Morphology transcrystallinity

A type of transcrystalline morphology can also occur during cooling, when columnar crystals preferentially nucleate perpendicular to the reinforcing fibers. This effect is observable under a polarizing optical microscope. 

Zapeiropoulos NE, Baillie CA, Matthews FL (2001) A study of transcrystallinity and its effect on the interface in flax fibre reinforced composite materials. Compos A 32(3) 525-543 Hagstrand PO, Oksman K (2001) Mechanical properties and morphology of flax fiber reinforced melamine-formaldehyde composites. Polym Comp 22(4) 568-578 Vazquez A, Dominguez V, Kenny JM (1999) Bagasse-fiber-polypropylene based composites. J Therm Compos Mater 12 477-497... 

Son SJ, Lee YM, Im SS (2000) Transcrystalline morphology and mechanical properties in polypropylene composites containing cellulose treated with sodium hydroxide and cellulose. J Mater Sci 35 5767-5778... 

During the cooling of crystallizing Hot melt adhesives, the presence of the snbstrate can lead to surface nucleation, giving a colnmnal transcrystalline polymer morphology in the interfacial region. There have been reports that such layers influence measured adhesion, but conclusive demonstration has proved elusive. ... 

A Lustiger, CN Marzinsky, RR Mueller, HD Wagner. Morphology and damage mechanisms of the transcrystalline interphase in polypropylene. J Adhesion 57 1-14, 1995. 

Neat isotactic polypropylene (iPP) crystallized from melt exhibits spherulitic morphology of the crystalline phase (72,73). In some cases and under very specific conditions, cylindrites, axialites, quadrites, hedrites, and dendrites may be formed of iPP (74). In general, crystallization from quiescent melts results in spherulitic morphology, whereas crystallization fi-om melts subjected to mechanical loads results in cylindrites (75). Crystalline supermolecular structure caused by oriented crystal growth from heterogeneous surfaces is commonly termed transcrystallinity (76). 

Transcrystalline morphology is formed when crystallization takes place on the solid surface of fillers or reinforcements. Transcrystallizafion takes place when the density of the crystal nuclei is substantially greater on the surface of solid inclusions than in the melt bulk (77). Because polyhedral sphemlites cannot develop due to restricted lateral growth on the solid surface, crystallites are allowed to grow only in stacks perpendicularly to the surface plane (78). In the case when only one crystal form occurs in a polymer, Keller (79) confirmed that the microstructure of transcrystalline layer and bulk crystalline phase is identical. For PP, however, the situation is more complicated by the polymorphism so that one crystal form can exist in the transcrystalline layer and another in the polymer bulk. The nature of nucleation of the transcrystalline layer is still somewhat con-... 

The morphology of high-modulus carbon-fiber (HM-CF) reinforced iPP was investigated by AFM using chemically etched specimens [7]. The images exhibit typical features of a-transcrystalline morphology for samples which were crystallized from quiescent melts, and nucleated on HM-CF. In melts sheared by fiber pulling, ap-cylindritic columnar... 

Keywords atomic force microscopy (AFM), structure, morphology, spherulite, hedrite, lamella, conformation, chain packing, films, scanning force microscopy (SFM), tapping mode, syndiotactic PP, (3-PP, transcrystallinity, corona treatment, biaxial orientation. 

The first extensive SEM investigation of PA6/PET-based MFCs and their precursors performed by Evstatiev et al. [82] undoubtedly showed the fibrillar structure of the PET reinforcements preserved after the PA6 matrix isotropization. Since then, electron microscopy has been used to visualize the orientation and morphology of the matrix and reinforcing components in almost every report on MFCs. It is worth noting some more recent studies on MFCs comprising LDPE and PET as matrix and reinforcement, respectively [30,31]. Several microscopic techniques were used, e.g., SEM, polarizing light microscopy (PLM) and TEM. Thus, by SEM it was demonstrated that the isotropic LDPE matrix embedded PET microfibrils with random orientation. Thin slices of PLM and TEM showed the orientation in the machine direction. The latter method also revealed the formation of transcrystalline layers of LDPE on the oriented PET microfibrils. 

There exist a limited number of studies on the occurrence of transcrystaUinity in MFC. Li et al. [38,42,43] studied the crystal morphology of iPP/PET in situ MFC, prepared by a slit extrusion, hot stretching-quenching process, and foimd that transcrystallinity occurred aroimd the PET in situ microfibrils. The authors propose different nucleation mech-... 

Stern T, Marom G and Wachtel E (1997) Origin, morphology and crystallography of transcrystallinity in PE-based single polymer composites, Compos Part A 28 437-444. 

---