ISSN:
0032-3888
Keywords:
Chemistry
;
Chemical Engineering
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
,
Physics
Notes:
Kinetic studies on shear degradation of a polystyrene (M̄n = 115,700 and P̄n = 1113) during extrusion in a model extruder were made at different temperatures (170, 190, 210, and 230°C) and shear stresses (340,406, and 472 g/cm2) for determination of rate constants for degradation, reaction order, and effects of temperature and stress on the rate constants. Mechanical energy and effective activation energy (E*) of bond rupture were related to temperature and applied stress. The following results were obtained. The degradation process is found to be satisfied by a second order reaction over the temperatures and stresses studied with respect to the changes in number average chain length (Pt - P∞), thus -dP/dt = k(Pt - P∞)2, where k is a reaction rate constant and t and ∞ refer to degradation times. The mechanical energy of bond rupture has a maximum and the rate constant a minimum at about 180°C, indicating that the least effective temperature for mechanical degradation is about 180°C. E* decreases with increasing applied stress (τ) as a linear relationship, i.e., E* = EA - ατ. At τ = 0, E* becomes equal to the activation energy for thermal degradation with the value EA = 48.6 kcal/mole which agrees well with literature data. Temperature and stress effects on the rate constant are well expressed for our study by the Arrhenius equation proposed by Zhurkov, et al., i.e., k = A exp[-(Ea - ατ)/RT] where A and α are coefficients.
Additional Material:
8 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/pen.760181012
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