摘要:

Films of highly syndiotactic polypropylene (sPP) were quenched at different temperatures between 0°C and 100°C and analyzed as soon as prepared and after 1 month of aging at room temperature. Wide-angle X-ray diffractograms (WAXDs) showed that all the samples crystallized in the disordered helical form I, with the crystallinity increasing both on increasing the quenching temperature and on aging, although to a lower extent. The analysis of sorption and diffusion of dichloromethane vapor at low activity shows that, in some samples, the fraction of impermeable phase is consistently higher than the crystalline fraction. This induced us to hypothesize the presence of an intermediate phase, or mesophase, not crystalline, yet impermeable to the vapors. The fraction of mesophase decreases on increasing the quenching temperature, and it is a very small quantity at 100°C. The dynamic-mechanical analysis showed two transitions in the aged samples, which could correspond to the lower and upper glass transitions, already suggested for aged films of isotactic polypropylene (IPP).

ISSN:0022-2348    

DOI:10.1081/MB-100100397

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Toluene, carbon tetrachloride, and tetrahydrofuran (THF) sorption and desorption by polypropylene (PP) and 20% and 40% talc-filled PPs were studied, and the effects of the solvent presence on the structure and mechanical properties were measured. The diffusion coefficients were related to the affinity of each solvent for the PP and their molecular volume. Whatever the solvent, the rate of solvent uptake and the equilibrium sorption decreased as the talc content increased as a consequence of the impermeable nature and lack of effect on sorption of the talc particles. All the materials showed highly reversible plasticization by the solvents. The relative decrease in the modulus of elasticity and tensile strength was the same in unfilled and filled PPs. However, important ductility increases, not seen in the unfilled PP, were obtained in the composites as the solvent content increased, probably due to the presence of both cavitation and rubberlike behavior.

ISSN:0022-2348    

DOI:10.1081/MB-100100398

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

A series of 50:50 polycarbonate–poly(butylene terephthalate) (PC-PBT) blends were formed via reactive melt blending in a torque rheometer. A controlled degree of transesterification between the two homopolymers was initiated by the incorporation of an alkyl titanium catalyst during melt blending and finally quenched by the addition of a transesterification inhibitor. The resultant materials were characterized using differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). As the degree of transesterification increased, the composition of the blends became increasingly complex, comprising mixtures of the homopolymers and variousAB-type copolymers of PC and PBT, resulting in significant changes in their thermal behavior. A corresponding transformation in the morphology of the blends was observed due to the formation of increasing concentrations of copolyesters. Thus, the initial coarse (>5 μm) bicontinuous morphology developed into a more finely dispersed submicron-scale structure, exhibited by blends containing significant volumes of interphase material; finally, at high degrees of transesterification, a homogeneous, amorphous material was formed.

ISSN:0022-2348    

DOI:10.1081/MB-100100399

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

A sample of commercial semicrystalline polyethylene (PE), characterized by aMwof 300,000 and an estimated crystallinity of 73%, was structurally characterized through constant wavelength (CW) X-ray powder diffraction and the Rietveld method. The space group is Pnam; the cell parameters area= 7.4241(7) Å;b= 4.9491(5) Å;c= 2.5534(1) Å. The structure of crystalline PE was refined to a respectable level for X-ray powder diffraction experiments, including isotropic displacement parameters and hydrogen atom coordinates. The refinement indicates a C─C bond distance (ca. 1.53 Å) and a C─C─C (ca. 113°) intrachain bond angle, comparable to those reported for other polymers and PE. The inclusion of the amorphous fraction, through a Debye-type function, and some 1% by weight of monoclinic PE allows the proper fitting of the broad band in the 10°–30° 2θ. The derived correlation distancesrof the amorphous PE are in substantial agreement with those reported in reference data from especially suited experiments. The correlation limit has been estimated to be of the order of 23 Å.

ISSN:0022-2348    

DOI:10.1081/MB-100100400

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Small-angle X-ray scattering (SAXS) patterns are used to identify features of semicrystalline polymers composed of alternating lamellar crystals and amorphous regions. Provided that lamellae are wide and flat, the structure is a one-dimensional stack with an average periodLestablished by distributions of crystal thicknessH(y) and amorphous thicknessh(z) and with crystallinity α = [ybar]/[xbar], where average crystal thickness is [ybar], and average long period is [xbar]. The one-dimensional intensityI1(s1) givesLB, while the one-dimensional correlation function γ1(r) and the one-dimensional interface distribution functiong1(r) also provide measures of periodicityr*andr3, respectively. Obvious features of γ1(r) andg1(r) also permit estimation of crystallinity, designated αγand αgrespectively.I1(s1), γ1(r) andg1(r) are calculated for models having symmetric and positively skewed distributionsH(y) andh(z) and for stacks of finite heightN[xbar]. For all conditions, it is found thatLB≥r*≥r3, and that αg≥ α ≥ αγ. With symmetric distributions and infiniteN,LBnearly equals the weight-average period [xbar]w, andr3= [xbar]. These equalities do not hold when thickness distributions are skewed. Small stack heightN[xbar] distortsI1(s1) and γ1(r), but the interface distribution functiong1(r) is scarcely affected, returningr3= [xbar] and αg= α. It is recommended that all three functions be analyzed to obtain the most complete picture of the semicrystalline microstructure.

ISSN:0022-2348    

DOI:10.1081/MB-100100401

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Temperature scanning techniques, including synchrotron small-angle X-ray scattering (SAXS), wide-angle X-ray diffraction(WAXD), and temperature-modulated differential scanning calorimetry (TMDSC), were used to study melting recrystallization in semicrystalline polyoxymethylene (POM). The isothermal crystallization of POM was also studied by time-resolved SAXS. From SAXS profiles, several morphological variables were calculated, including the long periodL, lamellar thicknesslc, interlamellar amorphous thicknessla, and scattering invariantQ. The lamellar parameters were also obtained using tapping atomic force microscopy (AFM) for two thermal histories, and some lamellar-scale and larger-scale morphological changes were characterized before and after partial melting. These real-space images also provided support to interpretation of SAXS analysis in the interpretation of first- and second-order intensity maxima. During melting at constant heating rates,lafrom SAXS increased slowly starting at about 100°C, suggesting melting of thin inserted lamellae, and at about 150°C,lcbegan to increase combined with a more rapid increase inladue to further melting of inserted lamellae and some recrystallization into separate stacks of lamellae. The end of melting was about 182°C. TMDSC data also characterized the level of melting and recrystallization starting at low temperatures for a quenched sample. The DSC data provided the total extent of melting, and this was contrasted with the drop in SAXS and WAXD intensities. SAXS and TMDSC temperature scans on a quenched, but still highly crystalline, POM sample were compared with the data from a high-temperature (145°C) isothermally crystallized POM sample with a higher degree of crystal perfection.

ISSN:0022-2348    

DOI:10.1081/MB-100100402

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Polyamide 6 (PA 6)/clay hybrid (NCH) nanocomposites containing 2 and 5 wt% of clay were melt spun at take-up velocities from 1 to 5 km/min, and the effect of clay on the fiber structure formation was investigated. As the reference, neat PA 6 was spun at take-up velocities from 1 to 7 km/min. The NCH fibers showed higher crystallinity in the whole take-up velocity range, although there was no remarkable crystallinity dependence on the clay content. The birefringence of NCH fibers exceeded that of neat polymer only in the low take-up velocity region (i.e., up to 3 km/min). The orientation-induced crystallization was observed to start at about 2 km/min for NCH and at 4 km/min for neat PA 6. Also, at these take-up velocities, the peaks of α-form crystals appeared in the wide-angle X-ray diffraction equatorial (WAXD) scans, indicating that the orientation-induced crystallization was related to the direct formation of α-form crystals in the spinline. The NCH fibers were superior in Young's modulus; however, their tenacity was higher only in the low take-up velocity region in which the crystallization in the spinline of neat PA 6 did not occur yet. That variation of tenacity was attributed to the molecular orientation, whereas the modulus was supposed to be determined by the stiffness of intercrystalline regions.

ISSN:0022-2348    

DOI:10.1081/MB-100100403

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

High-speed spun poly(ethylene terephthalate) (PET) fibers that had higher crystallinity, larger crystallite sizes, and lower birefringence than ordinarily spun PET showed higher penetrability to Fe3(CO)12and its derivatives in supercritical carbon dioxide fluid at a temperature of 50°C–80°C and a pressure of 18.2–19.3 MPa. The sizes of the channels caused by the fibrillation of PET fibers in supercritical CO2fluid influenced the penetrability of these organometallic compounds.

ISSN:0022-2348    

DOI:10.1081/MB-100100404

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Dynamic mechanical properties of sulfonated butyl rubber ionomers neutralized with different amine or metallic ion (zinc or barium) and their blends with polypropylene (PP), high-density polyethylene (HDPE), or styrene-butadiene-styrene (SBS) triblock copolymer were studied using viscoelastometry. The results showed that glass transition temperatures of ion pair–containing matrix and ionic domains (Tg1andTg2, respectively) of amine-neutralized ionomers were lower than those of ionomers neutralized with metallic ions, and the temperature range of the rubbery plateau on the storage modulus plot for amine-neutralized ionomers was narrower. The modulus of the rubbery plateau for amine-neutralized ionomers was lower than that of ionomers neutralized with zinc or barium ion. With increasing size of the amine, the temperature range for the rubbery plateau decreased, and the height of the loss peak at higher temperature increased. Dynamic mechanical properties of blends of the zinc ionomer with PP or HDPE showed that, with decreasing ionomer content, theTmof PP or HDPE increased andTg1decreased, whereasTg2or the upper loss peak temperature changed only slightly. TheTg1for the blend with SBS also decreased with decreasing ionomer content. The decrease ofTg1is attributed to the enhanced compatibilization of the matrix of the ionomer-containing ion pairs with amorphous regions of PP or HDPE or the continuous phase of SBS due to the formation of thermoplastic interpenetrating polymer networks by ionic domains and crystalline or glassy domains.

ISSN:0022-2348    

DOI:10.1081/MB-100100405

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor