Filler aspect ratio

Fig. 8.3 Percolation threshold for different aspect ratio fillers and...

Celzard A, McRae E, Deleuze C, Dufort M, Furdin G, Mareche JF. Critical concentration in percolating systems containing a high-aspect-ratio filler. Physical Review B. 1996 Mar 1 53(10) 6209-14. 

The coefficents of thermal expansion of mineral fillers are considerably less than those of thermoplastic polymers and thus their incorporation can significantly reduce that of a composite material. This is a generally useful effect. High aspect ratio fillers, when aligned by processing, will often give rise to anisotropic effects, leading to problems of warp age [69]. 

This factor approaches 1 for aspect ratios above 10, pointing out the importance of using high aspect ratio fillers. 

The most common reasons for adding fillers, especially high aspect ratio fillers, to polymers is to improve physical properties such as increased modulus (stiffness) or reduced creep. 

Distribution of fibers Aspect ratio Filler Frequency of oscillation Coefficient of expansion of filler Shear modulus Gibbs free energy Heat of reaction, change Hildebrand unit, solubility parameter value High-density (linear) polyethylene Heat deflection temperature... 

In addition to its use as glass fiber (discussed in Section 7.5), glass is used in the form of low-aspect-ratio filler particles to provide useful properties and the economic advantages. 

Casciola M, Bagnasco G, Domiadio A, Micoli L, Pica M, Sganappa M, Turco M (2009) Conductivity and methanol permeability of Nafion-zirconium phosphate composite membranes containing high aspect ratio filler particles. Fuel Cells 9 394-400... 

High aspect ratio fillers, such as woUastonite and glass fibers can have an even stronger effect than talc and mica on increasing the modulus of elasticity, tensile strength, and heat-distortion temperature of poly(lactic acid) (PLA)-based systems. 

Improper location of the gate or multiple gates may produce a zone where the two melt fronts meet (weldline). For unfilled polymers, this region usually has inferior properties compared to other locations within the part mechanical weakness becomes more pronounced in the presence of high aspect ratio fibers and flakes, which may not interpenetrate and instead lie in their most unfavorable orientation for effective reinforcement. A more moderate detrimental effect on properties has been observed vdth low aspect ratio fillers. In general, fibrous fillers cause up to 50% loss in... 

The organization of this edition follows that of the earlier one. Part I (Chapters 1-3) provides an introduction to the types and properties of functional fillers and their polymer composites, including melt mixing aspects. Part II (Chapters 4-6) discusses different types of surface modifiers and coupling agents for fillers. Part III discusses in detail individual types of man-made, natural, in-situ generated and mineral fillers, and their functions. High aspect ratio fillers (Chapters 7-10), low aspect ratio fillers (Chapters 11-16), and a variety of specialty fillers for specific applications (Chapters 17-24) are included in Part III. Each filler chapter, typically, contains information on (a) production methods, (b) structure and properties, (c) suppliers, (d) cost/availability, (e) environmental/toxicity considerations, and (f) applications based on primary and secondary functions. 

Fillers with high aspect ratios (length diameter ratio) are better at reinforcing a polymer than chimky particles with a roughly spherical shape. High aspect ratio fillers will normally produce a significant increase in modulus, heat distortion temperature and creep resistance. 

High aspect ratio fillers include wollastonite and talc, and mica, a lamellar or plate-like filler, also has a modest reinforcing effect. 

From this analysis, it is clear that high aspect ratio filler particles, which are needed to achieve stiffness in a composite will inevitably cause increased stresses in the polymer matrix near the particle edges, which will facilitate failure under impact loads. 

High aspect ratio fillers give high permanent set, (e.g., talcs). It is thought that increases in aspect ratio have the effect of increasing the stresses generated internally between filler particles when a compound is stressed. This in turn leads to increased flow rates between the filler particles, which results in increased permanent set... 

In this section we are going to discuss the effect high aspect ratio fillers have in the polymer matrix and subsequent properties. We will discuss the effect the filler shape, size, distribution and orientation have on the polymer matrix focusing especially in the resulting morphology. 

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