Using scalls to study the thermal behavior of polymers in solution

Robertson, Divann (2015-04)

Thesis (PhD)--Stellenbosch University, 2015.

Thesis

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.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/96940
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