Changes of spin–spin relaxation time for EPR composites during mixing process

The changes of the mobility of rubber molecules for carbon black-filled EPR composites during mixing process in an internal mixer have been elucidated from T₂ measurement using pulsed nuclear magnetic resonance (NMR). The thickness of the tightly bound region which is formed by the direct interaction with carbon black was stabilized with mixing but the restriction of the molecular mobility increased with further mixing. The amount of the loosely bound region increased considerably throughout the mixing, indicating that this region is formed by entanglement and crosslinking of the molecules. T₂ of the mobile region which is a predominant part in the composites is independent of the mixing time. EPR has the thinner tightly bound shell and longer T_2s compared with EPDM, showing the effect of unsaturated bond in EPDM which can become a strong bond site with carbon black.     

Pulsed NMR study on the silica-filled rubber systems

Proton spin–spin relaxation time has been measured by the pulsed NMR technique for the bound rubbers extracted from both silica-filled polyisoprene and polybutadiene composites. Two relaxation times T_2t (short) and T_2l (long) are observed for all samples. They are ascribed, respectively, to the relaxation of the tightly and loosely bound rubber components. When the silica filled polybutadiene composite is heat treated at 120°C, loosely bound rubber is preferentially formed, which leads to the increase in the total bound rubber fraction in the composite. During the heat treatment of silica-filled polyisoprene composite, a part of the loosely bound rubber phase is transformed into tightly one, and simultaneously the chain mobilities of both phases become more constrained state. These changes are accompanied by the degradation of polyisoprene molecules probably due to the strong chemical interaction of silanol group and rubber molecules. At a prolonged heat treatment, the fraction of total bound rubber in the composite decreases as a result of the degradation of the loosely bound rubber molecules.     

Sepiolite hybridized commercial fillers,and their effects on curing process,mechanical properties,thermal stability,and flammability of ethylene propylene diene monomer rubber composites

Ethylene propylene diene monomer rubber (EPDM)-based composites containing sepiolite (sep) hybridized with calcium carbonate (CaCO₃), silica (Sil) or carbon black (CB) were prepared on a two-roll mill. The influence of fillers’ contents on the curing, mechanical, thermal and flammability of the composites was investigated. In comparison with EPDM/sep at 30 parts per hundred rubbers (phr) as a control composite, EPDM/sep/CB composites exhibited an outstanding improvement in tensile strength followed by EPDM/sep/Sil and EPDM/sep/CaCO₃ composites. EPDM/sep/CB displayed the highest thermal stability and also improved flammability resistance. In addition, a higher amount of carbon black gave higher tensile strength. The results were influenced by the ability of CB to disperse well and form protective layers acting as mass transport barriers in the matrix. The field emission scanning electron microscopy analyses proved better dispersion of CB in the matrix. The presence of protective layers on the surface of samples consequently improved the thermal properties of the EPDM composites. The mechanism of formation of char protective layer in hybrid EPDM composites was also investigated based on morphological observations of char residues. According to this work, Sil and CB were able to hybrid with sep, while sep could be a potential substitution of CaCO₃ in the EPDM composites.     

Influence of chloroacetate group on physical properties of natural rubber and its interaction with fillers

Filler–rubber composites were prepared by mixing chloroacetated natural rubber (CNR) with silica, carbon black (CB), or calcium carbonate using a two‐roll mill. The interactions between the CNR and fillers, including silica, carbon black, and calcium carbonate, were characterized based on glass transition temperature (T_g) and shear storage modulus (G′). The results showed that both the T_g and G′ values of the CNR‐Si composite were found to be higher than those of the CNR–CB and CNR–CaCO₃ composites, indicating the existence of the CNR and silica interaction. The outstanding direct interaction between the CNR rubber matrix and silica without using a coupling agent was believed to be due to hydrogen bonds that formed between the hydroxyls of the silanol groups of silica and the carbonyls in the chloroacetate groups of CNR molecules. Moreover, it was also found that silica dispersed and distributed in the CNR matrix much better than in the natural rubber matrix. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43076.     

Dynamic rheology–morphology relationship of PP/EPDM blends prepared by melt mixing under Sc-CO2

It was demonstrated that the high mixing efficiency of twin screw extruder (TSE) helped to disperse the ethylene–propylene–diene terpolymer (EPDM) domains in polypropylene (PP) matrix, but could not lead to the uniform distribution of EPDM phase with small sizes because of the thermodynamical immiscibility between PP and EPDM. So supercritical carbon dioxide (Sc-CO₂) was environmentally and economically introduced to the twin screw extrusion to assist the melt mixing of PP and EPDM. The scanning electron microscopy photographs showed that co-continuous phase morphology was formed to some extent for the PP/EPDM 60/40 blend prepared with Sc-CO₂, especially with 2.5 wt% Sc-CO₂. This was the one important reason for that the complex viscosity and storage modulus of PP/EPDM 60/40 blend increased with the increase of Sc-CO₂ concentration.     

石墨/炭黑/EPDM复合材料的性能研究

研究石墨/炭黑/EPDM复合材料的物理性能、动态力学性能和导电性能.结果表明:石墨对炭黑填充EP-DM复合材料具有补强作用,并显著提高其导电性能;石墨/炭黑/EPDM复合材料的电导率-压力曲线表现出“山峰”形变化趋势,升高温度或增大石墨用量时该峰向低压力区移动;石墨用量越大,复合材料电导率的温度依赖性越强,石墨粒子滑移...     

Utilization of fly ash acid residue as a reinforcing filler in ethylene propylene diene monomer rubber

Fly ash acid residue (FAAR), a by‐product of circulating fluidized bed fly ash extracted Al₂O₃ by acid leaching method, has been posing problems because of its disposal. The major chemical components of FAAR are amorphous SiO₂ (66.38 wt %) and unburned carbon (20 wt %). Attempts were made for its application as a reinforcing filler for ethylene propylene diene monomer (EPDM) rubber in this article. Surface modification for FAAR by silane coupling agent (Si69) was carried out. The effect of surface modification and unburned carbon existing in FAAR on the performance of FAAR was characterized by Fourier transform infrared and dispersibility test. The results indicated that surface modification could reduce the hydrophilicity of FAAR and unburned carbon also had positive effect on the dispersion of FAAR particles in kerosene. The effect of partial replacement of carbon black by FAAR on the curing behavior, mechanical properties, and morphological characteristics of EPDM rubber was also studied. It was proved that with partial replacement of carbon black by FAAR, the cure time (t₉₀) and maximum torque (M_H) of EPDM composites increased with the content of FAAR. The mechanical properties were significantly improved when 15 wt % of carbon black was replaced by FAAR. SEM micrographs confirmed that surface modification can improve the compatibility between FAAR and rubber matrix. Unburned carbon existing in FAAR was also beneficial to the interface bonding. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Effect of maleic anhydride grafted ethylene propylene diene monomer (MAH‐g‐EPDM) on the properties of kaolin reinforced EPDM rubber

Due to pollution issue and dark color of carbon black, nonblack filler are getting more importance for reinforcing elastomer. EPDM‐kaolin composites with variable maleated EPDM concentration have been prepared by mixing on a two roll mill. Optimum cure time increases with increasing compatibilizer concentration without decreasing torque value indicating that acidic functional groups comes from compatibilizer could retard cure rate and increase optimum cure time rather than change in ultimate cure state. As the concentration of filler increases, the edge to edge and face to edge interaction between filler and EPDM increases and the free volume between EPDM molecules is reduced, leading to less solvent swelling increasing crosslinking density. The results obtained shows that with increasing filler concentration the modulus and elongation at break increases due to the intertubular diffusion of EPDM inside the clay. The morphological study revealed that homogeneity of filler dispersion increases with increase in compatibilizer concentration which support the results obtained from tensile test. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Tack and green strength of filled blends of bromobutyl and EPDM rubbers

Effect of fillers on tack and green strength of blends of EPDM and bromobutyl rubbers has been studied. The fillers used are carbon black and china clay. Test temperature and mode of mixing are varied. Tack increases with the addition of carbon black and china clay. The highest value of tack strength is achieved when the loading of filler is 50% in each phase or all in EPDM phase. The tack strength of filled blends decreases with an increase of test temperature. Tack index, a ratio of tack strength divided by cohesive strength measured under the same geometry, also decreases with test temperature. It has been found that tack strength (G_a) of filled blends is proportional to the contact time (t) and varies as t^1/2 or t^1/4. Green strength of carbon black filled mixes is much higher than that of china clay filled mixes. The green strength falls with a rise of temperature in both cases. Green strength of carbon black filled mixes increases with the increase of bromobutyl content in the mix. China clay mixes show a reverse trend.     

Ionic interphase of glass fiber/polyamide 6,6 composites

Interfacial polymerization to polyamide 6, 6 followed by introduction of ionic groups was performed on the surface of short glass fibers. The ionic interphase-modified fibers were used with poly(ethylene-co-methacrylic acid) (DuPont Surlyn) to prepare composites with specific fiber-matrix interactions. Fiber treatment increased composite tensile and bending properties. An increase in the average fiber length was observed, which was attributed to a decrease in the fiber attrition during mixing. The effect of increasing temperature on the composite mechanical properties was studied. Different behavior was observed before and after the glass transition temperature, T_g, of the matrix. The dynamic mechanical measurements showed an increase in the T_g of the matrix after the treatments, which is attributed to a decrease in chain mobility at the interface resulting from increased interactions of the treated fiber surface with the polymer. Scanning electron microscopy of fractured composites after tensile tests revealed a smooth fiber surface with no polymer at the surface for the untreated composites. Adhered polymer was clearly observed on the surface of treated fibers, indicating better fiber wetting by the matrix. This improved adhesion was attributed to the grafted nylon molecules at the glass fiber surface.     

Improvement of toughness of reaction bonded silicon carbide composites reinforced by surface-modified SiC whiskers

To improve the reliability, especially the toughness, of the reaction bonded silicon carbide (RBSC) ceramics, silicon carbide whiskers coated with pyrolytic carbon layer (PyC-SiC_w) by chemical vapor deposition (CVD) were introduced into the RBSC ceramics to fabricate the SiC_w/RBSC composites in this study. The microstructures and properties of the PyC-SiC_w/RBSC composites under different mass fraction of nano carbon black and PyC-SiC_w were investigated methodically. As a result, a bending strength of 550 MPa was achieved for the composites with 25 wt% nano carbon black, and the residual silicon decreased to 11.01 vol% from 26.58 vol% compared with the composite of 15 vol% nano carbon black. The fracture toughness of the composites reinforced with 10 wt% PyC-SiC_w, reached a high value of 5.28 MPa m^1/2, which increased by 39% compared to the RBSC composites with 10 wt% SiC_w. The residual Si in the composites deceased below to 7 vol%, resulting from the combined actively reaction of nano carbon black and PyC with more Si. SEM and TEM results illustrated that the SiC_w were protected by PyC coating. A thin SiC layer formed of outer surface of whiskers can provide a suitable whisker-matrix interface, which is in favor of crack deflection, SiC_w bridging and pullout to improve the bending strength and toughness of the SiC_w/RBSC composites.     

Synthesis and Properties of a Novel Intumescent Flame Retardant (IFR) and Its Application in Halogen-Free Flame Retardant Ethylene Propylene Diene Terpolymer (EPDM)

The PDP, a novel intumescent flame retardant (IFR) with high charred residue of 40.8% in N2 at 700°C by TGA was synthesized successfully for preparing halogen-free flame-retardant EPDM composites. The UL-94 V-0 rating was achieved for EPDM composites with 20 phrs carbon black at the same time by using only 60 phrs PDP. In situ FTIR spectroscopy reveals that P–N rich charred residues are formed through the interaction between hydrogen atom in weak base of P–NH–C and phosphate. SEM characterizes the formation of intumescent chars during burning. The mechanical properties of composites are also discussed.     

Stability of electrical properties of carbon black‐filled rubbers

Conducting composites were prepared by melt mixing of ethylene–propylene–diene terpolymer (EPDM) or styrene‐butadiene rubber (SBR) and 35 wt % of carbon black (CB). Stability of electrical properties of rubber/CB composites during cyclic thermal treatment was examined and electrical conductivity was measured in situ. Significant increase of the conductivity was observed already after the first heating–cooling cycle to 85°C for both composites. The increase of conductivity of EPDM/35% CB and SBR/35% CB composites continued when cyclic heating‐cooling was extended to 105°C and 125°C. This effect can be explained by reorganization of conducting paths during the thermal treatment to the more conducting network. EPDM/35% CB and SBR/35% CB composites exhibited very good stability of electrical conductivity during storage at ambient conditions. The electrical conductivity of fresh prepared EPDM/35% CB composite was 1.7 × 10⁻² S cm⁻¹, and slightly lower conductivity value 1.1 × 10⁻² S cm⁻¹ was measured for SBR/35% CB. The values did not significantly change after three years storage. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

3-Aminopropyltriethoxysilane as a promoter in the crosslinking of carboxylated nitrile rubber by surface-oxidized carbon black

The role of aminopropyltriethoxysilane in the interaction between ISAF carbon black and carboxylated nitrile rubber was studied by measurements of bound rubber, physical and dynamic mechanical properties of the vulcanizates, and Monsanto Rheometric studies on the rubber-filler mixes. It is believed that  NH₂ groups of the silane interact with  COOH groups of the rubber, while  OC₂H₅ groups of the silane interact with  OH groups on the filler surface. Weak rubber-filler bonds formed during mixing are converted into a crosslinked structure during high-temperature molding. The extent of crosslinking of the rubber phase by the active sites on the filler surface is greater in the case of oxidized ISAF carbon black, as compared to the nonoxidized grade. © 1996 John Wiley & Sons, Inc.     

Particle size distribution,mixing behavior,and mechanical properties of carbon black (high‐abrasion furnace)–filled powdered styrene butadiene rubber

High‐abrasion furnace black (HAF, grade N330)–filled powdered styrene butadiene rubber [P(SBR/HAF)] was prepared and the particle size distribution, mixing behavior in a laboratory mixer, and mechanical properties of P(SBR/HAF) were studied. A carbon black–rubber latex coagulation method was developed for preparing carbon black–filled free‐flowing, noncontact staining SBR powders, with particle diameter less than 0.9 mm, under the following conditions: carbon black content > 40 phr, emulsifier/carbon black ratio > 0.02, and coating resin content > 2.5 phr. Over the experimental range, the mixing torque τ_α of P(SBR/HAF) was not as sensitive to carbon black content and mixing temperature as that of HAF‐filled bale SBR (SBR/HAF), whereas the temperature build‐up ΔT showed little dependency on carbon black content. Compared with SBR/HAF, P(SBR/HAF) showed a 20–30% mixing energy reduction with high carbon black content (>30 phr), which confers to powdered SBR good prospects for internal mixing. Carbon black and the rubber matrix formed a macroscopic homogenization in P(SBR/HAF), and the incorporation step is not obvious in the internal mixing processing results in these special mixing behaviors of P(SBR/HAF). A novel mixing model of carbon black–filled powdered rubber, during the mixing process in an internal mixer, was proposed based on the special mixing behaviors. P(SBR/HAF) vulcanizate showed better mechanical properties than those of SBR/HAF, dependent primarily on the absence of free carbon black and a fine dispersion of filler on the rubber matrix attributed to the proper preparation conditions of noncontact staining carbon black–filled powdered SBR. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 2494–2508, 2004     

Sol-gel derived TiO2–carbon composites with adsorption-enhanced photocatalytic activity and gas sensing performance

We report the in-situ sol-gel synthesis of TiO₂–carbon composites (black TiO₂) by carbonization of the gel. With ultra-fine anatase TiO₂ nanoparticles dispersed homogeneously on amorphous carbon, the as-prepared black TiO₂ possesses a BET surface area as high as 145.4 m²/g. Due to the synergy effect of adsorption and photocatalysis, the as-synthesized black TiO₂ is demonstrated to exhibit enhanced photocatalytic activity. The gas sensing properties of black TiO₂ have been rigorously investigated with and without UV illumination at room temperature. It is found that increased adsorption of gas molecules can effectively improve the sensor response. The mechanism of the adsorption-enhanced gas sensing performance of black TiO₂ has been detailedly discussed.     

Study on Tensile,Electrical, and Thermal Properties of Aluminium Particle Filled Natural Rubber (NR) and Ethylene-Propylene-Diene Terpolymer (EPDM) Composites

Comparative studies on the effect of aluminium particles in natural rubber (NR) and ethylene-propylene-diene terpolymer (EPDM) were conducted. The incorporation of aluminium particles in NR or EPDM composites increased the cure time, t ₉₀, and scorch time, t _S2 . At a fixed filler loading, EPDM composites exhibited longer t ₉₀ and t _S2 than NR composites. The results also indicate that the maximum torque, M _H of aluminium filled NR and EPDM composites increase with increasing filler loading. For tensile properties, EPDM composites show lower tensile properties than NR composites. Thermogravimetric analysis (TGA) results show that aluminium filled EPDM composites have better thermal stability than aluminium filled NR composites.

The results for electrical properties indicate that the electrical properties of aluminium filled NR and EPDM composites increase with increase in filler loading.     

The impact of a fullerene-like concept in carbon black science

A discussion on the role of fullerene-like structure in carbon black has been presented. Starting from the definition of fullerene-like structure, from the experimental detection of these sites and from general properties of fullerenes, it is shown the electron affinity of fullerene-like structures in carbon black should exceed that of C₆₀ fullerene. Therefore the fullerene-like sites in carbon black should act as free radical acceptor sites where the rubber chain macroradicals formed by chain scission or hydrogen abstraction during mixing could add in competition with other known sites, to form chemical bonds, grafting the rubber on the carbon black surface. Fullerene-like structures in carbon black play a crucial role in bound rubber formation. Techniques to increase their concentration in order to improve the carbon black reinforcing effect and to reduce the mechanical hysteresis of the rubber compound containing the modified carbon black are briefly discussed.     

Tensile,thermal, flammability and morphological properties of sepiolite filled ethylene propylene diene monomer (EDPM) rubber composites

The effect of sepiolite loading content on the curing characteristics, tensile mechanical, thermal, swelling, flammability and morphological properties of sepiolite-filled ethylene propylene diene monomer (EPDM) composites was investigated. The composites were prepared with sepiolite loadings of 0–70 part per hundred (phr) of rubber using a two-roll mill. The results highlighted the improvement in the tensile properties and cross-link density values peaked at 60 phr of sepiolite loading. The scorch time, curing time, swelling percentage, and linear burning rate of the composites decreased with an increase in sepiolite loading. Thermogravimetric analysis showed an increasing trend with increase in sepiolite loading. The temperatures corresponding to 5, 25 and 50% weight loss (T_5wt%, T_25wt% and T_50wt%) and the percentage of char residue gradually increased with increase in sepiolite loading. The homogenous dispersion of the sepiolite particles in the EPDM matrix and the formation of zigzag structures, especially at 60 phr, were the main reasons of the improvement of mechanical properties which were confirmed by the morphological studies. The formation of a protective layer, which acted as a barrier against heat transfer into the deeper layers, enhanced the flammability resistance of the composites. Notably, the EPDM filled with 60 phr sepiolite exhibited excellent performance in the aspects of mechanical, thermal stability and flammability properties and resistance towards swelling.     

Carbon nanowire formation in electron-energy controlled plasma produced by CH4/Ar rf discharges with small coaxial electrodes

Carbon nanowires are formed on a surface of nanoparticles made of diamond-like carbon produced on a nickel plate placed in CH₄–Ar plasma. The dissociation of CH₄ is controlled by changing the mixing position of CH₄ along the Ar plasma produced in a small coaxial tube electrode. When CH₄ is introduced in low electron temperature T_e region, we observed an appearance of nanowires on the surface of microparticles. On the other hand, carbon nanowalls and/or nanoplatelets are formed when the CH₄ is mixed in the high T_e region.