Self-assembled natural rubber/silica nanocomposites: Its preparation and characterization

A novel natural rubber/silica (NR/SiO₂) nanocomposite is developed by combining self-assembly and latex-compounding techniques. The results show that the SiO₂ nanoparticles are homogenously distributed throughout NR matrix as nano-clusters with an average size ranged from 60 to 150 nm when the SiO₂ loading is less than 6.5 wt%. At low SiO₂ contents (4.0 wt%), the NR latex (NRL) and SiO₂ particles are assembled as a core-shell structure by employing poly (diallyldimethylammonium chloride) (PDDA) as an inter-medium, and only primary aggregations of SiO₂ are observed. When more SiO₂ is loaded, secondary aggregations of SiO₂ nanoparticles are gradually generated, and the size of SiO₂ cluster dramatically increases. The thermal/thermooxidative resistance and mechanical properties of NR/SiO₂ nanocomposites are compared to the NR host. The nanocomposites, particularly when the SiO₂ nanoparticles are uniformly dispersed, possess significantly enhanced thermal resistance and mechanical properties, which are strongly depended on the morphology of nanocomposites. The NR/SiO₂ has great potential to manufacture medical protective products with high performances.     

纳米二氧化硅粒径对橡胶复合材料力学性能的影响

以不同粒径的纳米二氧化硅为填料加到天然橡胶中制备纳米二氧化硅/天然橡胶(NR)复合材料。研究了不同粒径纳米二氧化硅(15,30和80nm)对复合材料的力学性能、应力软化效应、Payne效应、动态热机械性能、压缩生热和损耗因子等基本特性的影响。结果表明,随着纳米二氧化硅粒径的增大,复合材料的抗拉强度变大,应力软化效应增大;同时,复合材料的Payne效应和损耗因子越低,其动态压缩温升越低。Payne效应分析及扫描电镜观察还表明,大粒径纳米二氧化硅在橡胶基体中易于分散均匀,粒子间聚集程度更小,而小粒径的则表现出较明显的团聚现象,粒子在橡胶基体中的分散性对复合材料力学性能有直接影响。     

Combination of photocatalytic and antibacterial effects of silver oxide loaded on titania nanotubes

Silver nanoparticles were photodeposited on titania nanotubes and their antibacterial activity was tested. Investigation of the structure and morphology of the nanostructures showed nanometer size silver oxide particles homogeneously distributed on titania nanotubes. Furthermore the modified titania nanotubes were spin-coated as thin films and their antibacterial activity was examined under visible light irradiation and in complete darkness. Although silver oxide loaded titania nanotubes (TiNT-AgO) has a potential for antibacterial activity in both conditions with and without light irradiation, enhanced activity was observed in visible light irradiation condition.     

Organosulfonic acid-functionalized mesoporous composites based on natural rubber and hexagonal mesoporous silica

This study is the first report on synthesis, characterization and catalytic application of propylsulfonic acid-functionalized mesoporous composites based on natural rubber (NR) and hexagonal mesoporous silica (HMS). In comparison with propylsulfonic acid-functionalized HMS (HMS-SO₃H), a series of NR/HMS-SO₃H composites were prepared via an in situ sol–gel process using tetrahydrofuran as the synthesis media. Tetraethylorthosilicate as the silica source, was simultaneously condensed with 3-mercaptopropyltrimethoxysilane in a solution of NR followed by oxidation with hydrogen peroxide to achieve the mesoporous composites containing propylsulfonic acid groups. Fourier-transform infrared spectroscopy and ²⁹Si MAS nuclear magnetic resonance spectroscopy results verified that the silica surfaces of the NR/HMS-SO₃H composites were functionalized with propylsulfonic acid groups and covered with NR molecules. After the incorporation of NR and organo-functional group into HMS, the hexagonal mesostructure remained intact concomitantly with an increased framework wall thickness and unit cell size, as evidenced by the X-ray powder diffraction analysis. Scanning electron microscopy analysis indicated a high interparticle porosity of NR/HMS-SO₃H composites. The textural properties of NR/HMS-SO₃H were affected by the amount of MPTMS loading to a smaller extent than that of HMS-SO₃H. NR/HMS-SO₃H exhibited higher hydrophobicity than HMS-SO₃H, as revealed by H₂O adsorption–desorption measurements. Moreover, the NR/HMS-SO₃H catalysts possessed a superior specific activity to HMS-SO₃H in the esterification of lauric acid with ethanol, resulting in a higher conversion level.     

Aerosol-assisted synthesis of nanoporous silica/titania nanoparticles composites and investigation of their photocatalytic properties

Nanoporous silica/titania nanoparticles composites with relatively large TiO2 content are successfully synthesized by aerosol-assisted co-assembly. By the hybridization of titania with nanoporous silica having high surface area, both the adsorption capability and the reaction rates for the photocatalytic decomposition of methylene blue (MB) are dramatically improved in comparison with unmodified titania nanoparticles without nanoporous silica. Through the quantitative evaluation of the amount of adsorbed and photo-decomposed organic molecule throughout the reaction process, the role of nanoporous silica layers on titania surface is clarified. Rational design of future hybrid photocatalyst with precisely controlled nanostructure will be possible by optimization of our synthetic procedure and careful study of the adsorption and photocatalytic properties.     

Improving properties of modified acrylic sheet via addition of graft natural rubber

The mechanical properties of a modified acrylic sheet prepared by bulk copolymerization of methyl methacrylate (MMA) and styrene (ST) were improved by the addition of a small amount of graft natural rubber (GNR). The graft copolymerization of MMA and ST onto natural rubber latex was carried out by emulsion polymerization using potassium persulfate as an initiator. The properties of the modified acrylic sheet containing GNR with 22.5 wt.% graft copolymer were investigated as a function of GNR content. The results indicated that the impact resistance, tensile strength and elongation at break of the modified acrylic sheet increased with the increase in the amount of GNR in the range of 0.5-4 parts. From the stress-strain behavior, the characteristic of the modified acrylic sheet shifted from brittle to ductile when the amount of GNR was increased. The scanning electron micrographs of the modified acrylic sheets show the relatively smooth fracture surface with relatively few small cracks. This implies that the GNR can be used as an impact modifier for acrylic plastics.     

Silsesquioxane-based hybrid nanocomposites with methacrylate units containing titania and/or silver nanoparticles as antibacterial/antifungal coatings for monumental stones

The present paper reports on the evaluation of two silsesquioxane-based hybrid nanocomposites with methacrylate units containing titania and/or silver nanoparticles aimed as antibacterial coatings for monumental stones. Sol–gel reaction of titanium isopropoxide and/or 3-(trimethoxysilyl)propyl methacrylate, in the presence of silver nitrate and a primary amine surfactant, yielded new types of hybrid nanocomposites with high antibacterial/antifungal efficacy. Different polymer behaviours regarding a frequently used monumental stone originating from Romania were evidenced through Fourier-transform infrared (FTIR) spectroscopy and powder X-ray diffraction (PXRD) technique. Conclusions regarding the stones acid-resistant character and lower influence of salt weathering on its durability, as well as a better protective coating containing titania units were revealed.     

Novel mesoporous composites based on natural rubber and hexagonal mesoporous silica: Synthesis and characterization

The present study is the first report on the synthesis and characterization of mesoporous composites based on natural rubber (NR) and hexagonal mesoporous silica (HMS). A series of NR/HMS composites were prepared in tetrahydrofuran via an in situ sol–gel process using tetraethylorthosilicate as the silica precursor. The physicochemical properties of the composites were characterized by various techniques. The effects of the gel composition on the structural and textural properties of the NR/HMS composites were investigated. The Fourier-transform infrared spectroscopy (FTIR) and ²⁹Si magic angle spinning nuclear magnetic resonance (²⁹Si MAS NMR) results revealed that the surface silanol groups of NR/HMS composites were covered with NR molecules. The powder X-ray diffraction (XRD) and transmission electron microscopy (TEM) data indicated an expansion of the hexagonal unit cell and channel wall thickness due to the incorporation of NR molecules into the mesoporous structure. NR/HMS composites also possessed nanosized particles (∼79.4 nm) as confirmed by scanning electron microscopy (SEM) and particle size distribution analysis. From N₂ adsorption–desorption measurement, the NR/HMS composites possessed a high BET surface area, large pore volume and narrow pore size distribution. Further, they were enhanced hydrophobicity confirmed by H₂O adsorption–desorption measurement. In addition, the mechanistic pathway of the NR/HMS composite formation was proposed.     

天然橡胶/羧甲基壳聚糖抗菌复合膜的力学性能研究

采用胶乳共混法制备得到了天然橡胶羧甲基壳聚糖(NR/CCS)复合胶膜,通过NMR交联密度仪、拉力测试机、动态热力学分析仪等对复合材料的性能进行了表征。结果表明,复合胶膜的交联密度略微增大(5.75×10-5mol/cm3),力学性能增强到11.25MPa,并且复合胶膜的弹性模量增大,刚性增强,并通过这些测试证明了NR与CCS分子存在氢键的作用。     

Effect of multi-wall carbon nanotubes on the mechanical properties of natural rubber

Multi-walled carbon nanotubes (MWNTs) were used to prepare natural rubber (NR) nanocomposites. Our first effort to achieve nanostructures in MWNTs/NR nanocomposites were formed by incorporating carbonnanotubes in a polymer solution and subsequently evaporating the solvent. Using this technique, nanotubess can be dispersed homogeneously in the NR matrix in an attempt to increase the mechanical properties of these nanocomposites. The properties of the nanocomposites such as tensile strength, tensile modulus, tear strength, elongation at break and hardness were studied. Mechanical test results show an increase in the initial modulus for up to 12 times in relation to pure NR. In addition to mechanical testing, the dispersion state of the MWNTs into NR was studied by transmission electron microscopy (TEM) in order to understand the morphology of the resulting system. According to the present study, application of the physical and mechanical properties of carbon nanotubes to NR can result in rubber products which have improved mechanical, physical and chemical properties, compared with existing rubber products reinforced with carbon black or silicone.     

Effect of doping levels on the pore structure of carbon nanotube/silica xerogel composites

This letter reports the effect of CNT doping levels on the pore structure of carbon nanotube (CNT)/silica xerogel composites, which would greatly influence the composite's physical behaviors and their applications in the field of optics. The composites were prepared by sol-gel technique and carried out pore structure analysis. The results show that there are mainly two grades of pores, centering at 8 and 15 nm respectively, that existed in the structure. The relative ratio of the two-grade pores, also BET surface area and pore volume of the composites, change with the different CNT doping levels. The reason may be that the addition of CNTs can act as inhomogeneous crystalline sources, seduce the silica xerogel network to grow around them and therefore change the gel formation process of silica granules.     

硅藻土/硅橡胶可陶瓷化复合材料的制备及性能

硅橡胶耐热性不佳严重制约着其在耐高温领域的应用。针对这一问题,分别采用低熔点氧化物Sb_2O_3和Bi_2O_3作为助溶剂,研究其对硅藻土/硅橡胶复合材料可瓷化性能的影响。采用TG分析Sb_2O_3和Bi_2O_3对硅藻土/硅橡胶复合材料的热稳定性影响,万能力学试验仪测试热解后试样的弯曲强度,场发射扫描电镜(FESEM)和能谱仪(EDS)分析热解产物的微观形貌和成份,XRD探索复合材料的可瓷化机制。结果表明:Sb_2O_3和Bi_2O_3金属氧化物会加速硅橡胶的分解,但可以明显提高热解后试样的弯曲强度。FESEM观测到Sb_2O_3和Bi_2O_3有助于复合材料在热解过程中形成连续的桥连结构,通过EDS分析计算可知,Sb_2O_3与SiO_2,Bi_2O_3与SiO_2在热解过程中可能发生共熔反应,有助于陶瓷化结构的形成。XRD表明,加入助溶剂后的硅藻土/硅橡胶复合材料的热解后形成非晶相结构,提高陶瓷层的强度。     

Effect of fillers on natural rubber/high styrene rubber blends with nano silica: Morphology and wear

The blends of high styrene rubber (HSR) and natural rubber (NR) with nano silica were prepared using a blending technique in presence of different types of carbon black. The effect of filler on morphological and wear characteristics was studied. ISAF (Intermediate Super Abrasion Furnace) type of carbon black have showed a significant effect on optimum cure time, cure rate index and mechanical properties by reacting at the interface between HSR and NR matrix. All the samples show only one melting peak on the DSC curve; this is attributed to the same backbone structure of the matrix and the carbon black reinforcement. The samples containing 30 wt.% of HSR with ISAF type of carbon black has shown maximum heat buildup, lower swelling and lower compression set value. Blends containing ISAF type of carbon black with 30 wt.% of HSR showed high abrasion resistant properties against Du-Pont abrader, DIN abrader and different mining rock surfaces and also is found to be the toughest rubber against all types of rock. Coal is main abrader against the rubber under this study.     

Effect of processing methods on physicochemical properties of titania nanoparticles produced from natural rutile sand

Titania (TiO₂) nanoparticles were produced from natural rutile sand using different approaches such as sol–gel, sonication and spray pyrolysis. The inexpensive titanium sulphate precursor was extracted from rutile sand by employing simple chemical method and used for the production of TiO₂ nanoparticles. Particle size, crystalline structure, surface area, morphology and band gap of the produced nanoparticles are discussed and compared with the different production methods such as sol–gel, sonication and spray pyrolysis. Mean size distribution (d₅₀) of obtained particles is 76 ± 3, 68 ± 3 and 38 ± 3 nm, respectively, for sol–gel, sonication and spray pyrolysis techniques. The band gap (3.168 < 3.215 < 3.240 eV) and surface area (36 < 60 < 103 m² g^?1) of particles are increased with decreasing particle size (76 > 68 > 38 nm), when the process methodology is changed from sol–gel to sonication and sonication to the spray pyrolysis. Among the three methods, spray pyrolysis yields high-surface particles with active semiconductor bandgap energy. The effects of concentration of the precursor, pressure and working temperature are less significant for large-scale production of TiO₂ nanoparticles from natural minerals.     

天然橡胶/改性碱木素复合材料的制备及性能研究

对碱木素进行羟甲基化改性,并以此为原料制备天然橡胶/改性碱木素复合材料。研究了复合材料的力学性能、热稳定性、加工性能以及碱木素的微观形貌。结果表明:当甲醛用量为1.0mol/kg碱木素,改性碱木素添加量为10%,丙三醇添加量为6g/100g改性碱木素时,复合材料的力学性能最优。热重分析显示:天然橡胶和复合材料的热稳定性十分接近,复合材料的成炭量有所增加。橡胶加工性能分析(RPA)表明:碱木素经改性后,在天然橡胶中的分散性得到了改善,与天然橡胶基体的相容性得到了提高;复合材料的储能模量、损耗模量和损耗因子增加。     

Simultaneous control of size and surface functionality of silica particle via growing method

Although silane treatment has been studied as a simple and powerful tool to modify the surface of silica particle, there are still several difficulties in terms of controlling surface functionality and size of nanoparticles. Here we develop a growing method to overcome above drawback. The method was processed by continuously injecting precursor using syringe pump. According to the continuous injection, the concentration of precursors in media are properly controlled, and then the continuous injection of precursor promotes the growth of silica particles. When the functional silanes (silane coupling agents) are used, the method can control the amount of surficial functional groups on the silica particle, and can adjust diameter of the particle simultaneously. Furthermore, well-controlled functional silica particles made by growing method are used for catalytic reaction, Knoevenagel reaction, as a solid state catalyst.     

Quantification of silver ion release, in vitro cytotoxicity and antibacterial properties of nanostuctured Ag doped TiO2 coatings on stainless steel deposited by RF magnetron sputtering

Surface treatments on biomaterials using several methods have greatly reduced the in vivo bacterial attachment, surface colonization and formation of biofilm. In this study, the effect of silver (Ag) ion release against in vitro antibacterial activity and cytotoxicity of 1-4wt% Ag doped titania (TiO₂) thin film coatings were evaluated. These coatings were deposited for 1-6 h onto stainless steel substrate (SS) using (radio frequency) RF magnetron sputtering technique. The coatings predominantly in the crystalline anatase phase were configured using X-ray Diffraction (XRD). Scanning electron microscopy (SEM) observation showed the presence of Ag-TiO₂ nanoparticles of less than 100 nm in all the coated surfaces confirming the formation of nanostructured coatings. An initial rapid release, followed by a sustained lower release of Ag ion concentration was measured between 0.45 and 122 ppb when all the coated substrates immersed in Phosphate Buffered Saline (PBS) for 1-10 days. The obtained concentration was less than the maximum toxic concentration for human cells; yet achieved antibacterial concentration, sufficient to kill or inhibit the growth of bacteria. In vitro cytotoxicity results have indicated that 1-4 wt% of Ag doped TiO₂ coatings had no adverse effect on mouse fibroblast proliferation, confirming its cytocompatibility. The antibacterial assessment was performed on 1 and 2 wt% Ag-TiO₂ coatings using Staphylococcus aureus (S. aureus) whereby significant antibacterial activity was observed in 2 wt% Ag-TiO₂ coatings.     

Correlation between the acoustic and dynamic mechanical properties of natural rubber foam: Effect of foaming temperature

Acoustic absorbing foam materials are produced from dry natural rubber (NR) with the addition of sodium bicarbonate as a blowing agent. The acoustical efficiencies of NR foams were studied, and the results show a significant influence of the viscoelastic and damping properties of the base matrix. Both of these properties are governed by the average cell size, relative density, crosslink density and number of cells per unit volume. The lowest foaming temperature, 140 °C, yielded the NR foam (NR 140) with the highest relative density, crosslink density, smallest average cell size and greatest number of cells per unit volume. Consequently, these foam cell characteristics resulted in a superior sound absorption coefficient and a high storage modulus, which indicates that the NR 140 foam exhibits a better elastic behavior. On the other hand, the NR foam that expanded at 160 °C (NR 160) exhibited great potential for insulating sound and possessed good damping properties, which was characterized by its high transmission loss and tan δ values.     

Barrier properties of natural rubber/ethylene vinyl acetate/carbon black composites

Composites based on natural rubber (NR), ethylene vinyl acetate (EVA) and carbon black were prepared. Three types of carbon black viz.; semireinforcing furnace (SRF), high-abrasion furnace (HAF) and intermediate superabrasion furnace (ISAF) were used for reinforcement. The barrier properties of these filled samples were examined in an atmosphere of petrol, kerosene and diesel. Blends loaded with ISAF exhibited the lowest liquid uptake which has been attributed to the higher filler reinforcement and crosslink density of the matrix. Among the three vulcanising systems used, viz.; sulphur (S), dicumyl peroxide (DCP) and mixed (S+DCP), DCP crosslinked samples exhibited high barrier properties to the probe molecules. Diesel showed the lowest interaction with the composites compared to petrol and kerosene. The sorption data were used to estimate the enthalpy, entropy and free energy of the transport process.     

Controlled release of phenytoin for epilepsy treatment from titania and silica based materials

Template technique was used to obtain well ordered nanostructured materials: mesoporous silica and nanostructured titania tubes. This technique permits the synthesis of solids with controlled mesoporosity, where a large variety of molecules that have therapeutic activity can be hosted and further released to specific sites. In this work phenytoin (PH), a drug used in epilepsy treatment, was loaded in ordered mesoporous silica (SBA 15) and nanostructured titania tubes (TiO₂). The pure materials and those containing PH were characterized by X-ray diffraction, FTIR spectroscopy, transmission electron microscopy (TEM), scanning electron microscopy (SEM) and N₂ adsorption–desorption at 77 K. In order to determine the loading capacity of the antiepileptic drug on these silica- and titania-based materials, the loading and release of PH was investigated using UV–vis spectroscopy. Tubular structures were found for the titania samples, for which the X-ray diffractograms showed to be formed by anatase and rutile phases. On the other hand, an amorphous phase was found in the silica sample. A highly ordered hexagonal structure of 1D cylindrical channels was also observed for this material. Loaded PH showed a good stability inside the used materials as observed by spectroscopy analysis. The adsorption and desorption of PH are faster in nanostructured TiO₂ tubes than in mesoporous silica matrix.