STRAIN-INDUCED CRYSTALLIZATION AND MECHANICAL PROPERTIES OF NBR COMPOSITES WITH CARBON NANOTUBE AND CARBON BLACK

The Synergistic Effect of Carbon Black/Carbon Nanotube Hybrid Fillers on the Physical and Mechanical Properties of EPDM Composites after Exposure to High-Pressure Hydrogen Gas

This study investigated the synergistic effect of carbon black/multi-wall carbon nanotube (CB/MWCNT) hybrid fillers on the physical and mechanical properties of Ethylene propylene diene rubber (EPDM) composites after exposure to high-pressure hydrogen gas. The EPDM/CB/CNT hybrid composites were prepared by using the EPDM/MWCNT master batch (MB) with 10 phr CNTs to enhance the dispersion of CNTs in hybrid composites. The investigation included a detailed analysis of cure characteristics, crosslink density, Payne effect, mechanical properties, and hydrogen permeation properties. After exposure to 96.3 MPa hydrogen gas, the hydrogen uptake and the change in volume and mechanical properties of the composites were assessed. We found that as the MWCNT volume fraction in fillers increased, the crosslink density, filler-filler interaction, and modulus of hybrid composites increased. The hydrogen uptake and the solubility of the composites decreased with an increasing MWCNT volume fraction in fillers. Moreover, after exposure to hydrogen gas, the change in volume and mechanical properties exhibited a diminishing trend with a higher MWCNT volume fraction. We conclude that the hybridization of CB and CNTs formed strong filler-filler networks in hybrid composites, consequently reinforcing the EPDM composites and enhancing the barrier properties of hydrogen gas.

HEAT-TRIGGERED SHAPE MEMORY EFFECT OF PEROXIDE CROSS-LINKED ETHYLENE–METHACRYLIC ACID COPOLYMER/NITRILE–BUTADIENE RUBBER THERMOPLASTIC VULCANIZATES WITH SEA-ISLAND STRUCTURE

Designing shape memory polymers (SMPs) based on thermoplastic vulcanizates (TPVs) is an essential research topic. An efficient SMP is designed with typical sea-island structured ethylene–methacrylic acid copolymer/nitrile–butadiene rubber (EMA/NBR) TPVs in which the heat-control switched phase performed by the EMA phase is related to the shape fixity ability. The results show that the heat-triggered SMPs exhibit surprising shape memory properties (shape fixity >95%, shape recovery >95%, and fast recovery speed <30 s at the switching temperature of 95 °C). Through X-ray diffraction characterization, it is seen that the shape fixity of TPVs is achieved mainly through ethylene crystallization. The switching temperature is largely determined by the melting temperature (98 °C) obtained by differential scanning calorimetery.

High-Temperature-Aging Induced Sequential Recovery of Shape Memory Nitrile Butadiene Rubber Composites

The sacrificial bonds in natural materials have inspired the preparation of shape memory polymer (SMP), which can be prepared through the construction of dual cross-linking networks in a polymer matrix. With the rise of 4D printing technology, fine control over the shape recovery of SMPs, especially control over the recovery time, is urgently needed. In this study, the high-temperature aging method is adopted to tune the shape recovery time of dual cross-linked SMPs. Shape memory acrylonitrile butadiene rubber composite (i.e., NBR-C) is prepared by introducing Zn²⁺-C≡N coordination bonding and sulfur covalent cross-linking networks into the rubber matrix and then thermal aging at 180 °C for various time frames. Aging increases the covalent cross-linking density, ruptures rubber chains, and generates imine structures. Moreover, the composition of the coordination bonding network becomes diversified because of the formation of coordination bonds between imines and Zn²⁺ ions. The mechanical "tough-brittle" transition of aged NBR-C is observed, and its glassy temperature increases with aging time, which in turn changes the shape recovery time at the same recovery temperature. On the basis of these findings, the special shape memory rubber components with sequential recovery are fabricated by partially aging the NBR-C strings. This methodology provides novel solutions for the preparation of sequential SMP products without programming heating design or using redundant chemical materials. We believe that this work will be able to help promote comprehensive research of SMPs and widen applications of SMPs in the industry.

Nanocarbon Reinforced Rubber Nanocomposites: Detailed Insights about Mechanical, Dynamical Mechanical Properties, Payne, and Mullin Effects

The reinforcing ability of the fillers results in significant improvements in properties of polymer matrix at extremely low filler loadings as compared to conventional fillers. In view of this, the present review article describes the different methods used in preparation of different rubber nanocomposites reinforced with nanodimensional individual carbonaceous fillers, such as graphene, expanded graphite, single walled carbon nanotubes, multiwalled carbon nanotubes and graphite oxide, graphene oxide, and hybrid fillers consisting combination of individual fillers. This is followed by review of mechanical properties (tensile strength, elongation at break, Young modulus, and fracture toughness) and dynamic mechanical properties (glass transition temperature, crystallization temperature, melting point) of these rubber nanocomposites. Finally, Payne and Mullin effects have also been reviewed in rubber filled with different carbon based nanofillers.