Carboxyl stabilized

Metal carboxyiates have been considered as nucleophilic agents capable of removing aHyUc chlorine and thereby affording stabilization (143). Typical PVC stabilizers, eg, tin, lead, or cadmium esters, actually promote the degradation of VDC polymers. The metal cations in these compounds are much too acidic to be used with VDC polymers. An effective carboxylate stabilizer must contain a metal cation sufftcientiy acidic to interact with aHyUc chlorine and to facihtate its displacement by the carboxylate anion, but at the same time not acidic enough to strip chlorine from the polymer main chain (144). 

Most thermal stabilizers for poly (vinyl chloride) are metal salts of carboxylic acids or mercaptans. The commonly used metals are cadmium, barium, zinc, lead, calcium, and dibutyltin. Originally it was assumed the metal salts act as scavengers for hydrogen chloride. However, Frye and Horst (7, 8) found evidence for the introduction of ester groups in the polymer from metal carboxylate stabilizers, which led them to postulate that thermal stabilizers function by substituting the unstable chlorine atoms with the ligands of the stabilizer to yield derivatives which are more thermally stable than the original chloride. 

The residue from carboxylate stabilizers was dissolved with acetone and titrated potentiometrically with 0.1N silver nitrate in the presence of 100 ml. of water and 5 ml. of concentrated nitric acid. 

Meadowfoam is composed of unique long-ehain fatty aeids with 5-eieosenoie acid (62%) as the major fatty aeid. The other main eomponents are 5,13-doeosa-dienoic acid (19%), 5-docosenoic acid (3%) and 13-docosenoic acid (10%). The A5 unsaturation provides an excellent chemical moiety for synthetic modifications to the oil or fatty acids by providing a site at which a carboxylate stabilized carbocation can form. In addition, the A5 unsaturation has enhanced resistance to oxidative degradation (8) as evidenced by the high OSI of the oil (246.9 h at 110°C) or its methyl ester (69.4 h at 90°C). 

FTIR (wavenumber-assignment) cm V- 1714,1715, 1718, 1720,1730 (carbonyl) 1785 (acid chloride) 1510 (carboxylate stabilizer) 3476-3420 (hydroperoxide) 3460 (hydroxyl) 1650 (isolated double bond) 1580 (conjugated double bond) ... 

The commercial products in this area often use acids other than lauric, or use blends. Those with an odd number of carbon atoms yield esters that are more resistant to hydrolysis than those with even numbers (a factor also in plasticizer selection). If hydrolysis occurs during processing, there may be volatilization of irritating maleic anhydride fumes. Modem tin carboxylate stabilizers have overcome this problem. In supphers literature, they are often designated as sulfur-free, rather than as orga-notin carboxylates. 

In both cases, toners may be added to provide a bluish tint. General purpose (nonfood-grade) clear sheet traditionally used 2.0-2.5 phr of a carboxylate stabilizer, such as PlastiStab 2808, Therm-Chek 835, Reatinor 460 or 480, or Interstab T-876 or T-878 or a carboxylate/mercaptide, such as Mark T-634 or 2270F, or Akcrostab T-5507A. With the advent of low-odor tin mercaptides, much of this has been converted from the more expensive carboxylates. For clear extruded sheet, the following is typical ... 

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