Yucai Ke

The effects of promoter and curing process on exfoliation behavior of epoxy/clay nanocomposites

The effects of a catalyst and coupling agent as well as a curing process on exfoliation behavior of CH3(CH2)15NH3+–montmorillonite clay in an anhydride-cured epoxy–clay system have been investigated by XRD, DSC, and TEM. The results have shown that the organoclay is easily intercalated by the epoxy precursor during the mixing process, and the clay galleries continue to expand during the curing process, but the Na+–montmorillonite clay is not intercalated during either the mixing or the curing process. The results also suggest that in the cured system without any promoter although partial exfoliated clay layers have already formed, an amount of the intercalation structure still remains. Although addition of a promoter or coupling agent into the cured system significantly lowers the maximum reaction temperature, and during the curing process the layered organoclay can be gradually broken into nanoscale structures, in which no d001 diffraction peaks are observed, the complete exfoliation is achieved at gel time or before. The possible mechanism for the complete exfoliation is discussed on the thermodynamic and kinetic point of view.

Impact fracture morphology of nylon 6 toughened with a maleated polyethylene-octene elastomer

This study aimed at using scanning electron microscopy to study the Izod impact fracture surface morphology of super-tough nylon 6 blends prepared by blending nylon 6 with a maleic anhydride-grafted polyethylene-octene elastomer (POE) in the presence of a multifunctional epoxy resin (CE-96) as compatibilizer. The fracture surface morphology and the impact strength of the nylon 6 blends were well correlated. The fracture surface morphology could be divided into a slow-crack-growth region and a fast-crack-growth region. Under low magnification, the fractured surface morphologies of the low-impact-strength nylon 6 blends appeared to be featureless. The area of the slow-crack-growth region was small. There were numerous featherlike geometric figures in the fast crack growth region. The fractured surface morphologies of the high-impact-strength nylon 6 blends exhibited a much larger area in the slow-crack-growth region and parabola markings in the fast-growth region. Under high magnification, some rubber particles of the low-impact-strength nylon 6 blends showed limited cavitation in the slow-crack-growth region and featherlike markings in the fast-crack-growth region. Rubber particles of high-impact-strength nylon 6 blends experienced intensive cavitation in the slow-crack-growth region and both cavitation and matrix shear yielding in the fast-crack-growth region, allowing the blends to dissipate a significant amount of impact energy. A nylon 6 blend containing 30 wt % POEgMA exhibited shear yielding and a great amount of plastic flow of the matrix throughout the entire slow-crack-growth region, thus showing the highest impact strength.

Nonisothermal Crystallization Behavior of In-Situ Formed Polyethylene/Montmorillonite (PE/MMT) Nanocomposites Through Ethylene Copolymerization

PE/MMT nanocomposites containing different amount of MMT were measured for isothermal crystallization. The combination of Ozawa equation and Avrami equation was found applicable in explaining the crystallization behavior of the nanocomposites. In certain range of MMT loadings, MMT particles played the role of nucleating agents that pro- moted the crystallization rate of the polymer matrix, thus making the adjustment of the crystallinity of PE nanocomposites flexible and convenient.

Blends of Syndiotactic Polystyrene and Isotactic Polypropene Prepared Using a Ziegler‐Natta Catalyst Containing a Novel Donor

Blends of syndiotactic polystyrene (sPS) and isotactic polypropene (iPP) have been prepared using TiCl 4 /MgCl 2 /β-diketone activated with methylaluminoxane (MAO). The influences of the Al/Ti ratio and the polymerization temperature on the catalyst activity and the blend composition have been investigated. It is shown that the polymerization temperature is an important factor in determining catalyst activity and the blend composition. Through controlling the polymerization conditions, blends containing a wide composition range of styrene/ propene molar fractions can be prepared. The supported catalyst shows a good activity of about 1.5 × 10 5 (g blend).(mol Ti) -1 .h -1 . 13 C NMR analysis allows the composition of the blends to be calculated. Dynamic mechanical analysis (DMA) reveals that the blends of sPS/iPP prepared this way are partially compatible; the two glass transition temperatures (T g s) of the components shift towards each other. The values of T g . as well as the peaks of sPS intensity, increase with an increasing molar fraction of styrene in the blend. When the sPS content is in the range of 59-80 wt.-%, dual phase continuity occurs in the blends. The morphology found by microscopic observation is consistent with the DMA results.

Novel approach to synthesizing poly(propylene)-graft-poly(styrene) (PP-g-PS)

A novel synthetic route used for preparing PP-g-PS was designed. With this synthetic route, a series of graft copolymers with different contents of PS chain were synthesized successfully, and characterized by13C-NMR, DSC, GPC.

Polymorphic Crystals and Melting Behavior of sPS/iPP Blends Prepared by Polymerization

Blends of sPS/iPP of various compositions from 55/45 to 82/18 were prepared with a novel catalyst by polymerization. Crystal forms, crystallinity and melting behavior of sPS/iPP blends have been studied by FTIR spectroscopy, XRD and DSC. The results obtained show that the polymerization blending and the processing at 290 °C are favorable for formation of α-form crystals in neat sPS and in sPS/iPP blends. Melting points (T m ) and crystallinity of sPS and iPP in blends are reduced. The reflection peaks of sPS in the blends are diffuse and not easily depicted in X-ray patterns. The crystallization rate of iPP is slightly affected by blending, while the crystallization rate of sPS is strongly reduced.