Micropores
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Micropores
During the injection moulding process, volume contraction (see: processing shrinkage) occurs as the material cools. In areas where material has accumulated, this volume contraction of the melt is greater, and the reduced volume cannot be replaced by fresh melt. As a result, tensile residual stresses build up within the material.
Micropores occur when the solidified surface layer is sufficiently stable to counteract the internal tendency to contract. Due to the tensile stresses acting within the material, the moulding compound tears open at the centre of material accumulations. Micropores are very small shrink voids (vacuoles) that occur in the plastic core. As they are very small, they are largely inconsequential in terms of strength and stiffness, but can be observed as white discolouration in unfilled moulded parts. In transparent or translucent materials, however, they impair the optical properties (see Figure).
| Figure: | Micropores in a translucent plastic component made of polypropylene (abbreviation: PP) |
See also
- Micro-damage limit
- Failure analysis plastics products, VDI Guideline 3822
- Failure analysis – Basics
- Gas bubbles
- Shrink voids
- Hole formation films
- Hole formation plastics
References
| [1] | VDI 3822 Blatt 2.1.2 (2024-06): Failure Analysis – Defects of Thermoplastic Products Made of Plastics Caused by Faulty Processing |
Additional references on polymer diagnostics/damage analysis
- Ehrenstein, G. W.: Kunststoff-Schadensanalyse – Methoden und Verfahren. Carl Hanser, Munich Vienna (1992) (ISBN 978-3-446-17329-3; see AMK-Library under D 2)
- Ehrenstein, G. W.: SEM of Plastics Failure – REM von Kunststoffschäden. Carl Hanser, Munich (2010) (ISBN 978-3-446-42242-1; see AMK-Library under D 5)
- Engel, D., Klingele, H., Ehrenstein, G. W., Schaper, H.: Rasterelektronenmikroskopische Untersuchungen von Kunststoffschäden. Carl Hanser, Munich Vienna (1978) 1st Edition (ISBN 978-3-446-12560-5, see AMK-Library under D 8)
- Brostow, W., Corneliussen, R. D.: Failure of Plastics. Carl Hanser, Munich Vienna (1986) (ISBN 978-3-446-14199-5; see AMK-Library under D 10)
- Ezrin, Myer: Plastics Failure Guide – Cause and Prevention. Carl Hanser, Munich 2nd Edition (2013) (ISBN 978-1-56990-449-7; see AMK-Library under D 7)
- Kurr, F.: Praxishandbuch der Qualitäts- und Schadensanalyse für Kunststoffe. Carl Hanser, Munich (2014) (ISBN 978-3-446-43775-3; see AMK-Library under D 6-2)