Transcrystallization

Transkorper, m. trans substance, transkristallisieren, v.i. transcrystallize. translatorisch, a. translational. 

Morphology of Transcrystallized Isotactic PP Induced by Pulling of a Carbon Fiber... 

A. Dufresne, M. B. Kellerhals, and B. Witholt, Transcrystallization in Mcl-PHAs/cellulose whiskers composites. Macromolecules, 32 (1999) 7396-7401. 

Spherulites can be considered as special forms of dendritic growth. Dendrites are always produced when crystals grow in the direction of a strong temperature gradient in supercooled melts (see also Section 5.4.4). The liquid phase occurring between the dendrites often solidifies in a microcrystalline form. In addition, the nucleation can occur from the melt surface. Transcrystallization is the name given to this process, which is strongly influenced by diffusional processes. 

Transcrystallization is the name given to a crystallization in which the formation of a large number of adjacent nuclei occurs on the surfaces of the melt. It is considerably influenced by nucleation density. 

Dufresne A, Cavaille JY, Helbert W (1997) Thermoplastic nanocomposites filled with wheat straw cellulose whiskers. Part II effect of processing and modeling. Polym Compos 18 199 Dufresne A, Kellerhals MB, Witholt B (1999) Transcrystallization in Mcl-PHAs/cellulose whiskers composites. Macromolecules 32 7396-7401 Dufresne A, Dupeyre D, Vignon MR (2000) Cellulose microfibrils from potato tuber cells processing and characterization of starch-cellulose microfibril composites. J Appl Polym Sci 76 2080-2092... 

Fukuzumi H, Saito T, Iwata T et al (2008) Transparent and high gas barrier films of cellulose nanofibers prepared by TEMPO-mediated oxidation. Biomacromolecules 10 162-165 Garcia de Rodriguez NL, Thielemans W, Dulfesne A (2006) Sisal cellulose whiskers reinforced polyvinyl acetate nanocomposites. Cellulose 13 261-270 Gousse C, Chanzy H, Excoffier G et al (2002) Stable suspensions of partially silylated cellulose whiskers dispersed in organic solvents. Polymer 43 2645-2651 Gray DG (2008) Transcrystallization of polypropylene at cellulose nanocrystal surfaces. Cellulose 15 297-301... 

Further, this chapter provides a survey about the formation of a transciystalline layer in the composite system. The occurrence of transcrystallization was found to strongly depend on the type of chemical treatment of the fiber surface. Predominant nucleation ability was found for unmodified fibers. However, chemical modification of fiber surface slightly depressed the nucleation of polypropylene matrixes. 

Fig. 10.5 Optical micrographs showing the transcrystallization in flax fiber4>olypropylene composites, (a) crystallization temperature — 130°C, speed of fibers pulling —0.42 mm/s, (b) after selective melting in temperature — 150°C of sample showed in Fig. 10.5a...

A transcrystalline layer (TCL) is the supermolecular crystalline stmcture, induced by an oriented growth in the presence of the foreign surface. Transcrystallization occurs when the nucleation density of a solid filler that is in contact with melted... 

High density of nuclei on foreign surface causes disturbance in spherulites growth, which results in the only possible growth - perpendicularly to the surface. As a result, transcrystalline front will emerge parallel to the surface. Transcrystallization is possible when nucleation energy conditions are more favorable on the surface than in the bulk of the melt. The microscopic photograph of TCL is shown in Fig. 10.6. 

Presence of TCL changes the properties of crystalline matrix. Transcrystallization of isotactic polypropylene in the presence of different fibers has been thoroughly analyzed. Gray as the first one provided detailed description of isotactic polypropylene behavior in the presence of wood fibers using polarized light microscopy. He observed that when melted polymer is cooled down, it crystallizes in spherulite forms in nonisothermal and isothermal conditions, creating additionally a TCL. 

Results of many researches confirm the presence of TCL as the effect of nucleation ability of different substances. Among the factors inducing transcrystallization in polyolefin matrix, the following fillers can be listed ... 

Transcrystallization of Isotactic Polypropylene on the Surface of Lignocellulosic Fillers... 

The results of research described above prove univocally that the presence of lignocellulosic material in polymeric composites influences the crystallization process, altering the kinetic parameters, such as induction time, degree of crystallinity, conversion degree, etc., and characteristic temperatures. Using modification of the filler is not without the effect on crystallization of the matrix. An interesting phenomenon that has not been explained completely so far is the transcrystallization. Both the formation of transcrystallization and its effect on mechanical properties remain a disputable question among researchers. 

Varga J, Karger-Kocsis J (1994) The difference between transcrystallization and shear-induced cylindritic crystallizatirai in fibre-reinforced polypropylene composites. J Mater Sci Lett 13 1069-1071... 

Gray DG (2008) Transcrystallization of polypropyltme at cellulose nanocrystal surfaces. Cellulose 15 297-301... 

Thomason JL, Rooyen AA (1992) Transcrystallized interphase in thermoplastic composites. J Mater Sci 27 889-896... 

Grozdanov A, Bogoeva-Gaceva G (2003) Transcrystallization of maleated polypropylene In the presence of various carbon fibers. Polym Bull 50 397-404... 

Gray D (1974) Polypropylene transcrystallization at the surface of cellulose fibre. J Polym Sci 12 509-515... 

The transcrystallization in isotactic polypropylene occitrs beginning from a network of nucleating agents. The network provides continuous reinforcing stractures, which could be used to improve fiber-matrix adhesion and resist crack propagation. ... 

Carbon and aramid fiber produced a uniform transcrystalline layer in polyamide-66, the transcrystallization depended strongly on thermodynamic conditions such as ciystalli-zation temperature and cooling rate. ... 

JL Thomason, AA van Rooyen. Transcrystallized interphase in thermoplastics composites. Part II. Influence of interfacial stress, cooling rate, fibre properties and polymer molecular weight. J Mater Sci 27 897-907, 1992. 

J Varga, J Karger-Kocsis. The occurrence of transcrystallization or row-nucleated cylindritic crystallization as a result of shearing in a glass-fiber-reinforcd polypropylene. Composites Sci Tech 48 191-198, 1993. 

The strong effect of the surface topology on the epitaxial type of transcrystallization of iPP has been described by Hobbs (81,82). The primary factors affecting transcrystallization on the filler surface include temperature gradient near the filler surface, chemical composition of the filler surface, crystalline morphology of the filler surface, surface energy of the filler, adsorption of nucleants presented in the polymer, epitaxy, and topography of the filler (83-86). 

Transcrystallization was reported to occur during cooling of a quiescent PP melt being in intimate contact with various organic and inorganic substrates having high nucleation ability. In this case, the nucleation rate... 

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