Microscopy is an important, non-destructive method for examining plastics. In general, optical microscopy and electron microscopy are used for characterization.

Stereomicroscopes give a plastic image of the object with magnifications up to 200x.

Conventional microscopes allow magnifications up to 1300x, but with loss of plasticity.

Modern imaging techniques such as “extended depth of focus” allow sharp images, even of three-dimensional structures. Contrast enhancement is made possible by adapted illumination (incident light, transmitted light, bright field, dark field, polarization) and by interventions in the image (phase contrast, interference contrast). Computer-aided image processing and image analysis further extend these possibilities.

The examination of plastic samples in incident light requires absolutely flat surfaces. For this purpose, the samples are embedded in an epoxy resin, and after curing, they are ground and polished.

A grinding and polishing device is used for this purpose.

Scanning electron microscopy (SEM) allows magnifications up to 100,000x

But the biggest advantage of this method is the enormous depth of field of the images, which is ideal for three-dimensional objects. Different surface structures are clearly visible on the image. The quality with which the glass fibres or other fillers have been embedded in the plastic matrix, for example, can be assessed effectively.

In the case of scanning electron microscopy, the sample is scanned line by line with an electron beam in a high vacuum. This requires an electrically conductive sample. Otherwise the sample would become electrically charged and a blurred image would result.

Since plastics generally do not conduct electricity, they are vapour-deposited with a wafer-thin gold layer in a so-called “sputter”. This ensures electrical conductivity without changing the outer structures of the sample.