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This thesis presents the effective strategies for increasing the volume expansion ratio and the cell density of polycarbonate foams. The basic strategies are: (a) to use sufficiently high pressure all through the extrusion system; (b) to use branched material; (c) to use high pressure drop rate at the die exit; (d) to use sufficiently high contents of CO 2; (e) to optimize the processing temperature. The effects of processing and material parameters on foam morphologies were thoroughly studied using a single-screw tandem foam extrusion system. By tailoring the processing and material parameters, polycarbonate foams with an expansion ratio of up to 19 times with a cell density over 1010 cells/cm3 were successfully produced. A continuous extrusion process for the manufacture of low-density microcellular polycarbonate (PC) foams using CO2 is presented. Due to its outstanding mechanical properties and high thermal resistance, polycarbonate foams have been considered as a candidate that will broaden the applications of foams in new industrial areas with high temperature environments.
Combining the science of foam with the engineering of extrusion processes, Foam Extrusion: Principles and Practice delivers a detailed discussion of the theory, design, processing, and application of degradable foam extraction. In one comprehensive volume, the editors present the collective expertise of leading academic, research, and industry specialists while laying the scientific foundation in such a manner that the microscopic transition from a nucleus to a void (nucleation) and macroscopic movement from a void to an object (formation) are plausibly addressed. To keep pace with significant improvements in foam extrusion technology, this Second Edition: Includes new chapters on the latest developments in processing/thermal management, rheology/melt strength, and biodegradable and sustainable foams Features extensive updates to chapters on extrusion equipment, blowing agents, polyethylene terephthalate (PET) foam, and microcellular innovation Contains new coverage of cutting-edge foaming mechanisms and technology, as well as new case studies, examples, and figures Capturing the interesting evolution of the field, Foam Extrusion: Principles and Practice, Second Edition provides scientists, engineers, and product development professionals with a modern, holistic view of foam extrusion to enhance research and development and aid in the selection of the optimal screw, die design, and foaming system.
In order to promote a deeper understanding of the cell opening behavior during foaming, a failure analysis of a cell wall was performed according to the Considere and Failure criteria using the uniaxial experimental data of a polymer melt. A theoretical approach to prediction of the cell wall rupture moment was proposed using two adjacent cubic-shaped cells. This concept was further extended to arrive at an estimation of the minimum threshold diameter of a foam extrudate to produce an open-cell foam structure. A continuous extrusion process for the manufacture of low-density, microcellular, open-cell thermoplastic foams is presented using a single-screw tandem extrusion foaming system. Fundamental studies have been conducted to investigate the effects of various processing parameters and materials compositions on the basic properties (i.e., extensional behavior, solubility, diffusivity, and initial foam extrudate shape) of plastic melts and melt/gas solutions that influence the cell morphologies of thermoplastic foams. The observed phenomena were essential in understanding and devising the processing strategies to achieve a desired foam structure. Based on the fundamental studies, this thesis presents the basic strategies for promoting a low-density, microcellular, open-cell thermoplastic foam. The effects of polymer blending, additives, processing temperature, blowing agent content, die geometry, and surface quenching on the final foam morphologies were thoroughly investigated to verify the proposed strategies. By tailoring the material compositions and processing conditions, low-density (>10 fold), microcellular (109 cells/cm 3), open-cell (>95%) thermoplastic foams were successfully achieved. Furthermore, a procedure for estimating gas loss from a foam structure was proposed in order to understand the effect of gas loss during open-cell content measurement using a gas pycnometer, and the corresponding open-cell content errors were calculated.
This thesis describes a continuous extrusion process for manufacturing low-density, microcellular polystyrene foam sheets using carbon dioxide as a blowing agent. Microcellular polymer foams are characterized by a cell density greater than 10$\sp9$ cells/cm$\sp3$ and a cell size on the order of 10 $\mu$m. To date, most research on the continuous processing of microcellular polymer foams has focused on nucleation and cell growth phenomena. Little work has been done on their shaping aspect. Two extrusion systems; namely, a single-screw extrusion system and a tandem extrusion system with two die designs were used in this research. The systems were designed and analyzed based on an axiomatic design framework. Detailed design and construction of their components, which include an extruder screw for the second extruder, dies, a diffusion enhancing device, a heat exchanger, a cooling mandrel, and a take-up roll system, were carried out subsequently. Critical experiments were conducted to evaluate the performance of the systems. PS foam sheets with a cell density in the range of 10$\sp9$ to 10$\sp#x10;$ cells/cm$\sp3,$ a controlled volume expansion ratio in the range of 2.1 to 17.9, and a uniform sheet thickness were successfully obtained from the designed tandem foam extrusion system.
A continuous extrusion process for the manufacture of low-density, fine-celled polypropylene foams is presented. Due to its outstanding functional characteristics and low material cost, polypropylene foams have been considered as a substitute for other thermoplastic foams in industrial applications. However, only limited research has been conducted on the production of polypropylene foams because of the weak melt strength, and no research has been conducted to investigate the mechanisms that govern the expandability of polypropylene foams. This thesis presents the effective strategies for increasing the volume expansion ratio as well as the mechanisms governing the foam density of polypropylene foams. The basic strategies taken in this study for the promotion of a large volume expansion ratio of polypropylene foams are: (a) to use a branched material for preventing cell coalescence; (b) to use a long-chain blowing agent with low diffusivity; (c) to lower the melt temperature for decreasing gas loss during expansion; and (d) to optimize the processing conditions in the die for avoiding premature crystallization. The effects of processing and materials parameters on the foam morphologies of polypropylene materials were thoroughly studied using a single-screw tandem foam extrusion system. A careful analysis of extended experimental results obtained at various processing conditions indicates that the final volume expansion ratio of the extruded polypropylene foams blown with butane is governed either by loss of blowing agent or by crystallization of the polymer matrix. By tailoring the processing conditions in the die, ultra low-density, fine-celled polypropylene foams with very high expansion ratio up to 90-fold were successfully produced from the branched polypropylene resins. Fundamental studies have also been conducted to investigate the effect of various processing and materials parameters on the thermodynamic, thermal and melt fracture behaviors of polypropylene melts with foaming additives that influence the cell morphology of polypropylene foams.
Foamability of Thermoplastic Polymeric Materials presents a cutting-edge approach to thermoplastic polymeric foams, drawing on the latest research and guiding the reader through the fundamental science, foamability, structure-property-processing relationship, multi-phase polymeric materials, degradation characteristics of biodegradable foams and advanced applications. Sections provide detailed information on foam manufacturing technologies and the fundamental science behind foaming, present insights on the factors affecting foamability, cover ways of enhancing the foamability of various polymeric materials, with special focus on multi-phase systems, discuss the degradation of biodegradable foams and special morphology development for scaffolds, packaging, acoustic and super-insulation applications, as well as cell seeding studies in scaffolds. Each application has specific requirements in terms of desired properties. This in-depth coverage and analysis helps those looking to move forward with microcellular processing and polymer foaming. This is an ideal resource for researchers, advanced students and professionals interested in the microcellular processing of polymeric materials in the areas of polymer foaming, polymer processing, plastics engineering and materials science. Offers in-depth coverage of factors affecting foamability and methods for enhancing the foamability of polymeric materials Explores innovative applications in a range of areas, including scaffolds, acoustic applications, packaging and super-insulation Provides a comprehensive, critical overview of the state-of-the-art, possible future research directions, and opportunities for industrial application