Structural,thermal, and gas transport properties of HDPE/LLDPE blend‐based nanocomposites using a mixture of HDPE‐g‐MA and LLDPE‐g‐MA as compatibilizer

Nanocomposites based on high density polyethylene (HDPE)/linear low density polyethylene (LLDPE) blend were prepared by melt compounding in a twin‐screw extruder using organoclay (montmorillonite) as nano‐filler and a 50/50 wt% mixture of maleic anhydride functionalized high density polyethylene (HDPE‐g‐MA) and linear low density polyethylene (LLDPE‐g‐MA) as the compatibilizing system. The addition of a maleated polyethylene‐based compatibilizing system was required to improve the organoclay dispersion in the HDPE/LLDPE blend‐based nanocomposite. In this work, the relationships between thermal properties, gas transport properties, and morphology were correlated. The compatibilized nanocomposite exhibited an intercalated morphology with a small number of individual platelets dispersed in the HDPE/LLDPE matrix, leading to an significant decrease in the oxygen permeation coefficient of the nanocomposites. A decrease in the carbon dioxide permeability and oxygen permeability with increase of nanoclay was observed for the compatibilized nanocomposites. The carbon dioxide permeability of the compatibilized nanocomposites was lower than the carbon dioxide permeability of the uncompatibilized nanocomposites even with the low intrinsic barrier properties of the compatibilizer. These effects were attributed to a good dispersion of the inorganic filler, good wettability of the filler by the polymer matrix, and strong interactions at the interface that increased the tortuous path for diffusion. Theoretical permeability models were used to estimate the final aspect ratio of nanoclay in the nanocomposite and showed good agreement with the aspect ratio obtained directly from TEM images. POLYM. ENG. SCI., 56:765–775, 2016. © 2016 Society of Plastics Engineers     

Influence of carbon black in polychloroprene organoclay nanocomposite with improved mechanical,electrical and morphology characteristics

Abstract

The effect of carbon black on nanoclay filled polychloroprene (CR) composites has been investigated. The nanoclay loading is fixed at 5 part per hundred rubbers (phr), and carbon black loading varied from 5 to 20 phr in rubber compounds. The rubber nanocomposites are prepared in laboratory by mixing in two-roll mill. The addition of nanoclay enhances mechanical properties especially tear strength and decreases water absorption without change in electrical properties compared to gum rubber vulcanisates. Wide angle X-ray diffraction and transmission electron microscopy are used to study the microstructure of CR nanocomposites. The addition of 5 parts of nanoclay to 15 phr carbon black filled samples shows synergistic effect between the fillers and suggests that the reinforcement is due to a more developed filler network formation in hybrid filler system than that in single phase filler. Significant improvement in mechanical, electrical and low water absorption properties has been obtained with these nanoclay and carbon black filled rubber nanocomposites. The paper concludes that nanocomposites containing a mixture of organoclay and carbon black in right proportion can be a substitute for rubber components used in underwater cable and device encapsulation applications.     

Shape controlled spherical (0D) and rod-like (1D) silica nanoparticles in silica/styrene butadiene rubber nanocomposites: Role of the particle morphology on the filler reinforcing effect

Silica/styrene butadiene rubber (SBR) nanocomposites were prepared by blending method using shape-controlled spherical and rod-like nanoparticles with different aspect ratios as filler for the rubber reinforcement. The differently shaped silica particles were synthesized by sol–gel method using tetraethoxysilane (TEOS) and (3-mercaptopropyl) trimethoxysilane (MPTSM) as silica precursors, and cetyltrimethylammonium bromide (CTAB) as structure directing agent. This strategy allowed to study the influence of the particle morphology on the reinforcing effect independently of the silica surface chemistry and considering the aspect ratio as the only geometrical variance. Spherical and anisotropic rod-like particles, dispersed in the nanocomposites, formed a network of particles bridged by thin rubber layers throughout the SBR matrix. Moreover, differently oriented domains of aligned rods are observed when the aspect ratio of particles increases and is ≥2. Dynamic-mechanical properties demonstrated that the rod-like particles with the higher aspect ratio provided stronger reinforcement of the rubber. This was related to the self-alignment of the anisotropic particles and to the consequent larger filler/polymer interface, compared to that of spherical ones.     

An investigation on the bound rubber and dynamic mechanical properties of polystyrene particles‐filled elastomer

Polymeric nanoparticles have many advantages as the reinforcing filler of rubber. To investigate the mechanism of the reinforcement, nanocomposites of poly(styrene‐butadiene) rubber (SBR) filled with polystyrene (PS) particles as the reinforcing agents was prepared. Morphology and dynamical mechanical properties of PS particles‐filled SBR were investigated. It was found that the polymer chains of the elastomer could be absorbed onto the PS particles, in reminiscent to the concept of bound rubber in inorganic filler‐filled elastomeric system. The adsorbed polymer layer can form up glassy bridges between neighboring filler particles, leading to the agglomeration of the filler particles and the reinforcement of the elastomer. With higher filler content or smaller filler size, the numbers of the glassy bridges increase, and the modulus of the elastomer increases. With higher strain or higher temperature, the filler–filler interaction is disrupted and the material is softened. The study discovered the existence of bound rubber in PS particles‐filled elastomer and illustrated its influence on the dynamic mechanical properties, which could be helpful to design the polymeric nanoparticles for rubber reinforcement. POLYM. COMPOS., 38:1112–1117, 2017. © 2015 Society of Plastics Engineers     

Effect of nanoclay on the mechanical and damping properties of aramid short fibre‐filled styrene butadiene rubber composites

The effect of nanoclay loading on the alteration of tensile and dynamic mechanical properties of aramid short fibre‐filled styrene butadiene rubber composites was investigated. In all the composites, 20 phr of N330 black was used. Dynamic mechanical thermal analysis was used to investigate the viscoelastic damping at lower dynamic strains. Compressive hysteresis was evaluated to characterize higher strain static damping properties. Matrix–fibre interaction and filler distribution were investigated using morphological analyses. Matrix–filler interface, estimated by the half height width of the tan δ peak, plays a major role in energy dissipation. The matrix–fibre interaction parameter shows a similar trend with low strain tensile stress values. Nanoclay addition to the composites leads to improved elongation at break and frequency damping properties. Compressive hysteresis reflects no improvement of hysteresis with nanoclay loading. Dynamic storage moduli, matrix–fibre interaction parameter and energy dissipation properties of the short fibre‐filled composites are negatively affected by nanoclay addition. However, ultimate elongation is improved markedly on nanoclay addition. In respect of tensile strength and elongation at break values, two composite samples (KF5NC10 and KF10NC10) offer optimum properties. Copyright © 2009 Society of Chemical Industry     

Effect of carbon black/nanoclay hybrid filler on the dynamic properties of natural rubber vulcanizates

In this study, natural rubber (NR) nanocomposites based on carbon black (CB) and two poly(ethylene glycol) (PEG)‐modified clay hybrid filler were fabricated. The morphology and mechanical properties were studied. The dynamic properties of NR vulcanizates were investigated over a range of strain amplitude at two temperatures. It was found that NR with hybrid filler exhibits superior mechanical properties over that with CB as single phase filler. The hybrid filler causes a significant alteration in the dynamic properties of rubber. The Payne effect becomes more pronounced in rubber with modified clay. A decrease in loss factor (tanδ) was observed for rubber with hybrid filler also. The results revealed that the inclusion of nanoclay (NC) could induce a stronger and more developed filler network. Because of the anisotropy of the nanolayers, NC would depress the reconstruction of filler network, or lower the reformation rates when broken down under deformation, giving rise to lower tanδ value at broad temperature range as well as strain amplitude. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Modeling properties of nylon 6/clay nanocomposites using composite theories

The reinforcement of nylon 6 by layered aluminosilicates (LAS) and glass fibers was examined using the composite theories of Halpin-Tsai and Mori-Tanaka. Theoretical comparisons show that exfoliated LAS offer superior reinforcement to glass fibers owing to the filler's high modulus, high aspect ratio, and its ability to reinforce in two directions. The effect of incomplete exfoliation of simple stacks of LAS on nanocomposite modulus was also examined. Increasing the number of platelets per stack and the gallery spacing between platelets results in a dramatic decrease in reinforcing efficiency. The predictions were benchmarked against experimental data for nylon 6 nanocomposites based on organically modified montmorillonite and glass fibers. The quantitative determination of the morphology of the nanocomposites is non-trivial due to the large distribution of filler shapes and sizes present. Thus, a detailed experimental procedure for determining the aspect ratio of the nanocomposites is reported. The composite theories satisfactorily capture the stiffness behavior of both types of composites. Furthermore, experimental heat distortion temperatures and those predicted from modeling the dynamic mechanical properties of nanocomposites are in reasonable agreement.     

Transport properties of natural rubber latex layered clay nanocomposites

Natural rubber latex layered clay nanocomposites were prepared with low loadings of nanoclay using conventional compounding technique. A higher loading of clay resulted in processing difficulties due to viscosity build up. X‐ray analysis showed that nanocomposites in which layered silicate layers were either delaminated or ordered as in an intercalated structure was obtained. Partially exfoliated structure was observed from TEM photographs of nanocomposites with 3 phr nanoclay. The transport properties, sorption, diffusion, and permeation coefficients were measured using the solvent toluene at 303 K. A higher decrease for the diffusion coefficient for nanocomposites directs the presence of tortuous path for the diffusing molecules. Thermodynamic parameters show a better compatibility for the silicates with rubber resulted in the formation of an elastomeric network. Gas permeability results of the nanocomposites suggest a better barrier resistancefor oxygen molecules even in lower loading of nanoclay and different gas transport models (Nielsen, Bharadwaj, Cussler) were applied to describe the behavior of these nanocomposites. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Comparing styrene butadiene rubber–clay nanocomposites prepared by melt intercalation and latex‐coagulation methods

Among different methods for preparation of rubber–clay nanocomposites, melt intercalation and latex‐coagulation methods are more practiced. In this study, dispersion of pristine nanoclay by the latex‐coagulation method and organically modified nanoclay by the melt‐intercalation method in styrene butadiene rubber were compared, based on the same amount of mineral clay in the composites. Dispersion of nanoclay was examined by X‐ray diffraction before and after vulcanization, and by atomic force microscopy after vulcanization. It was shown that final structure of nanoclay in the composites was intercalated by both methods, with better dispersion resulting from coagulation of latex over mixing in the melt state. Dynamic–mechanical–thermal analysis and tension tests were used to further assess dispersion and polymer–filler interactions. These tests confirmed better dispersion and larger interfacial area for pristine nanoclay in the latex‐coagulated rubber through observing lower peak loss factor, higher growth of stress in stretching, and lower elongation at break when compared with those for the nanocomposite prepared by the melt mixing. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Nanocomposites based on epoxidized poly(styrene-co-butadiene) rubber and graphene nanoplatelets

Nanofillers play as reinforcing agents of the polymer matrix. The reinforcement and dynamic mechanical properties of nanocomposites based on filled epoxidized-poly(styrene-co-butadiene) rubber are investigated. The modification of the polymer matrix allows improvement in polymer–filler interaction, and thus the mechanical properties of the vulcanizates. Here, the rubber was modified by introducing the epoxy functional groups in the matrix. The quantification for epoxidation rate was analyzed by means of NMR and ~8.8% epoxidation was optimized. The nanocomposites were prepared by melt-mixing technique. The influence of rubber epoxidation in enhancing dynamic mechanical and thermal properties was demonstrated. Stable filler networking using exfoliated graphene nanoplatelets (xg C750) and carbon black (CB-N234) in epoxidized rubber is described through multihysteresis measurements. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47802.     

Effect of nano clay on the constrained polymer volume of chlorobutyl rubber nanocomposites

The dynamic mechanical properties of chlorobutyl rubber nanocomposites containing different varieties of clay have been investigated. The clay moieties have been chosen so that they vary in their organic modification, modifier concentration, and d spacing. The viscoelastic properties such as storage modulus, damping behavior, and loss modulus of polymer composites depends on matrix filler interaction, crystallinity, and extent of crosslinking. The prepared composites were characterized by X Ray Diffraction, and the extend of exfoliation/intercalation was studied. It has been observed that the storage modulus of the composites increased with the addition of filler due to the enhancement in stiffness of the material. The damping behavior was found to decrease with the addition of filler and this was attributed to the restricted movement of the polymer segments. The higher surface area to volume ratio of the layered silicate resulted in the better interaction between the polymer matrix and filler. The variation of loss as well as storage modulus of the nanocomposites were evaluated as a function of filler loading, and a comparison of the properties of the rubber nanocomposites containing different organic clay was also carried out. Finally, a calculation of constrained volume of polymer chains was done in the nanocomposites. POLYM. COMPOS., 36:2135–2139, 2015. © 2014 Society of Plastics Engineer     

Barrier properties of chlorobutyl nanoclay composites

Elastomeric materials are used as barriers to protect workers against exposure to chemicals. The effectiveness of a polymer as a chemical protective material depends on the rate of permeation of chemicals through it. The permeation rate is dependent on the type and amount of fillers added into the polymer matrix. In this study, Chlorobutyl nanoclay composites were prepared by addition of organically modified and unmodified nanoclays at different filler loadings. The nanocomposites were swollen in three solvents of varying cohesive energy density until equilibrium and desorption experiments were carried out. The data obtained from desorption experiments was used to determine the diffusion coefficients. The concentration‐dependent diffusion coeffecient (D) was calculated at high and low concentration regions and it was found that D is one‐order less in lower concentration region than in the higher concentration range. The aspect ratio of the nanoclay fillers in the composite was calculated by assuming square and disc shapes and it was found to vary with the type of solvent and the used and filler loading. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3630–3637, 2006     

Effect of surface modification of silicon carbide nanoparticles on the properties of nanocomposites based on epoxidized natural rubber/natural rubber blends

Improvement of the properties of rubber nanocomposites is a challenge for the rubber industry because of the need for higher performance materials. Addition of a nanometer‐sized filler such as silicon carbide (SiC) to enhance the mechanical properties of rubber nanocomposites has rarely been attempted. The main problem associated with using SiC nanoparticles as a reinforcing natural rubber (NR) filler compound is poor dispersion of SiC in the NR matrix because of their incompatibility. To solve this problem, rubber nanocomposites were prepared with SiC that had undergone surface modification with azobisisobutyronitrile (AIBN) and used as a filler in blends of epoxidized natural rubber (ENR) and natural rubber. The effect of surface modification and ENR content on the curing characteristics, dynamic mechanical properties, morphology and heat buildup of the blends were investigated. The results showed that modification of SiC with AIBN resulted in successful bonding to the surface of SiC. It was found that modified SiC nanoparticles were well dispersed in the ENR/NR matrix, leading to good filler‐rubber interaction and improved compatibility between the rubber and filler in comparison with unmodified SiC. The mechanical properties and heat buildup when modified SiC was used as filled in ENR/NR blends were improved. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45289.     

Effect of hybrid reinforcement based on precipitated silica and montmorillonite nanofillers on the mechanical properties of a silicone rubber

Silicone rubber (SR) nanocomposites containing precipitated silica (PS), montmorillonite (MMT), and PS/MMT hybrid fillers were prepared through melt‐mixing technique. In the SR/PS/MMT nanocomposite, the hybrid filler weight ratio was increased progressively from 0.4 to 1.7 while keeping the MMT weight constant. The viscosity, cure characteristics, and mechanical properties of the nanocomposites were subsequently measured. The optimum cure time increased, and the scorch time and rate of cure decreased. Furthermore, when the hybrid filler weight ratio was raised to its optimum, the tensile strength, Young's modulus, modulus at 100 and 300% elongation (M100 and M300), elongation at break, stored energy density at break, and hardness of the nanocomposite improved. The stress–strain properties of the nanocomposite with the hybrid filler improved at high deformation in comparison with those containing the PS and MMT fillers. The MMT filler exfoliated in the SR/MMT nanocomposite but did not in the nanocomposites containing the hybrid filler. Notably, the mechanical properties of the nanocomposite benefitted from the hybrid filler. This was due to the filler–filler and filler–rubber network formation in the rubber by the PS particles. Finally, effect of the PS, MMT, and hybrid fillers on the energy loss or hysteresis of the rubber was measured. POLYM. ENG. SCI., 54:1909–1921, 2014. © 2013 Society of Plastics Engineers     

Effect of nanostructures of modified clay–carbon black on physico‐mechanical,electrical, and acoustic properties of elastomer‐based composites

Elastomeric composites based on nitrile rubber (NBR), carbon black (CB), and organically modified nanoclay (NC) were prepared using a laboratory two‐roll mixing mill. Influences of the hybrid filler system (CB+NC) on various properties of NBR compound were analyzed. It was found that the addition of hybrid filler (CB+NC) over only carbon black enhances various properties. It was also found that the addition of nanoclay to the rubber matrix effectively improved key properties. Acoustics and electrical properties were modified with reduced water absorption because of layered clay platelets. The lower volume resistivity of NBR composites reflected better electrical conductivity attributed to the presence of nanoclay leading to effective filler connectivity. X‐ray diffraction and transmission electron microscopy measurements revealed that nanoclays were mostly intercalated and were uniformly dispersed. Use of calcium stearate facilitated dispersion of nanoclay in the rubber matrix which was observed through the formation of nanostructures including “nano” and “halo” units. Time temperature superposition in dynamic mechanical analysis test of the composites indicated lower mechanical loss in the frequency range of interest. The advantages accruing due to overall property enhancement, including lower water absorption, and better electrical and excellent acoustic properties of NBR composites make it suitable as underwater acoustic transparent materials for transducer encapsulation application. POLYM. COMPOS., 37:1786–1796, 2016. © 2014 Society of Plastics Engineers     

Tailoring Silica Surface Properties by Plasma Polymerization for Elastomer Applications

The surface properties of reinforcing fillers are a crucial factor for dispersion and filler–polymer interaction in rubber compounds, as they strongly influence the final vulcanized properties of the rubber article. Silica is gaining more and more importance as reinforcing filler for rubbers, as it allows for a reduction of rolling resistance and thus energy losses in tires, compared to the use of carbon black as filler. However, silica and common elastomers differ greatly in polarity and, therefore, are difficult to mix and thus have little interaction. In the present study plasma-coating of silica-filler with acetylene, thiophene and pyrrole is applied, and the surface-treated silicas are blended with S-SBR rubber, in an attempt to enhance the compatibility between the two. The dispersion and reinforcing effects of the modified silicas are investigated and compared with untreated and silanized silica. The relative rankings of the various coatings in reduction of filler–filler interaction, improved dispersion, enhanced polymer–filler interaction, apparent crosslink density and tensile mechanical properties are mutually different. Where the best silica dispersion and largest reduction in filler–filler interaction are obtained with polyacetylene coating and the worst with polythiophene coating, but the tensile properties achieved with the polythiophene coating are far better than all others. Apparently, the sulfur contained in the thiophene-moiety enhances the filler–polymer interaction and contributes to the degree of crosslinking. Unmodified silica performs worst in all aspects, also because its acidic nature harms the preferably alkaline vulcanization process. Silane treatment of silica has a positive effect on reduction of filler–filler interaction and improved dispersion, but has little effect on polymer–filler interaction in the still unvulcanized state. Its tensile properties after vulcanization are comparable with polyacetylene- or polypyrrole-coated silica. This investigation shows that the compatibility and interaction of silica with a polymer can be controlled by tailoring the surface energy of the filler by coating with plasma polymers. An appropriate monomer for the plasma polymerization process allows to improve the cured rubber properties.     

Permeation characteristics and modeling of barrier properties of multifunctional rubber nanocomposites

Nanocomposites used in various applications, like tires, diaphragms etc. must exhibit superior gas permeation behavior along with other properties. Oxygen permeability characteristics of such multifunctional styrene butadiene rubber based nanocomposites, including thermodynamics and kinetic aspects of transport have been discussed here. For the first time, these characteristics have been determined for nano, micro and dual filler based multifunctional nanocomposites. The permeability of the nanocomposites was remarkably decreased by the presence of high loadings of montmorillonite due to high aspect ratio and exquisite dispersion, ascertained from morphological studies. The results were explained by the increment in tortuosity and also correlated with the reduction in free volume. Relative permeabilities were compared to predictions of existing permeation models and a novel function was successfully introduced to address deviations. Finally, the enhanced barrier properties of dual filler based nanocomposites have been explained by the formation of zeta potential driven “nano-blocks” and “nano-channels”.     

Dynamic rheology studies of carboxylated butadiene–styrene rubber/cellulose nanocrystals nanocomposites: Vulcanization process and network structures

A series of dynamic strain amplitude oscillatory shear experiments for vulcanization process of carboxylated butadiene‐styrene rubber/cellulose nanocrystals (XSBR/CNs) nanocomposites were performed to investigate the relationship between non‐linear viscoelasticity behaviors and crosslink network including chemical crosslink of XSBR and CNs‐related filler networks. The results showed that CNs accelerated the onset of gelation of XSBR and provided additional cross‐links to the XSBR/CNs composites. Because of the high aspect ratio, a homogeneous dispersion of rod‐like CNs was easy to form a rigid filler network within XSBR matrix. The XSBR chains adsorbed onto the surface of CNs through the hydrogen bonding interaction functioned as the cushioning materials during the oscillatory strain shear, resulting in an equilibrium condition of breakage and reforming CNs‐related networks at a relative higher strain magnitude. The kinetic XSBR chains during vulcanization and curing temperature were beneficial to accelerated aggregate forming of CNs, resulting in a reduced onset dropping stain magnitude. POLYM. COMPOS., 36:623–629, 2015. © 2014 Society of Plastics Engineers     

Effect of polymer–clay interaction on solvent transport behavior of fluoroelastomer–clay nanocomposites and prediction of aspect ratio of nanoclay

Diffusion and sorption of methyl ethyl ketone and tetrahydrofuran through fluoroelastomer‐clay nanocomposites were investigated in the temperature range of 30–60°C by swelling experiments. Slightly non‐Fickian transport behavior was found for these nanocomposites, having variation of type of nanoclay and loading. Different transport parameters depend on the size and shape of the penetrant molecules. The results were used to study the effect of nanoclay on the solvent transport‐properties of nanocomposites and their interactions with solvents. The diffusion coefficient of methyl ethyl ketone at 30°C for neat rubber was 1.43 × 10^?8 cm² s^?1, while those of the unmodified and the modified clay filled samples at 4 phr loading were 0.24 × 10^?8 and 0.50 × 10^?8 cm² s^?1, respectively. At 8 and 16 phr loading of the unmodified clay, it was found to be 0.44 × 10^?8 and 0.64 × 10^?8 cm² s^?1, respectively. The samples were also reswelled after deswelling. Surprisingly, transport behavior became Fickian on reswelling. Interestingly, ratio of diffusion coefficients of the filled system to the neat system was found to be almost same for the first time swelling and reswelling experiments. The results showed that better polymer‐clay interaction in the case of the unmodified‐clay filled nanocomposites is responsible for enhanced solvent‐resistance property. From the permeation data, for the first time, aspect ratio of nanoclays in different composites was calculated and found to have good correlation with the morphology data obtained from transmission electron microscopy. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Effect of carbon‐based nanoparticles on the cure characteristics and network structure of styrene–butadiene rubber vulcanizate

The network structure of styrene–butadiene rubber (SBR) in the presence of carbon black (CB) with two different structures and multi‐walled carbon nanotubes (MWCNTs) was investigated. Swelling behaviour, tensile properties at various strain rates and cure kinetics were characterized. Experimental data were analysed using the Flory–Rehner model as well as the tube model theory. It is found that the network structure of CB‐filled SBR follows a three‐phase composite model including rigid particles, semi‐rigid bound rubber and matrix rubber. This bound rubber is postulated to be critical for the mechanical and deformational properties, development of crosslinking density in matrix rubber and polymer–filler interaction. For MWCNT‐filled SBR, the bound rubber does not show a substantial contribution to the network structure and mechanical performance, and these properties are greatly dominated by the higher aspect ratio and polymer–filler interaction. Additionally it is deduced that the crosslinking density of matrix rubber increases on incorporation of the fillers compared to unfilled matrix rubber. Copyright © 2012 Society of Chemical Industry