Biaxial deformation and experimental study of PET at conditions applicable to stretch blow molding

Abstract

This article is concerned with understanding the behavior of polyethylene terephthalate (PET) in the injection stretch blow molding (ISBM) process where it is typically biaxially stretched to form bottles for the packaging industry. A comprehensive experimental study was undertaken, analyzing the behavior of three different grades of PET under constant width (CW), simultaneous (EB), and sequential (SQ) equal biaxial deformation. Experiments were carried out at temperature and strain rate ranges of 80-1108C and 1 s 21 to 32 s 21 , respectively, to different stretch ratios. Results show that the biaxial deformation behavior of PET exhibits a strong dependency on forming temperature, strain rate, stretch ratio, deformation mode, and molecular weight. The tests were also monitored via a high speed thermal image camera which showed an increase in temperature between 58C and 158C depending on the stretch conditions. POLYM. ENG. SCI., FIG. 14. Average surface temperature of PET specimen (calculated from within the boxed area) following EB deformation at 908C and a strain rate of 16 s 21 to a stretch ratio of 3. (a) Before the deformation is conducted. (b) After the deformation is stopped.

A novel methodology to characterize the constitutive behaviour of polyethylene terephthalate for the stretch blow moulding process

“…However, these two factors affect the material behaviour during the deformation in opposite ways, i.e. the higher temperature makes the material softer but the higher deformation rate makes the material stiffer [10] [12]. Hence, the combination of high temperature and high deformation rate or low temperature and low deformation rate reduces the diversity in the gradient of the strain hardening region.…”

“…Numerous researchers world-wide have developed their own test platforms and enabled significant advances to be made in understanding the evolution of microstructure in PET materials under processing conditions [3][4][5][6][7][8][9], and to generate stress strain data that is suitable for developing and validating constitutive material laws [10][11][12][13].…”

The Effect of Selected Conditions in a Thermoforming Process on Wall Thickness Variations

“…This method is used in polymer processing primarily for measuring the temperature of both finished parts and processing tools [3,6,9,15,19]. The measurements were made using the V-20 II ER005-10 infrared camera from VIGO System S.A. and the Therm V 20 software.…”

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

“…Each part of the constitutive model was represented by complex equations that required a large amount of data to perform accurate curve fitting procedures. The material data used for the curve fitting procedure, and as a result the material constants, were determined from extensive material testing using the QUB biaxial stretcher [19,20] and strain history form the DIC analysis of the FSB trials. The biaxial testing was performed on 76x76x0.5mm samples of PET cut from extruded sheet, the same grade as the preform material.…”

“…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.…”