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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Q. Sun, G.M. Rizvi, V. Giuliani, C.T. Bellehumeur, P. Gu, May 2004
The application of Fused Deposition Modeling (FDM), a plastic based rapid prototyping technique, has been limited due to poor bonding between the filaments forming the parts. This study focuses on understanding the bonding mechanism and its dependence on processing parameters. The bond quality was experimentally assessed based on the growth of the neck formed between adjacent filaments and their failure under flexural loading. We present two thermally driven models which describe the formation of bonds due to sintering and molecular diffusion. Experimental results suggest that the diffusion model is more appropriate for this application.
Heat sealing properties of Linear Low Density Polyethylene (LLDPE) blend with varying proportions of High Density Polyethylene (HDPE) was investigated. Heat sealing properties of LLDPE namely, heat seal strength and hot tack strength are evaluated as a function of HDPE content in the binary blends. To elucidate their relevance, the thermal behaviour obtained by Differential Scanning Calorimetry (DSC) is correlated to these heat sealing properties. Keeping the process variables of seal pressure and dwell time constant, experimental results indicate that HDPE induced pronounced changes on the heat sealing ability of LLDPE.
Abbass Mokhtarzadeh, Avraham Benatar, Chung-Yuan Wu, May 2004
Clay-based nanocomposites have recently attracted attention in many industries due to their high specific strength, modulus and low permeability. A typical nanocomposite plastic has only about 3 to 6 percent by weight nanoclay, where after being purified and surface-treated they are mixed with pure resins to produce polymeric nanocomposites. As the usage of these nanocomposites increases in industry, knowledge of its weldability becomes important. The hot plate weldability of three specific Polypropylene nanocomposites with 0wt%, 3wt% and 6wt% nanoclay was investigated. A three factors (heating temperature, welding time and welding pressure), two level design of experiments (DOE) was used to screen welding parameters and obtain near optimum welding conditions. The maximum joint strength was found to be 94%, 79% and 62% of the bulk strength for 0wt%, 3wt% and 6wt% nanoclay samples, respectively. While increasing nanoclay levels in the composite improved the bulk material strength, it reduced the weld strength significantly.
David Grewell, Gang Zhou, L. James Lee, Avraham Benatar, Ed Lee, May 2004
This paper reviews experimental work on ultrasonic treatment of advanced thermoset composites. It has been proposed that treating these composites with high power ultrasonics (~10-50 W) may cause a decrease in void content without adverse effects, such as premature partial curing or a degradation of mechanical properties. Samples of advanced composites were treated with ultrasonic energy at various travel speeds, amplitudes, force, orientations of the horn to the surface and number of pregregs plies treated at once. Significant heating was observed but there was no evidence that the treatment had any adverse effects. It was seen that the treatment reduced the overall thickness of the samples, implying that the void content was decreased. In addition, there was evidence that ultrasonic treatment slightly increased the stiffness and short beam shear strength of the samples.
David Grewell, Ryan Gneiting, Gianna Strohm, Avraham Benatar, May 2004
This paper reviews experimental work that compares the various control algorithms for ultrasonic welding of plastic. The three algorithms/modes that were compared were time, energy and collapse. Amorphous and crystalline materials were studied using both energy director and shear joints. Welds were made with all materials and joint designs and tested for strength and final part dimensions. The standard deviation of the resulting strengths and final dimensions of the parts were compared for all the modes. It was found that the collapse mode produced the most consistent weld strengths and final dimensions. In addition, compared to each other the time and energy modes produced comparable consistency (strength and final dimensions) for the materials and samples studied.
Laser transmission welding of thermoplastics becomes more and more important in industrial series production due to an array of its advantageous properties. In the practice the interest in this technology increases continuously. At the same time, the demand for ongoing investigations and research – especially regarding the laser welding process and its understanding – is being noticed.In this report a simplified mathematic-physical model of laser transmission welding based on the finite-element-method (FEM) will be presented. For the primary calculations the material PA6 was chosen. The developed model comprises the whole laser welding process including the heating and the cooling phase. First of all, the boundary conditions as well as the relevant process parameters like the intensity of the laser beam, the joining pressure and the welding time will be specified and then the simulation will be started. As a result, flow and temperature profiles will be calculated. Due to an array of available boundary conditions it is possible to continuously improve the model while comparing the simulated data with the data got by experiments.
Chunmeng Lu, Yi-Je Juang, L. James Lee, David Grewell, Avraham Benatar, May 2004
The use of hot embossing for fabrication of polymeric microfluidic devices is gaining a great deal of attention in recent years because it is a relatively simple and low-cost process. Conventional microembossing is a relatively slow process that requires both the mold and the polymer substrate to be heated during embossing and cooled before de-embossing. In order to shorten the cycle time, a laser/IR-assisted microembossing (LIME) process was evaluated in this study. Since laser/IR heats the substrate rapidly and locally, the heating and cooling time can be substantially reduced. Experimental results have shown that both shorter cycle time and good replication accuracy can be achieved. In order to better understand this process, a commercially available FEM code DEFORM® was used for process simulation. Because the temperature distribution inside the polymer substrate is affected by the penetration of radiation energy flux from laser/IR heating, the relationship between penetration energy flux and temperature distribution was implemented into the FEM code. Rheological properties of selected amorphous and crystalline polymers were characterized and incorporated into the FEM code. Two different modes of IR embossing were simulated, in which either a transparent mold or transparent substrate was used. The flow patterns observed in the experiments agreed reasonably well with the DEFORM-3D simulation and a quantitative comparison between experimental and simulation results was made using DEFORM-2D.
R. Prabhakaran, M. Kontopoulou, G. Zak, P.J. Bates, B. Baylis, May 2004
Laser transmission welding is a relatively new joining process in which laser energy is used to melt polymer at the interface between laser-transparent and laser-absorbing components. This study examined the effect of diode laser speed, power, beam area and weld pressure on the meltdown, microstructure and weld strength of T-joints made from unreinforced nylon 6. The results show that meltdown increases strongly with line energy and is also affected by beam area and weld pressure. For the range of parameters selected, the strength was observed to depend largely on the ability to make welds free of local stress concentrations and degraded material. This can be achieved by obtaining a relatively uniform power flux distribution along the weld-line cross-section.
It is not easy to achieve the desired standard of welding, without causing surface thermal damage, in infrared welding of overlapped plastics when placing an infrared absorbing part in the irradiated side. The irradiated surface layer is heated up due to the intense absorption of infrared radiation and easily suffers from thermal damage such as shrinkage, burns, perforations, or other undesirable degradations. Our previous work which was an innovative solution for this problem employed a transparent heat sink in contact with the irradiated surface of the plastics during CO2 laser irradiation.This paper deals with the extended research concerning the penetration welding technique for overlapped thermoplastics by using infrared radiation heating with a transparent heat sink. In our previous study, a fixed wavelength of 10.6 ?m of a CO2 laser light was used. In this study, a quartz-halogen lamp with a transparent heat sink had been employed in order to examine the feasibility of deep penetration welding for various types of plastics without using dyes and pigments. Most plastics themselves have several weaker infrared absorption bands in the wavelength range emitted from the lamp than those emitted from a CO2 laser light. The results of welding experiments show that both visually transparent thermoplastics (polymethyl methacrylate and polycarbonate) and translucent thermoplastics (low density polyethylene) of several millimeters in thickness can be welded without causing thermal damage.
Extended research has been carried out concerning our proposed penetration welding technique for overlapped thermoplastics using infrared lasers with transparent heat sinks.Numerical simulations for a heat transfer model in welding process were conducted to test the effect of various kinds of welding conditions on the melt depth of plastics. The temperature profile variations in plastics to be welded during heating process were obtained by manipulating different parameters, such as the heat sink, the plastic material, the thickness of the plastic, the absorption coefficient, the incident radiation power density and the irradiation time.The results show that the melt depth and the starting time of melting greatly depend upon the radiation absorption and thermal diffusion in the plastics. For example, as the absorption coefficient of plastics increases, the starting position of melting in the plastics approaches the irradiated surface. It is therefore worthwhile for overlap welding to know the depth at which the maximum temperature appears inside of the plastics during radiation heating. This is dependent on the heat conductivity of heat sinks, the thickness of the plastic, the absorption coefficient, the radiation power density and the irradiation time.
Thermoplastic Polyolefin (TPO) has been used in automotive applications extensively. Polyolefin elastomer is one of the major modifiers in the TPO to improve the impact performance. The weld strength between the TPO and elastomer modifier could be used to indicate the adhesion between these two materials during compounding. Therefore, through transmission laser welding of these two materials was performed to evaluate the interfacial adhesion. Three different grades of elastomer modifiers and one TPO were studied. Three-factor two-level full factorial design of experiments was used to evaluate the effect of welding parameters on weld strength. The results indicated that the weld strength was proportional to the laser power and inverse proportional to the welding speed. In addition, the weld strength was proportional to the strength of the elastomer.
David Grewell, Chunmeng Lu, L. James Lee, Avraham Benatar, May 2004
This paper reviews experimental work on through-transmission infrared micro-embossing of thermoplastics for replication of micro-fluidic devices. Two separate modes were evaluated. In one mode, a transparent mold/die was used in where IR radiation was passed through a die and directed onto an opaque thermoplastic substrate. The substrate would heat and soften and then the die was pressed against the substrate, allowing the features of the mold/die to be transferred to the substrate. In contrast, the other mode that was evaluated involved passing IR radiation through a transparent substrate onto an absorbing die that would heat as it was pressed against the substrate. The parameters that were evaluated included: power density, heating time, preheating, holding time, and pressure. Optical microscopy evaluation of the samples allowed correlation of these parameters to image transfer quality, including depth of features (Over 100 ?m) and sharpness.
Chandramowli Krishnan, Darci Toussant, Avraham Benatar, May 2004
Plastic welding processes result in a wide range of heating and cooling rates of the welds and the heat affected zone. This results in a range of morphology and residual stress levels. The weld morphologies of polycarbonate and polypropylene were studied for hot-plate, vibration and ultrasonic welding. A microtome was used to cut 25-30 micron thick slices across the polypropylene welds for microscopic examination. For Polycarbonate, a diamond saw was used to cut 1-1.5 mm thick slices across the weld for microscopic examination. For both materials, polarized light microscopy was used. It was observed that rapid heating and cooling welding methods (Ultrasonic and Vibration) produced the narrowest weld lines and heat affected zones with a high degree of molecular orientation and low levels of crystallinity. Hot plate welding produced the widest heat affected zones with the lowest amount of molecular orientation.
A study was performed to evaluate the applicability of the resistive implant welding method for joining composite thermoplastic material, consisting of polyolefin matrix reinforced with 40% glass fibers, and to develop recommendations regarding the resistive implant selection. This paper presents the results of investigation of the factors affecting the joint formation and weld quality, including resistive implant characteristics, such as material properties, implant design and geometric characteristics (wire diameter, mesh size, type of contact between the wires); and process parameters, such as voltage output, heating time, and welding pressure.
Recent developments in magnetic implant induction welding have focused on optimizing mechanical performance of joints in reinforced plastics through continuous improvement to the welding technology (including magnetic implant material properties, SPC process control, joint design optimization, etc.). In this study, 33 wt. % fiber-glass reinforced Nylon 6 was used in a chain-optimization study to conduct a critical comparison of two alternatives for thermoplastic welding. Results demonstrate interactions between material composition, joint design, and welding process conditions.
Abdirahman A. Yussuf, Igor Sbarski, Jason P. Hayes, Nguyen Tran, Matthew Solomon, May 2004
The use of conductive polymers in welding of plastics offers the possibility of understanding and developing new welding techniques. Polyaniline, which absorbs the microwave energy and converts it to heat to perform the welding process, can be deposited and patterned locally. In this paper conductive polyaniline in a liquid form and single mode microwave technology was used to weld two polymethmethyacrylate (PMMA) substrates. These rapidly welded samples were then shear tested to determine the joint strength as a function of processing parameters such as heating time, microwave power, applied pressure, and quantity of polyaniline. During welding both the processing and operating parameters were varied in order to determine their effect on the resulting bond strength. It was found that increasing the microwave power, heating time and amount of polyaniline increased the joint strength. A heating time of 15 s and increasing power from 100 to 300 Watts increased joint strength from 1.7 to 6.8 MPa. The joint strength testing technique of a single lap shear was chosen and samples were prepared according to ASTM D 3164- 97. The dielectric properties of polyaniline and PMMA over a range of 18°C to 110°C at the frequency of 2.45 GHz are reported.
The melting mechanism of Polyvinyl Chloride (PVC) powder in a counter-rotating twin-screw extruder was studied by using an ultrasound in-line monitoring system. Ultrasound signal patterns were obtained at various processing conditions. The experimental results revealed that the dissipative or dispersed melting phenomenon was dominant in most melting process of PVC in the counter-rotating twin-screw extruder. The melting status of PVC particles was analyzed by ultrasound signal amplitude ratios. The changes of amplitude ratio showed that the material melting level in region I (between barrel and flight) was much higher than region II (between barrel and screw root), due to the combined effect of viscous shearing and heat conduction from barrel. It also revealed that PVC particles melted more uniformly at higher feeding rate due to the energy dissipation from particle interactions.
Yu-Hsin Lee, Anthony J. Bur, Steven C. Roth, May 2004
A new dielectric slit die sensor attached to the end of an extruder was designed to examine the melt properties of Nylon 11/ clay nanocomposites. Experimental data were fit with the Cole-Cole relaxation functions corrected for electrode polarization and DC conductivity. Two interesting features were discovered. Firstly, at processing temperature, only one relaxation, ?, was detected in the neat resin and yet two relaxations, ? and Maxwell-Wagner interfacial polarization (MW), were retrieved from the composites. MW was ascribed to the polarization at the polymer/ filler interface. A much broader relaxation time distribution appeared in MW compared to ? as each polymer/ filler interface, bearing various interfacial geometries, is polarized at a distinct time scale. Secondly, the MW relaxation frequency correlated well with the degree of filler dispersion and exfoliation throughout the polymer matrix. A much lower MW frequency was found in the system where a higher extent of silicate exfoliation was obtained. Additional on-line data were obtained from an optical sensor that monitored light transmission through the filled resins. The combination of optical and dielectric data was used to establish a degree of exfoliation scale.
Anthony J. Bur, Yu-Hsin Lee, Steven C. Roth, May 2004
Dielectric measurements were carried out during compounding of nylon/clay nanocomposites using a dielectric slit die that is attached to the end of a twin screw extruder. Contributions to the dielectric properties of nanocomposite melts arise from DC conductivity, dipolar relaxation and interfacial (Maxwell Wagner) polarization. Relationships between clay microstructure and dielectric properties were explored. The magnitude, characteristic frequency and distribution of relaxation times of the Maxwell-Wagner polarization were found to be dependent on the state of microstructure.
Mustapha Nourelfath, Fouad Erchiqui, Abdelkader Zeblah, May 2004
A major example of the use of transfer lines is in the high volume production of plastic parts. Such manufacturing production systems are often organized with machines or work centers connected in series and separated by buffers. To achieve a greater production rate or to achieve a greater reliability, systems are built with machines in parallel. The paper formulates a problem of the optimal design of a series-parallel manufacturing production line system where redundant machines and in-process buffers are included to achieve a greater production rate. The objective is to maximize production rate subject to a total cost constraint. Machines and buffers are chosen from a list of products available in the market. The buffers are characterized by their cost and size. The machines are characterized by their cost, failure rate, repair rate and processing time. The proposed method allows machines with different parameters to be allocated in parallel. To estimate series-parallel production line performance, an analytical decomposition-type approximation is used. To solve the formulated optimal design problem, we propose a biologically inspired heuristic. This heuristic is based on the ant colony optimization meta-heuristic.
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