Influence of part dimension on ageing of injection moulded thermoplastic materials: exemplary studies on amorphous polyc
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TECHNICAL PAPER
Influence of part dimension on ageing of injection moulded thermoplastic materials: exemplary studies on amorphous polycarbonate Steve Meister1 Received: 17 August 2020 / Accepted: 30 August 2020 Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Injection moulding of polymer micro parts often affects the inner structure due to process conditions with reduced part dimensions. Consequently, ageing effects can increase with reduced part dimensions. This paper investigates the ageing effects in different scaled tensile bars, exemplarily injection moulded of polycarbonate. The results reveal during the here applied artificial ageing conditions the chemical ageing effects have less influence and primary physical ageing effects take place. A reduction of part dimensions leads to increasing impact of ageing effects for the here investigated polycarbonate.
1 Introduction Micro and thin-wall parts are used in almost all technical applications, e.g. in the areas of medical technology, as components of optical systems, as micro gears, in micro fluidics, electronics or as a micro-electromechanical system (Angelov and Coulter 2004; Bibber 2004). Microinjection moulding appears to be one of the most efficient processes for a large-scale production of thermoplastic polymer micro parts (Drummer et al. 2012; Michaeli et al. 2002). For example, in MEMS application an annual growth rate of more than 13% is expected (Eloy 2011) which is due to the flexible adjustment of polymer materials with regards to mechanical, thermal or electrical requirements (Dormann and Juettner 2009; Liu 2007; Yang et al. 2013). Notwithstanding, it can be concluded that there are still a lot of questions especially regarding the part and process design (Farrugia et al. 2014). The properties of an injection moulded part are influences, besides the used material and part design, especially by the process conditions. With reduced part dimensions an increasing cooling and shearing have more influence on the development of the morphology and crystallinity as well as on the generation of orientations and residual stress (Giboz
& Steve Meister [email protected] 1
Gaudlitz GmbH, Callenberger Straße 42, 96450 Coburg, Germany
et al. 2007, 2009; Haberstroh and Brandt 2002; Jungmeier 2010; Schmiederer and Schmachtenberg 2006; Meister and Drummer 2013). A high melt flow velocity and high cooling rates favours the development of orientations. Thus, in parts with smaller dimensions a more orientations are to be expected, especially in surface areas. This is exemplarily shown in a scaled micro tensile bar in Fig. 1. Increasing cooling rates reduce the time for possible relaxation of process induced molecular orientations and lead to vacancies of about the atomic size, which is referred to as free volume (Ehrenstein 2001). This also results in a shift in the glass transition temperature to higher temperatures on cooling. Due to the temperature gradient across the component cross-se
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