Filler orientation

Whilst the injection moulding process has now been widely accepted for phenolics the transition from compression moulding has been less extensive with U-F materials. The basic reason for this is that the U-F materials are more difficult to mould. This has been associated with filler orientation during moulding, which can lead to stress peaks in the finished product which the somewhat brittle resin in less able to withstand than can a phenolic resin. 

For scaly fillers the increase of relative viscosity with filler concentration is not as pronounced as in case of fibrous fillers [177,178]. Owing to filler orientation, the flow curves for systems with different concentrations of a fibrous and a scaly filler may merge together at high shear rates [181]. In composites with a dispersed filler the decrease of the effective viscosity of the melt with increasing strain rate is much weaker. 

Filler orientation is not the only consequence of geometric effects in strained systems with an anisodiametric filler. The appearance of normal stresses has been named as another such phenomenon [169,171,185] which, like the abnormal viscosity behavior of suspensions, may not be due to the elasticity of system components. 

The electrical conduction process depends on several parameters, mainly on filler concentration. But filler morphology such as particle size and structure as well as filler-filler and filler-matrix interactions which determine the state of dispersion and filler orientation are key factors in determining the electrical properties. On the other hand, processing techniques also influence the electrical conductivity of... 

The effect of the drawing and filler orientation in PVC-P extrudates has been studied with improvements noted in mechanical properties (383). 

MECHANICAL PROPERTIES PF PLASTICIZED POLY(VINYL CHLORIDE) EFFECT OF DRAWING AND FILLER ORIENTATION... 

To make practical use of fillers, a knowledge of filler orientation during the flow is needed The best description of orientation principles can be obtained from modelling Figure 9.10 gives the coordinate system used to describe orientation of fibers. 

It is not only the blend morphology which is affected by filler presence filler orientation might be affected by its surface treatment, as was observed in the works on PC/ABS blends containing aluminum borate whisker. When the whisker surface was treated with epoxy silane, its reaction to flow in injection and compression molding processes changed, resulting in a different orientation even though all other parameters of process and composition were the same. ... 

Compression molding is an example of a simple process which does not require expensive equipment but produces cheaply and in simple shapes. Unlike most other processing methods, compression molding does make materials inexpensive through the use of large quantities of fillers. Compression molding applies unidirectional forces usually perpendicular to the material s surface which may thus affect filler orientation. 

If another average orientation state besides uniaxial alignment is of interest for an anisotropic filler, orientation tensors are used to perform orientation averaging [7]. 

Although the transition from compression molding to injection molding has been extensive for phenolics, the same cannot be said for UF Materials, because they are more difficult to mold, possibly because the UF are more brittle than a phenolic resin and so are less able to withstand the stress peaks caused by filler orientation during molding. A combination of compression and injection processes has therefore been developed in which a screw preplasticizing unit delivers preheated and softened material directly to a compression-mold cavity. 

For polyolefin composites, challenges include many variables such as aspect ratio of the fillers, orientation, and the interface. Controlling these properties of the additives can be an easy way to control and tailor the needed properties. 

This relationship has important implications. As shown in Figure 12.23, permeation must be extremely sensitive to particle shape, as expressed in the values of L/W. Thus cubes (or spheres, which are in this sense equivalent) are an order of magnitude less effective than thin plates lying parallel to the plane of the membrane. This trend is in accord with experience (Michaels and Bixler, 1961 Nielsen, 1967b). A second, practical implication is that processing techniques such as extrusion can lead to a significant degree of filler orientation. 

Particle size Volume fraction Fillers orientation... 

Particle Size, Volume Fraction, and Fillers Orientation... 

This is the inherent shrinkage of a material during injection moulding. Moulding conditions, orientation of fillers, orientation of flow and other factors can all influence the specific level of immediate shrinkage but the inherent quality is material dependent. Crystallisation occurring after moulding influences dimensional stability . 

As the measurements have shown, thermal properties of filled polymers depend considerably on filler orientation. Thermal conductivity and specific heat of glass plastics with formaldehyde and epoxy binder increase with increasing temperature, whereas thermal diffusivity falls in inverse proportion with temperature. The direction of the heat flux and orientation of the filler are responsible for the conductance and thermal diffusion in a given direction. Specific heat does not practically depend on the heat flux direction, since it characterizes the scalar value, i.e., energy accumulation. 

To make practical use of fillers, a knowledge of filler orientation during the flow is... 

---