Process Oils and Plasticizers

Viscosity reduction, hardness reduction, reduced modulus and tensile strength and extended gel times result when oils and plasticizers are blended with OH-BD. A 50 phr content of process oil is common and typical properties are shown in Table 12.2. 

Typical OH-terminated polybutadiene urethane elastomer formulations are usually prepared using an NCO/OH ratio of 105. All ingredients, other than the diisocyanate, are normally blended by mechanical stirring and then degassing for 30 min at 80°C after which the diisocyanate is added. Test sheets are usually cured for 24 h at 23°C and post-cured for 24 h at 80°C. Pot life can be varied by adjusting the catalyst concentration. 

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Solvent wiping. Rubbers tend to swell by application of solvents and the mechanical interlocking of the adhesive is favored. Although chlorinated hydrocarbon solvents are the most effective, they are toxic and cannot be used toluene and ketones are currently the most common solvents. The treatment with solvents is effective in the removal of processing oils and plasticizers in vulcanized mbbers, but zinc stearate is not completely removed and antiozonant wax gradually migrates to the mbber/polyurethane adhesive interface. Table 27.1 shows the moderate increase in adhesion produced in SBR by MEK wiping. 

Effect of Other Compounding Ingredients on Vulcanization. Other ingredients besides the elastomer and the cure system itself influence cure and scorch behavior. Usually the effect of a material on compound vulcanization is dependent upon the pH of the material. Ingredients which are basic in nature tend to accelerate the rate of both scorch and cure, whereas acidic materials exhibit the opposite effect. Reviews of the effect of antidegradants, fillers, process oils, and plasticizers are available (6,14,32,33). 

Used to partially replace process oils and plasticizers/ and aid flame retardemts by forming polyphosphoric acid char which inhibits flame propagation, reduces substrate temperature and acts as an oxygen barrier. 

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],... 

Plasticizer REO. [Akrochem] Paraffinic/ ntqththenic process oils and petroteum sulfonate mixture plasticizer, process aid for synthetic and natural rubber compds. 

First made commercially available in Germany in 1936, this elastomer is officially known as acrylonitrile butadiene, and is usually the product of an emulsion polymerization process that combines the two monomers acrylonitrile and butadiene. However, the polymer can also be made in a solution process, and with a variety of monomers. As a specialty polymer, and even though several commercial brands were available, Buna N (as it was first known) was little used until World War II, when the polymer s unique oil and plasticizer resistance and high heat resistance became very important for transportation products. Nitrile rubber also exhibits exceptional adhesion to metallic surfaces and is compatible with a wide range of additives and compounding ingredients. 

Nitrile polymers used for the manufacture of adhesives generally contain 25% or more acrylonitrile, but in the base polymer the acrylonitrile content can vary from 15% to 50%. Increasing the acrylonitrile content improves the oil and plasticizer resistance and increases the polarity of the compound. However, higher levels of acrylonitrile also increase the hardness and modulus of the polymer, reducing the elasticity of the resulting polymer. Nitrile rubber can be produced by a cold (5°C) or hot (25-50°C) process, with most adhesive polymers produced by the hot process which induces more chain branching. Nitriles can be combined with other monomers in solution polymerization which increases functionality and improves compatibility with other reactive resins like acrylics, epoxies, and polyurethanes. 

The Veba Combi-Cracking process is suitable for converting residue oil and plastics waste. 

In rubber compounding, different oils or plasticizers are proportionally used with the filler loading to achieve cured compound hardness and modulus targets and to improve the uncured processing characteristics. Also, many times the cost of process oil or plasticizer is cheaper than that of the base elastomer, thus reducing the total cost of the compound. 

The relative amounts and nature of these ingredients depend upon the desired application. The fillers and reinforcing particles increase modulus and tensile strength as well as reducing cost. The oils and plasticizers reduce these same mechanical properties but introduce flexibility. The processing aids improve the extrusion and moldability of the compounds. Curatives and curative accelerators allow for the efficient crosslinking of polymer systems, which prevent creep and cold flow. 

Oils and plasticizers, which are solvents, are commonly added to polymer compounds. Plasticizers are usually used to improve the material s processability and softness. Addition of a plasticizer into a compound reduces its melt viscosity and elastic modulus and, if miscible, the glass transition temperature (T ). 

Most types of CR are best plasticized with naphthenic process oils of varying viscosities and medium to high naphthenic/aromatic content. The trick in CR formulating after picking the appropriate grade is to balance the processability, heat resistance, UV resistance, crystallinity, and stress-strain properties through the selection of the plasticizer. This usually means a combination of vegetable oil, monoester, and process oil and becomes a trial and error exercise. 

Commercial cmde lecithin is a brown to light yeUow fatty substance with a Hquid to plastic consistency. Its density is 0.97 g/mL (Uquid) and 0.5 g/mL (granule). The color is dependent on its origin, process conditions, and whether it is unbleached, bleached, or filtered. Its consistency is deterrnined chiefly by its oil, free fatty acid, and moisture content. Properly refined lecithin has practically no odor and has a bland taste. It is soluble in aflphatic and aromatic hydrocarbons, including the halogenated hydrocarbons however, it is only partially soluble in aflphatic alcohols (Table 5). Pure phosphatidylcholine is soluble in ethanol. 

Xylenes. The main appHcation of xylene isomers, primarily p- and 0-xylenes, is in the manufacture of plasticizers and polyester fibers and resins. Demands for xylene isomers and other aromatics such as benzene have steadily been increasing over the last two decades. The major source of xylenes is the catalytic reforming of naphtha and the pyrolysis of naphtha and gas oils. A significant amount of toluene and Cg aromatics, which have lower petrochemical value, is also produced by these processes. More valuable p- or 0-xylene isomers can be manufactured from these low value aromatics in a process complex consisting of transalkylation, eg, the Tatoray process and Mobil s toluene disproportionation (M lDP) and selective toluene disproportionation (MSTDP) processes isomerization, eg, the UOP Isomar process (88) and Mobil s high temperature isomerization (MHTI), low pressure isomerization (MLPI), and vapor-phase isomerization (MVPI) processes (89) and xylene isomer separation, eg, the UOP Parex process (90). 

Process Oils, Plasticizers. Petroleum-based mbber process oils generally contain a mixture of paraffinic, naphthenic, and aromatic components. These oils vary in composition from grade to grade, but most contain some unsaturated moieties and this unsaturation can compete with the polymer for curatives. Therefore, state of cure can be decreased. This is not easily detected because oil softens the compound which masks the loss of state of cure. 

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