A novel one-step compression molding was proposed and successfully employed for preparation of closed-cell foams based on natural rubber (NR)/carbon black (CB) composite. The uniqueness of this new method was that both the foam density and expansion ratio became independent of the CB content. The rheometrical findings indicated that the increase in the CB content from 0 to 20 phr yielded a 0.91 and 3.51 N m increase in the initial and the final torque, respectively. The SEM results demonstrated that the prepared foam had three different layers including the skin, transition, and core layers. Almost 14-fold enhancement of the cell density (from 8 to 117 cells/cm 3 ) was obtained by increasing the CB content in a constant foam density. Although, curing properties, cell morphology, and mechanical properties of the foam improved by increasing the CB content, the gradual deterioration was observed for sound absorption properties.
With the ever-increasing development in science and technology, as well as social awareness, more requirements are imposed on the production and property of all materials, especially polymeric foams. In particular, rubber foams, compared to thermoplastic foams in general, have higher flexibility, resistance to abrasion, energy absorption capabilities, strength-to-weight ratio and tensile strength leading to their widespread use in several applications such as thermal insulation, energy absorption, pressure sensors, absorbents, etc. To control the rubber foams microstructure leading to excellent physical and mechanical properties, two types of parameters play important roles. The first category is related to formulation including the rubber (type and grade), as well as the type and content of accelerators, fillers, and foaming agents. The second category is associated to processing parameters such as the processing method (injection, extrusion, compression, etc.), as well as different conditions related to foaming (temperature, pressure and number of stage) and curing (temperature, time and precuring time). This review presents the different parameters involved and discusses their effect on the morphological, physical, and mechanical properties of rubber foams. Although several studies have been published on rubber foams, very few papers reviewed the subject and compared the results available. In this review, the most recent works on rubber foams have been collected to provide a general overview on different types of rubber foams from their preparation to their final application. Detailed information on formulation, curing and foaming chemistry, production methods, morphology, properties, and applications is presented and discussed.
The present study intends to study the ratcheting response of nylon fiber reinforced natural rubber (NR)‐styrene butadiene rubber (SBR) composite samples under asymmetric stress cycles. Uniaxial tests conducted on composite samples have shown how influential the weight fraction of short nylon fibers on the stress‐strain curves/loops under monotonic and cyclic loads is. NR/SBR composite samples with various fiber contents of 0, 10, 20, 30, and 40 per hundred rubber (phr) were tested under asymmetric stress cycles. In these tests, stress‐strain hysteresis loops were progressively shifted over stress cycles resulting in progressive plastic strain accumulation. Over stress cycles, ratcheting strain progressed within the first few cycles with a relatively high rate, and as the number of cycles increased, this rate decayed resulting in a plateau in strain accumulation (shakedown). The ratcheting strain rate and magnitude resulting in shakedown were highly affected by the nylon fiber content. The experimental observations showed that this plateau (shakedown) occurred after a number of cycles in NR/SBR composite samples where the widths of hysteresis loops stayed unchanged. Samples with no fiber and that with 10 phr fiber content possessed high ratcheting rates leading samples to failure after a few stress cycles. Fracture surfaces in these samples were further analyzed through SEM investigation.
A closed cell rubber foam, based on a natural rubber (NR)/nanoclay nanocomposite, was produced using a one-step foaming process with compression molding.
In this study, compression molding was used to produce elastomeric nanocomposite foams based on natural rubber (NR) with a hybrid reinforcing system containing organo-modified nanoscale (NC) and nanocarbon black (NCB). The effect of NC content (0-10 part per hundred rubber, phr) on the curing behavior, as well as the morphological and mechanical properties of elastomeric foams containing 10 phr of NCB was determined. Transmission electron microscopy and X-ray diffraction results showed that NC exfoliation occurred at low NC concentration (less than 5 phr), while increasing NC content up to 5 phr led to aggregation. Rheological data revealed that increasing the NC content up to 10 phr gradually changed the curing parameters such as 50% shorter scorch and curing time, two times faster curing rate, as well as higher initial (35%) and final (35%) torque. Scanning electron microscopy analysis also showed that increasing NC content from 0 to 5 phr produced foams with more uniform small cells, while 7 phr of NC changed the foam structure into two areas composed of different cell sizes and different cell densities. Higher NC content (10 phr) led to broken cell walls. With nanoparticles, higher foam modulus (83%) and hardness (104%) were observed. Finally, NC addition was found to improve the NR's thermal and thermooxidative resistance while the sound absorption coefficient was constant. K E Y W O R D Sfoams, hybrid composites, nanocarbon black, nanoclay, natural rubber
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