Static vulcanization

C. Preparation of Elastomer-Plastic Blends by Static Vulcanization... 

In another case where the twin-screw extruder was used, the rubber and plastic were melt mixed with all ingredients in a similar manner as described in blend compositions for static vulcanizations. The product was then dumped, cooled, and granulated. The premixed granules were then fed into a twin-screw extruder where a very narrow temperature profile was maintained with a relative high compression (2 1), and the screw speed was adjusted depending on the final torque and the flow behavior of the extruded stock. The stock was cured by shear force and temperature enforced by the twin-screw extruder. The dynamically crosslinked blend was taken out in the form of a strip or solid rod to determine the... 

TPVs are composed of a vulcanized rubber component, such as EPDM, nitrile rubber, and butyl rubber, in a thermoplastic olefinic matrix. TPVs have a continuous thermoplastic phase and a discontinuous vulcanized rubber phase. TPVs are dynamically vulcanized during a meltmixing process in which vulcanization of the rubber polymer takes place under conditions of high temperatures and high shear. Static vulcanization of thermoset rubber involves heating a compounded rubber stock under zero shear (no mixing), with subsequent cross-linking of the polymer chains. 

Blends of NR and ethylene-vinyl acetate copolymer (EVA) (physical blends and statically vulcanized) combine the good elastomeric and mechanical properties of NR with the excellent ageing and flex crack resistance of EVA. Blends of NR/EVA copolymer are becoming an important rubber/thermoplastic elastomer blend. Applications of these materials can be found in fields where... 

ISO 1431-1 2004 Rubber, vulcanized or thermoplastic - Resistance to ozone cracking -Part I Static and dynamic strain testing... 

Cross-Linking. A thermoset system is produced when a polymer is cross-linked under static conditions, as in a compression mold. This is the basis of the production of vulcanized articles or cross-linked polyethylene pipe and wire insulation. If the same polymer is lightly cross-linked while it is being sheared in the molten state, however, it will remain thermoplastic. If it is more heavily cross-linked during this process, the final product may contain significant quantities of gel particles, but the whole mass will still be tractable. 

Vulcanized mbber is an insulator (volume resistivity is 1015 Q-cm), and the static generated by mbber tires created serious problems in vehicles until the introduction of electrically conductive carbon black as a reinforcing pigment. An excellent correlation was found between the potential generated and the resistivity of the tires (127,128) (see Rubber NATURAL). 

The compound was made of scrap rubber from truck tires, essentially natural rubber, and sulfur. This compound is poor and vulcanization necessitates rather high pressure so as to compact the mixture. Nevertheless the final materials exhibit rather good mechanical properties measured either under static or dynamic conditions, as well as interesting qualities for absorption of impact noises [11]. 

A few results are thus given in terms of the static compression modulus which is expressed as a function of the pressure for different percentage of plasticizer with 2% sulfur in Figure 8.1 and with 5% sulfur in Figure 8.2. Moreover, the dynamic in-phase modulus E is measured as a function of the forcing frequency for different scrap rubber vulcanized with sulfur in Figure 8.3, whereas the corresponding values... 

An attempt is made in Chapter 6 to relate the mechanical property of the rubber under dynamic conditions to the state of cure. The mechanical properties of the unvulcanized rubber are also evaluated, with plasticity versus temperature and the scorch. The mechanical properties of the vulcanized rubber are then considered, in static and dynamic modes. 

The adhesion of textile or metal cord to polymers is essentially restricted to rubbers used in tires and to some extent in belting. The basic form of static test consists of measuring the force to pull a cord out of a block of rubber into which it has been vulcanized, and it is apparent that the result is critically dependent on the efficiency with which the test piece was molded. The measured force is also dependent on the amount that the rubber deforms during the test. 

Effects of vulcanization (Bateman et al., 1963 Hofnoann, 1967 Coran, 1978) on end-use properties are illustrated in Figure 7.2. It should be noted that static modulus increases with vulcanization to a greater extent than does the dynamic modulus. (Here, static modulus is more correctly the equilibrium modulus, approximated by a low-strain, slow-strain-rate modulus. Dynamic modulus is generally measured with the imposition of a sinusoidal, small strain at a frequency of 1-100 Hz.) The dynamic modulus is a composite of viscous... 

The application of ultrasonic waves to the process of devulcanizing rubber is an attractive field of study. Most references indicate that rubber is vulcanized by ultrasound rather than devulcanized. Rubber devulcanization by using ultrasonic energy has been first discussed in Okuda and Hatano (1987). It was a batch process in which a vulcanized rubber was devulcanized at 50 kHz ultrasonic waves after treatment for 20 min under static conditions. The process claimed to break down carbon-sulfur bonds and sulfur-sulfur bonds, but not carbon-carbon bonds. The properties of the revulcanized rubber were found to be very similar to those of the original vulcanizates. 

Figure 3.13 Effect of pre-stressing (static loading) on the volume fraction of rubber in the swollen gel of silica-filled vulcanized NR containing 4 pphr Si69 (reproduced from reference 44).

In dynamic testing of ozone resistance, a fabric-backed vulcanized rubber specimen is continuously flexed in the ozone chamber over a roller. The fabric backing is in the form of a belt. Any protective chemical films (e.g., certain waxes and antiozonants) that might build up on the surface of the specimen in static testing are quickly broken by the continuous flexing. ASTM test method D 1149 covers static testing and D 3395 covers dynamic testing in a controlled ozone atmospheres. 

When the crosslinked rubber level in the blend is high, the blends are rubbery with good elastic recovery properties, have low compression set values at elevated temperatures, and are processable as plastics. At low crosslinked rubber levels (<25%), these blends are tough and have very good impact resistance. Dynamic vulcanization was first practiced by Gessler [23] around 1958, when he described the preparation ofhalogenated butyl mbber and polypropylene on a heated roll mill. Most of the blends in the examples had only a small amount of rubber (20 wt%) and the curative used was a metal oxide. The mixing time was about 20 min at 320 ° F. It was shown that the dynamically vulcanized blends had better tensile properties than identical blends vulcanized at 320 °F under static conditions. Fischer [24] prepared... 

The standard phenomenology of carbon black-filled rubber will be presented and the influence on the constitutive response of temperature and filler concentration will be discussed. Although the focus is on traditional vulcanized rubber, other thermoplastic elastomers show similar mechanical properties even if their chemical composition is quite different. Moreover, from a macroscopic point of view, the behavior of such materials is very close to the behavior of some biological soft tissues, such as ligaments and tendons, for what concerns both their static and dynamic responses. 

Table 5.17 Relationship between static-mechanical load and the crack pattern ofrubber-vulcanizes after attack in an ozone-rich atmosphere [698]...

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