Key Takeaways & Executive Findings
- •• • Comprehensive rheological data for PP, PE, PS, ABS and their binary blends (PE/ABS, PP/ABS, PS/ABS) were obtained across shear rates 0.1–100 s⁻¹ and temperatures 180–250°C, filling a critical data gap for process design. • • All tested melts exhibited shear-thinning (n < 1), with PE showing the lowest flow behavior index and viscous flow activation energy, indicating highest shear sensitivity but lowest temperature sensitivity—critical for selecting processing conditions. • • A modified power-law model incorporating a component correction term achieved an average relative error of only 5.90% between predicted and measured viscosities, enabling accurate viscosity estimation for multi-component plastic systems. • • The viscosity of binary blends consistently fell between those of the pure components, and the model quantitatively captured the effect of mass fraction (0.5 < m ≤ 1) on viscosity, facilitating blend formulation and recycling process optimization.
Abstract
The non-Newtonian rheological properties of plastic melts are critical for regulating plastic processing, molding, and recycling processes, ensuring processing stability and product performance. However, rheological data for commonly used plastics and their blends remain incomplete. This study combined experimental testing and theoretical modeling to investigate the rheological behaviors of four pure plastics—polypropylene (PP), polyethylene (PE), polystyrene (PS), and acrylonitrile-butadiene-styrene copolymer (ABS)—and three binary blend systems: PE/ABS, PP/ABS, and PS/ABS. Rheological tests were conducted using a rheometer over a shear rate range of 0.1–100 s⁻¹ and temperatures from 180°C to 250°C. Results showed that the flow behavior index n was less than 1 for all samples, and apparent viscosity decreased significantly with increasing shear rate, indicating clear shear-thinning behavior. The consistency coefficient K followed the Arrhenius relationship with temperature, and melt viscosity decreased as temperature increased. The study quantitatively characterized the relationship between the mass fraction m (0.5 < m ≤ 1) of the main component in binary blends and melt viscosity. Based on experimental data, a component correction term was introduced into the traditional power-law model to construct a constitutive equation that simultaneously describes the effects of shear rate, temperature, and component fraction on melt viscosity. The average relative error between model predictions and experimental values was only 5.90%. These rheological data and the modified constitutive equation provide important theoretical support and data reference for optimizing process parameters in waste plastic recycling and injection molding.
1. Introduction
Plastic processing and recycling industries face a persistent bottleneck: the lack of reliable rheological data for molten plastics and their blends. Traditional empirical models often fail to predict viscosity under varying shear rates, temperatures, and compositions, leading to inefficient process design and product defects. This study addresses this gap by systematically measuring the rheological properties of four common plastics and three binary blends under industrially relevant conditions.
By integrating experimental data with a modified power-law constitutive equation, the authors provide a robust framework that quantitatively links viscosity to shear rate, temperature, and component fraction. The model's high accuracy (average relative error 5.90%) offers a practical tool for optimizing injection molding and waste plastic recycling, potentially reducing energy consumption and improving product quality.
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MA Shaoping, HAN Ying, WU Shuang, XIAO Yafeng, DONG Zhongtian, WANG Zhihui, ZHANG Qinghua, YANG Chao (2026). Measurement and Correlation of Rheological Properties of Molten Plastics and Their Blends. The Chinese Journal of Process Engineering. https://doi.org/10.12034/j.issn.1009-606X.225225
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Frequently Asked Questions
What is the shear rate and temperature range covered in the rheological measurements, and how do these conditions relate to typical plastic processing operations?
The measurements covered shear rates from 0.1 to 100 s⁻¹ and temperatures from 180°C to 250°C. These ranges are representative of low-to-intermediate shear conditions encountered in processes like extrusion and injection molding, where shear-thinning behavior significantly affects flow and filling.
How does the modified constitutive equation account for the effect of blend composition on viscosity?
The model introduces a component correction term based on the mass fraction m of the main component (0.5 < m ≤ 1). This term adjusts the power-law parameters to capture the experimentally observed viscosity variation with composition, achieving an average relative error of 5.90% across all tested blends.
What are the implications of PE exhibiting the lowest flow behavior index and activation energy for processing?
PE's low n (stronger shear-thinning) and low activation energy (less temperature sensitivity) mean that viscosity is more effectively reduced by increasing shear rate rather than temperature. This suggests that processes for PE should prioritize shear control over temperature adjustments to achieve desired flow properties, potentially saving energy.
Can the proposed model be extended to other plastic blends or multi-component systems?
The model's structure is general, but its parameters are empirical and derived from the specific polymers tested. Extension to other systems would require re-calibration using experimental data for those blends. However, the methodology provides a systematic approach for developing similar correlations.
How reliable are the viscosity predictions for industrial scale-up?
With an average relative error of 5.90%, the model offers good accuracy for engineering calculations. However, scale-up may involve higher shear rates and complex geometries not fully captured by the tested range. Users should validate predictions against pilot-scale data before full-scale implementation.
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