded part configurations. Several variations in each of these methods are attempted, with multiple types of sealants and materials. There is a definite trade-off in test duration and complexity of the test method. The results of this testing program are provided, with analysis of the failure types and recommendations for the development of an ASTM test method.

Mechanical Properties of Rotationally Moulded Nanocomposites
P.R.W. Hanna, T. McNally, E. Harknin-Jones, P. McMillian, May 2004

Polyethylene montmorillonite and quaternary tallow ammonium chloride modified montmorillonite nanocomposites were prepared by melt blending. The effect of compatibiliser concentration on composite mechanical properties was investigated. The nanocomposite morphology was examined using wide angle X-ray diffraction and scanning electron microscopy. Primarily intercalated structures were observed. The nanocomposites prepared were rotationally moulded using a peak internal air temperature of 200°C and an oven temperature of 300°C and injection moulded samples using a nozzle melt temperature of 220°C. No significant variation was evident in the shrinkage and warpage characteristics of the rotomoulded parts. The tensile, flexural and impact properties of specimens taken from both the rotomoulded and injection moulded parts varied with compatibiliser content. Generally, the properties of the injection-moulded parts were superior to that of the rotomoulded parts.

Polyethylene Nanocomposites – Investigating the Tensile Properties of Polyethylene Nanocomposites for Rotational Moulding
Michael Murphy, R. Truss, P. Halley, D. Martin, C.L. Ang, May 2004

Rotational moulding is continuously expanding into new markets which require improved material properties and shorter cycle times. Conventional PE, used in over 80% of the rotational moulding market is a relatively low strength material therefore high part wall thickness, long cycle times and design limitations are imposed.The development of polymer/clay nanocomposites has shown significant improvements in mechanical properties with small additions of organoclay, which have the ability to improve mechanical performances or reduce cycle times.In this work the effect of organoclay on the tensile properties of PE nanocomposites at a range of temperatures was investigated. Tests were also conducted at a range of cross head speeds (CHS) to illustrate the effect of slow rates of extension and instantaneous loading. Tensile testing shows the final nanocomposite properties depend significantly on organoclay loading with improvements of 25% in tensile modulus at room temperature and larger improvements at higher test temperatures being reported. The results also indicate the organoclay loadings investigated had an adverse effect on the tensile yield stress.

Investigation of the Processing Characteristics and Mechanical Properties of Metallocene Catalysed Polyethylene Foams for Rotational Moulding
E. Archer, E. Harkin-Jones, M.P. Kearns, A.M. Fatnes, May 2004

The object of this work is to investigate the foaming characteristics of three grades of metallocene-catalysed Linear Low Density polyethylenes for rotational moulding using both an exothermic and endothermic chemical blowing agent. This paper reports on the results of ongoing experimental investigations in which rheological and thermal parameters are related to the polymer structure and mechanical properties. Through adjustments to moulding conditions, the significant processing and physical material parameters, which optimise metallocene catalysed linear low-density polyethylene foam structure, have been identified. The results obtained from equivalent conventional grades of Ziegler-Natta-catalysed linear low-density polyethylene are used as a basis for comparison.

The Effect of Coupling Agents on Foaming with Polymer Microspheres in Rotational Molding
D. D’Agostino, E. Takács, J. Vlachopoulos, May 2004

The use of polymer microspheres for producing microcellular foams is a new development in rotational molding. In previous studies, some reduction in mechanical properties has been found due to the immiscibility between the polymer shell and the matrix polymer. Coupling agents can act as a molecular bridge at this interface and can also affect bubble growth by altering the rheological properties of the matrix polymer. The influence of different coupling agents on the melt properties of several resins was investigated, as well as the effect of these coupling agents on the mechanical properties of foamed rotationally molded parts.

Manufacturability of Fine-Celled Cellular Structures in Rotational Foam Molding
Remon Pop-Iliev, Donglai Xu, Chul B. Park, May 2004

Any closed-cell polyolefin foam production tends to achieve the highest possible cell size distribution uniformity, cell size reduction, and cell density augmentation. However, the control of the cell size of rotationally foam molded cellular structures formed on the base of a chemical blowing agent (CBA) might be often aggravated by some inherent limitations that are unique to the rotational molding process, which results in coarsercelled final cellular structures being yield. Although a finecelled morphology (cell size < 100 [?m] and cell density > 106 [cells/cm3]) in rotationally molded foams has been closely approached, it has not been actually achieved yet, nor it has been ever clarified whether it is actually achievable in rotational foam molding or not. This study attempts to provide an answer to this fundamental question by focusing on the understanding of the mechanisms governing the formation, growth, shrinkage, and collapse of CBA-blown bubbles in non-pressurized polymer melts originating from extrusion melt compounded foamable resins in a pellet form.

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