Phr Level Research Articles

Enhanced Mechanical and Electrical Properties of Styrene Butadiene Rubber Nanocomposites with Graphene Platelet Nano-powder

Nanocomposites are very important materials because it imparts superior properties than other composites with low level of filler loading. Styrene butadiene rubber (SBR) is a non-polar rubber which acts as an insulator and has low electrical conductivity. Graphene platelet nano-powder from 0.1 to 1.25 phr level is incorporated into SBR rubber in order to improve the electrical properties. Comparative studies on electrical and mechanical properties of styrene butadiene rubber with graphene platelet nano-powder (GPN) by varying the filler content are made. The incorporation of Graphene platelet nano-powder increases the electrical conductivity in styrene butadiene rubber. It has been observed that there is a gradual increase in electrical conductivity by increasing the amount of nanofiller at higher frequency of about 100 kHz. The mechanical properties of styrene butadiene rubber are improved by the incorporation of Graphene platelet nano-powder. The effect of applied pressure and temperature on the volume resistivity and electrical conductivity of the composites is also investigated at a constant frequency of 100 kHz. The electrical properties of the SBR/GPN nanocomposites increases with increase in pressure and temperature up to a certain limit and then becomes constant.

Continuous extrusion foaming process of biodegradable nanocomposites based on poly(lactic acid)/carbonaceous nanoparticles with different geometric shapes: An insight into involved physical, chemical and rheological phenomena

AbstractOne‐step extrusion foaming process of biodegradable poly(lactic acid) (PLA)‐based nanocomposites in the presence of chemical foaming agent and chain extender has great complexity to control. In this work, PLA‐based nanocomposites containing different carbonaceous nanoparticles with different geometric shapes were obtained through a co‐rotating twin‐screw extrusion process to get insight into the dominant phenomena, which control the structural and final properties of PLA foams. The reactive extrusion foaming of PLA melt was investigated in the presence of carbon black, carbon nanotubes (CNTs), graphene oxide (GO), and a chain extender additive as well as a chemical foaming agent. Nanoparticles affect the continuous extrusion foaming of PLA melt through several phenomena, including providing bubble heterogeneous nucleation sites, intensifying the chemical decomposition of the foaming agent, improving the PLA structural modification reaction, increasing PLA molecular weight and restricting the dissolved gas removal from the melt. By influencing the involved phenomena in process, the nanoparticles at low levels, especially CNT and GO, increased the void content and cell size of PLA foams. The incorporation of CNT and GO nanofillers at the 0.5 phr level increased the electrical conductivity of PLA foams sharply by 9 and 10 orders of magnitude, resulting in lightweight, biodegradable semi‐conductive foams.

Evidence of silane coupling in torrefied agro‐industrial residue‐filled poly(styrene‐co‐butadiene) rubber compounds

AbstractHeat‐treated rice hull residues were evaluated as fillers in poly(styrene‐co‐butadiene) rubber (SBR) compounds. The currently used precipitated silica filler was replaced with torrefied filler in concentrations varying from 0 to 100 wt%, and the influence of coupler concentration varying from 0% to 3% (7 parts per hundred rubber or phr total) on the filler‐rubber interaction was investigated. The curing process, dynamic properties, and mechanical properties of the SBR compounds were examined for silica‐filled and torrefied rice hull (TRH)‐filled materials with and without the coupling agent. Partial or full replacement of silica with TRH resulted in a systematic decrease in compound viscosity. Longer scorch (ts2) and shorter cure times (t90) were also observed. Incorporation of TRH increased compound modulus (stress at 100% elongation or M100 and Young's modulus) but decreased tensile strength and elongation. The presence of coupler brought about improved dynamic and mechanical properties and 30% lower tan δ at 3 phr level. Results provided the first evidence that, when used as a filler in an SBR compound, torrefied rice hulls can be chemically coupled to the SBR polymer, resulting in increased polymer‐filler interactions analogous to the conventional silica‐coupler‐polymer system.

Evaluation of suitability of sesame oil as an alternative for aromatic processing oil in natural rubber composites

Polycyclic aromatic oils, high in aromatic content are used in tyre compounds as processing aids and these have been found to be carcinogenic. Therefore, it is necessary to find processing aids consisting of a low content of aromatics which would help to overcome the problem associated with the use of petroleum-based aromatic oils. The main aim of this research was to develop carbon black filled natural rubber (NR) composites using environmentally friendly sesame oil as the processing aid. Initially sesame oil was characterized using Fourier Transform Infra-Red analysis. Thereafter, a series of NR based tyre tread compounds was prepared by varying the sesame oil loading from 3-9 phr at 2 phr intervals. Cure characteristics, physico-mechanical and swelling properties of these composites were evaluated and compared with those of the composite prepared with the aromatic processing oil, Dutrex-R (control). Dispersibility of carbon black in all the NR composites was assessed. Viscosity, processing safety and cure rate of the composite produced with 5 phr sesame oil were higher compared to the control and indicated that the oil behaves as a co-activator in rubber compounds. Hardness, modulus at 100% elongation and abrasion volume loss of the vulcanizates prepared with more than 5 phr sesame oil were lower, whereas tensile strength, elongation at break and resilience were higher than those of the control. Tear strength and compression set of the vulcanizates prepared with 5 phr sesame oil were comparable to those of the control. Further, the former vulcanizate showed a higher and lower swelling indices in toluene and water, respectively compared to the control. Furthermore, the vulcanizates prepared with sesame oil showed better ageing resistance in comparison to the control. Hence, sesame oil could be a suitable alternative for Dutrex-R in tyre tread compounds at 5 phr level.

Understanding the influence of anti‐reversion agent and metal oxide dose on natural rubber–carbon black system

AbstractSulfidic linkages that are formed during the vulcanization process of natural rubber (NR) are unstable at a higher temperature and can be reversed into conjugated diene. To overcome such issue and to build a compound that is hostile to inversion and with increasing service life, anti‐reversion agent (ARA), for example, N,N′‐4,4′‐diphenylmethyene bismaleimide (BMDM), is added into the formulation. This work explains the conjugation reaction mechanism of conjugated diene and BMDM by means of gas chromatography–mass spectrometry and Fourier transform infrared spectroscopy. The first phase of this study is associated with the change in ARA dosage keeping ZnO dosage the same. It is observed that 5 phr of BMDM and 2 phr ZnO combination (ARA4) shows lowest reversion at 160°C. The modulus value at 300% elongation increased 12% by the incorporation of BMDM as compared to the compound of no BMDM (ARA1). The second part is all about keeping BMDM dosage the same at 5 phr level and varying ZnO phr by 3, 4, and 5. From the overall results, it is observed that at a suitable dosage of BMDM and ZnO (5 phr BMDM and 3 phr ZnO combination [ARA5]), least reversion can be achieved and vulcanizates containing optimized BMDM and ZnO show better retention properties after aerobic aging as compared to ARA1.

Kinetics of degradation of PVC‐containing novel neem oil as stabilizer

AbstractThe effectiveness of adding epoxidized neem oil (ENO) in poly(vinyl chloride) (PVC) to enhance heat stability was investigated. Neem oil, of vegetable extract, was characterized for its fatty acid profile and other properties. The virgin oil was epoxidized at 60°C with peroxymethanoic acid (performic acid) generated in situ in the reaction mixture by reacting hydrogen peroxide and methanoic acid. ENO was characterized by FTIR and NMR studies, and the degree of epoxidation was measured with iodine value and oxirane oxygen content. Solubility parameters of neem oil and ENO were estimated. Thermal degradation of PVC‐containing ENO was studied using the static heat stability test and artificial aging at temperatures of 100, 110, 120, and 130°C. Results were compared with the samples prepared with conventional heat stabilizers systems used in PVC, such as Ca/Zn stearates and mixtures of both Ca/Zn stearates and ENO. The changes in elastic modulus of the ENO/PVC combination and the conventionally stabilized Ca/Zn system during aging were kinetically modeled, and the rate constants for the degradative influence of modulus were determined. The activation energies and preexponential factors for the degradative process were obtained from Arrhenius plots and their relationship through a compensation effect was found. In general, ENO was found to be an effective retarder of the degradation of PVC; use of 10 phr level of ENO showed the least degradation with the highest activation energy. A synergistic effect of ENO and Ca/Zn stearate system was also observed. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

MWCNTs Elastomer Nanocomposite, Part 1: The Addition of MWCNTs to a Natural Rubber‐based Carbon Black‐filled Rubber Compound

Multi‐walled carbon nanotubes (MWCNTs) were studied as reinforcing filler in a natural rubber based formulation as partial replacement of carbon black. Four levels of MWCNTs were tested at 2.5, 5, 10 and 15 phr in a compound already containing 50 phr of N375 carbon black. The data obtained were compared with the results of reference compounds filled exclusively with N375 carbon black at equal total filler loading as the nanocomposites. The effects of the addition of MWCNTs are dramatic and cause a strong increase in the green Mooney viscosity and in the cured hardness and moduli with a neat reduction of the elongation at break due to the stiffening effect of the MWCNTs. At 10 and 15 phr level of MWCNTs the 50% modulus results more than doubled in comparison to the reference compound. It is shown that the reinforcing effect imparted by MWCNTs to the natural rubber‐based nanocomposite is almost exclusively due to the hydrodynamic effect exerted by the large anisotropic factor of the MWCNTs molecular threads. Using the Enstein‐Guth equation, it has been shown that if the anisotropy factor (or shape factor) of a reinforcing carbon black is ∼6, in the case of MWCNTs used in the present work such factor reaches the value of 52.5, one order of magnitude higher. Drawbacks of the natural rubber nanocomposites prepared with MWCNTs appear under dynamic testing. The cyclic deformation of the nanocomposite specimens, both under compression or under extension, reveals a strong hysteresis and heat generation due to internal friction between the surface of the nanotubes and the rubber matrix. This fact confirms the poor surface interaction between MWCNTs and the natural rubber matrix.

MWCNTs Elastomer Nanocomposite, Part 2: The Addition of MWCNTs to an Oil‐extended SBR‐based Carbon Black‐filled Rubber Compound

Multi‐walled carbon nanotubes (MWCNTs) were tested in a styrene‐butadiene copolymer (E‐SBR)‐based rubber compound as partial replacement of N375 carbon black at 5 and 10 phr level. The composite studied was characterized by a high content of plasticizing oil. It is shown by the increase of the apparent shape factor of the MWCNTs that the oil permits a better dispersion and alignment of the MWCNTs in the rubber matrix. The reinforcing effect of MWCNTs has been studied both on sulphur‐cured and radiation‐cured nanocomposites. In both cases, a strong reinforcing effect has been measured at low elongations, but the extra‐reinforcement tends to disappear at higher elongations due to the poor interaction between the MWCNTs surface and the rubber matrix. The presence of high levels of plasticizer permits to partially reduce the strong heat build up and hence the strong mechanical hysteresis normally observed in nanocomposites prepared with MWCNTs.

Evaluation of Pyrolytic Oil from Scrap Tires as Plasticizer of Rubber Compounds

A heavy fraction of oil obtained from pyrolysis of rubber crumb derived from scrap tires was studied by H-NMR and FT-IR spectroscopy in comparison to a distillate aromatic extract (DAE) derived from petroleum and currently used as plasticizer in rubber mixes. The spectral data suggest a rough chemical analogy between the two oils although the viscosity and the density of the pyrolysis oil are significantly lower that that of the aromatic extract suggesting a significantly lower average molecular weight for the pyrolytic oil in comparison to the reference DAE oil. The two oils were tested at 10 and 15 phr level in a NR-based formulation and the cure kinetics and the mechanical properties of the rubber compounds have been measured. The pyrolytic oil gives accelerated cure kinetics, reduced scorch safety and lower compound viscosity in comparison to reference compounds with DAE oil. The mechanical properties of the cured compounds prepared with pyrolysis oil from scrap tires appear similar to the reference compounds prepared with DAE oil. However, the ageing resistance of the pyrolysis oil are worse than the reference compound with DAE oil.

Effect of incorporation of peanut and sesame oils and their epoxides on the structure of Poly Vinyl Chloride

Epoxidised soybean oil (ESO) is widely used as a p1.1sticizer for Poly Vinyl Chloride (PVC). The interactions of the sesame oil and the peanut oil and their epoxides with PVC wcre investigated in this study. The epoxidation of the oils were carried out zn situ using the perdcetic acid method. Epoxidation was conlirmed using H1 NMR and C NMR spectra. The interaction of oils and their eposides with PVC were evaluated using FT-IR (Fourier Transform Infrared) spectra. Soybe,~n oil was treated as the benchmark. According to the FT-IR analysis, the oils and their epoxy derivatives were found to interact with PVC molecules. These interactions solubilize the PVC in the plasticisers and hence make them compatible with PVC. It is also shown t hat these m olecules break the polymer-polymer interactions and mask the interact~ve sites of the PVC polymers. In comparison to soybean oil, molecular interactions of sesame oil with PVC is be~ter. However, peanut oil and soybean oil show better molecular interactions below 10 phr level, while sesame oil shows rnaxilnum interactions around 50 phr.

Effect of plasticizers on mechanical, electrical, permanence, and thermal properties of poly(vinyl chloride)

AbstractEffects of three different plasticizers and their blends with dioctyl phthalate (DOP) on thermal stability, flammability, mechanical, electrical, and permanence properties of poly(vinyl chloride) (PVC) compound were studied. Various plasticizers used were DOP, butyl benzyl phthalate (BBP), isodecyl diphenyl phosphate (IDDP), and polybutylene adipate (PBA) at concentrations of up to 40 phr level. Studies showed that processability and softness were improved by addition of BBP. An increase in the content of IDDP increased the electrical and flammability properties, whereas compositions with PBA exhibited the best permanence properties. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3278–3284, 2003

Effect of reactive compatibilizers on the mechanical properties of polycarbonate/poly(acrylonitrile-butadiene-styrene) blends

Polycarbonate (PC)/poly(acrylonitrile-butadiene-styrene) (ABS) blends compatibilized with both maleic anhydride (MA)-grafted polypropylene and solid epoxy resin (bisphenol type-A) were injection molded. The effects of the compatibilizer additions on the morphology and mechanical properties of the PC/ABS blends were investigated. Tensile and Izod impact tests revealed that the addition of epoxy at 2 phr level to the MA-grafted PC/ABS 70/30 blend led to a significant increase in both tensile ductility and impact strength. Consequently, epoxy content of 2 phr level was added to all the blends investigated. Moreover, tensile tests showed that the yield strength of PC decreased almost linearly with increasing ABS content. However, the tensile modulus showed a positive deviation from the rule of mixtures. Both MA copolymer and epoxy were effective to compatibilize the PC/ABS blends containing ABS content up to 30 wt%. In this case, the impact strength of these compatibilized blends was close to that of PC. Above 40 wt% ABS content, the impact strength of the compatibilized PC/ABS blends decreased significantly. Scanning electron microscopic examination showed that the ABS tends to disperse as large domains in PC matrix of the uncompatibilized PC/ABS blends. However, the size of ABS domains of PC/ABS blends with ABS ≤ 30 wt% was reduced dramatically owing to the incorporation of both compatilizers.

Studies on the electrical conductivity and galvanomagnetic characteristics of short carbon fibre filled thermoplastic elastomers

The electrical resistivity of short carbon fibre filled thermoplastic elastomers based on natural rubber-high density polyethylene (NR-HDPE) blend and styrene-isoprene-styrene (S-I-S) block copolymer has been studied by varying the concentration of fibre from the 0 to 40 phr level. A sharp drop in resistivity is observed in both cases after a critical concentration of fibre is reached, with the S-I-S system showing lower values of critical concentration. At higher concentrations, experimental values of the electrical conductivity agreed reasonably well with the calculated values from a theory based on the probability of formation of a conductive network. The effect of temperature on the resistivity of the composites has also been investigated in a temperature range of 27–120 °C and 27–90 °C for the NR-HDPE system and S-I-S system, respectively. The type of carrier in both the composites is found to be n-type, i.e. electrons, and the activation energy of hopping of the electrons for both the systems has been calculated. A Hall effect study has also been carried out to determine the carrier concentration and drift mobility of both the composites.

Properties of tetra‐N‐glycidyl‐4,4′‐diamino diphenyl methane (TGDDM) cured thick films

AbstractThick films of tetra‐N‐glycidyl epoxy resin of p,p′‐diaminodiphenyl methane (TGDDM) were prepared using p,p′‐diaminodiphenyl methane (DDM), p,p′‐diaminodiphenyl sulfone (DDS) and diethylene triamine (DETA) as curing agent with or without the epoxy fortifiers PGEHA and VCDRC (at 20 phr level). These thick films were used to evaluate various physical, mechanical, chemical resistant and dielectric properties.

Effects of Fortifier on Glass/Carbon Fiber Reinforced Tetrafunotional Epoxy Resin

Abstract Glass fiber reinforced epoxy composites were prepared using tetra-N-glycidyl-p,p′-diaminodiphenyl methane (TGDDM) as a resin matrix with/without fortifier PGEHA/VCDRC (at 20 phr level) using DDM/DDS as curing agent; the composites were evaluated for their various physical, mechanical, chemical, and electrical properties. Carbon fiber (i.e., unidirectional, bidirectional, and chopped) reinforced composites of TGDDM with/without epoxy fortifier PGEHA/VCDRC (at 20 phr level) were also prepared and evaluated for their physical and some mechanical and chemical properties. It is observed that incorporation of fortifier (at 20 phr level) improves these properties significantly.

Natural Rubber Compounds for Truck Tires

Abstract An 80 NR/20 BR truck tread compound containing a semi-EV cure system and modified with a 6.0 phr level of stearic acid has been shown to exhibit excellent resistance to reversion when compared to a similar compound containing a normal 2.0 phr level of stearic acid. Improvements in the retention of laboratory abrasion resistance, heat generation, and most physical properties have been identified on test pieces subjected to typical truck retread overcure conditions. In highway fleet testing trials of 1100 × 22.5 truck retreads fitted to both third and fourth drive axles of tipper trucks, the modified compound displayed a 42% improvement in treadwear performance over the normal compound in the lower severity third axle positions while performance in the higher severity fourth axle positions was inferior by 20%. In comparison to a 55 SBR/45 BR truck tread, both NR compounds displayed superior wear performance on the fourth axles while some further adjustments of the modified compound are required to match the synthetic compound on the third axles. The reversal of wear performances for all compounds between third and fourth axles is due to the different abrasion mechanisms encountered. Laboratory abrasion rankings do not correlate with wear performances of compounds on the fourth drive axle of trucks, but they do correlate with wear performances on third drive axles. Despite the reversion characteristics of the normal semi-EV compound, no significant adverse effect on treadwear performance was evident at the start of tire life. The low heat generation of the modified compound in laboratory tests is confirmed in actual tire testing. Advantages in rolling resistance characteristics are also evident for the modified compound. Current studies at MRPRA suggest that further modifications of cure system design, in combination with the optimization of NR/BR ratios and mixing methods, will potentially provide NR dominant truck tread compounds which will exhibit superior wear performance in both the higher and lower abrasion severities encountered in heavy-duty truck tire service conditions.

Heat Aging Performance of Ethylene Propylene Elastomers in Electrical Insulation Compounds

Abstract It is possible to develop an EPDM insulation compound with outstanding heat stability in the 160–180°C temperature range. Several key compounding ingredients are necessary in order to achieve the desired heat aging performance. They include the use of EPDM with high ethylene, low unsaturation, polychloroprene at the 5–10 phr level, zinc oxide at the 10–15 phr level, TMPT at the 2–4 phr level, hydrated alumina as the major mineral filler, reaction product of acetone and diphenylamine at 1 phr level, zinc salt of methylmercapto benzoimidazole at the 2–3 phr level, and dicumyl peroxide at the 5–6 phr level.

Effect of curing systems and temperatures on the activity of retarder in natural rubber mixes

The effect of vulcanization temperature (150° and 180°C) on the structure and technical properties of gum natural rubber vulcanizates with four different 2-(morpholinodithio)-benzothiazole (MDB) — sulphur ratios in presence of N-(cyclohexyl thio)-phthalimide (CTP, 0.5 phr) has been determined at the respective optimum cure times. The influence of curing system, temperature and retarder on (a) the chemical crosslink density, (b) the distribution of crosslink types, (c) the extent of sulphidic main chain modification and (d) the zinc sulphidic formation have been investigated. The network results have been correlated with the technical properties. Increasing the cure temperature by 30°C (from 150° to 180°C) does not alter the activity of CTP. It is effective in all curing systems, but effectiveness was maximum in the conventional system. At 0.5 phr level, CTP caused reduction in most technical properties.

Distribution of Carbon Black in SBR

Abstract The interparticle distance between black aggregates in rubber was estimated by Fraunhofer diffraction with the mask of an electron micrograph of filled rubber. Up to 40 phr, the distribution of interpartiele distance has a sharp peak centered at 8000 A˚ with 20 phr and at 7000 A˚ with 40 phr. Above 60 phr, the interparticle distance distributes broadly in the vicinity of 4000 A˚. The size of black aggregates at 20 phr extends from 300 A˚ (one particle) to 3000 A˚, and the average diameter is 1200 A˚. Above 40 phr, black trends to aggregate more than at 20 phr, and the average diameter is about 1500–1600 A˚, the maximum diameter being 5000 A˚. In one black aggregate, there are about 40 spherical particles. The relation between the size and interparticle distance shows that isolated black aggregates are distributed in rubber under 40 phr and that at 40 phr they begin to connect partly with each other. Above 60 phr, a network of chains of black develops everywhere. The contact of black aggregates at 40 phr level corresponds to the abrupt change of physical properties of filled rubber.

Distribution of carbon black in SBR

AbstractThe distribution of HAF carbon black in SBR was studied with the electron microscope and Fraunhofer diffraction. The interparticle distance between black aggregates is 8000 Å at 20 phr and 7000 Å at 40 phr, but above 60 phr it spreads broadly in the vicinity of 4000 Å. The size of black aggregates at 20 phr extends from 300 Å to 3000 Å, and the average diameter is 1200 Å. At 40 phr and 60 phr, black trends to aggregate more than at 20 phr and the average diameter is about 1500–1600 Å; the maximum diameter exceeds 5000 Å. In a black aggregate, there are about 40 spherical particles independently of filler concentration. From the relation between the size and interparticle distance, the connection of black aggregates initiates at 40 phr level and affects the physical properties of filled rubber.