In-Process R eometry Studies of LDPE Compounds

Abstract

The initial part of a comprehensive study into the investigation and validation of in-process measurements on a low density polyethylene (LDPE) compound during extrusion is reported. An unfilled, commercial grade of low density polyethylene was processed using fully instrumented, computer monitored, single and twin screw extruders in the Interdisciplinary Research Centre (IRC) laboratories, University of Bradford. Three in-process rheometers were used; a prototype Rosand capillary on-line rheometer (OLR), a four sensor slit die in-line rheometer (ILR) and a six sensor slit die ILR. Off-line comparisons were carried out using a Rosand RH twin bore capillary rheometer. All devices allowed shear ow characterisation at a range of processing rates, and the capillary rheometers also provided a measurement of entry pressure drop through the use of orifice dies. The six-sensor ILR also allowed measurement of entry pressure drop into the slit, although the differences in ow geometry meant these measurements were not directly comparable with the capillary devices, and exit pressures were extrapolated from ILR pressure drops. The in-process devices exhibited very good agreement with measurements made off-line, in both shear ow and entry pressures. In-line slit die measurements were very close to those made using capillary dies, despite the in-line tests being non-isothermal and employing a different geometry of measurement section. Differences in melt rheology between single and twin extrusion were observed, due to the amount of mechanical work input by each extruder. Overall, good agreement was observed from the four different routes to measurement, for the LDPE examined.

Rheological properties of polypropylene composites with calcium carbonate under high shear rates

“…In an analytical approach, tests conducted on a small amount of material taken from either the raw material or the finished product, shifted in time relative to the technological process, are named off-line measurements [16]. Off-line measurements enable an extensive rheological characteristic of polymeric materials to be made; however, they do not allow the control of the technological process as it runs and the assessment of the behavior of the polymers in flows occurring in real processing conditions [16,17]. The analysis of the actual behavior of a polymer in processing constitutes a basis for the control of the process and its stability and the quality of the finished product [18,19].…”

“…The analysis of the actual behavior of a polymer in processing constitutes a basis for the control of the process and its stability and the quality of the finished product [18,19]. An investigation technique that enables the control of the production process and the rheological analysis of the whole polymeric material being processed (100% of flow) are in-line measurements [9,16,17]. The processes are conducted in the extrusion or injection moulding, and the function of a rheometer is taken over by a special-design head [10,20] or injection mould [21,22].…”

Reactive Processing of Thermoplastic Polymers: A Review of the Fundamental Aspects

“…Kelly et al [364] compared the performances of three methods i. e., in-line (slit rheometer), on-line (capillary rheometer) and offline rheometry (commercial rheometer) for extrusion of low density polyethylene. They concluded that these three different methods showed good agreement for the material extruded.…”

In‐process rheological monitoring of extrusion‐based polymer processes

“…[61][62][63] Comparisons between in-line slit rheometry and on-line and off-line capillary rheometry showed good agreement for an LDPE. 64,65 On-line capillary rheometers, coupled to the die or between the extruder and die, are preferred for industrial compounding and reactive extrusion, as they do not interfere with production. A material stream is detoured from the main flow channel, conditioned to the required testing temperature and shear rate (usually by means of a gear pump), and a measurement is made (Fig.…”

“…In‐line capillary rheometry is relatively scarce 61–63 . Comparisons between in‐line slit rheometry and on‐line and off‐line capillary rheometry showed good agreement for an LDPE 64,65 . On‐line capillary rheometers, coupled to the die or between the extruder and die, are preferred for industrial compounding and reactive extrusion, as they do not interfere with production.…”