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A novel generation of porous implants based on Ultra High Molecular Weight Polyethylene (UHMWPE) for knee and hip joints has been developed. These porous, rather than solid (non-porous) commercial PE implants, could help to provide internal lubrication with synovial fluid to reduce wear and erosion of implants. The porous structure has been developed by a non-foaming, leaching (washing-out) technique using commercial water-soluble mineral salts as fillers (porogens). The size, shape and content of the salts determine the size, shape and amount of interconnected pores in the samples produced by compression molding process. The porous structure and mechanical properties have been studied and compared with non-porous UHMW-PE materials.
In this work, porous polyethylene films were prepared by the template-leaching method. The leachable component was tapioca starch, which was blended with low density polyethylene (LDPE) to respectively produce blends of 2, 4, 6, 8, 10, and 12% by weight of starch. Each blend was melt-extruded to obvtain LDPE/starch films having thicknesses of 50, 80, and 100 ?m. The porous structure of the films was then formed by removing starch particles from the films via either acidic or enzymatic hydrolytic leaching techniques. For acidic hydrolysis, the films were immersed in solutions of HCL, H2SO4, and HNO3 under various conditions while a solution of ?-amylase was employed for enzymatic hydrolysis. For acidic hydrolysis, starch particles were best removed using 5 N HNO3 at 65°Celsius corresponding to a reduction in the starch level of ca. 85%, whereas, for enzymatic hydrolysis, the reduction was much lower at ca. 35%.
For about the first-third of the rotational molding heating cycle, the polymer free of the mold surface flows as a powder. Although it appears that the powder is cohesionless at room temperature, there is strong evidence that there is increasing cohesion during heating. This changes the nature of powder flow from avalanche to block flow with frictional or shear flow occurring between the mold surface and the powder layer against it. Stress analyses on the powder bed show that shear forces between powder particles and between the particles and the mold surface are linearly proportional to the normal force on the powder, and yield two fundamental powder properties, powder cohesiveness and particle-to-particle coefficient of friction. The parameters that affect these relationships and methods of measuring them are discussed.
Instantaneous Property Predictive Models are very valuable in the operation of a multiple reactor high-density polyethylene (HDPE) process. The purpose of these models is to accurately predict resin physical properties, such as density, melt index (MI2) and molecular weight distribution (MWD) from reactor synthesis conditions. This paper describes how a predictive model was developed by regressing Gel Permeation Chromatograms (GPC) deconvolution constants versus reactor synthesis conditions. Briefly, the model generates a GPC trace of the resin produced in each stage of reaction; the data from all the stages are summed up to give a composite trace; the number average (Mn) and weight average (Mw) molecular weights are calculated from the composite. Previously published correlations (1) are then used to predict MI2, MWD and density from the composite Mn and Mw and comonomer concentrations. Predictive results for thirty-four resins are presented.
The flow of melt in runner systems of injection molds takes place in channels whose cross section can be either circular, square, rectangular or of any other geometrical form. In order to obtain a uniform distribution of the melt at low pressures, knowledge of the pressure drop along the flow path is important. Based on the modern developments in rheology, this paper presents easily applicable relationships for calculating pressure drop in the flow channels of different geometry taking flow rate, resin type and melt temperature into account. Worked-out examples illustrate the use of the equations presented, which were found to agree well with the results in the practice.
The shrinkage behavior plays an important role in the determination of the final dimensions of plastic injection molded parts. Materials used, mold and part designs, and processing conditions all can have great influence on parts' final dimensions. In this study, the experimental design approach of L27 array is used to study the effects of three processing parameters (melt temperature, mold temperature, and holding pressure) on the shrinkage behavior (along-the-flow and across-the-flow directions) of injection molded parts of polystyrene. A multiple regression model is set up to predict the dimensions and the goodness of the model is verified by the confirmation data. Previous research results are reviewed and compared with.
A microcellular plastic part with an injection molding method can be treated as a sandwich structure in which a foamed core encased by a skin frame. It is unique characteristics for microcellular plastic injection molding part because of a uniform cell distribution across the foamed section except the skin. The simple models based on this structure for prediction of mechanical properties of microcellular plastics are proposed and verified by the injection molding microcellular sample tests. The weight reduction percentage of the whole part and the skin thickness are used as input data to calculate the mechanical properties. The effect of skin-core ratio for the mechanical properties of foamed part is also discussed in this paper.
The Plastics Resources for Educators Program (PREP) has produced a vast array of multimedia training materials for plastics educators and the plastics industry. Products completed so far include graphics, animations, and teaching modules. The latest product is a suite of plastics processing simulators called the PREP Virtual Factory." This fully interactive teaching facility includes "machines" for extrusion injection molding and blow molding. Using these tools learners can discover proper operating procedures and investigate the influence of various process parameters on product properties."
A study of pressurization and energy characteristics of strainer disk elements for different sizes of ZSK twin-screw extruder with PE-HD are presented. The work compares the results of a complex 3D CFD model of ZSK40 strainer disks with some experimental results. As the manual setup of such a complex CFD model is rather expensive, a method has been developed to decompose the complete model into two simple parts. These parts can be set up easily in a batch procedure. Finally the effect on the pressurization and energy characteristics is discussed when doing a scale up from a ZSK40 to a ZSK92 or a ZSK250.
The objective of this work was the development of a procedure to establish the optimization design basis of plastic parts by using Computer Aided Design (CAD)/Computer Aided Engineering (CAE) software. An example is show applying the procedure on a specific problem where the part evaluated was a commercial compact disk (CD) case. The simulation results were obtained through a filling/cooling simulation program for the injection molding process and a three-dimension solid modeler program. After modifying the process conditions, gate dimensions and part design, a new case design was evaluated. The simulation results, maximum wall shear stress and shear stress in service showed a best behavior in use for the new proposal.
Many sources of variation in the process can contribute to product inconsistencies among a batch of molded parts in the injection molding process. These sources include materials, machine control capability and conditions, human factors, and environment. This paper provides an overview of the means for measuring process capability and the methods for maintaining process robustness in injection molding. Furthermore, an experimental study utilizing statistical methods provides a simple and effective means of identifying capable switchover methods in the injection molding cycle to maintain the shot-to-shot process repeatability for injection molding operation. Five switchover modes are compared.
Basell currently has over 25 polyolefin production lines at our various plants throughout the world utilizing NMR for advanced process control. These units include online units, which provide virtually continuous process feedback control as well as offline and laboratory units to provide checks of the various processes. Correlations have been developed to monitor a number of process variables of interest. The use of NMR for advanced process control has reduced the need for frequent wet" tests has reduced "off-spec" materials has improved product transition times and has allowed the reallocation of resources to other parts of the plants. The intent of this paper is to give a general overview of process control by NMR and in particular at Basell and how it is implemented."
Applications of nanometer-sized particles can facilitate the formation of microcellular foams in the continuous extrusion foaming process. Both intercalated and exfoliated polystyrene/nanoclay composites were foamed using CO2 as the foaming agent. The resulting foam structure is compared with that of pure polystyrene and polystyrene/talc composite. It is found that unique foam structure can be created by changing the content and the dispersion of nanoclay particles. The effects of nanoclay dispersion on the polymer melt rheology and the foaming process are discussed. Combining nanoclay compounding with microcellular foaming provides a new technique for the design and control of foam structure.
In order to develop a polycarbonate (PC)/ acrylonitrile-butadiene-styrene (ABS) product with a high content of recycled PC, a low molecular weight virgin PC was added to recycled PC to minimize batch-to-batch property variations in the compounded product. Six PC/ABS blends were prepared on a twin screw extruder by mixing 50 wt% virgin ABS and 0-25 wt% low molecular weight virgin PC with 25-50 wt% high purity recycled PC recovered from end-of-life electronics. These blends were characterized rheologically and mechanically. Results showed that this strategy could yield consistent quality resin blends with a high recycle content.
Ethylene-1-butene, ethylene-1-pentene, ethylene-1-hexene, ethylene-1-heptene, ethylene-octene and ethylene-1-nonene random copolymers were prepared by Ziegler-Natta catalyst system and their rheological and thermal properties were determined. The rheological properties (zero shear viscosity, zero shear first normal stress coefficient, steady state viscosities and components of complex modulus are decreasing with the increase of co-unit size because the entanglement density decreases with the increase of co unit side group length. The melting point, heat of fusion also decrease with the increase of co-unit side group length because of the decrease of crystallinity.
This works tries to correlate the influence of the thermal and deformation histories that the polymer blend undergoes during its manufacturing on its microstructure. This is done by using a rheological model for polymer blends in the numerical simulation of this deformational field. The applied model is a modification of Bousmina et al in the Grmela's  model for two immiscible viscoelastic fluids and allows to obtain the size and shape of the dispersed particle of these heterogeneous systems through the deformational parameters, as shear rate and physical properties, as interfacial tension and viscosity of the polymers.
Plastics are undivided parts of today's human life and their possibilities in new applications are growing almost every day. Production and processing of plastics are very promising industries and research fields. In this work it will be presented history and present situation, and future possibilities in Croatian plastics industry. It will be also presented educational and research institutions that are concentrated at four Croatian Universities in: Zagreb (the biggest one), Osijek, Rijeka and Split, their field of interests, research results and knowledge that they are offering to students and industry experts.
Advances in plastic expansion technology have created a new class of gasket material, called expanded polytetrafluoroethylene (ePTFE). The material comprises a highly fibrillated and porous microstructure that contributes to its excellent sealing capability. Its mechanical and sealing properties have been studied by the room temperature tightness test. The results suggest that ePTFE has better compressibility, creep resistance and sealability than other PTFE-based gaskets. These properties combined with excellent chemical resistance and thermal stability make ePTFE one of the most versatile gasket materials available today. The key factor that leads ePTFE to its excellent properties is the specialized process technology.
Low molecular weight polypropylene (Eastman, Epolene N-15) has been chemically modified during reactive processing using a catalytic hydrosilylation reaction in a batch mixer under various processing conditions (1,2). The hydrosilylated PP (Si-PP) has been blended with a commodity polypropylene resin (Montell, KF 6100) in a batch mixer at concentrations ranging from 5-20 wt%. This PP blends have been characterized in terms of their rheological properties as well as their thermal and impact properties. Addition of the hydrosilylated PP reduces the processing torque and the shear viscosity, while the impact properties depend on the crystallinity, Si-PP content and dispersed phase morphology.
The Saint-Gobain Advanced Ceramics Corp. of Amherst, N.Y. introduces, CarboGlide™, a new family of polymer process aids for thermoplastic resins. These boron nitride based polymer process aids eliminate shark skin melt fracture and postpone, to much higher shear rates, the onset of gross melt fracture. Extrusions of CarboGlide™ and mLLDPE into blown film have resulted in a three-fold increase in rate. In addition, improvements in film quality, such as, better caliper control, mitigation of film streaking, control of coefficient of friction, enhanced gloss, reduced haze and enhanced heat seal-ability are realized with CarboGlide™. Mechanical properties of the film, such as yield strength and Graves tear, are not debased. This unique combination of both process and product improvements, at equivalent to fluoroelastomer process aid costs, demonstrates that CarboGlide™ is the next generation of polymer process aids.
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