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The Extrusion of Microcellular Foams...

Miller, Dustin Michael.

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The Extrusion of Microcellular Foams Utilizing Gas-Saturated Pellets and Solid-State Nucleation.

Record Type:	Electronic resources : Monograph/item
Title/Author:	The Extrusion of Microcellular Foams Utilizing Gas-Saturated Pellets and Solid-State Nucleation./
Author:	Miller, Dustin Michael.
Description:	198 p.
Notes:	Source: Dissertation Abstracts International, Volume: 73-07(E), Section: B.
Contained By:	Dissertation Abstracts International73-07B(E).
Subject:	Mechanical engineering. -
Online resource:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=3501676
ISBN:	9781267234940

The Extrusion of Microcellular Foams Utilizing Gas-Saturated Pellets and Solid-State Nucleation.
Miller, Dustin Michael.

The Extrusion of Microcellular Foams Utilizing Gas-Saturated Pellets and Solid-State Nucleation. - 198 p.

Source: Dissertation Abstracts International, Volume: 73-07(E), Section: B.

Thesis (Ph.D.)--University of Washington, 2011.

This work explores the use of solid-state nucleation in pellets as a means to decouple cell nucleation in extrusion from cell growth. This is achieved by using gas-saturated PLA pellets as input to the extruder. The research presented in this dissertation explores the creation of microcellular and nanocellular polymer foam structures and covers the fundamental aspects of polymeric foam formation from a variety of polymers using sub-critical carbon dioxide as a physical blowing agent. Various foam processing techniques were developed during the course of this work, all of which utilize solid-state nucleation and sub-critical gas pressures. The influence of thermodynamic variables that control foam formation are studied in detail. Resultant foam morphologies are characterized and related back to processing conditions. Advances in foam processing developed in this work also led to the investigation of material properties to determine the effect structure, specifically cell size, has on material properties. The motivation for this work stems from the need to develop environmentally benign foams and processes for applications ranging from biodegradable food packaging to insulation and aircraft components.

ISBN: 9781267234940Subjects--Topical Terms:

649730
Mechanical engineering.

The Extrusion of Microcellular Foams Utilizing Gas-Saturated Pellets and Solid-State Nucleation.
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020 $a 9781267234940
035 $a (MiAaPQ)AAI3501676
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100 1 $a Miller, Dustin Michael. $3 3174052
245 1 4 $a The Extrusion of Microcellular Foams Utilizing Gas-Saturated Pellets and Solid-State Nucleation.
300 $a 198 p.
500 $a Source: Dissertation Abstracts International, Volume: 73-07(E), Section: B.
500 $a Adviser: Vipin Kumar.
502 $a Thesis (Ph.D.)--University of Washington, 2011.
520 $a This work explores the use of solid-state nucleation in pellets as a means to decouple cell nucleation in extrusion from cell growth. This is achieved by using gas-saturated PLA pellets as input to the extruder. The research presented in this dissertation explores the creation of microcellular and nanocellular polymer foam structures and covers the fundamental aspects of polymeric foam formation from a variety of polymers using sub-critical carbon dioxide as a physical blowing agent. Various foam processing techniques were developed during the course of this work, all of which utilize solid-state nucleation and sub-critical gas pressures. The influence of thermodynamic variables that control foam formation are studied in detail. Resultant foam morphologies are characterized and related back to processing conditions. Advances in foam processing developed in this work also led to the investigation of material properties to determine the effect structure, specifically cell size, has on material properties. The motivation for this work stems from the need to develop environmentally benign foams and processes for applications ranging from biodegradable food packaging to insulation and aircraft components.
520 $a The primary focus of this dissertation resides in the development and characterization of the Gas-Saturated Pellet (GSP) extrusion process. This work initially sought to find out if the GSP extrusion process could be used to create microcellular foams in new materials other than that produced in previous work with polyvinylchloride. The result of this work has been the extension of the GSP extrusion process to incorporate two new polymer systems including polylactide and polyetherimide. The GSP process and resulting foam structures were characterized for these two polymers, enabling both future academic and industrial paths to continue forward.
520 $a In addition to the development of suitable processing conditions to create microcellular foams in new polymers, a significant effort of this work was spent on developing a better scientific understanding of the GSP process. The two new polymers systems in addition to further work on polyvinylchloride provide the vehicle for this exploration. The first area of interest at the beginning of this work was the characterization of gas diffusion in polymer pellets. Although a great deal of work has previously been done in the field of solid-state foams on gas diffusion in polymer sheet, no attempts to date had previously been made to model gas diffusion in pellets for use in extrusion. A framework for the investigation of diffusion in polymer pellets is presented here on spherical polylactide. These methods may also be directly applied to additional polymers in the future, and with small modifications, can be extended to cylindrical or other geometric forms. The investigation into the diffusion in spherical polymer pellets in this work culminates in the development and verification of a finite difference model that predicts the gas sorption as a function of time across multiple pressures and also gives the gas concentration profile through the thickness of a pellet as a function of time. The finite difference model can immediately be used for either future research or the industrial commercialization of the GSP extrusion process.
520 $a Prior work done on the GSP extrusion process hypothesized that the process utilized solid-state nucleation as the basis for foam creation. This hypothesis purposes a significant departure from the well studied microcellular gas-injection extrusion process which uses supercritical gas pressures and a rapid pressure drop device to induce high nucleation densities in the polymer melt. Although logical arguments for the existence of solid-state nucleation in the GSP process have been made, no supporting data had been produced. The question of whether the GSP extrusion process relied on solid-state nucleation became a primary question to investigate in this work, and constituted the most challenging, but most scientifically interesting aspects of this work. The results of this work serve to support the solid-state nucleation hypothesis through indirect evidence of extrusion pressure drop and pressure drop rates. These pressures are compared to those required for homogeneous nucleation in the gas-injection extrusion process and show that equivalent bubble densities produced by the GSP extrusion process can be achieved at pressure drop rates multiple orders of magnitude lower than the gas-injection methods. The significance of this finding means that the GSP extrusion process can now be shown as a unique microcellular extrusion process to that of other foaming techniques. The GSP extrusion processes ability to separate nucleation from cell growth will serve to motivate future work focusing on exploiting this attribute of the process to potentially achieve greater control and flexibility in foam morphologies.
590 $a School code: 0250.
650 4 $a Mechanical engineering. $3 649730
650 4 $a Polymer chemistry. $3 3173488
690 $a 0548
690 $a 0495
710 2 $a University of Washington. $3 545923
773 0 $t Dissertation Abstracts International $g 73-07B(E).
790 $a 0250
791 $a Ph.D.
792 $a 2011
793 $a English
856 4 0 $u http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=3501676