This work studied the properties of spent coffee ground (SCG) filled natural rubber (NR). The SCG was initially characterized by various techniques, prior to being added into rubber. Results revealed that SCG had relatively large particle size with very low specific surface area. It is mainly composed of organic compounds (such as protein, fatty acid, cellulose, hemicellulose, and lignin) with small quantity of inorganic substances (oxides of potassium, silicon, magnesium, calcium, and phosphorous). The incorporation of SCG in NR gave relatively low reinforcement and tended to retard vulcanization due to the presence of hydroxyl groups on the SCG surface. In addition to untreated SCG, reinforcement of SCG treated by liquid epoxidized natural rubber (LENR) and bis-(3-triethoxysilylpropyl) tetrasulfide (TESPT) was investigated. Improvement of rubber properties was observed when SCG surface was treated. Overall, TESPT-treated SCG gave the rubber with the highest mechanical properties, followed by LENR-treated SCG and untreated SCG, respectively.
With great concern of environmental threats, attempts have been made to reduce the consumption of zinc oxide (ZnO) in rubber products. This research aims at fabricating a new type of ZnO by depositing ZnO on microcrystalline cellulose (MCC) surface using an ultrasonic-assisted hydrothermal process.The concentration ratio of Zn(NO 3 ) 2 to NaOH is varied from 1:1 to 1:4. The obtained products, namely MCC-ZnO, are characterized by various techniques such as field emission scanning electron microscope, Fourier transform infrared spectroscopy, X-ray diffraction, Brunauer-Emmett-Teller, and Thermogravimetric analysis. Results show that the amount of deposited ZnO and the specific surface area of MCC-ZnO increase continuously with increasing NaOH concentration. The MCC-ZnO (1:3) containing approximately 55.6 wt% of deposited ZnO is selected for investigating the curing efficiency in natural rubber (NR) and compared with the commercial ZnO (C-ZnO). Obviously, the state of cure progressively increases with increasing either MCC-ZnO or C-ZnO content. At the same content, MCC-ZnO exhibits a significantly higher crosslink density than C-ZnO leading to the superior elasticity and mechanical properties. This could be explained by the greater specific surface area and, thus, the higher reactivity of MCC-ZnO. Clearly, a considerably lower quantity of MCC-ZnO is required to attain a similar level of crosslink density or mechanical properties as compared to C-ZnO.
The severe threat to aquatic environment from zinc oxide (ZnO) in tread debris has become a serious issue for tire manufacturers. Various attempts including the utilization of composite ZnO have therefore been made to reduce ZnO content in tread compounds. In this study, a new composite ZnO was prepared by depositing ZnO nanoparticles on microcrystalline cellulose (MCC) through hydrothermal reactions, called M-ZnO. After characterization by various techniques, cure activation efficiency of M-ZnO in truck tire tread compound was investigated and compared with that of active ZnO (A-ZnO).The results showed that M-ZnO contained approximately 66.7% w/w of ZnO and had comparable specific surface area to A-ZnO. Regardless of the ZnO type, crosslink density increased with increasing ZnO content up to 3 phr leading to the improved mechanical properties of the rubber vulcanizates, that is, hardness, modulus, and abrasion resistance. Tensile and tear strengths, however, were found maximum at 2 phr of both A-ZnO and M-ZnO. Although wet grip index was independent of ZnO content, rolling resistance tended to reduce with increasing ZnO content. The results clearly show the great potential of utilizing M-ZnO to replace conventional A-ZnO in tread compounds when more stringent environmental regulations are imposed.
Attempts to use bagasse ash (BA) as a filler in natural rubber (NR) have been made. Acidolysis/alkaline extraction method was used to purify BA. The purified BA (PBA) was subsequently characterized by various techniques such as X‐ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and so forth. After the purification, PBA had a lower particle size and a higher specific surface area. XRD results showed that silica was the main composition of PBA while FTIR results revealed the existence of hydroxyl groups on the PBA surface. The reinforcement magnitude of PBA in NR was subsequently evaluated both without and with the addition of surface modifying agents, namely, bis‐3‐triethoxysilylpropyl tetrasulfide (TESPT) and epoxidized natural rubber (ENR). Due to its large particle size, PBA acted as a semi‐reinforcing filler for NR, that is, the small increases of hardness, modulus and tensile strength were observed in the presence of PBA. As TESPT and ENR could improve the extent of rubber‐filler interaction, mechanical properties of the NR vulcanizates filled with PBA‐TESPT and PBA‐ENR were slightly higher than those of the PBA‐filled NR vulcanizate. For instance, tensile strength exhibited approximately 22% increase after the surface treatment. In this study, both PBA‐TESPT and PBA‐ENR showed comparable degree of reinforcement.
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