Photochemical reduction of molecular weight and number of double bonds in natural rubber film

Abstract

Natural rubber (NR) can be degraded depending on various factors such as heat, mechanical force, chemical reaction, and light. Light is a very interesting factor because it can cause the NR to degrade under low temperature and pressure. The photo-degradation of NR films was carried out to investigate the effects of the light and the temperature on the reduction of the weight-average molecular weight (Mw) and the double bonds in the NR films. The NR films, with and without catalysts, titanium dioxide (TiO 2 ), and potassium persulfate (K 2 S 2 O 8 ), were exposed to light from a mercury light bulb at 7,000 and 36,000 lux, and at the temperature of 25 o C and 80 o C for 192 hrs. After exposure, the Mw of the NR films was analyzed by gel permeation chromatography (GPC). Changes in the Mw were used to construct a kinetic model for the process, (1/Mw)=(1/Mw 0 )+(kt/2M 0 ) where k is the rate constant, and M 0 is the Mw of the monomer unit. The linear relationship between 1/Mw and time suggested pseudo first-order processes with random scission. The Mw distribution information from the GPC was used to calculate the number of double bonds in the NR films. The trend of the double bonds reduction curves was quite similar to the result obtained from the calculation from the FTIR spectra. This indicated that this calculation method might possibly be another alternative way to obtain the number of double bonds in the NR.

Study on Degradation of Natural Rubber Latex Using Hydrogen Peroxide and Sodium Nitrite in the Presence of Formic Acid

“…The degradative reaction of the LNR chains can be determined as a second-order reaction with respect to the number of bonds broken during depolymerization [ 25 , 26 , 27 ]. Referring to Equation (2), the intrinsic viscosity obtained can be calculated to the M n values.…”

Preparation and Characterization of Low-Molecular-Weight Natural Rubber Latex via Photodegradation Catalyzed by Nano TiO2

“…The depletion of the C=C and C–C bonds suggests that both groups were involved in the chain breaking by means of at least two different mechanisms, namely, oxidation at the C=C bond by the oxygen species and the activity of radicals at the C–C bond. Furthermore, both groups were also able to absorb UV light to enter into an excited state, followed by chain breaking [49,50,51].…”

Thiosalicylic acid as a devulcanizing agent for mechano-chemical devulcanization

“…However, the T B values of the revulcanized rubber DVR/NR composites with a DVR composition of 5, 10 and 15 phr were slightly smaller than those of the NV rubber. This decrease in the T B value is likely to be mainly caused by the low-molecular-weight component and by the polymer structural changes that occurred during the devulcanization process [16,31,32]. It is noteworthy that, in contrast, a 5-10% improvement in the E B was obtained at a DVR content of 5-15 phr.…”