Low-Temperature Mechano-Chemical Rubber Reclamation Using Terpinene as a Swelling Agent to Enhance Bond-Breaking Selectivity

Common swelling agents used in the mechano-chemical rubber devulcanization process usually require high temperatures to achieve satisfactory swelling effects, which results in severe production of pollutants and reduces the selectivity of bond scissions. This work presents an environmentally friendly swelling agent, terpinene, which can swell the rubber crosslink structures at low temperatures. Both a rubber swelling experiment and a rubber reclaiming experiment with a mechano-chemical devulcanization method are conducted to explore the swelling effects of terpinene. After soaking in terpinene at 60 °C for 90 min, the length elongation of the rubber sample reaches 1.55, which is much higher than that in naphthenic oil and is comparable to that in toluene. When adding 3 phr of terpinene for every 100 phr of waste rubber during the reclaiming process, the bond scissions exhibit high selectivity. After revulcanization, the reclaimed rubbers have a tensile strength of 17 MPa and a breaking elongation of 400%. Consequently, the application of terpinene as the swelling agent in the LTMD method can greatly improve the properties of reclaimed rubbers, thereby enhancing the dual value for the economy and environment.

Synthesis of nano zinc oxide and its effect on the cure characteristic and properties of natural rubber vulcanizates

In this work, nano ZnO was synthesized by a simple method using a polymeric substance as a dispersing agent. Characterization of the synthesized ZnO by XRD and SEM confirmed the ZnO was nanometric in size and had a wurtzite structure. The synthesized nano ZnO was used as an activator for natural rubber vulcanization. Different amount of ZnO, 1, 2 and 3 phr, was investigated in the rubber formulation and compared to convention ZnO at a typical amount (6 phr). The sample with 3 phr nano ZnO showed the lowest curing induction time with the highest (ML-MH) at all studied temperatures. Furthermore, the rubber sample with 3 phr ZnO achieved the best properties, i.e., crosslink density, rebound resilience, and hardness compared to the rubber sample with 6 phr conventional ZnO. Interestingly, the properties of rubber sample with 2 phr nano ZnO were probably equivalent and comparable to that of 6 phr conventional ZnO. Thus, it suggested that the synthesized nano ZnO could replace the convention ZnO as an activator for rubber vulcanization even at a lower amount.

Configuration of Novel Experimental Fractographic Reverse Engineering Approach Based on Relationship between Spectroscopy of Ruptured Surface and Fracture Behaviour of Rubber Sample

A novel fractographic approach based on a combination of (i) mechanical behavior of cured rubber in uniaxial tensile loading and (ii) spectroscopy of fracture on a ruptured surface was experimentally validated. This approach related the migration of paraffin oil from a matrix to the ruptured rubber surface, to the tearing energy related to the deformation speed responsible for total rubber sample rupture, and the approach itself was configured experimentally. It was evaluated on cured natural rubber (NR) for two different paraffin oil concentrations. Single edge notched tensile (SENT) samples were subjected to uniaxial tensile loadings at two different deformation speeds. First, the tearing energy as a function of deformation speed was determined for each defined oil concentration. Secondly, at specific locations on the ruptured surfaces, infrared (IR) spectroscopy was performed to quantify a characteristic absorbance peak height of migrated paraffin oil during the rupture process. The results of the IR analyses were related to the deformation speed to understand the relation between the amount of migrated paraffin oil during the fracture process and the deformation speed which brought about such a fracture. This novel approach enhanced the reverse engineering process of rubber fracture related to the cause of tearing energies during critical failure.

An Alternative Crosslinking of Epoxidized Natural Rubber with Maleic Anhydride

This study investigated a novel crosslinking agent for epoxidized natural rubber (ENR). The result showed that it was possible to thermally crosslink ENR with maleic anhydride (MA). No additional catalyst was needed. FT-IR spectra revealed that after heating the ENR mixed with MA, there was the formation of the ester linkages. The crosslinking of ENR via these newly formed linkages was confirmed by the formation of gel once the heated rubber sample was immersed in toluene. The rheographs indicated that the crosslinking can take place at 80 °C and the curing rate and degree of crosslinking were dependent of the MA content. The cured ENR with MA showed higher decomposition temperature and better tensile strength than the uncured one.

Control of Thermal-Oxidative Degradation of Natural Rubber STR 5L by Using Cysteine Encapsulated with Alginate/Chitosan Microcapsules

This research was to study the efficiency of cysteine (Cys) acted as a natural antioxidant, which was encapsulated in alginate/chitosan (AG/CS) microcapsules to control the thermal oxidative degradation of natural rubber STR 5L. The microcapsules were prepared by a combined method based on ionic gelation and electrospraying techniques. The preparation of AG/CS microcapsules were executed to find the appropriate parameters such as applying voltage and concentration of alginate and chitosan. The applied voltage achieved for controlling the particle size as well as narrow size distribution of microcapsule. The AG/CS/Cys microcapsules were found to be a spherical shape and the average size was approximately 120 μm. The percentage of cysteine encapsulated within AG/CS microcapsules was increased with the increasing of chitosan concentration and encapsulation efficiency of cysteine in the microcapsules is about 81%. Core-shell structure of the microcapsule was confirmed by confocal laser scanning microscopy. After that, the natural rubber STR 5L mixed with AG/CS/Cys microcapsules was evaluated the oxidative resistance by Wallace plasticity. Thermal aging test according to standard ASTM D1349 at 70°C of the STR 5L mixed with AG/CS/Cys microcapsules were carried out. Weight-average molecular weight (w) of the rubber sample before and after aging test was also investigated by gel permeation chromatography. Thewof rubber sample before and after aging test presented clearly results depending on the aging time. Concisely, the AG/CS/Cys microcapsules have a potential to control release Cys and can be used to control the deterioration of raw STR 5L. The model of this encapsulation is expected to be applied with other applications.