Mastication procedure

The mechanical degradation and production of macroradicals can also be performed by mastication of polymers brought into a rubbery state by admixture with monomer several monomer-polymer systems were examined (10, 11). This technique was for instance studied for the cold mastication of natural rubber or butadiene copolymers in the presence of a vinyl monomer (13, 31, 52). The polymerization of methyl methacrylate or styrene during the mastication of natural rubber has yielded copolymers which remain soluble up to complete polymerization vinyl acetate, which could not produce graft copolymers by the chain transfer technique, failed also in this mastication procedure. Block and graft copolymers were also prepared by cross-addition of the macroradicals generated by the cold milling and mastication of mixtures of various elastomers and polymers, such as natural rubber/polymethyl methacrylate (74), natural rubber/butadiene-styrene rubbers (76) and even phenol-formaldehyde resin/nitrile rubber (125). 

Three polybutadiene/poly isoprene diblocks were provided to us by Paul Rempp of CRM, Strasbourg. Details of the molecular weights and the expected diene microstructures were discussed earlier (1,13) and are summarized in Table I. Homopolymers of corresponding microstructures and molecular weights (1,13) are also described in Table I. The molecular-weight distributions of the homopolymers are considerably broader than those of the block polymers, owing to a mastication procedure (13) carried out on these samples to lower their molecular weights. To insure that" the microstructures of the homopolymers were well matched to the constituent blocks in the copolymers, 60-MHz NMR spectra were obtained on a Varian T-60 apparatus for the diblocks, the individual homopolymers, and three equivalent homopolymer blends (13). 

The vulcanization recipe wasi EPDM 100, stearic acid 1.0, zinc oxide 5 0, accelerator M 0.5, TMTD 1.5, HAF 50, sulfur 1.5 phr. Peroxide-curing of E-P copolymers was carried out with a modified procedure of (6) EPR 100, dicumyl peroxide 3, zinc oxide 3, TMTD 0.5, HAF 50, sulfur 0.2 phr, the mixture being masticated for 20 minutes at 0-50°C and cured at lb0°G. 

Initial viscosity (Lo) Effect of mastication time and procedure of milling. Effect of peptisers... 

Vinyl tile is a commorily used material for the floors in a laboratory because it is easy to maintain and inexpensive to install. Ease of maintenance is not the case for a tile floor in a laboratory using mercury, because of the propensity of the extremely small (20 microns or less) mercury droplets to collect in the cracks. A seamless vinyl or poured epoxy floor should be used instead, with the joints of the floor with the wall being curved or coved. Similarly, the bench top should be curved where it joins the back panel. Existing tile floors, especially the smaller 9 inch X 9 inch size, frequently represent an additional maintenance problem since a large proportion contain asbestos, as may the mastic holding them to the floor. When these tiles need replacing, the work must be done in conformance with EPA and OSHA asbestos standards and can be very costly. One procedure to be avoided at all costs is to grind up the old tile. This can distribute asbestos fibers so widely that the already expensive asbestos removal can be made prohibitively so. 

The temperature set points of the mixer are adjusted to 100°C and the torque calibration procedures are carried out with the rotors in motion (e.g., at 40 rpm). The rubber is then added (with the rotors running) and masticated for 2 min, after which the rotors are run in the reverse direction (reverse jog) to remove 10.0 +0.2 g of the rubber. The 10.0 g of masticated rubber is put aside in a paper cup to keep it relatively warm for readdition a little later in the procedure. 

The larger batches, each weighing 275.35 g, were mixed in a Brabender Prep Mixer measuring head, electrically heated, air cooled, with stock temperature thermocouple, fitted with Banbury-type rotors) at 40 rpm. The start-up procedure was similar to that used with the smaller mixing head however, the amount of masticated rubber temporarily removed from the mixer (to make room for the addition of the bulky carbon black) was scaled up from 10 g (taken from the 70-g batch) to 40 g. Fatigue resistance was measured by the Monsanto Fatigue to Failure Tester (ASTM D 4482). 

Table 5.14 [86]. Reaction conditions are the same as described for the system natural rubber-methyl methacrylate. The effect of monomer concentration and temperature on styrene polymerization [88] is illustrated in Fig. 5.18. The mastication reaction is slower than in vibromilling. It is useful to underline that in this last case the tests were run at temperatures well below the glass transition temperature of the resins and the system viscosities are nearly the same. The initial polymerization rate is influenced predominantly by the softening effect of added monomer. Subsequently, the reaction is strictly dependent on the properties of the plastomer product [86]. For extensive grafting, a step procedure is suggested to avoid a major initial softening effect [86].

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