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Microstructure spherulite

Semicrystalline materials are often considered as composite materials at a nanoscale and then the use of micromechanical models to predict the macroscopic properties is quite natm al. But semicrystalline materials camiot be put so easily in one of the three classical previous modeled families defined for composites and polycrystalline materials because the crystalline microstructure is complex and organized at several scales. Therefore, the first question is At which scale do we have to consider this composite material At a microscale, that is the scale of the crystalline microstructure (spherulites, shish-kebabs) Or at the nanoscale of the crystalline lamellae ... [Pg.56]

The formation of the microstructure involves the folding of linear segments of polymer chains in an orderly manner to form a crystalline lamellae, which tends to organize into a spherulite structure. The SCB hinder the formation of spherulite. However, the volume of spherulite/axialites increases if the branched segments participate in their formation [59]. Heterogeneity due to MW and SCB leads to segregation of PE molecules on solidification [59-65], The low MW species are accumulated in the peripheral parts of the spherulite/axialites [63]. The low-MW segregated material is brittle due to a low concentration of interlamellar tie chains [65] and... [Pg.284]

The volume inside the semicrystalline polymers can be divided between the crystallized and amorphous parts of the polymer. The crystalline part usually forms a complicated network in the matrix of the amorphous polymer. A visualization of a single-polymer crystallite done [111] by the Atomic Force Microscopy (AFM) is shown in Fig. 9. The most common morphology observable in the semicrystalline polymer is that of a spherulitic microstructure [112], where the crystalline lamellae grows more or less radially from the central nucleus in all directions. The different crystal lamellae can nucleate separately... [Pg.159]

Polyolefin foams are easier to model than polyurethane (PU) foams, since the polymer mechanical properties does not change with foam density. An increase in water content decreases the density of PU foams, but increases the hard block content of the PU, hence increasing its Young s modulus. However, the microstructure of semi-crystalline PE and PP in foams is not spherulitic, as in bulk mouldings. Rodriguez-Perez and co-workers (20) showed that the cell faces in PE foams contain oriented crystals. Consequently, their properties are anisotropic. Mechanical data for PE or PP injection mouldings should not be used for modelling foam properties. Ideally the mechanical properties of the PE/PP in the cell faces should be measured. However, as such data is not available, it is possible to use data for blown PE film, since this is also biaxially stretched, and the texture of the crystalline orientation is known to be similar to that in foam faces. [Pg.12]

Looking at the structure of these crack tip plastic zones in more detail, it is found that the individual crazes are less straight compared to the low temperature crazes (Fig. 21). This indicates a more pronounced influence of the crystalline microstructure on craze formation. Figure 21a and b demonstrate for fine spherulitic, highly isotactic PP the interaction between the crazes and the microstructural features. Most of the... [Pg.249]

The PP microstructure modifications obtained in presence of the different fillers were analysed degree of crystallisation X. (from DSC analysis), and spherulite size Dj measured from... [Pg.41]

The content of amorphous phase and the small size of spherulites lead to an improvement of the fracture toughness of Polypropylene [16]. In presence of mineral filler, the particle surface chemistry can induce some specific microstructural characteristics of the PP matrix parameters such as degree of crystallisation, spherulite size, and p phase content (a/p ratio) [16]. [Pg.42]

With CaC03, the spherulite size is significantly reduced (Ds = 10-15 pm) and the particle surface chemistry induces some specific microstructural characteristics of the PP matrix small size surface treated CaC03 particles promote formation of the p phase. Without surface treatment, CaC03 has a nucleating effect the degree of crystallisation is increased by about 20%(X(. = 65%). [Pg.42]

Ultrafine Si02 particles have no significant effect on the PP microstructure the degree of crystallisation is constant, and the spherulite size is slightly reduced. This could be explained by the amorphous structure of Si02, and the size of the particles (10 to 10 times smaller than Ds). [Pg.43]

In the case of semi-crystalline PET, comparing the TEM photographs and the measured spherulite sizes, it can be assumed that the individual reactive particles should be distributed in within the spherulitic structure. Concerning the non-reactive one it is highly probable, knowing the small size of the semi-crystalline microstructure, that the modifier clusters remain outside the spherulites. [Pg.73]

Finally, crystalline microstructure of PET is not significantly modified by the blending if one except a small nucleating effect of the non-reactive additive that can be observed in laboratory conditions. However, this nucleating effect is not due to the nodule itself [20] as no transcrystallisation can be observed on particles. Additionally, this nucleating effect does not lead to significant evolution in mean spherulite diameter in injection moulded parts. [Pg.73]

Figure 16.7 Temporal evolution of the crystalline microstructure in the 50/50 iPP/EPDM blend, following a T-quench from the isotropic melt to a supercooled temperature below both the UCST spinodal gap, showing the growth of spherulitic front in the concentration field, but the overgrowth of this spherulitic boundary on the bicontinuous SD domain structures can be seen clearly only in the enlarged version. Figure 16.7 Temporal evolution of the crystalline microstructure in the 50/50 iPP/EPDM blend, following a T-quench from the isotropic melt to a supercooled temperature below both the UCST spinodal gap, showing the growth of spherulitic front in the concentration field, but the overgrowth of this spherulitic boundary on the bicontinuous SD domain structures can be seen clearly only in the enlarged version.
In the case of a semicrystalline polymer such as PP, the microstructural features are likely to appear at the scale of the spherulites (typically 5-100 pm in diameter) or even closer at the scale of the long period of the lamellar stacks (10-100 nm). In order to accede to the latter details, it was shown previously (48) that etching of the polished surface with oxidizing acids engraves the amorphous interstices and let the crystalline morphology appear lamellae, or at least stacks of lamellae, become visible. [Pg.587]

All materials belong to the class of semi-crystalline thermoplastic polymers. Characteristic appearances of spherulitic microstructures of the polymers are shown in Figures 4 and 5 for the examples of POM and PA66. [Pg.6]

The results of Figure 11 indicate that the polymers studied were subject to different microstructural deformation mechanisms. In this connection it must be borne in mind that the maximum nominal deformation of POM and PA66 was only 1% whereas PP and PTFE were deformed up to 1.8% and 3.3% respectively. Therefore it may be assumed that for POM and PA66 only an instantaneously reversible deformation of the amorphous matrix of the spherulitic microstructure occurred (18) whereas for PP and PTFE some irreversible effects, like interlamellar shearing or reorientation of the lamellae may have taken place. [Pg.13]

The third design feature is the polymer microstructure. Morphology of polymer can influence wear resistance of polymers. For example, in a semicrystalline polymer, both amorphous and crystalline phases coexist. The amorphous phase has been shown by Tanaka (8) to be weaker than the crystalline phase, thus the former wears faster than the latter. In addition to the difference in phases, the size of the spherulites and the molecular profile can also influence the wear rates. Thus, a control of the morphology through crystallization can improve the wear resistance of a polymer such as polytetrafluoroethylene (11). [Pg.79]

In spite of much research, some details of the microstructure of semicrystalline polymers are still unknown. Polymer development has proceeded empirically, with microstructural knowledge being acquired later, and then used to explain mechanical and physical properties. The order of presentation is that of increasing size scale Bonding in the crystal unit cell, the shape of lamellar crystals, the microstructure of spherulites, the overall crystallinity and the processes of crystallisation. Details of polymer crystal structures and microstructures can be found in literatures listed in Further Reading . [Pg.77]

Recent advances in catalysis have allowed the production of polyolefins with low crystallinity. Spherulitic structures (see next section) only occur in propylene-ethylene copolymers when the crystallinity exceeds 45% (Fig. 3.22). Sheaf-like structures occur when the crystallinity is between 30 and 45%, whereas axialites and isolated lamellae occur between 15 and 30% crystallinity. Axialites are multi-layer aggregates of lamellar crystals which splay out from a common edge. Embryonic axialites occur for crystallinity from 5 to 15%. Therefore, as the crystallinity is reduced, the microstructures become simpler. [Pg.82]

The microstructural factors that have the greatest effect on mechanical properties are the per cent crystallinity and the preferred orientation of the crystals (if any). Composite mechanics concepts will be needed to explain the mechanical properties of spherulitic polymers hence we return to them at the end of the next chapter. [Pg.94]

In most spherulitic polymers, touching spherulites occupy whole of the space. Their microstructure is too complex to be completely modelled, especially if there is twisting of lamellar stacks about spherulite radii. Consequently, models simplify the structure, and use composite micromechanics concepts. A stack of parallel lamellar crystals with interleaved amorphous layers (Fig. 3.20) has a similar geometry to a laminated rubber/metal spring (Fig. 4.1). The crystals have different Young s moduli E, Eb and E (Section 3.4.3), and different shear moduli when the... [Pg.117]

If crystallisation occurs in an oriented melt, then non-spherulitic microstructures can form, with preferred orientation of the crystals (Section 3.4.10). Fibrous nuclei, believed to contain fully extended polymer chains, can form in an oriented melt. Figure 6.7a shows several fibrous nuclei, in a polyethylene injection moulding, aligned with the flow direction. On either side of these dark nuclei is a bright layer, where lamellar crystals have grown from the nucleus. The c axes of the lamellar crystals are parallel to the fibrous nucleus the microstructure of platelet crystals skewered by a rod-like nucleus has been described as a shish kebab. The rest of the microstructure consists of small spherulites. [Pg.182]

In an extrusion blow-moulded polyethylene container with a 1 mm wall, about 5 s elapse before crystallisation takes place at the inner surface (Eq. 5.2). During this time, the melt tensile stresses relax, so the microstructure will be spherulitic, even though the spherulites may be somewhat distorted. In contrast there is high orientation in the wall of a stretch blow-moulded PET bottle (Section 2.4.7) because crystallisation occurred while the preform was stretching. [Pg.182]

For semi-crystalline polymers, the average orientation function 2 for the crystal c axes can be calculated from X-ray diffraction measurements (Chapter 3). Figure 8.15 shows how 2 increases linearly with the draw ratio, for polypropylene fibres and films, while the spherulitic microstructure survives. At 2 = 0.9, where the spherulites are destroyed and replaced by a microfibrillar structure, there is an increase in the slope of the 2 versus true strain relationship. It is impossible to achieve perfect c axis orientation... [Pg.247]

Olley et al. (1999) examined the microstructure of fabricated acetabular cups inside the particles, there is no obvious spherulitic microstructure. Regions of about 6 xm diameter contain lamellae of width typically 0.5 xm (Fig. 15.15). These are surrounded by a looser boundary of 2 xm wide lamellae, consisting of lower molecular weight material. Such material diffuses to the boundaries to effect the bonding process. [Pg.459]


See other pages where Microstructure spherulite is mentioned: [Pg.516]    [Pg.544]    [Pg.181]    [Pg.189]    [Pg.27]    [Pg.82]    [Pg.278]    [Pg.434]    [Pg.57]    [Pg.100]    [Pg.392]    [Pg.228]    [Pg.355]    [Pg.587]    [Pg.249]    [Pg.152]    [Pg.214]    [Pg.23]    [Pg.203]    [Pg.997]    [Pg.158]    [Pg.189]    [Pg.516]    [Pg.84]    [Pg.113]    [Pg.232]    [Pg.248]   
See also in sourсe #XX -- [ Pg.545 , Pg.569 ]




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