Comparative analysis of the application of old sandpaper versus new sandpaper

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If the surface of a sample polished with worn-out sandpaper appears smoother and more reflective than that polished with new sandpaper. Therefore, does old sandpaper produce better polishing results than new sandpaper?

Let's discuss the reasoning why this is not the case.

Taking silicon carbide sandpaper, the most common type, as an example, sandpaper is manufactured by bonding sharp abrasive particles onto a paper backing using adhesive, usually a type of resin. Since sandpaper polishing is a micro-abrasion process, the damage or deformation caused by worn-out abrasives on the sample is greater compared to sharp abrasive particles.

The cross-sectional comparison image below clearly shows the difference between new and old sandpaper. The abrasive particles on new sandpaper protrude sharply, while after some usage, the abrasive particles become fractured, losing their sharp edges and embedding completely within the bonding layer. At this point, the material removal rate slows down, and there is increased opportunity for rubbing and contact.

The depicted abrasion marks were obtained using new and old sandpaper, and you may wonder which one represents a better surface preparation. The answer is that the abrasion marks from new sandpaper appear clearer and exhibit a three-dimensional morphology, with one mark overlapping another. In contrast, the abrasion marks from old sandpaper lack a distinct three-dimensional appearance and appear flattened on a plane. However, in this case, the depth of the sample's deformed layer will be significantly increased. It is only because the marks appear flatter and the sample's reflectivity improves that an illusion of more successful preparation is created. Now, you probably know the correct answer.

Therefore, during the polishing process, do not fear scratches. The clear, three-dimensional, and regular scratches left by new sandpaper represent successful material removal. Timely replacement of the sandpaper will help you obtain samples with less residual damage.

In summary, although the surface polished with old sandpaper may initially appear smoother and more reflective, it is due to the flattening of the abrasion marks and the increased deformation of the sample. In terms of effective material removal and achieving optimal surface preparation, new sandpaper always outperforms old sandpaper. Embrace the scratches left by the new sandpaper as they indicate successful material removal. Remember to replace the sandpaper promptly to minimize residual damage on the samples.