Deproteinized Rubber

As normally produced, natural rubber contains a small amount of protein -perhaps 2.5% by weight. Latex can be treated with a bioenzyme that hydrolyzes the protein into water-soluble compounds. The latex is then diluted and the rubber is coagulated with acid and processed into a block rubber called DPNR. Compounds made with this rubber have reduced water absorption. With a careful selection of the vulcanizing system, vulcanizates can be produced with low creep properties under stress, a quality sought after in such items as rubber building mounts. 

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Watson and coworkers (68,69) studied in details the mechanical reaction of systems of natural rubber plus poly(methyl methacrylate), using a laboratory masticator at 76 rpm, in a nitrogen atmosphere at 15° C. Prior to mastication, the deproteinized crepe rubber was extracted with acetone, imbibed with mdnomer and allowed to homogenize for 16 h, in the absence of light It must be underlined that, with limited mastication and reaction heat dissipation, the actual rubber temperature was much higher the maximum recorded was about 50° C and... 

On the other hand, the low molecular weight fraction (Mn=10,000) of natural rubber, which was obtained by fractionation of Hevea rubber purified by deproteinization of a commercial latex, showed small signals characteristic of the C-l methylene and C-5 methyl carbon atoms in internal trans units at 39.80 ppm and 16.02 ppm, respectively, as shown in Fig. 6. The signals due to the terminal units were not detected at 59.0 ppm and 17.7 ppm,... 

The third category of natural rubbers are the specialty materials, which include liquid low molecular weight rubber, methyl methacrylate grafted polymers, oil-extended natural rubber, deproteinized natural rubber, epoxidized natural rubber, and superior-processing natural rubber. 

RSS Ribbed Smoked Sheet DPNR Deproteinized Natural Rubber. 

Figure 5.30 Corrected mass uptake measurements for engineering rubbers in sea water at 23 °C. A, deproteinized NR B, lead oxide cured polychlor-oprene C, nitrile rubber D, conventional NR E, conventional poly-chloroprene.

J. Suksaeree, P. Boonme, W. Taweepreda, G.C. Ritthidej, W. Pichayakom, Characterization, in vitro release and permeation studies of nicotine transdermal patches prepared from deproteinized natural rubber latex blends. Chemical Engineering Research and Design, ISSN 0263-8762 90 (7) (July 2012) 906-914. http //dx.doi.0rg/lO.lOl6/j. cherd.2011.11.002. 

Compared with higher purity or deproteinized Hevea rubber, guayule rubber has a higher propensity for straiu-induced ciystallization (107,108). This behavior is ascribed to the presence of higher levels of nonrubber impurities iu guayule rubber. 

Dry RubbGr. Because of its enhanced crystallizability, guayule rubber can exhibit superior failure properties in unfilled rubber compositions. As a double network, an elastomer cured a second time while in a deformed state guayule rubber exhibits substantially better fatigue resistance than deproteinized Hevea rubber (118). When compounded with carbon black, guayule rubber and Hevea rubber behave similarly (119). In tread and wire skim stocks, the compoimding and performance behavior of guayule rubber was comparable to that of Hevea rubber (Tables 7, 8) (120). 

Based on infrared evidence, ester groups in natural rubber were initially reported to be due to the presence of lactone functional groups. " Subsequently, C-NMR studies on deproteinized natural rubber showed that the ester groups were due to the presence of fatty acids bonded to the rubber molecule, of which 80% was saturated fatty acids and 20% unsaturated fatty acids. The fatty acids were later identified to be the acyl component of phosphoHpids hnked to the a-terminal end of the rubber molecule. The phospholipids were also postulated to be the branching point of the natural rubber molecule. The effects of these groups on natural rubber s properties have been discussed above. 

It should be noted that not all the rubber proteins and non-rubbers can be removed by one centrifugation under the operating conditions employed at the latex concentrate plants. Residual soluble proteins and those associated with the latex particles are still present in HA latex concentrate (Table 4.3). Hence latex-dipped products such as medical gloves made from this latex would still contain water-extractable rubber proteins. The same applies to the latex obtained from purification by creaming (see Section 4.5.3). NR latex with very low water-extractable rubber proteins can be produced by further treatment to dislodge the proteins associated with latex particles. These are known as low protein or deproteinized NR latex and will be discussed further later. The concern over rubber proteins is that they can cause allergic reactions in certain individuals who are sensitized to them (see Section 4.5.6). 

The photoreactive nanomatrix structure was formed by graft copolymerization of the inclusion complex of NDMA with p-CD onto deproteinized natural rubber. The content, conversion and residual methacryloyl group of NDMA for the graft copolymerization were 1.81%, 58.5% and 45.3%, respectively, at NDMA feed of 150 g/kg rubber and initiator concentration of 0.033 mol/kg rubber. The TEM observation of the resulting graft copolymer showed that natural rubber particles of about 1.0 pm in diameter were dispersed in a poly(NDMA) matrix of 10 nm in thickness. 

Total nitrogen content, X, of both untreated and deproteinized mbbers, is shown in Table 1. The total nitrogen content of HANR was reduced to 0.017 wt% after enzymatic deproteinization (E-DPNR), as reported in the previous study (Tanaka et al., 1997). On the other hand, it was reduced to 0.020 wt% after the treatment with urea, being similar to the nitrogen content of E-DPNR. This implies that most proteins present in NR are attached to the mbber with weak attractive forces. To remove further the proteins, the treatment with nrea was carried out after the enzymatic deproteinization of HANR latex. The nitrogen content of the resulting rubber, EU-DPNR, was 0.008 wt%, less than that of E-DPNR and U-DPNR. This suggests that the most of proteins are removed by denaturation with urea, whereas the residue must be removed with proteolytic enzyme in conjunction with nrea. 

Fukushima, Y, Kawahara, S., and Tanaka, Y. (1998). Synthesis of graft copolymers from highly deproteinized natural rubber. J. Rubb. Res. 1(3), 154-166. 

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