Crystallization of Poly ethylene Terephthalate

The crystallization of poly(ethylene terephthalate) at different temperatures after prior fusion at 294 C has been observed to follow the Avrami equation with the following parameters applying at the indicated temperatures ... 

Takeda, H., Ehara, M., Sakai, Y. and Choi., Thermal crystallization of poly(ethylene terephthalate) and its copolyesters effect of degree of polymerization and copolymerized components. Textile Res. J., 61, 429-432 (1991). 

Negative Ea values (Figure 8) have been obtained experimentally by Vyazovkin et al. [24] for the melt crystallization of poly(ethylene terephthalate), poly(ethylene oxide) [25], and poly(ethylene 2,6-naphthalate) [26]. Similar dependencies have also been reported by other workers... 

Figure 8. Change of the o-Ps hole distribution before ( ) and after (O, A) crystallization of poly(ethylene terephthalate) by heat treatment. It is clearly shown that the small size holes have disappeared due to the crystallization. (Adopoted from ref 29)...

Hu WB (2005) Molecular segregation in polymer melt crystallization simulation evidence and unified-scheme interpretation. Macromolecules 38 8712-8718 Hu WB, Cai T (2008) Regime transitions of polymer crystal growth rates molecular simulations and interpretation beyond Lauritzen-Hoffman model. Macromolecules 41 2049-2061 Jeziomy A (1971) Parameters characterizing the kinetics of the non-isothermal crystallization of poly(ethylene terephthalate) determined by DSC. Polymer 12 150-158 Johnson WA, Mehl RT (1939) Reaction kinetics in processes of nucleation and growth. Trans Am Inst Min Pet Eng 135 416-441... 

Effective routes for acceleration of the inherent slow crystaUization rate of PL A are the increase of the nudeation density by addition of heterogeneous nucle-ators and the increase of the chain mobility by addition of plasticizers [14, 57]. Chemical nudeation agents such as organic salts of sodium, which successfully were employed to accelerate the crystallization of poly(ethylene terephthalate) or polycarbonate, failed in the specific case of PLA [14, 57, 58]. Physical nudeation agents, in contrast, have been shown to be effective to enhance the crystallization of PLA. Among these, talc has been proven superior, most effective, and cost... 

Nucleating agent comprises a Si02 core grafted with bis(2-hydroxyethyl) terephtha-late. This combination accelerates the crystallization of poly(ethylene terephthalate) in injection molding. ... 

Yang Y, Xu H, Gu H (2006) Preparation and crystallization of poly(ethylene terephthalate)/ Si02 nanocomposites byin-situ polymerization. J Appl Polym Sci 102(l) 655-662... 

Pijpers et al. (2002) have shown the utility of using fast scan rates to prevent crystallization of poly(ethylene terephthalate) (PET). In Fig. 2.85 during cooling at 100°C/min, no crystallization occurs, only vitrification. On reheating PET at 10°C/min, devitrification is observed, followed by extensive cold crystallization near 150 C. This is followed by melting at 23(>-260°C. However, on the first heating of PET at lOO C/min, cold crystallization is nearly eliminated and the subsequent melting is quite small. 

Blundell DJ et al. (1996) Characterization of strain induced crystallization of poly(ethylene terephthalate) at fast draw rates using synchrotron radiation. Polymer 37 3303. 

Napolitano and coworkers studied the cold crystallization of poly(ethylene terephthalate) (PET) and poly(L-lactide) (PLEA) films confined between two Al layers (i.e., sandwiched films) [50, 53]. They reported that, after thermal annealing at a temperature where the maximum crystallization rate in the bulk was achieved, crystallization was inhibited when the thickness of the films was less than 20 nm for PET or less than 10 nm for PLEA. Such a threshold corresponds to the thickness of the adsorbed layers (i.e., a great reduction in the molecular mobility compared to the bulk) formed between the two solid substrates. Judging from the ratio between the thicknesses of the adsorbed layers and corresponding Rg of the polymers, their adsorbed layers are considered as the interfacial sublayer in our classifications. Hence, the discrepancy is noticed between the uncapped PE and PEO interfacial sublayers, where we can clearly see the seaweed structures (Fig. 6.5a), and the sandwiched PET and PLEA interfacial sublayer. This contrast... 

The isotherms that represent crystallization that is solvent induced do not always give the typical sigmoidal shape found in conventional crystallization. (95,96,98-104) Examples are given in Fig. 13.35 for the solvent induced crystallization of poly(ethylene terephthalate) by either dioxane or nitromethane.(96) The isotherms in this figure do not resemble those of the Avrami type. It can be suspected that the penetration of the solvent and its diffusion through the sample is rate determining. This suspicion is confirmed by the plots in Fig. 13.36.(104) Here the crystallinity is... 

Figure 30 Crystallization of poly(ethylene terephthalate) was monitored by tapping-mode AFM. (a) Phase images were recorded in situ at 233 °C. Image analysis gives (b) time dependence of the mean crystal thickness and (c) thickness distribution in the final state. Reprinted with permission from Ivanov, D. Amalou Z. Magonov S. N. Macromo/ecu/es 2001, 34,8944. Copyright 2001 American Chemical Society.

Properties of PET Molding Resins. The fliU crystal stmcture of poly(ethylene terephthalate) has been estabhshed by x-ray diffraction (134—137). It forms triclinic crystals with one polymer chain per unit cell. The original cell parameters were estabhshed in 1954 (134) and numerous groups have re-examined it over the years. Cell parameters are a = 0.444 nm, b = 0.591 nm, and c = 1.067 nm a = 100°, (3 = 117°, and 7 = 112° and density = 1.52 g/cm. One difficulty is determining when crystallinity is fliUy developed. PET has been aimealed at up to 290°C for 2 years (137). 

Alfonso, G. C., Pedemonte, E. and Ponzetti, L Mechanism of densifica-tion and crystal perfection of poly(ethylene terephthalate), Polymer, 20, 104-111 (1979). 

Lee, C. H., Saito, H. and Inoue, T., Time-resolved light scattering studies on the early stages of crystallization in poly(ethylene terephthalate), Macromolecules, 26, 6566-6569 (1993). 

Statistical copolymerization of ethylene glycol and 1,4-butanediol with dimethyl ter-ephthalate results in products with improved crystallization and processing rates compared to poly(ethylene terephthalate). Polyarylates (trade names Ardel, Arylon, Durel), copolymers of bisphenol A with iso- and terephthalate units, combine the toughness, clarity, and proce-sibility of polycarbonate with the chemical and heat resistance of poly(ethylene terephthalate). The homopolymer containing only terephthalate units is crystalline, insoluble, sometimes infusible, and difficult to process. The more useful copolymers, containing both tere- and isophthalate units, are amorphous, clear, and easy to process. Polyarylates are used in automotive and appliance hardware and printed-circuit boards. Similar considerations in the copolymerization of iso- and terephthalates with 1,4-cyclohexanedimethanol or hexa-methylene diamine yield clear, amorphous, easy-to-process copolyesters or copolyamides,... 

Poly(trimethylene terephthalate). Poly(trimethylene terephthal-ate) (PIT) is a crystalline polymer that is used for fibers, films, and engineering plastics. The polymer has an outstanding tensile elastic recovery, good chemical resistance, a relative low melting temperature, and a rapid crystallization rate. It combines some of the advantages of poly(ethylene terephthalate) (PET) and poly(butylene terephthalate) (PBT). Disadvantageous are the low heat distortion temperature, low melt viscosity, poor optical properties, and pronounced brittleness low temperatures. 

Fig. 16a and b. Phase diagrams of poly(ethylene terephthalate-co-oxybenzoate). a. Crystal melting temperatures b. Glass transition temperatures. All samples with two glass transitions are most likely two-phase samples. The black circles up to 63 mol- % represent one-phase samples. Filled triangles W. J. Jackson, Jr. and H. F. Kuhfuss, J. Polymer Sci., Polymer Chem. Ed. 14, 2043 (1976). Open triangles R. W. Lenz and K. A. Feichtinger, Polymer Preprints, Am. Chem. Soc. Div. Polymer Chem. 20, 114 (1979). Filled circles Ref. 20). Open circle J. Menczel and B. Wunderlich, J. Polymer Sci, Polymer Phys. Ed., 18, 1433 (1980)... 

Figure 3 Polarizing optical micrographs of poly(ethylene terephthalate) (PET) crystallized at 240°C in the absence (A) and in the presence (B) of a shearing. As a consequence of the shearing, nucleation becomes increasingly profuse, and the shape of the spherulites becomes elliptical. (From ref. 11)...

The Avrami equation can describe some, but not all, systrans investigated. The crystallization isotherms of poly(ethylene terephthalate) can be fitted by Equation... 

Copolymerization reactions can use many other combinations, but one interesting reaction involves the modification of poly(ethylene terephthalate) by reacting the preformed polymer with -acetoxybenzoic acid. This has the effect of introducing a mesogenic unit to the structure at the points where the two units combine, producing a thermotropic liquid crystal polymer with a flexible spacer. 

Imai, M., Mori, K., Mizukami, T., Kaji, K., and Kanaya, T., Structural formation of poly(ethylene terephthalate) during the induction period of crystallization 1. Ordered structure appearing before crystal nucleahon. Polymer, 33, 4451-4456 (1992). 

Jackson and Kiitifuss reported a thermotropic liquid crystalline polymer which was a copolyester of poly(ethylene) terephthalate (PET) and parahydroxybenzoic acid (PHB). In this copolyester, PET has a flexible chain conformation while PHB has a stiff, rod-like conformation and the polymer is indicated to be the liquid crystal forming component. Schematically, this copolyester... 

In copolymers of poly(ethylene terephthalate-co-naphthalate)s with low amounts of naphthalate, a melting point depression is observed, while the glass transition temperatures are higher than that of PET. The crystallization rates of the copolymers decrease with increasing comonomer content. The tensile properties of the copolymers with 3 % of naphthalate are significantly improved compared to PET. Thus, the properties of PET can be improved with the use of small amounts of naphthalate, with no significant increase of cost [29]. 

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