Stretch blow moulding of PET; structure development and constitutive model

Abstract

International audienceMicrostructure of PET in stretch blow moulding is studied combining controlled tension followed by quenching, free-blow and ISBM. Due to quenching, observed final microstructure is often closer to a mesophase than to crystal. Texture is, for its part, controlled by the loading path. In fact stretching only induces appearance of an oriented precursor-phase that will become a crystal during cooling steps providing that this latter is slow enough. Microstructure evolution does not obey the classical "nucleation -growth" schematic. This enlightens development of constitutive models demonstrating the irrelevance of the crystallinity ratio as parameter and of the Avrami-like approach as part of the model. One, model based on revisited network approach is suggested

Strain-induced crystallization of poly(ethylene 2,5-furandicarboxylate). Mechanical and crystallographic analysis

“…This result validates the way conditions were defined using DMTA master curve. The value of 6 is higher than classical NDR obtained for PET whose order of magnitude is 2-3 [4,5,35,39]. Above this NDR, PEF exhibits an impressive strain hardening which can be the witness of a strong chains microstructural organization thanks to the stretching process.…”

Experimental characterisation and modelling of polyethylene terephthalate preform for injection stretch blow moulding

“…Some researchers also pointed out that modifications occurring to microstructure during the PET blow stretching for the different phases of ISBM are likely to control the process in terms of end-use properties of the final part (Yan et al, 2017). These phenomena are not yet completely understood but lead toward the development of a new class of constitutive model as discussed in (Billon et al, 2014;Cosson et al, 2012). Independently of the theoretical background, every constitutive model requires proper experimental testing to identify all the material parameters.…”

Measuring and modelling air mass flow rate in the injection stretch blow moulding process

“…The material characterisation technique using the biaxial stretching machine was not able to replicate the sequential deformation type for every foreseeable stretch scenario; indeed, only constant width and pure biaxial deformation were captured. The amount of initial linear stretch, and therefore the onset of orientation and eventual strain hardening [19][20][21][22][23][24][25][26][27][28][29], significantly affects the inflation of the preform.…”

“…The simulation is still at an early stage of development and no correlation between simulation and experiment is available. Billon et al [4] has focused on understanding how PET behaves during stretch blow moulding. The microstructure of formed bottles and 'free blown' bottles have been analysed showing how the crystallinity and orientation develops during stretch blow moulding and a numerical model of PET has been developed to capture these features based on an Edwards Vilgis hyperelastic model.…”