Process efficiency in polymer extrusion: Correlation between the energy demand and melt thermal stability

Chamil Abeykoon,Adrian L Kelly,Javier Vera-Sorroche,Elaine C Brown,Phil D Coates,Jing Deng,Kang Li,Eileen Harkin-Jones,Mark Price

doi:10.1016/j.apenergy.2014.08.086

Chamil Abeykoon, Adrian L Kelly + Show 7 more

Open Access

https://doi.org/10.1016/j.apenergy.2014.08.086

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Abstract

Thermal stability is of major importance in polymer extrusion, where product quality is dependent upon the level of melt homogeneity achieved by the extruder screw. Extrusion is an energy intensive process and optimisation of process energy usage while maintaining melt stability is necessary in order to produce good quality product at low unit cost. Optimisation of process energy usage is timely as world energy prices have increased rapidly over the last few years. In the first part of this study, a general discussion was made on the efficiency of an extruder. Then, an attempt was made to explore correlations between melt thermal stability and energy demand in polymer extrusion under different process settings and screw geometries. A commodity grade of polystyrene was extruded using a highly instrumented single screw extruder, equipped with energy consumption and melt temperature field measurement. Moreover, the melt viscosity of the experimental material was observed by using an off-line rheometer. Results showed that specific energy demand of the extruder (i.e. energy for processing of unit mass of polymer) decreased with increasing throughput whilst fluctuation in energy demand also reduced. However, the relationship between melt temperature and extruder throughput was found to be complex, with temperature varying with radial position across the melt flow. Moreover, the melt thermal stability deteriorated as throughput was increased, meaning that a greater efficiency was achieved at the detriment of melt consistency. Extruder screw design also had a significant effect on the relationship between energy consumption and melt consistency. Overall, the relationship between the process energy demand and thermal stability seemed to be negatively correlated and also it was shown to be highly complex in nature. Moreover, the level of process understanding achieved here can help to inform selection of equipment and setting of operating conditions to optimise both energy and thermal efficiencies in parallel.

Highlights

Polymeric materials are widely used all over the world primarily due to their superior properties such as high strength to weight ratio; high temperature/chemical/corrosive resistance; non-conductivity; high clarity; re-processability; low cost and so forth
The typical relationship between process thermal stability and energy efficiency may differ depending on the processing conditions; material and machine being used while the quality of the process monitoring and control may have considerable effects
The results showed that the specific energy consumption (SEC) of the extruder reduces with the screw speed regardless the screw geometry

Summary

Introduction

Polymeric materials are widely used all over the world primarily due to their superior properties such as high strength to weight ratio; high temperature/chemical/corrosive resistance; non-conductivity; high clarity; re-processability; low cost and so forth. DT the level of the melt temperature fluctuations across the melt flow gextruder q the extruder energy efficiency the density of the material q the average density of the material gextruder;thermo the thermal efficiency of an extruder l the viscosity l0 the viscosity at zero shear rate c the shear rate k the relaxation time xsc screw speed. Polymeric materials are showing a great potential of saving energy consumption in aerospace, automotive, marine and transport sector. They are quite easy to form into complex shapes compared to other conventional materials. The energy requirement for processing of polymers is considerably lower than other conventional materials such as steel and glass Perhaps, these may be among the major reasons for growing popularity of polymeric materials in diverse industrial sectors. More details on the process mechanisms, operational requirements, and the available process analytical techniques (PAT) of polymer extrusion can be found in the literature [13,14,15,16]

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