Yinxi Zhang

Effect of different clay treatment on morphology and mechanical properties of PVC-clay nanocomposites

Three kinds of polyvinyl chloride (PVC)/montmorillonite (MMT) nanocomposites were prepared by melt blending of PVC with Na+-MMT and two organically modified MMTs. The nanostructure and relaxation behavior of the PVC/MMT nanocomposites were studied by wide angle X-ray diffraction (WAXD), transmission electron microscopy (TEM) and dynamic mechanical thermal analysis (DMTA). It was found that partially intercalated and disordered structure formed in PVC/Na+-MMT nanocomposites, while partially intercalated and partially exfoliated structures coexisted in the two PVC/organic MMT nanocomposites. The stiffness and impact strength of the three kinds of nanocomposites were improved simultaneously within 0.5–3 wt% MMT content with respect to that of bulk PVC. Below 5 wt% MMT content, the three kinds of nanocomposites retain good optical clarity. In addition, the addition of organic MMT should be kept below 5 wt% in order to enhance the mechanical properties and improve the processing stability of the PVC/MMT nanocomposites.

Influence of clay modification on the structure and mechanical properties of EPDM/montmorillonite nanocomposites

Abstract Conditions were established for dispersing organic montmorillonite (OMMT) nanolayers into ethylene–propylene–diene rubber (EPDM) matrix in a HAAKE mixer. The experimental results of X-ray diffraction and transmission electron microscopy showed that the MMT modified with trimethyloctadecylamine or dimethylbenzyloctadecylamine existed in the form of an intercalated layer structure and the MMT modified with methlybis(2-hydroxyethyl)cocoalkylamine was fully exfoliated in the EPDM matrix. The expansion of the distance between the silicate layers firstly took place after the HAAKE mixing, then the silicate layers were exfoliated in the EPDM matrix after the EPDM/OMMT composite was cured. The EPDM/OMMT composites had good mechanical properties. The EPDM composite containing 15 phr OMMT which was modified with the alkylamine containing hydroxyl groups showed high tensile strength of 25 MPa. Dynamic mechanical analysis revealed that the glass transition temperature (Tg) of the composites was higher than that of gum EPDM vulcanizate. The OMMTs had delaying effects on the vulcanization reaction and decreased the crosslink density of the EPDM/OMMT composites.

Brittle–ductile transition of PP/POE blends in both impact and high speed tensile tests

Abstract Polypropylene (PP)/octene-ethylene copolymer (POE) blends were studied in both impact and high speed tensile tests, in which the practical strain rate was 208/s. With the increase of the POE content, brittle–ductile transition (BDT) of PP/POE blends occurred in both the impact and high speed tensile tests. BDT also occurred with the decrease of the tensile speed when any of the PP/POE blends was drawn. The impact deformation of the notched impact samples was analyzed in details. Most of the strain loading of the notched impact samples is taken by the deformation of the narrow region near the notch tip in impact tests. The microunits of the deformation region deform in two methods: high speed tensile deformation and shear deformation because of the tensile speed gradients in the deformation region. At the beginning of impact tests, the strain rate at the notch tip reaches almost 6000/s. In rubber toughened plastics, the shear deformation decreases greatly because of the rubber particle cavitation. Thus, the impact deformation is really a high speed tensile deformation at the narrow region near notch tips. The BDTs in both impact and high speed tensile tests share the same mechanism. The notch sensitivity of plastics is essentially the tensile speed sensitivity of plastics.

Rheological characterization of storage-stable SBS-modified asphalts

Abstract The high-temperature storage stability of styrene–butadiene–styrene triblock copolymer (SBS) modified asphalt can be improved significantly with the addition of elemental sulfur. The dynamic mechanical properties of SBS-modified asphalts before and after adding sulfur were characterized by using dynamic shear rheometry. The addition of sulfur to SBS modified asphalt resulted in the formation of a chemically vulcanized SBS network structure in the modified binders, and the high temperature performance of the binders was improved and their temperature susceptibility was reduced to a great extent. The SBS content has a great effect on the rheological properties of the asphalts. The rheological properties of SBS modified asphalts depended strongly on the sulfur level. Increasing sulfur levels led to increasing crosslinking density in the modified binders, and consequently the rheological properties of SBS-modified asphalt was improved. A comparison was made among the properties of the asphalts modified by three different SBS structures. The SBS structure affected the compatibility and storage stability of SBS-modified asphalts, which were improved by the addition of sulfur. As determined by a rotational viscometer, the increase in asphalt viscosity is not directly proportional to the SBS content before and after adding sulfur. The morphology of SBS-modified asphalts, which was characterized by optical microscopy, showed that the compatibility and storage stability of SBS modified asphalt were improved by the addition of sulfur.

Effect of nano-CaCO3 on mechanical properties of PVC and PVC/Blendex blend

Abstract The effects of nanoscale calcium carbonate (nano-CaCO 3 ) particles on the mechanical properties of different ductile polymer matrices were investigated. Polyvinyl chloride (PVC) and PVC/Blendex (BLENDEX ® 338) blend were used as the matrix in this study. The nano-CaCO 3 particles were observed to be dispersed uniformly on the nanoscale in both PVC and PVC/Blendex blend by means of transmission electron microscopy. The impact strength, flexural modulus and Vicat softening temperature of PVC and PVC/Blendex blend were significantly enhanced after addition of 0–15 phr nano-CaCO 3 , but the tensile properties of the two matrices showed different changes in the presence of nano-CaCO 3 . The yield strength and elongation at break of PVC could be increased by the addition of nano-CaCO 3 , while those of PVC/Blendex were decreased. Dynamic mechanical thermal analysis showed that the addition of nano-CaCO 3 led to an increase in storage modulus and glass transition temperature for both PVC and PVC/Blendex blend.

Effect of nucleating agent on the structure and properties of polypropylene/poly(ethylene–octene) blends

Abstract The effect of the sorbital nucleating agent on properties of the ethylene–octene copolymer (POE) toughened polypropylene (PP) was studied. The results show that the addition of POE increases notched Izod and Charpy impact strength significantly but impair the tensile strength and flexural modulus. As a nucleating agent (1,3,2,4-di(p-methylbenzylidene) sorbitol, DM) was added, the toughness and stiffness of toughed PP increased simultaneously at the same content of POE. This result shows that the toughness and stiffness of toughed PP are in balance. Polarized light microscopy analysis shows that with the addition of POE and nucleating agent, only a low level of PP spherulites were observed.

Melt grafting of maleic anhydride onto low-density polyethylene/polypropylene blends

Grafting of maleic anhydride (MAH) onto low-density polyethylene/polypropylene (LDPE/PP) blends was performed by melt extruding in the presence of dicumyl peroxide (DCP). The melt viscosities of the grafted blends were measured by a capillary rheometer and the grafting degrees were determined by a back-titration procedure. Compared to the MAH grafted LDPE, the MAH grafted LDPE/PP (90/10) blend had lower viscosity when the DCP or MAH concentration increased in the grafting procedure. However, the grafting degree of the MAH grafted LDPE/PP (90/10) blend was almost the same as or a little higher than that of the MAH grafted LDPE. The characteristic groups of MAH in the grafted products were measured by Fourier transform infrared spectroscopy (FT-IR). The results showed that MAH had grafted onto both LDPE and PP in the blend.

Maleated polypropylene as a coupling agent for polypropylene–waste newspaper flour composites

This paper reports on the influence of maleated polypropylene (MAPP) on the properties of polypropylene (PP)/newspaper flour (PF) composite, and the compatibilization mechanism was also studied. The results of mechanical tests and scanning electron microscope (SEM) showed that MAPP was a true coupling agent for PP/PF blends. The existence of chemical bonds between paper flour and MAPP was proved by gravimetric analysis, while the cocrystallization between bulk PP and PP segments of MAPP was evidenced by differential scanning calorimeter (DSC) and wide angle X-ray diffraction (WAXD) analysis.

EPDM/polyamide TPV compatibilized by chlorinated polyethylene

Abstract A thermoplastic vulcanizate (TPV) of ethylene-propylene-diene (EPDM) and polyamide (PA) with excellent mechanical properties was prepared by dynamic vulcanization. The effects of the vulcanizing agents, compatibilizer, PA content, aging and reprocessing on mechanical properties of EPDM/PA thermoplastic vulcanizate were investigated. Experimental results indicate that chlorinated polyethylene has a better effect in compatibilizing the EPDM/copolyamide blends compared with the other compatibilizers, including maleic anhydride grafted ethylene propylene rubber (MAH-G-EPR), maleic anhydride grafted EPDM (MAH-G-EPDM) and epoxidised ethylene-propylene-diene rubber. Tensile strength and elongation at break go through a maximum value at a compatibilizer resin content (on total rubber content) of 20%. EPDM/PA TPV using sulfur as a vulcanizing agent has higher tensile strength and elongation than that of TPVs using a brominated tert-butyl phenolic resin or peroxide as vulcanizing agent. Tensile strength and elongation at break increase with PA content. DMA results indicated a phase separation in the blend system of EPDM/CPE/PA. The glass transition temperature (Tg) of PA moves towards a high temperature with increasing CPE content, but the Tg of EPDM changes very slightly toward a lower temperature. The loss factor, tanδ, of PA also increases with increasing CPE content. In the blend EPDM/CPE/PA, small PA contents do not cause an immediate increase of storage modulus (E′). Scanning electron microscopy was used to examine the phase morphology of the blends; the results show that the particles of the dispersed EPDM phase have an average size of 2 μm in the dynamically vulcanized EPDM/CPE/PA TPV.

In situ preparation of zinc salts of unsaturated carboxylic acids to reinforce NBR

Through the neutralization reaction of zinc oxide (ZnO) and methacrylic acid (MAA) or acrylic acid (AA), zinc methacrylate (ZMA) or zinc acrylate (ZA) was in situ prepared in nitrile rubber (NBR). The mechanical properties and crosslinking structure of the resulting peroxide-cured NBR vulcanizates were studied. The results showed that ZnO/MAA (AA) had a great reinforcing effect for NBR, and their amounts and ratio played important roles in influencing the mechanical properties. Such vulcanizate contains both covalent crosslinks and salt crosslinks, and the change in the tensile strength of the vulcanizate was related to the variation of the salt crosslink density.