Rubbers, additives Antiozonants

Plastic and rubber additives are both commodity chemicals and specialties. The Handbook of Plastic and Rubber Additives [27] mentions over 13 000 products antioxidants and antiozonants amount to more than 1500 trade name products and chemicals [28], flame retardants to some 1000 chemicals [29] and antimicrobials to over 1200 products [30]. 

At Goodyear laser-desorption MS has been used for direct analysis of rubber additives (e.g. antioxidants, antiozonants, vulcanising agents, processing oils, silica fillers, etc.), in situ at the surface of an elastomeric vulcanisate [74,75]. 

LD-MS has proven a uniquely useful technique for the direct characterisation of ruhher-compound surface species. Mass spectra were obtained for intact molecular ions (M+) of organic chemical rubber additives such as the aromatic processing oil, and the aromatic antiozonant and antioxidants incorporated to protect the rubber. MW information from... 

Laser desorption MS has been used for direct analysis of rubber additives, in situ at the surface of elastomeric vulcanisates [201,202]. For example, the technique was used to analyse a sample of truck tyre that displayed premature sidewall cracking. By using a single laser pulse, the molecular ions of several intact molecular species (AOs, antiozonants and a production impurity of an additive) were observed on the rubber surface. Also McClennen et al. [203] have used controlled laser energy to desorb organic additives from a rubber vulcanisate. 

Lykke et al. [177,262] have used L MS (ToF-MS, FTMS) in resonant and non-resonant mode for the molecular analysis of complex materials, including polymer/additive systems. Different wavelengths for the post-ionisation step (near-UV, far-UV, VUV) permit selectivity that provides important additional information on the chemical constitution of these complex materials. LDI techniques render more accessible analysis of complex materials such as polymers and rubbers containing a wide variety of additives and pigments. Lykke et al [218] also compared laser desorption, laser desorption/post-ionisation and laser ionisation in both direct and extract analysis of three vulcanised rubbers (natural rubber, SBR and poly(c/5 -butadiene)). Desorption (532, 308, 266 nm)/post-ionisation (355, 308, 266, 248, 213, 118 nm) was carried out with various lasers. Desorption (308 nm)/post-ionisation (355 nm) with REMPI detection allows preferential detection of various additives (antiozonant HPPD, m/z 268, 211, 183, 169 antioxidant poly-TMDQ, m/z 346, 311) over the ubiquitous hydrocarbons in a rubber (Fig. 3.13). 

Rubber is protected against ozone attack by addition of physical and/or chemical antiozonants. Hydrocarbon waxes are the most common type of physical antiozonants, and p-phenylenediamine derivatives are the prevalent chemical antiozonants. Waxes bloom to the rubber surface and form a protective barrier. 

Anorin-38 has also shown an interesting effect as a multifunctional additive (a single additive to replace many of the conventional additives) for natural rubber (NR). It showed excellent blending behavior and compatibility with NR. Aorin-38 enhances the tensile properties and percent elongation, decreases fatigue, acts as an antioxidant and antiozonant, and positively affects many of the other properties, apart from acting as a process aid and a cure enhancer [183-186]. 

LDPE or HDPE extracts has been determined colorimet-rically at 430 nm by oxidation with H202 in the presence of H2S04 [66]. p-Phenylenediamine derivatives such as Flexzone 3C, used as antiozonants in rubber products, have been determined colorimetrically after oxidation to the corresponding Wurster salts [67]. A wide range of amine AOs in polyolefins has been determined by the p-nitroaniline spectrophotometric procedure [68]. Monoethanolamine (MEA) in a slip agent in PE film has been determined as a salicylaldehyde derivative by spectrophotometric quantification at 385 nm [69]. Table 5.6 contains additional examples of the use of 1JV/VIS spectrophotometry for the determination of additives in polymers. 

FAB has been used to analyse additives in (un) vulcanised elastomer systems [92,94] and FAB matrices have been developed which permit the direct analysis of mixtures of elastomer additives without chromatographic separation. The T-156 triblend vulcanised elastomer additives poly-TMDQ (AO), CTP (retarder), HPPD (antiozonant), and TMTD, OBTS, MBT and A,lV-diisopropyl-2-benzothiazylsulfenamide (accelerators) were studied in three matrix solutions (glycerol, oleic acid, and NPOE) [94]. The thiuram class of accelerators were least successful. Mixture analysis of complex rubber vulcanisates without chromatographic separation was demonstrated. The differentiation of matrix ions from sample ions was enhanced by use of high-resolution acquisition. 

FD-MS is also an effective analytical method for direct analysis of many rubber and plastic additives. Lattimer and Welch [113,114] showed that FD-MS gives excellent molecular ion spectra for a variety of polymer additives, including rubber accelerators (dithiocar-bamates, guanidines, benzothiazyl, and thiuram derivatives), antioxidants (hindered phenols, aromatic amines), p-phcnylenediamine-based antiozonants, processing oils and phthalate plasticisers. Alkylphenol ethoxylate surfactants have been characterised by FD-MS [115]. Jack-son et al. [116] analysed some plastic additives (hindered phenol AOs and benzotriazole UVA) by FD-MS. Reaction products of a p-phenylenediaminc antiozonant and d.v-9-lricoscnc (a model olefin) were assessed by FD-MS [117],... 

Antiozonant additives are employed with unsaturated rubbers such as natural rubber, nitrile rubber, styrene-butadiene rubber, etc., to minimise the atmospheric ozone degradation reaction. Common antiozonant types include the parapheny-lene diamines such as N-(l,3-dimethylbutyl)-AT-phenyl-p-phenylene diamine (6PPD) and N-isopropyl-N7 phenyl-p-phenylene diamine (IPPD). Both these antioxidants can be identified and quantified using GC- or LC-based techniques. 

Benzofuran derivatives and enolethers are offered as chemical antiozonants for light coloured rubber compounds. Benzofuran derivatives are used in CR and its blends with other rubbers and give ageing protection in addition to ozone protection. 

The solubility of wax in vulcanised rubbers is low (of the order of 0.5% for NR) but enough wax has to be added to a rubber compound to ensure that once the compound has been vulcanised and the rubber cools, the rate of migrational movement of the wax from the rubber mass to the surface of the rubber is rapid. Dependant upon the application, the addition level of wax can be up to about 10 phr. Migration of the wax to the rubber surface will also carry other ingredients such as antioxidants, antiozonants and other materials (e.g., vulcanisation residuals), to enhance the surface protection. 

Although Monsanto can rely on only two of its own raw materials, tertbutylamine and p-nitrochlorobenzene, for its range of additives, it is regarded as an efficient producer and a pioneer in antiozonants based on p-phenylenediamine and prevulcanization inhibitors. It has one of the most complete ranges of additives for rubber and the most modern units to manufacture them. 

The heat and ozone resistant [126] EPR was made by incorporating acrylic rubber, dicumyl peroxide, triaUyl cyanurate, ZnO and carbon-black into the matrix. Triallyl cyanurate increases the crosslinking efficiency probably due to an addition reaction between polymeric and aUyl radicals and leads to stable chemical crosslinks. Thus ozone because there is no unsaturation cannot initiate a degradation reaction. Digteva et al. [127] prepared sealants for use at high temperature by adding aromatic diaminodisulfide, MgO, ZnO and carbon black in EPR. The aromatic diaminodisulfide is an antiozonant and functions both as an antioxidant and a... 

DOPDA has been u sed as an additive to rubber. compositions at the time of manufacture for the purpose of providing ozone resistance to elastometers. Mixtures of DOPDA with solvents such as acetone (usually in 50/50 ratio) are flammable and toxic, causing skin irritation. The material covered by US Military Specification MIL-D-50000A(MR), July 1966 is intended for use as an externally applied (brush or dip) solution to rubber items, particularly tires. This chemical functions as an antiozonant, preventing cracking of stressed, vulcanized rubber items in outdoor storage Requirements and tests covered by the above Spec are as follows ... 

This reference documents the chromatographic properties of over 100 rubber-related amine and phenolic antioxidants, antiozonants, guanidines, accelerators, and amine hydrochlorides. This reference examined the chromatographic characteristics of the cited additives and, thus, did not characterize acmal polymers. 

Disharmonies in the Conception of the Direct 0 /Antiozonant Reaction Importance. Four antiozonant theories have been formulated within the last 25 years. Ozone scavenging theory suggests a preferential direct reaction of an antiozonant with ozone on the rubber surface as a decisive process (26-27). As the antiozonant is depleted via direct ozonation on the surface, fresh antiozonant diffuses rapidly from the rubber bulk to reestablish the equilibrium surface concentration. At a comparable additive concentration and migration rate, the antiozonant efficiency of an additive should be therefore dependent on its ozonation rate and the vulcanizate will be protected until the antiozonant is depleted below the lowest critical concentration. From this point of view, the ozonation rate seems to be a more important factor than the total amount of ozone scavenged by one mole of an antiozonant (this latter phenomenon may be called ozonation factor). Relations between antiozonant efficiency in vulcanizate and antiozonant ozonation rate or antiozonant surface concentration have been indeed reported in some papers and an appreciable higher ozonation rate of PD in comparison with rubber unsaturation, a preferential consumption of an antiozonant in model olefin solution or in rubber were observed. The rubber surface was not attacked by ozone until the antiozonant was almost completely consumed (28). ... 

In later papers in this series, there was more emphasis on direct analysis of the rubber or plastic material by field ionizationJ Figure 6.15 is the total ion current (TIC) vs. time (or temperature) profile for a diene rubber compoimd. ° The sample was heated in e direct probe from 50-750°C, with FI-MS. There are two distinct regions in which TIC maxima are observed. The first occurs between 50-400°C and largely represents the evaporation of organic additives from the rubber (Figure 6.16). Additives in the rubber include fatty acid (MW 256,284), a p-phenylenediamine antiozonant (MW 332),... 

Jackson, A. T., Jennings, K. R., and Scrivens, J. H., Analysis of a fivepolymer additives by means of high energy mass spectrometry and tandem mass spectrometry. Rapid Commun. Mass Spectrom., 10,1449, 1996. Lattimer, R. P., Layer, R. W., and Rhee, C. K., Mechanisms of antiozonant protection Antiozonant-rubber reactions during ozone exposure. Rubber Chem. Technol, 57, 1023, 1984. 

Toxicology LD50 (oral, rat) 3580 mg/kg, (skin, rabbit) > 7940 mg/kg mod. toxic by ing. low toxicity by skin contact TSCA listed Hazardous Decomp. Prods. Heated to decomp., emits toxic vapors of NOx Uses Staining antioxidant/antiozonant for rubber polymer stabilizer Manuf./Distrib. Akrochem http //www.akrochem.com] Atofina http //WWW. atofinachemicais. com] Bayer/Fi ber, Addits., Rubber http //www.bayerus.com] Crompton/Uniroyal... 

The term antiozonant denotes any additive that protects rubber against ozone deterioration. Most frequently, the protective effect results from a reaction with ozone, in which case the term used is chemical antiozonant. Ozone is generated naturally by electrical discharge and also by solar radiation in the stratosphere. These sources produce ground-level ozone concentrations of 1-5 parts per hundred million (pphm). In urban environments, however, ozone reaches much higher levels, up to 25 (pphm) due to the ultraviolet photolysis of pollutants. Only a few parts per hundred million of ozone in air can cause rubber cracking, which may destroy the usefulness of elastomer products. Some desirable properties of an antiozonant additive are as follows ... 

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