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The Crystallization Behavior Of PET And Its Copolyesters

Posted on:2003-01-23Degree:DoctorType:Dissertation
Country:ChinaCandidate:J BianFull Text:PDF
GTID:1101360062475891Subject:Polymer Chemistry and Physics
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The crystallization behavior of polyethylene terephthalate(PET); random poiy (ethylene /tetramethylene terephthalate) (P(ET/BT)); poly(ethylene terephthalate/ isophthalate) (P(ET/EI)) and poly(ethylene terephthalate/adipate) (P(ETIEA)) copolyesters; and block polyethylene terephthalate/polyethylene glycol (PET/PEG) and polyethylene terephthalate/polytetramethylene glycol (PET/PBG) were studied by DLI (depolarized light intensity); DSC,WAXD;PLM and IR technique. Their crystallization and nucleating mechanism; the physics meaning of Avrami exponent and glass transition were investigated.The crystallization behavior of PET with lower viscosity average molecular weight (M, ~6l70) is significantly different from which with higher molecular weight(M1 i~ 12600). Their crystal structure also exists some difference. When the molecular weight of PET is about 7500, the crystallizing process in which the PET chains with different molecular weight formed their own crystallization regions taken palace. And the phenomena of double crystallization regions in DSC and WAX]) analysis appear. The formation of hydrogen bond between free hydrocarbyl at the ends of the chains and oxygen atoms is a necessary process when amorphous PET crystallizes and the double regions result from the different type of hydrogen bond.It was demonstrated that some level of order exists in glassy poly(ethylene terephthalate) by depolarized light intensity (DLI) technique, but this order is different from that in crystalline PET. The degree of order in glassy PET decrease with the increasing temperature between 1 5-~70 'C. The IIIR analysis indicated that this order relates to gauche structure of the ethyleneglycol fragments. The decrease of order with temperature comes from the increase of distance between the order segments.In term of Avrami equation, the influence of different initial state (from the melt; quenched in ice-water; quenched in alcohol at room temperature) on crystallization kinetics of PET were studied using depolarized light intensity (DLI) technique. It wasivshown that the regularities of half-crystallization time and Avrami exponent values vs. isothermal crystallization temperature are different. The various dimension and mobility of the germ nuclei, the clusters of order segments whose sizes are less than one critical value, result in this difference.The results of the influence of various nucleating additive on the PET crystallization process indicated that there may not be a really heterogeneous nucleating agent for PET and its copolyesters crystallization. The influences of the additive on the crystallization arise from (I) the reaction with the molten macromolecular chains of PET; (2) the formation of coordination bonds with PET chains and fixation them when PET crystallizing. The crystallization ability would decrease when too many these bonds formed for the regularity and symmetry were destroyed; (3) the increasing in the degree of order and the interaction between the order ET segments when the crystal structure of PET and additive or its reaction products is matching. And one additive can possess the different acceleration mechanisms.The reason why Avrami exponents in the crystallization processes of polymer are not integer caused by (I) the distribution of effective germ nuclei around the growth nuclei are not symmetric and thus result in the odd growth points in the crystal nuclei; (2) the probability of the formation from germ nuclei to growth nuclei is in the intermediate state; (3) the difference mechanism which can exit in the same isothermal crystallization process. So Avrami exponent indicate the number of growth points in one crystal nucleus and it is a function of the ratio of the effective number of the germ nuclei (N) to the number of growth nuclei (M) namely nocNlM.In term of the PBC (periodic bond chain vector) theory of P. Hartman, the crystallization morphology of polymer was predicted should be crystal lamellar (disk-like or two dimension's growth), and the values o...
Keywords/Search Tags:Crystallization
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