Mechanical properties and transition temperatures of cross-linked oriented gelatin

This study is an extension of previous work on cellulosics [(1994)Colloid Polym Sci 272: 284, 393] that showed that unusually good mechanical properties can be obtained by drying a swollen network of semirigid chains in a state of strain. This novel approach is applied in this investigation to gelatin, because of its attractive environmental characteristics but poor mechanical properties in the unmodified form. Since drawing of non-crosslinked gelatin is not practical, crosslinking by formaldehyde was used, followed by swelling, drawing and drying at fixed length. Mechanical tests were performed in static and dynamic modes. In this way improvements of Young's modulusE, and stress at break _b were determined as a function of gelatin concentration during drying. An increase inE and _b up to 2–3 times, and in the dynamic modulusE up to 6 times, was obtained when the draw ratio reached 4–5, after whichE, E, and _b were found to decrease. Such behavior is explained by the highest orientation being achieved at =4–5, as proved by x-ray analysis. At =10–20 the orientation is lost due to relaxation of chain segments, which is preceded by partial destroying of the network structure (chemical and physical), possibly via chain scission, but probably mostly by the pulling out of chains from crystallites. In any case, the mechanical properties become poor again.The improvements reported above were referred to the undrawn but crosslinked gelatin. Compared to the starting isotropic non-crosslinked material, the improvement is slightly higher. The observation that the improvements are less than those obtained for the cellulosics is explained by the coexistence of interpenetrating chemical and physical networks, which is typical of gelatin. This structural feature drastically reduces the orientability of the chains and the improvements that can be expected in the mechanical properties.     

RECOVERY OF AMORPHOUS POLY(ETHYLENE TEREPHTHALATE)FILM UNIAXIALLY DRAWN JUST BELOW THE GLASS TRANSITION TEMPERATURE*

Isothermal recovery in the macroscopic length of homogeneously deformed specimens of amorphous poly(ethyleneterephthalate) (PET) film sample uniaxially drawn at 69℃ to the draw ratios λ_0=1.26～2.20 were studied at temperaturesaround the glass transition temperature (T_g = 73℃). Experimental results indicate that the length recovery took place in twodistinct steps: a fast first step (fast relaxation) followed by a slow second step (slow relaxation). The relaxation processeswere accompanied by the reversion of trans-conformers (1340 cm~(-1)) to gauche, and the dichroic function of the 1340 cm~(-1)band characterizing the segmental orientation along the chain direction decreased to a very low value at the end of the fastrelaxation. This fact led us to assign the fast relaxation as the segmental orientation while the slow relaxation as relaxation ofthe global chain orientation. It was found that the slow relaxation follows a single exponential function, with relaxation timesstrongly dependent on the temperature resembling the glass transition process. The fast relaxation does not follow a singleexponential decay, presumably a distribution of relaxation times is involved.     

Non-isothermal crystallization kinetics of hot drawn polyester films

The non-isothermal crystallization kinetics of hot drawn poly(ethylene terephthalate) films were studied using the Kissinger and Ozawa equations. The influence of the initial drawing on the crystallization kinetics was investigated. The values of the apparent activation energy and of the Avrami exponent indicates that the nucleation and growth of crystallites depend greatly on the stress submitted to the samples.     

Frontier orbital interactions of electron pushing and drawing substituents with ferrocenyl group

The frontier orbital interactions of electron pushing and drawing substituents with ferrocenyl group were analyzed based on the electrochemical,UV visible spectral and spectroelectrochemical results of five ferrocene derivatives,R-Fc-A1(PⅠ),A1-Fc-A1(PⅡ),D-Fc-R (PⅢ),D-Kc-A1(PIV) and D-Fc-A2(PV)(R,CH2OH;A1 CHO;A2,CH=C(CN)2 and D,(C18H37)2N-C6H4-CH=CH) It was found that there are strong interactions of the LUMO (πA) of electron drawing substituents with le2g(dxy,dx2 y2)and e2u of the ferroeenyl group because the energy levels of πA and e2g,C2U of (Cp )2 are close,which lower not only the energy levels of bonded orbits,πA+ and dx2-y2+[πA] of PⅠ,PⅡ,PⅣ and PⅤobviously,but also those of their non-bonded orbu dxy For PⅢ,PⅣ and PⅤ,there are strong interactions of HOMO(πD) of the electron pushing substituent with le of the ferrocenyl group because the levels of πD and e of (Cp)2 are close,which result in the formation of anti-bonded orbit,πD- and bonded orbit     

浅析在生产中对光纤性能参数的控制

叙述了光纤的生产工艺,说明了光纤强度下降的原因及预防措施.分析了在不同拉丝速度下,光纤几何参数的变化.     

Drawings of planar graphs with few slopes and segments

We study straight-line drawings of planar graphs with few segments and few slopes. Optimal results are obtained for all trees. Tight bounds are obtained for outerplanar graphs, 2-trees, and planar 3-trees. We prove that every 3-connected plane graph on n vertices has a plane drawing with at most segments and at most 2n slopes. We prove that every cubic 3-connected plane graph has a plane drawing with three slopes (and three bends on the outerface). In a companion paper, drawings of non-planar graphs with few slopes are also considered.     

Parabolic and hyperbolic contours for computing the Bromwich integral

Some of the most effective methods for the numerical inversion of the Laplace transform are based on the approximation of the Bromwich contour integral. The accuracy of these methods often hinges on a good choice of contour, and several such contours have been proposed in the literature. Here we analyze two recently proposed contours, namely a parabola and a hyperbola. Using a representative model problem, we determine estimates for the optimal parameters that define these contours. An application to a fractional diffusion equation is presented.

     

Oriented crystallization of poly(L‐lactic acid) in uniaxially oriented blends with poly(vinylidene fluoride)

This article describes the oriented crystallization of poly(L ‐lactic acid) (PLLA) in uniaxially oriented blends with poly(vinylidene fluoride) (PVDF). Uniaxially drawn films of PLLA/PVDF blend with fixed ends were heat‐treated in two ways to crystallize PLLA in oriented blend films. The crystal orientation of PLLA depended upon the heat‐treatment process. The crystal c‐axis of the α form crystal of PLLA was highly oriented in the drawing direction in a sample cold‐crystallized at T_c = 120 °C, whereas the tilt‐orientation of the [200]/ [110] axes of PLLA was induced in the sample crystallized at T_c = 120 °C after preheating at T_p = 164.5–168.5 °C. Detailed analysis of the wide‐angle X‐ray diffraction (WAXD) indicated that the [020]/ [310] crystal axes were oriented parallel to the drawing direction, which causes the tilt‐orientation of the [200]/ [110] axes and other crystal axes. Scanning electron microscopy (SEM) suggested that oriented crystallization occurs in the stretched domains of PLLA with diameters of 0.5–2.0 μm in the uniaxially drawn films of PVDF/PLLA = 90/10 blend. Although the mechanism for the oriented crystallization of PLLA was not clear, a possibility was heteroepitaxy of the [200]/[110] axes of the α form crystal of PLLA along the [201]/[111] axes of the β form crystal of PVDF that is induced by lattice matching of d₁₀₀(PLLA) ≈ 5d₂₀₁(PVDF). © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1376–1389, 2008     

A new proof of Vázsonyi's conjecture

The diameter graph G of n points in Euclidean 3-space has a bipartite, centrally symmetric double covering on the sphere. Three easy corollaries follow: (1) A self-contained proof of Vázsonyi's conjecture that G has at most 2n−2 edges, which avoids the ball polytopes used in the original proofs given by Grünbaum, Heppes and Straszewicz. (2) G can be embedded in the projective plane. (3) Any two odd cycles in G intersect [V.L. Dol'nikov, Some properties of graphs of diameters, Discrete Comput. Geom. 24 (2000) 293-299].     

Initial stage of fiber structure development in the continuous drawing of poly(ethylene terephthalate)

The initial stage of fiber structure development in the continuous neck‐drawing of amorphous poly(ethylene terephthalate) fibers was analyzed by in situ wide‐angle X‐ray diffraction, small‐angle X‐ray scattering, and fiber temperature measurements. The time error of the measurements (<600 μs) was obtained by synchrotron X‐ray source and laser irradiation heating. A highly ordered fibrillar‐shaped two‐dimensional (smectic‐like) structure was found to be formed less than 1 ms after necking. By analyzing its (001′) and (002′) diffractions, the length of the structure 60–70 nm were obtained. A three‐dimensionally ordered triclinic crystal began to form with the vanishing of the structure around 1 ms after necking. The amount and size of the crystal were almost saturated within several milliseconds of necking, during which time a mainly exothermic heat of crystallization was also observed. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2126–2142, 2008