Deproteinized NR

Figure 11.21 H-NMR spectra of (a) low molecular weight fraction of deproteinized NR (b) two-trans Betulapreno-16 and (c) three-trans Ficaprenol-12, observed at...

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.

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). 

Table 1. Nitrogencontent and incubation time for HANR, Fresh NR, and Deproteinized NR. ...

OPA, o-phthalaldehyde NQS, -naphthoquinone-4-sulfonate ex, excitation em, emission ISP, lonspray APCI, atmospheric pressure chemical ionization MSPD, matrix soid-phase dispersion SPE, solid-phase extraction deprtn, deproteinization acidfn, acidification RP, reversed phase NR, not reported. 

In previons work (Allen et al., 1963 Tangpakdee et al., 1997), NR coagulated from fresh NR latex, just after tapping from Hevea brasiliensis, was found to be soluble in tolnene, cyclohexane, and tetrahydrofuran. In contrast, the mbber from latex preserved in the presence of ammonia contained about 30-70% gel fraction, which was insolnble in the solvents. The formation of the insoluble fraction would be concerned with the interactions of mbber and proteins, because the gel fractions are reported to be soluble in the solvents after the enzymatic deproteinization (Eng et al., 1994 Tangpakdee et al., 1997). If the interactions are physical but not chemical, it is possible to remove the proteins from the mbber after denaturation of the proteins with urea. Here, the removal of the proteins from fresh NR latex and preserved high-ammonia latex was investigated with mea in the presence of surfactant. 

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. 

To assure the difference in the role between the proteolytic enzyme and mea, the treatment of fresh NR latex was made as well as HANR latex. The total nitrogen content of both untreated and deproteinized mbbers, which were prepared from fresh NR latex, is also shown in Table 1. The total nitrogen content of fresh NR was reduced to 0.014 wt% after enzymatic deproteinization (fresh E-DPNR), and 0.005 wt% after enzymatic deproteinization followed by the treatment with urea (fresh EU-DPNR), as in the case of HANR. On the other hand, after treatment with urea (fresh U-DPNR), the total nitrogen content of fresh NR was 0.004 wt%, being the least among the deproteinized mbbers. This may be explained in that most proteins present in fresh NR are attached to the mbber with weak attractive forces, which are able to be distmbed with urea. Thus, it is possible to expect that almost all proteins present in fresh NR are removed rapidly from the mbber by nrea treatment. 

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