Effects of in‐situ functionalization of carbon nanotubes with bis(triethoxysilylpropyl) tetrasulfide (TESPT) and 3‐aminopropyltriethoxysilane (APTES) on properties of epoxidized natural rubber–carbon nanotube composites

Composites of carbon nanotubes (CNT) and epoxidized natural rubber (ENR) were prepared by in‐situ functionalization of CNT with two alternative silane coupling agents: bis(triethoxysilylpropyl) tetrasulfide (TESPT) and 3‐aminopropyltriethoxysilane (APTES). The reactions of ENR molecules with the functional groups on CNT surfaces and with the silane molecules were characterized by Fourier transform infrared. Furthermore, cross‐link density, relaxation behaviors, curing, mechanical, electrical, and morphological properties of pristine ENR and the ENR composites were investigated. Very low percolation thresholds, at CNT concentrations as low as 1 phr, were observed in the ENR–CNT and the ENR–CNT–TESPT composites. This might be attributed to improvements in the chemical linkages between ENR molecules and functional groups on CNT surfaces that led to a homogenous dispersion of CNTs in the ENR matrix, with loose CNT agglomerates. POLYM. ENG. SCI., 55:2500–2510, 2015. © 2015 Society of Plastics Engineers     

Enhancement of electrical conductivity and other related properties of epoxidized natural rubber/carbon nanotube composites by optimizing concentration of 3‐aminopropyltriethoxy silane

Carbon nanotube (CNT)‐filled epoxidized natural rubber (ENR) composites were prepared by mixing in an internal mixer and thereafter on a two‐roll mill. Silane coupling agent, namely 3‐aminopropyltriethoxy silane (APTES), was directly incorporated in the ENR‐CNT composites during mixing of rubber and CNTs in the mixer, to perform in situ functionalization. It was found that pre‐crosslinking of ENR and APTES occurred especially at high APTES concentrations, such as 0.06 mL/(g of CNTs) and caused strong CNT agglomeration in the ENR matrix. However, the pre‐crosslinking could be reduced or avoided by decreasing the APTES concentration. In the concentration range 0.01–0.015 mL/(g of CNTs) of APTES, the APTES molecules were grafted on the CNT surfaces and generated new chemical linkages with the ENR. This improved the CNT dispersion in the ENR matrix and enhanced the composite properties. A very low approximately 0.5 phr of CNT threshold concentration for electric percolation was achieved in this type of composites. Also, three‐dimensional connected CNT networks were found to form in the ENR matrix at very low APTES levels. Thus, the electrical conductivity achieved in these composites reached the level required of conductive materials. POLYM. ENG. SCI., 57:381–391, 2017. © 2016 Society of Plastics Engineers     

Effect of carbon nanotubes decorated with silver nanoparticles as hybrid filler on properties of natural rubber nanocomposites

Decoration of carbon nanotube (CNT) surfaces with silver nanoparticles (AgNPs) was performed using N,N-dimethylformamide reducing agent. The CNT-decorated with AgNP (CNT-AgNP) was then used to prepare natural rubber (NR) nanocomposites via latex mixing method. Cure characteristics, mechano-thermal relaxation, electrical conductivity, and thermal properties of the composites were investigated. It was found that the CNT-AgNP gave cure properties improved over plain NR compounds in terms of scorch time, degree of vulcanization, and activation energy. In addition, temperature scanning stress relaxation measurement revealed stronger network formation after incorporation of AgNP into the NR matrix due to the interaction among CNT and AgNP particles. This also provided high conductivity and low percolation threshold concentration for the CNT-AgNP filled NR, relative to plain CNT filled NR composites. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47281.     

Optimizing mechanical and morphological properties of biodegradable thermoplastic elastomer based on epoxidized natural rubber and poly(butylene succinate) blends

Biodegradable thermoplastic elastomer (BTPE) blends of epoxidized natural rubber (ENR) and poly(butylene succinate) (PBS) were prepared by the melt mixing process. Influences of the processing parameters mixing temperature, rotor speed, and mixing time on mechanical and morphological properties of BTPE were investigated. Taguchi method was applied to improve the mechanical and morphological properties by optimizing the processing parameters. That is, the experimental design adopted the L9 Taguchi orthogonal array with three manipulated factors (i.e., mixing temperature, rotor speed, and mixing time). Analysis of mean and analysis of variance were also exploited and the mixing temperature was found to be the most significant processing parameter regarding mechanical properties. The mixing temperature showed large contributions to Young's modulus, 100% modulus, tensile strength, and elongation at break, namely 45.33, 40.38, 49.31, and 36.04%, respectively. Furthermore, the optimum conditions found for mixing temperature, rotor speed, and mixing time were 140 °C, 100 rpm and 10 min, respectively. The result was confirmed by atomic force microscopy and scanning electron microscopy micrographs showing fine‐grained co‐continuous phase morphology of the ENR/PBS blends. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46541.     

The effect of surface functionalization of carbon nanotubes on properties of natural rubber/carbon nanotube composites

The objective of this study was to prepare natural rubber composites filled with carbon nanotubes (CNTs) that show an electrical percolation threshold at very low CNT concentrations. Therefore, two methods of surface functionalization of CNTs were investigated to enable an improved dispersion of CNTs and chemical interaction between CNTs and rubber matrix. On one hand, the CNTs have been functionalized ex situ by acid treatment and silanization reaction with bis(triethoxysilylpropyl) tetrasulfide before mixing with the rubber and otherwise in situ functionalization was directly carried out during the processing of the composites in the internal mixer. The grafting of silane molecules onto CNT surface was established by Fourier transform infrared spectroscopy and scanning electron microscopy. Tensile tests revealed the outstanding properties of composites prepared by in situ silanization method. The in situ silanization led to a better dispersion of the CNTs and the formation of chemical linkages between CNT surface and rubber and this became manifest in higher reinforcement of the rubber, higher crosslink densities, and a lower electrical percolation threshold. It was also shown that the in situ silanization is retarding the vulcanization reaction. POLYM. COMPOS., 36:2113–2122, 2015. © 2014 Society of Plastics Engineer