Isothermal crystallization and melting

During the last several years, much effort has been spent on developing new materials, based on iPP/elastomers blends. This interest is related to the fact that addition of the rubber phase improves the impact strength of the iPP, The present paper reports on a study of the isothermal crystallization and melting behaviour of thin films of isotactic polypropylene blended with an ethylene--propylene diene terpolymer and three samples of polyisobutylene with different molecular mass. 

Cao, D. and Wu, L. (2009) Poly(L-lactic acidj/sUicon dioxide nanocomposite prepared via the in situ melt polycondensation of L-lactic acid in the presence of acidic silica sol Isothermal crystallization and melting behaviors. Journal of Applied Polymer Science, 111, 1045-1050. 

Yang HS, Yoon JS, Kim MN (2005) Dependence of biodegradability of plastics in compost on the shape of specimens. Polym Degrad Stab 87 131-135 Yasuniwa M, Tsubakihara S, Satou T, lura K (2005) Multiple melting behavior of poly(butylene succinate).II. Thermal analysis of isothermal crystallization and melting process. J Polym Sci B Polym Phys 43 2039-2047... 

Wang ZG, Hsiao BS, Srinivas S, Brown GM, Tsou AH, Cheng SZD, Stein RS (2001) Isothermal Crystallization and Melting of Isotactic Polypropylene Analyzed by Time- and Temperature-dependent Small-angle X-ray Scattering Experiments Polymer 42 7561-7566. 

Table 21.2. Crystalline orientation, non-isothermal crystallization and melting characteristics of PP nanocomposites...

The importance of SAXS experiments for studies of the basic mechanisms of polymer crystalUzatiou and melting is demonstrated with four examples. (1) Time aud temperature dependent measurements on s-PP during isothermal crystallization and melting yidd the dependencies between... 

Table 3.4 collects the differential scanning calorimetry (DSC) studies of iioii-isothermal crystallization and melting behavior of PP and its nanocomposites produced by the one-step technique. The data show that the melting point of PP is nearly not affected by the nano-silica. It means that no transition of... 

Zapata-Espinosa A, Medellin-Rodriguez F J, Stribeck N, Almendarez-Camarillo A, Vega-Diaz S, Hsiao B S and Chu B (2005) Complex isothermal crystallization and melting behavior of nylon 6 nanoclay hybrids. Macromolecules 38 4246-4253. 

Figure 2.30 X-ray powder diffraction patterns of sPP samples isothermally crystallized from melt at indicated temperatures.172 Indices of 211 and 020 reflections are given for unit cell of form I of Figure 2.29a.

Figure 20.26 Polarized optical micrographs of isothermal crystallized (4h) melt blends (x400) (a) 210°C (b) 230°C (c) 210°C (d) 230°C [44], From Park, J. K Park, Y. H., Kim, D. J. and Kim, S. H., Crystallization kinetics of TLCP with polyester blends, J. Korean Fiber Soc., 37, 69-76 (2000). Reproduced with permission of The Korean Fiber Society...

PLA crystallizes usually between 83 and 150°C but its fastest rate of crystallization occurs between 95 and 115°C [83]. The value of the crystallization half time (t, j) varies according to author. In the temperature range 95-115 °C the tj 2 of PLLA for crystallization from the melt varies between 1.5 min to 5 min [45, 79, 84]. Nevertheless the optimum, 1.5 min, is obtained at around 110°C for isothermal crystallization from melt (Figure 8.6) [45]. Not only does the tj of PLA depend widely on the crystallization temperature, but it is also linked to the crystallization type (isothermal or non-isothermal, from cold or melted state). So upon isothermal crystallization from the cold state, t is below 2 min [79, 85, 86]. Eventually, upon non-isothermal crystallization, t also lies around 2 min [85,87,88]. The further the isothermal crystallization is from this optimum, the more tj increases. For isothermal crystallization below 90°C or above 130°C, tj can be beyond 10 min [45, 69]. 

In this section experimental results are discussed, concerned with analyses of melting and crystallization kinetics, as well as reversibility of the phase transition. The frame of the discussion is set by Fig. 3.76, which will be supported by experimental data on poly(oxyethylene). The thermal analysis tools involved are TMDSC, optical and atomic-force microscopy, DSC, adiabatic calorimetry, and dilatometry. Most of these techniques are described in more detail in Chap. 4. Results from isothermal crystallization, and reorganization are attempted to be fitted to the Avrami equation. This is followed by a short remark on crystallization regimes and finally some data are presented on the polymerization and crystallization of trioxane crystals. 

Wu, L. and Hou, H. (2010) Isothermal cold crystallization and melting behaviors of poly(L-lactic acid)s prepared by melt polycondensation. J. Appl. Polym. Sci., 115, 702-708. 

Relaxation profiles obtained as loss peak in imaginary dielectric curve and as step jump of real permittivity line Partial miscibility might exhibit multiple relaxation peaks overlaying or towards individual components, or display diverse relaxation rate even >T, Non-isothermal crystallization by isochronal temperature sweep DSC (cold crystallization and melting discernible as sudden drop and steep rise of static dielectric permittivity, respectively) Crystallization onset predicted using DRS relaxation time in coupUng model faster than the experimental time... 

Stress-strain relationships are determined by DMA and temperature scans reveal glass transitions, crystallization and melting information. Blends of polypropylene and rubber have been studied by where the intensity of one of the two crystallization exotherms was used as a measure of the polypropylene domains and compared to the size determined by TEM cryomicrotomy and osmium tetroxide staining methods [25]. Isothermal annealing of PET above the crystallization temperature was shown to influence the morphology and increase thermal stability by combined SAXS and DSC analysis [26]. An excellent text edited by Turi [21] described the instrumentation and theory of thermal analysis and its application to thermoplastics, copolymers, thermosets, elastomers, additives and fibers. 

The crystallite formation during isothermal crystallization was studied in time-dependent SAXS experiments. Subsequent to the isothermal crystallization the melting was monitored in temperature dependent SAXS measurements up to the melting point. Fig. 1 displays as an example the curves K"(z) for s-P(P-co-0)4 and s-P(P-co-0)15 during and subsequent to isothermal crystallization processes. 

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