Polypropylene antioxidants, addition

Increasingly, plastics are being used as parenteral packaging (qv) materials. Plastics such as poly(vinyl chloride), polyethylene, and polypropylene are employed. However, plastics may contain various additives that could leach into the product, such as plasticizers (qv) and antioxidants. PermeabiUty of plastics to oxygen, carbon dioxide, and water vapor must be tested in the selection of plastic containers. Furthermore, the plastic should withstand sterilization. Flaking of plastic particles should not occur and clarity necessary for inspection should be present. 

Polyolefins such as polyethylene and polypropylene contain only C—C and C—H bonds and may be considered as high molecular weight paraffins. Like the simpler paraffins they are somewhat inert and their major chemical reaction is substitution, e.g. halogenation. In addition the branched polyethylenes and the higher polyolefins contain tertiary carbon atoms which are reactive sites for oxidation. Because of this it is necessary to add antioxidants to stabilise the polymers against oxidation Some polyolefins may be cross-linked by peroxides. 

Polypropylene differs from polyethylene in its chemical reactivity because of the presence of tertiary carbon atoms occurring alternately on the chain backbone. Of particular significance is the susceptibility of the polymer to oxidation at elevated temperatures. Some estimate of the difference between the two polymers can be obtained from Figure 1J.7, which compares- the rates of oxygen uptake of eaeh polymer at 93°C. Substantial improvements can be made by the inclusion of antioxidants and such additives are used in all commercial compounds. Whereas polyethylene cross-links on oxidation, polypropylene degrades to form lower molecular weight products. Similar effects are noted... 

In many polypropylene formulations three or more additives must be used to produce a resin with the desired stability. A wide variety of antioxidants and other stabilizers are available for this purpose. The choice of antioxidant for a given application is determined by compatibility, stabilizing efficiency, color, odor, toxicity, and cost (15). 

A variety of methods for evaluating antioxidants in polypropylene has been developed during the past several years. Polymer producers, end-use manufacturers, additive suppliers, academicians, and others have developed widely disparate test methods, all of which presumably yield the same results—i.e., the test methods rate the antioxidants and antioxidant systems in the same relative order of effectiveness. Many of these test methods are useful tools in distinguishing unstabilized polymer, moderately stabilized polymer, and highly stabilized polymer systems. Today, all of the polypropylene producers offer highly stabilized polymers. Effective antioxidants are available from several additive suppliers. How does one select the best antioxidant or polymer formulation for a particular end use This paper compares the results obtained by various test methods used to evaluate the two basic types of oxidative stability, processing stability and end-use or environmental stability. The correlation or lack... 

TPOs are basically two-component elastomer systems consisting of an elastomer finely dispersed in a thermoplastic polyolefin (such as polypropylene). The thermoplastic polyolefin is the major component. Thermoplastic elastomers (TPEs) include TPOs, TPVs (thermoplastic vulcanizates), etc. Properties of TPOs depend upon the types and amounts of polymers used, the method by which they are combined, and the use of additives such as oils, fillers, antioxidants, and colors. Blends and reactor-made products compete primarily with other TPEs and metals. There are vulcanizates (TPVs) that have higher elastomeric properties. They compete primarily with TS elastomers. 

Regular and crosslinked polyethylene (PE) and polypropylene (PP) have an effect or influence the RM process such as molding temperature, grinding and mixing conditions, type and level of additive (pigment, anti oxidant, etc.), mold material of construction, and inner atmosphere.272 As an example the use of increased amounts of antioxidant in the plastic, or the use of an inert atmosphere, delays the degradation but does not prevent it. 

Plastics that are commonly processed by extrusion include acrylics (polymethacrylates, polyacrylates) and copolymers of acrylonitrile cellulosics (cellulose acetate, propionate, and acetate butyrate) polyethylene (low and high density) polypropylene polystyrene vinyl plastics polycarbonates and nylons. The material properties and extrusion properties have been reviewed by Whelan and Dunning.Additives that may be included to modify or enhance proper-ties include lubricants and antislip agents to assist processing during extrusion plasticizers to achieve softness and flexibility stabilizers and antioxidants to retard or prevent degradation and dyes and pigments. 

Aqueous solutions of sorbic acid without the addition of antioxidants are rapidly decomposed when stored in polypropylene, polyvinylchloride, and polyethylene containers. 

The properties of hindered diazacycloalkanones were evaluated as light stabilizers and antioxidants for polypropylene. A totally hindered piperazinone was found to be excellent light stabilizer with many other desirable properties as a polymer additive. Partially hindered decahydroquinoxalinone derivatives were found to be surprisingly good antioxidants. The relationship between structure parameters and activity was investigated. 

Materials. Experiments were carried out on a polypropylene composite filled with chalk and containing the following additives a hindered phenolic antioxidant IRGANOX 1010 (CIBA-GEIGY product) 0.028-0.113... 

The additives were tested in polypropylene (Profax 6501, Hercules) films containing 0.1% Goodrite 3114 (phenolic antioxidant of B.F. Goodrich Co.) and. 05% calcium stearate. The candidate additives were added at 0.25% or 0.5% final concentrations as methylene chloride solutions (100 ml methylene chloride/lOOg polypropylene) and the mixture stirred 15-20 mins, while the solvent was allowed to evaporate. The resultant powder was then dried and extruded into 3/32 inch strand, which was cut into pellets. After drying, the pellets were extruded into a broad (8") band. A 1/4" section was slit from the band and oriented by drawing at 175°F at a 7 1 draw ratio. The dimensions of the oriented film are about 1 x 80 mils. 

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