Influence of the size of ultrafine CaCO3 powder on PP crystallization

The effects of CaCO3 on the crystallization behavior of polypropylene (PP) were studied by means of DSC and WAXD. The average sizes of the CaCO3 powders used were 0.1 mum (UC) and 0.5 mum (GC), respectively. The PP/CaCO3 composites at compositions of 1 phr and 10 phr were investigated. The results showed that the addition of CaCO3 reduced the supercooling, the rate of nucleation and the overall rate of crystallization (except for the 10 phr UC/PP sample). The crystallinity of PP was increased and the size distribution of the crystallites of alpha -PP; was: broadened. On the other hand,the crystallization rate of 10 phr UC/PP is 1.5 times higher than that of neat PP. It has an overall rate of crystallization 2 times as much as that of the neat PP and has the maximum crystallinity. The sizes of crystallites and the unit cell parameters of alpha -PP were varied by the addition of CaCO3. beta -PP was formed by addition of Ge and was not detected by addition of UC. The differences of crystallization behaviors of PP might be attributed to the combined effects of the content and size of CaCO3 filled.

Functionalization of isotactic polypropylene with maleic anhydride by reactive extrusion: mechanism of melt grafting

In this work, chemical structures and molecular parameters of grafted materials of PP-g-MAH prepared by melt reactive extrusion were studied by using electrospray ionization-mass spectrometer and gel permeation chromatography. It was found that the initial radicals, due to homolitic scission of dicumyl peroxide could be combined with maleic anhydride (MAH) monomers as well as polypropylene (PP) molecular chains. The homopolymerization of MAH cannot occur and the MAH radicals undergo a dismutational reaction under the processing condition (180-190 degreesC). A modified mechanism of melt grafting MAH onto PP has been proposed tentatively on the basis of our experimental results and other experimental findings published in the literature. (C) 2001 Elsevier Science Ltd. All rights reserved.

Mechanical and thermal induced chain conformational transformations in syndiotactic polypropylene (sPP)

Stretching a stacked sPP lamellar morphology at room temperature leads to a mechanical induced transformation from the (t(2)g(2))(2) (helical) into the (tttt) (zigzag) chain conformation of the polymer. The so prepared samples exhibit after annealing above 80 degreesC a thermal induced retransformation into the cell I and cell III crystal structure of the helical chain conformation. The mechanical induced chain conformational transformation as well as the thermal induced retransformation was studied by means of transmission electron microscopy and electron diffraction. (C) 2001 Kluwer Academic Publishers.

Conformation transformation of syndiotactic polypropylene induced by stretching and annealing

Conformation transformation of syndiotactic polypropylene(sPP) induced by stretching and annealing processes has been investigated by WAXD, IR and DSC, The results indicate that not only the quenched samples but also the isothermally crystallized samples can form the crystals with all-trans conformation by means of uniaxially stretching at room temperature. The all-trans conformation crystals are of metastability, which can transform to stable crystals with (TTGG)(2) helical conformation at higher annealing temperatures.

Studies on the interfacial adhesion between functionalized polypropylene and polyamide 1010

The interface behavior of polyamide 1010 (PA1010) and polypropylene (PP) was studied. In order to improve their interfacial adhesion, functional PP was prepared by means of grafting glycidyl methacrylate (GMA) on PP main chains and used instead of plain PP. Several technological characterizations were performed here on their interfaces. ESCA was used to confirm that some kind of reaction occurred between end groups of PA1010 and epoxy species of PP-g-GMA. The peel test was adopted to measure interfacial adhesion. It was found that the fracture energy of interfaces between PA1010 and PP-g-GMA was dramatically increased with the content of GMA. Their interfaces were observed as being blurred by using SEM and TEM and a crack that could be seen in the case of the interfaces of the PA1010 and the plain PP disappeared.

On morphology and the competition between crystallization and phase separation in polypropylene-polyethylene blends

Blends of polypropylene (PP) and low density polyethylene (LDPE) have been examined for a series of compositions using differential scanning calorimetry and permanganic etching followed by transmission electron microscopy. Thermal analysis of their melting and recrystallization behaviour suggests two possibilities, either that below 15 wt % PP the blends are fully miscible and that PP only crystallizes after LDPE because of compositional changes in the remaining melt, or else that the PP is separated, but in the form of droplets too small to crystallize at normal temperatures. Microscopic examination of the morphology shows that the latter is the case, but that a fraction of the PP is nevertheless dissolved in the LDPE. (C) 1998 Kluwer Academic Publishers.

Controlling factors for the occurrence of heteroepitaxy of polyethylene on highly oriented isotactic polypropylene

The controlling factors for the epitaxial crystallization of high-density polyethylene (HDPE) on highly oriented isotactic polypropylene (iPP) substrates have been studied in detail by means of transmission electron microscopy and electron diffraction. The results obtained in this work indicate that the crystallization process must be considered in the investigation of epitaxial growth of polymers on polymeric substrates, because of the unique morphological and crystallization characteristics of polymers. Crystallization rate has an important effect on the epitaxial crystallization of polymers. Higher rates result in the formation of thicker epitaxial layers. Isothermal crystallization temperature is another factor affecting epitaxial growth of polymers. Lower temperatures are favorable to epitaxial crystallization of polymers. There exists a critical epitaxial temperature at given experimental conditions, above which no epitaxial growth occurs at all. The influence of crystal dimensions of both the substrates and the deposited polymers on epitaxial growth confirms that secondary nucleation is an important controlling factor for the occurrence of epitaxial crystallization in polymers. The requirement satisfying the secondary nucleation criterion is that the substrate crystal dimension in the matching direction must be greater than the crystal thickness of the deposited polymer. Once the requirement of the secondary nucleation is satisfied, subsequent epitaxial growth is based on the lamellar growth habit of the deposited polymer itself. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.

Tremolite-reinforced nylon 66 composites: Mechanical and rheological properties

The reinforcement effect of an acicular inorganic filler, tremolite, on nylon 66 was studied. The mechanical properties of tremolite-filled nylon 66 composites and the effect of the filler particle size on them were obtained. The dynamic mechanical properties and rheological properties of the composites were measured. Two treatments, silane and unsaturated polyester, were used to improve the interface between tremolite and the nylon matrix. The morphologies of the composites were investigated using SEM. (C) 1998 John Wiley & Sons, Inc.

Morphological studies of polyamide 1010/polypropylene blends

Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to examine the morphology of blends of PA1010 and polypropylene (PP) compatibilized with polypropylene grafted with glycidyl methacrylate (PP-g-GMA). It is found that the morphologies are dependent on the content of glycidyl methacrylate in PP-g-GMA and the mixing time. The size of the dispersed PP particles decreases as the content of GMA in the PP-g-GMA increases for binary blends of PA1010 and PP-g-GMA. Similar results are obtained for changing the mixing time. Ternary blends of PA1010, PP, and PP-g-GMA indicate that morphologies depend on the content of glycidyl metyacrylate in the PP-g-GMA and the miscibility of PP and PP-g-GMA. By changing the content of GMA in PP-g-GMA, it was possible to introduce significant changes of morphology. A matrix removal TEM method is used to investigate the interfacial structure of PA1010/PP blends containing PP-g-GMA as a compatibilizer. This technique shows the reaction product between PA1010 and PP-g-GMA to be located at interface as a surrounding layer around domain particles. SEM observation on the interface shows that the adhesion between PA1010 and pure PP is very weak and their interface boundary is sharp. For the samples of PA1010 and PP-g-GMA, it was found that the interface was not so obvious, and the reaction between PA1010 and PP-g-GMA strengthens the interface significantly. (C) 1997 Elsevier Science Ltd.

Critical crystallization temperature for the occurrence of epitaxy between high-density polyethylene and isotactic polypropylene

The crystallization behavior of high-density polyethylene (HDPE) on highly oriented isotactic polypropylene (iPP) at elevated temperatures (e.g., from 125 to 128 degrees C), was studied using transmission electron microscopy and electron diffraction. The results show that epitaxial crystallization of HDPE on the highly oriented iPP substrates occurs only in a thin layer which is in direct contact with the iPP substrate, when the HDPE is crystallized from the melt on the oriented iPP substrates at 125 degrees C. The critical layer thickness of the epitaxially crystallized HDPE is not more than 30 nm when the HDPE is isothermally crystallized on the oriented iPP substrates at 125 degrees C. When the crystallization temperature is above 125 degrees C, the HDPE crystallizes in the form of crystalline aggregates and a few individual crystalline lamellae. But both the crystalline aggregates and the individual crystalline lamellae have no epitaxial orientation relationship with the iPP substrate. This means that there exists a critical crystallization temperature for the occurrence of epitaxial crystallization of HDPE on the melt-drawn oriented iPP substrates (i.e., 125 degrees C). (C) 1997 John Wiley & Sons, Inc.

Studies on the PTC/NTC effect of carbon black filled low density polyethylene composites

The positive temperature coefficient (PTC) and negative temperature coefficient (NTC) effect of carbon black (CB) filled low density polyethylene (LDPE) composites was studied using electrical resistivity spectra, DSC, tensile mechanical analysis (TMA) and small-angle X-ray scattering (SAXS) techniques. The three LDPEs used have a similar crystallinity and different melting index (MI). The experimental results indicate that the CB has no significant effect on the crystallinity and the long spacing of crystalline domains of LDPE. Based upon the TMA and dynamic elastic modulus spectra, it can be concluded that the PTC effect is related to the thermal expansion of the polymer matrix, and the NTC effect is caused by a decrease of the elastic modulus of the polymer at high temperatures. The NTC effect can be reduced by enhancing either the elastic modulus or the interaction between carbon black and matrix. (C) 1997 Elsevier Science Ltd.

Critical surface tension of acrylamide-grafted polypropylene copolymer by the contact angle method

The contact angles theta of polar liquids on PP-g-AM copolymer (AM content 0.19, 0.26, and 0.37 wt%) were measured. The critical surface tension gamma(c) of PP-g-AM films were evaluated by the Zisman plot (cos theta versus gamma(L)), the Young-Dupre-Good-Girifalco plot (1 + cos theta) versus 1/gamma(L)(0.5), and the log(1 + cos theta) versus log gamma(L) plot. The gamma(L) values estimated by the plot log(1 + cos theta) versus log gamma(L) were smaller than those obtained by the other plots.

Reinforced effect of wollastonite on phenolphthalein poly(ether ketone)

The mechanical properties of wollastonite-filled phenolphthalein poly(ether ketone) (PEK-C) composites have been studied at room temperature and 200 degrees C. The dispersion of wollastonite particles in PEK-C matrix were investigated by means of scanning electron microscope. The modulus and strength of the composites increased with filler content. The reinforced effect of wollastonite on PEK-C is more marked at elevated temperature. The glass transition temperature of the composites is higher than that of PEK-C and is independent of filler content. The restriction effect of tiller particles on the molecular mobility of the polymer matrix should be attributed to the reinforcement. (C) 1997 John Wiley & Sons, Inc.

Morphological, thermal, and mechanical properties of polypropylene/polycarbonate blend

This work deals with the effect of compatibilizer on the morphological, thermal, rheological, and mechanical properties of polypropylene/polycarbonate (PP/ PC) blends. The blends, containing between 0 to 30 vol % of polycarbonate and a compatibilizer, were prepared by means of a twin-screw extruder. The compatibilizer was produced by grafting glycidyl methacrylate (GMA) onto polypropylene in the molten state. Blend morphologies were controlled by adding PP-g-GMA as compatibilizer during melt processing, thus changing dispersion and interfacial adhesion of the polycarbonate phase. With PP-g-GMA, volume fractions increased from 2.5 to 20, and much finer dispersions of discrete polycarbonate phase with average domain sizes decreased from 35 to 3 mu m were obtained. The WAXD spectra showed that the crystal structure of neat PP was different from that in blends. The DSC results suggested that the degree of crystallization of PP in blends decreased as PC content and compatibilizer increased. The mechanical properties significantly changed after addition of PP-g-GMA. (C) 1997 John Wiley & Sons, Inc.

Crystallization of syndiotactic polypropylene (sPP) from oriented melts

The influence of the syndiotacticity on the crystallization behaviour of syndiotactic polypropylene (sPP) has been investigated. The syndiotacticity has been measured by C-13-NMR spectroscopy and the phase formation has been observed by electron diffraction of oriented samples. It is shown that the crystal phase formation depends strongly on the perfection of the tacticity of the macromolecules.