Experimental Study of Preform Reheat Temperature in Two-Stage Injection Stretch Blow Molding B. Demirel, 1 F. Daver 2 1 Faculty of Engineering, Department of Materials Science and Engineering, Erciyes University, Melikgazi 38039 Kayseri, Turkey 2 School of Aerospace, Mechanical and Manufacturing Engineering, Bundoora, RMIT University, Victoria 3083, Australia Plastic bottles used for carbonated soft drink (CSD) packages are most commonly made from poly(ethylene terephthalate) (PET) by injection stretch blow molding (ISBM). The required bottle performance criteria vary with its application but typically include top-load strength, burst strength, optical clarity, thermal stabil- ity, and barrier properties. An experimental study of the preform reheat temperature was carried out for a 1.5-l PET bottle produced by a two-stage ISBM machine. The overall temperature of the preform was changed by controlling the reheat temperature of the preform; all the other process variables and preform dimensions were kept constant. Performance of the PET bottles for differing preform reheat temperatures was meas- ured experimentally in terms of top-load strength, burst pressure resistance, environmental stress crack- ing resistance (ESCR), and thermal stability. It was observed that the ESCR values and the burst strength decreased with the increasing reheat temperature, whereas the top-load strength increased. Thermal sta- bility tests confirmed that high-preform reheat temper- atures had a detrimental effect on the self-standing feature of the bottles. Decreasing the reheat tempera- ture as low as possible, while maintaining a certain preform temperature profile, ensured high ESCR and burst strength values and prevented the concaveness at the bottom of the bottle. POLYM. ENG. SCI., 53:868– 873, 2013. ª 2012 Society of Plastics Engineers INTRODUCTION PET bottles are usually produced in either one-stage or two-stage ISBM machines. The process starts with injec- tion molding of a tube-like ‘‘preform.’’ The preform is stretched axially by a stretch rod and radially by pressur- ized air until it takes up the shape of the bottle mold. During the blow stage, a preblow is applied to prevent the axial stretch rod contacting the inside of the preform, which may result in defects in the bottle. When the rod reaches the bottom of the container, a high-blow pressure is applied to impart intricate details of the bottle mold and to improve the cooling efficiency. In single-stage ISBM process, injection-molded preform is blown in situ once it has cooled to just above its glass transition temperature; whereas in the two-stage ISBM process, injection-molded preforms are stored until subsequent blow molding usually at the bottle filling stage. Hence, the preforms require reheating [1]. During ISBM process, PET molecules undergo biaxial orientation and associated strain hardening. Biaxial defor- mation of PET strongly depends on forming temperature, strain rate, stretch ratio, deformation mode, and molecular weight [2]. The subsequent biaxial orientation of PET molecules directly influences mechanical and barrier prop- erties of the bottles [3, 4]. Strain hardening, which is tem- perature and strain rate-dependent, provides a self-leveling effect on the stretching preform, which is important in achieving uniform wall thickness. For a two-stage ISBM process, the preform reheat temperature dictates the mate- rial distribution in the bottle as well as the clarity and the ease of processing. In industrial applications, the preform is generally reheated using infrared (IR) lights [5], which take advantage of the semitransparent behavior of amor- phous preforms, resulting in an axial surface temperature profile between 80 and 1158C [6, 7]. Both the neck above the support ring and the preform base are kept cooler relative to the preform body temperature to prevent the distortion of the bottle closure and to avoid piercing of the preform base by the stretch rod. However, the preform body temperature may also vary because of tapering in the thickness of the wall. When the temperature of the preform body is not quite right, too much material may reside in the sidewalls and not in the base [8]. The tem- perature of the preform is also known to affect the final morphology of the petaloid bases of the CSD bottles [9]. In one of the earlier experimental study conducted by Correspondence to: B. Demirel; e-mail: bilaldemirel@erciyes.edu.tr DOI 10.1002/pen.23333 Published online in Wiley Online Library (wileyonlinelibrary.com). V V C 2012 Society of Plastics Engineers POLYMER ENGINEERING AND SCIENCE—-2013