Preparation,crystallization, and spinnability of poly(ethylene terephthalate)/silica nanocomposites

Poly(ethylene terephthalate) (PET)/silica nanocomposites were successfully prepared by in situ polymerization. Silica nanoparticles were uniformly dispersed in the process of polymerization. By means of hot‐stage polarization microscope and DSC, the influence of nanosilica on the crystallization of PET/silica nanocomposites has been clarified. The results show that nanosilica does not behave as a nucleating agent in PET but postpones the appearance of crystallite. This phenomenon is very favor to improve spinnability. The investigation on melt spinning of PET/silica nanocomposites also shows that it is advantageous to spinning with descending the spinning temperature. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2564–2568, 2007     

纳米二氧化硅表面改性及其补强天然胶乳研究

简述了纳米二氧化硅的表面结构、表面改性机理及方法,介绍国内外对纳米二氧化聩表面化学改性及纳米二氧化硅改性天然橡胶复合材料的制备工艺进行详述,最后对纳米二氧化硅改性天然胶乳存在的问题和发展方向进行了展望。     

Barrier effect of flame retardant systems in poly(methyl methacrylate): Study of the efficiency of the surface treatment by octylsilane of silica nanoparticles in combination with phosphorous fire retardant additives

In this work, flame retardant systems comprising ammonium polyphosphate (AP423) and hydrophilic (A200) or hydrophobic (R805) nanometric silica were incorporated into PMMA. The following techniques were performed to detail the fire behaviour of the composites: mass loss cone calorimetry, pyrolysis‐combustion flow calorimetry, pyrolysis‐gas chromatography–mass spectrometry, thermogravimetric analysis, X‐ray diffraction analysis, Fourier transform infrared spectroscopy and microscopic observations. The best fire behaviour was obtained with the surface‐treated silica in the presence of AP423. The formation of a new crystalline phase from the interactions between AP423 and R805 silica and a strong barrier effect due to a layered residue were the main modes of action of this system. Moreover, we have shown that the difference between the AP423 + R805 and AP423 + A200 systems was due to poor dispersion of the silica into the PMMA matrix in the latter formulation. Copyright © 2011 John Wiley & Sons, Ltd.     

纳米二氧化硅透水混凝土新拌流变及硬化性能

针对传统透水混凝土工作性能不佳和强度偏低的问题,研究了纳米二氧化硅改性透水混凝土的新拌流变性能与硬化性能.结果表明:纳米二氧化硅能够改善新拌透水混凝土中浆体的黏聚性并减少振动时浆体的向下流动,当纳米二氧化硅质量分数达到1.00%时,透水混凝土中浆体的塑性黏度和触变环面积分别提高了64.74%和235.96%;纳米二氧化硅能够通过提高浆体强度来改善透水混凝土的抗压强度,当纳米二氧化硅质量分数超过0.50%后,其对透水混凝土抗压强度的增强效果不再明显;纳米二氧化硅还可以略微提高透水混凝土的透水性能,推测与纳米二氧化硅使得透水混凝土在竖直方向上的孔隙均匀分布有关.     

聚醋酸乙烯酯/纳米SiO_2复合乳液的制备与性能

采用原位乳液聚合法制备了聚醋酸乙烯酯／纳米二氧化硅复合乳液。考察了纳米二氧化硅在聚醋 酸乙烯酯乳液内及乳胶膜中的分散性:纳米二氧化硅用量对复合乳液性能的影响。结果表明:与普通乳液相 比,复合乳液的干态粘接强度和耐水性明显提高。     

The characteristics of hot mixed asphalt modified by nanosilica

The objective of this research is to investigate the characteristics of the hot mixed asphalt modified by 2%, 4%, 6%, and 8% nanosilica by weight of binder. Marshall stability, dynamic creep, and indirect tensile tests were used to study effects of nanosilica on performance characteristics of the mixtures. Results showed that nanosilica can improve Marshall stability, resilient modulus, indirect tensile strength, and fatigue life compared to unmodified mixtures. However, the tensile strength ratio parameter in the moisture sensitivity tests indicated a decrease in the resistance of the modified mixtures against moisture damage.     

Influence of colloidal nanosilica on hydration kinetics and properties of CaO/CaSO4-activated slag binderOA

To solve the energy consumption and CO₂ emission during cement production, the new binders must be developed as an alternative to cement. CaO/CaSO₄-activated slag binder is an eco-friendly and safe cementitious material; however, its low strength during initial stages limits its applications. In this study,colloidal nanosilica(CNS) was employed as an additive to improve the strength of CaO/CaSO₄-activated slag binder, and the effects of CNS on the workability, hy...     

Polyethylene nanocomposites by gas‐phase polymerization of ethylene in the presence of a nanosilica‐supported zirconocene catalyst system

BACKGROUND: Much of the current research related to the development of in situ nanocomposites of olefins by polymerizing them with metallocenes in the presence of surface‐treated fillers is carried out in the slurry phase. In slurry‐phase methods a large amount of solvent is required and there is always a need of purification of the final product due to the possibility of traces of solvents present in the product. To overcome these drawbacks, to perform solvent‐free metallocene‐catalysed polymerizations with in situ incorporation of inorganic nanoparticles, we have used a gas‐phase polymerization technique as this does not require solvents and also utilizes monomer feed stocks efficiently. RESULTS: The catalyst used for the synthesis of in situ polyethylene nanocomposites by gas‐phase polymerization was nanosilica‐supported zirconocene. The fillers used were Cloisite‐20A, kaolin and nanosilica. Three different in situ polyethylene nanocomposites, i.e. Cloisite‐20A‐filled polyethylene (CFPE), kaolin‐filled polyethylene (KFPE) and nanosilica‐filled polyethylene (SFPE), were prepared by gas‐phase polymerization. The nanocomposites were obtained in the form of fine powder. The polyethylene content in the developed nanocomposites is in the orthorhombic crystalline phase. Using our approach, it is observed that the nanofillers are completely encapsulated by a thin layer of polyethylene. Significantly higher molecular weight polyethylene was formed in the case of KFPE in comparison to CFPE and SFPE. The thermal decomposition temperature, melting temperature and enthalpy are also observed to be higher for KFPE. CONCLUSIONS: The gas‐phase polymerization technique has been successfully carried out for the synthesis of in situ polyethylene nanocomposites. Copyright © 2007 Society of Chemical Industry     

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     

气相纳米SiO2·nH2O粒径控制与形貌研究

研究了利用粉煤灰与氟化钙等以气相法直接制备纳米级SiO2·nH2O的工艺。通过有效控制酸解和水解的速度,研究了在水解过程中加入乙醇、乙二醇、丙三醇、十二烷基硫酸钠、柠檬酸作为水解添加剂和分散剂时,对颗粒粒径的良好控制作用,并制备出不同粒径的纳米SiO2·nH2O。研究还发现,以柠檬酸作为分散剂时,粒子表面出现多孔结构。