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- Title
Kinetics of the thermal dehydrochlorination of vinylidene chloride barrier polymers.
- Authors
Howell, B. A.
- Abstract
Vinylidene chloride copolymers containing a predominance of vinylidene chloride (85-90%) have long been important barrier polymers widely used in the plastics packaging industry. These materials display excellent barrier to the ingress of oxygen and other small molecules (to prevent food spoilage) and to the loss of food flavor and aroma constituents (to prevent flavor scalping on the supermarket shelf). While these polymers have many outstanding characteristics, which have made them commercial successes, they tend to undergo thermally-induced degradative dehydrohalogenation at process temperatures. The dehydrochlorination occurs at moderate temperatures (120-200°C) and is a typical chain process involving initiation, propagation and termination phases. Defect structures, namely internal unsaturation (allylic dichloromethylene groups), serve as initiation sites for the degradation. These may be introduced during polymerization or during subsequent isolation and drying procedures. If uncontrolled, sequential dehydrohalogenation can lead to the formation of conjugated polyene sequences along the polymer mainchain. If sufficiently large, these polyenes absorb in the visible portion of the electromagnetic spectrum, and give rise to discoloration of the polymer. The dehydrochlorination process may be conveniently monitored by thermogravimetric techniques. Both initiation and propagation rate constants may be readily obtained.
- Subjects
DICHLOROETHYLENE; ORGANOCHLORINE compounds; ANALYTICAL mechanics; THERMAL analysis; POLYMERS; COPOLYMERS
- Publication
Journal of Thermal Analysis & Calorimetry, 2006, Vol 83, Issue 1, p53
- ISSN
1388-6150
- Publication type
Article
- DOI
10.1007/s10973-005-7051-7