ISSN:
0193-7197
Keywords:
Chemistry
;
Chemical Engineering
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
,
Process Engineering, Biotechnology, Nutrition Technology
Notes:
Vinylidene chloride copolymers have a number of superior properties, most notably, a high barrier to the transport of oxygen and other small molecules. As a consequence, these materials have assumed a position of prominence in the packaging industry. At processing temperatures these copolymers tend to undergo degradative dehydrochlorination. The dehydrochlorination reaction is a typical chain process with distinct initiation, propagation, and termination phases. It has been demonstrated that initiation of degradation is strongly facilitated by the presence of unsaturation along the backbone. Such unsaturation may be introduced via interaction of the polymer with a variety of agents which might commonly be encountered during polymerization or processing. The presence of an unsaturated unit within the polymer generates an allylic dichloromethylene, which may function as a major defect (labile) site for the initiation of degradation. The conversion of these dichloromethylene units into nonreactive groups would interrupt propagation of the dehydrochlorination reaction and lead to the stabilization of the copolymer. Potential stabilization in the presence of metal formates has been examined using a vinylidene chloride/methyl acrylate (5 mol%) copolymer and thermogravimetric techniques. The effect of the metal formate on the stability of the polymer reflects the relative halogenophilicity of the metal cation present. Metal formates of low cation acidity [sodium, calcium, nickel(II) and to a lesser extent lead(II), cadmium, manganese(II) and magnesium] may be expected to be ineffective as stabilizers for vinylidene chloride copolymers. At the other extreme, metal formates that contain cations sufficiently acidic to actively strip chlorine from the polymer backbone, e.g., zinc formate, will function to enhance the degradation process. An effective carboxylate stabilizer must contain a metal cation sufficiently acidic to interact with allylic chlorine and to facilitate its displacement by the carboxylate anion. Copper(II) formate may possess the balance of cation acidity and carboxylate acitvity to function as an effective stabilizer for vinylidene chloride copolymers.
Additional Material:
2 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/vnl.730150405
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