Effect of platelet orientation

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.

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

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. 

Wick P, Louw-Gaume AE, Kucki M, Krug HF, Kostarelos K, Faded B, Dawson KA, Salvati A, Vazquez E, Ballerini L, Tretiach M, Benfenati F, Plahaut E, Gauthier L, Prato M, Bianco A (2014) Classification framework for graphene-based materials. Angew Chem Int Ed 53 2-7 Wilder JWG, Venema LC, Rinzler AG, Smalley RE, Dekker C (1998) Electronic structure of atomically resolved carbon nanotubes. Nature 391 59-62 Yalcin B, Valladares D, Cakmak M (2003) Amplification effect of platelet type nanoparticles on the orientation behavior of injection molded nylon 6 composites. Polymer 44 6913-6925 You Z, Mills-Beale J, Foley JM, Roy S, Odegard GM, Dai Q, Goh SW (2011) Nanoclay-modified asphalt materials preparation and characterization. Construct Build Mater 25 1072-1078... 

M. (2003) Amplification effect of platelet type nanoparticles on the orientation behavior of injection molded nylon 6 composites. Polymer, 44, 6913-6925. 

Because the cells can intermpt the optical path in random orientations, individual scattering intensities are not proportional to cell volume. However, because thousands of cells of each type pass through the flow cell, the effects of orientation can be averaged To a first approximation HCT and platelet crit (PCT), the percentage of blood sample volume occupied by platelets, is proportional to the sums of the scattering intensities of the ted cells and platelets, respectively. MCV can be computed from HCT and RBC, whereas MPV can be computed from PCT and PLT. The accuracy of MCV deterrnined by this method is tied to the RBC accuracy, as is the case for the manual MCV method. Ortho Instmments Corporation s ELT-8 uses these counting and sizing methods. 

The most efficient orientation fields are exten-sional. Using convergent and divergent flow one may control orientation of anisometric particles. Most of the work in this area has been done with fiber-filled materials but the effects are equally important for flow of neat semicrystafline polymer melts or liquid crystal polymers [Goettler and Shen, 1983 Goettler, 1984]. There is less information on the flow-induced orientation of platelets. In extensional flow, these particles are less susceptible to orientation. Two-stage orientation mechanism was observed in converging flow [Utracki, 1988]. 

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. 

Mixtures of clay platelets and polymer chains compose a colloidal system. Thus in the melt state, the propensity for the clay to be stably dispersed at the level of individual disks (an exfoliated clay dispersion) is dictated by clay, polymer, stabilizer, and compatibilizer potential interactions and the entropic effects of orientational disorder and confinement. An isometric dimension of clay platelets also has implications for stability because liquid crystalline phases may form. In addition, the very high melt viscosity of polypropylene and the colloidal size of clay imply slow particulate dynamics, thus equilibrium structures may be attained only very gradually. Agglomerated and networked clay structures may also lead to nonequilibrium behavior such as trapped states, aging, and glassy dynamics. 

The jxSR study by Grosse et al. (1999) used mosaics of oriented single-crystal platelets. LaS, the lower concentration limit (x = 0), is diamagnetic. The ZF spectra are static Gaussian Kubo-Toyabe patterns originating from the nuclear moments on La. Full decoupling needs only LF=10G. Between 300 K and 4K only a minute change in static width is seen, which can be accounted for by thermal contraction. These data show that effects of muon diffusion are not discemable. US, the upper concentration limit (x = 1) is a FM (7c = 177 K and fiu = 1.7 Ub). The reduction in moment was... 

Metallic effect pigments consist of small reflecting platelets. They mostly occur plane-parallel to the plastic surface. Pearl effects occur when the metallic effect pigment is colorless, or, at most, consists of thin platelets of iridescent color. Mother-of-pearl effects occur when orientation effects are also present. 

Both fillers, for aspect ratios sufficiently high, have similar levels of ultimate reinforcement, reaching the same plateau, which corresponds to the rule of mixtures (horizontal solid lines). However fiber-like fillers approach maximum reinforcement already for aspect ratios of 100, while platelet-like fillers need aspect ratios higher than 2000. It can therrfore be concluded that, in the imidirectional case, fibers are more effective than platelets. This is, however, different for the situation of randomly distributed fillers. Figure 12.3b shows the reinforcement of 3D randomly oriented fiber-like and platelet-like fillers, of different aspect rahos, in a polypropylene (PP) matrix. The observation that fiber fillers reach the maximum reinforcement for aspect ratios much smaller than those necessary in the case of platelet filler shll holds. This effect is also more prominent since randomly distributed platelets need an aspect ratio of 10,000. Nevertheless, the plateau relative to platelet fillers is twice as high as for fibers filler. It can therefore be concluded that, in the case of randomly oriented filler, platelets are more effective than fibers but only for aspect ratios higher than 100. 

A simple tortuous 2 D model developed by N ielsen to depict the effect of the size and aspect ratio a of platelet fillers with orientation perpendicular to the diffusion path on the barrier properties of the polymer composite related Eqs. (8.1) and (8.2) are found in Chapter 8. 

Equations accounting for the effects of deviation from planar orientation of flakes on film permeability in the presence of a second impermeable crystalline phase [21]), and in the case of randomly oriented layered clay platelets [28, 29]. 

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