Comparative study of pineapple leaf microfiber and aramid fiber reinforced natural rubbers using dynamic mechanical analysis

Natural fiber is often considered inadequate for high performance reinforcement of polymer matrix composites. However, some natural fibers have relatively high mechanical properties with modulus close to that of high-performance synthetic fibers. Since the reinforcing efficiency of a short fiber is determined not only by the fiber modulus, but also by other physical properties such as the length to diameter ratio. Here it is shown, for the first time, that pineapple leaf fiber, whose modulus is somewhat lower than that of aramid fiber, can be used to reinforce natural rubber more effectively than aramid fiber. The situation was achieved by breaking down the fiber bundles into the constituent microfibers to gain very high aspect ratio. Comparisons were made at fiber contents of 2, 5 and 10 parts (by weight) per hundred of rubber (phr) using dynamic mechanical analysis over a range of temperature. The results reveals that at temperature below the glass transition of the matrix rubber and low fiber contents of 2 and 5 phrs, aramid fiber displays slightly better reinforcement efficiency. At high temperatures of 25 and 60 °C and high fiber content of 10 phr, pineapple leaf microfiber clearly displays higher reinforcement efficiency than does aramid fiber. Surface modification of the fiber by silane treatment provides a slight improvement in reinforcing efficiency.     

Development of Natural Rubber-Fibrous Nano Clay Attapulgite Composites: The Effect of Chemical Treatment of Filler on Mechanical and Dynamic Mechanical Properties of Composites

Common nano clay fillers have layered structure. Some nano clays like Attapulgite (AT), Sepiolite have rod like fibrous structure. Compared to layered structured clay fibrous clay AT can undergo better dispersion in polymer matrix leading to better improvement in composite properties. Chemical modifications of AT are done through amine treatment as well as by amine+silane treatment to get chemically modified fillers AAT and SAT respectively. In the present investigation, nano composites are prepared using natural rubber (NR) filled with AT, AAT and SAT. Three different loadings of each filler are used namely 2.5, 5, and 10 phr (parts per hundred of rubber). Mechanical properties like tensile strength, elongation at break increase with the increase in filler loading up to 5 phr there after these properties marginally fall when loading is increased to 10 phr due to problem of filler dispersion at higher loading. However, modulus at 300% elongation and tear strength increases with the increase in filler loading up to 10 phr. Very similar trend can also be observed for composites with chemically modified fillers, AAT and SAT. But the degree of reinforcement is higher in the case of AAT and SAT compared to that of unmodified filler AT for the same filler loading. This difference is mainly due to better polymer-filler interaction and filler dispersion in the case of chemically modified clays AAT and SAT compared to unmodified AT. Tear strength of composites increases remarkably with the addition of AT and which is further enhanced when chemically modified clays AAT and SAT are added. Dynamic-mechanical analyses of different clay composites give idea about the difference in the degree of polymer–filler interaction due to chemical treatment of filler.     

Towards novel super‐elastic foams based on isoperene rubber: Preparation and characterization

A novel and conventional closed cell polyisoprene rubber (IR) foams were produced by a single step limited‐expansion and two step unlimited‐expansion foaming process, respectively. The effect of 3 to 12 part per hundred rubber (phr) of azodicarbonamide (ADC) foaming agent on their structure and properties of developed novel foams were studied. In developed novel foams, the density was strangely independent of ADC content; however, the cell sizes conversely related to ADC content and it decreased by 60% (555‐330 μm) and the internal cell pressure build up from 1 to 3.7 atm, which was related to pressure‐free foaming method. The both reasons of compressed gas trapped inside cells and constant density not only caused unique enhancement in novel foams mechanical properties as hardness and modulus but also improved their dynamic properties as hysteresis and elasticity. Results of conventional IR foams showed that, their foam density as well as dynamic and mechanical properties sharply decreased with increasing ADC content from 3 to 12 phr. For clear expression, in samples with 12 phr of ADC, novel developed foams have more foam density (180%), more hardness (240%), more modulus (290%), and smaller cell size (75%) than conventional foams. Finally, novel developed foams were super‐elastic material with no hysteresis and no plastic deformation while conventional foams had 40% hysteresis and 10% plastic deformation under the same compression conditions.     

Rubber networks containing unattached macromolecules. I. Linear viscoelastic properties of the system butyl rubber–polyisobutylene

Mixtures of butyl rubber with polyisobutylene (molecular weights 0.055 and 2.3 × 10⁶) up to 50% by weight were crosslinked by sulfur, leaving the polyisobutylene molecules free to reptate in the butyl rubber network. Linear viscoelastic properties were measured in shear creep for periods up to 5 × 10⁵ sec at 25°C and oscillating shear deformations from 0.1 to 3 Hz, at temperatures from 2 to 63°C. Comparison with the properties of a butyl rubber crosslinked without polyisobutylene showed contributions to creep and mechanical loss attributable to the reptating species. Comparison with the properties of polyisobutylene (higher molecular weight) showed that the relaxation times associated with the reptating species in the upper part of the terminal zone are the same for different polyisobutylene contents (25% and 50%) and for 100% polyisobutylene in which no permanent network is present; their contributions to modulus appear to be proportional to the volume fraction of polyisobutylene to a power of about 2/3. The time required in stress relaxation for the portion of the modulus attributable to the reptating species to decay to half its plateau value is, based on the two molecular weights employed, proportional to the polyisobutylene molecular weight to the third power. The magnitude of the associated mechanical loss and its location on the frequency scale can thus be controlled independently.     

Optimisation of physical and mechanical properties of rubber compounds by response surface methodology--Two component modelling using vegetable oil and carbon black

Response surface methodology was used for predicting the optimal composition of vegetable oil and carbon black in rubber compounding. Central composite rotatable design for two variables at five levels was chosen as the experimental design. The data obtained from measurement of properties was fitted as a two variable second order equation and were plotted as contour plots using programme developed in MATLAB v.5. It is observed from the contour plots that the increase in cross-link density caused by the formation of rubber mono-layer from its multi-layer on increasing the carbon black loading upto the central point (50 phr) of experimental region increases 300% modulus and elongation at break and reduces the ultimate properties like tear strength and tensile strength. On the other-hand hardness increases with increase in solid inclusion of carbon black. From the contours it is observed that the addition of vegetable oil upto 2-3 phr, cross-link density increases due to its coupling action leading to increase in hardness and modulus and lowering of ultimate properties like tensile strength and elongation at break. Addition of further amount of vegetable oil shows less coupling and more plasticising effect leading to increase in tear strength, tensile strength and elongation at break and decrease in hardness and 300% modulus.     

Effect of high temperature on reduction-controlling reaction rate of agricultural waste chars and coke with steelmaking slag

In the present research, mechanical and thermal properties of high-density polyethylene/wood flour were improved by incorporating nanoclay (Cloisite 30B) and antioxidant (Irganox B225) in the compound. Design of experiments was carried out to optimize composition among nine compounds and to investigate the effect of nanoclay and antioxidant (0–5 phr) and (0–0.4 phr), respectively. The results of mechanical tests showed approximately 24% increase in the tensile strength of compounds containing 2.5 and 5.0 part per hundred (phr) of the nanoclay in the composite compared with the same samples without nanoclay. The tensile modulus of composites increased 7.3% by increasing the level of nanoclay from 0 to 2.5 phr. However, a further increase in the nanoclay content led to a 4.3% decrease in tensile modulus. Evaluation of the thermal oxidation stability of samples confirmed that the thermal oxidation of composites decreased with increasing nanoclay from 0 to 5.0 phr and increased significantly with the addition of the antioxidant.

     

Radiation vulcanization of NR/SBR composite enhanced with different polyfunctional monomers

The effect of different polyfunctional monomers (PFMs) as enhancing agents on the properties of natural rubber/styrene-butadiene rubber blend reinforced with 40 (phr) part per hundred part of rubber, by weight of HAF carbon black and vulcanized with gamma irradiation was investigated. The coagents N,N’ methylene diacrylamide (MDA), trimethylol propane-trimethacrylate (TMPTMA) and trimethylol-methane tetraacrylate (TMMTA) were used at a constant content of 5 phr. The physico-chemical properties such as tensile strength, tensile modulus at 100 % elongation, elongation at break, gel fraction and swelling number were studied. The results indicated that the properties are greatly improved by PFMs at lower doses. TMMTA as coagent is more effective than TMPTMA and MDA.     

Effect of Electron Beam Irradiation and Ethylene Vinyl Acetate Copolymer on the Properties of NBR/HDPE Blends

The mechanical and physical properties of blends based essentially on nitrile butadiene rubber (NBR) and different ratios of high density polyethylene (HDPE) up to 25 parts per hundred part of rubber (phr) before and after electron beam irradiation were investigated. The values of tensile strength (TS), tensile modulus at 50% elongation (M₅₀), hardness and gel fraction % (GF%) of NBR/HDPE blends were increased with both irradiation dose and by increasing the content of HDPE in the blends. On the other hand, the values of elongation at break (E _b ) were decreased with both irradiation dose and the content of HDPE in the blends. By loading NBR/HDPE (100/25) blend with ethylene vinyl acetate (EVA) copolymer the mechanical and physico-chemical properties were improved. Moreover, the degree of improvement is proportional to the loading content of EVA.     

Morphology and Mechanical Properties of Palm Based Fly Ash Reinforced Dynamically Vulcanized Natural Rubber/Polypropylene Blends

Palm based fly ash (PFA) is a solid waste of palm oil processing industry which contains silica components. These components are typically used to improve the mechanical properties of rubber-based products. This research aims to study the effect of the PFA as a filler on the morphology and properties of thermoplastic vulcanizate (TPV) based on a mixture of natural rubber (NR) and polypropylene (PP). TPV samples were prepared using the internal mixer at a mass ratio of NR/PP 70/30. Maleated polypropylene (MA-g-PP) 5% mass was added as a compatibilizer, filler content was varied from 15 to 45 per hundred rubber (phr). Paraffin and palm oil were added as a plasticizer with contents of 5 to 50 phr. Other additives include ZnO 5 phr, stearic acid 2 phr, trimethylquinone 1 phr, mercaptodibenzo-thiozyldisulfide 0.6 phr and 3 phr sulfur. The results showed that the use of PFA provides good tensile strength properties, a relatively homogeneous morphology, and low water absorption rate. The use of paraffin plasticizer produces a higher tensile strength compared to palm oil, but the elongation at break which produced the contrary. The best morphology and tensile properties of TPV (NR/PP 70/30) are on PFA and paraffin contents of 30 phr and 25 phr, respectively.     

High performance hybrid reinforcement of nitrile rubber using short pineapple leaf fiber and carbon black

Rubber composites with very high moduli at low elongation, high elongation at break and high ultimate breaking strength have been developed. The matrix was acrylonitrile butadiene rubber (NBR) and the hybrid (fibrous and particulate) reinforcements were short, fine pineapple leaf fiber (PALF) and carbon black. The amount of PALF was fixed at 10 parts (by weight) per hundred of rubber (phr) while that of carbon black was varied from 0 to 30 phr. Uniaxial NBR composites were prepared. Tensile strength, elongation at break, modulus and tear strength of the hybrid composites were characterized in both longitudinal (parallel to the fiber axis) and transverse (perpendicular to the fiber axis) directions. The addition of carbon black causes the slope of the early part of the stress–strain curve to increase and also extends breaking to greater strains. At carbon black contents of 20 phr and above, the stress–strain relation displays an upturn at high elongations, providing greater ultimate strength. Comparison with the usual carbon black filled rubber shows that the composite behavior at low strains is determined by the PALF, and at high strains by the carbon black. This high performance PALF-carbon black reinforced NBR shows great promise for engineering applications.     

Preparation and Properties of Nanostructured Rubber Composites with Montmorillonite

Montmorillonite exfoliated nanoclay was prepared by treating montmorillonite with an alkyalmmonium salt. It has been characterized by FT-IR spectroscopy and thermal analysis (TGA-DTA). The nanoclay composites, in which the rubber matrix was introduced by mixing solutions of the elastomer with the organically modified clay was then compounded with carbon black filler at 2.5, 5, 10, 15 phr loading level of nanoclay. The sulfur cured rubber samples were tested against a reference compound not filled with the nanoclay. Rheometrical and scorch measurements have shown that the nanoclay increases the curing speed and reduces the scorch safety. A very high reinforcement and stiffening effect due to the nanoclay was observed especially at 5 and 10 phr nanoclay filling level and especially at low extension modulus which can be increased up to 40% its original level than in the reference compound. An anisotropic behavior has been recorded in the stress-strain curve: for instance the 50% modulus was found >20% higher when measured parallel to the alignment of the exfoliated nanoclay lamellae in comparison to the modulus perpendicular to the lamellae orientation. The compounds with nanoclay show no adverse effects in tensile strength and in tear resistance, in De Mattia crack initiation and in abrasion resistance. Nanoclay reduces also the hysteresis and heat build up of the rubber compounds.     

Curing and Physical Properties of Natural Rubber/Wood Flour Composites

Natural rubber based composites were prepared by incorporating Wood flour of two different particle size ranges (250–300 µm) and (300–425 µm) and concentrations (15 and 30 phr) into the matrix, using a Banbury® internal mixer according to a base formulation. Curing characteristics of the samples were studied. Influence of particle size and loading of filler on the properties of the composites was analyzed. Results obtained show that the addition of wood flour to natural rubber increased scorch time and curing time and caused improvement in modulus at 300% strain and in tear properties. However, it decreased tensile strength and elongation at break. The particle size range of 300–425 µm was found to offer the best overall balance of mechanical and dynamic properties (tan δ and viscous torque). Swelling behavior of the composites in toluene was also analyzed in order to determine the rubber volume fraction and crosslinking density. Composites with the bigger particle size wood flour were found to have greater crosslinking density than the ones with smaller particle size, fact that could possibly indicate a better rubber-filler interaction in the former. Major percentage of filler increased slightly this interaction. Water absorption behavior of the composites with wood flour reached a maximum of 12% w/w when 30 phr of filler were incorporated; nonetheless, particle size did not affect this property. The ageing study in presence of air at 70 °C revealed that natural rubber composites with wood flour maintained the same classification cell with temperature as the pure rubber. A compound with 30 phr of carbon black was prepared for comparative purposes. Results obtained were as expected. Scorch time decreased and higher values of modulus at 300% strain and tensile strength were achieved, due to strongest interaction between filler and elastomer.     

Effects of epoxidized natural rubber as a compatibilizer in melt compounded natural rubber-organoclay nanocomposites

Nanocomposites containing natural rubber (NR) as matrix, epoxidized natural rubber (ENR) as compatibilizer and organophilic layered clay (organoclay) as filler were produced in an internal mixer and cured using a conventional sulphuric system. The effects of ENR with 25 (ENR 25) and 50 mol% epoxidation (ENR 50), respectively, were compared at 5 and 10 parts per hundred rubber (phr) concentrations. The organoclay content was fixed at 2 phr. Cure characteristics, clay dispersion, (thermo)mechanical properties of the nanocomposites were determined and discussed. Incorporation of ENR and organoclay strongly affected the parameters which could be derived from Monsanto MDR measurements. Faster cure and increased crosslink density were attributed to changes in the activation/crosslinking pathway which was, however, not studied in detail. The organoclay was mostly intercalated according to X-ray diffraction (XRD) and transmission electron microscopic (TEM) results. The best clay dispersion was achieved by adding ENR 50. This was reflected in the stiffness of the nanocomposites derived from both dynamic mechanical thermal analysis (DMTA) and tensile tests. The tensile and tear strengths of the ENR 50 containing nanocomposites were also superior to the ENR 25 compatibilized and uncompatibilized stocks.     

Structure and properties of natural rubber/butadiene rubber (NR/BR) blend/sodium-montmorillonite nanocomposites prepared via a combined latex/melt intercalation method

75/25 (wt %) NR/BR blend/clay nanocomposites were prepared via a combined latex/melt intercalation method, for the first time. At first, NR latex was mixed with various amounts of the aqueous sodium montmorillomte (Na-MMT) dispersion. Obtained mixtures were co-coagulated by dilute solution of the sulfuric acid, washed several times with the distilled water and dried under vacuum. The NR/ clay compounds were then mixed with given amounts of the BR and vulcanizing ingredients in a 6-inch two-roll mill and then vulcanized at 150°C in a hot press. The nanocomposites have better mechanical properties than the clay-free NR/BR blend vulcanizates. Furthermore, modulus and hardness (Shore A) increased by increase of the clay loading in the range of 0–15 phr while tensile strength and elongation at break increased with increasing the clay content up to 5 phr and then decreased gradually by further increase of the clay loading. It was concluded from results of the XRD and mechanical test that nanocomposites containing less than 10 phr clay may show the fully exfoliated structure. With increasing the clay content to 10 and 15 phr, both non-exfoliated (stacked layers) and exfoliated structures may be observed simultaneously in the nanocomposites. TGA results indicated an improvement in main and end decomposition by increasing the clay loading.     

The Effect of 3-aminopropyltrimethyoxysilane (AMEO) as a Coupling Agent on Curing and Mechanical Properties of Natural Rubber/Palm Kernel Shell Powder Composites

This research is conducted using palm kernel shell powder (PKS) as filler in natural rubber The effect of 3-aminopropyltrimethoxysilane as coupling agent on composites were studied at different palm kernel shell loading i.e, 0 5, 10, 15 and 20 phr The palm kernel shell was crushed and sieved to an average particle size of 5.53 μm The palm kernel shell filled natural rubber composites were prepared using laboratory size two roll mill The curing characteristics such as scorch time, cure time and maximum torque were obtained from rheometer The palm kernel shell powder filled natural rubber composites were cured at 150^oC using hot press according to their cure time Curing characteristics, tensile properties, rubber-filler interaction and morphological properties of palm kernel shell powder filled natural rubber were studied Scorch time and cure time show reduction but tensile strength, elongation at break, modulus at 100% (M100) and modulus at 300% (M300) increased with the presence of 3-aminopropyltrimethyloxysilane Rubber-filler interaction studies showed that rubber filler interaction in natural rubber filled with palm kernel shell powder improved with incorporation of 3-aminopropyltrimethyoxysilane.     

The effect of alkanolamide loading on properties of carbon black-filled natural rubber (SMR-L), epoxidised natural rubber (ENR), and styrene-butadiene rubber (SBR) compounds

The effect of Alkanolamide (ALK) loading on properties on three different types of carbon black (CB)-filled rubbers (SMR-L, ENR-25, and SBR) was investigated. The ALK loadings were 1.0, 3.0, 5.0 and 7.0 phr. It was found that ALK gave cure enhancement, better filler dispersion and greater rubber–filler interaction. ALK also enhanced modulus, hardness, resilience and tensile strength, especially up to 5.0 phr of loading in SMR-L and SBR compounds, and at 1.0 phr in ENR-25 compound. Scanning electron microscopy (SEM) proved that each optimum ALK loading exhibited the greatest matrix tearing line and surface roughness due to better rubber - filler interaction.     

Comparative study on the effect of partial replacement of silica or calcium carbonate by bentonite on the properties of EPDM composites

The effects of the partial replacement of silica or calcium carbonate (CaCO₃) by bentonite (Bt) on the curing behaviour, tensile and dynamic mechanical properties and morphological characteristics of ethylene propylene diene monomer (EPDM) composites were studied. EPDM/silica/Bt and EPDM/CaCO₃/Bt composites containing five different EPDM/filler/Bt loadings (i.e., 100/30/0, 100/25/5, 100/15/15, 100/5/25 and 100/0/30 parts per hundred rubber (phr)) were prepared using a laboratory scale two-roll mill. Results show that the optimum cure (t₉₀) and scorch (t_S2) time decreased, while the cure rate index (CRI) increased for both composites with increasing Bt loading. The tensile properties of EPDM/CaCO₃/Bt composites increased with the replacement of CaCO₃ by Bt from 0 to 30 phr of Bt. For EPDM/silica/Bt composites, the maximum tensile strength and E_b were obtained at a Bt loading of 15 phr, with enhanced tensile modulus on further increase of Bt loading. The dynamic mechanical studies revealed a strong rubber-filler interaction with increasing Bt loading in both composites, which is manifested by the lowering of tan δ at the glass transition temperature (Tg) for EPDM/CaCO₃/Bt composites and tan δ at 40 °C for EPDM/silica/Bt composites. Scanning electron microscopy (SEM) micrographs proved that incorporation of 15 phr Bt improves the dispersion of silica and enhances the interaction between silica and the EPDM matrix.     

Properties Investigation of novel nitrile rubber composites with rockwool fibers

Rockwool is an inorganic fiber with interesting properties obtained from basaltic rocks. It can possibly be used in rubber technical products which work under critical conditions in several industries. This study aims to investigate properties of three short rockwool fibers/nitrile rubber composites. Ten formulations were prepared with 10, 25 and 40 phr of rockwool fibers with different length and modification. The composites were assessed on its morphological aspects, thermal, rheological, and mechanical behaviors. The results remarked that the rockwool fiber with chemical modification had better interfacial interaction with the polymer enhancing modulus at 100% of deformation, Shore A hardness, tear strength, Payne effect and stress relaxation under a compressive regime. An outstanding result was observed for the composite with 10 phr of fiber with chemical modification that had less stress relaxation when compared with the unfilled NBR indicating an excellent possibility of use of this fiber in materials that work under compressive forces. The difference in length of the rockwool fibers (125 μm–300 μm) did not interfere significantly on most of the results.     

Effects of thinner on RTV silicone rubber nanocomposites reinforced with GR and CNTs

The effects of thinner on rubber specimens with carbon nanotubes (CNTs) and graphitic nanofillers (GR) was studied for robotics applications. Rubber specimens were prepared by dispersing GR, CNTs and thinner in room temperature vulcanized (RTV) silicone rubber through solution mixing. Microscopic studies have confirmed occurrence of swelling in polymer chains due to migration of thinner. It results an increase in topological depth from 40 nm (no thinner) to 120 nm (40 phr of thinner). An elastic modulus of ~4.4 MPa (without thinner) was higher than 2.8 MPa (10 phr of thinner). At 100% strain, the lower dissipation losses of 110% (without thinner) and 70% (40 phr of thinner) were obtained. The resistance increases from 4.6 kΩ (without thinner) to 5.7 kΩ (10 phr of thinner). At 0.4‐mm‐thick elastomer slab, an actuation displacement of 0.81 mm (without thinner) was obtained which increased to 1.1 mm (60 phr of thinner). Thus, the thinner can be useful for easier processing, controlled stiffness, minimizing dissipation losses, increasing the actuation displacement and decreasing the cost of the device. Copyright © 2017 John Wiley & Sons, Ltd.     

Properties of rubber filled with montmorillonite with various surface modifications

Layered silicate/natural rubber composites were prepared by direct polymer melt intercalation. Na‐montmorillonite Kunipia‐F and its organic derivates (organo‐clays) prepared by ion exchange were used as clay fillers. Silica (SiO₂) Ultrasil VN3, a filler commonly used in the rubber industry, was used in combination with clay fillers. The effect of clay or organo‐clay loading from 1 up to 10 phr without (0 phr) or with silica (15 phr) showed significant improvement of the tensile properties (stress at break, strain at break and modulus M100). Modification of montmorillonite by three alkylammonium cations with the same length of alkylammonium chain (18 carbons) and different structure resulted in altered reinforcing and plasticizing effects of the filler in composites with rubber matrix. Copyright © 2011 John Wiley & Sons, Ltd.