Narrow molecular weight fractions of Poly(ε-caprolactone) were successfully obtained using the successive precipitation fractionation technique with toluene/n-heptane as a solvent/nonsolvent pair. Calorimetric studies of the melting behavior of fractions that were crystallized either isothermally or under constant cooling rate conditions suggested that the isothermal crystallization of the samples should be used for a proper evaluation of the molecular weight dependence of the observed melting temperature and degree of crystallinity in PCL. The molecular weight and temperature dependence of the spherulitic growth rate of fractions was studied in the context of the Lauritzen-Hoffman two-phase model and the Strobl three-phase model of polymer crystallization. The zero-growth rate temperatures, determined from spherulitic growth rates using four different methods, are consistent with each other and increase with chain length. The concomitant increase in the apparent secondary nucleation constant was attributed to two factors. First, for longer chains there is an increase in the probability that crystalline stems belong to loose chain-folds, hence, an increase in fold surface free energy. It is speculated that the increase in loose folding and resulting decrease in crystallinity with increasing chain length are associated with the ester group registration requirement in PCL crystals. The second contribution to the apparent nucleation constant arises from chain friction associated with segmental transport across the melt/crystal interface. These factors were responsible for the much stronger chain length dependence of spherulitic growth rates at fixed undercooling observed here with PCL than previously reported for PE and PEO. In the case of PCL, the scaling exponent associated with the chain length dependence of spherulitic growth rates exceeds the upper theoretical bound of 2 predicted from the Brochard-DeGennes chain pullout model. Observation that zero-growth and equilibrium melting temperature values are identical with each other within the uncertainty of their determinations casts serious doubt on the validity of Strobl three-phase model. A novel method is proposed to determine the Porod constant necessary to extrapolate the small angle X-ray scattering intensity data to large scattering vectors. The one-dimensional correlation function determined using this Porod constant yielded the values of lamellar crystal thickness, which were similar to these estimated using the Hosemann-Bagchi Paracrystalline Lattice model. The temperature dependence of the lamellar crystal thickness was consistent with both LH and the Strobl model of polymer crystallization. However, in contrast to the predictions of Strobl’s model, the value of the mesomorph-to-crystal equilibrium transition temperature was very close to the zero-growth temperature. Moreover, the lateral block sizes (obtained using wide angle X-ray diffraction) and the lamellar thicknesses were not found to be controlled by the mesomorph-to-crystal equilibrium transition temperature. Hence, we concluded that the crystallization of PCL is not mediated by a mesophase. Metallocene-catalyzed linear low-density (m-LLDPE with 3.4 mol% 1-octene) and conventional low-density (LDPE) polyethylene blends of different compositions were investigated for their melt-state miscibility and concurrent crystallization tendency. Differential scanning calorimetric studies and morphological studies using atomic force microscopy confirm that these blends are miscible in the melt-state for all compositions. LDPE chains are found to crystallize concurrently with m-LLDPE chains during cooling in the m-LLDPE crystallization temperature range. While the extent of concurrent crystallization was found to be optimal in blends with highest m-LLDPE content studied, strong evidence was uncovered for the existence of a saturation effect in the concurrent crystallization behavior. This observation leads us to suggest that co-crystallization, rather than mere concurrent crystallization, of LDPE with m-LLDPE can indeed take place. Matching of the respective sequence length distributions in LDPE and m-LLDPE is suggested to control the extent of co-crystallization. / Ph. D.

While conducting pilot studies into the usefulness of fusion to TELSAM polymers as a potential protein crystallization strategy, we observed novel properties in crystals of two TELSAM–target protein fusions, as follows. (i) A TELSAM–target protein fusion can crystallize more rapidly and with greater propensity than the same target protein alone. (ii) TELSAM–target protein fusions can be crystallized at low protein concentrations. This unprecedented observation suggests a route to crystallize proteins that can only be produced in microgram amounts. (iii) The TELSAM polymers themselves need not directly contact one another in the crystal lattice in order to form well-diffracting crystals. This novel observation is important because it suggests that TELSAM may be able to crystallize target proteins too large to allow direct inter-polymer contacts. (iv) Flexible TELSAM–target protein linkers can allow target proteins to find productive binding modes against the TELSAM polymer. (v) TELSAM polymers can adjust their helical rise to allow fused target proteins to make productive crystal contacts. (vi). Fusion to TELSAM polymers can stabilize weak inter-target protein crystal contacts. We report features of these TELSAM–target protein crystal structures and outline future work needed to validate TELSAM as a crystallization chaperone and determine best practices for its use.

<p>Crystallization is a key solid-liquid separation and purification technique used in pharmaceutical industry. Some of the critical quality attributes (CQAs) of a product from crystallization process include crystal size distribution (CSD), purity, polymorphic form, morphology, etc. Different size and polymorphs of a drug substance may have different dissolution profiles and different bioavailability, which can have adverse effect on human health. Therefore, it is important to design and control crystallization process to meet product CQAs. In recent years, drug substances are becoming more complex, often being heat sensitive, which may limit the temperature that can be used in the crystallization step. Consequently, the traditional cooling only crystallization may not be well suited to recover the high value drug substances. For these systems, antisolvent crystallization is typically employed to improve the yield. On the other hand, the solvent composition can significantly impact the polymorphic outcome. Therefore, designing combined cooling and antisolvent crystallization (CCAC) processes to solve the challenges of active pharmaceutical ingredient (API) crystallization in a highly regulated environment is a complex engineering problem. </p> <p>With rising energy costs and intense price competition from generic pharmaceutical companies, the pharmaceutical industry is looking for ways to reduce the cost of manufacturing via process intensification (PI). This thesis focuses on different PI techniques for CCAC of drug substances. Continuous or smart manufacturing is gaining popularity due to its potential to lower the cost of manufacturing while maintaining consistent quality. Continuous crystallization is an important link in the continuous manufacturing process. The first part of the thesis shows PI of a commercial drug substance, Atorvastatin calcium (ASC) for target polymorph development via continuous CCAC using an oscillatory baffled crystallizer (OBC). An existing batch CCAC process for ASC was compared with the continuous CCAC in OBC and it was found the continuous process 30-fold more productive compared to the batch process. An array of process analytical technology (PAT) tools was used in this work to assess key process parameters that affect the polymorphic outcome and CSD. The desired narrower CSD product was obtained in the OBC compared to that from a batch crystallizer.</p> <p>The next part of the thesis focused on model-based PI technique for efficient determination of crystallization kinetics of a polymorphic system in CCAC. A novel experimental design was proposed which significantly reduced the number of experiments required to determine crystallization kinetics in a CCAC process. The kinetic parameters were validated, and a validated polymorphic model was used to perform an in-silico design of experiment (DoE) to develop a design space that can be used to identify operating conditions to achieve a desired crystal size and polymorphic form. </p> <p>The final part of the thesis combines the experimental and model-based approach for designing a continuous CCAC process for ASC in a cascade of Coflore agitated cell reactor (ACR) and three-stage mixed suspension mixed product removal (MSMPR). A combined artificial neural network (ANN) and principal component analysis (PCA) method was used to calibrate an ultraviolet (UV) probe which was used to monitor ASC solute concentration in the cascade process. The crystallization kinetic parameters were estimated in ACR and MSMPR which was used to build a digital model of the cascade process. The digital model was then used to obtain a design space with different temperature profile in the three-stage MSMPR that yielded narrow CSD of ASC form I. Overall, this thesis demonstrates the benefits of applying PI in the CCAC of drug substances using a holistic approach including novel equipment, application of an array of PAT tools, and model-based digital design to achieve desired CQAs of the product.</p>

The crystallization and melting behavior of linear polyethylene and of a series of random ethylene/styrene copolymers was investigated using a combination of classical and temperature modulated differential scanning calorimetry. In the case of linear polyethylene and low styrene content copolymers, the temporal evolutions of the melting temperature, degree of crystallinity, and excess heat capacity were studied during crystallization. The following correlations were established: 1) the evolution of the melting temperature with time parallels that of the degree of crystallinity, 2) the excess heat capacity increases linearly with the degree of crystallinity during primary crystallization, reaches a maximum during the mixed stage and decays during secondary crystallization, 3) the rates of shift of the melting temperature and decay of the excess heat capacity lead to apparent activation energies that are very similar to these reported for the crystal ac relaxation by other techniques. Strong correlations in the time domain between the secondary crystallization and the evolution of the excess heat capacity suggest that the reversible crystallization/melting phenomenon is associated with molecular events in the melt-crystal fold interfacial region. In the case of higher styrene content copolymers, the multiple melting behavior at high temperature is investigated through studies of the overall crystallization kinetics, heating rate effects and partial melting. Low melting crystals can be classified into two categories according to their melting behavior, superheating and reorganization characteristics. Low styrene content copolymers still exhibit some chain folded lamellar structure. The shift of the low melting temperature with time in this case is tentatively explained in terms of reorganization effects. Decreasing the crystallization temperature or increasing the styrene content leads to low melting crystals more akin to fringed-micelles. These crystals exhibit a lower tendency to reorganize during heating. The shift of their melting temperature with time is attributed to a decrease in the conformational entropy of the amorphous fraction as a result of constraints imposed by primary and secondary crystals. To further understand the mechanism of formation of low melting crystals, quasi-isothermal crystallization experiments were carried out using temperature modulation. The evolution of the excess heat capacity was correlated with that of the melting behavior. On the basis of these results, it is speculated that the generation of excess heat capacity at high temperature results from reversible segmental exchange on the fold surface. On the other hand, the temporal evolution of the excess heat capacity at low temperature for high styrene content copolymers is attributed to the reversible segment attachment and detachment on the lateral surface of primary crystals. The existence of different mechanisms for the generation of excess heat capacity in different temperature ranges is consistent with the observation of two temperature regimes for the degree of reversibility inferred from quasi-isothermal melting experiments. In a second project, the chain length and temperature dependences of spherulitic growth rates were studied for a series of narrow fractions of poly(ethylene oxide) with molecular weight ranging from 11 to 917 kg/mol. The crystal growth rate data spanning crystallization temperatures in regimes I and II was analyzed using the formalism of the Lauritzen-Hoffman (LH) theory. Our results are found to be in conflict with predictions from LH theory. The Kg ratio increases with molecular weight instead of remaining constant. The chain length dependence of the exponential prefactor, G0, does not follow the power law predicted by Hoffman and Miller (HM). On this basis, the simple reptation argument proposed in the HM treatment and the nucleation regime concept advanced by the LH model are questioned. We proposed that the observed I/II regime transition in growth rate data may be related to a transition in the friction coefficient, as postulated by the Brochard-de Gennnes slippage model. This mechanism is also consistent with recent calculations published by Toda in which both the rates of surface nucleation and substrate completion processes exhibit a strong temperature dependence. / Ph. D.

No description available.

This study focused on two active pharmaceutical ingredients (APIs) that are used to treat two of the most notorious diseases in Africa, i.e. human immunodeficiency virus/acquired immune deficiency syndrome (HIV/AIDS) and malaria. It is well known that many African countries lack effective regulatory control over medicines and patients are subsequently at risk of receiving sub-standard treatments. This study set out to investigate how the modification of the crystal packing (i.e. polymorphism) of these APIs may impact on their quality, safety and efficacy. Efavirenz (an antiretroviral) and Pyrimethamine (an antimalarial) were selected as the two model APIs for investigation during this study. It was found that a novel amorphous form (Form A) of Efavirenz had been prepared during this study through quench cooling. Form A was extensively characterised and compared to the preferred crystalline Form I, with the aim of providing a means of distinguishing between these two Efavirenz forms. In contrast to popular belief (that amorphous form should have improved dissolution and solubility properties over the crystalline counterpart), the powder dissolution of Form A was significantly lower than that of Form I. Further investigation indicated that this was due to the occurrence of agglomeration and phase-mediated transformation. This observation had led to the belief that Form A had poor thermodynamic stability. The glass transition temperature and the crystallisation activation energy, required for the recrystallisation of Form A, were subsequently determined in an attempt to elucidate its thermodynamic stability. The glass transition temperature of Form A was found to be unfeasibly low, hence confirming its tendency towards agglomeration. The crystallisation activation energy of Form A was determined by non-isothermal determinations, using differential scanning calorimetry (DSC), hot stage microscopy (HSM) and capillary melting point (CMP) analysis. These studies not only elucidated the required activation energy for the conversion of Form A into Form I, but it also found that the results from CMP were similar to those of the universally accepted DSC technique, allowing for the proposal of CMP as a cost-effective alternative to DSC for the quantitative measurement of the crystallisation of Efavirenz. Isothermal studies revealed that Form A had a short half-life, which, together with its poor dissolution performance, exemplified why this form was unsuitable for pharmaceutical use. The Pyrimethamine study focused on recrystallisation as a means of modifying its crystal packing and on an evaluation of the effect that such crystal modification may have on its safety and manufacturability. Anhydrous Pyrimethamine was recrystallised, using methanol, acetone, n-propanol, ethanol, N,N-dimethylformamide and N,N-dimethylacetamide. Ethanol, acetone and n-propanol altered the crystal habit of Pyrimethamine, without any modification of its crystal lattice. The different habits exhibited clear differences in flowability and compressibility, which could in turn affect manufacturing and therefore the quality of the finished pharmaceutical product (FPP). These habits were subsequently extensively characterised by means of in-silico molecular modelling predictions. It was found that recrystallisation from methanol, N,N-dimethylformamide and N,N-dimethylacetamide had resulted in solvatomorphism. These solvatomorphs contained their respective solvents in concentrations exceeding the allowed residual solvent limits, as set by the International Conference on Harmonisation (ICH) guidelines. These undesirable solvatomorphs were also comprehensively characterised as a service to the pharmaceutical industry, in order to identify the distinct characteristics that distinguish these forms from the preferred non-toxic form, and to provide techniques for transforming the toxic forms into the non-toxic form. / PhD (Pharmaceutics), North-West University, Potchefstroom Campus, 2015

This study focused on two active pharmaceutical ingredients (APIs) that are used to treat two of the most notorious diseases in Africa, i.e. human immunodeficiency virus/acquired immune deficiency syndrome (HIV/AIDS) and malaria. It is well known that many African countries lack effective regulatory control over medicines and patients are subsequently at risk of receiving sub-standard treatments. This study set out to investigate how the modification of the crystal packing (i.e. polymorphism) of these APIs may impact on their quality, safety and efficacy. Efavirenz (an antiretroviral) and Pyrimethamine (an antimalarial) were selected as the two model APIs for investigation during this study. It was found that a novel amorphous form (Form A) of Efavirenz had been prepared during this study through quench cooling. Form A was extensively characterised and compared to the preferred crystalline Form I, with the aim of providing a means of distinguishing between these two Efavirenz forms. In contrast to popular belief (that amorphous form should have improved dissolution and solubility properties over the crystalline counterpart), the powder dissolution of Form A was significantly lower than that of Form I. Further investigation indicated that this was due to the occurrence of agglomeration and phase-mediated transformation. This observation had led to the belief that Form A had poor thermodynamic stability. The glass transition temperature and the crystallisation activation energy, required for the recrystallisation of Form A, were subsequently determined in an attempt to elucidate its thermodynamic stability. The glass transition temperature of Form A was found to be unfeasibly low, hence confirming its tendency towards agglomeration. The crystallisation activation energy of Form A was determined by non-isothermal determinations, using differential scanning calorimetry (DSC), hot stage microscopy (HSM) and capillary melting point (CMP) analysis. These studies not only elucidated the required activation energy for the conversion of Form A into Form I, but it also found that the results from CMP were similar to those of the universally accepted DSC technique, allowing for the proposal of CMP as a cost-effective alternative to DSC for the quantitative measurement of the crystallisation of Efavirenz. Isothermal studies revealed that Form A had a short half-life, which, together with its poor dissolution performance, exemplified why this form was unsuitable for pharmaceutical use. The Pyrimethamine study focused on recrystallisation as a means of modifying its crystal packing and on an evaluation of the effect that such crystal modification may have on its safety and manufacturability. Anhydrous Pyrimethamine was recrystallised, using methanol, acetone, n-propanol, ethanol, N,N-dimethylformamide and N,N-dimethylacetamide. Ethanol, acetone and n-propanol altered the crystal habit of Pyrimethamine, without any modification of its crystal lattice. The different habits exhibited clear differences in flowability and compressibility, which could in turn affect manufacturing and therefore the quality of the finished pharmaceutical product (FPP). These habits were subsequently extensively characterised by means of in-silico molecular modelling predictions. It was found that recrystallisation from methanol, N,N-dimethylformamide and N,N-dimethylacetamide had resulted in solvatomorphism. These solvatomorphs contained their respective solvents in concentrations exceeding the allowed residual solvent limits, as set by the International Conference on Harmonisation (ICH) guidelines. These undesirable solvatomorphs were also comprehensively characterised as a service to the pharmaceutical industry, in order to identify the distinct characteristics that distinguish these forms from the preferred non-toxic form, and to provide techniques for transforming the toxic forms into the non-toxic form. / PhD (Pharmaceutics), North-West University, Potchefstroom Campus, 2015

Résumé : Le poly(acide lactique) ou PLA est une famille de polyester thermoplastique linéaire qui a connu un essor commercial important durant la dernière décennie. L'enthousiasme pour le PLA vient de sa nature biosourcée, de ses bonnes propriétés mécaniques comme un module élastique élevé et de la possibilité de le biodégrader. Toutefois, certaines carences comme une faible résistance thermique et une faible élasticité à l’état fondu limitent son champ d’application. Fait à noter, le monomère d’acide lactique possède deux stéréo-isomères (L et D). Il est possible de polymériser les isomères L ou D pour former respectivement le PLLA ou le PDLA mais de façon surprenante, le mélange de PLLA et de PDLA permet la formation d’une structure cristalline distincte appelée le stéréocomplexe. Cette forme cristalline a un point de fusion 50[degré]C plus élevé par rapport aux formes cristallines du PLLA ou de PDLA d’où un premier intérêt pour augmenter la résistance thermique du matériau. Dans ce travail, l’usage de petites quantités (0-5 % massique) de PDLA comme additif dans une phase majeure de PLLA sera analysé. L’effet du stéréocomplexe formé à haute température sur la nucléation du PLLA et sur les propriétés rhéologiques du mélange sera plus particulièrement étudié. La présente thèse comprend une revue de littérature sur la cristallisation des PLA suivie de quatre parties expérimentales, conclusions et recommandations. La revue de littérature a pour objectif de réinterpréter l’ensemble des données disponibles sur la cristallisation du PLA afin d’en tirer des conclusions claires. La première partie expérimentale porte sur la cinétique de formation du stéréocomplexe à l'état fondu. Il a été constaté que la formation du stéréocomplexe est lente aux températures usuelles de mise en forme du PLLA ( 180[degré]C). De plus, la coexistence d’une morphologie baptisée dans ce travail « structure en réseau » et d’une morphologie sphérulitique a été révélée pour la première fois. Il a été démontré que la structure de réseau a une température de fusion moins élevée que la structure sphérulitique. Dans la seconde partie du travail, la cinétique de stéréocomplexation a été améliorée significativement pour adapter celle-ci aux cycles de refroidissement courts typiques des méthodes de mise en forme à l’état fondu. Ceci a été réalisé en ajoutant des agents nucléants qui initient la cristallisation à plus haute température et des agents plastifiants qui viennent augmenter la mobilité des polymères. Cette stratégie a permis de réduire le temps de cristallisation d’un ordre de grandeur. Dans un troisième temps, l'effet du stéréocomplexe sur les propriétés rhéologiques d’un mélange PDLA/PLLA a été investigué. En raison de son point de fusion élevé, le stéréocomplexe peut être préservé dans une matrice PLLA fondue et ainsi changer significativement les propriétés rhéologiques. La présence du stéréocomplexe a mené à une augmentation significative de la viscosité et de l'élasticité du PLA expliqué par la formation de points de « réticulation physique » dans la matrice amorphe. Enfin, dans la dernière partie expérimentale, le stéréocomplexe a été utilisé pour améliorer le comportement en moussage du PLA. Des expériences de visualisation et de moussage en mode discontinu ont montré que la présence de stéréocomplexe augmente la densité de nucléation de bulles et améliore significativement la morphologie de la mousse finale grâce à un effet de nucléation et à l’augmentation de l’élasticité du fluide. La revue de littérature et les trois premières parties expérimentales sont présentées sous forme d’articles scientifiques. La dernière partie expérimentale est à titre prospectif pour la suite du projet et ne sera pas soumise pour publication. // Abstract : Poly(lactic acid), or PLA, is a family of linear thermoplastic polyesters that has experienced strong market growth over the past decade. The enthusiasm for PLA originates from its bio-based nature, its good properties and its biodegradability. However, some of PLA deficiencies such as low thermal resistance and low melt elasticity have limited the development of this polymer. It is noteworthy that the lactic acid monomer has two stereo-isomers (L and D) that can be polymerized respectively into PLLA and PDLA but surprisingly, blending of PLLA and PDLA can lead to the formation of a “stereocomplex” which has a distinct crystalline structure from that of the homopolymers. This crystalline form has a melting point 50 oC greater than the crystalline PDLA or PLLA forms, thus it has by itself an interest in terms of heat resistance. In this work, the use of small amounts of PDLA (0-5%) in a matrix of PLLA will be explored. Particular emphasis will be on the nucleating ability of the stereocomplex (formed at high temperature) on PLLA crystallization and on its effect on the blends rheological properties. The current thesis comprises a literature review on PLA crystallization followed by four experimental sections. The objective of the literature review was to reinterpret the large body of data available on PLA in order to draw clear conclusions on PLA crystallization. The first experimental part of the work focused on the kinetics and conditions of stereocomplex formation in the melt state. It was found that stereocomplex formation is slow in the melt processing temperature range of PLLA (180 oC). Co-existence of a so-called “network structure” with a spherulitic structure was revealed for the first time. It was shown that the network structure has a lower melting point than the spherulitic one. In the second part of the work, stereocomplexation kinetics was improved significantly to match it with the fast cooling cycles typical of melt processing techniques. This was achieved by adding nucleating agents that initiated crystallization at higher temperatures and plasticizers that enabled more polymer fluidity. This strategy enabled an order of magnitude decrease in crystallization time. The third part of the work was the investigation of rheological properties upon formation of the stereocomplex structure in 0-5% PDLA in PLLA blends. Due to its higher melting point, the stereocomplex can be preserved in molten PLLA and alter significantly the blend melt rheology. Stereocomplex formation was monitored through rheological measurements and compared to classical calorimetry data. The presence of the stereocomplex lead to a significant increase in viscosity and in melt elasticity explained through the presence of physical crosslink points in the amorphous matrix. Finally, in the last experimental part of the work, the stereocomplex was employed to enhance PLA foaming behavior. Foaming visualization experiments as well as batch foaming tests showed that the presence of the stereocomplex can increase bubble nucleation density and led to a finer and more uniform foam morphology due to its nucleating effect and to the increased melt elasticity. The literature review and the three first experimental sections are presented in Peer-reviewed journal format. The last experimental section is meant as an exploratory and prospective part for the project and will not be submitted for publication.

Thesis (PhD)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: This study involves the analysis of crystallization and melting behavior of polymers in solution, using Solution crystallization by laser light scattering (Scalls) as analytical tool. Various other techniques such as differential scanning calorimetry (DSC), Fourier-transform infrared spectroscopy (FTIR) and dynamic light scattering (DLS) were used for further characterization of the polymer materials. For the first time the solution behavior (crystallization and dissolution kinetics) of two biopolymers namely, poly(lactic acid) (PLA) and poly(butylene succinate) (PBS), was monitored by Scalls. Non-isothermal solution crystallization and dissolution behavior of both enantiomers (D and L) PLA and their blends were studied. It was found that addition of the D- enantiomer (PDLA) to the L- enantiomer (PLLA) in solution resulted in the formation of stereocomplex crystals (SC) and the nucleation-effect of the crystals were intensified with an increase in PDLA content leading to an earlier onset of crystallization and increased crystallization peak area. DSC analysis confirmed the formation of SC during solution crystallization. Overall, results obtained by Scalls provided promising information regarding PLA crystallization kinetics which significantly influences practical applications of this biopolymer. Binary blends consisting of PLLA and PBS were prepared in various blend ratios. Scalls was used to investigate the non-isothermal crystallization and melting behavior of these PLLA/PBS blends from dilute solutions. Addition of PBS up to 30 wt% increased crystallization temperatures of PLLA through a nucleation effect in the molten PBS state. Results indicated that the crystallization rate of PLLA can be improved by additions of small amounts of PBS, and this is of significant interest for practical applications due to the low crystallization rate that PLLA is known to exhibit. DSC thermograms showed an increase in PLLA crystallization exotherm at PBS loadings below 50 wt%, providing further evidence of the enhancement in PLLA crystallization kinetics. A series of linear polyethylene samples with varying molecular weights were studied by Scalls. The effect of molecular weight (Mw) on the solution crystallization temperature (Tc) were monitored and compared to literature where the conventional Crystaf technique was used. Experimental Scalls data correlated well with reported theoretical models. Dissolution studies were also done to study the effect of Mw on the solution melting temperature (Tm) and for the first time, an equation was generated to model solution melting temperatures of linear polyethylenes in Scalls. The solution behavior of a PE-1-octene linear low-density polyethylene (LLDPE) copolymer in a range of solvents including trichlorobenzene (TCB), ortho-dichlorobenzene (o-DCB), decalin and xylene were successfully studied. Scalls allowed for rapid analysis of crystallization and dissolution during a single experiment and offered clearer insight into crystallization kinetics when using different solvents for fractionation. Peak temperatures for analyses in TCB and o-DCB were almost identical but remarkably different to those observed when decalin and xylene was used. The study revealed that solvent type plays an important role in the solution behavior of polymers as well as ultimately the interpretation of these results. / AFRIKAANSE OPSOMMING: Hierdie studie behels die ontleding van kristallisasie en smelt gedrag van polimere in oplossing, met behulp van Oplossing kristallisasie deur laser lig verstrooiing (Scalls) as analitiese instrument. Verskeie ander tegnieke soos differensiële skandeer kalorimetrie (DSC), fourier-tranform infrarooi spektroskopie (FTIR) en dinamiese lig verstrooiing (DLS) was gebruik word vir verdere Karakterisering van die polimeer materiaal. Vir die eerste keer is die oplossingsgedrag (kristallisasie en smelting kinetika) van twee biopolimere naamlik, poli(melksuur) (PLA) en poli(butileen suksinaat) (PBS), deur Scalls gemonitor. Nie-isotermiese oplossing kristallisasie en smelt gedrag van beide enantiomere (D en L) van PLA en hul mengsels was ge-analiseer. Daar is gevind dat byvoeging van die D-enantiomeer (PDLA) tot die L-enantiomeer (PLLA) in oplossing gelei het tot die vorming van stereokompleks kristalle (SC) en die nukleasie-effek van die kristalle is versterk met 'n toename in PDLA inhoud wat gelei het tot 'n vroeër aanvang van kristallisasie en toename in kristallisasie piek-area. DSC analise het die vorming van SC gedurende oplossing kristallisasie bevestig. Algeheel, die resultate wat verkry was deur Scalls het belowende inligting oor PLA kristallisasie kinetika verskaf wat aansienlik praktiese toepassing van hierdie biopolimeer beïnvloed. Binêre mengsels bestaande uit PLLA en PBS was voorberei in verskillende mengsel verhoudings. Scalls was gebruik om die nie-isotermiese kristallisasie en smelt gedrag van hierdie PLLA/PBS mengsels, vir die eerste keer, in verdunde oplossings te ondersoek. Byvoeging van PBS tot 30 wt% het ‘n toename in kristallisasie temperature van PLLA veroorsaak deur 'n nukleasie-effek in die gesmelte PBS toestand. Resultate dui aan dat die tempo van PLLA kristallisasie versnel kan word deur byvoegings van PBS in klein hoeveelhede, en dit is van beduidende belang vir praktiese toepassings weens die lae kristallisasie-tempo waarvoor PLLA bekend is. DSC termogramme het 'n toename in PLLA kristallisasie eksoterm aangedui by PBS inhoud onder 50 wt%, wat 'n verdere bewys is van die verbetering in PLLA kristallisasie kinetika. 'n Reeks lineêre poliëtileen monsters met wisselende molekulêre massas was met Scalls geanaliseer. Die effek van molekulêre massa (Mw) op die oplossing kristallisasie temperatuur (Tc) was gemonitor en vergelyk met literatuur waar die konvensionele Crystaf tegniek gebruik is. Eksperimentele Scalls data het goed gekorreleer met gerapporteerde teoretiese modelle. Smelting studies is ook gedoen om die effek van Mw op die oplossing smelt temperatuur (Tm) te bestudeer en vir die eerste keer, is 'n vergelyking ge-genereer vir die modellering van oplossing smelt temperature van lineêre poliëtileen met behulp van Scalls. Die oplossing-gedrag van ‘n PE-1-okteen lineêre lae-digtheid poliëtileen (LLDPE) kopolimeer was suksesvol bestudeer in 'n verskeidenheid oplosmiddels, insluitend trichlorobenseen (TCB), ortodichlorobenseen (o-DCB) , decalin en xileen. Scalls het toegelaat vir vinnige analise van die kristallisasie en smelting in 'n enkele eksperiment en het dieper insig gegee oor die kristallisasie kinetika tydens fraksionering met die gebruik van verksillend oplosmiddels. Piek temperature vir analises in TCB en o-DCB was byna identies, maar merkwaardig verskillend van dié wat waargeneem was in die geval waar decalin en xileen gebruik was. Hierdie studie het getoon dat die tipe oplosmiddel 'n belangrike rol speel in die oplossing-gedrag van polimere en uiteindelik asook die interpretasie van hierdie resultate. Verder blyk Scalls na ‘n nuttige metode vir die ontleding van polimere in oplossing te wees.

No description available.