Prediction of the yellowing of styrene-stat-acrylonitrile and acrylonitrile-butadiene-styrene during processing in an internal mixer

Touria Achtioui; Catherine Lacoste; Marie Le Baillif; Damien Erre

doi:10.1515/polyeng-2017-0305

Article

Prediction of the yellowing of styrene-stat-acrylonitrile and acrylonitrile-butadiene-styrene during processing in an internal mixer

Touria Achtioui , Catherine Lacoste , Marie Le Baillif and Damien Erre

Published/Copyright: September 22, 2018

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From the journal Journal of Polymer Engineering Volume 38 Issue 10

Abstract

The objective of this study was to build a model that can predict the yellowing of styrene-stat-acrylonitrile (SAN) and acrylonitrile-butadiene-styrene (ABS) during processing in an internal mixer. Considering the change of color of SAN and ABS as they degrade, we correlate the yellowing of SAN and ABS to process parameters. We propose a method to represent the energy of mixing of polymer blends in an internal mixer to understand the complex mixing process of materials under different mixing conditions. Indeed, during processing, the properties of polymers could be affected by both thermal and mechanical degradation leading to several mechanisms of degradation. We presented a simplified model “h” taking into account the contribution of each process parameters applied in the internal mixer. Three process parameters were studied: the temperature T, the rotation speed of the blades V, and the residence time t. Thanks to this method of approach, a good correlation between the yellowing of styrenics and the mixing energy in the internal mixer was described. We validated this equation with two polymers: SAN and ABS, and this model can now predict the yellowing of SAN and ABS as a function of the process parameters in an internal mixer.

Keywords: ABS; internal mixer; mixing energy; SAN; thermo-mechanical degradation

Acknowledgments

The authors would like to thank Albea group for having graciously supplied ABS and SAN polymers. The present work would not have been possible without the Thalia 2 project and Champagne-Ardenne council who financially supported this study. We are also thankful to Professor Jean Leopold Leblanc for useful discussions on the subject and Serge Odof for helping with the colorimetric tests.

Conflict of interest statement: The authors declare no conflicts of interest regarding the publication of this article.

Appendix

The constant K was calculated thanks to the work of Bousmina et al. [15].

(21)K=β2−18π2LRe(1+g2)

Considering that in an internal mixer, each set of cylinders is considered as a simple Couette with a rotor having a radius R_i (here 17.7 mm) and a wall having a radius R_e (19.7 mm), β is the ratio between R_e and R_i. L is the length of the cylinders (47.7 mm), and g is the gear ratio between the two blades (2/3).

Abbreviations

∇νν: velocity gradient (s⁻¹)
λ: characteristic time (s)
τ: shear stress (pascal)
Γ: torque induced by the material on the blades of the internal mixer (N⋅m)
Q˙: amount of heat involved in a chemical reaction added or removed per unit volume (W⋅m⁻³)
W˙: specific mechanical power per unit volume (W⋅m⁻³)
γ˙: shear rate (s⁻¹)
ABS: acrylonitrile-butadiene-styrene
C_p: specific heat of the material (J⋅g⁻¹⋅K⁻¹)
E_a: activation energy (J⋅mol⁻¹)
K′: consistence index
k: thermal conductivity (W⋅m⁻³⋅K⁻¹)
n: flow index
N: rotor speed of the blade turning faster (s⁻¹)
P: power (kW)
R: the universal gas constant in J⋅mol⁻¹⋅K⁻¹
SAN: styrene-stat-acrylonitrile
SME: specific mechanical energy (kJ/kg)
T: temperature of the material (K)
T_w: temperature on the wall (K)
V: for rotor speed (rpm=revolution per minute)
V_b: volume of the batch (m³)
YI: yellowness index
η: effective viscosity of the blend (Pa⋅s)
ρ: density (g⋅m⁻³)

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Received: 2017-08-29

Accepted: 2018-05-22

Published Online: 2018-09-22

Published in Print: 2018-11-27

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Articles in the same Issue

https://doi.org/10.1515/polyeng-2017-0305

Keywords for this article

ABS; internal mixer; mixing energy; SAN; thermo-mechanical degradation