A number of studies were conducted to demonstrate C-H activation for the construction of C-B bonds. Investigations revealed that the conversion of C-H bonds to C-B bonds was both thermodynamically and kinetically favorable. The reaction at a primary C-H bond of methane or a higher alkene B 2(OR)4 formed an alkylboronate ester R' -B(OR)2 and the accompanying borane H-B(OR2. The ester and the borane were formed on the basis of calculated bond energies for methylboronates and dioaborolanes. The rates of key steps along the reaction pathway for the conversion of a C-H bond in an alkane or arene to the C-B bond in an alkyl or arylboronate ester were favorable. These studies also highlighted the accessible barriers for C-H bond cleavage and B-C bond formation during the borylation of alkanes and arenes.

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C−H Activation for the Construction of C−B Bonds

Environmentally beneficial composites can be made by replacing glass fibres with various types of cellulose fibres. Fibres from pine or eucalyptus wood and also one-year crops such as coir, sisal, etc. are all good candidates. The poor resistance towards water absorption is one of the drawbacks of natural fibres/polypropylene composites. New natural fibres/polypropylene composites were made and the water absorption in them was studied by immersion of the composites in water at three different temperatures, 23, 50 and 70 °C. The process of absorption of water was found to follow the kinetics and mechanisms described by Fick's theory. In addition, the diffusivity coefficient was dependent on the temperature as estimated by means of Arrhenius law. A decrease in tensile properties of the composites was demonstrated, showing a great loss in mechanical properties of the water-saturated samples compared to the dry samples. The morphology change was monitored by scanning electron microscopy studies of the samples before and after exposure to water and the devastating effect of water on the fibre structure was shown.

Comparison of water absorption in natural cellulosic fibres from wood and one-year crops in polypropylene composites and its influence on their mechanical properties

Optimization Techniques with FORTRAN

Crystallization kinetics and nucleation activity of filler in polypropylene/surface-treated SiO2 nanocomposites

Effect of in situ prepared silica nano-particles on non-isothermal crystallization of polypropylene

The moisture absorption and mechanical properties of wood flour–filled polypropylene composites in a hydrothermal environment have been studied by immersing the composites in water at 23, 60, and 100°C. The degree of moisture absorption was found to be dependent on the modification of matrix, the weight percentage, mesh size, and surface treatment of wood flours. It increased with increasing the immersion temperature. The tensile strength of all composites with wood flours of different contents, mesh sizes, and surface treatments increased after immersion in water baths of various temperatures, to either greater or lesser extents. The flexural strength and modulus followed a similar trend when immersed in water at ambient temperature. However, the contrary was true for composites when immersed in 60 and 100°C water baths. The impact strength increased after immersion in water at each immersion temperature, and the extent of such increment decreased with increasing the immersion temperature. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2824–2832, 2002

Effect of hydrothermal environment on moisture absorption and mechanical properties of wood flour–filled polypropylene composites

The effects of an organic phosphorus nucleating agent on the crystallization behavior and mechanical properties of poly(propylene) were investigated. As the concentration of nucleating agent increased from 0 to 0.8%, the tensile and flexural strengths of the nucleated poly(propylene) resin increased by 15%, the flexural modulus increased by 35%, the crystallization peak temperature increased by 10°C, and the nucleation density (calculated with the nonlinear Voltrra integral equation) increased by 106 times. Mechanical properties increased with nucleation density. Linear equations between the mechanical properties and the logarithmic nucleation density were revealed. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 297–301, 2003

Effects of an organic phosphorus nucleating agent on crystallization behaviors and mechanical properties of poly(propylene)

Several types of functionalized polyolefins, grafted with maleic anhydride, were synthesized and used to modify the surface of fiberglass in reinforced polypropylene composites. The influence of maleated polyolefin, matrix, and compounding conditions on the interfacial bonding strength of composite were studied by measuring interfacial shear strength. The results showed that strong interactions, e.g., chemical bonding, were formed between maleated polyolefin and fiber surface. When the modified fibers were compounded with polypropylene, firm entanglements of molecular chain were formed due to the segmental interdiffusion between maleated polyolefin and matrix polypropylene. As a result, the degree of fiber-matrix adhesion was improved. The extent of such improvement depended on the grafting degree, chain length of maleated polyolefin, and the compatibility between maleated polyolefin and matrix resin. At the same time, the compounding temperature and the cooling procedure affected the interfacial adhesion too. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1359–1365, 2000

Influence of functionalized polyolefin on interfacial adhesion of glass fiber-reinforced polypropylene

The crystallization behavior of polypropylene (PP) copolymer obtained by in situ reactor copolymerization with or without a nucleating agent and/or nano-CaCO3 particles was investigated both by thermal analysis and by polarized light microscopy. The Avrami model is successfully used to describe the crystallization kinetics of the studied copolymer. The results of the investigation show that a dramatic decrease of the half-time of crystallization t1/2, as well as a significant increase of the overall crystallization rate, are observed in the presence of the nucleating agent. These effects are further promoted in the presence of the nano-CaCO3 particles. The incorporation of the nucleating agent and nano-CaCO3 particles into PP copolymer remarkably improved the mechanical properties and heat distortion temperature. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 431–438, 2004

Crystallization behavior and mechanical properties of polypropylene copolymer by in situ copolymerization with a nucleating agent and/or nano-calcium carbonate

Mica-filled polypropylene (PP)-based GMT (PP–mica–GMT) was prepared by a double-belt press and its mechanical properties were tested. The effect of the mica content on the mechanical properties of PP–mica–GMT was investigated. It was found that with a lower mica content in matrix the tensile and flexural properties were improved; however, at a high mica content level, the tensile and flexural properties decreased. With respect to the impact strength, there is a maximum value at an approximate 20 wt % mica content level. These results were attributed to the influence of mica on fiber–matrix adhesion. It is most likely that low mica content enhances fiber–matrix adhesion; however, high mica content is unfavorable to fiber–matrix adhesion. Maleic anhydride-grafted PP (MPP) was used to enhance the fiber–matrix adhesion at a higher mica loading level for PP–mica–GMT. With increasing MPP content in the matrix, the tensile properties were significantly improved, whereas the Izod impact strength decreased. In addition, with 5 wt % MPP and 40 wt % mica in the PP matrix formulation, the effect of the mica particle size and glass fiber content on the mechanical properties of PP–mica–GMT was investigated. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2719–2728, 2001

Gance Dai

Papers

Effect of hydrothermal environment on moisture absorption and mechanical properties of wood flour–filled polypropylene composites

Effects of an organic phosphorus nucleating agent on crystallization behaviors and mechanical properties of poly(propylene)

Influence of functionalized polyolefin on interfacial adhesion of glass fiber-reinforced polypropylene

Crystallization behavior and mechanical properties of polypropylene copolymer by in situ copolymerization with a nucleating agent and/or nano-calcium carbonate

Study of the mechanical properties of mica‐filled polypropylene‐based GMT composite