Platelets filler

To achieve the goal of required performance, durability, and cost of plate materials, one approach is improvement of the control of the composition and microstructure of materials, particularly the composite, in the material designing and manufacturing process. For example, in the direction of development of thermoplastics-based composite plate, CEA (Le Ripault Center) and Atofina (Total Group) have jointly worked on an irmovative "microcomposite" material [33]. The small powders of the graphite platelet filler and the PVDF matrix were mixed homogeneously by the dispersion method. The filler and matrix had a certain ratio at the microlevel in the powder according to the optimized properties requirements. The microcomposite powders were thermocompressed into the composite plate. 

Figure 12 shows the temperature dependence of the logarithmic decrement of neat IPN and filled IPN. The logarithmic decrement of neat IPN showed relative high attenuation, while filled IPN prepared by adding platelet fillers showed an even higher attenuation over a wide temperature range. 

Judging from the results of dynamic mechanical analyses, IPNs showed more effective damping properties than commercial chloroprene rubber at elevated temperatures. In addition, filled IPNs prepared by adding platelet fillers showed even higher attenuation (logarithmic decrement). 

A recent paper by Cussler, et al., (9) using a regular array model also predicted quite high barrier improvements. Their equation (Equation 2) predicted that aspect ratio and volume fraction of filler would be the major variables. They incorporated a universal correction designated, /j, as a geometric factor to correct for the reality that available platelet fillers were not shaped like uniform rectangular parallelepipeds of uniform size and shape. 

During initial studies, blends of several types of ethylene vinyl alcohol copolymers were made with all three types of platelet fillers, aluminum flake, mica and talc. Blend loadings were from 9 to 33 wt % filler. Thin films, 1 to 2 mils in thickness, were melt pressed from these composites and used to measure oxygen and water permeation rates. 

A three-fold improvement in gas barrier has been demonstrated with a mica platelet filler in EVOH. This suggests that a value of about 0.3 would be appropriate as the geometric factor in the Cussler model using irregular flakes of nonuniform size typical of commercially available fillers. 

The effects of composite formation are not only restricted to the improvement of mechanical properties, such as toughness, tensile strength, and many other, but also include, improvement of thermal and electric conductivities (carbon black, pol yrrole), reduction of water migration (platelet fillers such as talc and mica), improvement fire resistance (alumina trihydrate), improvement of quality (wood-like feel with wood filler), and decorative value. 

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. 

Complex viscosity vs. frequency data would show that viscosity increase would be the highest for fibrous fillers and lowest for spherical fillers whereas particulate and platelet fillers would lie in between. Further rigid fillers would show higher complex viscosity than flexible fillers at the same frequency if their dimensions were similar. 

In general, steady shear viscosity and extensional viscosity bear very similar results when the effecte of the various parameters are considered. Additirar of fillers increases the viscosity of the base polymer. The ctent of viscosity increase is the lowest for 3-dimensional spherical fillers, higher for 2-dimensional platelet fillers and the highest for 1-dimensional fibrous fillers. Rigid fillers show greater increases in the level of viscosity than flexible fillers. 

---