Mechanochemical Devulcanization Of Ground Tire Rubber In Solid State And Preparation Of Its Composites

In this study, the devulcanization of ground tire rubber (GTR) at ambienttemperature was realized through solid state mechanochemical milling using apan-mill type mechanochemical reactor. Theoretical analysis demonstrated that thisequipment can exert fairly strong squeezing force in the normal direction andshearing force in both radial and tangential directions on milled materials,functioning like pairs of three-dimensional scissors. The effect of various chemicalagents on mechanochemical devulcanization was investigated. In order to elucidatethe mechanism of mechanochemical devulcanization, the process of devulcanizationof NR vulcanizates was investigated. NR/GTR and GTR/waste tire fiber compositeswere successfully prepared through solid state mechanochemical co-milling. Thevulcanization kinetics and mechanical properties of NR/GTR composites weresystematic analyzed. The main results are as follows:1. The devulcanization of GTR at ambient temperature was realized throughsolid state mechanochemical milling without the use of any chemical agents. Itsrevulcanizates was also prepared. By taking advantages of the difference betweenbond energies, selectively break of crosslink bonds was realized in the strong shearing force field of mechanochemical milling. Gel fraction and crosslink densityof the mechanochemically devulcanized GTR were substantially reduced, confirmedthe occurrence of mechanochemical devulcanization. The maximum devulcanizationdegree is about 40ï¼…. The mechanical properties of the revulcanized GTR weresignificantly improved through mechanochemical devulcanization. The tensilestrength and elongation at break of revulcanized GTR obtained the maximum valueof 10.9 MPa and 290ï¼…respectively after mechanochemical milled 40 cycles.Compared with the revulcanized raw GTR, the tensile strength and elongation atbreak enhanced by 374ï¼…and 314ï¼…, respectively.2. The effect of various chemical agents on mechanochemical devulcanizationof GTR was investigated. The results showed that, accelerator TMTD, antioxidantBHT and plasticizer HP-T can not accelerate the mechanochemical devulcanizationof GTR. At other hand, by co-milling the D-Link devulcanizing agent with GTR, theelongation at break of revulcanized GTR was further improved. Compared with theusually employed D-Link devulcanization technology, the mechanochemicalco-milling technology can further improve the devulcanization degree anddevulcanization efficiency.3. The mechanism of mechanochemical devulcanization of NR vulcanizateswere investigated. During the process of mechanochemical milling, vulcanized NRsuffered strong squeezing force and shearing force exerted by the pan-millequipment, which induce energy concentrate on crosslink bonds in a short time. As aresult, the crosslink bonds were broken and the devulcanization was realized.4. The vulcanization kinetics of NR/GTR composites was investigated.Addition of GTR into NR vulcanizates leads to the increase of cure torque and thedecrease of scorch time (ts2) and optimum cure time (t90), but the variation is smalland did not affect the scorch security and cure processing efficiency. Compared withthe Composites prepared from raw GTR, the cure torque of the composites preparedfrom devulcanized GTR was improved, and the ts2 and t90 was decreased.5. The mechanical properties of the dGTR/NR vulcanizates were much better than those of the rGTR/NR vulcanizates, which are comparable to or even betterthan the virgin vulcanizate, indicating the significant benefit of mechanochemicaldevulcanization. In particular, at the GTR content of 10ï¼…, the tensile strength of thedGTR/NR blends increased to 22.8 MPa from 13.2 MPa of the rGTR/vNR blends,enhanced by 73ï¼…through devulcanization of GTR, and the elongation at breakincreased by 28ï¼….6. The GTR/waste tire fiber composites were successfully prepared bymechanochemical milling without any treatment of waste fibers and additives. Thedispersion of waste fiber into GTR matrix and the adhesion between the fiber andrubber matrix is improved by co-milling fiber with waste rubber. Compared with theGTR/waste tire fiber composites prepared by conventional mixing, the tensileproperties and elongation at break of the composites prepared throughmechanochemical co-milling was enhanced by 95.5ï¼…and 66.6ï¼…respectively. Theoptimum filler loading of waste tire fiber into GTR is 5 wtï¼…. The fiber-filledcomposites show anisotropy in stress-strain properties due to preferential orientationof the short fibers along the roll-milling direction (longitudinal). However, thedegree of fiber orientation is relatively low.