Solidification of semicrystalline polymers in rotational
| Title |
Solidification of semicrystalline polymers in rotational |
| Publication year |
2004 |
| Language |
English |
| Author |
Glomsaker, Terje |
| Co-Authors |
Andreassen, Erik - Larsen, Åge - Ommundsen, Espen (Norner) |
| Source |
Esaform 2004, Trondheim, Norway, April 28-30, 2004 |
| Abstract |
Rotational moulding is a common process for producing large hollow components in various types of plastics. Plastic powder is distributed and melted/sintered in a rotating temperature-controlled mould. During the cooling stage, the mould is cooled by air or water. The outer surface of the polymer component, which is in contact with the mould, is cooled faster than the inner wall, which is in contact with air. This creates a solidification front moving from the outer surface towards the inner surface, and thus the inhomogeneous volume contraction, due to temperature and crystallinity gradients, induces asymmetric residual stresses and warpage of the final product. We have in this work developed an experimental technique that is able to quickly rate different materials with respect to warpage under typical rotational moulding conditions. The technique is based on melting of a pressed plate which is subsequently cooled from one side only. The technique has been applied to create reproducible results for a different short chain branched polyethylenes (also known as linear low density polyethylene, LLDPE) in order to rate the materials in terms of warpage versus stiffness. We have also developed a numerical model in order to simulate the induced residual stresses and warpage. The model includes a non-isothermal kinetic crystallisation model fitted to DSC measurements at a range of different cooling rates, and is used to discuss various models for the mechanical properties after the liquid-solid transition and adhesion to the substrate. |