Natural rubber swollen

Swift, P. McL. Bulk polymerization in natural rubber swollen by methyl methacrylate. J. Appl. Chem. 8, 803 (1958). 

For comparison with experimental data, we follow equation (6-93) and plot aE0 dV n / 2(As -1/A2) as a function of Vr4/3 / As. In Figure 6-8 we see that for natural rubber swollen to various degrees, the data all fall on a straight line with the same slope (C2) and intercept (Q) in excellent agreement with theory. The... 

If the degradation is conducted in the presence of a second monomer block and/or graft copolymers may be formed. One of the first reported examples was the mastication of natural rubber swollen with methyl methacrylateAlthough small quantities of pol3r (methyl methacrylate) and natural rubber resulted, the yield of block copol mier was very high. Excellent discussions of the mechanical preparation of block (and/or graft) are given in several reviews (107),... 

Homolytic bond cleavage, producing free radicals used in block copolymer formation, has also been reported. One of the first examples was the mastication of natural rubber swollen with methyl methacrylate (9). Photolytic degradation of polystyrene, capped with bromine containing groups (10) or copolymerized with carbon monoxide (11), has also been used in block copolymer preparation. Similarly ultrasonic degradation of homopolymers in the presence of a second monomer has been reported (12). 

Mullins, studying natural rubber swollen with -decane, found m = 0 However, Flory and Tatara have reported m = 1/2 for poly(dimethylsiloxane) in benzene and m between 0 and 1/2 for the results on natural rubber in n-decane obtained by Allen and co-workersIn summary, the decrease of the slope of [P] versus a with swelling shows a dependence on either vf (m = 0) or v (m = 1 /2). 

An example of natural rubber swollen in benzene (Figure 9.21) gives a value for Ci that is relatively constant and values of C2 that decrease as V2 decreases. The parameter 2Ci can then be considered to be the contribution to the modulus from cross-links that is not affected by the solvent, whereas 2C2 is the contribution to the modulus from entanglements (interactions) that is reduced by the presence of the solvent. 

FIG U RE 9.21 Stress-strain data for cross-linked natural rubber swollen to various degrees in benzene plotted according to Equation 9.92. (Data from Gumbrell, S. et al., Trans. Faraday... 

FIGURE 3.24 Plots of volume fraction of the filled rubber in the swollen gel (Vrf) against aging temperature for acrylic rubber (ACM)-silica and epoxidized natural rubber (ENR)-silica hybrid nanocomposites. (From Bandyopadhyay, A. and Bhowmick, A.K., Plastic Rubber Comp. Macromol. Eng., 35, 210, 2006. Courtesy of Money Publishers.)... 

Gee ° has applied this method to the determination of the interaction parameters xi for natural rubber in various solvents. Several rubber vulcanizates were used. The effective value of VelV for each was determined by measuring its extension under a fixed load when swollen in petroleum ether. Samples were then swollen to equilibrium in other solvents, and xi was calculated from the swelling ratio in each. The mean values of xi for the several vulcanizates in each solvent are presented in Table XXXVI, where they are compared with the xi s calculated (Eq. XII-30) from vapor pressure measurements on solutions of unvulcanized rubber in some of the same solvents. The agreement is by no means spectacular, though perhaps no worse than the experimental error in the vapor pressure method. 

Natural rubber Gain Enlarged, swollen, soft, brittle... 

Polymers with solubility parameters differing from those of the solvent by at least 2.0 H, will not dissolve in the solvent at room temperature. Thus although unvulcanized natural rubber (NR), unvulcanized styrene-butadiene elastomer (SBR), unvulcanized butyl rubber, and EPDM dissolve in gasoline or benzene, the vulcanized (cross-linked) polymers are swollen but will not dissolve due to the presence of the crosslinks. 

Fig. 39 Improvement of physical properties of various rubbers through incorporation of clay or swollen clay 50% modulus (a), tensile strength (b), elongation at break (c), and the stress-strain plots for natural rubber (d). The strain was measured on the basis of clamp distance measurements...

Price,C., Allen,G., de Candia,F., Kirkham,M.C., Subramaniam,A. Stress-strain behavior of natural rubber vulcanized in the swollen state. Polymer (London) 11, 486-491 (1970). 

This same value is calculated for the molecular segment weight in benzene-swollen natural rubber (28). 

The system Cl-buty 1-natural rubber (or cw-polyisoprene) could not be resolved by differential solvent techniques because the polymeric solubility parameters were too similar. At one end of the spectrum—i.e., with styrene at — 25 °C—natural rubber could be highly swollen while restricting the chlorobutyl swell, but the reverse was not possible, as indicated by the swelling volumes in the trimethylpentane. As displayed in Table II, attempts to use a highly symmetrically branched hydrocarbon with a very low solubility parameter, served only to reduce both the swelling of natural rubber and chlorobutyl. (Neopentane is a gas above 10°C and a solid below — 20°C). Therefore, for this report the use of differential solvents in the study of interfacial bonding in blends was limited to systems of Cl-butyl and cw-polybutadiene or SBR. 

Figure 2.16 Pressure permeation (reverse osmosis) of iso-octane and methyl ethyl ketone through crosslinked 265-p.m-thick natural rubber membranes. The change in the concentration gradient in the membrane as the applied pressure is increased is illustrated by the inserts. At high applied pressures, the concentration gradient and the permeation fluxes approach their limiting values [4]. Reprinted from Pressure-induced Diffusion of Organic Liquids Through Highly Swollen Polymer Membranes, D.R. Paul and O.M. Ebra-Lima, J. Appl. Polym. Sci. 14, 2201 Copyright 1970. This material is used by permission of John Wiley Sons, Inc.

Butadiene styrene Toluene 1. Abrasion followed by brushing. Grit or vapor blast or 280-grit emery cloth followed by solvent wipe. 2. Prime with butadiene styrene adhesive in an aliphatic solvent. 3. Etch surface for 1-5 min at RT following method 2 for natural rubber. Excess toluene results in swollen rubber. A 20-min drying time will restore the part to its original dimensions... 

If the environment slowly attacks either the substrate or the membrane, the interposition of a brick lining between the contained liquid and the substrate or membrane will reduce to a tiny trickle the amount of chemical that reaches the membrane or substrate. Corrosion products, if any, are trapped behind the brick and cannot be washed away to uncover further material to be corroded, so that the corrosion slows down and may eventually stop. Example In a dished bottom, cylindrical steel tank containing a mixture of acid and oil, the steel was lined originally with sheet natural rubber. The rubber lining swells as the oil enters it, but the brickwork holds it in place until the rubber has swollen into all the pores of the brickwork and blocked them preventing any more of the contained liquid from passing behind the brick. 

Neoprene is less affected by gasoline and oil and is more elastic than natural rubber. It resists abrasion well and is not swollen or dissolved by hydrocarbons. It is widely used to make hoses for oil and gasoline, electrical insulation, and automobile and refrigerator parts. 

Solvents produce different effects than do corrosive chemicals. Both silica and carbon black filled natural rubbers were more resistant to solvents than unfilled rubber. Also, the cure time was important, indicating that the bound rubber plays a role in the reduction of a solvent sorption. The diffusion coefficient of solvents into rubbers decreases with longer cure times and higher fillers loadings. Polychloroprene rubber swollen with solvent has a lower compression set when it is filled with carbon black. 

The above units are randomly arranged in emulsion copolymers, but in solution the polymers may occur in uniform blocks of varying length. These block copolymers are resilient and rubber-like at room temperature, but are thermoplastic at higher temperatures. SBRs are similar to natural rubber, in that they are susceptible to atmospheric oxidation and ozone cracking when stretched in air. They are swollen and weakened by hydrocarbons and halogenated hydrocarbons. However, their resistance to abrasion and ageing is superior to natural rubber. 

Figure 6-8. Effect of swelling on the Mooney-Rivlin plot of natural rubber where Vr is the volume fraction of elastomer in the swollen sample, (swelling liquid, n-decane). [After Mullins, J. Appl. Polym. Sci., 2, 257 (1959), by the permission of John Wiley Sons, Inc.]...

In trying to increase the resolution of the CP-MASS spectra of the highly cross-linked rubber networks, the samples were swollen in benzene to equilibrium. The gel was then packed into the rotor and spectra accumulated as if the sample was a dry solid. Figure 16 shows the spectra of natural rubber cross-linked with 25 phr peroxide, obtained from the CP-MASS experiment... 

NATURAL RUBBER 2S PHR ROOR SWOLLEN IN BEN2ENE 1 PULSE EXP... 

Figure 16. Spectra of natural rubber cross-linked with 25 phr ROOR. Spectrum (A) swollen in benzene to equilibrium swelling. Spectrum obtained under conditions of NFT experiment. Spectrum (B) same sample as (A), obtained under CP-MASS. The asterisk marks resonance of benzene solvent. Spectrum (C) the difference between (A-B).

Isobutyl acetate [110-19-0] is a colorless, neutral liquid with a pleasant, fruity odor. It is miscible with organic solvents, but immiscible with water. Isobutyl acetate has a high solvency for cellulose nitrate, colophony, damar resin, ketone and ketone-formaldehyde resins, maleate resins, urea and melamine resins, and phenolic and alkyd resins. Polymers such as polystyrene, poly(vinyl ethers), poly(vinyl acetate), polyacrylates, chlorinated rubber and vinyl chloride copolymers, as well as fats, greases, and oils are readily dissolved. Postchlorinated poly(vinyl chloride) is less soluble. Polyisobutene, cellulose ethers, polymethacrylates, poly(vinyl butyrals), natural rubber, and manila copal are swollen. Shellac, cellulose acetate, cellulose acetobutyrate, poly(vinyl chloride), and poly(vinyl formal) are insoluble. 

Jackson, C. L., and McKenna, G. B., On the anomalous freezing and melting of solvent crystals in swollen gels of natural rubber. Rubber Chem. TechnoL, 64, 760-768 (1991b). 

Figure 11-6. Reduced stress aw / (a — a ) of cross-linked natural rubber as a function of the reciprocal strain ratio at 45° C in the unswollen state (02 = 1) and in the swollen state in decane at various swell ratios. (After J. E. Mark.)...

These techniques rely upon high shear to cause bond scissions. Ruptured bonds result in formations of free-radical and ionic species. When this application of shear is carried out in the presence of monomers, block copolymers can form. This approach is exploited fairly extensively. Such cleavages of macromolecules can take place during cold mastication, milling, and extrusion of the polymers in the viscoelastic state. Both homolytic and heterolytic scissions are possible. The first yields free-radical and the second ionic species. Heterolytic scissions require more energy but should not be written off as completely unlikely." Early work was done with natural rubber. It swells when exposed to many monomers and forms a viscoelastic mass. When this swollen mass is subjected to shear and mechanical scission, the resultant radicals initiate polymerizations. The mastication reaction was shown to be accompanied by formation of homopolymers. Later, the technique was applied to many different polymers with many different monomers. ... 

FIGURE 29.5. Mooney-Rivlin reduced stress plot showing comparison of experimental data with modified constrained chain model (MCC) predictions for dry (o) and swollen ( ) natural rubber networks [112,117]. Swelling agent n-Decane. continuous lines are theoretical curves calculated with paremeters /cT/l/o = 0.17MPa and kq =2.0. 

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