Natural Rubber Surface Research Articles

Starch-based films: Tuning physical properties driven by nanocellulose-natural rubber latex composites

The excessive use of petroleum-based plastic packaging has raised concerns about its environmental impacts, leading to research on sustainable and economically viable biopolymer-based nanocomposites. However, there are still challenges related to the intrinsic characteristics of some biopolymers that differ substantially from conventional polymers, in terms of mechanical properties and water affinity. To address these issues, natural rubber (NR) latex coated with cellulose nanocrystals (CNCs) composites were explored as an effective alternative to tuning up physical properties of biopolymers. The deposition of CNCs on NR surface was innovatively devised through the utilization of the freeze-drying method, employing a green approach that eliminates the need for organic solvents. The NR coated with CNCs was incorporated into the starch matrix, varying the nanofiller mass percentage in the biopolymer (2, 5, and 10 wt%), the NR content in the nanofiller (0, 1, and 5 wt%), and the nanofiller preparation method (liquid nitrogen – N and gradual freezing – F). All starch-based films demonstrated notable transparency to visible light, and the incorporation of CNC/NR from N led to a reduction of 28 % in water vapor transmission rate compared to starch with glycerol, aligning with the filler percentage in the matrix. The addition of CNC/NR contributed to an increase of 76 % in the tensile strength and 53 % in the Young’s modulus of the bionanocomposites compared to starch with glycerol. Notably, the freeze-drying method allowed for the compatibilization of NR with a hydrophilic matrix without compromising the mechanical properties of starch-based bionanocomposites. Furthermore, films containing the CNC/NR nanofillers assisted in delaying the ripening of fresh-cut bananas, in addition to accelerating the biodeterioration of starch-based films. These findings indicate a promising avenue for the development of a new generation of green nanofillers that can be conveniently hydrophobically tailored to suit carbohydrate polymeric matrices.

Grafting photochromic spiropyran polymer brushes on natural rubber surface via surface-initiated ring-opening metathesis polymerization

The modification of stereoregulated functionalized polymers on the surface of natural rubber (NR) is a challenging task. This work provided a practicable grafting method to design photochromic polymer brushes on the NR surfaces using surface-initiated ring-opening metathesis polymerization (SI-ROMP). The designed photochromic polymer brushes were based on norbornenes with spiropyrin (SP) pendents, and grew from the surface of NR films in the presence of Grubbs 2nd catalyst. The results showed that the grafting rate of polymer brushes with photoisomerization structure reached up to 44.91 %. The modified natural rubber (NR-SP) films exhibited rapid coloring/decolorization property under UV irradiation and visible light. This photochromic property initiated by the light-induced isomerisation of the spiropyran structure and the increased surface energy under light stimuli. NR-SP films exhibited stable photochromic characteristics and outstanding anti-fatigue properties after exposing to over six cycles of consecutive UV/Vis irradiation. A simple and practical strategy for the preparation of highly sensitive photochromic natural rubber materials is proposed and provides a potential application in the fields of information storage and anti-counterfeiting.

Highly conductive rubber-based electrode with a robust wrinkled mesh-like copper coating for stretchable triboelectric nanogenerator

Stretchable triboelectric nanogenerators (TENGs) have gained increasing attention for their potential applications in wearable electronics. However, the fabrication of metal-coated flexible electrodes with a robust metal-polymer interface, high conductivity, and stretchability remains challenging for stretchable TENGs. Herein, a stretchable triboelectric nanogenerator (TENG) was designed using a highly conductive natural rubber (NR) electrode with a wrinkled mesh-like copper coating, which was chemically plated onto its surface by polymer-assisted metal deposition (PAMD) technology. To enable the PAMD process, a layer of polyacrylic acid (PAA) polymer brushes was first grafted onto the NR surface. This could not only assist the chemical plating but also improve the interfacial adhesion between the copper coating and the NR substrates. More importantly, the PAA layer facilitated the interconversion between the wrinkled structure and mesh-like structure of the copper coating during stretching cycles to ensure its conductivity and mechano-electrical stability. With this intrinsically stretchable rubber-based electrode, TENG devices were designed in a contact-separation configuration, which could effectively harvest mechanical energy in both pressing and stretching modes and show excellent electrical output performance. Notably, the rubber-based TENG could work stably at 100 % strain and produce a maximum power density of 0.14 mW/m2 at the resistance load of 3×107 Ω. Therefore, the stretchable rubber-based TENG in this work demonstrated a potential solution to flexible micromechanical energy harvesters for wearable devices.

Bio-Polyester/Rubber Compounds: Fabrication, Characterization, and Biodegradation.

Biobased and biodegradable polymers (BBDs) such as poly(3-hydroxy-butyrate), PHB, and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) are considered attractive alternatives to fossil-based plastic materials since they are more environmentally friendly. One major problem with these compounds is their high crystallinity and brittleness. In order to generate softer materials without using fossil-based plasticizers, the suitability of natural rubber (NR) as an impact modifier was investigated in PHBV blends. Mixtures with varying proportions of NR and PHBV were generated, and samples were prepared by mechanical mixing (roll mixer and/or internal mixer) and cured by radical C-C crosslinking. The obtained specimens were investigated with respect to their chemical and physical characteristics, applying a variety of different methods such as size exclusion chromatography, Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), thermal analysis, XRD, and mechanical testing. Our results clearly indicate that NR-PHBV blends exhibit excellent material characteristics including high elasticity and durability. Additionally, biodegradability was tested by applying heterologously produced and purified depolymerases. pH shift assays and morphology analyses of the surface of depolymerase-treated NR-PHBV through electron scanning microscopy confirmed the enzymatic degradation of PHBV. Altogether, we prove that NR is highly suitable to substitute fossil-based plasticizers; NR-PHBV blends are biodegradable and, hence, should be considered as interesting materials for a great number of applications.

Wettability Study on Natural Rubber Surfaces for Applications as Biomembranes

This manuscript reports an experimental study on surfaces of natural rubber membranes modified by incorporation of calcium phosphate particles. In particular, we focused on the wettability, a subject for biological aspects. Five surfaces of natural rubber (NR) membranes (pure, polymer-bioceramic composite (NR-CaP), and three modified surfaces subjected to a simulated body fluid (NR-SBF)) were produced and characterized by confocal Raman-spectroscopy, AFM, SEM, and XPS, and the results were correlated with the wetting properties. Seven liquids (water, formamide, di-iodomethane, ethylene glycol, hexadecane, simulated body fluid, and human blood droplets) were used in different experimental sections. Static and dynamic contact angle measurements were conducted to obtain the solid-liquid tensions, work of adhesion, and depinning forces. The incorporation of CaP particles in the polymer decreases the roughness and increases the interfacial adhesion, and there was no dependence between the morphology and equilibrium contact line. The hydrophobic state of the NR surfaces is preserved. After exposure to a biological environment, the NR surfaces were chemically modified increasing blood wettability and decreasing the negative surface charges and the contact angle to values close to those associated with protein adsorption and cell adhesion, therefore opening possibilities for applications of these materials as biomembranes. On the other hand, the concepts applied, regarding different wettability aspects, should enable the evaluation of biomaterial surfaces and provide new insights allowing a better understanding of body fluid-material interfaces.

Biodegradation of unvulcanized natural rubber by microorganisms isolated from soil and rubber surface: A preliminary study

ABSTRACTThe Natural rubber (NR) biodegradation by three microorganisms has been evaluated: a yeast (Rhodotorula mucilaginosa) and a bacterium (Pseudomonas sp.), isolated in a liquid culture from soil, and a filamentous fungus (Alternaria alternata), isolated on a solid culture from an NR surface, were tested. The biodegradation was conducted for four months in liquid culture, at 30°C, in agitated and stationary conditions, using a Mineral Salt Medium with NR as the only carbon source. The growth behaviour of the yeast and the bacterium was evaluated by means of optical density measurements (OD650). At the end of the incubation, the dry weight biomass of the microorganisms was measured. R. mucilaginosa showed a higher biomass production in the agitated culture, while a more efficient production was observed in static conditions for the Pseudomonas and A. alternata strains. The highest enzymatic activity of Lignin peroxidase (LiP) and Manganese-dependent peroxidase (MnP) was obtained in static conditions for A. alternata. The laccase production was probed by guaiacol oxidative polymerization on agar plates. The microorganism biodegradation capability was assessed through a combination of SEM analysis, FTIR-ATR spectroscopy, and Size Exclusion Chromatography techniques. An extended mycelium-substrate interphase and a decrease in the NR molecular weight were observed.

Eco-friendly natural rubber–silver (NR–Ag) composites for photo-assisted degradation of methyl orange dye

An environmental friendly, low cost composite for the photo-assisted degradation of methyl orange (MO) is proposed. Here, natural rubber–silver (NR–Ag) composites are formed through soft thermal reduction. The characteristics of the NR–Ag composites were investigated using UV–vis spectroscopy, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. The deposition of Ag on the surface of natural rubber was proven by the XRD diffraction peaks, attributed to metallic Ag and the appearance of the surface plasmon resonance of Ag, at ~ 420–460 nm in the UV–vis spectrum. The degradation of MO dye by NR–Ag composite under UV light source showed positive results for the degradation of dye even with minute amounts of Ag content. The degradation mechanism of MO involved the generation of hydroxyl radicals from the UV-irradiated NR–Ag composite by the formation of superoxide species as the important radical intermediate. Several parameters such as the Ag salt concentration and pH of the MO dye were investigated. Complete degradation of MO was achieved when the composites containing 2 × 10−3 wt% of Ag (NR–Ag4) were employed at pH 3. Under this condition, complete degradation occurred within 30 min. Kinetic studies were conducted to understand the degradation phenomenon.

Mechanical Behavior of Polystyrene-Grafted Natural Rubber/Natural Rubber Blend: Effect of Polystyrene Grafting Percentage

Polystyrene-grafted natural rubber (PS-GNR) at various graft levels was evaluated to improve mechanical properties of natural rubber (NR). PS-GNR was synthesized by emulsion copolymerization at 60°C at different reaction times between 15 and 360 mins to control the grafting levels of PS in the PS-GNR co-polymer. The resultant PS-GNR co-polymers were then blended into NR latex. The vulcanized NR compounds were investigated for the effect of PS grafting percentage in PS-GNR/NR compounds on mechanical properties, including tensile, tear strength and hardness. A core-shell structure was revealed with PS encapsulating the NR core via transmission electron microscopy. The polystyrene grafting percentage was determined to be 12.7%, 17.1%, 22.1% and 23.6% for polymerization times of 15 min, 60min, 120min, and 360 min, respectively. Addition of PS-GNR into NR exhibited biphasic behavior, resulting in a decrease in the tensile strength and tear strength. With further increase in grafting percentage of PS, the tensile strength and tear strength continues to decrease. The rigid chain of PS grafted onto NR surface reduced the elasticity of NR chain resulting in lower tear strength and the tensile strength. Fracture surface revealed a decrease in ductility of material with increasing grafting percentage of PS. On the other hand, modulus and hardness of PS-GNR/NR compounds were found to increase with increasing grafting percentage of PS. The addition of PS-GNR to rubber compound had shown an impact on dynamic behavior. With further increase in grafting percentage of PS in PS-GNR, an enhancement of storage modulus of rubber compound was clearly observed.

Silica Based Superhydrophobic Nanocoatings for Natural Rubber Surfaces

Silica based nonfluorinated superhydrophobic coatings for natural rubber surfaces have been developed. The coating was synthesized using nanosilica dispersion and a polychloroprene type binder as a compatibilizer. This nanocoating of silica was applied on to the surface of finished natural rubber gloves, by spray coating or dipped coating methods. The nanocoating demonstrates a water contact angle of more than 150° and sliding angle of 7°. The morphological features of the coating have been studied using scanning electron microscopy and atomic force microscopy while Fourier transform infrared spectroscopy was used to understand the nature of surface functional groups. Both imaging techniques provided evidence for the presence of nanosized particles in the coating. Coated gloves demonstrated comparable mechanical properties and significantly better alcohol resistivity when compared to those of the uncoated gloves.

Development and Characterization of Asymmetric Swelling-Induced Wrinkles on Natural Rubber Surface

Development and Characterization of Asymmetric Swelling-Induced Wrinkles on Natural Rubber Surface

Surface Modification of Natural Rubber by Sulfur hexafluoride (SF6) Plasma Treatment: A New Approach to Improve Mechanical and Hydrophobic Properties

Plasma treatments have faced growing interest as important strategy to modify the hydrophobic/hydrophilic characteristics of materials. However, challenges related to the plasma modification of polymers are the improvement of the chemical resistance without decreasing the mechanical resistance. In this letter, we present for the first time a plasma treatment, using Sulfur hexafluoride (SF6), analogous to vulcanization process, of natural rubber surface, which resulted in a chemical and tension resistance improvements. The natural rubber membranes were coated with glow discharge plasmas generated in sulfur hexafluoride (SF6) atmospheres at a total pressure of 160 mTorr and applying 70 W of radiofrequency. Plasma treatment increases the contact angles from 64° to 125° i.e. leading to a hydrophobic surface. The tension at rupture increased from 3.7 to 6.1 MPa compared to natural rubber without plasma treatment demonstrated by stress-strain investigation. These results provide a fast alternative approach to improve mechanical and chemical properties of rubber-based products.

Non-Destructive Evaluation of Protective Coatings on AA2024-T3 Aluminum Alloy Used in Aeronautical Parts by Electrochemical Impedance Spectroscopy

Plasma treatments have faced growing interest as important strategy to modify the hydrophobic/hydrophilic characteristics of materials. However, challenges related to the plasma modification of polymers are the improvement of the chemical resistance without decreasing the mechanical resistance. In this letter, we present for the first time a plasma treatment, using Sulfur hexafluoride (SF6), analogous to vulcanization process, of natural rubber surface, which resulted in a chemical and tension resistance improvements. The natural rubber membranes were coated with glow discharge plasmas generated in sulfur hexafluoride (SF6) atmospheres at a total pressure of 160 mTorr and applying 70 W of radiofrequency. Plasma treatment increases the contact angles from 64° to 125° i.e. leading to a hydrophobic surface. The tension at rupture increased from 3.7 to 6.1 MPa compared to natural rubber without plasma treatment demonstrated by stress-strain investigation. These results provide a fast alternative approach to improve mechanical and chemical properties of rubber-based products.

Surface characterization of polybutadiene and natural rubbers oxidized by silver(II)

ABSTRACTSilver (II) ion is a powerful oxidizing mediator that was used for surface modification of vulcanized polybutadiene rubber (BR) and natural rubber (NR) through mediated electrochemical oxidation (MEO). Scanning electron microscopy (SEM) pictures showed that surface morphology of the oxidized rubbers was changed so that some cracks and holes appeared on the surface in macroscopic scale. This is possibly due to chain scission caused by alkane group formation which is in turn in accordance with the attenuated total reflection Fourier transform infrared (ATR-FTIR) spectra. The amounts of hydroxyl and carbonyl type surface functional groups were also increased in both oxidized rubbers. The results obtained by atomic force microscopy (AFM) showed that the surface roughness for both rubbers was changed significantly from nano- to micro-scale. Energy dispersive X-ray analysis (EDXA) expresses that surface concentration of atomic oxygen for both BR and NR was increased significantly. Also surface polarity of the treated rubbers was enhanced based on contact angle measurements leading to a higher hydrophilicity. Finally it was found that silver(II) has a somewhat greater oxidation impact on the surface of natural rubber than polybutadiene rubber.

Macromolecular photoinitiators enhance the hydrophilicity and lubricity of natural rubber

ABSTRACTA mild and facile strategy to coat natural rubber (NR) with a hydrophilic coating is described that uses light and photoinitiator copolymers. Five high molecular weight photoinitiator copolymers, composed of hydrophilic (e.g., 2‐hydroxyethyl acrylate [HEA], poly(ethylene glycol) [PEG], N‐vinylpyrrolidone [NVP], N‐isopropylacrylamide [NIDAM], and acrylic acid [AA]) and hydrophobic benzophenone (BP) units, are synthesized and evaluated for coating NR on UV irradiation. When the HEA/BP, NVP/BP, and AA/BP macromolecular photoinitiators attach to the NR surface, the latter becomes hydrophilic. The resulting hydrophilic coatings on NR sheets are analyzed via FT‐IR spectroscopy, scanning electron microscopy, atomic force microscopy, contact angle measurements, and transwell cytotoxicity assays using NIH 3T3 fibroblast cells. The addition of high molecular weight hydrophilic polymers (e.g., polyvinylpyrrolidone and poly(2‐methacryloyloxyethyl phosphorylcholine)) to the coating further enhances the coating's hydrophilicity and lubricity. The application of these non‐cytotoxic, hydrophilic, and lubricious coatings on NR expands current applications and usage of NR. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43930.

Photo-patterned natural rubber surfaces with tunable tribological properties

The present work highlights the use of UV induced thiol–ene click chemistry for designing elastomer surfaces with tailored friction properties. A two-step surface modification strategy based on two consecutive photoinduced thiol–ene reactions has been developed which enables controlled and patterned immobilization of micro-scaled inorganic particles onto diene-rubber surfaces. The influence of the coupled particles on both surface topography and surface roughness is determined by microscopic techniques whilst tribological studies are carried out to characterize the friction properties. The results give evidence that the attachment of selected micro-scaled particles provides a distinctive increase in surface roughness and a considerable decrease in the coefficient of friction. Both are influenced by the amount of particles immobilized onto the elastomer surface. The application of photolithographic techniques further provides elastomer materials with precisely and spatially controlled tribological properties. Whilst elastomer surfaces with randomly attached particles exhibit isotropic coefficients of friction, the tribological properties of micro-patterned elastomers are anisotropic.

Influence of the Surfactant Nature on the Occurrence of Self‐Assembly between Rubber Particles and Thermally Reduced Graphite Oxide during the Preparation of Natural Rubber Nanocomposites

The natural rubber (NR) latex consists of polymer particles charged negatively due to the adsorbed phospholipids and proteins molecules. The addition of stable aqueous suspension of thermally reduced graphite oxide (TRGO) stabilized by ionic surfactants to NR latex can favor the occurrence of interaction between the stabilized TRGO and NR particles. Herein, the use of two surfactants of different nature, namely, sodium dodecyl sulfate (SDS) and dodecyltrimethylammonium bromide (DTAB), for the preparation of (TRGO)/NR nanocomposites, is reported. Zeta potential and particle size measurements indicated that the use of DTAB as cationic surfactant results in the flocculation of NR particles and promoted the formation of ion‐pair interactions between TRGO and the proteins and/or phospholipids present on the NR surface. This indicates that the use of DTAB can promote a self‐assembly phenomenon between TRGO with adsorbed DTAB molecules and NR particles. The occurrence of self‐assembly phenomenon allows obtaining homogenous dispersion of TRGO particles in the polymer matrix. The TRGO/NR nanocomposites prepared by the use of DTAB exhibited superior mechanical properties and excellent electrical conductivities reaching values of stress at 500% strain of 3.02 MPa and 10−4 S/cm, respectively.

Organic acids and protein compounds causing the photoluminescence properties of natural rubber membranes and the quenching phenomena from Au nanoparticle incorporation.

Natural rubber membranes were fabricated using latex from Hevea brasiliensis trees (clone RRIM 600) by casting, and controlling the time and temperature of thermal treatment. Three temperatures were used: 65, 80 and 120 °C and the corresponding annealing times of 6, 8, 10 and 12 h. The centrifugation of the latex produces the constituent phases: solid rubber (F1), serum or protein components (F2) and bottom fraction (F3). The photoluminescence properties could be correlated with organic acid components of latex. Natural rubber membranes were used as the active substrate (reducing agent) for the incorporation of colloidal Au nanoparticles synthesized by in situ reduction at different times. The intensity of photoluminescence bands assigned to the natural rubber decreases with the increase in amount of nanoparticles present on the membrane surface. It can be assumed that Au nanoparticles may be formed by reduction of the Au cation reacting with functional groups that are directly related to photoluminescence properties. However, the quenching of fluorescence may be attributed to the formation of a large amount of metal nanostructures on the natural rubber surface.

The Effect of Wollastonite on Curing Characteristics, Tensile and Morphology of Natural Rubber Compounds

Wollastonite filled natural rubber (NR) compounds were prepared using a laboratory two-roll mill. The filler was loaded into NR at different loading, i.e., 0, 10, 20, 30 and 40 part per hundred of rubber (phr). The effect of wollastonite on curing characteristic, tensile and morphology properties has been studied. Results indicated that the cure time (t90), scorch time (t2), tensile strength and elongation at break of the NR compounds decrease with increasing wollastonite loading but the maximum torque, tensile modulus M100 (stress at 100% elongation), M300 (stress at 100% elongation) increase with increasing wollastonite loading. The fracture surface morphology of the NR compounds was investigated with a scanning electron microscope (SEM). More filler detachment from NR surface was observed with increasing wollastonite loading.

Influence of Non-Rubber Components on NR Surface Modification by Chlorination

Natural rubber (NR) is a very useful elastomer and renewable polymer with outstanding properties compared to synthetic elastomers. However, as a natural polymer, the non-rubber species (proteins, phospholipids, carbohydrate, etc.) have to be considered carefully for the understanding of the surface and interfacial properties. Especially these components can markedly affect the frictional and adhesive properties of the rubber surface. Although many methods can be used to modify the surface properties, chlorination remains one of the easiest way.The present study deals with surface modification of peroxide crosslinked NRs and synthetic cis-1,4 polysioprene as reference samples by chlorination. Surface and frictional properties of these different rubbers were analyzed by various complementary techniques The influence of critical parameters on wetting, frictional and mechanical properties were investigated and will be discussed

Cure behavior and antimicrobial performance of sulfur‐cured natural rubber vulcanizates containing 2‐hydroxypropyl‐3‐piperazinylquinolinecarboxylic acid methacrylate or silver‐substituted zeolite

This work used 2‐hydroxypropyl‐3‐piperazinylquinolinecarboxylic acid methacrylate (HPQM) or silver‐substituted zeolite (SSZ) as antibacterial agents for natural rubber (NR) compounds vulcanized by conventional vulcanization (CV), semi‐efficient vulcanization, and efficient vulcanization (EV) systems. The cure behavior and antibacterial performance of the NR vulcanizates were studied by varying the loadings of HPQM or SSZ, contact times, and vulcanization systems. The antibacterial performance of the rubber compounds was examined by halo test and plate‐count‐agar methods against Escherichia coli (E. coli, ATCC 25922) and Staphylococcus aureus (S. aureus, ATCC 25923) as the testing bacteria. The cure time and crosslink density were dependent on the vulcanization recipe used but were not affected by the addition of HPQM or SSZ. Diphenylguanidine at the level of 1.0 phr (parts by weight per hundred parts of resin) in NR vulcanized by the EV system had the ability to kill the E. coli and S. aureus bacteria. The NR vulcanized by the CV system showed the most pronounced antibacterial performance, as compared with the other two vulcanization systems, via migration and diffusion of HPQM or SSZ onto the NR surfaces, this being identified by the relatively large reduction of contact angle values. The HPQM showed the most preference for NR compounds vulcanized with the CV system with a contact time of 120 min or longer to achieve a bacteria‐killing efficacy of 99.0–99.9%, the efficacy being more pronounced for E. coli bacteria. J. VINYL ADDIT. TECHNOL., 19:123–131, 2013. © 2013 Society of Plastics Engineers