Study On The Surface Modification Of Silica And Its Effect On The Structure And Performance Of Silica/Natural Rubber(NR) Nano-composites

As a non-carbon reinforcing filler,silica has been increasingly applied in the rubber reinforcement,gradually replacing the carbon black,because replacing carbon black with silica is conducive in reducing petroleum resource consumption.Silica has a nature of self-aggregation and shows poor compatibility with hydrophobic rubber macromolecules,because silica contains numerous hydroxyl(-OH)groups on the surface.Previous researchers confirmed that silica modification is an effective way to reduce the self-aggregation of silica and improve the compatibility between silica and rubber.Different kinds of modifier are widely used in reducing the hydroxyl groups on the silica surface,but the traditional mechanical blending method of adding coupling agents to silica while mixing silica with rubber at the same time may suffer from problems such as low efficiency and high processing temperature,which can cause high energy consumption and complex compounding procedures.Meanwhile,the above mentioned modification methods makes the modification reaction uncontrollable and difficult to identify.To solve the problems listed above,we firstly study the effect of the structure of modifier on the silica modification.Then,we try to select different kinds of modifiers to use together in silica modification;moreover,we try to design and synthesize several kinds of new modifier to provide some new methods for silica modification.The main research contents are as follows:(1)Silica modified by using 3-mercaptopropyl-ethyoxyl-di(tridecyl-pentamethoxy)-silane(Si-747),which is a silane coupling agent with long arms,was investigated in this research.The Si-747 that had a physical interaction with silica(Phy-747)and had a chemical interaction with silica(Che-747)could be separated by the extraction.The efftect of Che-747 and Phy-747 on the silica modification were confirmed by thermal gravimetric analyzer(TGA),Fourier transform infrared(FT-IR)and X-ray photoelectron spectroscopy(XPS).We confirm that the amount of Phy-747 and Che-747 is affected by the modified temperature.Both Che-747 and Phy-747 have effect on reducing the hydrophilicity of silica.As SCA with two long arms,Si-747 can form abundant and concentrated hydrogen bonds with silica.Therefore,the Phy-747 can be removed by ethanol but can hardly be removed by water.Meanwhile,the Che-747 also has physical interaction with silica.The silica modified by Si-747 was used to prepare silica/natural rubber(NR)masterbatches by latex compounding method.Both Phy-747 and Che-747 were conducive to the co-coagulation in the preparation of silica/NR masterbatches.The silica/NR masterbatches containing silica modified by Si-747 in different temperature were used to prepare silica/NR composites.The performance of these composites was investigated by a rubber process analyzer(RPA),transmission electron microscopy(TEM)and a tensile tester.We confirm that both Che-747 and Phy-747 can improve the dispersion of silica in silica/NR compounds,resulting in improving the mechanical and dynamic properties of silica/NR composites.The Che-747 plays a more important role than the Phy-747 in terms of improving properties of silica/NR composites,because of "coupling bridge".Meanwhile,the Phy-747 serves as a plasticizer in silica/NR composites.(2)Realizing and manipulating a fine dispersion of silica nanoparticles in the polymer matrix is always a great challenge.In this work,we firstly successfully utilized the alcohol polyoxyethylene ether(AEO)in silica modification.Through the Fourier transform infrared(FT-IR)and X-ray photoelectron spectroscopy(XPS)analyses,we verify that the physical interaction and the chemical interaction were simultaneously formed between silica and AEO;therefore,there was a multi-interaction existing between AEO and silica,resulting in an organic shell formed on the silica surface.Because of this special multi-interaction,AEO was more effective than sulfur-containing silane coupling agent on reducing the hydrophilicity of silica and promoting the destruction of silica aggregates,indicated by scanning electron microscopy(SEM)and dynamic light scattering.Moreover,AEO contribute significantly to improve the compatibility between silica and rubber,resulting in improving silica dispersion in rubber matrix.However,AEO has no chemical interaction with rubber.(3)The study of preparing silica/rubber composites used in tires with low rolling resistance in an energy-saving method is fast-growing.In this study,a novel strategy is proposed,in which silica was modified by combing alcohol polyoxyethylene ether(AEO)and 3-mercaptopropyltri ethoxy silane(K-MEPTS)for preparing silica/natural rubber(NR)masterbatches.A thermal gravimetric analyzer and Raman spectroscopy results indicated that both AEO and K-MEPTS could be grafted on to the silica surface,and AEO has a chance to shield the mercaptopropyl group on K-MEPTS.Silica modified by AEO and K-MEPTS together was completely co-coagulated with the rubber in preparing silica/NR composites using the latex compounding method with the help of the interaction between AEO and K-MEPTS.The performance of composites prepared by silica/NR masterbatches was investigated by a rubber process analyzer(RPA),transmission electron microscopy(TEM)and a tensile tester.These results demonstrate that AEO forms a physical interface between silica and rubber,resulting in good silica dispersion in the matrix.K-MEPTS forms a chemical interface between silica and rubber,enhancing the reinforcing effect of silica and reducing the mutual friction between silica particles.In summary,using a proper combination of AEO and K-MEPTS is a user-friendly approach for preparing silica/NR composites with excellent performance.(4)Imprving the dispersion of silica in the polymer matrix is always the goal of the silica modifcation.In this work,we firstly successfully synthesized N,N’-bis[3-(triethoxysilyl)propyl-isopropanol]-propane-1,3-diamine(TSPD),which is a new interface modifier,aiming to promote the dispersion of silica NPs.Through the Fourier transform infrared(FTIR)spectroscopy,mass spectroscopy and nuclear magnetic resonance(NMR)analyses,we verify that the synthesized TSPD contains together six ethoxy groups at its two ends.Then we use this TSPD to perform the surface modification of pure silica NPs for the first step,which is realized indicated by the TGA examination,scanning electron microscopy(SEM)analyses and dynamic light scattering(DLS)results.It is clearly observed that the silica NPs modified by TSPD(referred to D-MS)are connected to one another but are not conglutinated tightly,exhibiting a novel pre-dispersed structure with a certain extent of inter-particle distance,which is around 1-2nm supported by the SEM image and the theoretical calculation.Next we fabricated the following four elastomer nanocomposites such as pure silica/natural rubber(NR)composite(PS-NR),D-MS/NR composite(DMS-NR),TESPT modified silica/NR composite(TS-NR)and TESPT modified D-MS/NR composite(T&DMS-NR),and find that the Payne effect is the smallest for T&DMS-NR via the combination use of the D-MS and the traditional coupling agent TESPT,attributed to its best dispersion state evidenced by the TEM results.Moreover,by measuring a series of other important mechanical performance such as the stress-strain,the dynamic strain dependent of the loss factor and the dynamic heat build-up,the T&DMS-NR system greatly exceeds those of the three other systems.(5)Preparing silica/rubber composite by an environmental way is always a great challenge.In this work,we successfully synthesized epoxy-terminated polybutadiene(ETPL),which is a new coupling agent,aiming to eliminate the emission of volatile organic compounds(VOC)in the silica modification for preparing silica/rubber composite.Through the Fourier transform infrared(FTIR)spectroscopy,mass spectroscopy and nuclear magnetic resonance(NMR)analyses,we verified that the ETPL has a structure as designed and has a low molecular weight.Then we used this ETPL to modify the pure silica at 80℃,90℃,100℃ and 110℃,and these modified silica was realized by the thermal gravimetry analyzer(TGA)examination and FTIR results.It is clearly confirmed that ETPL is fully grafted on the silica surface at the temperature of modification above 100℃.Therefore,the silica modification was completely at a relatively low temperature and without any VOC byproduct.Next,we also confirmed the existing of chemical interaction between ETPL and rubber macromolecular by the help of differential scanning calorimeter(DSC).Finally,we fabricated the following four elastomer nanocomposites such as pure silica/natural rubber(NR)composite(PS-NR),alcohol polyoxyethylene ether(AEO)modified silica/NR composite with additional vulcanization accelerator and sulfur(AMS-NR&T),ETPL modified silica/NR composite with additional vulcanization accelerator(EPMS-NR&T)and bis-(y-triethoxysilylpropyl)-tetrasulfide(TESPT)modified silica/NR composite(TS-NR).Through the characterization of these four kinds of silica/NR composites,we found that AMS-NR&T,EPMS-NR&T and TS-NR has almost the same silica dispersion,evidenced by the Payne effect and TEM result.Moreover,by measuring a series of other important mechanical performance such as the stress-strain and the dynamic strain dependent of the loss factor,the EPMS-NR&T system has the same performance as TS-NR,which is the commonly used silica/NR composite for preparing tires.