DYNAMIC VULCANISATION

Fig. 4. Phase arrangement in hard polymer/elastomer combinations in which the elastomer phase has been dynamically vulcanised.

Subsequently, much improved thermoplastic polyolefin rubbers were obtained by invoking a technique known as dynamic vulcanisation. This process has been defined (Coran, 1987) as the process of vulcanizing elastomer during its intimate melt-mixing with a non-vulcanizing thermoplastic polymer. Small elastomer droplets are vulcanized to give a particulate... 

A manufacturer considering using a thermoplastic elastomer would probably first consider one of the thermoplastic polyolefin rubbers or TPOs, since these tend to have the lowest raw polymer price. These are mainly based on blends of polypropylene and an ethylene-propylene rubber (either EPM or EPDM) although some of the polypropylene may be replaeed by polyethylene. A wide range of blends are possible which may also contain some filler, oil and flame retardant in addition to the polymers. The blends are usually subject to dynamic vulcanisation as described in Section 11.9.1. 

An investigation is reported of the dynamic mechanical response of aluminium silicate filled closed cell microcellular ethylene-octene copolymer (Engage) vulcanisates. The effect of blowing agent, frequency and temperature on dynamic mechanical properties is studied, and the strain-dependent dynamic mechanical properties of microcellular Engage are also investigated. 25 refs. INDIA... 

Fletcher W. P. and Gent A. N. (1953). Non-Linearity in the Dynamic Properties of Vulcanised Rubber Compounds, Trans. Inst. Rubber Ind. 29, pp 266-280... 

As a result of its saturated polymer backbone, EPDM is more resistant to oxygen, ozone, UV and heat than the low-cost commodity polydiene rubbers, such as natural rubber (NR), polybutadiene rubber (BR) and styrene-butadiene rubber (SBR). Therefore, the main use of EPD(M) is in outdoor applications, such as automotive sealing systems, window seals and roof sheeting, and in under-the-hood applications, such as coolant hoses. The main drawback of EPDM is its poor resistance to swelling in apolar fluids such as oil, making it inferior to high-performance elastomers, such as fluoro, acrylate and silicone elastomers in that respect. Over the last decade thermoplastic vulcanisates, produced via dynamic vulcanisation of blends of polypropylene (PP) and EPDM, have been commercialised, combining thermoplastic processability with rubber elasticity [8, 9]. 

McKinney, J. E., H. V. Belcher and R. S. Marvin The dynamic compressibility of a rubber-sulfur vulcanisate and its relation to free volume. Trans. Soc. Rheology 4, 347-362 (1960). 

There are two further possibilities for preventing segregation in complex immiscible mixtures. The first one Implies crosslinking reaction of the dispersed phase, associated with interfacial bonding and leads to the well-known dynamic vulcanisation (17). The second one results from mechanical interlocking of the phases which are created in interpenetrated polymer networks (IPN). 

The resins in the friction dust area tend to be rigid and the flexibility and plasticity associated with the long alkyl chain of phenolic lipids have been used in natural rubber vulcanisation by for example incorporating crosslinking with phosphorylated cardanol (ref. 252). Unpolymerised CNSL phenols have been used in natural or diene rubber compositions for tyre treads to give an improved dynamic elastic modulus but with the same hardness as formulations without the phenolic addition (ref. 253). 

ISO 4664 1998 Rubber—Determination of dynamic properties of vulcanisates for classification purposes (by forced sinusoidal shear strain). 

Donskoi and co-workers [54] showed that each of the components of a chlorosulfonated polyethylene (CSPE) mix has its own influence on the fireproofing properties and chemical processes that occur. In this case, the thermal properties of the vulcanisates of CSPE were studied, and also the heat flows from the flame on the surface of the specimen. It was established that the thermooxidative breakdown of CSPE and vulcanisates based on it during heating under dynamic conditions, is a multi-stage process. The results of tests involving various fillers and plasticisers made it possible to create rubber-like, high-impact resistant materials. 

The structure and physical properties of the thermoplastic vulcanisates (TPE-V) produced in the process of the reactive processing of polypropylene (PP) and ethyl-ene-octene elastomer (EOE) in the form of alloy, using the cross-linking system was analyzed. With the DMTA, SEM and DSC it has been demonstrated that the dynamically produced vulcanisates constitute a typical dispersoid, where semicrystal PP produces a continuous phase, and the dispersed phase consists of molecules of the cross-linked ethylene-octene elastomer, which play a role of a modifier of the properties and a stabilizer of the two-phase structure. It has been found that the mechanical as well as the thermal properties depend on the content of the elastomer in the blends, exposed to mechanical strain and temperature. The best results have been achieved for grafted/cross-linked blends with the contents of iPP/EOE-55/45%. 

Starch nanocrystals were used to reinforce a non-vulcanised NR matrix. The NR was not vulcanised to enhance biodegradability of the total biocomposite. Non-linear dynamic mechanical experiments demonstrated a strong reinforcement by starch nanocrystals, with the presence of Mullins and Payne effects. The Payne effect was able to be predicted using a filler-filler model (Kraus model) and a matrix-filler model (Maier and Goritz model). The Maier and Goritz model showed that adsorption-desorption of NR onto the starch surface contributed the non-linear viscoelasticity. The Kraus model confirmed presence of a percolation network. ... 

Nagano and Nishimoto [11] used this technique to study the degradation due to weathering of styrene-butadiene vulcanisates. The degradation of these vulcanisates subjected to outdoor exposure in the Arizona desert for a year was studied. The dynamic viscoelasticity of sample sheets 2 mm thick and sliced films 0.2 mm thick was measured. SEM images of the surface and sheet cross-sections were also taken to observe microscopic changes in the samples. 

The Yerseley Mechanical Oscillograph supplied by ATS FAAR measures, according to ASTM D945 [142], the mechanical properties of rubber vulcanisations in the small range of deformation that characterises many technical applications. These properties include resilience, dynamic modulus, static modulus, kinetic energy, creep, and set under a given force. 

The composition of the vulcanisation systems and the dynamics of vulcanisation can affect the bond strength significantly [6]. The flow behaviour of the stocks is controlled by the vulcanisation rate. During vulcanisation gradual transition from plastic flow... 

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