Particle size, aspect ratio and pith: why filler geometry matters

Read a mesh specification correctly #

The phrase 20–60 mesh is useful only when the sieve convention and retained/passing fractions are defined. It is not a universal optimum. Two fillers with the same nominal mesh label can contain different mixtures of fines and elongated particles.

Stark and Rowlands compared several wood-flour sizes in polypropylene. Their results included different trends for notched and unnotched impact, illustrating why a larger particle cannot simply be labelled better. A separate investigation of wood flour and polyethylene considered size, aspect ratio and moulding temperature together. [R20,R21]

Look beyond the particle width #

Aspect ratio is length relative to width or diameter under a stated measurement method. Specify whether it was measured before compounding or in the finished composite. The distinction matters when a process changes the reinforcement geometry.

Canola straw with pith and depithed straw is a sensible comparison to investigate, but this collection does not claim a verified numerical advantage for either. A study of wood-flour geometry provides a more general basis for keeping particle form and processing history visible in the comparison.

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A practical supplier comparison #

Request the sieve distribution, microscopy method, moisture result and batch identity. Compare fillers using the same polymer, equipment and test conditions before changing production specifications. Add the handling question: can the filler be fed consistently at the required output?

For specifiers, the consequence is simple. A supplier's particle-size claim may explain part of its process, but the finished product still needs the relevant performance evidence. Mesh numbers do not replace a board test.

Evidence and source scope #

[1] Experimental study; official abstract.

[2] Experimental study.

[3] Experimental study; geometry, not proof of a canola-pith result.

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