Injection Stretch Blow Moulding Research Articles

Effects of mechanical recycling on PET stretchability

Two commercial polyesters, a virgin (VPET) and a recycled (RPET), were mechanically recycled in a closed loop with a pilot recycling line designed for bottle-to-bottle recycling. The stretchability after one, two and four loops were measured by uni-axial drawing experiments above the glass transition temperatures of the polymers. Thanks to the time-temperature equivalence principle, the materials were deformed in a physical state equivalent to the one encountered during the injection stretch-blow molding (ISBM) process. The mechanical recycling of the commercial VPET leads to a significant loss of drawability. The lower drawability of RPETs (commercial or produced by the pilot line) could explain the more numerous bottles explosions during ISBM. A microstructural interpretation is proposed through SEC chromatography and DSC analysis.

A Comparative Study on Crystallisation for Virgin and Recycled Polyethylene Terephthalate (PET): Multiscale Effects on Physico-Mechanical Properties.

Poly(Ethylene Terephthalate) (PET) is one of the most used polymers for packaging applications. Modifications induced by service conditions and the means to make this matter circular have to be understood to really close the loop (from bottle to bottle for example). Physico-chemical properties, crystalline organisation, and mechanical behaviour of virgin PET (vPET) are compared with those of recycled PET (rPET). Using different combined experimental methods (Calorimetry, Small Angle X-ray Scattering [SAXS], Atomic Force Microscopy [AFM], Dynamic Mechanical Analysis [DMA], and uniaxial tensile test), it has been proven that even if there is no change in the crystallinity of PET, the crystallisation process shows some differences (size and number of spherulites). The potential impact of these differences on local mechanical characterisation is explored and tends to demonstrate the development of a homogeneous microstructure, leading to well-controlled and relevant local mechanical property characterisation. The main contribution of the present study is a better understanding of crystallisation of PET and recycled PET during forming processes such as thermoforming or Injection Stretch Blow Moulding (ISBM), during which elongation at the point of breaking can depend on the microstructure conditioned by the crystallisation process.

Construction of the visco-elastic constitutive model for polyethylene terephthalate in a rubbery state

Polyethylene terephthalate (PET) is an important commercial engineering polyester thermoplastic used in beverage bottles. PET is usually biaxial stretched above its glass transition temperature (T g ) and molded into containers by injection stretch blow molding (ISBM) under a rubbery state. This paper constructs a visco-elastic constitutive model for PET above T g . The stress-strain behaviors of PET can be explained by the Eyring activation mechanism and the Arruda-Boyce eight-chain rubber model(A-B model). In the constitutive model, the overall stress of PET is equivalent to the sum of Eyring dashpot and A-B model stresses. The uniaxial tensile test data confirms the constitutive model under three stretch rates and temperatures. The constitutive model can furtherly be applied in the numerical simulation of the PET ISBM process.

Determination of The Best Injection Stretch Blow Molding Process Parameters in Polyethylene Terephthalate Bottle Service Performance

Polyethylene terephthalate (PET) bottles which are thermoplastic materials are used very commonly for the storage and transport of carbonated beverages. The most used production method for PET bottles is the Injection Stretch Blow Molding (ISBM) process. There is a variety of parameters affecting the produced PET bottles’ performances. Amongst these parameters, stretch rod movement, blowing pressure and preform surface temperature are the most important ones. Assignation of the optimal design parameters in PET bottles is taken into account. The effects of the parameters such as Preform Temperature (°C), Stretch Rod Position (mm) and Final Pressure (Bar) were analysed with the Taguchi method (TM), Grey relational analysis (GRA) and ECHIP. Body-weight (gr) (R1), Top Load (Pa) (R2), Burst Pressure (Bar) (R3), Stress Crack Resistance (Min.) (R4) and Tg (oC) (R5) were consiedered as performance parameters. The experimental design proposed by Taguchi involves using orthogonal arrays. An L9 orthogonal array was chosen for the procedure. Primarily, the performance parameters were optimized with the ECHIP Design of the Experiment (DOE). Thereafter, all of the factors were optimized together with TM, GRA and ECHIP.

Numerical Simulation of Recycled PET Preforms Infrared Heating Including Force Convection Effect in the Industrial ISBM Ovens

Nowadays, injection stretch blow molding (ISBM) process represents the most employed technology to produce plastic bottles. An important step of this process is the heat conditioning stage which is performed within infrared ovens by the use of powerful halogen lamps. Homogenizing the temperature distribution along and inside the preform at the end of this conditioning stage is one of the key parameters to determine the final quality of the bottle (thickness, mechanical properties, transparency...). In this research work, a numerical software has been developed to simulate recycled PET (rPET) preforms infrared heating inside the industrial ISBM ovens, where both rotation and translation of the preform across different heating modules occur. In addition, the presence of a fan system involving a forced convective condition inside the ovens is also considered using a Computational Fluid Dynamics (CFD) approach instead of using a conventional heat transfer coefficient.

Infrared heating modeling of recycled PET preforms in injection stretch blow molding process

Relatively recent citizen’s consciousness about plastic pollution forces industrial actors of packaging to re-invent their shaping processes and materials. Specifically, for plastic bottle industry shaping, classical Polyethylene Terephthalate (PET) material is little by little replaced by recycled PET (rPET). The change in material composition due to recycling loops leads to an inevitable adaptation of the Injection Stretch Blow Molding (ISBM) process used to shape bottles at a satisfactory production rate. Indeed, rPET contains contaminants which modify its optical properties, so the heating stage becomes material-dependent and unstable regarding the polymer supplier. The approach adopted in this article is to build a numerical model able to simulate the infrared heating of rPET preforms, sensitive enough to predict changes in temperature due to the recycling rate. To do so, the optical properties of 50% and 100% rPET are measured by spectrometry and implemented in the simulation. Thermal radiative heat transfer between infrared lamps and rPET preforms is simulated by ray tracing method using an in-house software so-called RAYHEAT. Then, the result of the infrared ray tracing computation is used as the input heat source for thermal simulation by commercial software COMSOL Multiphysic®in order to simulate the temperature distribution of the preform. The numerical results are then confronted to experimental ones obtained on a research Stretch Blow Molding pilot, instrumented with thermography. The results show that the temperature obtained at the end of a classical heating cycle of the 100% recycled grade is 8 °C higher than the virgin one. Also, simulations confirm that this difference is attributed to changes in optical properties. Finally, heating 100% rPET at a sufficient forming temperature is about 8% less energy consuming than for virgin PET.

A proposal for enhanced microstructural development of Poly(ethylene 2,5-furandicarboxylate), PEF, upon stretching: On strain-induced crystallization and amorphous phase stability improvement

Poly(ethylene 2,5-furandicarboxylate), PEF, has been described regarding its ability at developing strain-induced crystallization (SIC). The influence of several stretching settings on its microstructural development has been investigated. Based on the time/temperature superposition principle, the stretching settings have been chosen to draw the material in its rubbery-like state. Two equivalent strain rates, defined at the reference temperature of 100 °C, have been selected. For each equivalent strain rate, two strain rate/temperature couples (“slow” and “rapid”) are selected. It appears that the strain rates (“slow” or “rapid”) have an influence on the induced microstructure in terms of crystal perfection, amorphous phase rigidity and thermal stability. Depending on the strain rate, the presence (for “rapid” tests) or the absence (for “slow” tests) of self-heating upon stretching is reported. Indeed, it could be the key point to determine the final definition of the crystal obtained. Additionally, the amorphous domain mobility is impacted: the stability of the amorphous domain with temperature has been increased with the use of “rapid” conditions. SIC occurs for all the stretching settings applied but the use of couples with rapid strain rates/high temperatures could be more efficient to improve the microstructure definition and stability: these results are of prime interest regarding industrial applications such as ISBM (Injection Stretch Blow Moulding) or thermoforming.

Infrared Heating Modeling of Recycled Pet Preforms in Injection Stretch Blow Molding Process

Infrared Heating Modeling of Recycled Pet Preforms in Injection Stretch Blow Molding Process

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

Polyethylene terephthalate (PET) is a widely used polymer in the production of bottles by injection stretch blow moulding (ISBM). In this work, we present a characterisation method to identify material properties directly from a preform, considering temperature and stress-relaxation effects related to its viscoelastic response. A customised oven and gripping system were designed to perform uniaxial tests in a proper temperature range on tubular specimens obtained from preforms. A visco-hyperelastic model is then proposed: a Marlow-type strain energy function coupled with a Prony series and William-Landel-Ferry equation to include time and temperature dependency. Finally, a case study of ISBM process is implemented in a finite element code considering this constitutive model. Strain maps and predicted thickness of the bottle wall were evaluated as process quality indicators. Simulation results showed good agreement with measurements on the real processed bottle, confirming the usefulness of the approach for product or process parameters optimisation.

Optimization of Injection Stretch Blow Molding: Part I – Defining Part Thickness Profile

Abstract This paper suggests a methodology based on a neuroevolutionary approach to optimize the use of material in blow molding applications. This approach aims at determining the optimal thickness distribution for a certain blow molded product as a function of its geometry. Multiobjective search is performed by neuroevolution to reflect the conflicting nature of the design problem and to capture some possible trade-offs. During the search, each design alternative is evaluated through a finite element analysis. The coordinates of the mesh elements are the inputs to an artificial neural network whose output determines the thickness for the corresponding location. The proposed approach is applied to the design of an industrial bottle. The results reveal the validity and usefulness of the proposed technique, which was able to distribute the material along the most critical regions to obtain adequate mechanical properties. The approach is general and can be applied to products with different geometries.

The effect of the deformation rate on the wall thickness of 1.5LT PET bottle during ISBM (Injection Stretch Blow Molding) process

The biaxial orientation of deformation during the ISBM process forms the final desired volume of the plastic container. The ISBM process comprises stretching and blowing of a preheated preform inside a mold for the formation of a beverage container. The current study deals with the numerical investigation of the effect of deformation rate on the final bottle thickness wall distribution. It was considered that the stretching rod velocity varies from 0.6-0.8m/s and the preblowing pressure from 0.4-1.6MPa. Additionally, the advantage of stretching versus free blow conditions is being discussed. It was found that highest is the stretching velocity, the higher is the resulting material concentration at the base of the bottle. Additionally, it was found that the higher preblowing pressure accumulates thick material at the central region of the bottle while the upper and bottom regions of the bottle get thinner.

Non-contact measurement of the temperature profile of PET preforms

This paper describes a system for the measurement of the internal and external temperature profiles of PET preforms used in the Injection Stretch Blow Moulding (ISBM) process. Many works in literature highlighted the importance of these quantities to improve the production quality of PET bottles, but none addressed the development of a measuring system suitable for this scope. A measuring system based on two thermopiles for the identification of the internal temperature profile and a thermal camera for the measurement of the external one has been designed. The adopted sensors were individually calibrated and the uncertainty budget, accounting for both instrumental uncertainties and the effect of multiple reflections, was derived. A prototype of the measuring system was tested on an industrial ISBM machine. The dependence of the preforms temperature profile on the settings of the ISBM machine was investigated. Results evidenced that the minimum variations of the machine settings induced temperature differences significantly larger than the measurement uncertainty, thus proving the effectiveness of the proposed system.

Simulation on Effect of Preform Diameter in Injection Stretch Blow Molding

Polyethylene terephthalate (PET) is the most common material of resin for manufacturing plastic bottle by injection stretch blow molding due to its excellent properties. As various issues of health and environmental hazards due to the PET use have risen, PET bottle manufacture may be improved by minimizing the wall thickness to reduce the PET use. One of the critical qualifications of the manufacturing process which lead to the wall thickness distribution is the initial preform diameter. In this project, we used the ANSYS Polyflow with aim to evaluate the wall thickness distribution of PET bottle for different diameter of initial preform. As a result, only 4 mm preform diameter presented wall thickness below than 1 mm. On the other hand, at least 6 mm preform diameter can permit the wall thickness 1.3 mm i.e. at the shoulder area.

Optimisation of mould surface temperature and bottle residence time in mould for the carbonated soft drink PET containers

Polyethylene terephthalate (PET) bottles, which are usually produced by injection stretch blow moulding (ISBM) are widely used for carbonated soft drinks (CSD) storage and transportation. Stretch rod movement, blow pressure, preform temperature profile, mould surface temperature and material properties are among the most important factors affecting the final product's quality in terms of the thickness distribution, burst pressure and top-load resistance of the bottles. However, the residence time of the blown bottle inside the mould is also an important factor affecting its final properties. Especially in PET bottle production for hot fillings, the residence time is a very important factor because the longer the residence time the better the crystalline structure of the PET. In this production, the lid section is desired to have a fully crystalline form so that it can withstand hot fluids. In this study, the aim was to optimise the mould surface temperature and the blown bottle's residence time inside the mould for 1 L soft drink PET bottle production based on the final properties using the ECHIP 7 design of experiment (DOE) program. The method employed through this program was a quadratic one. Optimum process parameters were determined by the response surface method (RSM) and the process settings ensuring maximum top-load, burst pressure, Tg and degree of crystallinity were regarded to be optimum. It was found that the optimum mould surface temperature and blown bottle residence time inside the mould were 10 °C and 20 s, respectively.

Finite element simulations of stretch-blow moulding with experimental validation over a broad process window

Injection stretch blow moulding is a well-established method of forming thin-walled containers and has been extensively researched for numerous years. This paper is concerned with validating the finite element analysis of the free-stretch-blow process in an effort to progress the development of injection stretch blow moulding of poly(ethylene terephthalate). Extensive data was obtained experimentally over a wide process window accounting for material temperature and air flow rate, while capturing cavity pressure, stretch-rod reaction force and preform surface strain. This data was then used to assess the accuracy of the correlating FE simulation constructed using ABAQUS/Explicit solver and an appropriate viscoelastic material subroutine. Results reveal that the simulation is able to give good quantitative correlation for conditions where the deformation was predominantly equal biaxial whilst qualitative correlation was achievable when the mode of deformation was predominantly sequential biaxial. Overall the simulation was able to pick up the general trends of how the pressure, reaction force, strain rate and strain vary with the variation in preform temperature and air flow rate. The knowledge gained from these analyses provides insight into the mechanisms of bottle formation, subsequently improving the blow moulding simulation and allowing for reduction in future development costs.

Free-stretch-blow investigation of poly(ethylene terephthalate) over a large process window

This paper highlights for the first time a full comprehension of the deformation procedure during the injection stretch blow moulding (ISBM) process of poly(ethylene terephthalate) (PET) containers, namely thin-walled rigid bottles. The processes required to form PET bottles are complicated and extensive; any development in understanding the nature of material deformation can potentially improve the bottle optimisation process. Removing the bottle mould and performing free-stretch-blow (FSB) experiments revealed insight into the bottle forming characteristics at various preform temperatures and blowing rates. Process outputs cavity pressure and stretch-rod force were recorded using at instrumented stretch-rod and preform surface strain mapping was determined using a combination of a unique patterning procedure and high speed stereoscopic digital image correlation. The unprecedented experimental analysis reveals that the deformation behaviour varies considerably with contrasting process input parameters. Investigation into the effect on deformation mode, strain rate and final bottle shape provide a basis for full understanding of the process optimisation and therefore how the process inputs may aid development of the preferred optimised container.

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

The injection stretch blow moulding process involves the inflation and stretching of a hot preform into a mould to form bottles. A critical process variable and an essential input for process simulations is the rate of pressure increase within the preform during forming, which is regulated by an air flow restrictor valve. The paper describes a set of experiments for measuring the air flow rate within an industrial ISBM machine and the subsequent modelling of it with the FEA package ABAQUS. Two rigid containers were inserted into a Sidel SBO1 blow moulding machine and subjected to different supply pressures and air flow restrictor settings. The pressure and air temperature were recorded for each experiment enabling the mass flow rate of air to be determined along with an important machine characteristic known as the ‘dead volume’. The experimental setup was simulated within the commercial FEA package ABAQUS/Explicit using a combination of structural, fluid and fluid link elements that idealize the air flowing through an orifice behaving as an ideal gas under isothermal conditions. Results between experiment and simulation are compared and show a good correlation.

Analysis and Simulation of the Free-Stretch-Blow Process of PET

This paper is concerned with understanding the behaviour of Polyethylene Terephthalate (PET) in the injection stretch blow moulding (ISBM) process where it is typically bi-axially stretched to form bottles for the packaging industry. Preforms which have been pre sprayed with a pattern and heated in an oil bath have been stretched and blown in free air using a lab scale ISBM machine whilst being monitored via high speed video. The images have subsequently been analysed using a digital image correlation system (VIC 3D). The results have been used to validate appropriate simulations of the free-blow process using ABAQUS®/Explicit FEA with a suitable viscoelastic material model, along with experimental process data obtained using an instrumented stretch rod.

Numerical simulation of the thermodependant viscohyperelastic behavior of polyethylene terephthalate near the glass transition temperature: Prediction of the self‐heating during biaxial tension test

The poly ethylene terephthalate near the glass transition temperature highlights a strongly non linear elastic and viscous behaviour when biaxially stretched at high strain rates representative of the injection stretch blow moulding process. A non linear visco‐hyperelastic model, where characteristics are coupled to the temperature, has already been identified from equi‐biaxial tension experimental results. The weak form of the mechanical part of the model is presented and implemented into a finite element code developed in the Matlab environment and validated by comparing numerical simulation of equi‐biaxial testing with the analytical solution in the isothermal case. Considering the thermal aspects, an experimental study, where PET sheets are heated using infrared (IR for short) lamps is also presented. The modeling of the IR radiation of the sheet helps to identify the thermal properties of the PET. The thermal model is then implemented in the finite element code, coupled to the 2D viscoelastic model. A discussion is made to justify the accuracy of the assumption made on homogeneity of the temperature field through the thickness. The simulation of the 2D plane stress equibiaxial test shows the important influence of the thermal aspects and the coupled thermo‐mechanical software is used to quantify the self‐heating phenomenon in the case of the biaxial elongations of PET sheets at high strain rates. POLYM. ENG. SCI., 53:2683–2695, 2013. © 2013 Society of Plastics Engineers

Experimental Investigation of Stretch Blow Molding, Part 1: Instrumentation in an Industrial Environment

AbstractIn spite of intensive research, computational modeling of the injection stretch blow molding (ISBM) still cannot match the accuracy of other polymer processes such as injection molding. There is a lack of understanding of the interdependence among the machine parameters set up by the operators, process parameters, material behavior, and the resulting final thickness distribution and performance of the molded product. The work presented in this paper describes a set of instrumentation tools developed for investigation of the ISBM process in an industrial setting. Results are presented showing the pressure and air temperature evolution inside the mold, the stretch rod force and displacement history, and the moment of contact of the polymer with seven discrete locations on the mold. © 2012 Wiley Periodicals, Inc. Adv Polym Techn 32: E771–E783, 2013; View this article online at wileyonlinelibrary.com. DOI 10.1002/adv.21320