Preparation by dynamic vulcanization

Excellent elastomeric NBR-nylon compositions have also been prepared by dynamic vulcanization during the melt-mixing of intimate blends of NBR with various nylons. In this case, the effect of curatives was complicated by the fact that some nitrile rubbers tend to self-cure at temperatures of mixing. Sulfur,... 

Other Elastomeric Compositions Prepared by Dynamic Vulcanization... 

Fischer [97] used the DV process to prepare compositions containing partially vulcanized rubber. It has since been found that improved, very strong elastomeric compositions of EPDM and polypropylene could be prepared by dynamic vulcanization provided that the rubber was completely vulcanized [98]. 

Excellent elastomeric NBR-nylon compositions have also been prepared by dynamic vulcanization during the melt-mixing of intimate blends of NBR with various nylons. In this case, the effect of curatives was complicated by the fact that some nitrile rubbers tend to self-cure at temperatures of mixing. Sulfur, phenolic, maleimide, or peroxide curatives can be used. The thermoplastic elastomeric compositions prepared by the dynamic vulcanization of nylon-NBR blends are highly resistant to hot oil. As in the case of the EPDM-polyolefin blends, increases in the amount of rubber in the composition reduce stiffness but increase resistance to permanent set. 

Figure 3.21 Brabender Plastograph results for TPV preparation by dynamic vulcanization.

In PP/EPDM systems (e.g. Vestolen EM, Hiils), advantage has been taken of the combination of crystalline tmd amorphous polymer properties. The blends are formulated by selecting molecular weights of the components and concentration of the elastic segments in the EPDM. Some of these blends are prepared by dynamic vulcanization. 

Nowadays, the development of TPEs concern many branches of macromol-ecular chemistry cationic and radical polymerizations, chemical modification, enzymatic catalysis or the use of microorganisms. Their respective contributions are analyzed in Section 2. The elastomers based on halogen-containing polyolefins [37] and those prepared by dynamic vulcanization [38] are also included in the TPE family. More information on these materials and techniques is given in Section 2. 

Okamoto M and Shiomi K (1994) Structure and mechanical properties of poly(but-ylene terephthalate)/rubber blends prepared by dynamic vulcanization, Bolymer 35 4618-4622. 

In these cases a dispersed phase of a crosslinkable rubber is vulcanized in the presence of a matrix of a second, immiscible, non-vulcanizable polymer during the residence time of melt processing. Examples have also been reported in which a mixture of two vulcanizable polymers has been employed. Coran [1995] has summarized five key requirements for preparing optimum compositions by dynamic vulcanization ... 

Mechanical properties of asphalt can be improved [16] by modification with some polymers, especially stirene-butadiene-stirene (SBS) tri-block copolymer. SBS/ asphalt blends are prepared via dynamic vulcanization. Recycled tire crumb rubber is incorporated as a major component in its multi-layer construction [17] for a stadium field-turf. 

In addition to EPDM-polyolefln and NBR-nylons combinations, a large number of other rubber-plastic combinations have been used to prepare thermoplastic vulcanizates by dynamic vulcanization (Coran et al., 1982). 

Rheological behaviour of the TPVs that were prepared from dynamic vulcanization of NR-g-PMMA and PMMA blends using various vulcanization systems including conventional vulcanization (CV) and efficient sulphur vulcanization (EV) systems were studied by Nakason et al The ingredient formulas of each vulcanization systems are summarized in Table 18.6. 

The more important grades of thermoplastic natural mbber, which fall into the olefinic class of thermoplastic elastomers, are prepared with the natural mbber phase partially cross-linked during blending, a process known as dynamic vulcanization. The hardness of the soft blends is controlled by the natural mbber content, and typical properties of those of 50—90 hardness (Shore A) are shown in Table 7. 

Conventional crosslinking agents, such as sulphur, accelerators, and peroxide, etc., used in dynamic vulcanization and melt-mixing of two polymers is the first step in the preparation of an EA. The dynamic vulcanization is done by dynamic shear at a high temperature to activate the process. 

The specimen was prepared by the following method. After mixing HAF carbon black (50 phr) with natural rubber (NR) in a laboratory mixer, carbon gel was extracted from unvulcanized mixture as an insoluble material for toluene for 48 h at room temperamre and dried in a vacuum oven for 24 h at 70°C. We made the specimen as a thin sheet of the carbon gel (including carbon black) by pressing the extracted carbon gel at 90°C. The cured specimen was given by adding sulfur (1.5 phr) to the unvulcanized mixture and vulcanized for 30 min at 145°C. The dynamic viscoelastic measurement was performed with Rheometer under the condition of 0.1% strain and 15 Hz over temperatures. 

Fig. 6 Variation of viscoelastic properties as a function of strain amplitude of uncrosslinked and dynamically vulcanized blends at 180°C (a) storage modulus, (b) loss modulus. CD2 TPV prepared by preblending, PD2 TPV prepared by phase mixing, SD2 TPV prepared by split addition...

Polyurethane-based FTPEs are produced by reacting fluorinated polyether diols with aromatic disocyanates. The resulting block copolymers contain fluorinated polyether soft segments.68 Another possible method of preparation of fluorinated TPE is dynamic vulcanization. Examples are a blend of a perfluoroplastic and a perfluoroelastomer containing curing sites or a combination of VDF-based fluo-roelastomers and thermoplastics, such as polyamides, polybutylene terephtalate, and polyphenylene sulhde.69 70... 

Copolymer formation by displacement reaction Solid-state chlorination of PP may lead to low levels of chlorine incorporation along the PP chain with minimal PP molecular weight degradation. Coran and Patel [1983 b] have blended (internal mixer, T = 190°C) 50 parts chlorinated PP with 45 parts NBR containing 5 parts amine-terminated NBR. The blend was characterized by mechanical properties vs. the use of unfunctionalized PP. Compatibilization resulted from copolymer formation through displacement reaction of chloride by amine groups. The blend was prepared in the presence of a vulcanization agent (3.75% of dimethylol phenol + 0.5% of SnCl ) to cause concomitant dynamic vulcanization of the rubber phase. 

Gupta et al. (39) has studied the effect of dynamic cross-linking on tensile yield behavior of PP/EPDM rubber blends. They prepared blends of PP/EPDM in internal mixer by simultaneous blending and dynamic vulcanization. Dimethyl phenolic resin vulcanized PP/EPDM blends showed higher yield stress and modulus than unvulcanized PP/EPDM blend (Fig. 14.17 and Table 14.1). They found the increase in... 

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