Risch, Brian G.,
Thesis (Ph. D.)--Virginia Polytechnic Institute and State University, 1994. / Vita. Abstract. Includes bibliographical references. Also available via the Internet.
19 September 2018
No description available.
Chu, Edward F.-H. (Feng-Hwa)
No description available.
01 January 1973
(has links) (PDF)
The distortion of molecular chains in amorphous crosslinked networks from their most probable configuration by Stretching gives rise to a decrease in configurational entropy. As a consequence, the tendency toward crystallization is so enhanced that even natural rubber can crystallize upon stretching at room temperature. e Crystallization developed in rubber strtched in sim- A pie extension has been directly investigated by X-ray, Ik density and other methods , When crystallization takes place in rubber upon stretching, the resulting crystallites prevent slippage of chain molecules past each other because these crystallites act as multifunctional crosslinkages . As a consequence, raw rubber docs not show any plastic flow at higher extensions. This was observed by Treloar^ from an experiment on the recovery of deformed rubber to its original length upon warming.
Design and operation of enzymatic reactive crystallization: Applications in chiral purity and kinetically controlled synthesisEncarnacion-Gomez, Luis G. 07 January 2016 (has links)
The work presented in this thesis is aimed to design efficient reactive crystallization operations that could potentially be implemented in the manufacture of enantiomerically pure compounds and β-lactam antibiotics. Multiple aspects of solution thermodynamics, reaction engineering and crystallization from complex solutions are involved and will be discussed in detail through the following chapters. The first piece of this work utilizes reactive crystallization for the manufacture of enantiomerically pure amino acids. Chemo-enzymatic stereoiversion reactions are used to enrich saturated or supersaturated solutions to favor the selection of a desired enantiomer. L-Methionine and L-Phenylalanine were resolve successfully from racemic mixtures by cyclic stereoinversion. r D-amino acids were oxidized by D-amino acid oxidase (D-AAO) and the resulting ketoacid was subsequently reduced by ammonia borane producing a racemic-mixture After the necessary enantiomeric enrichment was reached, system conditions were changed to induce supersaturation and promote crystal formation. In each case crystals with chemical and enantiomeric purities greater than 99% wt. were recovered. experimental information about reaction and crystallization kinetics was used to developed models. Such models were used to design model-based optimizations in which the productivity of the operation was enhanced by selecting an optimal temperature profile. The second example is a reactive crystallization towards the manufacture of β-lactam antibiotics. One of the major drawbacks of the utilization of enzymes towards the manufacture of β-lactam antibiotics is the fact that the same enzyme that catalyzes the synthesis of the antibiotic also catalyzes its hydrolysis and thus, its degradation. The reaction scheme is a kinetically controlled synthesis in which the desired product is an intermediate within the network. Hence, the focus of this work is to design an efficient reactive crystallization in which the product is crystallized before it is consumed by hydrolysis. In order to accomplish this goal we have study solution equilibria, reaction kinetics, and crystallization kinetics. Even though crystallization kinetics of ampicillin has been previously reported; the reported models are not applicable to a reactive crystallization scheme for a variety of reasons. In this work, we have developed a robust model that can be applied to multiple crystallization protocols that are consistent with the conditions at which the enzymatic reaction can be performed. Finally, a reactive-crystallization scheme in which ampicillin was successfully recovered from solution was developed. In this work, crystal seeds were used to promote crystallization of the desired product from the complex media. The results indicated that is possible to perform the reaction and crystallization in parallel, and still recover crystals with high purity. This work is the first example in which ampicillin was produced and recovered with high purity in a single stage. Previous work on reaction crystallization of antibiotics reported ampicillin crystallization; however, this was accompanied by precipitation of by-products which greatly reduces the applicability of the operation as product purification is required after the reaction.
Heat of Fusion, Crystallization Kinetics Analyses and Morphology of Poly[(ethylene)-co-(trimethylene terephthalate)]sWang, Chuan-Liang 01 July 2003 (has links)
These developmental grade samples were supplied by the Union Chemical Laboratories of Industrial Technology Research Institute(ITRI). The compositions of a series of copolyesters were identified by C1-NMR and H1-NMR. The ethylene terephthalate(ET) units are 8.9¡B33.7¡B37.9% and trimethylene terephthalate(PT) units are 91.1¡B66.3¡B62.1% in the copolyesters with sample codes of C2¡BC3¡BC4. Differential scanning calorimeter(DSC) was used to study the isothermal crystallization kinetics and melting behaviors and Polarizing Microscope(PLM) was used to study the spherulite growth rates and spherulite patterns. The Hoffman-Weeks linear plot and M-X nonlinear plot gave an equilibrium meiting temperature(Tmo ) oC of C2¡BC3¡BC4 are (240.6¡B275.5)¡B(208.8¡B247.0)¡B(194.3¡B229.4). The growth rates (£gm/s )of different samples in the different crystallination temperature(Tc) oC are C2(0.614~0.061, 180~207)¡BC3(0.112~0.021, 130~166)¡BC4(0.0213~0.003, 120~160). From the different equilibrium meiting temperature(Tmo ) and different T¡Û = ( Tg-30, Tg-51.6 oC) to analysis the regime transition temperature (T¢º¡÷¢») in units of oC are C2(234.0¡B237.1¡B240.6¡B275.5¡A195.9¡Ó0.3, 196.2¡Ó0.4)¡BC3(193.1¡B198.9¡B208.8¡B247.0¡A147.5¡Ó0.2, 147.5¡Ó0.1)¡BC4(184.1¡B187.9¡B194.3¡B229.4¡A133.3¡Ó0.4, 133.6¡Ó0.2). Compare the results with the results that using the half-time of crystallization(t1/2) from DSC (C2(193.6 oC)¡BC3(147.3 oC)¡BC4(1140.4 oC)). It can find that C2 is over 2.3 and 2.6 oC and C3 is the same and C4 is under 6.8 and 7.1 oC. From the morphology of spherulite patterns and regime transition temperature (T¢º¡÷¢») oC, the results indicated that the change from the morphology is closed to regime transition temperature. Regular spherlites were exhibited at temperature(Tc) between 180 and 196 oC and banded spherulites were observed between 197 and 208 oC in the C2. The band spacing increase with increasing crystallization temperature. Regular spherlites were exhibited at temperature(Tc) between 130 and 147 oC and banded spherulites were observed between 148 and 172 oC in the C3. The band spacing increase with increasing crystallization temperature. Regular spherlites were exhibited at temperature(Tc) between 120 and 134 oC and banded spherulites were observed between 135 and 160 oC in the C4. The band spacing increase with increasing crystallization temperature. Combine the results of M-X plot and spherulites pattern and melting behaviors at a heating rate of 80 oC/min . It indicated that the regime transition temperature (T¢¹¡÷¢º) oC are in the range of crystallization temperature of C2¡BC3¡BC4 are (210~213¡B174~178¡B160~164 oC). The heat of fusion (¡µHu) of C3 is 4.88¡Ó0.06 kcal/mol and B is 1.47¡Ó0.05 cal/c.c from the experimental. The heat of fusion(¡µHu) of C4 is 2.56¡Ó0.22 kcal/mol and B is 4.45¡Ó0.36 cal/c.c from the experimental. Compare the results with PET(¡µHu = 5.6 kcal/mol) and PTT(¡µHu = 7.2 kcal/mol). It indicated that PTT > PET > C3 > C4.
Johnson, Rolfe Bradley
21 May 2010
Multi-walled carbon nanotubes (MWNTs) are a nanofiller that has desirable multifunctional properties. They have been shown to offer improved mechanical, thermal, and electrical properties in composites. Research has been studying their incorporation into polymer composites. Polyamide 12 is a polyamide of interest that has been manufactured to have lower moisture absorption and higher ductility than other commercial polyamides such as 6 and 6,6 at room temperature. In these studies, MWNTs have been incorporated into polyamide 12 at different weight loadings and using MWNTs with differing outer diameters. The composites were melt processed and characterized using differential scanning calorimetry (DSC) to understand the effects of MWNTs on the crystallization behavior of polyamide 12. A melt peak splitting behavior was observed in the polyamide 12 and composite samples when the specimens were not allowed to fully anneal. Total crystallinity in the samples remained the same between the polyamide 12 and composites when the samples were fully annealed. Total crystallinity increased by 1 to 4 percent in the composites over the polyamide 12 when samples were not fully annealed. The addition of MWNTs to the polyamide 12 system increased the amount of crystallization contained in the lower temperature melting peak. An increase in MWNT concentration resulted in an increase in the crystallinity contained in the lower temperature peak. The addition of smaller diameter MWNTs resulted in a further increase in the lower temperature peak when the outer diameter was below a critical size.
Yang, Li-yin, 1952-
The crystallization kinetics of diphenylhydantoin (DPH) has been studied at constant conditions in a small mixed suspension mixed product removal (MSMPR) crystallizer. Supersaturation is created by changing the pH of a DPH solution in the crystallization vessel. Crystal size distributions (CSD's) are measured by an in situ zone sensing method. Effects of pH and supersaturation on crystallization kinetics and CSD are summarized. The effect of an additive on the crystal growth of DPH has been studied in a batch system. Avoidance of nucleation in the early stages of crystallization is essential to the effect investigated.
Zipp, Gail Lea, 1959-
No description available.
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