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Rheological Modeling of Warpage in Polymeric Products Under High Temperature
Thermoforming process is one of the most popular techniques in the polymer processing. Wide applications of thermoforming are due to its high performance, simplicity, compactness and relatively low-cost equipment. The fundamental defect inherent to the thermoforming technology is warpage of the products during their application which becomes particularly apparent under high temperatures. The warpage defect is understood as the process of non-uniform (heterogeneous) change of the geometric dimensions of products in time resulting in a change (distortion) of their original form. The results of this work allow us to find out the causes of this warpage and ascertain the conditions that give rise to this defect, thereby making it possible to work out valid recommendations for its partial and, in some cases, complete elimination.
Recycling and Reuse of Vinyl Wallpaper
Vinyl wallpaper has two principal materials of natural and synthetic origin used in its manufacture: Thermoplastic polymer (PVC) Polyvinyl chloride combined with cellulose fibre. The present paper will follow an interdisciplinary approach aimed at producing strategies for the recovery and reuse of these materials, thereby minimising the level of wallpaper waste entering landfill. Consideration will be given to preparation, characterisation and properties of the compounded and moulded recyclate. A range of techniques used to characterise these materials will be discussed, including image analysis, thermo gravimetric analysis, compressive strength, impact and recovery measurements.
Numerical Simulation of Stress on the Mold in Beads Expansion Process and Thickness of Foam Product in the Recovery Process
The expanded polypropylene foam beads (EPP) production process, which consists of steaming, depressurizing, cooling and ageing processes, was simulated by a mathematical model. The model was developed by extending Yang and Lee's ageing model of extrusion foam products in terms of fundamental aspects of evaporation, condensation of blowing agents and heat conduction phenomena during the steam chest molding. The governing equations were established by coupling the mass transfer equation of steam and air at the interfoam cell walls, constitutive equation of evaporation and condensation in each cell, equation of heat conduction from the mold to foams, with mechanical force balances equation on the cell walls. The model could simulate the stress exerted to the foaming mold and expansion behavior of the cells in the EPP foam board.
Nonisothermal Crystallization Kinetics and Crystalline Structure of Nylon 6/Functionalized Multi-Walled Carbon Nanotube Composites
Nylon 6/functionalized multi-walled carbon nanotube (f-MWNT) composites were prepared by mixing the nylon 6 and carboxylic group containing MWNT in formic acid solution. DSC and XRD have been used to investigate the nonisothermal crystallization kinetics and crystalline behavior of nylon 6/f-MWNT composites. DSC data shows that the activation energy (Ea) drastically increases with the presence of 0.25 wt% f-MWNT in nylon 6/f-MWNT composites and then slightly increases with increasing f-MWNT content. These results indicate that the addition of 0.25 wt% f-MWNT into nylon 6 significantly reduces the transportation ability of polymer chains during crystallization process. By adding more f-MWNT into nylon 6 probably induces the heterogeneous nucleation in which the Ea slightly increased. XRD results indicate that the addition of f-MWNT favored the formation of the thermodynamically stable ? crystalline structure at various cooling rates, compared to that of pure nylon 6 matrix.
Study on the Weld Line Strength of Thin-Wall Molded Nanocomposites
Current study investigates tensile strength of Nylon6/ Fluoromica nano-composites (Unitika®), injection molded parts at different molding conditions such as melt temperature, mold temperature, packing pressure, and injection speed. Experimental results indicate that the tensile strengths of 1.0mm injection molded specimens (with weldline or without weldline) are stronger than that of 2.5mm. The tensile strength of weldline becomes significantly weak as compared to the non-weldline. As melt temperature, mold temperature, packing pressure, and injection speed increases the weldline and non-weldline tensile strengths of molded nanocomposites also increase.
Ultra-Thin Polymer Films: Elastic Response in the Rubbery Regime
Using a novel microbubble inflation technique developed within our laboratory, we are able to measure the absolute biaxial compliance of polymer films as thin as 13 nm. Experiments performed on both poly(vinyl acetate) (PVAc) and polystyrene (PS) films show that large reductions in the glass transition temperature at the nano-scale are nonuniversal, viz., the PVAc shows no reduction even for the thinnest films while the PS shows a significant reduction at a thickness below approximately 80 nm. More surprisingly, the rubbery plateau region for both materials shows dramatic stiffening (>300 times), perhaps due to surface pinning of the entanglement network. The compliance increases as approximately the square of film thickness.
Comparative Study of Organic and Inorganic Impact Modification of PVC
We have developed an inorganic material based on synthetic amorphous silicon dioxide with an average primary particle size of 150 nm and a specific surface area of 20 m2/g, called SIDISTAR®.These spherical particles can be optimally dispersed throughout the polymer matrix and will dissipate the impact energy over their particle surface so that in any direction the transmitted energy value is smaller than necessary for crack initiation or propagation.TEM (transmission electron microscopy) investigations prove that on impact the particles create a space between them and the surrounding polymer matrix thus avoiding energy transmittance.
Structure-Properties Relationship in Methylphenylsiloxane - Modified Epoxy Systems
The fracture resistance of epoxy resins was significantly improved through a new molecular toughening mechanism without sacrificing the desired thermal and mechanical properties. A liquid diglycidyl ether of bisphenol-A type epoxy resin (DGEBA) was modified with various methylphenyl siloxane (MPS) modifiers and then cured with two types of amine curing agents, meta-phenylenediamine (mPDA) and polyoxypropylene diamine (POPDA). The effects of such variables as the modifier type and concentration, and the curing agent type and curing cycle on the properties and the morphologies of the MPS-modified DGEBA systems were investigated. The glass transition temperatures (Tg) of the siloxane-modified DGEBA/mPDA systems were well-maintained. Chemically modified DGEBA samples by various MPS modifiers demonstrate greater enhancements in both the fracture toughness (KIc) and the fracture energy (GIc) compared with the unmodified epoxy system. With an increasing siloxane content, both the values of KIc and GIc increase. The improvement of fracture toughness can be attributed to shear band formation, crack path deflection, trans-particle fracture, particle tearing and localized plastic deformation.
Direct Closed-Loop Quality Control for Injection Molidng
In this study, an online quality control system has been proposed and developed. A quality index, part weight, is measured in each cycle. The difference between this measurement and a quality target is used to adjust mold separation, a process variable. In a cascading fashion, the mold separation is controlled via switchover point and holding pressure, two machine variables, in cycle-to-cycle and within-cycle control. Compared to conventional cavity pressure-based control, the present implementation results in a significant improvement in both long-term and shortterm consistency in part quality. In addition, direct quality feedback control has numerous benefits, such as 100% quality inspection and automatic process tuning.
Materials and Processing Methods Used in the Production of Polymer Composite Bipolar Plates for Fuel Cells
A method of producing bipolar plates with high electrical conductivity, adequate mechanical properties, and the ability for rapid formation of channels into the surfaces is described. Polyphenylene Sulfide (PPS) based wet-lay composite plates have in-plane conductivities of 200-300 S/cm, tensile strength of 57 MPa, and a flexural strength of 96 MPa. These values exceed industrial as well as Dept. of Energy targets or requirements and have never been reached before for composite bipolar plates. The use of wet-lay material also makes it possible to choose different components including polymer, graphite particles, and reinforcement for the core and outer layers of the plate to optimize the properties and/or reduce the cost of the plate. Using polyvinylidene fluoride (PVDF) doped with graphite as an outer skin layer has potential to reduce the processing time for generation of the channels and reduce manufacturing cost.
Structure to Property Relationships in Polycarbonate/Polydimethylsiloxane Copolymers
Block copolymers based on polycarbonate (PC) and polydimethylsiloxane (PDMS) have been known for over 40 years. These materials have achieved considerable commercial success due to a favorable combination of low temperature impact, melt processibility, weathering resistance and unique surface properties. Most commercial products are opaque due to scattering by the PDMS domains dispersed in the PC matrix. By controlling synthesis conditions, optically opaque or transparent materials may result from the same combination of base monomers and both types of materials have been prepared and characterized. Lower PDMS block lengths lead to higher levels of light transmission. Opaque materials typically have siloxane domains in the 0.1 to 10 um region while low haze products can be achieved when domains are less than 20 nm. Small siloxane domain copolymers can exhibit considerable mixing of PC into the PDMS blocks. This likely alters the effective refractive index of the PDMS phase and contributes to the low haze measured in these copolymers.
Response Surface Modeling of Formaldehyde-Free Wood Composites
A response surface model using a Box-Behnken design was constructed to statistically model the material compositions-processing conditions-mechanical property relationships of formaldehyde-free wood composite panels. Three levels of binding agent content, pressing time and press temperature were studied and regression models were developed to describe the statistical effects of the formulation and processing conditions on the mechanical properties of the panels. Linear models best fit both the flexural strength (MOR) and internal bond (IB) strength of the panels. Increasing any of the manufacturing variables resulted in greater MOR and IB strength. Flexural stiffness (MOE) was best described by a quadratic regression model. Increased MOE could be obtained through higher pressing times, binding agent concentrations and/or pressing temperatures. However, binding agent concentration had less effect on increasing the MOE at higher pressing temperatures.
Bio-Based Polyurethane Nanocomposites
Polyols derived from soybean oil are new polyurethane raw materials derived from the renewable resources, and with isocyanates they produce polyurethanes that can compete in many aspects with ones derived from the petrochemical polyols. Combined with polyisocyanurates, they produce materials of good thermal, oxidative and weather stability.The main objective of this research is to synthesize mechanically reinforced polyurethanes, and study the influence of the concentration of nanoparticles on the properties of the new material. Two different soybean oil based polyols, SOY169 and SOY201 were selected to synthesize the polyurethane nanocomposites using a diisocyanate (pure MDI) as a curing agent. The clay used at different concentrations (0%, 1%, 3%, and 5%) in the synthesis of the nanocomposite polyurethanes was organo modified Montmorillonite clay, Cloisite®10A. Methanol was chosen as solvent media in preparing the samples.Several methods were used to analyze the samples like, mechanical tests – Tensile strength, Flexural modulus, and Notched Izod Impact strength; Thermal analysis – Differential Scanning Calorimetry (DSC), Thermomechanical Analysis (TMA), and Thermogravimetric Analysis (TGA); Structural analysis – Atomic force microscopy (AFM), Fourier Transform Infrared spectra (FTIR).
Modification and Scale-Up of the New Miniature Mixer-APAM
Our previous papers show that the Alberta Polymer Asymmetric Minimixer (APAM, 2ml, see Figure 1) is very effective mixing equipment for blending polymers and nanocomposites in the small scale. There are different capacity requirement for different applications, therefore, more flexible designs of the APAM are needed. For example, to have enough material for mechanical property testing, 10ml or more may be required. The simplest way to have a larger capacity is to increase the radius of the outer cup, which will increase the minimum clearance as well. Another way is to scale up the entire mixer. These changes will definitely affect the flow and thermal fields. In this paper, Polyflow 3.10 (Fluent Inc.) is used to model the transient non-isothermal process of polystyrene in these modified mixers. Simulation results show that it takes longer time for the thermal field to develop with increasing size of the cup and the mixer. The flow fields inside these modified mixers are characterized by radial and axial veloc ity profiles. The shear rate and shear stress change due to the modification. The transient temperature value at a point increases, and the steady state temperature distribution shows the effect of viscous dissipation.
Performance of Susceptor Materials in High Frequency Magnetic Fields
Joining of thermoplastics by electromagnetic implant welding is a mature process, yet little information is found in the literature to describe the relationship between the properties of magnetic susceptor particles, the plastic matrix materials in which they are dispersed, and their interaction with high frequency electromagnetic fields.Magnetic implant welding uses susceptors that couple, due to ferromagnetic hysteresis, with high frequency electromagnetic radiation to generate controllable heat in the plastic. The relationship of coupling distance, power level, and frequency to the heating response of susceptors is studied.Conclusions are presented, based on the results of statistically designed experiments, that suggest optimal conditions for effective welding processes.
Optimization of Process Parameters of an Injection Moulded Gear Using Taguchi Methodology
This paper suggests a systematic approach to reduce defects in injection moulded components. The component taken for analysis was an injection molded gear made of Stanyl (Nylon 4, 6)-15% Carbon Filled, used in an automobile. The analysis applies Taguchi Methodology to investigate the effects of process conditions on the shrinkage and warpage characteristics of the product made from a two cavity injection mould. The effect of seven process parameters on the Shrinkage and Warpage of the component were analyzed. An L18 standard orthogonal array (seven parameters with three levels) was chosen. The samples selected at random from each experiment were measured for warpage and shrinkage. The data thus obtained were analyzed with quality control tools like ANOVA (Analysis of Variance) and Factor Plots. Based on the results from ANOVA, the parameters which have significant effect on the quality of the product were identified. The factor plots gave information regarding the optimum levels of parameters to be maintained . The optimum levels of the parameters were used for conducting confirmatory experiments, which gave products with shrinkage and warpage within acceptable limits.
Enhanced Anhydride Coupling Agents for Wood Polymer Composites
In this study, we report on next generation coupling agents based on high molecular weight, random copolymers of ethylene and anhydride functional monomers that have been specifically designed for wood-polymer applications. A standard high-pressure free radical synthesis technique was used to create a high molecular weight ethylene copolymer with a very high level of reactive functionality (greater than 3 weight percent anhydride). This anhydride-functional- ethylene copolymer has been shown to improve the flexural strength and decrease the water absorption of wood-polymer composites when incorporated at loadings as low as 0.5 weight percent in the final part.
Ultrasound Aided Extrusion Process for Preparation of Polypropylene-Clay Nanocomposites
Two methods for the fabrication of PP/clay nanocomposites using a continuous ultrasound assisted process are compared. In the first approach a two stage process was implemented. The nanocomposites were prepared using a co-rotating twin screw extruder followed by a single screw extruder equipped with an ultrasonic die attachment. In the second method a single stage process was used. The nanocomposites were compounded using a single screw extruder with mixing elements and an ultrasonic die attachment. Two regimes of feeding were realized, namely, starved and flood feeding. The gap size in the ultrasonic treatment zone was varied. Die pressure and power consumption were measured. Similarities and differences of nanocomposites obtained by these two methods are discussed based on their rheological, mechanical properties, and structural characteristics.
Shape Memory Polymer Orthodontics
Shape memory polymers (SMPs) have been intensively investigated for multiple medical applications in recent years. In our lab, we have developed several SMPs with tailored transition temperatures, excellent shape fixing and shape recovery, and variable stiffness, with values ranging from > 1 GPa (hard) to < 1 MPa (soft). Recently, we have endeavored to apply two particular SMPs, a castable shape memory polymer (CSMP) and a shape memory rubber, to orthodontic appliances. We have measured the mechanical properties, water absorption, stain resistance, and stress stability and compared the results with currently used orthodontic polymers, revealing significant advantages. Prototype appliances are presently under evaluation. In this presentation, we will introduce the progress we have achieved and propose how SMPs can offer unique functionality to orthodontic appliances.
Development of a High-Pressure Slit Rheometer
In thin - wall injection molding processes, parts thinner than 1 mm are produced using high injection pressures and velocities. Modeling has not been successful in predicting process physics during molding. We have built a high pressure slit rheometer that enables us to measure the rheological properties of polymers at elevated pressures and temperatures. Measurements were done with polystyrene, and the results showed the effect of pressure and the effect of viscous heating on the viscosity. Results from such measurements will allow us to introduce viscosity pressure effects during mold filling of Thin-Wall Injection Molding.
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