Radiation vulcanization of natural rubber

Radiation vulcanization of natural rubber latex by low energy electron beams — Use of... 

Polymers are the materials most often treated by radiation. Therefore in the recent past the IAEA has organized Cooordinated Research Projects (CRPs) in closely related areas, namely the stability and stabilization of polymers under irradiation, the radiation vulcanization of natural rubber latex, the modification of polymers for biomedical applications such as the radiation synthesis of membranes, hydrogels and adsorbents. 

It has been reported earlier that radiation vulcanization of natural rubber latex can be. sensitized by normal butil acrylate (nBA) and carbon tetrachloride (CCl 4 ). The irradiated latex can be used for producing rubber goods, such as ballon, and industrial gloves (1-3). 

S. Ono, F. Yoshii, K. Makuuchi and I. Ishigaki, Proceedings of the International Symposium on Radiation Vulcanization of Natural Rubber Latex, Tokyo and Takasaki. JAERI-M 89-228, 1989, p. 198. 

Haque, M.E., Dafader, N.C., Akhtar, F., Ahmad, M.U. Radiation dose required for the vulcanization of natural rubber latex. Radiat Phys. Chem. 48, 505-510 (1996)... 

The prevulcanization of natural rubber in latex form has also been a subject of much investigation. The cross-linking mechanism is not yet fully understood, but the water apparently plays a major role in it. Irradiation results in the cross-linking of the rubber molecules and in coarsening of the latex particles. A process of cross-linking of natural rubber latex has been developed to the point that it can be used for an industrial-scale application. The irradiation is performed in aqueous media by electron beam without a prorad (sensitizer) at a dose of 200 kGy (20 Mrad) or in the presence of n-butyl acrylate at considerably lower doses, typically 15 kGy. The cross-linked film exhibits physical properties comparable to those obtained from sulfur cured (vulcanized) film. As an alternative, the addition of a variety of chloroal-kanes makes it possible to achieve a maximum tensile strength with radiation doses of less than 5 Mrad (50 kGy). ... 

The structural formula of natural rubber (NR) is shown in Scheme 12.1. NR is sticky and non-elastic by nature. Crosslinking is a reaction of polymers to form a three-dimensional network. Crosslinking of rubber is called vulcanization. The crosslinking of NR makes it elastic. When NR is irradiated by high-energy radiation, hydrogen atoms of the trunk chain, mainly of methylene groups oc to double bonds, are ejected and radical sites are formed (Scheme 12.2), and these radical sites are combined into C-C crosslinks. ... 

Crosslinking of natural rubber is an essential requirement for producing desirable properties. Vulcanization of diene polymers can be achieved by using sulfur, peroxides, other reagents, or radiation. Our work involved crosslinking of natural rubber by heating with sulfur and therefore we will restrict our discussion to vulcanization by sulfur. 

In the case of rubber this cross linking is called vulcanization. Experiments conducted in 1946 at the Clinton Pile (D6) demonstrated a slight curing action of pile irradiation on natural rubber. Charlesby has shown that the degree of cross linking is directly proportional to radiation dose. Approximately 50 X 106 r. produces one cross link/90 isoprene units. 

Development of rubber glove production using by radiation vulcanized natural rubber latex (RVNRL) or irradiated latex in the pre.sence of 5 phr 2-ethyl acrylate and 1 phr carbon tetrachloride has been done. The combustion... 

Zinc oxide is commercially the most important compound of zinc and it is used to a considerable extent in the rubber, ceramic and paint industries. It is utilized to activate the organic accelerator of the vulcanization process for natural rubber and for most synthetic rubbers. Also zinc oxide serves as the accelerator for some types of elastomers. Further, it provides reinforcement to the rubber, it improves its heat conduetivity, it limits the degradation by UV radiation and it improves adherence. Typically, rubber eontains 2 % zinc oxide. A very broad range of other compounds are of extensive interest in chemistry, biology and physics and they make great practical contributions to the chemical, ceramic, fertilizer, paint, plastics, textile and electronics industries. 

Stephen, R., Jose, S., Joseph, K., Thomas, S., Ommen, Z. Thermal stability and ageing properties of sulphur and gamma radiation vulcanized natural rubber (NR) and carboxylated st3 rene butadiene mbber (XSBR) latices and their blends. J. Polym. Degrad. Stab. 91, 1717-1725 (2006)... 

Fig. 8.11. Tensile strength of pure gum natural rubber vulcanizates plotted against 1/Mc for various vulcanizing systems. O accelerated sulphur x TMT sulphurless peroxide A high energy radiation. (After Greensmith et al,...

---