Polyolefin stabilization methods

Gray RL (1990) Accelerated Testing Method for Evaluating Polyolefin Stability. In Koemer RM (ed) (leosynthetic Testing for Waste Ckmtainment Applications ASTM special technical Publication 1081. American Society for Testing and Materials (ASTM), West Conshohocken, pp 57-74... 

The growth of polyolefin fibers continues. Advances in olefin polymerization provide a wide range of polymer properties to the fiber producer. Inroads into new markets are being made through improvements in stabilization, and new and improved methods of extmsion and production, including multicomponent extmsion and spunbonded and meltblown nonwovens. 

UV3346) offer superior compatibility, low volatility, excellent resistance to extraction and contribute to heat stability. The nonextractable nature of these additives makes their quantification challenging. The quantification of Chimassorb 944 in polyolefins is possible using an UV absorption method after dissolution of the polymer [596]. 

Derivitization reactions have previously been employed to extend the sensitivity and resolution of IR, ultraviolet and X-ray photo-electron spectroscopy (7-13). Yet no proposed method has the range to accommodate the major oxidation products from polyolefins. As part of an ongoing study of polymer oxidation and stabilization, we discuss here a series of reactions with small, reactive gas molecules. The products from these reactions can be rapidly identified and quantified by IR. Some of these reactions are new, others have already been described in the literature, although their products have not always been fully identified. 

London, 16th-18th Sept.1992, p.3/1-3/10. 6E IMPROVED METHOD FOR MEASURING THE STABILITY OF POLYOLEFINS... 

Two different approaches for lifetime prediction are presented. The underlying lifetime limiting processes have been identified in two cases. Mathematical expressions of chemical/physical relevance were used for the lifetime predictions for PE hot-water pipes and cables insulated with plasticized PVC. Accelerated testing, extrapolation and validation of the extrapolation by assessment of the remaining lifetime of objects aged during service conditions for 25 years were successfully applied to cables insulated with chlorosulfonated polyethylene. Polyolefin pipes exposed to chlorinated water showed a very complex deterioration scenario and it was only possible to find a method suitable for predicting the time for the depletion of the stabilizer system. 

Hydroperoxides are potent photoinitiators and their decomposition into inactive products is an important method of stabilization in polyolefins for it prevents generation of radicals by reactions such as (4), (5), (14), and (15). Decomposition of hydroperoxides can be achieved by a reaction with phosphite esters or nickel chelates or by a catalytic action by a range of compounds including dithiocarbamates and mercaptoben-zothiazoles. Decomposition of hydroperoxides formed during processing is important for the stabilization ofPVC. 

Determination of the residual antioxidant content in polymers by HPLC and MAE is one way to determine the amoimt needed for reasonable stabilization of a material, and also to compare different antioxidants and their individual efficiencies. During ageing and oxidation of PE, carboxyhc acids, dicarboxylic acids, alcohols, ketones, aldehydes, n-alkanes and 1-alkenes are formed [86-89]. The carboxyhc acids are formed as a result of various reactions of alkoxy or peroxy radicals [90]. The oxidation of polyolefins is generally monitored by various analytical techniques. GC-MS analysis in combination with a selective extraction method is used to determine degradation products in plastics. ETIR enables the increase in carbonyls on a polymer chain, from carboxylic acids, dicarboxyhc acids, aldehydes, and ketones, to be monitored. It is regarded as one of the most definite spectroscopic methods for the quantification and identification of oxidation in materials, and it is used to quantify the oxidation of polymers [91-95]. Mechanical testing is a way to determine properties such as strength, stiffness and strain at break of polymeric materials. 

One of the studies of cloth diapers assumed a life of 92 uses (a study funded by the disposable industry), whereas the other assumed 167 uses (a study funded by the cloth diaper industry). A study funded by the disposable diaper industry assumed an energy cost for transporting the cotton to China where the diapers were made. One would have to check to see what fraction of cloth diapers are made this way. Disposable diaper makers have pushed composting as a method of disposal. Most cities do not compost this type of waste. The polyolefins would not degrade well in this process, even though the lack of stabilizers in the polypropylene might allow it to become powder. 

ASTM D 5885 Standard Test Method for Oxidative Induction Time of Polyolefin Geosynthetics by High-Pressure Differential Scanning Calorimetry Principally, this is the same test as the above and is performed using a DSC, except now with a high-pressure cell that can sustain a pressure of 5500 kPa. The test is designed for highly stabilized materials. It is applicable only to materials whose... 

To prepare multilayer membranes, another irradiation method to prepare cross-linked microporous multilayer membranes with enhanced thermal stability has been developed. It is realized by two steps. First, the polymer-blended layers, such as poly(ethylene glycol) diacrylate/poly(ethylene glycol) methyl ether acrylate are coated onto polyolefin microporous membranes. Second, the resultant membranes are irradiated to form chemically cross-linked membranes. They exhibited higher thermal and electrochemical properties compared to conventional separators. TOth the increase of irradiation dose, the thermal stability of the resultant membranes increases accordingly. By using the microporous multilayer membranes, the advantages of each component layers are well combined. 

---