Organomodified montmorillonite as filler in natural and synthetic rubber

Mechanical Properties and Equilibrium Swelling Characteristics of Some Polymer Composites Based on Ethylene Propylene Diene Terpolymer (EPDM) Reinforced with Hemp Fibers

EPDM/hemp fiber composites with fiber loading of 0-20 phr were prepared by the blending technique on a laboratory electrically heated roller mill. Test specimens were obtained by vulcanization using a laboratory hydraulic press. The elastomer crosslinking and the chemical modification of the hemp fiber surface were achieved by a radical reaction mechanism initiated by di(tert-butylperoxyisopropyl)benzene. The influence of the fiber loading on the mechanical properties, gel fraction, swelling ratio and crosslink degree was investigated. The gel fraction, crosslink density and rubber-hemp fiber interaction were evaluated based on equilibrium solvent-swelling measurements using the Flory-Rehner relation and Kraus and Lorenz-Park equations. The morphology of the EPDM/hemp fiber composites was analyzed by scanning electron microscopy. The water absorption increases as the hemp fiber loading increases.

Structure, physicochemical properties, and adsorption performance of the ethyl cellulose/bentonite composite films

Ethyl cellulose (EC) was filled with bentonite (Bent) particles by mechanical dispersion to produce composite film materials that were studied using various methods. According to X-ray diffraction (XRD) analysis, the inter-chain separation length was larger in EC/Bent composite then those in pure polymer. Infrared spectrometry indicated a formation of hydrogen bonds between the hydroxyl groups of EC and the silanol groups of clay. Tests showed an increase in tensile strength of the polymer material (by 35-40%) when doped with bentonite. It was found that modification of polymer with bentonite resulted in increasing of the adsorption efficiency of methylene blue (MB): the equilibrium concentration of MB ions in adsorbent phase increased 2.5 times. The MB adsorption kinetics obeyed the pseudo-first-order mechanism. Isotherms were in good agreement with Langmuir model. For the composite, the maximum monolayer adsorption capacity was 4 times higher than that for pure polymer.

Polyaniline Synthesized by Different Dopants for Fluorene Detection via Photoluminescence Spectroscopy

The effects of different dopants on the synthesis, optical, electrical and thermal features of polyaniline were investigated. Polyaniline (PANI) doped with p-toluene sulfonic acid (PANI-PTSA), camphor sulphonic acid (PANI-CSA), acetic acid (PANI-acetic acid) and hydrochloric acid (PANI-HCl) was synthesized through the oxidative chemical polymerization of aniline under acidic conditions at ambient temperature. Fourier transform infrared light, X-ray diffraction, UV-visible spectroscopy, field emission scanning electron microscopy, photoluminescence spectroscopy and electrical analysis were used to define physical and structural features, bandgap values, electrical conductivity and type and degree of doping, respectively. Tauc calculation reveals the optical band gaps of PANI-PTSA, PANI-CSA, PANI-acetic acid and PANI-HCl at 3.1, 3.5, 3.6 and 3.9 eV, respectively. With the increase in dopant size, crystallinity is reduced, and interchain separations and d-spacing are strengthened. The estimated conductivity values of PANI-PTSA, PANI-CSA, PANI-acetic acid and PANI-HCl are 3.84 × 101, 2.92 × 101, 2.50 × 10-2, and 2.44 × 10-2 S·cm-1, respectively. Particularly, PANI-PTSA shows high PL intensity because of its orderly arranged benzenoid and quinoid units. Owing to its excellent synthesis, low bandgap, high photoluminescence intensity and high electrical features, PANI-PTSA is a suitable candidate to improve PANI properties and electron provider for fluorene-detecting sensors with a linear range of 0.001-10 μM and detection limit of 0.26 nM.

Polybutadiene Vitrimers with Tunable Epoxy Ratios: Preparation and Properties

Traditional crosslinked diene rubber has excellent thermal-mechanical properties and solvent resistance, yet it is incapable of being recycled via universal molding or injecting. Vitrimers, a new class of covalently crosslinked polymer networks, can be topologically rearranged with the associative exchange mechanism, endowing them with thermoplasticity. Introducing the concept of vitrimers into crosslinked networks for the recycling of rubbers is currently an attractive research topic. However, designing tailored rubber vitrimers still remains a challenge. Herein, polybutadiene (PB) vitrimers with different structures were prepared via partial epoxidation of double bonds and ring-opening esterification reactions. Their mechanical and relaxation properties were investigated. It was found that the increasing crosslinking density can increase tensile strength and activation energy for altering the network topology. The influence of side-group effects on their relaxation properties shows that an increase in the number of epoxy groups on the polybutadiene chain can increase the chance of an effective exchange of disulfide units. This work provides a simple network design which can tune vitrimer properties via altering the crosslinking density and side-group effects.

Modified Nanoclays/Straw Fillers as Functional Additives of Natural Rubber Biocomposites

Increasingly, raw materials of natural origin are used as fillers in polymer composites. Such biocomposites have satisfactory properties. To ensure above-average functional properties, modifications of biofillers with other materials are also used. The presented research work aimed to produce and characterize elastomeric materials with a straw-based filler and four different types of montmorillonite. The main research goal was to obtain improved functional parameters of vulcanizates based on natural rubber. A series of composites filled with straw and certain types of modified and unmodified nano-clays in various ratios and amounts were prepared. Then, they were subjected to a series of tests to assess the impact of the hybrids used on the final product. It has been shown that the addition of optimal amounts of biofillers can, inter alia, increase the tensile strength of the composite, improve damping properties, extend the burning time of the material and affect the course of vulcanization or cross-linking density.

Synthesis, Characterization and Electrical Conductivity of Silver Doped Polyvinyl Acetate/Graphene Nanocomposites: A Novel Humidity Sensor

In the present study, we have synthesized conducting polymer nanocomposites consist of silver nanoparticles (AgNPs), graphene, and polyvinyl acetate (PVAc) emulsion. The synthesized nanocomposite was characterized by UV/Vis, FT-IR, XRD, TGA, and SEM techniques. SEM images showed that AgNPs and graphene sheets are well dispersed in the PVAc matrix. The electrical conductivities of the nanocomposites were examined using the impedance analyzer instrument. It was ascertained that polymer composite containing silver nanoparticles and graphene exhibit higher conductivities. The PVAc-AgNPs/Graphene nanocomposite was also used as potential conducting materials for humidity measurement.

Buildup of Multi-Ionic Supramolecular Network Facilitated by In-Situ Intercalated Organic Montmorillonite in 1,2-Polybutadiene

The development of a sacrificial bond provided unique inspiration for the design of advanced elastomers with excellent mechanical properties, but it is still a huge challenge to construct a homogenous polar sacrificial network in a nonpolar elastomer. In this effort, we proposed a novel strategy to engineer a multi-ionic network into a covalently cross-linked 1,2-polybutadiene (1,2-PB) facilitated by in-situ intercalated organic montmorillonite (OMMT) without phase separation. XRD, SEM, and TEM analysis were carried out to characterize the microstructure of the resulting polymers. Crosslinking density, dielectric performance, and cyclic tensile tests were used to demonstrate the interaction of zinc methacrylate (ZDMA) and OMMT. The dynamic nature of ionic bonds allowed it to rupture and reform to dissipate energy efficiently. Stretching orientation brought parallelism between polymer chains and OMMT layers which was beneficial for the reconstruction of the ionic network, ultimately resulting in high strength and a low stress relaxation rate. Overall, our work presented the design of a uniform and strong sacrificial network in the nano-clay/elastomer nanocomposite with outstanding mechanical performances under both static and dynamic conditions.

Effect of Compatibilization on Biobased Rubber-Toughened Poly(trimethylene terephthalate): Miscibility, Morphology, and Mechanical Properties

Fabrication of partially biobased poly(trimethylene terephthalate) (PTT) elastomeric blends was done via melt processing. Both natural rubber (NR) and epoxidized NR (ENR) were investigated as impact modifiers at 40 wt % loading to avoid lowering the overall biobased content of the blend system below that of the PTT alone (35% renewable content), along with maleated polybutadiene rubber (MR) and dicumyl peroxide (DCP) as reactive compatibilizers. The compatibility of the blend components was investigated using contact angle, rheometry, and scanning electron microscopy (SEM). The interfacial tensions and work of adhesions indicated that ENR was more miscible than NR in the PTT blend system, which was corroborated by the higher shear viscosity of the ENR blends and strong shear thinning behavior. Additionally, the predictive modeling of viscosity ratios on the elastomer-thermoplastic morphology was found to match the SEM micrographs with the dispersed elastomeric phase within the PTT matrix. The SEM images of the blends also establish that both the compatibilizers reduced the rubber inclusions size, though DCP hampered the impact performance as compared to the MR. In the presence of the MR, there was an increased cross-linking and observed variation in the Fourier transform infrared peaks demonstrating chemical interactions between the maleic anhydride groups with the PTT that allowed for the impact strength to reach 137 J·m^-1 or 4.5 times that of the neat PTT, with the modulus of toughness increased by 82% and an elongation at yield of 50% because of the flexibility and amorphous nature of the rubber constituent.

The Effect of Clay/Multiwall Carbon Nanotube Hybrid Fillers on the Properties of Elastomer Nanocomposites

The hybrid fillers of 1D multiwalled carbon nanotubes (MWNT) and 2D montmorillonite (MMT) have led to excellent physical and chemical properties in high performance elastomer nanocomposites. In this study, the hybridization of PDDA (polydiallyldimethylammonium chloride) functionalized MWNT (P-MWNT) and hydroxyl-functionalized MMT (H-MMT) was prepared by the electrostatic interaction between the positive charge on the MWNT and the negative charge on the MMT using a simple solution mixing process. Also, a styrene-butadiene rubber (SBR) nanocomposite containing the hybrid nanofillers was prepared to improve the dispersion of nanofillers with SBR latex. The SBR nanocomposites with the hybrid nanofillers exhibited outstanding mechanical properties including modulus, tensile strength, and elongation at break, due to the enhanced interfacial bonding with the elastomer matrix. Furthermore, the hybrid nanofillers in the SBR matrix showed superior thermal and electrical properties and gas barrier performance at low loadings. The synergistic effects of the SBR produced by the hybridized nanofillers will open up new opportunities for elastomer composites with high performance.

Design of Self-Healing Supramolecular Rubbers by Introducing Ionic Cross-Links into Natural Rubber via a Controlled Vulcanization

Introducing ionic associations is one of the most effective approaches to realize a self-healing behavior for rubbers. However, most of commercial rubbers are nonpolar rubbers without now available functional groups to be converted into ionic groups. In this paper, our strategy was based on a controlled peroxide-induced vulcanization to generate massive ionic cross-links via polymerization of zinc dimethacrylate (ZDMA) in natural rubber (NR) and exploited it as a potential self-healable material. We controlled vulcanization process to retard the formation of covalent cross-link network, and successfully generated a reversible supramolecular network mainly constructed by ionic cross-links. Without the restriction of covalent cross-linkings, the NR chains in ionic supramolecular network had good flexibility and mobility. The nature that the ionic cross-links was easily reconstructed and rearranged facilitating the self-healing behavior, thereby enabling a fully cut sample to rejoin and retain to its original properties after a suitable self-healing process at ambient temperature. This study thus demonstrates a feasible approach to impart an ionic association induced self-healing function to commercial rubbers without ionic functional groups.

Thermal oxidative and ozone oxidative stabilization effect of hybridized functional graphene oxide in a silica-filled solution styrene butadiene elastomer

Modification of fGO and preparation of SSBR nanocomposites; the thermal oxidative stability mechanism of the fGO sheets-filled SSBR nanocomposites.

New insight into the flocculation behavior of hydrophilic silica in styrene butadiene rubber composites

We propose that modified silica filled rubber composites with moderate silica flocculation possesses preferable resistance to crack growth by the crack tip deflection mechanism.