Rubber content

Rubber compounds Rubber content Rubber latex... 

In the early stages of development of polypropylene rubbers, particularly butyl rubber, were used to reduce the brittleness of polypropylene. Their use declined for some years with the development of the polypropylene copolymers but interest was greatly renewed in the 1970s. This interest has been centred largely around the ethylene-propylene rubbers which are reasonably compatible in all proportions with polypropylene. At first the main interest was with blends in which the rubber content exceeded 50% of the blend and such materials have been designated as thermoplastic polyolefin elastomers (discussed in Section 11.9.1). There is also increasing interest in compounds with less than 50% rubber, often referred to as elastomer-modified thermoplastics. It is of interest to note... 

A high-impact polystyrene (polystyrene SBR blend) may have seven times the impact strength of ordinary polystyrene, but about half the tensile strength, a lower hardness and a softening point some 15°C lower. Because of the rubber content there may be a reduction in light and heat stability and stabilisers are normally incorporated. 

Natural latex is polydisperse (size of individual particles may vary from 0.01 to 5 p.m). Flowever, synthetic latex has a relatively narrow particle size, and therefore the viscosity at a given rubber content is higher in synthetic rubber (polyisoprene) solutions. The average molecular weight is typically about I million g/mol, although it depends on the gel content. 

The main characteristics of NR latex are as follows high gel content high molecular weight high cohesive strength high self tack and high rubber content. 

Values in parentheses are the rubber content in W-EPDM. Ratios of W-EPDM to R-EPDM in different mixes were as follows (total rubber content in each case being constant at 70 parts) Fq,0 100, F[o,10 90, F2o,20 80 F3q,30 70 F40,40 60. 

FIGURE 11.29 Effect of grafted natural rubber content on the mechanical properties of STR5L-PMMA blends at ratios of 50 50 ( ) and 70 30 ( ). (From Suriyachi, P., Kiatkamjomwong, S., and Prasassarkich, P., Rubber Chem. Technol., 77, 914, 2004.)... 

Abbreviation for dry rubber content, generally of latices and similar dispersions. 

A hydrometer with a special scale, used for the determination of the approximate dry rubber content of latex. 

Polystyrene is an amorphous polymer and shrinkage and coefficient of thermal expansion are rather low depending on the possible rubber content. The absorption and alteration by moisture exposure are low. 

The MEK absorption of these cured resins is a strong function of the rubber content. Increasing the weight percent of rubber increases the amount of MEK absorbed very dramatically. Curves 1 and 2 are data for 5 minute immersions, while curves 3 and 4 are for 10 minute immersions. The... 

Berlin and coworkers (5,56) desired to obtain a material with an increased mechanical strength. They carried out a plasticization of bulk ami emulsion polystyrene molecular weight 80000 and 200000 respectively at 150-160° C, with polyisobutylene, butyl rubber, polychloroprene, polybutadiene, styrene rubber (SKS-30) and nitrile rubber (SKN 18 and SKN 40). The best results were obtained with the blends polystyrene-styrene rubber and polystyrene-nitrile rubber. An increase of rubber content above 20-25% was not useful, as the strength properties were lowered. An increase in the content of the polar comonomer, acrylonitrile, prevents the reaction with polystyrene and decreases the probability of macroradical combination. This feature lowers the strength, see Fig. 14. It was also observed that certain dyes acts as macroradical acceptors, due to the mobile atoms of hydrogen of halogens in the dye, AX ... 

Fig, 29. Dependence of the impact strength of the composition poly(vinyl chloride), epoxy resin, nitrile rubber on rubber content. 1 0% of SKN18M 2 5% of SKN18M 3 10% of... 

The original coupling agents, which were called promotors, were used to ensure a good bond between rubber and the carbon black filler. These promotors increase the tensile strength, modulus, and the bound rubber (the insoluble mixture of filler and rubber) content of rubber. Although natural rubber is soluble in benzene, it becomes less soluble when carbon black or amorphous silica is added. 

Another attempt by Tricas et al. to modify the surface of carbon black was by the plasma polymerization of acrylic acid [34]. Treatment with acrylic acid made carbon black hydrophilic. Plasma-coated carbon black was mixed with natural rubber and showed increased filler-filler interaction. The bound rubber content was reduced after the surface treatment of the filler. The authors also concluded that the surface of the carbon black was completely covered by the plasma polymer film, preventing the carbon black surface from playing any role in the polymer matrix. 

Bound rubber - The bound rubber content was measured with toluene as solvent [48,49]. The nonvulcanized samples (0.2 g) were cut into small pieces and put into a steel-wire basket of very fine mesh, which was immersed in 100 mL of toluene at room temperature for 72 h. The solvent was renewed after 24 h. The extracts were collected and left for 24 h in air and 24 h in vacuo at 105°C to evaporate the solvent. The amount of bound rubber (BdR) is expressed as the percentage of the total polymer content in the compound. 

Figure 18 shows the bound rubber content of samples filled with untreated silica, plasma-treated silicas, and silane-modified silica, as representative of the filler-polymer interactions. Samples SPTh and SPA show the highest bound rubber contents, and the ST the lowest value. The SPPy sample shows a bound rubber content slightly lower than that of SU. 

Fig. 18 Bound rubber content of untreated silica, PA-, PPy-, and PTh-silicas, and silane-modified silica in S-SBR...

In Fig. 23, the bound rubber values are shown of S-SBR/EPDM-blend samples filled with untreated silica, plasma-coated silicas, and silane-modified silica. The plasma-treated silicas show in all cases a significantly higher bound rubber content... 

The rubber content of the ABS polymer, is expressed in terms of the weight of the original rubber feed, rather than of the grafted rubber produced during polymerization. This is not necessarily the same as that charged to the reaction mixture. 

This arises, because the rubber is necessarily in the polymeric part of the reaction mixture such that removal of unreacted monomer after polymerization has reached the desired level, will result in a correspondingly higher proportion of rubber in what remains. The conversion of monomers to polymer can be run from 30 to 99%. For example, if monomer separation is carried out after only 50% conversion of the monomers, then the rubber content would... 

Analysis of the processes of polymerization revealed that the production volume of the ABS resin increases by shortening the processing time with a shorter reaction time, an increase in the rubber content of latex, a decrease in the rubber content of the final ABS injection molding products and extrusion products, or an increase in the total solid content of latex (9). 

Originally, processes were common that involve the feeding of a solution of rubber in a mixture of styrene and acrylonitrile monomers to the polymerization mixture. These processes have the inherent limitation in that they cannot produce polymers with a high rubber content. This occurs because in spite the rubber dissolves readily in styrene. However, its solubility in a mixture of styrene and acrylonitrile monomers decreases with the concentration of acrylonitrile. 

High rubber levels are desired and such levels have been reached by only coagulation procedures. Using coagulation techniques, rubber contents of greater than 70% were not reached (5). 

The resultant polymer latex has a butadiene/styrene rubber content of 77.5% by weight, with an overall butadiene content of 73.6%. 

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