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The Effects of Crosslinking on Foaming of EVAChen, Nan 20 August 2012 (has links)
The effects of crosslinking on EVA foaming are studied in this thesis. A fundamental approach was applied to describe the influences of crosslinking on EVA/gas viscosities, gas solubility and diffusivity in EVA, EVA foaming nucleation and early stage of bubble growth, which leads to a better understanding of the plastic foaming mechanism.
Although crosslinked polyolefin foaming technology has been well applied in industry, more fundamental and thorough studies are demanded to understand the mechanism, which can serve to improve the present technology. The shear and extensional viscosities have been measured for the chemically crosslinked EVA with dissolved gas which could not be found from literature. Furthermore, by controlling the crosslinking agent amount, the polymer melt strength/viscosity can be controlled, so as to obtain optimum foam morphology. The crosslinking also has effects on the diffusivity and solubility of a blowing agent inside EVA. The solubility and the diffusivity of the blowing agent in the EVA decrease with the crosslinking degree increases. The diffusivity decrease makes more gas is utilized for the foaming rather than leak out of the polymer matrix quickly.
This thesis also presents the fundamental studies on the effects of crosslinking on cell nucleation and early bubble growth. Theoretical work and in-situ visualization experimental results indicate that partial crosslinking leads to higher cell nucleation density and slower bubble growth, both of which benefit a fine-cell foam morphology generation.
Last but not least, an optimized foaming process was conducted to produce chemically crosslinked EVA foams with large expansion ratios in a batch system, using a chemical blowing agent. The results determine that an optimal crosslinking degree is critical for the crosslinked EVA foaming with maximum expansion ratio. Furthermore, all research results not only benefit the foaming of crosslinked EVA, but also serve the better production of other crosslinked polyolefin foams.
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The Effects of Crosslinking on Foaming of EVAChen, Nan 20 August 2012 (has links)
The effects of crosslinking on EVA foaming are studied in this thesis. A fundamental approach was applied to describe the influences of crosslinking on EVA/gas viscosities, gas solubility and diffusivity in EVA, EVA foaming nucleation and early stage of bubble growth, which leads to a better understanding of the plastic foaming mechanism.
Although crosslinked polyolefin foaming technology has been well applied in industry, more fundamental and thorough studies are demanded to understand the mechanism, which can serve to improve the present technology. The shear and extensional viscosities have been measured for the chemically crosslinked EVA with dissolved gas which could not be found from literature. Furthermore, by controlling the crosslinking agent amount, the polymer melt strength/viscosity can be controlled, so as to obtain optimum foam morphology. The crosslinking also has effects on the diffusivity and solubility of a blowing agent inside EVA. The solubility and the diffusivity of the blowing agent in the EVA decrease with the crosslinking degree increases. The diffusivity decrease makes more gas is utilized for the foaming rather than leak out of the polymer matrix quickly.
This thesis also presents the fundamental studies on the effects of crosslinking on cell nucleation and early bubble growth. Theoretical work and in-situ visualization experimental results indicate that partial crosslinking leads to higher cell nucleation density and slower bubble growth, both of which benefit a fine-cell foam morphology generation.
Last but not least, an optimized foaming process was conducted to produce chemically crosslinked EVA foams with large expansion ratios in a batch system, using a chemical blowing agent. The results determine that an optimal crosslinking degree is critical for the crosslinked EVA foaming with maximum expansion ratio. Furthermore, all research results not only benefit the foaming of crosslinked EVA, but also serve the better production of other crosslinked polyolefin foams.
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Surface Tension Measurement of High Density Polyethylene and Its Clay Nanocomposites in Supercritical NitrogenWei, Hua 08 1900 (has links)
Surface tension of a polymer melt in a supercritical fluid is a principal factor in
determining cell nucleation and growth in polymer microcellular foaming.
Previous work has presented the surface tension of the amorphous polymer, polystyrene
(PS), in supercritical CO2 determined by Axisymmetric Drop Shape Analysis-Profile
(ADSA-P), together with theoretical calculations for a corresponding system. The
dependences of the surface tension on temperature, pressure and polymer molecular weight
were discussed and the physical mechanisms for three main experimental trends were
explained using Self Consistent Field Theory (SCFT).
This thesis introduces recent work on the surface tension measurement of the crystalline
polymer, high density polyethylene (HDPE), in supercritical N2 under various temperatures
and pressures. The surface tension was determined by ADSA-P and the results were
compared with those of the amorphous polymer PS. The dependence of the surface tension
on temperature and pressure, at temperatures above the HDPE melting point, ~125°C, was
found to be similar to that of PS; that is, the surface tension decreased with increasing
temperature and pressure. Below 125°C and above 100°C, HDPE underwent a process of
crystallization, where the surface tension dependence on temperature was different from that
above the melting point, i.e., decreased with decreasing temperature. Differential Scanning
Calorimetry (DSC) characterization of the polymer was carried out to reveal the process of
HDPE crystallization and relate this to the surface tension behavior. It was found that the
amount of the decrease in surface tension was related to the rate of temperature change and hence the extent of polymer crystallization.
In the second part of the thesis, surface tension dependences on temperature, pressure
and clay concentrations were studied for HDPE nano-clay composites (HNC) and compared
with pure HDPE. It was found the trends with temperature and pressure were the same with
PS in CO2 and HDPE in N2; that is, the surface tension decreased with increasing
temperature and pressure. In all nanocomposite samples, the surface tension decreased
compared with pure HDPE. This could be a good explanation for the better polymer foaming
quality with the addition of clay in the polymer. A minimum surface tension was found with
the sample at ~3% concentration of clay. The degree of crystallinity of HNC was analyzed
by Differential Scanning Calorimetry (DSC) at different clay concentrations. A minimumz
crystallinity was also found at the clay concentration of 3%. The possible relationship
between surface tension and polymer crystallinity was discussed.
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Surface Tension Measurement of High Density Polyethylene and Its Clay Nanocomposites in Supercritical NitrogenWei, Hua 08 1900 (has links)
Surface tension of a polymer melt in a supercritical fluid is a principal factor in
determining cell nucleation and growth in polymer microcellular foaming.
Previous work has presented the surface tension of the amorphous polymer, polystyrene
(PS), in supercritical CO2 determined by Axisymmetric Drop Shape Analysis-Profile
(ADSA-P), together with theoretical calculations for a corresponding system. The
dependences of the surface tension on temperature, pressure and polymer molecular weight
were discussed and the physical mechanisms for three main experimental trends were
explained using Self Consistent Field Theory (SCFT).
This thesis introduces recent work on the surface tension measurement of the crystalline
polymer, high density polyethylene (HDPE), in supercritical N2 under various temperatures
and pressures. The surface tension was determined by ADSA-P and the results were
compared with those of the amorphous polymer PS. The dependence of the surface tension
on temperature and pressure, at temperatures above the HDPE melting point, ~125°C, was
found to be similar to that of PS; that is, the surface tension decreased with increasing
temperature and pressure. Below 125°C and above 100°C, HDPE underwent a process of
crystallization, where the surface tension dependence on temperature was different from that
above the melting point, i.e., decreased with decreasing temperature. Differential Scanning
Calorimetry (DSC) characterization of the polymer was carried out to reveal the process of
HDPE crystallization and relate this to the surface tension behavior. It was found that the
amount of the decrease in surface tension was related to the rate of temperature change and hence the extent of polymer crystallization.
In the second part of the thesis, surface tension dependences on temperature, pressure
and clay concentrations were studied for HDPE nano-clay composites (HNC) and compared
with pure HDPE. It was found the trends with temperature and pressure were the same with
PS in CO2 and HDPE in N2; that is, the surface tension decreased with increasing
temperature and pressure. In all nanocomposite samples, the surface tension decreased
compared with pure HDPE. This could be a good explanation for the better polymer foaming
quality with the addition of clay in the polymer. A minimum surface tension was found with
the sample at ~3% concentration of clay. The degree of crystallinity of HNC was analyzed
by Differential Scanning Calorimetry (DSC) at different clay concentrations. A minimumz
crystallinity was also found at the clay concentration of 3%. The possible relationship
between surface tension and polymer crystallinity was discussed.
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Carbon Dioxide Physical Foaming of Polymer Blends:-Blend Morphology and Cellular Structure- / 高分子ブレンドの二酸化炭素物理発泡成形-ブレンドモルフォロジーと多孔構造Rahida Wati Binti Sharudin 24 September 2012 (has links)
Kyoto University (京都大学) / 0048 / 新制・課程博士 / 博士(工学) / 甲第17163号 / 工博第3653号 / 新制||工||1555(附属図書館) / 29902 / 京都大学大学院工学研究科化学工学専攻 / (主査)教授 大嶋 正裕, 教授 山本 量一, 教授 宮原 稔 / 学位規則第4条第1項該当
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Experimental Preparation of Microcellular Polymer Blend Foams by Exploiting Structural non-Homogeneity / 構造的不均質性を利用した微細発泡高分子ブレンド体の創製に関する研究Kohlhoff, Dominik 26 November 2012 (has links)
Kyoto University (京都大学) / 0048 / 新制・課程博士 / 博士(工学) / 甲第17229号 / 工博第3656号 / 新制||工||1556(附属図書館) / 29975 / 京都大学大学院工学研究科化学工学専攻 / (主査)教授 大嶋 正裕, 教授 瀧川 敏算, 教授 山本 量一 / 学位規則第4条第1項該当
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