Rubber formulation Properties

Tristar polybutadienes prepared by the intermediacy of lithium acetal initiators were also converted to three dimensional networks in a liquid rubber formulation using a diisocyanate curing agent. Table IV shows normal stress-strain properties for liquid rubber networks at various star branch Hn s. It can be seen that as the branch Mn increases to 2920, there is a general increase in the quality of the network. Interestingly, the star polymer network with a star branch Mn of 2920 (Mc=5840) exhibits mechanical properties in the range of a conventional sulfur vulcani-zate with a Me of about 6000-8000. 

Filler, in general, can be defined as finely divided particles that are often used to enhance the performance and various desirable properties of the host matrix, depending on a typical application. A great deal of research endeavors have been dedicated to the development and the use of different fillers with a dimension at the nanometer level. In rubber technology the term nano is not unfamiliar to a rubber specialist. Since the start of the twentieth century, carbon black and silica have been utilized as effective reinforcing agents in various rubber formulations for a variety of applications. The primary particle sizes of these fillers remain in the nanometer range. However, with these conventional fillers the dispersion toward individual... 

The state of the art in friction and wear of PTFE-filled rubbers include the effects of many important system parameters, such as the composition of the rubber formulation, particle dispersion, bulk mechanical properties, ability of transfer film formation, and the chemistry between PTFE powder and the rubber matrix. Although the present study has explicitly highlighted the potential of PTFE powder in rubber matrixes with significant property improvements in the friction, wear, and physical properties, it has simultaneously opened a new field regarding the use of PTFE powder in rubber compounds, with some challenging tasks for chemists, engineers, and material scientists. 

Lyophilization stoppers must not allow moisture from the atmosphere into the container or be a significant source of moisture themselves. Stoppers are principally composed of synthetic and/or natural rubbers, fillers to strengthen the stoppers, and curing agents to crosslink the rubber formulation. The selection of these components affects the moisture uptake and drying properties of the stopper [1]. Due to proprietary reasons, the stopper manufacturers do not disclose the composition of stoppers to the pharmaceutical companies. Therefore, establishment of a clear relationship between stopper components and their moisture gain property is not possible. Consequently, we need to develop efficient procedures for achievement of the required level of drying of the stoppers. 

Figure 10-18 presents the GC/MS analysis of a rubber formulation for an elastomeric insulator for devices to replace those that had been characterized after field-aging. In this example, a high quality silicone rubber was selected for inherent resistance to oxidation and UV damage, plus favorable dielectric properties. Figure 10-18 presents the GC/MS analysis of this elastomer, confirming pure silicone rubber and Tinuvin P, a UV absorbing polymer stabilizer. To reduce cost, many suppliers provide silicone rubber components that are often combined with butyl or nitrile rubber to reduce cost. 

As indicated above, the properties of certain plastics may be temporarily modified by the combination effects of moisture and temperature during the autoclaving cycle. In general, the physical properties of rubber formulations are not affected by the moist heat sterilisation other than the fact that closure systems may absorb moisture (depending on the rubber formulation/ materials employed) during the autoclave cycle. This can be an issue for lyophilised products or aseptically filled dry powders where long drying cycles for the rubber closures are sometimes employed to prevent desorption of moisture from the closure into the product. 

Fillers are added to the elastomer in order to add bulk, lower cost and/or to improve physical properties such as hardness, strength and abrasion resistance. Typical fillers are materials such as carbon black, talc, china clay and whiting. Carbon black has been shown to contain polynuclear aromatics (PNAs) and there is concern regarding their carcinogenicity (Lee and Hites, 1976). However, despite extra controls there has been a move away from the use of carbon black as a filler in applications involving the primary packaging of parenterals. Its use continues as a pigment or colourant in rubber formulations but at substantially lower levels than that as a filler. 

Advances by reputable manufacturers have removed some of the perceived disadvantages of rubber, in particular the refinement of rubber formulations to reduce the level of extractives. The development of a fluoropolymer-based laminate under the FluroTec product range to provide real barrier properties has simplified the complex process of rubber closure selection and offered a level of security not available with a conventional closure. The use of such laminated closures is predicted to increase in the future, in particular these are likely to be specified as the closure system for biopharmaceutical applications. 

Methylene chloride is a volatile, colorless, nonflammable liquid. It is slightly soluble in water and miscible with many other solvents, such as acetone, chloroform, carbon tetrachloride, and alcohol. Under speciflc conditions it may burn. Its commercial formulations for paint stripping are particularly flammable. Methylene chloride is a widely used solvent where quick drying (i.e., high volatility) is required. Such application areas include adhesives, cellulose acetate flber production, blowing of polyurethane foams, and metal and textile treatment. It dissolves oils, fats, waxes, many plastics, bitumen, and rubber. This property is used in paint stripper formulations. It is used as an aerosol solvent, and for extraction operations in the pharmaceutical industry. It was previously used in fire-extinguishing products. ... 

Although the dynamic mechanical properties and the stress-strain behavior iV of block copolymers have been studied extensively, very little creep data are available on these materials (1-17). A number of block copolymers are now commercially available as thermoplastic elastomers to replace crosslinked rubber formulations and other plastics (16). For applications in which the finished object must bear loads for extended periods of time, it is important to know how these new materials compare with conventional crosslinked rubbers and more rigid plastics in dimensional stability or creep behavior. The creep of five commercial block polymers was measured as a function of temperature and molding conditions. Four of the polymers had crystalline hard blocks, and one had a glassy polystyrene hard block. The soft blocks were various kinds of elastomeric materials. The creep of the block polymers was also compared with that of a normal, crosslinked natural rubber and crystalline poly(tetra-methylene terephthalate) (PTMT). 

The author has had experience with Daikyo Flurotech stoppers (available from the West Company), which produce a moisture increase of only about 0.1% under conditions where the butyl rubber stoppers produced an increase of over 1%. It is possible that the Flurotech coating (a fluorocarbon polymer coating) is responsible for the low moisture release properties. However, we have also found that Teflon-coated butyl rubber stoppers release moisture essentially in an equivalent fashion to stoppers of the same rubber formulation without the coating. Thus the low moisture properties of the Flurotech stoppers are more likely due to the rubber formulation. 

A typical rubber formulation, for example, that demonstrates the surface area properties of silica sol can be seen in the Talalay process for making foam rubber [24] the elastomer foam is in a latex form, to which is added an accelerator, an antioxidant, a vulcanizing agent, and carbon black. The mixture is then foamed, either mechanically or chemically, gelled, vulcanized to... 

The use of silica in rubber mixes cannot be considered as new at all, because this filler has been used in rubber formulations since the beginning of the 20th century (Voet et al., 1977). Silicas are not reinforcing fillers in the proper sense, because silica-reinforced mixes exhibit much lower mechanical properties, particularly considering modulus at break and abrasion resistance. So silicas weren t used as reinforcing fillers but mainly in association with carbon black. 

Processing oils in a rubber formulation serve primarily as a processing aid. Oils fall into one of three primary categories paraffinic, naphthenic, and aromatic. The proper selection of oils for inclusion in a formulation is important. If the oil is incompatible with the polymer, it will migrate out of the compound with consequent loss in required physical properties, loss in rubber component surface properties, and deterioration in component-to-component adhesion, as in a tire. The compatibility of an oil with a polymer system is a function of... 

Uses Plasticizer for PVC and rubber formulations such as wire and cable coatings offering good elec, props., film, tape, and coated fabrics Features Good humidity stability, migration resist, to rubber, oil and hexane resist., low volatility Properties Low odor med. m.w. 

Other compounds commonly used in vulcanization, in addition to sulfur and accelerators, are zinc oxide and saturated fatty acids such as stearic or lauric acid. These materials are termed activators (as opposed to accelerators). Zinc oxide serves as an activator, and fatty acids are used to solubilize the zinc into the system. Rubber formulations can also include fillers such as fumed silica and carbon black, and compounds such as stabilizers and antioxidants. Further complicating the situation is the engineering practice of blending various elastomers to obtain the desired properties. 

Fillers, or reinforcement aids, such as carbon black, clays, and silicas are added to rubber formulations to meet material property targets such as tensile... 

These properties will in turn control both the performance of the resin in a specific rubber formulation and the compound processing characteristics. 

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