Natural Rubber Foam Research Articles

A Silica-Lignin Hybrid Filler in a Natural Rubber Foam Composite as a Green Oil Spill Absorbent.

Oil spills in the marine environment are a rising concern due to their adverse impacts on living creatures and the environment. Hence, remediation methods have been used to remove the oil from the contaminated water. A sorbent material is considered the best method for oil spill absorption. However, commonly used commercial sorbents are made from nonrenewable and nonenvironmentally friendly materials. In this research, natural rubber foam (NRF) was used as a sorbent material with the addition of a filler, i.e., silica and a silica–lignin hybrid, to increase its oil sorption capacity and reusability. The silica and silica–lignin hybrid were extracted from rice husk waste by means of the precipitation method. The silica–lignin hybrid-filled NRF exhibited excellent hydrophobicity, with a water contact angle of 133°, and had more stable reusability compared to unfilled NRF and silica-filled NRF. In addition, the optimum oil absorption capacity of silica–lignin hybrid-filled NRF was 1.36 g g−1. Overall, the results showed that silica–lignin hybrid-filled NRF has the potential to be developed as a green oil absorbent material and is promising in terms of economic and environmental aspects.

Constructing conductive titanium carbide nanosheet (MXene) network on natural rubber foam framework for flexible strain sensor

Sensors, as one of the crucial components of wearable electronics, have attracted much attention due to their extensive application in healthcare, human–machine interfaces, electronic skins (E-skins), rehabilitation, and internet of things. However, there is still a challenge to fabricate flexible strain sensors with both good sensitivity and large working strain range. Herein, a facile, scalable, and low-cost strategy is developed to prepare highly sensitive strain sensors based on natural rubber foam and Ti3C2Tx nanosheeets (MXene/NR) by dip-coating method. The fabricated MXene/NR composite exhibits excellent strain sensitivity and large strain range. The gage factor of the MXene/NR composite reaches 14 in the strain range of 0–5% with a low pressure limitation of detection (435 Pa). Additionally, the sensing range is as large as 0–80% of strain and shows good stability during the pressing and relaxing cycles. It is demonstrated that the MXene/NR composite could be used to detect motions, such as finger pressing and step monitoring, suggesting it is a promising candidate for fabricating wearable electronics.

Effect of potassium oleate on chemical structure-compression relationship of natural rubber foam

Rubber foam-based products, such as mattresses, pillows, and cushions, are becoming increasingly popular. Rubber foam's formulation is still being developed to improve the properties, because of its wide range of applications. Potassium oleate is a surfactant for producing the rubber foam, although it can be used in different concentrations to prepare the different properties of rubber foam. The Dunlop method was used in this work, due to its simplicity and easy-to-use in the foam preparation. The effect of potassium oleate, which was used as a foaming agent, was investigated in this study by reducing the amount of potassium oleate. The density, compression, and Fourier transform infrared (FTIR) spectroscopy results showed that both density and compression of foam samples with half amounts of potassium oleate are higher than those of control sample with normal amounts of potassium oleate. Moreover, the FTIR result revealed a significant change in spectra with the reductions of potassium oleate contents. Therefore, rubber foam formulations are still developed to provide the optimum properties for suitable applications.

Evaluation of azodicarbonamide (ADC) on density, expansion ratio and closed cell properties of natural rubber foam

Natural rubber foams were made with a one-step foaming process, the effect of density, expansion ratio, and closed-cell properties via microscope were investigated. This research aims to investigate novel half vulcanization and full vulcanization process with three various blowing agents by compression moulding to fabricate natural rubber and carbon black foams. Closed cells of natural rubber used as shoe soles were formed by azodicarbonamide (ADC) and organic blowing agents. The experimental design used three blowing agent of Azodicarbonamide (ADC) A, B C, and control. The data analysis for images was performed in ImageJ software to get more quantitative results. Experimental data were created to perform a full (AF; BF; and CF) and half vulcanization (AH; BH; and CH) process. The different structure model based on digital microscope images was shown. The AH, BH, and CH with half vulcanisation process revealed a higher expansion ratio and cell number value. The microscope showed that rubber foam with the highest expansion ratio and cell number has a more homogenous structure with more cell connection of AH, causing a lower density value of 0.6480. In addition, AH and CH with ADC showed higher values than BH with an organic blowing agent, respectively.

Classification of natural rubber foam grades by optimising the azodicarbonamide content

This study aimed to focus on classifying rubber foam grades according to ASTM D1056. The natural rubber foams were prepared by varying the Azodicarbonamide (ADC) content from 2 - 10 phr. The results were evaluated on their physical and mechanical properties. The relative foam density of the foams decreased, and the expansion ratio increased with the addition of ADC. This was due to the increase in the gas phase raised by ADC. In addition, adding ADC also decreased hardness and compression-deflection of the foams, whereby the values obtained were higher after oven aging due to the radical recombination caused by chain breaking. According to ASTM D1056, the compression-deflection values of the foams were 2A2 and 2A3 grades, where the ADC content at 6 – 10 phr met the basic properties required by the same standard. Furthermore, the ADC content at 6 phr is strongly suggested when considering the foam morphology.

Development of natural rubber foam with water as a blowing agent via microwave and convection heating methods

Development of natural rubber foam with water as a blowing agent via microwave and convection heating methods

Enhanced photocatalysis of natural rubber foams filters boosted by modified-titanium oxide hybrid fillers: Gaseous benzene removal, antibacterial properties and air permeability

Enhanced photocatalysis of natural rubber foams filters boosted by modified-titanium oxide hybrid fillers: Gaseous benzene removal, antibacterial properties and air permeability

Effects of blowing agents and curing temperatures on physical and mechanical properties of natural rubber foam for laminated floor tiles

Falling on the floor has been one of the most common causes of breaking a bone. Falls in senior homes and care facilities can lead to immobility symptoms and treatments. Rubber flooring is a great alternative for fall protection. Thus, this study aimed to investigate the effects of organic blowing agents (dinitroso pentamethylene tetramine and azodicarbonamide) on the physical and mechanical properties of natural rubber foam used for laminated floor tiles. The curing temperatures were also examined in the range of 140–160 oC. From the experimental results, the blowing agent was an important component added to the rubber foam layer at various contents and temperatures. The compression set increased when curing temperatures and adding blowing agent increased. With an increase in the curing temperature, the elongation at break decreased. The findings indicated that the mechanical properties of natural rubber foam were significantly affected by the kind of blowing agent and the curing temperature. Finally, an optimal energy absorption was found in the dinitroso pentamethylene tetramine condition with 3 phr and the curing temperature of 160°C, which offers the maximum energy absorption value of 110 J.

Fabrication of microcellular epoxidized natural rubber foam with superior ductility by designable chemical and physical crosslinking networks

Though the introduction of microcells improves the impact strength of polymer, it weakens the tensile properties since microcells act as defects, leading to stress concentration and crack initiation during stretching. Reducing the cell size to micro/nano-scale is a facile strategy to eliminate the stress concentration. Herein, we propose supercritical CO2 assisted post-vulcanization approach to fabricate microcellular epoxidized natural rubber-SiO2 foam (f-ENR-SiO2) with high ductility. The designable chemical and physical crosslinking networks facilitated by vulcanization and SiO2 increase the complex viscosity and storage modulus of ENR, while did not induce second nucleation. These effects reduced the cell size to 1 µm and endowed f-ENR-SiO2 with 600% elongation at break and high cell structure stability (the cell structure stays intact without deformation after 250 stretching cycles), far superior to those of the reported microcellular foams. Overall, this study adopted superimposed crosslinking networks to fabricate flexible microcellular rubber foam with excellent ductility.

Development of Structural Insulated Panels Made from Wood-Composite Boards and Natural Rubber Foam.

An experimental study was carried out to develop and examine the properties of a new type of structural insulated panel (SIP). SIP prototypes conducted from this research consisted of insulated foam manufactured from natural rubber filled with wood particles as the core layer and three kinds of commercial wood-composite boards (plywood, cement particleboard, and fiber-cement board) as the surface layers. Polyurethane was used as an adhesive bond between the surface and the core layer. This preformed panel was placed into a clamping device and compressed until adhesive curing was achieved. The physical and mechanical properties of the SIP prototypes were consequently evaluated. The test results indicated that the types of surface layer materials played a significant effect on the SIP properties. The SIP covered with cement particleboard and fiber-cement board revealed high mechanical properties and high water resistance. The SIP prototype covered with plywood showed desirable properties (such as low density, high resistance of screw withdrawal, and low thermal transmittance). However, high water absorption and low fire resistance were drawbacks of the SIP covered with plywood. These properties should be improved.

Physical Hybrid of Nanographene/Carbon Nanotubes as Reinforcing Agents of NR-Based Rubber Foam.

Natural rubber (NR) foams reinforced by a physical hybrid of nanographene/carbon nanotubes were fabricated using a two-roll mill and compression molding process. The effects of nanographene (GNS) and carbon nanotubes (CNT) were investigated on the curing behavior, foam morphology, and mechanical and thermal properties of the NR nanocomposite foams. Microscope investigations showed that the GNS/CNT hybrid fillers acted as nucleation agents and increased the cell density and decreased the cell size and wall thickness. Simultaneously, the cell size distribution became narrower, containing more uniform multiple closed-cell pores. The rheometric results showed that the GNS/CNT hybrids accelerated the curing process and decreased the scorch time from 6.81 to 5.08 min and the curing time from 14.3 to 11.12 min. Other results showed that the GNS/CNT hybrid improved the foam’s curing behavior. The degradation temperature of the nanocomposites at 5 wt.% and 50 wt.% weight loss increased from 407 °C to 414 °C and from 339 °C to 346 °C, respectively, and the residual ash increased from 5.7 wt.% to 12.23 wt.% with increasing hybrid nanofiller content. As the amount of the GNS/CNT hybrids increased in the rubber matrix, the modulus also increased, and the Tg increased slightly from −45.77 °C to −38.69 °C. The mechanical properties of the NR nanocomposite foams, including the hardness, resilience, and compression, were also improved by incorporating GNS/CNT hybrid fillers. Overall, the incorporation of the nano hybrid fillers elevated the desirable properties of the rubber foam.

Impact responses of an open‐cell natural rubber foam impregnated with shear thickening fluid

AbstractThis research aims to investigate the impact responses of an impact absorbing material prepared from natural rubber (NR). Shear thickening fluid (STF) was developed in order to improve compatibility, and impact response capability of a NR foam. The material was prepared by impregnating NR foam with STF (30 wt% nanosilica with 10 nm). The obtained material is soft under normal circumstances, but immediately stiff when undergoing sudden impact before softening again. The effects of foam densities (0.098, 0.15, 0.24 g/cm3), STF contents (10, 20, 30 vol%), and fluid filling techniques were investigated. Experimental results show that the absorbed force tends to increase by increasing the foam density and the fluid content. Impact absorption capability of the proposed STF (STFA)/NR foam is higher than that of the conventional STF (STF0)/NR foam. In other words, STFA can improve the impact responses of the material providing comparable results with the commercial kneepad, which has the dilatant behavior.

Nano-Titania Doped NR Foams: Influence on Photocatalysis and Physical Properties

Natural rubber (NR) composite foams filled with various amounts of anatase- and rutile-titanium dioxide (TiO2) were prepared. Confirmation of each types of TiO2 was done from XRD, FTIR and particle size analyzer. Also, the properties of NR/TiO2 foams in terms of tensile strength and toughness, morphologies, photocatalytic and photo-oxidative properties were elucidated. Results showed that, the incorporation of both TiO2 into NR foams enhanced its mechanical, photocatalytic and UV stabilizing properties and reached an optimum concentration at 15 phr in case of anatase-TiO2. This can be explained in terms of different particulate structure of both TiO2 based on particle size, surface area and degree of electron recombination. In addition, the photocatalytic activity of the resulting foams by the degradation of methylene blue (MB) solution and benzene solvent under UV irradiation was examined and clearly exhibited a change in color of MB solution and benzene concentration. Particularly, in case of anatase-TiO2, the results were well correlated to the UV stability as confirmed from the ATR-FTIR spectrum, which exhibited a considerable reduction in the specific peak intensity, corresponds to the functional groups. The incorporation of anatase-TiO2 retards the propagation of photo-oxidation of NR foams. Therefore, the results clearly indicate the applicability of these modified NRs for NR foam-based furniture and filter.

The Relationship between the Morphology and Elasticity of Natural Rubber Foam Based on the Concentration of the Chemical Blowing Agent.

Concentrated natural latex was used to produce a rubber foam that is porous, elastic and well ventilated. The mechanical properties can be either soft or firm, depending on the formulation of the latex used. Briefly, concentrated natural latex was mixed with chemical agents to make the rubber foam on a laboratory scale using the Dunlop process. In this work, we changed the concentration of the chemical blowing agent in the latex. The morphological properties of the rubber foam were characterised using scanning electron microscopy, and the mechanical properties, or elasticity, were studied using compression experiments and the Mooney–Rivlin calculation. The results show that the concentration of the chemical blowing agent affects the morphological properties of the rubber foam but not the mechanical properties, indicating the heterogeneous structure of the rubber foam. The thermodynamic parameters (∆G and ∆S) and the internal energy force per compression force (Fu/F) of the rubber foam with various amounts of chemical blowing agent were also investigated. This study could be applied in the foam industry, particularly for pillow, mattress and insulation materials, as the present work shows the possible novel control of the morphological structure of the rubber foam without changing its mechanical properties. The difference in cell sizes could affect the airflow in rubber foam.

Current challenges in thermodynamic aspects of rubber foam

Natural rubber (NR) foam can be prepared by the Dunlop method using concentrated natural latex with chemical agents. Most previous studies have focused on the thermodynamic parameters of solid rubber in extension. The main objective of this study is to investigate the effect of the NR matrix concentration on the static and dynamic properties of NR foams, especially the new approach of considering the thermodynamic aspects of NR foam in compression. We found that the density and compression strength of NR foams increased with increasing NR matrix concentration. The mechanical properties of NR foam were in agreement with computational modelling. Moreover, thermodynamic aspects showed that the ratio of internal energy force to the compression force, Fu/F, and the entropy, S, increased with increasing matrix concentration. The activation enthalpy, ∆Ha, also increased with increasing matrix concentration in the NR foam, indicating the greater relaxation time of the backbone of the rubber molecules. New scientific concepts of thermodynamic parameters of the crosslinked NR foam in compression mode are proposed and discussed. Our results will improve both the knowledge and the development of rubber foams based on the structure–properties relationship, especially the new scientific concept of the thermodynamical parameters under compression.

Effect of Carbon Synthesized from Durian Bark on Properties of Natural Rubber Composite Foam

Natural rubber foam is used in industries as a gasket and insulation product. Dimensional expansion of specimen is the crucial problem of rubber foam specimen, especially in the automotive parts assembly. This work aims to understand the behavior of natural rubber foam (NRF)/carbon composites on microstructure and properties of NRF before being used. Carbon was synthesized from durian bark which was the agricultural waste that had the potential for using as reinforcing filler. The result showed the fast sulfur vulcanization rate with small bubble size at high amount of carbon. In addition, the young modulus of NRF/carbon composites increased with increasing carbon content.

Effect of carbon allotropes on foam formation, cure characteristics, mechanical and thermal properties of NRF/carbon composites

Natural rubber composite foam with carbon such as carbon black (CB), carbon synthesized from durian bark (CDB), graphite (GPT), graphene oxide (GO), graphene (GPE) and multi-walled carbon nanotubes (MWCNT) was studied in this work to investigate the relationship between foam formation during decomposition of chemical blowing agent mechanism and crosslink reaction of rubber molecules by sulphur. Natural rubber composite foam with carbon particle was set at 3 parts per hundred of rubber (phr) to observe the effect of carbon allotropes on foam formation with different microstructure and properties of natural rubber composite foam. The balancing of crosslink reaction by sulphur molecules during foam formation by the decomposition of chemical blowing agent affects the different morphology of natural rubber foam/carbon composites leading to the different mechanical and thermal properties. The result showed the fastest cure characteristics of natural rubber foam with 3 phr of graphene (NRF-GPE3) which was completely cure within 6.55 minutes (tc90) measured by moving die rheometer resulting in the smallest bubble diameter among other formulas. Moreover, natural rubber foam with 3 phr of MWCNT (NRF-MWCNT3) had the highest modulus (0.0035 ± 0.0005 N/m2) due to the small bubble size with high bulk density. In addition, natural rubber foam with 3 phr of GPT (NRF-GPT3) had the highest thermal expansion coefficient (282.12 ± 69 ppm/K) due to high amount of gas bubbles inside natural rubber foam matrix and natural rubber foam with 3 phr of GO (NRF-GO3) displayed the lowest thermal conductivity (0.0798 ± 0.0003 W/m.K) which was lower value than natural rubber foam without carbon filler (NRF). This might be caused by the effect of bubble diameter and bulk density as well as the defect on surface of graphene oxide compared to others carbon filler.

Feasibility of Using Natural Rubber (NR) Latex Foam as a Soft Robotic Finger: Role of Foaming Agent in Morphology and Dynamic Properties of NR Latex Foam

Sarcopenia caused by ageing and muscle loss is mostly found in the elderly people. Since a number of older people have been increased, a device which assists with grasping can play an important role in an ageing society. The purpose of this research is to select the material which is potentially a part of soft robotic actuator. Natural rubber (NR) latex produced locally in Thailand is intentionally chosen and chemically vulcanized by using a conventional vulcanization system into a molded fingered foam. The research focuses on varying the amount of foaming agent (Benzene sulfonyl hydrazide, BSH). Effect of foaming agent quantity on morphology and dynamic properties of the prepared natural rubber foam was elucidated. The suitable foam formula is selected and molded as the human fingers in the structure of a potential soft robotic actuator which were tested for the movement.

Effect of Fillers on the Recovery of Rubber Foam: From Theory to Applications.

Natural rubber foam (NRF) can be prepared from concentrated natural latex, providing specific characteristics such as density, compression strength, compression set, and so on, suitable for making shape-memory products. However, many customers require NRF products with a low compression set. This study aims to develop and prepare NRF to investigate its recoverability and other related characteristics by the addition of charcoal and silica fillers. The results showed that increasing filler loading increases physical and mechanical properties. The recoverability of NRF improves as silica increases, contrary to charcoal loading, due to the higher specific surface area of silica. Thermodynamic aspects showed that increasing filler loading increases the compression force (F) as well as the proportion of internal energy to the compression force (Fu/F). The entropy (S) also increases with increasing filler loading, which is favorable for thermodynamic systems. The activation enthalpy (∆Ha) of the NRF with silica is higher than the control NRF, which is due to rubber–filler interactions created within the NRF. A thermodynamic concept of crosslinked rubber foam with filler is proposed. From theory to application, in this study, the NRF has better recoverability with silica loading.

Effectiveness of microwave processing approach and green blowing agents usage in foaming natural rubber

This study mainly concerns the role of foam heating process techniques and its impact on cellular micromorphology, density and gas liberation mechanism of natural rubber foam with distilled water as blowing agent. Three different modes of heating process techniques and varying amount of distilled water have been examined on the foam density and cellular morphology, having rather identical morphological formation, cell distribution and relatively reducing densities but significant cell wall thickness. It is deduced that the increase in the water loading substantially affects the decrease in the foam densities, cell uniformity and stability. However, the heating process techniques influence the cell distribution and stability more than the amount of water content loading. The combine microwave oven process technique has improved the process of moisture diffusion into the water-blown open cell natural rubber foam unlike the slower procedure of conventional heating technique. In addition, the natural rubber foam physical properties and microstructure is improved better than the conventional heating technique. In all the simultaneous combine microwave oven technique is the best among the evaluated technique from the experiment because of density increment, cell distribution, pores flaccidity and uniform cells.