SPE Library

The improvement of oxygen-barrier properties of glassy polyesters by orientation was examined. Poly(ethylene terephthalate) (PET), poly(ethylene naphthalate) (PEN), and a copolymer based on PET in which 55 mol % of the terephthalate was replaced with bibenzoate (PET-BB55) were oriented by constrained uniaxial stretching. In a fairly narrow window of stretching conditions near the glass-transition temperature, it was possible to achieve uniform extension of the polyesters without crystallization or stress whitening. The processes of orientation and densification correlated with the conformational transformation of glycol linkages from gauche to trans. Oxygen permeability, diffusivity, and solubility decreased with the amount of orientation. A linear relationship between the oxygen solubility and polymer specific volume suggested that the cold-drawn polyester could be regarded as a one-phase densified glass. This allowed an analysis of oxygen solubility in accordance with free-volume concepts of gas permeability in glassy polymers. Orientation was seen as the process of decreasing the amount of excess-hole free volume and bringing the nonequilibrium polymer glass closer to the equilibrium (zero-solubility) condition.

The water vapour transmission rate (WVTR) of carton boards can be critical in high performance packaging applications. The authors have developed moisture barrier paperboards using aqueous-based (water-based) emulsion polymers, and the results obtained with these materials are presented. These polymers include polyethylene terephthalate (PET), polyvinylidene chloride (PVdC), and styrene-based emulsions. A range of these coated and laminated carton boards were prepared using a hand coater to achieve a controlled range of barrier layer thickness (24-100 microns), and analysed for WVTR over a range of temperatures and relative humidities. In addition, some boards were pre-coated with a primer coat before the application of the barrier topcoat, to investigate the effect of carton board topography on the moisture barrier properties. Low WVTRs in the range of 5-10 g/m2/day were achieved using several of the emulsion polymers, and it is clearly shown that by precoating the surface of a board with a primer before applying a barrier coat can lower the WVTR further even with a thinner overall layer of coating. Anisotropic characteristics of boards coated on one side only are clearly shown, with lower WVTRs always being achieved when the coated side of the board is adjacent to the higher humidity.

Films were prepared from a range of mPE resins of various comonomer types (hexene and octene), using a Killion blown film extrusion system. The films were manufactured at a constant blow up ratio of 1.6 by maintaining constant haul off speeds and screw speeds to give a uniform thickness of 50 microns. To effect the change in frostline height the rate of cooling was changed. Tensile analysis of the samples showed that modulus and tensile stress were related to both comonomer type and polymer density and that frostline height variation had an effect on the final film properties. DSC analysis showed that the degree of crystallinity was more dependent on extrusion processing conditions and polymer density than comonomer type.

In this work, the performance of a new in-line scanning camera system for the study of bubble instabilities in film blowing extrusion is presented. Three commercial film grades, metallocene catalyzed linear polyethylene (LmPE), LLDPE and LDPE, were used to generate the bubble instabilities. Reliable and objective criteria for differentiating the various bubble instabilities such as draw resonance, helicoidal instability, frost line height (FLH) instability are proposed. Detailed dynamics of each bubble instability was carefully investigated as a function of time in a broad range of take-up ratio (TUR), blow-up ratio (BUR) and frost line height. It was found that the new system can capture the main characteristics of all bubble instabilities quantitatively. It was also found that the magnitude and periodicity of radius variation during draw resonance of LmPE is decreased as TUR is increasing at a given FLH and BUR implying that the origin of draw resonance in film blowing seems not to be the same phenomenon that the one observed in fiber spinning. In the case of helicoidal instability, eccentricity, which defines the deviation of the bubble center from the center of the die decreases as TUR is increased.

Converters often overlook the lowly wound roll of blown film as an incoming raw material requiring quality specifications. The film’s layflat uniformity is critical to printing, laminating, and sealing operations. This presentation focuses on the impact of melt temperature variation during film extrusion, and covers:How excessive melt temperature variation affects film and layflat quality.Some of the causes of melt temperature variation.The basics of setting up temperature profiles – speaking to the screwHow to read temperature controllers – listening to the responseHow to measure and track screw performance – are we communicating?

Films were prepared from a range of conventional and metallocene polyethylene (mPE) resins of various comonomer types (butene, hexene, octene), using a Killion blown film extrusion system. The films were manufactured using blow up ratios (BUR) 1.3 – 2.5, haul-off rates, and screw speeds to give a uniform thickness of 50 microns. Tensile analysis of the samples showed that modulus and elongation were related to both comonomer type and polymer density. The mPE resins showed considerable improvement in mechanical performance compared to conventional PEs. Differential Scanning Calorimetry analysis showed that the degree of crystallinity was more dependent on extrusion processing conditions and polymer density than comonomer type.

A model is developed for the film blowing process including the effects of viscoelasticity, flow-induced crystallization and bubble cooling. A molecularly based constitutive model is coupled with the macroscopic balance equations. The ability of the model to accurately predict velocity and temperature profiles along the film line given the bubble shape (currently from experimental data) is demonstrated. The macroscopic deformations are predicted to be larger than the molecular deformations in both the machine and hoop directions due to viscoelastic effects, as expected. An important feature of the model is its ability to predict the locked-in stresses and microstructure, which are related to final film properties.

Polyethylene films prepared from a range of m- LLDPE, LLDPE and ULDPE resins containing 0 and 8% PIB, were manufactured using a Killion cast film extrusion system. FTIR, DSC and mechanical analysis techniques were used to investigate the effect of co-monomer type, density and MFI on the mechanical performance, orientation and crystallinity of these films. The study established that co-monomer type and MFI were the greatest factors influencing mechanical performance and crystallinity. Crystallinity was found to be the most influential factor governing PIB migration in these films and this in turn was related to polymer type, density and MFI.

In this paper the use of Neural Networks for the on-line prediction of cure cycle performance is presented. The need of an on-line fast tool for the prediction of the cure cycle characteristics according to real time measurements of the cure process is apparent for the whole polymer composite industry. Various Neural Network architectures and set-ups are presented, discussed and tested to provide the fastest and more reliable solution. The training of the Neural Networks is performed using a 1-D simulation tool. Finally, some ideas about the implementation of this tool in the on-line control of the cure process are presented.

Ultrasonic velocity measurements have been made during cure of DCPD. This material is under investigation for use in reactive rotational moulding in which the moulded part is manufactured using liquid DCPD and a layering technique. Each layer must be sufficiently cured to support the weight of subsequent layer addition. Ultrasound is being explored as a non-intrusive process-monitoring tool to detect mechanical property changes during early cure and enable use of the layering technique. Velocity is observed to decrease, simultaneous with temperature rise. Velocity is then observed to increase as cure progresses. The technique can distinguish variations in rate of cure.

Development of a wireless pressure sensor is motivated to reduce instrumentation and mold modification cost, improve lifecycle robustness, and thereby facilitate the widespread use of in-process sensing for process monitoring and control. In the presented design, the dynamic pressure in the mold cavity compresses a stack of piezoelectric rings, which generate a proportional electrical charge. Using an oscillator-based threshold switching device, the collected charge is relayed to an ultrasonic transmitter, which sends an acoustic signal at specific center frequencies to a receiver outside of the mold. Such a mechanical-electrical transduction process enables the online measurement of mold cavity pressure in a wireless fashion, without any external power supply.

This research investigates the application of ultrasound for monitoring conditions inside microcavities too small to be sensed using conventional sensors. An ultrasonic transducer was installed on an injection mold containing micro-cavities such that the sound pulse would strike the surface of the mold cavity and reflect back to the transducer. Changes in the intensity of reflected echoes are shown to be sensitive to the presence of polymer in the mold. By monitoring this changing reflected echo a signal is produced that is sensitive to conditions in the mold during processing. Two distinct advantages of the sensor are first, that it can sense conditions inside a micro-cavity, and second, that it can potentially do this from the outside of the mold plate, allowing an installation that requires no machining of the mold.

Control of melt temperature in molding of high-precision components depends on the non-linear heat transfer and fluid dynamics behavior governing the process. Such systems are difficult to represent in a standard control strategy, especially if the material changes or set-point profiles are modified frequently in the process. This paper presents a strategy for combining computational-fluid-dynamics (CFD) with active process control to optimize controller performance. In this case the strategy is applied to control simulations of melt temperature in injection molding.

The effect of filler content on penetration depth of infrared temperature sensors is described, both in extrusion and in a specially designed imposed temperature gradient cell. White magnesium hydroxide and carbon black fillers were compounded with polyethylene in various levels and measurements made during extrusion and in the static cell. Filler content had significant effect on measured temperature in extrusion, causing changes in absorption coefficient of the compound. Effective penetration depths were quantified using the static gradient cell and emission spectra obtained from in-process infrared spectroscopy.

Analysis of polymer production processes using spectroscopic and ultrasonic techniques is becoming more prevalent. Such at-process methods allow realtime chemical and physical information on melt characteristics to be obtained for process monitoring and control.This work will demonstrate real-time monitoring during extrusion of ethylene vinyl acetate (EVA) random copolymers with varying vinyl acetate (VA) content 1-40 % wt. In-line transmission near infrared and Raman spectroscopy has been used simultaneously with ultrasonic transit time measurements. The efficiency of the respective methods for determination of VA content is investigated and multivariate analysis of the spectroscopic data acquired is presented.

Mineral filler concentration and dispersion are important pieces of information for the production of mineral-charged polymers. In order to achieve timely control of product quality, a technique capable of providing real-time information on filler concentration and dispersion is highly desirable. In this work, ultrasound, temperature, and pressure sensors as well as an amperometer of the extruder motor drive were used to monitor the extrusion of mineralfilled polymers under various experimental conditions in terms of filler type, filler concentration, feeding rate, screw rotation speed, and barrel temperature. Then, neural network relationships were established between the filler concentration, filler dispersion index, and some of the process variables and the measurement data provided by the sensors. By using these networks and ultrasonic measurement data as input of the networks, we were able to achieve a better than 1 wt% average accuracy on the estimation of filler concentration and a better than 0.06 accuracy on the estimation of filler dispersion index. This study has demonstrated the feasibility of using ultrasound and neural networks for in-line monitoring of filler concentration and dispersion during extrusion processes of mineral-charged polymers.

We have used a temperature sensitive fluorescent dye, doped into polycarbonate, to monitor the true resin temperature during extrusion processing. For this measurement, a fluorescent dye, perylene, was doped into the polycarbonate at very low concentration. We apply this measurement concept to extrusion processing by using an optical sensor that accesses the machine at standard instrumentation ports. The sensor has a confocal optics design that permits the measurement of temperature profiles. With the sensor looking over the screw of a single extruder, temperature profiles from the barrel wall to the core of the screw were obtained as a function of screw speed, screw design and melt flow index.

Co-injection is a specialized injection molding process in which two or more materials are sequentially or simultaneously injected into a mold. The resulting plastic part will consist of a skin of the first material covering a core made of the second material. This can allow for an ergonomic surface finish without jeopardizing mechanical strength. It also can help reduce material costs by allowing lower quality material to be incorporated into the core. The focus of this research was to determine the effect of processing parameters and wall thickness on the core geometry and penetration depth. With a better understanding of the co-injection process, it can be implemented for more parts and a potential cost savings can be realized.

Imbalances occur in powder injection molding of multi cavity molds, which are sometimes opposite to the shear induced imbalances of conventional plastic materials. In a previous study it was found that melt rotation technology not only reduced imbalances, but also helped reduce differences between the mechanical properties of parts molded in multi-cavity molds. This paper presents the results of a study that expands on a previous work to include effects of fill rate, additional variations in runner geometries, and designs of melt rotation technologies for eliminating the variations.

During the startup and operation of new multicavity molds, it is expected that cavity-to-cavity filling variations will be found. This will occur despite the use of geometrically balanced runners. With cold runners, this imbalance is dominated by either steel variations in the mold, or shear induced variations developed in the runner. In order to correct the imbalances, it is important to be able to separate these two causes and to quantify their contribution. A method, here referred to as “The Five-Step Process” was developed for this purpose. This paper presents a study to determine how robust The Five Step-Process is in diagnosing steel variations in a mold.