Latex Foam Research Articles

Effects of BET Surface Area and Silica Hydrophobicity on Natural Rubber Latex Foam Using the Dunlop Process.

To reinforce natural rubber latex foam, fumed silica and precipitated silica are introduced into latex foam prepared using the Dunlop process as fillers. Four types of silica, including Aerosil 200 (hydrophilic fumed silica), Reolosil DM30, Aerosil R972 (hydrophobic fumed silica), and Sipernat 22S (precipitated silica), are investigated. The latex foam with added silica presents better mechanical and physical properties compared with the non-silica foam. The hydrophobic nature of the fumed silica has better dispersion in natural rubber compared to hydrophilic silica. The specific surface area of silica particles (BET) also significantly influences the properties of the latex foam, with larger specific surface areas resulting in better dispersity in the rubber matrix. It was observed that exceeding 2 phr led to difficulties in the foaming process (bulking). Furthermore, higher loading of silica also affected the rubber foam, resulting in an increased shrinkage percentage, hardness, compression set, and crosslink density. The crosslink density increased from 11.0 ± 0.2 mol/cm3 for non-silica rubber to 11.6 ± 0.6 mol/cm3 for Reolosil DM30. Reolosil DM30 also had the highest hardness, with a hardness value of 52.0 ± 2.1 IRHD, compared to 45.0 ± 1.3 IRHD for non-silica foam rubber and 48 ± 2.4 IRHD for hydrophilic fumed silica Aerosil 200. Hydrophobic fumed silica also had the highest ability to return to its original shape, with a recovery percentage of 88.0% ± 3.5% compared to the other fumed silica. Overall, hydrophobic fumed silica had better results than hydrophilic silica in both fumed and precipitated silica.

Effects of oil palm trunk biochar as filler on physical and mechanical properties of deproteinised and epoxidised natural rubber latex foam

Effects of oil palm trunk biochar as filler on physical and mechanical properties of deproteinised and epoxidised natural rubber latex foam

Natural aging behavior and lifetime prediction of rubber latex foam with various natural-to-synthetic ratios

Rubber latex foam (RLF) is a low-density, three-dimensional porous material that is susceptible to aging factors such as oxygen, heat, and light, leading to a loss of its excellent performance. This study conducted natural aging tests of the RLF with various proportions. The experimental conditions were divided into two categories: with and without fabric covering to better simulate the actual usage conditions. Subsequently, the performance of the RLF were conducted before and after aging, investigating the natural aging patterns of the RLF, and the influence of fabric covering conditions on aging. The results indicated that RLF with low N/R ratios has better aging resistance, and during natural aging, the N/R ratio did not show a significant relationship with the aging rate of the samples. From a microscopic perspective, samples covered with fabric maintain a more intact porous structure compared to those without fabric covering. In the process of thermo-oxidative aging, all samples underwent oxidation reactions. Finally, using the yellowness index as an evaluation criterion, the storage life of RLF was predicted by the variable activation energy method, and the quality and safety in actual production were further determined.

Dual-functional natural rubber latex foam composites for solar-driven clean water production and heavy metal decontamination

Solar steam generation (SSG) offers a sustainable approach to fresh water production. Herein, a novel dual-functional natural rubber/carbon black composite foam evaporator is presented for a cost-efficient SSG system that both produces fresh water and eliminates heavy metals present in the water. The composite foam is produced using the Dunlop process, and in its optimized form, it absorbed >96 % of sunlight. The foam evaporator exhibited a thermal conductivity of 0.052 W/m⋅K, a water evaporation rate of 1.40 kg/m2/h, converted 83.38 % of light to heat under 1 sun irradiation, and showed outstanding stability. The technology required to produce this composite foam is already available to make large-scale production feasible, while the natural raw materials are abundant. On the basis of its performance qualities, the rubber foam composite appears to be an excellent candidate for application as a viable solar absorber for SSG to produce fresh, clean water for commercial purposes.

A comparative study of surfactant-treated natural latex foam morphology, thermodynamic relationships and energy absorption: Talalay vs. dunlop processing

This study investigates the relationships between the morphology, energy absorption, and thermodynamic parameters of natural latex foams (NLFs) processed by the Dunlop and in-house Talalay methods, using different surfactant blends. Both methods involved mixing, moulding, and heating; the additional steps for the Talalay method involved cooling and gelation, a gel-freezing technique wherein the frozen foam is exposed to CO2 gas, inducing its transformation into a gel. The morphology of the internal structure of the NLFs was studied using 2D scanning electron micrographs and 3D micro- computerised tomography images. Two different surfactants, potassium laurate and pluronic, were used. Adding the blended surfactants reduced the porosity and increased the foam density of the NLF samples, improving mechanical properties. The cell size distribution of the NLF samples prepared using the Talalay method was broader than that of those prepared using the Dunlop method. In terms of the mechanical properties and energy absorption capabilities, the Talalay process resulted in samples with 20% lower compressive strength and 7% lower energy absorption than the control sample. A power-law relationship between the energy absorption per unit volume and the compression speed of the different foam samples was also observed. The ratio of the internal energy to the total compression force of the NLF samples prepared using the Talalay process was also lower than those prepared using the Dunlop process. The empirical insights derived from this study show how the mechanical properties and process technology associated with the producing of material foams could be improved.

Fabrication and characterization of latex foam shoe insoles made from novel ammonia-free natural rubber latex concentrate

Fabrication and characterization of latex foam shoe insoles made from novel ammonia-free natural rubber latex concentrate

EFFECT OF EGG WHITE PROTEIN AND WATER CONTENT ON THE STABILIZATION MECHANISMS OF NATURAL RUBBER LATEX FOAMS OBTAINED FROM MICROWAVE RADIATION

The global plastic consumption, as one of the paramount concerns of our society, open new paths of investigation in green materials. This study presents our contribution to the field with the obtention of natural rubber latex foams using egg white powder as bio stabilizing agent. The route followed to develop these samples is based on a two‐step process, a previous aeration, followed by microwave dehydration. This synthesis route is greener and eco‐friendlier than conventional ones due to the use of biobased bulk materials, the utilisation of microwave radiation which reduces the energy consumption in comparison with conventional heating methods and the elimination of the vulcanization process typically used when producing latex foams. In this work a deep study of the effect of egg white protein on natural rubber latex foams obtained at three water content levels (i.e. 40, 70, 90 phr) is carried out. The density and cellular structure parameters are measured for the formulations of liquid and solid foams which led to stable final samples in order to comprehend the stabilization mechanisms due to the presence of the egg white and the effect of water content in these systems. With the route developed in this research it has been possible to produce open cell natural rubber latex foams with densities as low as 53 kg/m3 and cell sizes as low as 114 µm.This article is protected by copyright. All rights reserved.

Effects of latex type and processed-mica waste loading on the structural and thermo-physical properties of natural rubber latex foam composites

Mica waste, a type of commercial waste produced in bulk quantities by the mica mining industry, was processed and added to Natural Rubber Latex Foams (NRLF) made of centrifuged and creamed latex. Following the Dunlop method, NRLF composites with various Processed Mica Waste (PMW) loadings (0, 2, 4, 6, 8, and 10 Phr) were prepared, and the thermo-physical characteristics were compared. Thermal conductivity, electrical resistivity of NRLF against the latex type and mica loading were compared for the first time. NRLFs prepared using creamed latex exhibit 33 and 50 μm (width and height) cell diameter, 3 ibf hardness, 281 % swelling index improvements and 0.05 Wm−1K−1 thermal conductivity, and 1 °C glass transition temperature (Tg) reductions than centrifuged NRLF and indistinguishable electrical resistivity. With the addition of mica (0–10 Phr), both NRLF types showed a similar ascending trend in hardness (42 ibf), water absorption (16 %), Tg (7 °C), thermal conductivity (0.54 Wm−1K−1), electrical resistivity (69 × 103 Ω m) with decreasing gel time (3 min) and swelling index (550 %). The key objective of this research was to prepare PMW-filled NRLF and compare structural, electrical and thermo-physical properties, for the first time, against mica content and latex type.

Research on the effects of jute fibers filler content and surface treatment on the mechanical properties of natural rubber latex foam

AbstractNatural rubber latex foam (NRLF) filled with untreated and alkali/silane coupling agent‐treated jute fibers (JFs) were prepared using the Dunlop method. The JFs fillers were added at 0, 1, 3, and 5 phr. The density, crosslinking degree, and surface morphology of the untreated jute‐filled NRLF were studied, and the tensile and compression properties of the untreated and surface‐treated NRLF were compared. The results showed that the density, the modulus at 100% elongation (M100), and compression set of the untreated jute‐filled NRLF increased with increasing JFs filler content. The crosslinking degree, tensile strength, elongation at break, and recovery rate decreased with increasing JFs filler content. Regarding mechanical properties, the surface‐treated JFs‐filled NRLF exhibited higher tensile strength and M100 than the untreated group, indicating that alkali/silane coupling agent treatment enhanced the interaction between JFs and the matrix. However, the elongation at break was lower. As for the compression set and recovery rate, there was no significant difference between the two groups, indicating that alkali/silane coupling agent treatment had little effect on the compression set and recovery rate of JFs‐filled NRLF.

Cushion performance of eco-friendly natural rubber latex foam composite with bamboo leaf fiber for impact protection of guava

This study investigated the performance of an eco-friendly cushion foam net comprised of natural rubber latex and bamboo leaf fiber. It compared this innovative BambooLatex foam net (thickness of 2.52 and 3.57 mm) with a commercial expanded polyethylene foam net (EPE) (thickness of 5.85 and 7.30 mm) as well as a control group with no cushioning. Key cushioning properties including thickness, mass, modulus, compressive strength, damping coefficient, and energy absorption were investigated. To assess cushion performance was conducted a simulated impact test involving guavas dropped from varying heights (200, 300 and 400 mm). The impacted fruits were subsequently stored at 20 ºC and 75% relative humidity for 4 days. During this period, we monitored bruising development using an image analysis technique, evaluating bruise area, fractal dimension, and grayscale as fruit quality parameters. Our findings indicated that thicker cushions offered superior protection, exemplified by the 7.30 mm EPE. However, the cushion material's damping coefficient and energy absorption capacity significantly influenced its ability to reduce impact energy. This resulted in the thinner BambooLatex foam net performing comparably to the EPE foam net. All cushion treatments significantly reduced impact bruising of guava fruit to less than 2% of the bruise area) as compared to the control (4–7% of the bruise area). There was no significant difference in fractal dimension and grayscale values among the four cushioning treatments. The bruise area parameter was recommended as it gave a better resolution for classifying impact fruit bruising severity in the cushion study. Ongoing developments are aimed at further reducing the weight of the eco-friendly natural rubber latex cushion and incorporating additional active functions.

Development of Deproteinized Natural Rubber Latex Foam for Seat Cushions

In the transportation industry, seat cushions are crucial since they are directly responsible for the comfort and safety of the occupant. In this study, recently developed deproteinized natural rubber (DPNR) latex foam is used to make seat cushions for the first time through the Dunlop batch foaming process. A CONFORMat™ pressure sensor system and a mannequin were used to investigate the pressure-relief performance of seat cushions made from DPNR latex foam. Flexible polyurethane (PU) and memory foam (PM) were used as a comparison. The study found that DPNR latex foam has a lower peak pressure value than PU foam, comparable to PM foam. The vibration transmissibility properties of the foam samples were examined using a UCON VT-9008 vibration machine according to ASTM D3580-95. DPNR latex foam has the lowest attenuation frequency, which could be related to the low stiffness and high resilience properties of the material. Overall, the findings suggest that the novel DPNR latex foam has both excellent pressure-relief and vibration isolation performance, making it an ideal candidate material for seat cushions intended for the transportation industry.

Compressive Stress-Strain and Rebound Resilience Properties of Deproteinized Natural Rubber Latex Foam

Deproteinized natural rubber (DPNR) latex is a modified version of natural rubber (NR) latex that is hypoallergenic and odorless when used in products. However, due to the lack of studies in this field, there are relatively few DPNR latex foam products to date. Our laboratory has developed a novel manufacturing technique that involves a heat-enzymatic reaction followed by a concentration procedure to generate DPNR latex directly from freshly tapped latex and to manufacture a novel DPNR latex foam using the Dunlop batch foaming procedure. To investigate the mechanical properties of the foam, ball-rebound resilience studies and compression tests were conducted on DPNR latex, commercial grade polyurethane (PU) and polyurethane memory (PM) foams as a comparison. Compressive stress-strain study revealed that the hysteresis loss ratio of DPNR latex foam, PU foam, and PM foam is 0.19, 0.66, and 0.86, respectively. DPNR latex foam exhibits the lowest hysteresis loss ratio due to its elastic behavior thus able to store a high amount of energy when under compressed. On the other hand, the rebound resilience of DPNR latex foam, PU foam, and PM foam is 74%, 29%, and 9%, respectively, indicating that DPNR latex foam has the highest rebound resilience. The resilience property is correlated with the elasticity, dimensional stability and durability of foam materials. Thus, DPNR latex foam is suitable for heavy-duty cushion applications including seats for transportation industry.

EFFECTS OF FOAMING PARAMETERS ON PHYSICAL PROPERTIES OF MICROWAVE-VULCANIZED NATURAL RUBBER LATEX FOAMS (IVCST2021)

This work reported the use of microwave vulcanization coupled with Dunlop process to prepared natural rubber latex foam (NRLF). Optimization of microwave heating for curing step was firstly carried out using a commercially available domestic microwave oven. The processing window and optimum condition for making NRLF were obtained. The optimum power and time of the irradiation were found at 600 W and 6 min, respectively. Using the optimum microwave vulcanization, effects of stirring time (2, 4, 6, 8, and 10 min) and speed (650, 950, 1250, 1550, and 1850 rpm) of foaming step on cell structure, bulk density, compressive properties, and hardness of NRLFs were investigated. Generally, the increases in the stirring time and speed in foaming step both gave rise to the volume of the air incorporated into the latex compound. This resulted in the increases in the bulk density and the number of cell but, the decrease in foam cell size. The stirring speed in a range of 950 to 1550 rpm was successfully used for preparing the NRLF. Too low and too high foaming speeds caused unstable latex compounds and failed to produce NRLF. The foam cell structure changed dramatically as the foaming speed increased. The foam mechanical properties, both compressive strength and hardness, were found to be linearly related to the foam bulk density.

Properties and cost of natural rubber latex foam using biomass ash filler from agarwood pellets

The purpose of this work was to add value to biomass ash, which is a waste product from combustion of agarwood pellets as fuel. Ash was used as filler in accordance with the Bio-Circular-Green economy model to reduce the cost of manufacture of natural rubber latex foam (NRLF) produced with the Dunlop technique. The agarwood pellet biomass fuel was heated in an incinerator at 700 to 750 °C for 6 h to start the process. The mixture was then passed through a 120-mesh sieve after ball milling for 72 h. The next step involved dispersing 10% agarwood pellet biomass ash (APBA) at 0, 1.5, 2.5, 3.5, or 4.5 phr loadings in latex. This was followed by other actions such as visual inspection of the foaming and gelling stages. The influence of APBA loading on density, hardness, compression set and morphological properties of NRLF were investigated, and also the cost of production was estimated. The findings revealed that NRLF with 1.5 phr of APBA exhibited good physical properties, having a smooth surface and small foam cells. Moreover, the compression set properties of NRLF with 1.5 phr APBA comply with the Thai Industrial Product Standard (TIS 173-2529) for NRLF (Industrial Product Standard Act, 1986). Regarding the production costs, they were below those of filler- free NRLF by 0.03 USD/kg.

Thermo‐Oxidative Aging Behavior and Lifetime Prediction of Rubber Latex Foam with Various Natural‐to‐Synthetic Ratios

Rubber latex foam (RLF) is widely used in daily life and its characteristics are active areas of research. However, the thermo‐oxidative aging behaviors of RLF at high temperatures have not been elucidated in detail. Herein this study, the aging degree and characteristics of five types of RLF materials with various ratios of natural rubber latex and synthetic rubber latex are investigated by using the yellowness index (YI), whiteness index, cross‐linking density, indentation density, and infrared spectrum. It is indicated in the results that the structural failure degree, YI, and cross‐linking density of the sample increased linearly with increasing natural‐to‐synthetic ratio (N/R ratio). It is observed that all RLF samples with various N/R ratios undergo aging reactions during the aging process, but the aging degree and aging rate of the samples differ. Furthermore, a lifetime prediction model is calculated by the standard method and the variable activation energy method, and the YI of RLF is used as an index to evaluate the service life, which serves as a useful tool for the quality evaluation of RLF.

Boosting the Antibacterial Performance of Natural Rubber Latex Foam by Introducing Silver-Doped Zinc Oxide.

Natural rubber (NR) latex foam is one of the rubber products that are increasingly in demand in the market. This is simply because of its lightweight, good thermal insulation, and resilience. The applications of NR latex foam are mostly for pillows and mattresses. This has resulted in these products requiring antibacterial performance which is very important for the safety of the end-users. In this study, the antibacterial NR latex foam was prepared by incorporating the silver-doped zinc oxide (Ag-doped ZnO) into the NR latex foam. Ag-doped ZnO was prepared by microwave-assisted method and then characterized through morphological characteristics and X-ray diffraction (XRD). The content of Ag doped onto ZnO was designed by varying the AgNO3 content at 15 wt%, 50 wt%, and 100 wt% of ZnO. The results confirmed that the Ag was successfully doped onto ZnO. The silver particles were found to be in the 40-50 nm range, where the size of ZnO ranges between 300 and 400 nm, and the Ag attached to the ZnO particles. The XRD patterns of Ag-doped ZnO correspond to planes of hexagonal wurtzite ZnO structure and cubic metallic Ag. This Ag-doped ZnO was further added to NR latex foam. It was observed that Ag-doped ZnO did not affect the physical properties of the NR latex foam. However, it is clear that both the inhibition zone and percent reduction of bacteria (e.g., E. coli and S. aureus) were enhanced by the addition of Ag-doped ZnO. It showed a decrease in the amount of cell growth over contact time. The content of 100 wt% AgNO3 could reduce E. coli and S. aureus up to 64.72% and 58.90%, respectively, when samples were maintained for 24 h. This study provides a scientific understanding of how Ag-doped ZnO could facilitate the development of eventual rubber foam products based on the respective results.

Effect of modified zinc oxide nanoparticles on enhancement of mechanical, thermal and antibacterial properties of disinfectant natural rubber latex foams

Natural rubber latex foams (NRLF) filled with unmodified zinc oxide (ZnO) and modified ZnO nanoparticles (ZnOnp) through the chemical coating on the calcium carbonate (CaCO3) are manufactured. This aimed to develop the mechanical, thermal, antibacterial properties of the NRLF for creating new innovative products and turn the NRLF to be the disinfectant NRLF. Various specific properties were considered, particularly the structure of modified ZnOnp and the antimicrobial activity of foams. It was found that the use of ZnOnp-coated CaCO3 at a ratio of 90:10 (ZnOnp-Ca10) indicated the highest of reinforcement efficiency, crosslink density based on the observed Mooney-Rivlin, and thermal stability. This related to the smaller particles, surface contacting area to the rubber chains, and shorter band gap in the activated states relative to the ZnO and unmodified ZnOnp. This NRLF had also the highest % inhibition of bacterial activity within 1 h by killing 94.01% of gram-native E.Coli bacteria. Relating the indication of the inhibition zone, NRLF filled with ZnOnp-Ca10 also showed strong efficiency for prohibiting the E.Coli and gram-positive S.Aureus bacteria. This affirmed the achievement of the disinfectant NRLF by using less ZnO purity in the foam which can support the preparation of other end rubber foam products.

Effects of oil palm trunk biochar on the thermal stability and acoustic properties of specialty natural rubber latex foam

Effects of oil palm trunk biochar on the thermal stability and acoustic properties of specialty natural rubber latex foam

Design strategy for porous carbon nanomaterials from rational utilization of natural rubber latex foam scraps

Design strategy for porous carbon nanomaterials from rational utilization of natural rubber latex foam scraps

Natural rubber latex cushioning packaging to reduce vibration damage in guava during simulated transportation

A conventional foam net is commercially applied to protect or reduce mechanical damage of guava fruit during transportation. This study investigated the utilization of natural rubber latex foam net (NRL-FN) cushioning material to protect Guava fruit against vibration damage. NRL-FN is an eco-friendly cushioning material which was designed to enhance its biodegradability by adding bamboo leaf fiber (BLF). Different loadings of the BLF were added into the NRL-FN (0.0, 2.5 and 5.0 phr). Cushioning performance of the NRLFNs were compared with a commercial polyethylene foam net (EPE-FN) using a bare fruit as the control. The cushioning test investigated thickness, energy (E), cushion coefficient (C) and percentage transmissibility (PT) using Glom Sali guava under simulated vibration at acceleration (Grms) (8.826 m s−2), frequency (13.5 Hz), and vibration duration (40 min). Guava fruit was stored at 20 °C under 80% RH for 4 d to assess vibration bruising on guava peel by digital image analysis as bruise area (BA), gray scale, normalized fractal dimension difference (ΔFD/FD0), browning index (BI) and total color difference (TCD). Results showed that NRL-FN+BLF0.0 phr and NRL-FN+BLF2.5 phr (thickness of 3.2 mm) gave lower C and higher E values than that of NRL-NF+BLF5.0 phr (thickness of 3.1 mm) and EPE-FN (thickness of 5.4 mm), while NRL-FN+BL0.0 phr and EPE-FN had the lowest PT value. The NRL-FN+BLF0.0 phr, NRL-FN+BL2.5 phr and EPE produced the lowest BA (<2.5%) on guava peel followed by NRL-FN+BL0.0 phr (6–7%) and a bare fruit (control) (30–45%). No significant differences in ΔFD/FD0, BI and TCD were found among the four cushioning treatments. The NRL-FN with lower BLF composition provided greater cushioning performance against vibration bruising on guava peel with reduced thickness and lower C and PT values. Results demonstrated that NRL-FN possessed a potential for application in distribution packaging as a new cushioning material to protect against fruit mechanical vibration damages.