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The Effect of Shrinkage Induced Interface Gap on the Thermal Contact Resistance between the Mold and Plastic in Injection Molding
Accurate modeling of the heat transfer from the vitrifying plastic to the mold is essential to obtain accurate simulation of the injection molding process. The thermal contact resistance is one parameter that affects the heat transfer in injection molding and is difficult to measure from laboratory experiments. In injection molding the thermal contact resistance in the post filling stage is shown to depend on the gap formed between the part and the mold wall due to part shrinkage. It is shown from shrinkage calculations that the thermal contact resistance is a time and space (location on the part surface) dependent parameter and its value can vary by orders magnitude during each molding cycle. The effects of this variation on the molding process are discussed.
A Procedure for Determination of Thermal Properties of Polymers from Transient Temperature Data
Thermal properties are important parameters in both process and product design. In the case of plastics, the need for quick and accurate determination of thermal properties is gaining importance due to large variety of blends and recycled materials that are becoming available. A procedure based on an inverse method is presented for the determination of thermal conductivity and specific heat. The method makes use of transient temperature measurements. The temperature measurements are made in reference metal blocks and no temperature sensors are inserted in the plastic specimen. The method shows potential for obtaining the thermal properties over a wide range of materials and temperatures, and as a function of pressure. The method has been tested in simulation and results are presented.
Improving Economic Efficiency - Key for Market Penetration of Continuous Carbon Fibre Reinforced Thermoplastics
Due to its outstanding properties continuous carbon fibre reinforced thermoplastic is ideal for many industrial applications. But, insufficient economic efficiency has been clearly identified to be the main obstacle for future penetration of the targeted markets. A significant potential for cost saving has been identified by process optimisation. Additional cost reduction is expected from the announced introduction of low cost carbon fibres. Cost analysis shows that the level of processing cost will fall significantly in the future. However, the investigation indicates that a cost level acceptable for mass markets like the automotive industry will not be achieved in general.
An Integrated Adaptive Control for Injection Molding
The objective of the research project is to investigate the possibility and develop a methodology and associated system to control the quality of injection molded parts on-line and adaptively. The project makes use of rigorous process simulation programs first to determine the initial machine-setup condition and then to predict the part quality. Such simulation programs are incorporated in the feed-forward loop of a multi-level control architecture which also consists of three feedback loops involving the machine parameters, process variables, and part-quality levels, respectively. This paper describes the research plans and some results up to date.
Process Monitoring and Optimisation in Injection Moulding with the Aid of New Measuring Sensors
With the aid of a newly developed, high-sensitivity measuring sensor system, it is possible to record the cavity pressure profile from outside the mould cavity, using the machine deformation as a directly correlating parameter. The measurement principle involves a pre-tensioned piezo element being coupled to the machine via a deformation cross-member. The system as a whole can be readily adapted, which means it can be retrofitted to existing injection moulding machines. The results of a study are presented, which looked into potential applications for this new generation of measuring sensors for process monitoring in injection moulding.
Optimization of Thermoforming with Process Modelling
The thermoforming process involves three stages, sheet reheat, forming and solidification. A polymeric sheet is heated in an oven to the desired forming temperature distribution. The sheet is then deformed to take the shape of the mould cavity and subsequently solidified. This work includes the modelling and experimental validation of both the sheet reheat and vacuum forming stages. The part considered is moulded in a box shape cavity mould that is supplied by Quality Thermoform. The modelling simulations and the corresponding experimental trials were performed at the Industrial Materials Institute. The heat transfer in the oven is modelled by employing combined radiation and natural convection. The sheet forming is modelled with a non-isothermal viscoelastic constitutive equation. The process stages are modelled in sequence, namely sheet reheat, sag and vacuum forming.
PP-EPDM Blends: Influence of Structure on Brittle-Ductile Transition
The impact behavior of polypropylene and polypropylene-rubber blends have been studied as function of temperature with notched Izod and single edged notched tensile methods. Varied are the rubber concentration (0-40 wt %) and the rubber particle size (0.3-4µm). With increasing rubber content and decreasing particle size the impact behavior is improved. The ductile deformation is accompanied with a strong temperature increase of the deformation zone and even a melting in the fracture zone. The impact enhancement process seem to be first a cavitation of the rubber particles, followed a strong plastic deformation of the matrix material ahead of the notch/crack. The deformation seem to be enhanced by a thermal blunting of the notch/crack.
TPE Behavior of Segmented Copolymers with Crystallizable Esteramide Units of Uniform Length
Segmented polyesteramides are synthesized fitm N,N'bisaibomethoxybenzoy)diamine as crystalline segments and poly(tetramethylene oxide) as soft segments. As diamine is mainly taken tetramethylene diamine, but also studied are C6 - C12 diamines. The crystalline segments are uniform in length. The poly tetramethylene oxide segments ranged in molecular weight from 250 - 2900. Also used are tetramethylene oxides with amine endgroups. As extender is sometimes used pentadiol. The polymerization is carried out in the melt at 250°C for 1 hour while vacuum is applied. The melting behavior of the copolymers is studied by differential scanning calorimetry. The mechanical properties are investigated on injection molded bars using dynamic mechanical analysis. The melting temperatures decrease with PTMO length and the length of the diamine. The glass transition temperatures were, for the polytetramethylene oxides of molecular weight of 650 and higher, little affected by the composition. The modulus decreased with PTMO length and the segmented copolymers have very high elongation's at break.
Crystallization Behavior of Regioregular Poly(3-Dodecylthiophene)
Non-isothermal and isothermal crystallization behavior of regioregular poly(3-dodecylthiophene) (P3DT) was investigated by differential scanning calorimetry (DSC) with an emphasis on the main chain crystallization. P3DT showed a sharp exothermic peak at 114°C which was attributed to the main chain crystallization and a broad one peaked at 59°C which was due to the side chain crystallization during cooling at 2.5°C/min from the melt. During heating, the side chains melted from 27 to 80°C, while the main chains exhibited up to three overlapped melting peaks. Avrami analysis for the non-isothermal crystallization revealed a sharp transition in the log(-ln(1-?)) vs. logt curves at the relative crystallinity of 63% for all cooling rates studied. The average Avrami exponent, n, was around 4.9 when the relative crystallinity was lower than 63%, while the n is around 1.5 when the relative crystallinity was higher than 63%. The non-isothermal crystallization activation energy was estimated to be 222kJ/mol by Kissinger method. Isothermal crystallization was also investigated at different temperatures. The formation of ordered structure and subsequent melting behavior were highly dependent on the crystallization temperatures and time. At lower crystallization temperatures, three melting peaks could be discerned. However, only one melting peak could be observed when the crystallization temperature was high.
The Fiber Melting Spinning of Thermotropic Liquid Crystalline/Nylon Blends
The morphology and properties of the composite systems of LCP, Vectra A 950 and Nylon 66 were investigated. The viscosity ratio of LCP and matrix has strong influence on their morphology. The tensile moduli of the LCP / Nylon composite fibers increase with LCP concentration, especially in the rich LCP concentration. The tensile strengths increase with LCP concentration only when LCP concentration is above 40 wt %. Compared to the pure Nylon 66 fiber, the 40 wt % LCP composite sample showed a 982.1 % increase in tensile modulus and a 123.3 % increase in tensile strength. The composite fibers have the negative effect in low LCP concentration. In rich LCP concentration, the strengths of composite fibers is above the linear addition values and the composite fibers have the positive effect.
In Situ Study of Microstructure Change during Polymerization of Thermotropic Liquid Crystalline Polymer
Microstructure change during polycondensation reaction for thermotropic liquid crystal polymer (LCP) poly(p-oxybenzoate/2,6-oxynaphthoate) was in situ studied by novel thin film polymerization technique. The polymerization was conducted on the heating stage of a microscope. The reaction process was observed in situ through the polarizing optical microscope. Reaction system started from a homogenous phase and changed into a heterogeneous one. Following sequence of morphological changes during the entire reaction was observed: generation of anisotropic phase, coalescence of liquid crystal (LC) droplets, formation of schlieren texture, annihilation of disclinations and formation of banded texture. Kinetics of the LC texture formation was investigated. The number of defects decreased with increasing reaction time through coalescence and annihilation. Annihilation process was studied. Copolymer was characterized by FTIR.
Thermal Decomposition Behavior of High Performance Liquid Crystalline Polymers Studied by TGA and TG-IR
The thermal decomposition behaviors of three liquid crystalline polymers were investigated. Namely, Polyester A is composed of p-hydroxybenzoic acid (HBA) and 2,6- hydroxynaphthoic acid (HNA) monomer units with a HBA/HNA molar ratio of 73/27; Poly(ester-amide) B is made of HNA, p-hydroxyl acetaniline (HAA), and terephthalic acid (TA) units with a HNA/HAA/TA molar ratio of 60/20/20; Polyester B is synthesized from HBA, biphenol (BP), and TA units with a HBA/BP/TA molar ratio of 2/1/1. The apparent activation energies (Ea) associated with the thermal degradation processes are determined by the Ozawa and Kissinger methods, using data from dynamic thermogravimetric analysis (TGA) experiments. The magnitudes of the Ea for these LCPs follow the order: Polyester B > Polyester A > Poly(ester-amide) B in both air and N2 environments. The stability of the samples at the beginning of the degradation processes follows the same order. Random chain scission and hydrogen abstraction are the main degradation mechanisms in N2 atmosphere. For all three LCPs, CO2 is the dominant degradation product during the entire testing periods in both N2 and air environments and the change of CO2 amount is consistent with the degradation rate. Relatively high percentages of O and N elements were found in the residues after TGA experiments in N2.
Surface Energy Investigation of Organic Light Emitting Polymers and its Substrates
The sessile-drop contact angle technique and the Lifshitz-van der Waals Acid-Base theory were utilized to investigate acid-base interactions and non-polar interactions of a polymer light emitting diodes (PLED) material, MEH-PPV. The same methodology was also applied to PLED substrate material, e.g., ITO films, without and with solvent cleaning treatments. Surface energy components of MEH-PPV and ITO films were calculated from the contact angle data with the 3-liquid approach. With above determined surface energy components, we further estimated the thermodynamic work of adhesion between the two solid films, MEH-PPV and ITO. Experimental data suggested that after solvent cleaning treatments, the Lifshitz-van der Waals parameter of surface energy (?LW) and hence the total surface energy of ITO films tended to increase. The methanol-treated ITO has the strongest adhesion with MEH-PPV in terms of acid-base work of adhesion, in other words, methanol is the most effective solvent in our studies for ITO films.
Thermal Degradation of Polyimide and Polyamide Liquid Crystalline Polymers
The thermal stability of a polymer is its most important property for applications in various fields. This paper reports some studies of the thermal degradation behaviour of polyimide and polyamide liquid crystalline polymers (LCP) in air and inert environments. It focusses on the determination of degradation kinetics and the evolved gas analysis of these LCPs. Characterization was done using thermo-gravimetric analysis (TGA) coupled with Fourier Transform Infra-Red (FTIR) spectroscopy. Observations indicated one-step degradation process in inert environment, while two steps were noticed in the case of air. The activation energies for these degradation processes were computed using Kissinger and Ozawa methods. Decomposition results show that polyamide is much less thermally stable than polyimide. Evolved gases are found to be H2O, CO, CO2 and various hydrocarbon fragments.
Evolution of Surface Free Energy during Thin Film Polymerization of Main-Chain Liquid Crystalline Polymers
By applying thin film polymerization technique and the Lifshitz-van der Waal-Acid-Base theory, we have determined, for the first time, time evolution of contact angle and surface free energy during the polymerization (or molecular weight increase) of liquid crystalline poly(p-oxybenzoate/2,6- oxynaphthoate). Surface free energy components of these main-chain liquid crystalline copolyesters were calculated from contact angle measurements using a Ramé-Hart goniometer and 3 liquids (water, glycerol and diiodomethane). Experimental data suggest that the Lewis-base parameter (?-) of poly(p-oxybenzoate/2,6- oxynaphthoate) decreases rapidly with progress of polymerization, while the Lewis acid parameter (?+) and the Lifshitz-van der Waals parameter (?LW) do not vary significantly.
Examination of Starve-Fed Single Screw Extrusion in Conventional and Barrier Feed Screws
An investigation of starved-fed single screw extrusion was initiated to study its improved mixing capabilities for the compounding of filler. Experiments were carried out in a 63.5 mm single screw extruder, examining the effect of degree of starvation on a conventional and barrier feed screw. Interest was focused on the mixing/melting mechanism of starved-fed solids-conveying as it affects the size and number of filler agglomerates observed in the extrudate. Both screws showed improved mixing quality with increased starvation. Trends in pressure, torque and power efficiency reflected the improvement in mixing.
Developments in High Strength I-PP: Technology Properties, Applications and Markets
In this paper the manufacture of a new family of high melt strength polypropylenes (HMS-PP), its benefits and application in the field of foam extrusion are discussed. A brief introduction into general pathways of influencing melt strength shows that it is the combination of both, a high strength and high drawability of the polymer melt (due to the introduction of some long-chain branches into the polymer structure) which is the main characteristic of these special materials. The rheological behavior is due to a special post polymerization (Daploy) process which introduces long-chain branches into the propylene polymer by comonomer bridging. The presentation of general properties resulting from the modified polymer architecture is followed by the discussion of benefits HMS-PP gives to polymer processing and to final material properties. In particular it is possible to manufacture non-crosslinked and thermoformable PP foams with a density range down to 0,1 g/cm3 and below by foam extrusion processes similar to the known from polyethylene and polystyrene. Main applications are lightweight packaging trays, beakers and containers as well as technical foams for automotive applications such as headliners, door liners, acoustic panels. In summary it is shown that the new family of high melt strength PP is a challenge and chance for PP to improve in existing and to enter into new polymer processing technologies, applications and markets.
Experimental Study of a New Dispersive Mixer
New dispersive mixing technology for extruders and mixing devices (1, 2) is based on creating strong elongational flow to achieve efficient dispersive mixing. These mixers are designed so that all fluid elements pass through the high stress regions several times. One version of the new mixer, CRD-4, was tested on a modular 45 mm extruder using a dryblend of polyethylene and polystyrene. The CRD-4 mixer was tested against a Leroy/Maddock mixer and a Maillefer mixer. The mixing capability was studied by microscopic analysis of the domain sizes of cross sections of extruded strands. The mixer performance was also analyzed with respect to pressure profiles, characteristic curves, and melt temperature distribution. It was found that the CRD-4 mixer achieves a fine level of dispersion under most circumstances. The Leroy/Maddock mixer has limited dispersive mixing capability at low screw speed; however, its dispersive mixing capability is better at high screw speed. The CRD-4 mixer is designed with forward pumping capability. As a result, the output-pressure characteristic of a screw with a 6D CRD-4 mixer is essentially identical to the same screw with the mixer replaced by a conveying section.
The Adjustable Grooved Feed Extruder
Grooved feed extruders have been around since about the 1960s. These extruders offer considerable advantages over conventional extruders, such as higher throughput, better stability, and the ability to process very high molecular weight polymers. There are some important disadvantages as well, for instance, higher motor load, wear is more likely, high pressures in the grooved region, and the screw design has to be adapted. The disadvantages of the grooved feed extruder disappear when the grooved feed extruder is made with a mechanism that allows adjustment of the groove depth. This paper will report on the development of grooved feed extruders that incorporate an adjustment mechanism that allows the depth of the grooves to be changed, during actual operation, from zero to full depth. Operational data from actual extrusion experiments are presented.
Use of Stereolithography for Extrusion Dies
Stereolithography has been used for many years to develop prototype parts. This is a good method for evaluating preliminary designs, but restricts the fabrication material to that used in the stereolithography equipment. It is more desirable to produce molds using stereolithography and prepare parts in the material of choice. This method has been successfully used for injection molding, but has not been evaluated for use in extrusion. This work examined the use of die inserts made by stereolithography for profile extrusion. An existing die was modified to allow epoxy inserts to be placed in the die so that the dimensions of the profile could be modified quickly without preparing a new metal die, but rather changing to a new epoxy die insert. This technique allows new profiles to be rapidly evaluated. In this work the lifetime of the epoxy inserts was determined for varying profile cross-sections. The effect of temperature and pressure on the lifetime of the epoxy die inserts was also measured.
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