Rubber mastication

Fig. 16a-

Table 13. Polymerization of monomers by vulcanized rubber mastication. Effect of vulcanization recipes (/, 70)... 

Fig. 17. Polymerization of monomers by synthetic rubber mastication. 1 13.8% methyl methacrylate in neoprene. 2 13.6% chloroprene in neoprene. 3 13.8% methyl methacrylate in polybutadiene-styrene. 4 13.6% chloroprene in polybutadiene-styrene. 5 14.5% styrene in polybutadiene-arylonitrile. c indicates that the rubber became a crumb at approximately the arrowed time of mastication. 6 11% methyl methacrylate in rubber — from Table X in original...

Fig. 18. Polymerization of styrene by natural rubber mastication. Effect of time, monomer concentration and temperature on monomer conversion. 1 13.2% styrene, 15° C 2 23.3% styrene, 15° C S 23.3 % styrene, 25° C 4 37.7% styrene, 15° C 5 37.7% styrene, 25° C (69)...

Fig. 20. Composition of copolymers formed by rubber mastication (A0, B0,C0) initial molar fractions of styrene, methyl methacrylate, and chloroprene, respectively. (Full lines) calculated compositions based on r, and r2 values of 0.50 and 0.44 for styrene and methyl methacrylate and of 0.083 and 6.12 for methyl methacrylate and chloroprene (69)...

Fig, 2l, Polymerization of methyl methacrylate and chloroprene by rubber mastication (69). 1 23.8% methyl methacrylate and 24.2% chloroprene added initially. 2 24.2% chloroprene polymerized, then 23.8% methyl methacrylate. 3 23,8% methyl methacrylate polymerized,... 

Fig. 22. Polymerization of methyl methacrylate by natural rubber mastication (68). ( ) extent of polymerization ( ) free rubber ( ) Block I (the numbers refer to the percentage of PMM in the samples) (Q) Block II (O) free PMM. The points correspond to a range of PMM concentrations as specified in the original reference...

Mary Beilis. Thomas Hancock Invented The Rubber Masticator, (www. about.com). 

Fabricated silicone rubber parts are traditionally made from high consistency silicone gum stock. Because of the stiffness of the gum stock, the material must be worked with rubber masticating equipment and preformed before fabrication. A new fabricating process using a low consistency liquid silicone rubber was introduced by Dow Corning Corporation recently (1, 3). This process is called liquid polymer system (LPS). 

In addition to PSAs, elastomers are used in the construction industry for mastic compounds. Neoprene and reclaimed rubber mastics are used to... 

It is now believed that high temperature mastication of rubber, at one time considered to be simply an oxidation process is influenced by mechanochemical reactions (Kuz minskii, 1966). The mechano-chemical generation of a relatively small number of free radicals provides the initiation step of the autoxidation process. Natural rubber masticated at KXPC oxidized more rapidly (as manifested by the development of carbonyl groups) than rubber oxidized without mechanical working at 150°C. 

Natural rubber mastication Natural and synthetic rubber and blacks EPDM... 

The addition of a stable free radical (product of the oxidation of 2,2,4-trimethyl-6-ethoxy-l,2-dihydroquinoline) to rubbers prior to mastication permitted the use of ESR in studying the rubber mastication process at near ambient temperature. The radical concentration has been determined in this way after a various number of masticator passes [115, 116]. 

Resonance in macroradicals increases their stability, opposes their tendency for disproportionation and favors recombination reactions. A typical example is natural rubber mastication, in which resonance causes the weak-... 

The NRPRA laboratory found a in the range 70,000-100,000 for natural rubber mastication [72] under standard conditions. The was relatively insensitive to processing conditions for tests in many different milling and mastication machines [40]. Goto and co-workers [73] have presented evidence that can be modified if the polymer is masticated with a second polymer or an inert filler (see Section V.D.2). 

Fig. 3.5 Influence of temperature on efficiency of rubber mastication in a size-B Banbury under nitrogen with 0.0925 m/1000 gm radical acceptors of different reactivity ( ) thiophenol (O) benzoquinone (O) azobenzene. Time of mastication, 30 min [8].

Important here are the results in inert atmospheres that show no degradation for rubber mastication above 140°C (see Fig. 3.5 [8]), and for polystyrene extrusion above 180°C [18]. The approximate agreement between the minimum degradation temperature calculated and observed for several polymers is thus likely fortuitous. In mastication, the polymer mass is nearly homogeneous. This is not the case on capillary extrusion. In addition, convection plays a different role in capillary extrusion and in mastication experiments. 

The effect of polymer composition on secondary reactions is easily seen in rubber mastication. The greater tendency for gelation and branching in styrene rubber is related to the radicals involved. The radicals from styrene rubber have a greater reactivity than allyl radicals [7] toward a-methylenic hydrogen atoms and double bonds. This behavior has been attributed previously to the pendant vinyl groups in certain synthetic rubbers [8,9]. Poly-chloroprene also forms a gel by addition of radicals to double bonds, whose activity is increased by the chlorine substituent [10]. 

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