ABSTRACT
Processing of thermoplastic polymers often leads to parts which are partially oriented and contain frozen-in stresses. Nevertheless, molecular orientation is often imparted to the processed part in order to improve mechanical properties. The resulting objects present a very high molecular orientation and show a great degree of springback once subjected to temperatures higher than their own glass transition. At sufficiently high temperatures, these oriented thermoplastic materials partially recoil, modifying the shape of the formed parts (see Figure 1). The total deformation is generally described as formed by instantaneous elastic, viscoelastic, and viscous (plastic) components [1-3]. This poor dimensional stability reduces the range of application for oriented thermoplastic materials and remains one of the major problems in the forging of plastics. In this regard, stiff fibers can be added to a polymer to improve dimensional stability and to minimize the shrinkage normally encountered in common polymer-processing operations upon cooling the material from the melt. Recoil of oriented polystyrene. https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781003418139/7816cb3f-30d1-479e-b0b8-ad1dcc749b65/content/fig20_1.tif" xmlns:xlink="https://www.w3.org/1999/xlink"/>
