The influence of displacements of tensioned fibers on the impregnation of fibrous layers with a polymer melt and on the final composite structure is studied. Using computer simulation, it is shown ...that, during impregnation, the structure of tensioned fibrous layers changes considerably depending on the initial arrangement and tensioning of fibers. The consolidated regions formed under the melt front move inside the impregnated layer with the advancing melt front. Displcement of the tensioned fibers and the formation of "washouts" favors the impregnation of internal layers, but cause significant inhomogeneity of the polymer structure. The surface (on the side of the melt flow) regions are more saturated with the polymer than the internal ones. A difference in the melt percolation mechanisms at various impregnation regimes is revealed. The effective permeability coefficients of a tensioned fiber layer are not constant but depend on the conditions and regimes of impregnation. Example given is a glass-fiber reinforced thermoplastic.
High-temperature thermoplastic polymers have made significant inroads in medical device applications during the last 20 years. These materials are characterized by their high heat resistance ...(>200°C); their strength, toughness, and durability; their ability to withstand several cycles and doses of all types of radiation; their ability to be molded into parts with extremely tight tolerances; their biocompatibility; and their long-term durability. The need for higher-temperature and higher-performance materials has led to the use of aromatic polysulfones (PSUs), aromatic polyimides, aromatic polyketones, and aromatic polysulfides in demanding components and applications like medical trays, surgical and dental instruments, medical electronic components, drug delivery components, and machined parts. Fluoropolymers have been used in packaging, tubing, insulating materials, endoscopic, endocardial and endotracheal devices, catheter liners, and surgical instruments. High-performance engineering thermoplastics comprise about 8% of all plastics used in medical devices. This chapter will discuss the use of aromatic polysulfones, aromatic polyimides, aromatic polyketones, aromatic polysulfides, and various fluoropolymers.
Polymer Modeling at The Dow Chemical Company Bicerano, Jozef; Balijepalli, Sudhakar; Doufas, Antonios ...
Journal of Macromolecular Science, Part C,
12/30/2004, Volume:
44, Issue:
1
Journal Article
Polymer modeling plays a vital role in industrial product and process development. Polymer modeling is an integral component of the research and development paradigm at The Dow Chemical Company. The ...integrated multidisciplinary and multiscale modeling paradigm implemented at Dow is reviewed first in this article. Overviews are then provided of polymer modeling performed in the context of seven different Dow projects, namely: mechanical properties of thermoplastic polymers; polymer/clay nanocomposites; polyol templating; flow induced crystallization and polymer process modeling; polymer design via high-throughput modeling; linear, branched, and/or network chain architectures; and water vapor transport in a polymer matrix composite.
Behavior of delamination crack growth in a carbon fiber reinforced plastic (CFRP) was investigated under static creep, two step creep and high temperature fatigue at 473K (200°C) using DCB specimens. ...The material was a unidirectional laminate, APC-2, which consists of carbon fibers, AS4, and a thermoplastic polymer, poly-ether-ether-ketone (PEEK). In the static and two step creep tests, the crack propagation rate against time, dl/dt, was governed by the energy release rate, G, regardless of the stress change. The crack propagation in high temperature fatigue was classified into time-dependent and cycle-dependent ones. In the former, the propagation rate against time, dl/dt, was correlated well with the energy release rate, G, and the relationship coincided with that in static creep (dl/dt=CcGmc; Cc and mc are material constants.). In the latter, the rate against load cycles, dl/dN, was controlled by the energy release rate range, ΔG(dl/dN=CfΔGmf; Cf and mf are material constants.). These imply that the crack grew under the small scale creep and small scale yielding condition, respectively. The condition of transition from the time-dependent crack propagation to the cycle-dependent one was given by a relationship, Cc∫t10Gmcdt=CfΔGmf, where t1 is the cycle period. The fracture surface in the time-dependent fatigue was characterized by the interface cracking between fibers and matrices. On the other hand, the matrix cracking near the fiber dominated in the cycle-dependent fatigue.
In this chapter, the fabrication of polymer 3D micro- and nanostructures by nanoimprint is reviewed. Multi-level and hierarchical 3D polymer structures can be directly fabricated by nanoimprint with ...prefabricated 3D molds or templates. Key applications of 3D nanoimprint, such as the fabrication of dual damascene structure for microelectronic fabrication and the fabrication of compound lenses for micro-optics are discussed. For multilayer 3D polymer structures, transfer bonding and sequential layer stacking are the standard fabrication techniques. Process details and fabrication examples are presented. Critical challenges in transfer bonding are also discussed and suggestions are provided for optimizing processing parameters to fabricate multilayer polymer micro- and nanostructures with high yield.
Flow characteristics of mixtures of ceramic powder and polymer were investigated with a cone and plate rheometer at high temperatures and at high solid concentrations (40-70 vol%). The ceramic ...powders were alumina powder and glass beads of various sizes and the polymers were thermoplastic polymers: polypropylene (PP), polyethylene (PE) and polystyrene (PS). The results are as follows: 1) The type of flow changed from Newtonian flow to non-Newtonian flow as the solid concentration increased and the particle size decreased. 2) The viscosity increased with decreasing particle size at a constant concentration of solid. 3) The apparent activation energy of flow evaluated at a constant rate of shear decreased with increasing particle size for the PP- and PS-ceramics systems. For the PE-ceramics system the activation energy was independent of the particle size.
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