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Manufacturing highly expanded thermo...

Kharbas, Hrishikesh Ashokrao.

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Manufacturing highly expanded thermoplastic polyurethane foams using novel injection molding foaming technologies.

Record Type:	Electronic resources : Monograph/item
Title/Author:	Manufacturing highly expanded thermoplastic polyurethane foams using novel injection molding foaming technologies./
Author:	Kharbas, Hrishikesh Ashokrao.
Published:	Ann Arbor : ProQuest Dissertations & Theses, : 2016,
Description:	161 p.
Notes:	Source: Dissertations Abstracts International, Volume: 78-10, Section: B.
Contained By:	Dissertations Abstracts International78-10B.
Subject:	Mechanical engineering. -
Online resource:	https://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=10189448
ISBN:	9781369679854

Manufacturing highly expanded thermoplastic polyurethane foams using novel injection molding foaming technologies.
Kharbas, Hrishikesh Ashokrao.

Manufacturing highly expanded thermoplastic polyurethane foams using novel injection molding foaming technologies. - Ann Arbor : ProQuest Dissertations & Theses, 2016 - 161 p.

Source: Dissertations Abstracts International, Volume: 78-10, Section: B.

Thesis (Ph.D.)--The University of Wisconsin - Madison, 2016.

This item must not be sold to any third party vendors.

This thesis summarizes the studies undertaken to achieve the objective of manufacturing injection-molded thermoplastic polyurethane (TPU) foams with high density reductions, desir-able microstructures, and customizable properties. TPU foams are quickly gaining market share in numerous applications in the sports and recreation as well as manufacturing industries. This is because TPU foams can be easily manufactured in a variety of densities, hardnesses, and mechanical properties, ranging from highly resilient to highly compressible foams, with different processing methods, such as injection molding, casting, and extrusion. Typically, TPUs are being foamed to a minimum density of 0.40 g/cm3 (400 kg/m3). It is the aim of this thesis to expand the understanding and processing knowledge of manufacturing TPU foams with densities as low as 0.25 g/cm3 (250 kg/m3), while maintaining desirable microstructures. It is also an aim of this thesis to develop a novel process to control foam properties locally in injection molded TPU foams. In the journey toward achieving the aforementioned objectives, five studies were conducted and are presented in this manuscript. An experimental study evaluating the CBA and PBA foaming of TPU has been undertaken. A novel foam injection molding process using CO2 + N2 as co-blowing agents to exploit the synergistic benefits of co-blowing agents was also evaluated in this study. It was found that PBA foaming can be vastly advantageous for foaming TPU by enabling large reductions in bulk densities without the harmful effects of chemical residue. This novel process of using co-blowing agents yielded the lowest bulk density while achieving the highest cell density and finest average cell size. In Chapter 3, nanoclay as a reinforcing filler was employed to increase the melt viscosity and to trigger heterogeneous nucleation in the TPU matrix, thereby improving the foamability of TPU while achieving a homogenous microstructure with low average cell size and high cell density. It is generally known that TPU's rebound resilience values decrease with decreasing foam density. It was observed that rebound resilience values could increase significantly if a tunable alignment of microcells can be produced within the part, even while reducing bulk densities. Through the action of mold inserts, the expanding microcells will thereby stretch and align with the intercellular TPU walls and individual molecules in the direction of mold opening. With aligned microcells, the softness of the foams improved significantly, while achieving lower hysteresis loss ratios or energy loss (dissipation). In Chapter 5, a core retraction mold capable of increasing cavity volume was designed and manufactured to enable further study of the phenomenon observed in Chapter 4, with better parameter control. Polypropylene (PP) was the material chosen to validate the capabilities of the mold and the applicability of this technology to materials other than TPU. Core retraction was used with the conventional microcellular injection molding (MIM) process to foam thick PP parts with high density reductions of 30% and 55%. The cavity volume was modified by changing the retraction distance, which resulted in varying density reductions. Mechanical and energy absorption properties of TPU foam can be varied with the density and microstructure of the foam. In Chapter 6, a new process is developed using core retraction and out-of-mold foaming to develop injection molded parts of varying cross-sections with varying mechanical properties. It was shown that, using this process, very low density foams of less than 0.25 g/cm3 can be produced while maintaining uniform and good microstructures. (Abstract shortened by ProQuest.).

ISBN: 9781369679854Subjects--Topical Terms:

649730
Mechanical engineering.
Subjects--Index Terms:

Foams

Manufacturing highly expanded thermoplastic polyurethane foams using novel injection molding foaming technologies.
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300 $a 161 p.
500 $a Source: Dissertations Abstracts International, Volume: 78-10, Section: B.
500 $a Publisher info.: Dissertation/Thesis.
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506 $a This item must not be sold to any third party vendors.
520 $a This thesis summarizes the studies undertaken to achieve the objective of manufacturing injection-molded thermoplastic polyurethane (TPU) foams with high density reductions, desir-able microstructures, and customizable properties. TPU foams are quickly gaining market share in numerous applications in the sports and recreation as well as manufacturing industries. This is because TPU foams can be easily manufactured in a variety of densities, hardnesses, and mechanical properties, ranging from highly resilient to highly compressible foams, with different processing methods, such as injection molding, casting, and extrusion. Typically, TPUs are being foamed to a minimum density of 0.40 g/cm3 (400 kg/m3). It is the aim of this thesis to expand the understanding and processing knowledge of manufacturing TPU foams with densities as low as 0.25 g/cm3 (250 kg/m3), while maintaining desirable microstructures. It is also an aim of this thesis to develop a novel process to control foam properties locally in injection molded TPU foams. In the journey toward achieving the aforementioned objectives, five studies were conducted and are presented in this manuscript. An experimental study evaluating the CBA and PBA foaming of TPU has been undertaken. A novel foam injection molding process using CO2 + N2 as co-blowing agents to exploit the synergistic benefits of co-blowing agents was also evaluated in this study. It was found that PBA foaming can be vastly advantageous for foaming TPU by enabling large reductions in bulk densities without the harmful effects of chemical residue. This novel process of using co-blowing agents yielded the lowest bulk density while achieving the highest cell density and finest average cell size. In Chapter 3, nanoclay as a reinforcing filler was employed to increase the melt viscosity and to trigger heterogeneous nucleation in the TPU matrix, thereby improving the foamability of TPU while achieving a homogenous microstructure with low average cell size and high cell density. It is generally known that TPU's rebound resilience values decrease with decreasing foam density. It was observed that rebound resilience values could increase significantly if a tunable alignment of microcells can be produced within the part, even while reducing bulk densities. Through the action of mold inserts, the expanding microcells will thereby stretch and align with the intercellular TPU walls and individual molecules in the direction of mold opening. With aligned microcells, the softness of the foams improved significantly, while achieving lower hysteresis loss ratios or energy loss (dissipation). In Chapter 5, a core retraction mold capable of increasing cavity volume was designed and manufactured to enable further study of the phenomenon observed in Chapter 4, with better parameter control. Polypropylene (PP) was the material chosen to validate the capabilities of the mold and the applicability of this technology to materials other than TPU. Core retraction was used with the conventional microcellular injection molding (MIM) process to foam thick PP parts with high density reductions of 30% and 55%. The cavity volume was modified by changing the retraction distance, which resulted in varying density reductions. Mechanical and energy absorption properties of TPU foam can be varied with the density and microstructure of the foam. In Chapter 6, a new process is developed using core retraction and out-of-mold foaming to develop injection molded parts of varying cross-sections with varying mechanical properties. It was shown that, using this process, very low density foams of less than 0.25 g/cm3 can be produced while maintaining uniform and good microstructures. (Abstract shortened by ProQuest.).
590 $a School code: 0262.
650 4 $a Mechanical engineering. $3 649730
650 4 $a Plastics. $3 649803
653 $a Foams
653 $a Injection molding
653 $a Microcellular
653 $a Thermoplastic polyurethane
690 $a 0548
690 $a 0795
710 2 $a The University of Wisconsin - Madison. $b Mechanical Engineering. $3 2094221
773 0 $t Dissertations Abstracts International $g 78-10B.
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792 $a 2016
793 $a English
856 4 0 $u https://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=10189448