Degradation of natural rubber during mill mastication

Changes in the molecular weight distribution of natural rubber, after mill mastication, have been studied by using a Water's gel permeation chromatography. This study indicates that as the polymer is milled the distribution is narrowed primarily through the breaking down of large molecular weight molecules. The peak of the distribution curve shifts to lower and lower molecular weight with increased milling time but it appears to be approaching a limiting molecular weight after 76 min. of milling time. One unexpected result is the development of a secondary hump in the distribution curve at the high molecular weight end. This hump gets larger and moves to lower molecular weight with increasing milling time until 76 min. of milling, at which time it disappears entirely.