Effect of electron‐beam irradiation on the thermal vulcanization of a natural rubber compound

Abstract

The influence of electron‐beam irradiation on the thermal vulcanization curing kinetics of a natural rubber compound was investigated by means of rheometric tests [moving die rheometry (MDR)] and differential scanning calorimetry (DSC). Differences in the storage moduli of compounds with different radiation doses were observed and assigned to a plasticizer effect by the zinc stearate mainly formed in the mixing stages; this compound migrated to the interphase region. This fact was confirmed by Fourier transform infrared spectroscopy. From the measurements performed by MDR and DSC testing, the induction time (to) was analyzed in the frame of the Claxton–Liska model, whereas the kinetic behavior of the nonirradiated and pre‐irradiated compounds were satisfactorily fitted with the Isayev–Deng and Kamal–Ryan models. Additionally, both curing characterization techniques corroborated the fact that the pre‐irradiated rubber compound showed an earlier t o and a lower activation energy in comparison with the nonirradiated compound. These facts were attributed to the effect of irradiation on the free sulfur content present in the rubber compound, which promoted more activated precursor species to crosslink with rubber. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47216.

Effects of Coagent Functionalities on Properties of Ultrafine Fully Vulcanized Powdered Natural Rubber Prepared as Toughening Filler in Rigid PVC

“…During the irradiation process, free radicals formed on the electron beam of the NR, caused crosslinking and scission of the polymer chain. The net effect of radiation on NR depended on the ratio between the degree of chain crosslinking and chain scission, which could be determined by using the Charlesby–Pinner equation as follows [ 27 ]: where s is the soluble fraction ( s = 1 − gel fraction), p is the chain scission probability, q is the chain crosslinking probability, u 1 is the number-average degree of polymerization, and D is the radiation dose [ 28 ]. The plot between 1/ D and s + s 1/2 is presented in Figure 2 c. The value of p / q = 0.147 could be obtained from the y-interception from linear fitting, and it implied that NR predominantly underwent crosslinking rather than scission in the range of radiation doses from 250 to 400 kGy [ 28 ].…”

“…where s is the soluble fraction (s = 1 − gel fraction), p is the chain scission probability, q is the chain crosslinking probability, u 1 is the number-average degree of polymerization, and D is the radiation dose [28]. The plot between 1/D and s + s 1/2 is presented in Figure 2c.…”

“…The plot between 1/D and s + s 1/2 is presented in Figure 2c. The value of p/q = 0.147 could be obtained from the y-interception from linear fitting, and it implied that NR predominantly underwent crosslinking rather than scission in the range of radiation doses from 250 to 400 kGy [28].…”

Investigation on the blooming behavior of additives in nitrile butadiene rubber at elevated temperature

“…The significant decrease in elongation at break of the rubber was attributed to the blooming of Zn(St) 2 . As well as the role of vulcanization accelerator, Zn(St) 2 is a significant plasticizer in rubber that reduces intermolecular forces between polymer chains 34,35 . When the NBR was annealed at 85°C, the intensified reaction between ZnO and SA led to an increase in Zn(St) 2 and consequently an increase in δ k .…”

“…As well as the role of vulcanization accelerator, Zn(St) 2 is a significant plasticizer in rubber that reduces intermolecular forces between polymer chains. 34,35 When the NBR was annealed at 85 C, the intensified reaction between ZnO and SA led to an increase in Zn(St) 2 and consequently an increase in δ k . However, with more annealing, blooming of Zn(St) 2 made its content in the rubber decrease significantly, which resulted in a sharp decline in δ k .…”