Zhong-Zhen Yu

A new process of fabricating electrically conducting nylon 6/graphite nanocomposites via intercalation polymerization

A new process was developed to fabricate electrically conducting nylon 6/graphite nanocomposites via intercalation polymerization of ϵ-caprolactam in the presence of expanded graphite. The transition from an electrical insulator to an electrical semiconductor for nylon 6 occurred when the graphite volume content was 0.75, which was much lower than that of conventional conducting polymer composites. The electrical conductivity reached 10−4 S/cm when the graphite content was 2.0 vol %. The TEM microphotographs suggested that the low percolation threshold and the great improvement of electrical conductivity could be attributed to the high aspect ratio (width-to-thickness), the high expansion ratio in c axis of the graphite sheets and the homogeneous dispersion of the nanoscale graphite particles in the nylon 6 matrix.

A new conception on the toughness of nylon 6/silica nanocomposite prepared via in situ polymerization

A novel method, in situ polymerization, was used for the preparation of nylon 6/silica nanocomposites, and the mechanical properties of the nanocomposites were examined. The results showed that the tensile strength, elongation at break, and impact strength of silica-modified nanocomposites exhibited a tendency of up and down with the silica content increasing, while those of silica-unmodified nanocomposites decreased gradually. It also exhibited that the mechanical properties of silica-modified nanocomposites have maximum values only when 5% silica particles were filled. Based on the relationship between impact strength of the nanocomposites and the matrix ligament thickness τ, a new criterion was proposed to explain the unique mechanical properties of nylon 6/silica nanocomposites. The nylon 6/silica nanocomposites can be toughened only when the matrix ligament thickness is less than τc and greater than τa, where τa is the matrix ligament thickness when silica particles begin to aggregate, and τc is the critical matrix ligament thickness when silica particles begin to toughen the nylon 6 matrix. The matrix ligament thickness, τ, is not independent, which related with the volume fraction of the inorganic component because the diameter of inorganic particles remains constant during processing. According to the observation of Electron Scanning Microscope (SEM), the process of dispersion to aggregation of silica particles in the nylon 6 matrix with increasing of the silica content was observed, and this result strongly supported our proposal.

Influence of interfacial adhesion on toughening of polyethylene–octene elastomer/nylon 6 blends

Super-tough nylon 6 was prepared by using polyethylene–octene elastomer (POE) grafted with maleic anhydride as a toughener. The influences of maleating and a compatibilizer on interfacial adhesion and mechanical properties of nylon 6/POE blends were investigated in terms of mechanical testing, Molau tests, SEM observations, IR analyses, and rheological behavior. The results show that the unmodified POE has hardly any contribution to toughness of nylon 6, whereas the maleic anhydride-grafted POE (POE-g-MA) significantly improves the compatibility of POE with nylon 6 and sharply reduces its size in the nylon 6 matrix due to the in situ formation of a graft copolymer between POE-g-MA and nylon 6 during melt processing. With the POE-g-MA, a transition from brittle to ductile occurs. Besides, the use of a compatibilizer in nylon 6/POE-g-MA system shifts the brittle–ductile transition curve to a lower POE-g-MA content, which is attributed, in part, to the chain-extending effect of CE-96 on the nylon 6 matrix leading to further reduction of the sizes of POE-g-MA in the matrix, in part, to the coupling reaction of CE-96 between POE-g-MA and nylon 6.

Toughening of nylon 6 with a maleated core-shell impact modifier

Super-tough nylon 6 was prepared by using maleic anhydride grafted polyethylene-octene rubber/semicrystalline polyolefin blend (TPEg) as an impact modifier. The morphology, dynamic mechanical behavior, mechanical properties, and toughening mechanism were studied. Results indicate that TPEg with a semicrystalline polyolefin core and a polyethylene-octane rubber shell, possesses not only a better processability of extruding and pelletizing with a lower cost, but also an improved toughening effect in comparison with the maleated pure polyethylene-octene rubber. The shear yielding is the main mechanism of the impact energy dissipation. In addition, the influence of melt viscosity of nylon 6 on toughening effectiveness was also investigated. High melt viscosity of matrix is advantageous to the improvement of notched Izod impact strength.

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.

Toughening and reinforcing polypropylene with core–shell structured fillers

An elastomer/rigid particle filler with core-shell structure was prepared by twin-screw extruder according to an encapulation model. It was used to toughen and reinforce polypropylene (PP). An original idea of a one-step processing method was adopted in creating PP/polyoctene-ethylene/talc ternary composites. The rheological behavior of PP was changed and the mechanical properties were improved. SEM observation showed that the core-shell structured filler dispersed better in copolypropylene than in homopolypropylene. Two reasons were proposed and proved by the rheology test and SEM observation.

The role of interfacial modifier in toughening of nylon-6 with a core-shell toughener

The effects of nylon 6 matrix viscosity and a multifunctional epoxy interfacial modifier on the notched impact strength of the blends of nylon 6 with a maleic anhydride modified polyethylene-octene elastomer/semi-crystalline polyolefin blend (TPEg) were studied by means of morphological observation, and mechanical and rheological tests. Because the viscosity of the TPEg is much higher than that of nylon 6, an increase in the viscosity of nylon 6 reduces the viscosity mismatch between the dispersed phase and the matrix, and increases notched impact strength of the blends. Moreover, addition of 0.3 to 0.9 phr of the interfacial modifier leads to a finer dispersion of the TPEg and greatly improves the notched impact strength of the nylon 6/TPEg blends. This is because the multi-epoxy interfacial modifier can react with nylon 6 and the maleated TPEg. The reaction with nylon 6 increases the viscosity of the matrix while the coupling reaction at the interface between nylon 6 and the maleated TPEg leads to better compatibilization.

Toughening of a copolyester with a maleated core‐shell toughener

A reactive extrusion process was developed to toughen an amorphous copolyester (PETG) of ethylene glycol, terephthalic acid and 1,4-cyclohexanedimethanol using either a maleic anhydride grafted polyethylene–octene elastomer (POEg), or a maleic anhydride grafted mixture (TPEg) of the polyethylene–octene elastomer and a semicrystalline polyolefin plastic as the impact modifier. TPEg showed an important toughening effect on the PETG. A sharp ductile-brittle transition was observed when the TPEg content was about 10 wt %. For POEg toughened PETG, the ductile–brittle transition required a higher content in POEg, ∼15 wt %. Evolution of the topography and morphology of the blends and the relationship between impact strength and topography were discussed.

Nonisothermal crystallization kinetics of in situ polyamide-6 blended with poly(phenylene oxide)

Blends of Polyamide-6/Poly(phenylene oxide) (PA-6/PPO) were prepared by in situ polymerization, in which the reactive compatibilizer SP was added. Based on two kinds of kinetic equation of nonisothermal crystallization proposed by Ozawa and Liu, the influences of PPO, the cooling rate, and the compatibilizer on crystallization process of PA-6 were investigated. At a given cooling rate, the presence of PPO reduces the overall crystallization rate of PA-6; for a fixed PPO level, the time of crystallization completed becomes shorter when the cooling rate is higher; the addition of SP impedes the development of crystal growth. Scanning electronic microscope (SEM) results fortified the above conclusion. According to the analysis result of experiment data, it shows that the Ozawa equation does not adequately describe the nonisothermal crystallization behavior of PA-6/PPO blends, whereas the Liu approach can be well applied in this studied system.