Elucidation of the principle of microwave rubber vulcanization based on dielectric parameters and vulcanization of tire rubber by variable frequency microwave

Abstract

The microwave vulcanization of tire rubber was investigated by monitoring the dielectric properties of the rubber polymer and other components of the formulation (including carbon filler, antioxidant, and vulcanization agents) as functions of frequency and temperature. The effect of the vulcanization reaction on the dielectric properties during heating was also assessed. The physical interaction between the crosslinked structure and the carbon black significantly favors the responsiveness to microwaves during the vulcanization reaction. Based on these basic data, microwave irradiation conditions were determined, and model tire samples were microwave vulcanized in a PTFE mold. It has achieved a shorter time of heating and 65% energy saving, but on the other hand, it has become clear that the vulcanization produces very poor physical quality compared to vulcanization by electric furnace heating. To solve this problem, we performed microwave irradiation using variable frequency microwave (VFM; 5.85 ~ 6.65 GHz) using glass fiber on polyetherketoneketone (PEEK/GF) mold. In VFM, compared to conventional fixed frequency microwave (FFM), successfully synthesized high‐quality tire rubber because it showed 4.2, 1.1, 2.0, 1.2, and 1.8 times higher values in terms of cross‐linking density value, hardness value, tensile strength, elongation at break, and 200% modulus, respectively.

Three-dimensional observations of the electric field distribution of variable frequency microwaves, and scaling-up organic syntheses

“…This was attributed to the suppression of microwave standing waves resulting from improved uniformity of the E -field. Other reports have shown improvements of the E -field uniformity under VFM irradiation in the vulcanization of rubber 27 , in adhesives 28 , and in nanoparticle printing 29 , thus forewarning the effectiveness of VFM irradiation in chemical reactions. However, although the distribution of the E -field has been established theoretically through simulations, an experimental distribution of the E -field intensity inside a multimode cavity under VFM irradiation has, to our knowledge, not been investigated.…”

Three-Dimensional Observations of the Electric Field Distribution of Variable Frequency Microwaves: Scaling-up Organic Syntheses

“…This was attributed to the suppression of microwave standing waves resulting from improved uniformity of the Eeld. Other reports have shown improvements of the Eeld uniformity under VFM irradiation in the vulcanization of rubber [27], in adhesives [28], and in nanoparticle printing [29], thus forewarning the effectiveness of VFM irradiation in chemical reactions.However, although the distribution of the Eeld has been established theoretically through simulations, an experimental distribution of the Eeld intensity inside a multimode cavity under VFM irradiation has, to our knowledge, not been investigated. For that reason, it is necessary to ascertain whether the VFM irradiation technology can suppress uneven heating and hot spots caused by the nonuniformity of the Eeld, which have been serious issues in microwave heating for many years.…”