Poly crystallization half-time

Figure 12.14 presents the values of the inverse of the half-crystallization time, I/Tsoo/, as a function of reported by Muller et al. [133] for a PLLA-6-PE and a corresponding homopolymer. The results clearly indicate that the PLLA block within the copolymer crystallizes at much slower rates than homo-PLLA when similar crystallization temperatures are considered by extrapolation. Such a decrease in the overall crystallization rate of the PLLA block within the copolymer (and the higher supercooling needed for crystallization) is considered responsible for the coincident crystallization effect that can be observed when the PLLA-6-PE diblock copolymer is cooled down from the melt at rates larger than 2°C/min. A similar effect has also been reported by Muller et al. for weakly segregated poly (p-dioxanone) -6-polycaprolactone diblock copolymers [135,136]. 

The dependence of the overall crystallization rate on the composition of these two blends differs from those of the growth rates.(77) The half-time for syndiotactic poly(styrene) crystallization is plotted against the crystallization temperature for both type blends in Fig. 11.33. The half-times for the pure syndiotactic polymer are represented again by the sohd circles. For this type of measurement the halftimes increase with the addition of either poly(vinyl methyl ether) or PPO. The addition of poly(vinyl methyl ether) causes a larger increase in the half-time and thus a greater reduction in the crystallization rate. The overall crystallization rate is a reflection of both initiation and growth of crystalUzation. Both of these processes... 

Sodium benzoate, nucleating agerrt for a-form of iPP, increases the crystallization temperature of iPP by 15 C and decreases its isothermal and nonisothermal crystallization half-times at concentrations that approach its eqirilibrirrm solubihty in the molten poly-... 

Addition of 1,3,5-benzenetricarboxyhc acid tris(cyclohexylamide) to iPP decreased its activation energy from 370 to 312 kJ/mol. " Also, half time of the crystallization (t,/2) of virgin iPP was larger than that of nucleated iPP and the required cooling rate of virgin iPP to reach the same relative crystallinity was higher than that of nucleated iPP. Nano-CaCOj decreased activation energy of poly(butylene terephthalate) even at very low concentrations. ... 

Foams were produced from poly(lactic acid) using wood fibers as nucleating agent. The cellulosic fibers, acting as crystal nucleating agents, increased the crystallization temperature and the crystallinity and decreased the crystallization half time. ... 

Table 4.1 Crystallization Half-Time (Min) for Poly(L-lactide-co-meso-lactide) (Kolstad, 1996)...

Fig. 4.24. A plot of the rate of crystallization of natural rubber, poly(l,4-c/ -isoprene), over an extended temperature range. The rate plotted is the reciprocal of the time required for half the total change in volume. From [152].

The crystallization of an isotactic poly(styrene) sample that was originally freeze dried from a 0.01 wt percent benzene solution vividly demonstrates the influence of chain entanglements on the kinetics.(50d) Such a sample has a minimal amount of entanglements since it essentially comes from a dilute solution. Consequently it was found that freeze dried samples crystallized, in terms of half-times, approximately nine times faster than the untreated polymer. Both samples crystallized from the pure melt in the conventional manner. This result is consistent with the Rory-Yoon calculations that the chains cannot disentangle each other from the melt during the time scale of the crystallization.(50e,50f) This calculation is consistent with the... 

Fig. 10.28 Plot of isothermal crystallization half-time against crystallization temperature for block copolymer (E/SEB63) and hydrogenated poly(butadiene) (E40). (From Loo et al. (64))...

Fig. 10.37 Plot of half-time, O/2, against crystallization temperature for long chain branched poly(butylene terephthalate). Number average degree of branching o zero O 0.5 0.6 A 0.6 > 1. (From Righetti and Munari (85))...

Fig. 11.7 Plot of half-time, tq.s, for the crystallization of poly(ethylene oxide) against crystallization temperatures of blends of poly(ethylene oxide)-poly(p-vinyl phenol). Composition o 100/0 90/10 80/20 70/30 A 65/35. (From Pedrosa etal. (18))...

Fig. 11.21 Plot of half-time of polyfethylene terephthalate) as a function of its concentration in blends with poly(butylene terephthalate). (a) Crystallization temperature 200 °C. (b) Crystallization temperature 130 °C. (From Escala and Stein (36))...

Fig. 11.33 Crystallization half-time, ti/2, as a function of crystallization temperature, To, for different blend compositions of syndiotactic poly(styrene) with either poly(vinyl methyl ether) or PPO. Composition syndiotactic poly(styrene)-PPO pure syndiotactic poly(styrene) 90/10 80/20. Composition syndiotactic poly(styrene)-poly(vinyl methyl ether) O 90/10 80/20. (From Cimmino et al. (77))...

Fig. 11.41 Plot of crystallization half-time for crystallization of poly(phenylene sulfide) in blends with linear polyethylene and with poly(ethylene terephthalate) as a function of crystallization temperature. Pure poly(phenylene sulfide) . Composition poly(phenylene sulflde)-linear polyethylene blends 50/50 A 75/25 o 90/10. Composition poly(phenylene sulfide)-poly(ethylene terephthalate) blends 50/50 T 75/25 A 90/10. (From Jog et al. (81))...

An interesting observation associated with crystallization under uniaxial deformation is the marked enhancement of the crystallization rate at constant tempera-tures.(43,44,55,56) For example, the crystallization rate constant of natural rubber increases by six to nine orders of magnitude with extension ratio at constant temper-atures.(43) This enhancement is also reflected in the crystallization half-time, which also increases by several orders of magnitude.(44,46,47,55,56) This enhancement of crystallization rate is not limited to rubber-like polymers. It is also observed in poly(pentenamer) (50) and in poly(ethylene terephthalate) (47 9,57,57a) when crystallized under uniaxial deformation. The change in rate can be attributed in part... 

---