G.discolor

The standard approach to reducing scorch (e.g. discoloration resulting from oxidation) involves addition of one or more antioxidants. Scorch retardants prevent premature decomposition of peroxides and cross-linking of polymers (pre-vulcanisation). 

In these packages, visible imperfections generated at the time of molding, e.g., discoloration, fish eyes, rough surface, etc., are significant problems that need to be addressed. Thus, several improvements in the process of producing an EVOH have been proposed. 

Isocalycinine (74) and discoguattine (75) are the only two aporphines of Guat-teria known to possess a 9,11-dioxygenated ring D, which had seemed to be a characteristic feature of Duguetia (Annonaceae) (67). Both alkaloids were isolated from G. discolor (24), and their structures were easily determined by the usual spectroscopic methods. In both, a meta-coupled AB system was the only outstanding feature recognizable in the H-NMR spectra which, however, had to be recorded in CSDSN to achieve adequate resolution and, in the case of isocalycinine (74), to confirm the location of the phenol function at C-9. 

Oxoisocalycinine (106), which cooccurs with the ring D-9,11-dioxygenated isocalycinine (74) and discoguattine (75) in G. discolor (24), is the only example to date of an oxoaporphine with this unusual substitution pattern. The alternative oxocalycinine and oxoisocalycinine structures were suggested by mass and H-NMR spectra, which are quite unexceptional, and the actual positions of the substituents were established by zinc-hydrochloric acid reduction to isocalycinine (74) (24). 

Guacolidine (121) and guacoline (122) were isolated from G. discolor (24). The mass spectrum of guacoline indicated the molecular formula C20H19NO5. Its... 

These compounds have the drawback of a relatively low reaction rate, thus requiring long residence times in the extmder. As a result, undesired side reactions, may occur, e.g., discoloration. 

Usually, an ample reserve of heat stabilizers is present in products to be recycled. PVC usually does not require further addition of additives. However, mixing recyclates that contain different classes of stabilizers may cause a problem, e.g.,discoloration by mixing lead and tin-type stabilizers. ... 

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