Effects of Microcrystallinity on Physical Aging and Environmental Stress Cracking of Poly (ethylene terephthalate) (PET)

 
 
 
 

Effects of Microcrystallinity on Physical Aging and Environmental Stress Cracking of Poly (ethylene terephthalate) (PET)

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dc.contributor.advisor Jabarin, Saleh A. en_US
dc.contributor.author Zhou, Hongxia en_US
dc.date.accessioned 2009-04-09T21:43:25Z
dc.date.available 2009-04-09T21:43:25Z
dc.date.created 2005 en_US
dc.date.issued 2009-04-09T21:43:25Z
dc.identifier.uri http://rave.ohiolink.edu/etdc/view?acc_num=toledo1122315621 en_US
dc.identifier.uri http://hdl.handle.net/2374.OX/103888
dc.description The dependence of polymer properties on structure has been of great practical importance. In this study, the microstructures of two types PET copolymer sheets made from different polymerization process and catalyst systems have been characterized in terms of density, crystallinity, modified structural factor, conformational isomer contents, as well as spherulite sizes. The relation of microcrystallinity to physical aging and environmental stress cracking was systematically evaluated. It is found that physical aging occurs in both amorphous and semi-crystalline PET stored above room temperature, but below the glass transition. Some physical property changes resulting from aging were recorded. Results indicate that after aging, samples become denser, exhibit higher glass transition temperatures, higher enthalpy of relaxation values (ΔH), as well as less trans and more gauche isomers. Tensile mechanical evaluations show that aging causes elongation to break to decrease dramatically. There is a correlation between the enthalpy of relaxation and the mode of failure. The critical ΔH also decreases linearly as levels of crystallinity increase. Activation energies for onset of embrittlement were calculated and morphological contributions to failure are discussed. The mechanism of physical aging was investigated. Differential scanning calorimetry (DSC) measurements were conducted to record a series enthalpy of relaxation values of the storage at different temperature for various times. The data were further analyzed with a semi-empirical Cowie-Ferguson (CF) model. Comparisons were made among different samples and storage temperatures. Results indicate that the rate of aging is accelerated by temperature and that the presence of a crystalline phase reduces the amount of amorphous regions available for aging and hinders the relaxation process. Dynamic differential scanning calorimetry (DDSC) experiments illustrated the existence of two amorphous regions in semi-crystalline PET, the contribution of each region to aging was resolved for samples aged at 65°C. Moisture absorption investigations demonstrated that moisture is one of the important factors affecting aging and that its effects cannot be ignored even for samples with high crystallinity. Environmental stress cracking resistance (ESCR) behavior of semi-crystalline PET was studied as a function of crystalline content and aging effect. With increasing crystallinity, critical stress was found to decrease linearly. Tie-molecules theory was used to explain the behavior. Physical aging reduced the ESCR of PET and lead to shortened service lifetime of materials. en_US
dc.format application/pdf en_US
dc.format 241p. en_US
dc.rights unrestricted en_US
dc.rights Copyright and permissions information available at the source archive en_US
dc.subject physical aging en_US
dc.subject environmental stress cracking en_US
dc.subject semi-crystalline en_US
dc.subject poly (ethylene terephthalate) en_US
dc.subject crystallinity en_US
dc.subject structure-property relations en_US
dc.title Effects of Microcrystallinity on Physical Aging and Environmental Stress Cracking of Poly (ethylene terephthalate) (PET) en_US
dc.type Electronic Thesis or Dissertation en_US
dc.degree.name PhD en_US
dc.degree.level doctoral en_US
dc.degree.discipline Chemical Engineering en_US
dc.degree.grantor University of Toledo en_US
dc.contributor.publisher University of Toledo / OhioLINK en_US

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