Degradation of Poly-Vinylpyrrolidone by Ball-Milling

Abstract

Molecular weight of poly-vinylpyrrolidone decreased by ball-milling in nitrogen, air or oxygen. After 420 hours of ball-milling, polyvinylpyrrolidone of molecular weight 9.6×10⁵ degraded to about 2×10⁴. Equation (1) was applied to the relation between -dM/dt and M.
-dM/dt=K_mM^β₁{1-(M_t=∞/M)^β₂} (1)
Numerical values of K_m, β₁ and β₂ for the case of ball-milling in oxygen were the largest and those for the case of nitrogen were the smallest. Gel filtration of the sample suggested much probability in the way that, in nitrogen, the segment of the molecular weight below 10⁵ was broken in order from the end of the polymer.
Investigation of elemental analysis, Nestler's reaction and decomposition point of the sample showed partial change in chemical structure caused by ball-milling. Partial change in solid constitution caused by ball-milling was also suggested by the measurement of glass temperature.
Equation (2) was applied to the first 150 hours of ball-milling, where S is the surface area of the sample.
dS/dt=k₁·exp(-k₂·S) (2)
Parameter k₁ was large for the case of ball-milling in an oxygen-containing atmosphere, similar to that of K_m in Equation (1).