Rubbers Curing

Silicone Heat-Cured Rubber. Sihcone elastomers are made by vulcanising high molecular weight (>5 x 10 mol wt) linear polydimethylsiloxane polymer, often called gum. Fillers are used in these formulations to increase strength through reinforcement. Extending fillers and various additives, eg, antioxidants, adhesion promoters, and pigments, can be used to obtain certain properties (59,357,364). 

The rubbers are also used for such diverse applications as blood transfusion tubing capable of sterilisation, antibiotic container closures, electric iron gaskets, domestic refrigerators and non-adhesive rubber-covered rollers for handling such materials as confectionery and adhesive tape. The cold-curing rubbers are of value in potting and encapsulation. 

Kraton Polymers has developed a multiarm SIS (Kraton 1320X [37,46,47,50]) and SBS (Kraton KX-222C, [48,49]) for rapid UV/e-beam cure. Besides heat resistance improvements, plasticizer resistance is also improved in cured rubber-based systems. The dioctyl phthlate plasticizer common in PVC backing films is soluble in the styrenic domains of SBCs. Crosslinking of the mid-block provides cohesion even after plasticizer attack [51]. 

Other transparent cured rubber goods Transparency, safe for food application, weatherability. heat resistance... 

Moorite Propellant. A series of rocket proplnts submitted to PicArsn for evaluation in 1949. They consisted of an oxidizer (such as K perchlorate) 70, and a cured rubber hydrocarbon plus accelerators, 30%. Although the examined samples proved to possess desirable props for rocket proplnt use, their thermal stability was poor and their press exponent undesirably high. It was concluded that further work was required on the method of prepn to eliminate these defects... 

Mooney viscometer is also used to measure the time it takes, from initial exposure of the compound to a particular temperature, to the time of onset of cure at that temperature [2]. This is known as the scorch time. Scorch time is an important parameter to the rubber processor, as a short time may lead to problems of premature vulcanization. As the test is taken past the onset of cure, the rotor tears the cured rubber, and therefore this device cannot be used to investigate rheological properties after the scorch time. 

Scheme 2.5 Cured rubber products. After Chu [73]. Reproduced by permission of Huthig GmbH...

Following this scheme, Coz and Baranwal [80] have reported the reverse engineering of four unknown cured rubber compounds, representing a radial passenger tyre tread, a radiator hose, an oil pan seal and an engine gasket. 

From a theoretical point of view, the equilibrium modulus very probably gives the best characterization of a cured rubber. This is due to the relationship between this macroscopic quantity and the molecular structure of the network. Therefore, the determination of the equilibrium modulus has been the subject of many investigations (e.g. 1-9). For just a few specific rubbers, the determination of the equilibrium modulus is relatively easy. The best example is provided by polydimethylsiloxane vulcanizates, which exhibit practically no prolonged relaxations (8, 9). However, the networks of most synthetic rubbers, including natural rubber, usually show very persistent relaxations which impede a close approach to the equilibrium condition (1-8). 

Relation [1] Is the frequency-dependent analogue of a formula proposed by Chasset and Thirion (2, 3) which has since been applied very frequently to relaxation measurements on cured rubbers. The next three equations are Inspired by similar relations In dielectrics (they are not derived from these) Equation [2] by the Cole-Cole and Equation [3] by the Davidson-Cole relation (15, 16). Both are special cases of the most general Equation [4] which contains five parameters (17). 

Time-crosslink density superposition. Work of Plazek (6) and Chasset and Thirion (3, 4) on cured rubbers suggests that there is one universal relaxation function in the terminal region, independent of the crosslink density. Their results indicate that the molar mass between crosslinks might be considered as a reducing variable. However, these findings were obtained from compliance measurements on natural rubber vulcanizates,... 

The formation on the surface of uncured or cured rubber of a thin coating of a compounding ingredient, often, but not necessarily, sulphur, which is present in excess of the amount which the rubber can dissolve. 

Ceramic Filter. The ceramic filter collects, volatilizes, and destroys particulates and condensible organics emitted from industrial process streams, such as paint spray, lost foam casting, condensible organics, tenter frames, and cured rubber... 

The costs, as for all plastics, fluctuate highly with the crude oil price. Most common TPE/PVCs are cheaper than SEES, TPVs and general-purpose cured rubbers such as EPDMs and polychloroprenes but are more expensive than TPOs and SES. 

S, static D, dynamic. Compositions 17 and 18 control compositions purely of cured rubber or polypropylene. 

It was shown, on the one hand, that gum-filler interactions are associated with the immobilization of a certain amount of rubber on the surface or inside the carbon black aggregates, and, on the other hand, that the corresponding bound or occluded rubbers play important roles in the reinforcement process due either to a restriction of elastomer chain mobility in the vicinity of the filler or to an increase of the effective volume of the latter. What are now the effects exerted by a filler on the stress-strain behavior and the modulus of cured rubbers ... 

Blemish - A superficial mark or impression on the surface of green or cured rubber lining. 

---