Poly crystallization rate

Poly(butylene terephthalate) (PBT) is a semicrystalline, thermoplastic polyester which is completely analogous to PET except that it has a longer, more flexible butylene chain linkage which imparts a rapid crystallization rate, thus making PBT well suited to injection moulding processes. This polyester is used widely for electrical and electronic components due to its high temperature resistance and good electrical properties (Chapter 8). 

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. 

Griffith, J. H., and B. G. RA.nby Dilatometric measurements on poly (4-methyl-l-pentene), glass and melt transition temperatures, crystallization rates and unusual density behavior. J. Polymer. Sci. 44, 369—381 (1960). 

Physical properties are related to ester-segment structure and concentration in thermoplastic polyether-ester elastomers prepared hy melt transesterification of poly(tetra-methylene ether) glycol with various diols and aromatic diesters. Diols used were 1,4-benzenedimethanol, 1,4-cyclo-hexanedimethanol, and the linear, aliphatic a,m-diols from ethylene glycol to 1,10-decane-diol. Esters used were terephthalate, isophthalate, 4,4 -biphenyldicarboxylate, 2,6-naphthalenedicarboxylate, and m-terphenyl-4,4"-dicarboxyl-ate. Ester-segment structure was found to affect many copolymer properties including ease of synthesis, molecular weight obtained, crystallization rate, elastic recovery, and tensile and tear strengths. 

The effects of morphology (i.e., crystallization rate) (6,7, 8) on the mechanical properties of semicrystalline polymers has been studied without observation of a transition from ductile to brittle failure behavior in unoriented samples of similar crystallinity. Often variations in ductlity are observed as spherulite size is varied, but this is normally confounded with sizable changes in percent crystallinity. This report demonstrates that a semicrystalline polymer, poly(hexamethylene sebacate) (HMS) may exhibit either ductile or brittle behavior dependent upon thermal history in a manner not directly related to volume relaxation or percent crystallinity. 

FIG. 15.8 Changes in UV-visible absorption spectrum of a poly(di-n-hexylsilane) spincast film in the course of crystallization to adopt an all-trans-zigzag conformation of the Si backbone at I5°C (a). Photocontrol of the crystallization rate as observed by the absorbance increases at 366 nm, corresponding to the increase of the all-trans-zigzag conformation of the Si chain (b). (From reference 39 copyright permission from the American Chemical Society.)... 

It is not only the crystallization rate, however, which is influenced by nucleating agents, but also the morphology. Isotactic poly(propylene) crystallizes monoclinically in the presence of / -/-butyl benzoic acid and pseudohexagonally when the quinacridone dyestuff. Permanent Red EBB, is added. 

Irrstead of the molar flux derrsity ft the crystal growth rate is often described by the displacement rate v of a crystal face (for irrstance v, for the 111 face). Note that every face can have different growth rates v at the same supersaturation. Let us assume spherical (poly)crystals. The growth rate is eqttal to the derivative of the radius with respect to time t (y = dr/dt) or the derivative G = 6L/6t with/, as the decisive length which is the diameter L for spheres. With the volume shape factor a = V /L and the srrrface shape factor P =. 4p/Z,, the following relationship between the mass flux density m (m = n M), the displacement rate v of the crystal surface, and the rate G = 2v of crystalhne particles is given... 

Particularly suitable polyesters considered in the past have been poly-e-caprolactone (PCL) and its copolymers. Nevertheless, films made of thermoplastic starch and PCL are tacky as extruded, rigid, and have low melt strength at temperatures over 130 °C. Moreover, due to the slow crystallization rate of such polymers, the complete cooling process needs a long time after production of the finished articles, giving an undesirable change of properties with time. 

Pan, R, Liang, Z., Cao, A. and Inoue, Y. (2009) Layered metal phosphonate reinforced poly(L-lactide) composites with a highly enhanced crystallization rate. Applied Materials and Interfaces, 1, 402-411. 

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]. 

C02-induced crystallization has also been observed for bisphenol A polycarbonate [33], tert-butyl poly(ether ether ketone) [34], and methyl substituted poly (aryl ether ether ketone) [35]. This C02-induced enhanced crystallization rate with increasing pressure has been explained in terms of the depression of Tg being far greater than the depression of the T. However, in contrast to the aforementioned polymers, it has been shown that exposure of poly(L-lactide) [36] and isotactic polypropylene [37] to CO2 suppresses the crystallization rate. This observation was suggested to be due to the being depressed to the same extent as the Tg, which prevents the formation of critical size nuclei. It has recently been shown by Hu et al. [38] that the crystallization of polycarbonate may be initiated under scCOz conditions using nano-scale days. 

The melting and crystallization rates of oligomers and polymers were first measured by microscopy in the presence of remaining crystal, to eliminate nucleation effects. Figure 3.94 illustrates data for poly (oxyethylene) as a function of molar mass. On extrapolation to monomer dimensions, the metastabdity gap disappears and one... 

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