A series of new Polypropylene (PP)-clay blends, containing 5 wt % clay, were prepared by melt compounding with maleic anhydride grafted poly(ethyleneco-octene) (MAH-g-POE) as the compatibilizer by varying its content from 0 to 20 wt %. The effect of MAH-g-POE on the PP-clay miscibility was examined by X-ray diffraction (XRD), scanning electronic microscope (SEM) observation, differential scanning calorimeter (DSC) analysis, dynamic mechanical thermal analysis (DMTA), and rheological testing in sequence. The results showed that the addition of MAH-g-POE could improve the dispersion of clay layers in PP matrix and promoted the interaction between PP molecules and clay layers. At 10 wt % MAH-g-POE, the PP-clay blend exhibited a highest value of Tc,onset and Tg as well as a biggest melt storage modulus (GЈ), indicating the greatest PP-clay interaction. On the other hand, improved toughness and stiffness coexisted in blends with 5-10 wt % loading of MAH-g-POE. In view of SEM and DMTA observations, MAH-g-POE was well miscible with the PP matrix, even with the concentration up to 20 wt %.
A series of polypropylene/maleic anhydride grafted polypropylene octane elastomer (MAH-g-POE)/clay (PPMC) nanocomposites were prepared with a novel compatilizer MAH-g-POE and different contents of octadecyl amine modified montmorillonite, and the effects of clay contents on the dynamic mechanical and rheological properties of these PPMC composites were investigated. With clay content increasing, the characteristic X-ray diffraction peak changed from one to two with intensity decreasing, indicating the decreasing concentration of the intercalated clay layers. The gradual decrease of crystallization temperature of PPMC composites with the increase of clay loading should be attributed to the preferred intercalation of MAH-g-POE molecules into clay interlayer during blending, which is also reflected by scanning electron microscopy observations. By evaluating the activation energy for the glass transition process of MAHg-POE and polypropylene (PP) in the PPMC composites, it is found that clay intercalation could cause the restriction effect on the glass transition of both MAH-g-POE and PP, and this restriction effect appears stronger for PP and attained the highest degree at 5 wt % clay loading. The melt elasticity of PP could be improved apparently by the addition of MAH-g-POE, and 5 wt % clay loading is enough for further enhancing the elastic proportion of PP.
ABSTRACT:The linear viscoelastic properties of copolypropylene (cPP)-clay nanocomposites (cPPCNs) prepared by melt intercalating with different amounts of clay were extensively examined by rheological measurements. Meanwhile, the clay effects on the cPP confinements were first estimated by calculating the activation energy of different cPP moving units, including the whole molecular chain, the chain segment, and smaller unit such as chain link. The results showed that the stability of cPPCNs melts wrecked when the clay loading was above 5 wt %. An increase in clay loading of cPPCNs gave rise to a strong low frequency solid-like response (GЈ Ͼ GЉ). Unlike the matrix polymer, cPPCN5 (with 5 wt % clay) exhibited a relaxation plateau as relaxation time prolonged above 100 s, and displayed a maximal linear modulus. The variations of the activation energy of different cPP moving units revealed that the mobility of cPP molecular chains was restricted by clay layers, while these restrictions were not only related to the clay loadings but also largely depended on the clay dispersion status in the matrix. The motions of cPP chain segments were greatly limited at 3-5 wt % loading of clay, but drastically activated with the addition of 7 wt % clay due to the increasing stacks of clay layers within the matrix. However, it was found that the presence of clay had little effect on the mobility of small cPP moving units such as chain links.
Three commercial organoclays pretreated with C 18 H 37 N þ H 3 , C 18 H 37 N þ (CH 3 ) 3 and (C 18 H 37 ) 2 N þ (CH 3 ) 2 , were used to prepare a series of copolypropylene (cPP)-clay nancomposites by melt blending. Then, the effects of the clay content and pretreatment history on the transition and relaxation of cPP molecules in different composites were investigated in detail by dynamic mechanical analysis. The results show that the a-relaxation, ascribed to the movement of polymer main chains within the crystalline regions of different cPP composites, is activated by the increase of clay content. The main b-relaxation, assigned to the glass-rubber transition of cPP segments in amorphous portions, is greatly limited by about 3-5 wt % clay loading, whereas drastically motivated with 7 wt % clay loading, which correlates closely with the dispersion order of clay layers in different composites. Lastly, the g-relaxation, associated with the motion of ethylene sequence of cPP chains, is restricted because of the increasing clay content. Additionally, it is found that the miscibility between cPP molecules and organoclay layers was strengthened as the clay premodifier varied from C 18 H 37 N þ H 3 to C 18 H 37 N þ (CH 3 ) 3 , but somewhat weakened when the premodifier changed as (C 18 H 37 ) 2 N þ (CH 3 ) 2 .
In this paper, irradiated samples by different irradiation doses of the beta/gamma radiation from a selected nuclear cable material, which were studied by tensile machine, DSC and DMTA. The research results show that the elongation at break (EAB) drops with absorbed dose of beta/gamma radiation and at the same dose the EAB drop for beta-irradiated samples is higher than that for gamma-irradiated samples, which means that this material becomes more brittler with more irradiation. The OITP value for the irradiated samples exhibits pronounced drop with absorbed beta/gamma irradiation dose. And moreover, the OITP value of these gamma irradiated samples drops faster than that of those beta irradiated samples. DMTA researches show that the storage modulus (E′) and the loss factor (tanδ = E″/E′, E″ represents the loss modulus) of the irradiated samples present higher values with the increase dose of beta /gamma radiation. It is interest that the E′ behaves firstly an increase, then decreases by rising the temperature within the temperature range of −30–20 °C, and this trend becomes pronounced with increase of irradiation dose, combined with the activation energy, correspond to the glass transition process, for all the irradiated samples which hints that the glass transition process may be hindered in terms of a higher activation energy, but the movement unit could be smaller with a lower Tg, as a result of the beta/gamma irradiation.
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