A Novel Approach to Improving the Mechanical Properties in Recycled Vulcanized Natural Rubber and Its Mechanism

Abstract

Vulcanized rubbers have three-dimensional chemical networks, and as a result they do not melt or dissolve. The presence of these networks creates a tremendous problem at the end of a product's life (i.e., recycling). Recently, R. J. Farris et al. have rediscovered a technique coined "high-pressure hightemperature sintering" (HPHTS) that fuses/sinters 100% vulcanized rubber powder into a solid mass recovering approximately 35-40% of the original mechanical properties. A method of enhancing the mechanical properties of sintered natural rubber powder by incorporating various organic compounds will be discussed in this paper. Additives of different chemical structures such as dienophiles (maleic acid and maleic anhydride), dipolarophiles (phthalimide), and organic acids (benzoic acid, salicyclic acid, and others) are employed. Attenuated total reflection infrared spectroscopy (ATR-IR) and electron ionization mass spectrometry (EIMS) are used to investigate the mechanisms of sintering and the underlying factors behind the enhancement of the properties that is seen with incorporation of these additives.

Rheological properties of a reclaimed waste tire rubber through high-pressure high-temperature sintering

“…The crumb rubber may consist of mixing between synthetic (SBR, EPDM) and natural rubber (Isoprene). The samples are prepared by coined method HPHTS [9,10] using custom made hydraulic hot press with temperature controlled heating. Sintered specimens of the recycled rubber powders are obtained by placing approximately 2 g of powder into a 30 mm diameter mold for an hour, applied pressure of 25 MPa and heating temperature of 200 C. During sample preparation, the starting temperature is about 27 C transiently increasing until 200 C for 17-20 minutes.…”

“…Reclaiming waste tires were usually performed by blending WTR with virgin rubber or by revulcanizing the dead rubber by treating it in physical and/or chemical ways. Morin et al [9] and Tripathy et al [10] proposed HPHT sintering to reclaim tire rubber based on supporting research by Tobolsky and coworkers [11][12][13][14]. Departing from fundamental theory of rubber scission and reformation, Morin et al [9] discovered that HPHT successfully reclaims WTR without the incorporation of virgin rubber.…”

“…In this process, the reclaimed rubber yields about 35-40% recovery of the original tire. The mechanical properties of that process were improved by Tripathy et al [10] by incorporating phthalimide, which raised the recovery yield to about 75% of the original rubber. Those results encouraged future efforts to achieve waste rubber revulcanization with a minimal use of virgin rubber.…”

“…This method, of course, provided some advantages such as simple execution and less production cost compared to other methods that are still need virgin rubber. The mechanical properties of the reclaimed waste rubber achieved 35-40% recovery of the original rubber (before reclaiming) [10]. Improvement of the work was conducted by Tripathy et al [10] by modifying the additives.…”

“…The mechanical properties of the reclaimed waste rubber achieved 35-40% recovery of the original rubber (before reclaiming) [10]. Improvement of the work was conducted by Tripathy et al [10] by modifying the additives. In general, the previous studies on mechanical properties of reclaimed waste tire were carried out under static tests.…”