Mechanical rubber group

MRG mechanical rubber group MVT moisture vapor transmission... 

Pawlowski. H.. and Dick, J.. Viscoelastic characterization of rubber with a new dynamic mechanical tester, presented at the Akron Rubber Group. April 23. 1992 (later published in Rubber World. June. 1992). 

The possibility was demonstrated of using the accelerator Disulfal MG as a replacement for the Altax or Sulphenamide Ts traditionally used in formulations of vulcanisates for mechanical rubber goods, provided that the appropriate adjustment was made to the composition of the vulcanising group and the vulcanisation time. 2 refs. (Full translation of Kauch.i Rezina, No.6, 1996, p.33)... 

In the mid-1970s there was a short period during which styrene was in very short supply. This led to the development of what were known as high-vinyl polybutadienes which contained pendent vinyl groups as a result of 1,2-polymer-isation mechanisms. These rubbers had properties similar to those of SBR and could replace the latter should it become economically desirable. 

This is the most widely used naturally occurring rubber. The literature search shows that many research groups have prepared nanocomposites based on this rubber [29-32]. Varghese and Karger-Kocsis have prepared natural rubber (NR)-based nanocomposites by melt-intercalation method, which is very useful for practical application. In their study, they have found increase in stiffness, elongation, mechanical strength, and storage modulus. Various minerals like MMT, bentonite, and hectorite have been used. 

Maleimides Alkyl and aryl maleimides in small concentrations, e.g., 5-10 wt% significantly enhance yield of cross-link for y-irradiated (in vacuo) NR, cw-l,4-polyisoprene, poly(styrene-co-butadiene) rubber, and polychloroprene rubber. A-phenyhnaleimide and m-phenylene dimaleimide have been found to be most effective. The solubihty of the maleimides in the polymer matrix, reactivity of the double bond and the influence of substituent groups also affect the cross-fink promoting ability of these promoters [82]. The mechanism for the cross-link promotion of maleimides is considered to be the copolymerization of the rubber via its unsaturations with the maleimide molecules initiated by radicals and, in particular, by allyfic radicals produced during the radiolysis of the elastomer. Maleimides have also been found to increase the rate of cross-linking in saturated polymers like PE and poly vinylacetate [33]. 

Aryloxyphosphazene copolymers can also confer fireproof properties to flammable materials when blended. Dieck [591] have used the copolymers III, and IV containing small amounts of reactive unsaturated groups to prepare blends with compatible organic polymers crosslinkable by the same mechanism which crosslinks the polyphosphazene, e.g. ethylene-propylene and butadiene-acrylonitrile copolymers, poly(vinyl chloride), unsaturated urethane rubber. These blends were used to prepare foams exhibiting excellent fire retardance and producing low smoke levels or no smoke when heated in an open flame. Oxygen index values of 27-56 were obtained. 

The exact mechanism of polymer initiation is unknown. Initiation of rubber synthesis has been studied in several plants and a common finding is that the end groups found in low molecular weight rubber (such as rubber from goldenrod and H. brasiliensis leaves) are not made up of c/x-isoprene units, unlike the bulk of the rubber [259, 260]. Structural studies [261, 262] have led to the suggestion that the Cl5 FPP may be the most common initiator in vivo, at least in H. brasiliensis. 

The macroradicals of natural rubber react with those of the styrene elastomer, due to the presence of the very reactive 1,2 pendent vinyl groups in the latter. This mechanism leads to a structure where the styrene rubber forms a gel network with grafted branches of natural rubber. 

Akutin (52) performed an exhaustive study on the influence of processing conditions and the nitrile rubber/poly(vinyl chloride) ratio on the mechanical characteristic of the product. The experiments were carried out in a Brabender Plastograph at 160-180° C and rotor speed of 10-50 rpm. The polyfvinyl chloride) molecular weight was 83500. A resin with an epoxy group content of 20.75% was added to the blend as plasticizer and stabilizer. Figure 29 shows that the... 

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