LLDPE, additives Antioxidants

Hoang, E.M., Liauw, C.M., AUen, N.S., Fontan, E., and Lafuente, P, Effect of Metal Stearate Antacid on the Melt StahiUzation Performance of Phenolic/Phosphite Antioxidants in Metallocene LLDPE. Part 1 Melt Processing Stahility /. Vinyl Addit. Technol., 10, 3, 137 (2004)... 

Linear-Low Density Polyethylene (LLDPE) and Ethylene -Propylene Diene (EPDM) Stabilization. Prevention of discoloration of LLDPE and EPDM are prime objectives in addition to thermal stabilization. While thermal stabilization is readily achieved by the use of phenolic antioxidants, prevention of discoloration requires a co-additive such as a phosphite. 

ASTM D 5815 Standard Test Method for Determination of Phenolic Antioxidants and Erucamide Slip Additives in Linear Low-Density Polyethylene Using Liquid Chromatography This ASTM is very similar to ASTM D 1996, except that LLDPE samples are analyzed, and extraction is performed with either isobutanol or isopropanol prior to liquid-chromatographic separation. Isopropanol is recommended as the extraction solvent for lower crystallinity LLDPE (density 0.925 g/ cm and below), and isobutanol is recommended as the extraction solvent for higher crystallinity LLDPE. As the standard notes, besides Irganox 1010, Irganox 1076, and Isonox 129, the test method should be applicable for the determination of other antioxidants such as Ultranox 626, Ethanox 330, Santanox R, and Topanol CA, but the applicability of this test method has not been investigated for these antioxidants. Precision of the procedure is somewhat poorer compared to that of ASTM D 1996 ... 

In packaging, three resins account for the majority of the market for antioxidants PP, PE, and HIPS. For PP, a combination of hindered phenol and phosphite antioxidants is commonly used, with the total concentration normally from 0.08 to 1%, depending on formulation and end use. Clba Specialty Chemicals has developed the phenolic antioxidant family of Irganox for use in PP and PE, and also the Irgafos family, which are phosphite stabilizers used in combination with phenolic antioxidants. For LDPE, BHT, a phenolic antioxidant, is normally incorporated at levels of 50 to 500 ppm however there is a tendency to employ less volatile additives to prevent their migration from the resin. For HDPE and LLDPE, antioxidants less volatile than BHT, such as polyphenols, at higher concentrations, are normally used In combination with phosphites. For HIPS, hindered phenols are used in combination with UV absorbers. Alpha-tocopherol (Vitamin E) is sometimes used as an antioxidant for polyolefins. 

Stabilization of crosslinked PE is assured by the same antioxidants used for noncrosslinked PE. The selection of the stabilization system with respect to compatibility performance and extraction resistance is a function of the PE to be stabilized (LDPE, LLDPE, HDPE, HMWHDPE) as well as of the cross-linking procedure and intended application. If there is direct contact between copper and polymer, addition of a metal deactivator is mandatory. 

Hoang EM, Liauw CM, Allen NS, Fontan E, Lafuente P. Effect of metal stearate antacid on the melt stabilization performance of phenolic/ phosphite antioxidants in metallocene LLDPE. Part 1 melt processing stability. J Vinyl Addit Technol 2004 10(3) 137 3. 

A brief review is presented on techniques for the analysis of polyolefins and additives in polyolefins. Techniques considered include high-temperature GPC combined with FTIR spectroscopy for the analysis of chemical composition as a function of molar mass, crystallisation fiactionation for the analysis of short-chain branching in LLDPE and of polyolefin blends and pyrolysis-gas chromatography-mass spectrometry for the determination of additives, such as antioxidants, in polyolefins. 13 refs. (3rd Annual UNESCO School lUPAC Conference on Macromolecules and Materials Science, Stellenbosch, South Africa, 2000)... 

---