Effects of partial replacement of commercial fillers by recycled poly(ethylene terephthalate) powder on the properties of natural rubber composites

Commercial fillers, including carbon black (N550), halloysite nanotubes (HNTs), and precipitated silica, were replaced by recycled poly(ethylene terephthalate) powder (R‐PET) in natural rubber (NR) composites. Five different compositions of NR/N550/R‐PET, NR/HNTs/R‐PET, and NR/silica/R‐PET compounds, i.e., 100/20/0, 100/15/5, 100/10/10, 100/5/15, and 100/0/20 parts per hundred rubber (phr), were prepared on a two‐roll mill. The curing behavior, tensile properties, and morphological characteristics of the natural rubber composites were investigated. The results indicated that the replacement of carbon black, HNTs, and silica by R‐PET decreased the tensile strength and tensile modulus, such that NR/silica/R‐PET composites showed the lowest effect, followed by NR/HNTs/R‐PET and NR/N550/R‐PET composites. The negative effect on these properties can be explained by the decrease of crosslink density. The curing results revealed that with the replacement of carbon black by R‐PET, the scorch time and cure time decreased, but that the NR/HNTs/R‐PET and NR/silica/R‐PET composites exhibited the opposite trend. Scanning electron microscopy investigation of tensile fracture surfaces confirmed that the co‐incorporation of N550/R‐PET improved the dispersion of R‐PET and enhanced the interaction between the fillers and NR matrix more than R‐PET and silica/R‐PET hybrid fillers. J. VINYL ADDIT. TECHNOL., 2012. © 2012 Society of Plastics Engineers     

Natural rubber vulcanizate reinforced by modified coal‐shale‐based fillers

Coal shale is considered a waste material in coal mining and washing processes. It comprises both inorganic and organic components. In this study, two kinds of coal shale were microcracked, burned, modified by enoxidation natural rubber (ENR), and then used as reinforcing fillers for natural rubber (NR). The NR vulcanizates reinforced with this modified filler were characterized by bounded rubber content, apparent crosslink density, and various mechanical property tests. The results show that the ultramicro coal‐shale powder was a good filler for NR. It could be mixed quickly, and it dispersed well in NR, which resulted in a significant enhancement. After modification by ENR, the reinforcement properties were improved further. The results suggest that this new type of filler could be used as a semireinforcing filler to replace or partially replace carbon black. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1397–1400, 2004     

Tailoring Silica Surface Properties by Plasma Polymerization for Elastomer Applications

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

Preparation of polydimethylsiloxane‐coated α‐alumina fillers with cold plasma for elastomer thermal interface materials

A novel method for the organic modification of a ceramic thermal conductive filler (α‐alumina) with cold plasma was developed for the preparation of elastomer thermal interface materials with high thermal conductivities and low moduli. The α‐alumina fillers were first coated with low‐molecular‐weight polydimethylsiloxane (PDMS) by solution dispersion and then treated in argon plasma for different time. The modified α‐alumina fillers were characterized with high‐resolution transmission electron microscopy, thermogravimetric analysis, Fourier transform infrared spectroscopy, and X‐ray photoelectron spectroscopy. The results revealed that a thin PDMS film with several nanometers thick was tightly coated on the surface of the alumina filler after plasma treatment, and this thin film could not be removed by 48 h of Soxhlet extraction with n‐hexane at 120°C. Plasma modification of the alumina could dramatically weaken the strength of the filler–filler networks and, thus, remarkably reduce the modulus of the alumina‐filled silicone rubber composites but did not affect the thermal conductivity of the composites. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Influence of filler–rubber interactions on the viscoelastic properties of carbon‐black‐filled rubber compounds

The specific role of filler–rubber interactions in dynamic properties was investigated. Natural rubber compounds, filled with N330 carbon black, were used, and the filler surface was modified through a gas treatment in the solid phase. The effects of this filler surface treatment on the dynamic properties were systematically studied at equal filler dispersion levels. The dynamic properties were assessed for both uncured and vulcanized compounds, and a number of advanced investigative techniques were used to characterize not only the modification of the carbon particle surface by an oxidative treatment but also the structure of the filled rubber compounds. Particular attention was paid to techniques that gave access to the segmental mobility to explain the benefit observed with modified carbon black. A molecular interpretation, based on NMR measurements, was considered that took into account physicochemical parameters. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 577–588, 2004     

Grafting hydroxy‐terminated polybutadiene onto nanosilica surface for styrene butadiene rubber compounds

Hydroxy teminated polybutadiene (HTPB) was grafted onto the surface of nanosilica particles via toluene di‐isocyanate (TDI) bridging to reduce filler–filler interactions and improve dispersion of nanosilica in rubber. Also, this prepolymer as modifier contains double bonds which participate in sulfur curing of styrene butadiene rubber (SBR) matrix to enhance filler/polymer interaction and reinforcement effects of silica. The reactions were characterized by titration and Fourier transforms infrared spectroscopy. Thermogravimetric analysis was utilized to evaluate the weight percentage of grafted TDI and HTPB. About 60% of the hydroxyl sites of silica were reacted with excess TDI in the first reaction. In the second reaction, HTPB as desired reactive coating was grafted on the functionalized nanosilica to constitute about 24 wt % of the final modified silica. The sedimentation experiments showed good suspension stability for the modified nanosilica in the organic media. Scanning electron microscopy revealed nanoscale dispersion of modified silica aggregates in the SBR matrix at concentration of about 14 phr. Also, vulcanization characteristics and mechanical properties of compounds demonstrated that HTPB grafting improved dispersion of nanosilica as well as its interaction to the rubber matrix as an efficient reinforcement. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

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

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

表面改性碳纳米管/天然橡胶复合材料的制备及性能研究

采用多巴胺对多壁碳纳米管(MWCNTs)进行非共价改性,得到多巴胺改性MWCNTs(简称PCNT)。将PCNT作为填料加入天然胶乳中制备PCNT/天然橡胶(NR)复合材料,并研究其性能。透射电子显微镜(TEM)分析结果表明MWCNTs经过多巴胺改性后在水中的分散效果明显改善。PCNT/NR复合材料的拉伸强度和撕裂强度明显提高,拉伸强度由22.7 MPa升至28.4 MPa,撕裂强度由26 kN·m^-1升至40 kN·m^-1。多巴胺用量适当的PCNT在NR基体中分散更均匀,填料与橡胶的相互作用较强,能够形成较好的填料网络结构,PCNT/NR复合材料的表面电阻显著降低。     

Cardanol grafted natural rubber: A green substitute to natural rubber for enhancing silica filler dispersion

Natural rubber (NR) usage is wide‐spread from pencil erasers to aero tyres. Carbon black and silica are the most common reinforcing fillers in the rubber industries. Carbon black enhances the mechanical properties, while silica reduces the rolling resistance and enhances the wet grip characteristics. However, the dispersion of polar silica fillers in the nonpolar hydrocarbon rubbers like natural rubber is a serious issue to be resolved. In recent years, cardanol, an agricultural by‐product of the cashew industry is already established as a multifunctional additive in the rubber. The present study focuses on dispersion of silica filler in natural rubber grafted with cardanol (CGNR) and determination of its technical properties. The optimum cure time reduces and the cure rate increases for the CGNR vulcanizates as compared to that of the NR vulcanizates at all loadings of silica varying from 30 to 60 phr. The interaction between the phenolic moiety of cardanol and the siloxane as well as silanol functional groups present on the silica surface enhances the rubber–filler interaction which leads to better reinforcement. The crosslink density and bound rubber content are found to be higher for the silica reinforced CGNR vulcanizates. The physico‐mechanical properties of the silica reinforced CGNR vulcanizates are superior to those of the NR vulcanizates. The CGNR vulcanizates show lower compression set and lower abrasion loss. The dynamic‐mechanical properties exhibit less Payne effect for silica reinforced CGNR vulcanizates as compared to the NR vulcanizates. The transmission electron photomicrographs show uniform dispersion of silica filler in the CGNR matrix. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43057.     

Dispersion of carbon black in high‐abrasion furnace black filled nonsulfur modified powdered polychloroprene rubber

High‐abrasion furnace black (HAF, grade N330) filled nonsulfur modified powdered polychloroprene rubber [P(CR231/HAF)] was prepared with the method of carbon black–rubber latex coagulation using CR231 latex as raw rubber material, HAF as reinforcing filler, and polymeric resin as coating resin. The influence of the content of dispersing agent and coating resin on contact staining and dispersion properties of carbon black in P(CR231/HAF) were investigated. The results show that the addition of dispersing agent and coating resins can decrease the contact staining level of carbon black effectively. When the dispersing agent/HAF (w/w) ratio was 0.12 or 0.1, 10 phr coating resin was added, and P(CR231/HAF) without contact staining can be prepared. The analysis on scanning electron microscopy and surface energy spectrum showed that free carbon black crumb on the surface and inner of P(CR231/HAF) particles causes its contact staining. The well dispersion of carbon black in the P(CR231/HAF) can eliminate contact staining effectively. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 192–196, 2006     

Surface morphology of styrene-butadiene rubber vulcanizate filled with novel electron beam modified dual phase filler by atomic force microscopy

Topographic and phase imaging in tapping mode atomic force microscopy (TMAFM) has been performed to investigate the effect of unmodified and modified dual phase fillers on the morphology of and the microdispersion of the filler particles in the rubber matrix. The above fillers were modified using acrylate monomer (trimethylol propane triacrylate, TMPTA) or a silane coupling agent (triethoxysilylpropyltetrasulphide, Si-69) followed by electron beam modification at room temperature. Both unmodified and surface treated fillers were incorporated in a styrene-butadiene rubber. The phase images of the above composites show three levels of contrasts that correspond to matrix, filler aggregates, and bound rubber around the filler aggregates. Also, the images further elucidate the aggregated nature of the filler due to modification, which is more pronounced in the case of electron beam modified acrylated filler loaded rubber. The corresponding topographic images have been characterized by various statistical quantities like roughness parameters and one- and two-dimensional power spectral densities (1D-PSD and 2D-PSD). As compared to the control, significant increase in surface roughness is observed in the case of the modified dual phase filler loaded composites. The higher fractal value of these vulcanizates confirms the above fact. AFM study also suggests that the electron beam modification of the above fillers significantly increases the filler-filler and filler-polymer interactions.     

Synergistic effects of hybrid carbon nanomaterials in room‐temperature‐vulcanized silicone rubber

This work examines nanocomposites based on nanofillers and room‐temperature‐vulcanized silicone rubber. The carbon nanofillers used were conductive carbon black (CB), carbon nanotubes (CNTs) and graphene (GE). Vulcanizates for CB, GE, CNTs as the only filler and hybrid fillers using CNTs, CB and GE were prepared by solution mixing. The elastic modulus for CNT hybrid with CB at 15 phr (4.65 MPa) was higher than for CB hybrid with GE (3.13 MPa) and CNTs/CB/GE as the only filler. Similarly, the resistance for CNT hybrid with CB at 10 phr (0.41 kΩ) was lower than for CB (0.84 kΩ) at 20 phr and CNTs as the only filler. These improvements result from efficient filler networking, a synergistic effect among the carbon nanomaterials, the high aspect ratio of CNTs and the improved filler dispersion in the rubber matrix. © 2016 Society of Chemical Industry     

Contribution of physico-chemical properties of interfaces on dispersibility, adhesion and flocculation of filler particles in rubber

Reinforcing fillers are added to elastomeric compounds to improve and adjust several mechanical, dynamical, tribological, etc. properties with respect to different applications, i.e. for automotive tires, or technical rubber goods. Carbon black and precipitated silica are widely used as rubber reinforcing fillers; however, some new classes of nanosized substances like organophilic modified clay or carbon nanotubes are presently intensive studied as possible future filler systems in combination with carbon black or silica.An important parameter for the dispersibility and compatibility of the filler in the polymer matrix of rubber compounds is the surface energy and surface polarity of the solid filler particles. Therefore, we systematically measured and compared the dynamic contact angles of a collection of different filler types (carbon blacks, silica, carbon nanotubes and organoclays) using the Wilhelmy method, whereby the particles were fixed as a thin layer at a double-sided adhesive tape. From the contact angle values the polar and disperse part of the surface energies of the filler particles were calculated by fitting Fowkes formula. For an estimation of the compatibility of the fillers with different types of rubber polymers we additionally analyzed the surface energy and polarity of the gum (unfilled) elastomers. From the evaluated surface energies and polarities, thermodynamic predictors for the dispersibility (enthalpy of immersion), the adhesion between filler particles and polymer matrix in the nanocomposite, and for the flocculation behaviour of the particles in a rubber matrix (difference in the works of adhesion) were derived. These thermodynamic predictors improve considerably the compounding process of novel rubber nanocomposites with respect to target-oriented adjustment of rubber properties.     

Preparation of nano‐zinc oxide/EPDM composites with both good thermal conductivity and mechanical properties

In this article, nano‐zinc oxide (ZnO) filled ethylene propylene diene monomer (EPDM) composites are prepared, and the mechanical (static and dynamic) properties and thermal conductivity are investigated respectively, which are further compared with the traditional reinforcing fillers, such as carbon black and nano‐silica. Furthermore, influence of in‐situ modification (mixing operation assisted by silane at high temperature for a certain time) with the silane‐coupling agent Bis‐(3‐thiethoxy silylpropyl)‐tetrasufide (Si69) on the nano‐ZnO filled composites is as well investigated. The results indicate that this novel reinforcing filler nano‐ZnO can not only perform well in reinforcing EPDM but can also improve the thermal conductivity significantly. In‐situ modification with Si69 can enhance the interfacial interaction between nano‐ZnO particles and rubber matrix remarkably, and therefore contribute to the better dispersion of filler. As a result, the mechanical properties and the dynamic heat build‐up of the nano‐ZnO filled composites are improved obviously by in‐situ modification, without influencing the thermal conductivity. In comparison with traditioanl reinforcing fillers, in‐situ modified nano‐ZnO filled composites exhibit the excellent performance in both mechanical (static and dynamic) properties and better thermal conductivity. In general, our work indicates that nano‐ZnO, as the novel thermal conductive reinforcing filler, is suitable to prepare elastomer products serving in dynamic conditions, with the longer expected service life. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Mechanical and dynamic mechanical properties of rice husk ash–filled natural rubber compounds

A laboratory‐sized two‐roll mill was used to incorporate rice husk ash into natural rubber (NR). A conventional vulcanization system was used for curing and cure studies were carried out on a Monsanto rheometer. Physical testing of the NR vulcanizates involved determining tensile and tear resistances and hardness. Swelling behavior of NR compounds and scanning electron microscopy were used to investigate the interaction between rice husk ash and natural rubber. Also, dynamical mechanical thermal analysis was used to assess filler–rubber interactions in terms of storage modulus (E′) and loss tangent (tan δ). For comparison purposes, two commercial fillers, precipitated silica (Zeosil‐175) and carbon black (N774), were also used. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2331–2346, 2002     

Multiwalled carbon nanotube/montmorillonite hybrid filled ethylene‐co‐vinyl acetate nanocomposites with enhanced mechanical properties,thermal stability,and dielectric response

Homogeneous multiwalled carbon nanotube/montmorillonite hybrid filler (HMM) dispersion was prepared by co‐ultrasonication and was subsequently used to prepare ethylene‐co‐vinyl acetate (EVA) nanocomposites by solution blending method. XRD and TEM analysis of HMM confirm significant interaction between the montmorillonite (MMT) layers and multiwalled carbon nanotubes (MWCNT) in line with previous reports. Analysis of the nanocomposites shows the constituent fillers to be homogeneously dispersed in EVA matrix. Mechanical properties of neat EVA are remarkably improved with HMM content up to 3 wt% followed by reversion. Maximum improvement observed in tensile strength, elongation at break, and toughness are 424%, 109%, and 1122%, respectively. Results show maximum thermal stability at 4 wt% and best dielectric response at 1 wt% HMM content. Exceptional mechanical and dielectric properties of EVA nanocomposites attained may be attributed to homogeneous dispersion of fillers and improved polymer–filler interaction. Comparison shows excellent synergy between MWCNT and MMT towards mechanical reinforcement of EVA. POLYM. ENG. SCI., 58:1155–1165, 2018. © 2017 Society of Plastics Engineers     

Styrene butadiene rubber/epoxidized natural rubber/carbon filler nanocomposites: microstructural development and cure characterization

Microstructural development of elastomeric nanocomposites based on (50/50 wt%) styrene butadiene rubber (SBR) and epoxidized natural rubber (50 mol% epoxidation, ENR50) as the rubber matrix including two types of carbon fillers, carbon black (CB) and functionalized multiwall carbon nanotube (NH₂-MWCNT), which were prepared through melt mixing, was studied. The results from FTIR analysis show that there is interaction between functional groups on MWCNT surface and the rubber chains. The AFM analysis also indicates good dispersion of filler particles in the rubber phases. FESEM images from cryo-fractured surface of samples have revealed that nanotubes were rarely pulled out of matrix and their diameter increased, resulting from good interaction between MWCNTs and rubber chains. The DMA results confirm good interfacial interaction between them. Furthermore, the reduced difference between the two T_gs of phases (ΔT_g) shows that the incorporation of 3 phr MWCNT into the blend leads to increment in rubber phase compatibility but at higher MWCNT content (5 phr) due to lower Mooney viscosity of SBR phase, MWCNTs tend to remain in this phase. The bound rubber was adopted to characterize the polymer–filler interaction, showing that bound rubber content has an increasing trend with increasing in fillers content. The cure rheometric studies reveal that MWCNTs accelerate the cure process due to the presence of amine groups on the nanotube surface. In addition, the mechanical properties of samples show an increasing trend by increasing nano-filler content.

     

Cold plasma modification of boron nitride fillers and its effect on the thermal conductivity of silicone rubber/boron nitride composites

Hexagonal boron nitride (h‐BN) fillers were first coated with low‐molecular‐weight polydimethylsiloxane (PDMS) by solution dispersion and then treated in argon plasma for different times. The modified h‐BN fillers were characterized by high‐resolution transmission electron microscopy, X‐ray photoelectron spectroscopy, and contact angle analysis. The results revealed that a thin PDMS film several nanometers thick was tightly coated on the surface of the h‐BN filler after plasma treatment, and this thin film could not be removed by 48 h Soxhlet extraction with n‐hexane at 120°C. Furthermore, the effect of plasma modification on the h‐BN filled silicone rubber composites was investigated. The results indicated that the plasma modification improved the interfacial interaction between h‐BN and the matrix, but hardly affected the distribution state of the h‐BN in the composites. The composites filled with the modified h‐BN exhibit significantly higher thermal conductivity than the composites filled with untreated h‐BN. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

Electron beam modification of filled fluorocarbon rubber

The effect of electron beam irradiation on the properties of carbon black‐, silica‐, and clay‐filled fluorocarbon rubber has been studied over a range of radiation doses, loadings, and nature of the fillers. Compared to the unfilled irradiated rubber, the tensile strength and modulus improve with a decrease in the particle size of the carbon black filler. Similar improvement in these properties is observed with an increase in both the radiation dose and the amount of the filler upto a certain level. The dynamic mechanical analysis reveal an increased glass transition temperature (T_g), a reduced value of the mechanical loss factor at T_g. and an enhanced dynamic storage modulus for the filled samples. The results are explained with the help of sol‐gel analysis and volume fraction of rubber. It is observed that higher reinforcement in the case of the filled vulcanizate is obtained by electron beam modification, as compared to that using the conventional curing system. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 2016–2025, 2000     

Application of rice husk ash as fillers in the natural rubber industry

Rice husk ash (RHA) obtained from agricultural waste, by using rice husk as a power source, is mainly composed of silica and carbon black. A two‐stage conventional mixing procedure was used to incorporate rice husk ash into natural rubber. For comparison purposes, two commercial reinforcing fillers, silica and carbon black, were also used. The effect of these fillers on cure characteristics and mechanical properties of natural rubber materials at various loadings, ranging from 0 to 40 phr, was investigated. The results indicated that RHA filler resulted in lower Mooney viscosity and shorter cure time of the natural rubber materials. The incorporation of RHA into natural rubber improved hardness but decreased tensile strength and tear strength. Other properties, such as Young's modulus and abrasion loss, show no significant change. However, RHA is characterized by a better resilience property than that of silica and carbon black. Scanning electron micrographs revealed that the dispersion of RHA filler in the rubber matrix is discontinuous, which in turn generates a weak structure compared with that of carbon black and silica. Overall results indicate that RHA can be used as a cheaper filler for natural rubber materials where improved mechanical properties are not critical. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 34–41, 2005