Dielectric andmechanical properties of rubber ferrite composites

Rubber ferrite composites (RFCs) containing powdered nickel zinc ferrite (Ni1 – xZnxFe2O4 ) in a natural rubber matrix have been prepared and their mechanical and dielectric properties have been evaluated. Variations in the relative permittivity of both the ferrite ceramics and RFCs have been studied over a range of frequencies, ceramic compositions, ceramic ller loadings, and temperatures, and the results have been correlated. Appropriate mixture equations have been formulated to calculate the dielectric permittivity of the composite from the dielectric permittivity of its constituents. Values calculated using these equations have been compared with experimental data on relative permittivity, and the two have been found to be in good agreement. In the present investigationit was also observed that for x=0·4 and for the maximum ferrite loading, the composite sample exhibits maximum magnetisation and optimum exibility

A microwave absorber based on strontium ferrite–carbon black–nitrile rubber for S and X-band applications

Flexible and thin single layer microwave absorbers based on strontium ferrite–carbon black–nitrile rubber composites have been fabricated employing a specific recipe and their reflection loss characteristics were studied in the S (2–4 GHz) and X-bands (8–12 GHz). The incorporation of carbon black not only reinforces the rubber by improving the mechanical properties of the composite but also modifies the dielectric permittivity of the composite. Strontium ferrite when impregnated into a rubber matrix imparts the required magnetic permeability to the composite. The combination of strontium ferrite and carbon black can then be employed to tune the microwave absorption characteristics of the resulting composite. The complex dielectric permittivity and permeability were measured by employing a cavity perturbation technique. The microwave absorption characteristics of composites were modelled in that an electromagnetic wave incident normally on the metal terminated single layer absorber. The influence of filler volume fraction, frequency, absorber thickness on the bandwidth of absorption are discussed and correlated

Effect of nickel nanofillers on the dielectric and magnetic properties of composites based on rubber in the X-band

Nickel–rubber nanocomposites were synthesized by incorporating ferromagnetic nickel nanoparticles in a natural rubber as well as neoprene rubber matrix. Complex dielectric permittivity and magnetic permeability of these composites were evaluated in the X-band microwave frequencies at room temperature using cavity perturbation technique. The dielectric loss in natural rubber is smaller compared to neoprene rubber. A steady increase in the dielectric permittivity is observed with increase in the content of nickel in both the composites. The magnetic permeability exhibits a steady decrease with increase in frequency and magnetic loss shows a relaxation at 8 GHz. The suitability of these composites as microwave absorbers is modeled based on the reflection loss which is dependant on the real and imaginary components of the complex dielectric permittivity and magnetic permeability.

Processability And Magnetic Properties Of Rubber Ferrite Composites Containing Barium Ferrite

Rubber ferrite composites (RFC) are magnetic polymer composites and have a variety of applications as flexible magnets, pressure=photo sensors, and microwave absorbers. The mouldability into complex shapes is one of the advantages of these magnetic elastomers. They have the potential of replacing the conventional ceramic materials, due to theire flexible nature. In the present study, the incorporation of pre-characterized hexagonal ferrites, namely barium ferrite (BaFe12O19), into natural rubber matrix is carried out according to a suitable recipe for various loadings of the filler. The processability of these compounds was determined by evaluating the cure characteristics: scorch time, cure time, and minimum and maximum torque. It has been found that the addition of magnetic fillers does not affect the processability of the composites, whereas the physical properties are modified. The magnetic properties of these composites containing various loadings of the magnetic filler were also investigated. The magnetic properties of RFC can be controlled by the addition of appropriate amount of the ferrite filler.

Magnetic and processability studies of nitrile rubber vulcanisates containing barium ferrite and carbon black

Fine particles of barium ferrite (BaFe12O19) belonging to the M-type hexagonal ferrites were prepared by the conventional ceramic techniques. They were incorporated into a nitrile rubber matrix according to a specific recipe for various loadings to produce rubber ferrite composites (RFC). The percolation threshold is not reached for a maximum loading of 130 phr (parts per hundred rubber). Here in this paper, the magnetic properties and processability of the nitrile rubber based RFCs containing barium ferrite (BaF) and HAF carbon black is reported. The magnetic properties of the ceramic ferrite and these rubber ferrite composites were evaluated and it was found that the coercivity values of RFCs were less than that of the ceramic BaF, but remained constant with the loading of both the ferrite filler and carbon black. However, other properties like saturation magnetization and magnetic remanence increased with the loading of ferrite filler.

Cure Characteristics and Mechanical Properties of Rubber Ferrite Composites Based on Nano-Nickel Ferrites

Ultra fine nickel ferrite have been synthesized by the sol-gel method. By heat treating different portions of the prepared powder separately at different temperatures, nano-sized particles of nickel ferrite with varying particle sizes were obtained. These powders were characterised by the X-ray diffraction and then incorporated in the nitrile rubber matrix according to a specific recipe for various loadings. The cure characteristics and the mechanical properties of these rubber ferrite composites (RFCs) were evaluated. The effect of loading and the grain size of the filler on the cure characteristics and tensile properties were also evaluated. It is found that the grain size and porosity of the filler plays a vital role in determining the mechanical properties of the RFCs

Cure Kinetics and Sorption Characteristics of Neoprene-Based Rubber Ferrite Composites

Rubber ferrite composites were prepared by incorporating nickel ferrite in a neoprene rubber matrix. Kinetics of the cure reaction were determined from the rheometric torque values and found to follow first-order kinetics. Analysis of the swelling behavior of the rubber ferrite composites in toluene elucidates the mechanism of solvent penetration and sorption characteristics, and reveals the extent of the physical interaction of the ferrite particles with the neoprene rubber matrix. Mechanical properties of rubber ferrite composites were determined, which support the reinforcing nature of nickel ferrite to the neoprene rubber matrix. These results show that magnetic composites with the required processing safety can be prepared economically by incorporating higher amounts of nickel ferrite in the neoprene rubber matrix

Flexible microwave absorbers based on barium hexaferrite, carbon black, and nitrile rubber for 2–12 GHz applications

Flexile single layer electromagnetic wave absorbers were designed by incorporating appropriate amounts of carbon black in a nitrile butadiene rubber matrix along with an optimized amount of magnetic counterpart, namely, barium hexaferrite for applications in S, C, and X-bands. Effective dielectric permittivity and magnetic permeability were measured using cavity perturbation method in the frequency range of 2–12 GHz. The microwave absorbing characteristics of the composites were studied in the S, C, and X-bands employing a model in which an electromagnetic wave is incident normally on a metal terminated single layer. Reflection loss exceeding 20 dB is obtained for all the samples in a wide frequency range of 2–12 GHz when an appropriate absorber thickness between 5 and 9mm is chosen. The impact of carbon black is clearly observed in the optimized composites on the mechanical strength, thickness, band width of absorption, dielectric properties,

Block Copolymers of Unsaturated Polyesters and Functional Elastomers

Block copolymers of unsaturated polyester were prepared by condensation polymerization of hydroxyl or carboxyl terminated liquid rubbers with maleic anhydride, phthalic anhydride, and propylene glycol. The condensate obtained was mixed with styrene monomer to get an unsaturated polyester resin formulation. In this study, copolymers of unsaturated polyesters with hydroxy terminated polybutadiene, carboxy terminated nitrile rubber, and hydroxy terminated natural rubber were prepared. Mechanical properties such as tensile strength, tensile modulus, elongation at break, toughness, impact strength, surface hardness, abrasion resistance, and water absorption were evaluated after the resin was cured in appropriate molds for comparison with the control resin. The fracture toughness and impact resistance of CTBN-modified unsaturated polyester show substantial improvement by this copolymerization without seriously affecting any other property

Utilization of waste expanded polystyrene: Blends with silica-filled natural rubber

Expanded polystyrene (EPS) constitutes a considerable part of thermoplastic waste in the environment in terms of volume. In this study, this waste material has been utilized for blending with silica-reinforced natural rubber (NR). The NR/EPS (35/5) blends were prepared by melt mixing in a Brabender Plasticorder. Since NR and EPS are incompatible and immiscible a method has been devised to improve compatibility. For this, EPS and NR were initially grafted with maleic anhydride (MA) using dicumyl peroxide (DCP) to give a graft copolymer. Grafting was confirmed by Fourier Transform Infrared Spectroscopy (FTIR) spectroscopy. This grafted blend was subsequently blended with more of NR during mill compounding. Morphological studies using Scanning Electron Microscopy (SEM) showed better dispersion of EPS in the compatibilized blend compared to the noncompatibilized blend. By this technique, the tensile strength, elongation at break, modulus, tear strength, compression set and hardness of the blend were found to be either at par with or better than that of virgin silica filled NR compound. It is also noted that the thermal properties of the blends are equivalent with that of virgin NR. The study establishes the potential of this method for utilising waste EPS

Amidino Thiourea as a Secondary Accelerator in Rubber Vulcanization

Earlier studies5773 in our laboratory showed that when a nucleophile is used along with disulphide or sulphenamide accelerators the vulcanization is accelerated greatly and the reaction mechanism is generally nucleophilic in nature. However it was observed that it also changes with the systems under review. The present study, deals with the use of unsubstituted amidino thiourea i.e. aminoimino methyl thiourea(AMT) V in the vulcanization studies of different elastorners and their blends. One of the aims of this study was to get further proof with regard to the theory of nucleophilic reaction mechanism in such binary systems.Mixes containing thiourea are used as controls. AMT is more nucleophilic than TU and this is clear from the fact that the fonner can condense with isothiocynate even in the absence of alkali while TU cannot". Also the guanidinyl group in AMT can facilitate the polarization of the C=S bond favouring a nucleophilic reaction

Natural Rubber Latex Filler Masterbatch by Soap Sensitised Coagulation-Preparation, Processing and Evaluation

Sensitisation of natural rubber latex by addition of a small quantity of an anionic surfactant prior to the addition of a coacervant results in quick coagulation. The natural rubber prepared by the novel coagulation method shows improved raw rubber characteristics, better cure characteristics in gum and carbon black filled compounds and improved mechanical properties as compared to the conventionally coagulated natural rubber. Compounds based on dried masterbatches prepared by the incorporation of fluffy carbon black in different forms of soap sensitised natural rubber latices such as fresh latex, preserved field latex, centrifuged latex and a blend of preserved field latex and skim latex show improved cure characteristics and vucanizate properties as compared to an equivalent conventional dry rubber-fluffy carbon black based compound. The latex masterbatch based vulcanizates show higher level of crosslinking and better dispersion of filler. Vulcanizates based on fresh natural rubber latex- dual filler masterbatches containing a blend of carbon black and silica prepared by the modified coagulation process shows very good mechanical and dynamic properties that could be correlated to a low rolling resistance. The carbon black/silica/nanoclay tri-filler - fresh natural rubber latex masterbatch based vulcanizates show improved mechanical properties as the proportion of nanoclay increased up to 5 phr. The fresh natural rubber latex based carbon black-silica masterbatch/ polybutadiene blend vulcanizates show superior mechanical and dynamic properties as compared to the equivalent compound vulcanizates prepared from the dry natural rubber-filler (conventional dry mix)/polybutadiene blends

Butyl rubber- ceramic composites for flexible electronic applications

The first chapter of the thesis gives a general introduction about flexible electronics, dielectrics and composites. The recent developments in flexible electronics also discussed in this chapter. The preparation and characterization techniques used for the butyl rubber ceramic composites are given in chapter 2. The synthesis and characterization of butyl rubber filled with low permittivity ceramic composites are described in chapter 3. The chapter 4 deals with the synthesis and characterization of butyl rubber-high permittivity ceramic composites. The effect of high permittivity ceramic fillers such as TiO2, Sr2Ce2Ti5O15 and SrTiO3 on dielectric, thermal and mechanical properties was studied. The present investigation deals with synthesis, characterization and properties of butyl rubber composites with low, high and very high ceramic fillers and also the effect of particle size on dielectric, thermal and mechanical properties of selected composites.

A Study on Futures Trading in Commodities With Special Reference to Rubber

Futures trading in Commodities has three specific economic functions viz. price discovery, hedging and reduction in volatility. Natural rubber possesses all the specifications required for futures trading. Commodity futures trading in India attained momentum after the starting of national level commodity exchanges in 2003. The success of futures trading depends upon effective price risk management, price discovery and reduced volatility which in turn depends upon the volume of trading. In the case of rubber futures market, the volume of trading depends upon the extent of participation by market players like growers, dealers, manufacturers, rubber marketing co-operative societies and Rubber Producer’s Societies (RPS). The extent of participation by market players has a direct bearing on their awareness level and their perception about futures trading. In the light of the above facts and the review of literature available on rubber futures market, it is felt that a study on rubber futures market is necessary to fill the research gap, with specific focus on (1) the awareness and perception of rubber futures market participants viz. (i) rubber growers, (ii) dealers, (iii) rubber product manufacturers, (iv) rubber marketing co-operative societies and Rubber Producer’s Societies (RPS) about futures trading and (2) whether the rubber futures market is fulfilling the economic functions of futures market viz. hedging, reduction in volatility and price discovery or not. The study is confined to growers, dealers, rubber goods manufacturers, rubber marketing co-operative societies and RPS in Kerala. In order to achieve the stated objectives, the study utilized secondary data for the period from 2003 to 2013 from different published sources like bulletins, newsletters, circulars from NMCE, Reserve Bank of India (RBI), Warehousing Corporation and traders. The primary data required for this study were collected from rubber growers, rubber dealers, RPS & Rubber Marketing Co-operative Societies and rubber goods manufacturers in Kerala. Data pertaining to the awareness and perception of futures trading, participation in the futures trading, use of spot and futures prices and source of price information by dealers, farmers, manufacturers and cooperative societies also were collected. Statistical tools used for analysis include percentage, standard deviation, Chi-square test, Mann – Whitney U test, Kruskal Wallis test, Augmented Dickey – Fuller test statistic, t- statistic, Granger causality test, F- statistic, Johansen co – integration test, Trace statistic and Max –Eigen statistic. The study found that 71.5 per cent of the total hedges are effective and 28.5 per cent are ineffective for the period under study. It implies that futures market in rubber reduced the impact of price risks by approximately 71.5 per cent. Further, it is observed that, on 54.4 per cent occasions, the futures market exercised a stabilizing effect on the spot market, and on 45.6 per cent occasions futures trading exercised a destabilizing effect on the spot market. It implies that elasticity of expectation of futures market in rubber has a predominant stabilizing effect on spot prices. The market, as a whole, exhibits a bias in favour of long hedges. Spot price volatility of rubber during futures suspension period is more than that of the pre suspension period and post suspension period. There is a bi-directional association-ship or bi-directional causality or pair- wise causality between spot price and futures price of rubber. From the results of the hedging efficiency, spot price volatility, and price discovery, it can be concluded that rubber futures market fulfils all the economic functions expected from a commodity futures market. Thus in India, the future of rubber futures is Bright…!!!