Platelet orientation

In addition to the nature of particulate platelet orientation induced during injection moulding, the associated consequences on molecular orientation and crystalline order of the host thermoplastic matrix have also been reported with particular regard to various flake-filled polypropylenes [174], together with an attempt to interrelate these higher order structural parameters with physical properties of the composites [175]. 

Single-crystal work by Walmer (37) (on a fully-ordered crystal) showed a maximum of the coercive force in the 111 direction and minima in the 110 and 100 directions, the 100 minimum being the lower of the two (Figure 10). Work by Brissonneau and coworkers (8) on the distribution of platelets in completely-ordered PtCo has led to a model shown in Figure 11, wherein each zone shown in the figure contains a fully-developed network of (110) platelets oriented in two of the three possible orthogonal directions. 

Polydiacetylenes. Single crystals of poly(TCDU) and poly— (DMDA) were deposited on a variety of alkali halide crystals. The resultant morphology of both the monomers and polymers were identical and were elongated platelets oriented in the substrates <110> directions (Figures 5 and 6). 

Chlorite replaces kaolinite, clay pseudomatrix, infiltrated clays, micas and heavy minerals. It occurs as rims composed of platelets oriented perpendicularly to grain surfaces. The rims were formed by replacing infiltrated smectitic clay coatings, which were originally oriented tangentially to grain surfaces (Fig. 14A) (see Moraes De Ros, 1990). These infiltrated clays were presumably introduced into the vadose zone of alluvial continental sediments under semi-arid conditions by episodic floods (Walker et al., 1978 Moraes De Ros,... 

Figure 20.2. Effects of platelet orientation relative to the direction of deformation, predicted by using the model of Brune and Bicerano [11]. The orientation angle is defined as the angle between the symmetry axis of the platelets and the direction of deformation, so that it is 90° if the platelets are aligned perfectly along the direction of deformation while it is 0° if the platelets are aligned completely perpendicular to the direction of deformation. The curves are labeled by the platelet aspect ratio Af. The platelet volume fraction was =0.025, the platelets were assumed to have a Young s modulus of 100 times that of the matrix, and a Poisson s ratio of 0.4 was assumed for both the matrix polymer and the platelets in these calculations.

BLOW-MOLDED CONTAINERS. Initial evaluation of SELAR OH Plus in extruded blow molding containers was disappointing. Barrier improvements of only 30 to 401 were measured compared to the expected 300%.. The resolution of this discrepancy provided some valuable insights into the role of platelet orientation in barrier improvement and the effects of die swell in multilayer extrusion blow molding. 

A set of bottles made on a customer s wheel-type machine showed negligible disorientation of the mica platelets. Barrier results on these samples gave the expected three-fold improvement (Table VI). Summarizing these results on platelet orientation in blow molded bottles versus related barrier enhancement (J /J ) (Table VII) shows that the same level of improvement is achieve ) as in other container processes when the platelets are aligned parallel to the container walls. 

Table VII. Effect of Platelet Orientation on Barrier Enhancement - Coextruded Blow Molded Bottles...

Process Modification Platelet Orientation to Plane of Wall Barrier Enhancement J /J... 

X-Ray Diffraction. This tecnnique has been used for lead formulation where lead phthalate and calcium carbonate show major x-ray peaks. Because of the morphology of the lead phthalate (platelets), oriented... 

Lenk97] Lenk R, Adler J (1997) SiC platelet orientation in a liquid-phase-sintered silicion carbide composite formed by thermoplastic forming techniques. J Eur Ceram Soc vol 17 No 2-3 pp 197-202... 

Utracki and Lyngaae-Jprgensen [2002] observed several common aspects of exfoliated CPNCs and liquid-crystal polymers (LCPs). Similar six-phase structures are predicted for CPNCs and observed in LCPs isotropic, nematic, smectic-A, columnar, house of cards, and crystal [Porter and Johnson, 1967 Balazs et al., 1999 Ginzburg et al., 2000]. These phases in CPNCs originate in a balance between the thermodynamic interactions, clay concentration, and platelets orientation, while in LCPs they depend mainly on temperature. Since it is more difficult on the one hand to prepare disk-shaped than rigid-rod molecules, and on the other to develop flow theory for LCPs with disk moieties, the number of publications on the latter systems is small [Ciferri, 1991]. 

FIGURE 16.8 TEM of PNC from Ube shows in-plane orientation of MMT platelets. Orientation in an unsheared specimen was random, with many hent clay platelets. (From Perrin... 

The proportionality between N and y has been observed at low deformation rates for concentrated LCP solutions in cresol [Kiss and Porter, 1980 Moldenaers and Mewis, 1992], for colloidal and noncolloidal suspensions, and fiber suspensions in a Newtonian matrix [Zirnsak et al., 1994], as well as for block copolymers and multibranched star polymers [Brady and Bossis, 1985 Kotaka and Watanabe, 1987 Masuda et al., 1987 English et al., 1997]. For LCP this behavior was considered originating in polydomain flow [Larson and Doi, 1991], while for rigid fiber suspensions in interparticle interactions [Zirnsak et al., 1994]. It is tempting to postulate that the clay platelet orientation is the origin of the difference. Evidently, the scan direction and the pre-shearing time between data points affect the orientation, but the proportionality Ni =ay and complexity of the ) = f(y) dependence remain. The Larson-Doi [1991] theory of polydomain flow leads to... 

Several authors used the continuum mechanics for modeling conventional polymer composites as well as PNC. Ren and Krishnamoorti [2003] used a K-BKZ integral constitutive model to predict the steady-state shear behavior of a series of intercalated nanocomposites containing an organo-MMT and a disordered styrene-isoprene diblock copolymer. The model predicts the low-y shear stress properties calculated from the experimental linear stress relaxation and the relaxation-based damping behavior. However, as it does not take into account the effect of clay platelet orientation, it is unable to predict the shear stress behavior at intermediate y and the normal stress behavior at all y and clay contents. 

R. Lenk, J. Adler, Influence of forming technique on the SiC platelet orientation in a hquid-phase sintered SiC-matrix, in Fourth Euroceramics, Vol. 2, Part II. Basic Science, C. Galassi (Ed.), Faenca Editrice Italy, pp. 407-414. 

Note that the two curves in Figure 4.2 seem to cross above the weight percent. For the specimens, the thermal expansion coefficient in the transverse direction is also reduced by the addition of montmorillonite clay, but not quite as efficiently as in the flow direction since the platelet orientation is not as great in the former case as it is in the latter case. The coefficient of thermal expansion in the normal direction actually inaeases as montmorillonite clay is added. These trends are quantitatively predicted by the theories discussed above [43]. 

Bartczak, Z., Rozanski, A., and Richert, J. Characterization of clay platelet orientation in polylactide-montmorillonite nanocomposite films by X-ray pole figures. Eur. Polym. J. 61 (2014) 274-284. 

In contrast with the above results, Zhang et al. (2003) reported a decreased orientation of iPP in iPP/PP-MA/o-MMT nanocomposites during dynamic packing injection moulding as compared to that of neat iPP solidified under the same conditions. Similarly, Medellin-Rodriguez et al. (2001) found that the overall molecular orientation of the crystals was found to decrease with the clay content in Nylon 6/clay nanocomposites subject to uniaxial deformation, with some clay platelets oriented perpendicular to the film surface and the molecular axis of the Nylon 6 crystals parallel to the stretching direction. This was explained by the presence of the clay platelets as well as the rotation of the clay platelets during deformation, which hindered the orientation of the nylon crystals. 

However, mostly, the ideal case of 0 = 0° is not achieved. To consider the influence of platelet orientations on permeability, Bharadwaj (2001) introduced an order parameter S into the above equation. S is defined as ... 

Mahesha C, Zumbrunnen DA, Parulekar Y. Novel clay nanocomposites with platelets oriented by chaotic advection. In Proceedings of the 63rd Annual Technical Conference 2005, Society of Plastics Engineers, Boston, MA. p. 1920-4. 

As can be seen in Figm e 15.7a, upon deformation, the stress is mainly taken up by the platelets particularly those that are close to being aligned parallel with the stretch-direction. In fact, the magnitude of the stress in the platelets is up to an order of magnitude greater than that in the polymer. Note that platelets orientated almost perpendicular to the stretch direction carry much less stress compaied with those parallel to it. 

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