Elaine C. Brown

In-process vibrational spectroscopy and ultrasound measurements in polymer melt extrusion

Spectroscopic techniques have the potential to provide powerful, molecular-specific, non-invasive measurements on polymers during melt processing operations. An exploration is reported of the application and assessment of sensitivity of in-process vibrational spectroscopy - on-line mid-infrared (MIR), on-line near-infrared (NIR), in-line NIR and in-line Raman - for monitoring of single screw extrusion of high-density polyethylene and polypropylene blends. These vibrational spectroscopic techniques are compared with novel in-line ultrasound velocity measurements, which were acquired simultaneously, to assess the sensitivity of each method to changes in blend composition and to explore the suitability for their use in real time process monitoring and control. © 2003 Elsevier Ltd. All rights reserved.

Melt temperature field measurement in single screw extrusion using thermocouple meshes

The development and validation of a sensor for extrusion melt temperature field measurement is described. A grid of opposing thermocouple wires was constructed and held in position by a supporting frame. Wires were joined together at crossing points to form thermocouple junctions, which were computer monitored. The mesh was used to monitor melt temperature fields during single screw extrusion at the die entrance. Design and construction of the mesh is described in addition to experimental optimization of wire diameter and junction forming. Calibration of the sensor and potential measurement errors including shear heating effects are discussed. Initial results from single screw extrusion are presented for a commercial grade of low density polyethylene using five- and seven-junction thermocouple meshes. The dependence of melt temperature profile on screw speed is illustrated. At low screw speeds melt temperature profiles were flat in shape and higher than set wall temperatures. At higher screw speeds the profiles became more pointed in shape. Use of higher resolution sensors exposed more complex temperature profiles with shoulder regions.

In line melt temperature measurement during real time ultrasound monitoring of single screw extrusion

Abstract Ultrasonic velocity measurements provide process related information to complement conventional temperature and pressure measurements, since velocity varies with material type and with temperature and pressure conditions. The technique is non-invasive, can be applied directly to the process, and results are available in real time. An ultrasonic virtual instrument has been used on industrial scale extruders in house. Experimental results are presented, showing ultrasonic velocity to be a powerful tool for improving knowledge of polymer melt bulk temperature during extrusion.

Real-time process monitoring of micromoulding using integrated ultrasonic sensors

Real-time, non-intrusive and non-destructive process monitoring of micromoulding has been performed using novel ultrasonic sensors integrated onto the barrel and mould insert with an ultrasonic pulse-echo technique. The relative variation of the polymer melt temperature inside the extrusion barrel can be obtained using the ultrasonic velocities of the melt measured at the barrel during extrusion. Melt flow arrival in the mould, and solidification, shrinkage and detachment of the polymer inside the mould cavity are also successfully monitored. The presented ultrasonic sensors and technique enable optimizing the micromoulding process, and improving quality of the moulded parts and process efficiency.

Water assisted injection moulding : development of insights and predictive capabilities through experiments on instrumented process in parallel with computer simulations

Abstract An idealised model of core-out in water assisted injection moulding (WAIM) is set up to isolate the effect of cooling by the water on the deposited layer thickness. Based on simulations, this is investigated for a specific case as a function of Pearson number and power law index. It is found that cooling significantly reduces the layer thickness to the extent that a change in the flow regime ahead of the bubble, from bypass to recirculating flow, is possible. For shear thinning melts with high temperature coefficient of viscosity, the simulations show very low layer thickness, which may indicate unfavourable conditions for WAIM. Although in the real moulding situation, other effects will be superimposed on those found here, the results provide new insights into the fundamentals of WAIM. Investigation of other effects characterised by Fourier and Reynolds numbers will be reported subsequently. Some early process measurement results from an experimental WAIM mould are presented. Reductions in residual wall thickness are observed as the water injection set pressure is increased and the duration of water bubble penetration through the melt is determined experimentally. The formation of voids within the residual wall is noted and observed to reduce in severity with increasing water injection pressure. The presence of such voids can be detected by the signature from an infrared temperatures sensor.

Vibrational spectroscopic and ultrasound analysis for the in-process monitoring of poly(ethylene vinyl acetate) copolymer composition during melt extrusion

Over the last decade, the demands for higher through-put in production, process optimisation and quality control in the polymer manufacturing industry has led to the implementation of a wide range of process analytical technologies. Techniques such as near-infrared (NIR) spectroscopy, Raman spectroscopy and ultrasound have become indispensable analytical tools for in-process monitoring allowing a molecular specific understanding of material characteristics, rheology and process trends. This paper reports the combined application of these three analytical techniques for assessment of co-polymer melt composition in-line during single screw extrusion to an accuracy of 0.16 wt%. The work demonstrates monitoring and characterisation of a series of ethylene vinyl acetate (EVA) random co-polymers with varying vinyl acetate (VA) content ranging from 2.0 to 43.1 wt%. The sensitivity of each technique to changes in copolymer composition and its ability to acquire real-time process data has been determined. Robust multivariate calibrations suitable for real-time predictions of VA content during processing have been developed and tested.

Near infra red spectroscopy as a multivariate process analytical tool for predicting pharmaceutical co-crystal concentration.

The use of near infra red spectroscopy to predict the concentration of two pharmaceutical co-crystals; 1:1 ibuprofen-nicotinamide (IBU-NIC) and 1:1 carbamazepine-nicotinamide (CBZ-NIC) has been evaluated. A partial least squares (PLS) regression model was developed for both co-crystal pairs using sets of standard samples to create calibration and validation data sets with which to build and validate the models. Parameters such as the root mean square error of calibration (RMSEC), root mean square error of prediction (RMSEP) and correlation coefficient were used to assess the accuracy and linearity of the models. Accurate PLS regression models were created for both co-crystal pairs which can be used to predict the co-crystal concentration in a powder mixture of the co-crystal and the active pharmaceutical ingredient (API). The IBU-NIC model had smaller errors than the CBZ-NIC model, possibly due to the complex CBZ-NIC spectra which could reflect the different arrangement of hydrogen bonding associated with the co-crystal compared to the IBU-NIC co-crystal. These results suggest that NIR spectroscopy can be used as a PAT tool during a variety of pharmaceutical co-crystal manufacturing methods and the presented data will facilitate future offline and in-line NIR studies involving pharmaceutical co-crystals.

Real-time ultrasonic diagnosis of polymer degradation and filling incompleteness in micromoulding

Abstract Injection moulding techniques have been miniaturised and refined to achieve micromoulding which aims to satisfy the need for mass production of low-cost micro- and nanoscale components. However, the microscale mould cavity features and extreme processing conditions which are inherent in the process can result in larger process variations than conventional injection moulding, with a corresponding increase in the probability of producing an unsatisfactory product. Accurate process diagnosis is required to ensure process reliability but integration of sensors onto the small and highly detailed mould units can be problematic and alternatives may need to be sought. Piezoelectric film ultrasonic transducers were integrated onto the extrusion barrel and mould insert of a micromoulding machine for real-time, non-destructive and non-intrusive process diagnosis with an ultrasonic pulse-echo technique. Polymer degradation owing to excessive heating at the extrusion barrel was successfully probed by measuring the ultrasonic velocities in the polymer at the mould insert. Filling incompleteness of the mould cavity was also sensitively detected by monitoring the ultrasonic energy variation transmitted into the part at different points along the melt flow length. The developed ultrasonic sensors and technique enable optimisation and in-process quality assurance of the moulded parts which ensures that maximum process efficiency can be achieved.

Melt temperature field measurements in extrusion using thermocouple meshes

Abstract Thermocouple grids have been shown to provide a unique insight into melt temperature fields and their time dependent behaviour in extruders. These systems have been extended from single axis designs to larger arrays for more detailed temperature measurements. Nine junction (3 × 3) arrays have provided a map of the temperature profile across the melt, and the technique has been used to assess the effect of extrusion conditions such as polymer type, screw geometry and melt pressure. The data are proving invaluable for extruder screw design and to inform more accurate computer modelling of polymer melt flows. Single axis grids have also been applied to twin screw compounding extrusion, and the results showed a significant amount of shear heating with the hottest points being along the centre line of the two screws.

Real time diagnostics of gas/water assisted injection moulding using integrated ultrasonic sensors

Abstract An ultrasound sensor system has been applied to the mould of both the water and gas assisted injection moulding processes. The mould has a cavity wall mounted pressure sensor and instrumentation to monitor the injection moulding machine. Two ultrasound sensors are used to monitor the arrival of the fluid (gas or water) bubble tip through the detection of reflected ultrasound energy from the fluid polymer boundary and the fluid bubble tip velocity through the polymer melt is estimated. The polymer contact with the cavity wall is observed through the reflected ultrasound energy from that boundary. A theoretically based estimation of the residual wall thickness is made using the ultrasound reflection from the fluid (gas or water) polymer boundary while the samples are still inside the mould and a good correlation with a physical measurement is observed.