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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.
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.
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.
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.
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.
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.
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.
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.
Nylon Casting is a thermo-chemical process carried approximately at 150° C. The process involves charging the reaction vessel with molten monomer and subsequent polymerisation associated with an exotherm taking final product temperature to 200° C. During this process phase change occurs, by studying the heat of exotherm and corresponding reaction time provides valuable information about casting process.If the reaction is too slow, resultant polymer has low molecular mass and high oligomer content. If the reaction is too fast the resultant polymer is prone to stress cracking, voids and of low molecular mass. Hence there is a tight production window into which production must fall.A technique for rapid, efficient and nondestructive online monitoring system for casting process was lacking. Various authors had monitored the reaction and studied reaction kinetics. But no readily monitoring system was available.The present technique represents a novel interpretation method based on gradient changes (differentiation). This interpretation is ‘real-time postcalculated’ based on buffer data management system. Calculations are activated by an upper trigger switch and calculation is back regressed on ‘nearest-minima’ basis. the calculated date is time stamped and saved to a secondary file. Calculated data is ‘reaction rate’ (dT / dt) and reaction end point (T65- nominal solidification point) are displayed on the screen.By using this tool blue print of the reaction can be obtained. This also includes pour temperature, tool temperature, oven temperature and reactions time that are essential for reaction optimization and defect reduction.
Crystallization of homopolymer poly (propylene) was monitored through the measurements of ultrasonic velocity and attenuation at a frequency of 2.8 MHz. The experiments, conducted under static conditions (no shear) at pressures up to 800 bars, included the simultaneous measurement of sample volume using an LVDT sensor. Temperature sweeps at constant pressure were started at a temperature of 250 °C down to 50 °C. Isothermal tests involving pressure steps of up to 600 bars were also carried out at a temperature slightly above Tc to investigate the effects of a suddenly applied load on the crystallization kinetics. The results indicate that the evolution of the ultrasonic characteristics (ultrasound attenuation and velocity) can be used to probe the different steps of the crystallization process (nucleation, crystallite growth.). The crystallization temperature increases linearly with pressure within the range studied. In the isothermal tests with a pressure step, the pressure effect is mostly prominent on the kinetics. A higher pressure results in a decrease of the induction time and an acceleration of the crystallization process.
A fluorescent dye, Nile Blue (NB), was used as molecular probe to monitor the microstructure of organo modified montmorillonite clays as they were compounded with nylon 11. Prior to compounding, the dye was incorporated into the gallery between silicate layers of the clay by an ion exchange process. The NB doped clays had no fluorescence due to concentration quenching. But, upon compounding the clay with nylon 11, the dye was released from the clay galleries during intercalation of the polymer and exfoliation of clay platelets. The process of exfoliation was monitored during compounding by measuring the fluorescence spectrum as a function of time. Experiments were carried out using a batch mixer that was instrumented with an optical fiber sensor.
Nanocomposites based on polyamide 66 (PA-66)/clay and polyamide 6 (PA-6)/clay were prepared using a twin-screw extruder. The nanocomposites were characterized with transmission electron microscopy (TEM), X-ray diffraction (XRD), differential scanning calorimetric (DSC), optical microscopy and tensile testing. Effects of processing condition and clay modifier were also studied. The results show that mixing, shearing elements and higher residence time in the twin-screw extruder are effective factors in enhancing exfoliation. The characteristics of the two types of nanocomposites will be compared.
Polystyrene/organoclay nanocomposites have been prepared by melt blending in a vertical co-rotating twin-screw mixer. Monodisperse polymers having molecular weights of 18k and 49k were investigated. Low molecular weight polystyrenes were chosen to take advantage of the high viscosities near Tg, allowing temperature variation to provide for several orders of magnitude of viscosity and to correspondingly change the shear stress. Melt rheology was the primary tool used to determine the extent of exfoliation in the nanocomposite samples. The highest amount of exfoliation at low clay loading was present in samples with an 18k matrix favoring low temperature. A bimodal polystyrene matrix facilitated dispersion, but the low molecular weight chains compromised the final moduli.
Models based on kinetic, thermodynamic and rheological equations have been developed to compute dispersion extent, batch temperature and rotor torque/power consumption at discrete intervals during a mix cycle in an internal mixer. Evaluating the models over successive time intervals allows the computation of dispersion, temperature, and torque/power profiles for a complete mix cycle. The mix models are found to describe experimental torque and temperature curves for mixing natural rubber with carbon black fillers over a range of particle sizes and loadings (0 to 50 phr) for rotor speeds ranging from 40 to 70 RPM in lab-scale internal mixers. Rate constants for filler dispersion, incorporation and erosion can be extracted from baseline mixes and subsequently used to simulate mixing at a variety of different operating conditions. The models thus permit convenient analysis and optimization of mixing protocols on a desk-top computer.
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