Cumulative erasing effect in the melt memory of nylon 6

The effect of melt annealing over a wide range of temperatures (240–300°C) and durations (0.5–120 min) on the induction period and the heat of crystallization of nylon 6 was studied by means of differential scanning calorimetry. It was found that the crystallization characteristics are determined by the total annealing time experienced by the melt at a given temperature; i.e., a cumulative effect on the erasure of the melt memory is observed. Complete destruction of the crystalline nuclei is achieved after annealing for 90 min at 280°C, the equilibrium melting point of nylon 6; the nuclei cannot be regenerated by nonisothermal crystallization. All the effects observed are explained by the existence of a wide distribution of size and perfection of nuclei.     

Piezoelectricity in uniaxially stretched and plasticized nylon 11 films

The combined effect of uniaxial stretching and plasticization of nylon 11 films on the resulting piezoelectric response was studied. Three different kinds of samples were studied for nylon 11 α′-form films: (1) uniaxially stretched at 150°C, (2) samples uniaxially stretched at 150°C and then plasticized by immersion in 2-ethyl 1,3-hexanediol, and (3) samples plasticized and then uniaxially stretched. The largest piezoelectric response was obtained from the samples which were plasticized prior to uniaxial stretching under identical poling conditions. For the case of nylon 11 δ′-form films, two different kinds of experiments were performed: (1) samples uniaxially stretched at room temperature were subsequently plasticized by immersion in the plasticizer and a comparison of their piezoelectric response made with that of the unplasticized samples as a function of poling field; (2) the plasticizer content dependence of the piezoelectric response from these samples was studied. In both cases, d₃₁ was observed to be higher for the plasticized films compared with the unplasticized films. The piezoelectric stress constant e₃₁ showed a small decrease with plasticization. X-ray diffraction studies indicated a small conversion of δ′-phase to α′-phase with plasticization. No significant changes were observed in the x-ray diffraction scans taken before and after poling.     

Properties and biodegradability of chitosan/nylon 11 blending films

Different ratios of nylon 11/chitosan blending films were prepared by solution casting method. The strength of the hydrogen bond in the blending films is weakened after addition of chitosan and spherulite growth is restricted as the ratio of chitosan increases. Sea-island morphology could be observed once the concentration of chitosan in the blends was more than 50%. Blending films are characterized by FTIR (Fourier transform infrared spectroscopy), X-ray, and scanning electron microscopy (SEM) and the biodegradability is also investigated. The extent of biodegradability for nylon 11/chitosan blending films is strongly affected by the addition percentage of chitosan.     

Structure of iodide ion arrays in iodinated nylon 6 and the chain orientation induced by iodine in nylon 6 films

Two species of iodide ions (I₃^? and I₅^?) are found in iodine—nylon 6 complexes. Orientation of I₅^? arrays (most likely I₂/I₃^? complex) along the polymer chain and I₃^? ions perpendicular to the chain axis in uniaxially drawn films and in films with planar orientation suggests that there is and intrinsic relation between the direction of iodide ion arrays and nylon 6 chains. When an unoriented film of nylon 6 in the amorphous or the α crystalline form is treated with an aqueous solution of iodine—potassium iodide, the I₃^? species in the resulting iodine—nylon complex lie in planes parallel to the surface of the film, and I₂/I₃^? units are oriented normal to the surface of the film. The γ form obtained by desorbing the iodine from this complex shows considerable uniaxial rientation with the nylon chains oriented perpendicular to the plane of the film; this orientation is maintained during the γ to α transition. It is proposed that the iodine-induced orientation of the nylon 6 chains is due to the nucleating effects of the iodide ion species as the iodine diffuses unidirectionally into the film.     

The effect of amorphous orientation on the oxygen permeability of polypropylene films

Oxygen permeability measurements have been made on uniaxially and biaxially oriented polypropylene samples. X-ray diffraction pole-figure measurements provided the crystalline orientation functions. These results combined with density and refractive index measurements provided the amorphous orientation functions based on the two-phase model. A good correlation has been found between the amorphous orientation and the oxygen permeability of the samples. © 1993 John Wiley & Sons, Inc.     

Field-induced dipole reorientation and piezoelectricity in heavily plasticized nylon 11 films

Nylon 11 films with very low initial crystallinity were made by dissolving the nylon 11 in 2-ethyl-1,3-hexanediol at 150°C. Films were cast from the solution and excessive plasticizer was removed in a vacuum oven. Films were then melt pressed and quenched to yield heavily plasticized nylon 11 films containing ca. 30% by weight of the plasticizer. These films were poled under vacuum to allow the plasticizer to evaporate in the presence of an electric field. A high piezoelectric response (d₃₁ = 7.1 pC/N) was observed for the films subjected to the maximum electric field (E_p = 350 kV/cm) while the sample contained a large fraction of plasticizer. Significant development of crystallinity was observed without apparent indication of orientation of the crystallites. These studies suggest that the observed piezoelectric response originates primarily from oriented hydrogen bonds in the amorphous regions of nylon 11.     

The effect of orientation on thermal expansion behavior in polyimide films

The anisotropy of the thermal expansion of polyimide films was investigated . Out-of-plane or thickness direction coefficients of linear thermal expansion (CTE) were calculated from the difference between the coefficient of volumetric expansion (CVE) and the sum of the in-plane or film direction coefficients of linear thermal expansion for commercial and spin-coated PMDA//ODA and BPDA//PPD films and spin coated BTDA//ODA/MPD films. The CVEs were obtained from a pressure-volume-temperature (PVT) technique based on Bridgeman bellows. The CVE was shown to be essentially constant, independent of molecular orientation and thickness. A decrease in the in-plane CTEs therefore occurs at the expense of an increase in the out-of-plane CTE. In all cases the calculated out-of-plane CTE was higher than the measured in-plane CTE. The ratio of the out-of-plane CTE to the in-plane CTE was 1.2, 3.8, and 49.3 for the spin-coated BTDA//ODA/MPD, PMDA//ODA, and BPDA//PPD films, respectively. © 1994 John Wiley & Sons, Inc.     

Influence of processing conditions on the photo-oxidation of polypropylene films

The kinetics of photo-oxidation of polypropylene films made from materials processed under various conditions has been followed by means of viscometric measurements and infra-red spectroscopy. When the processing conditions induce chain breaking, the photo-oxidation rate increases with decreasing molecular weight. The major effect in increasing the rate of photo-oxidation is, however, due to the introduction of oxygenated groups.     

The effect of polarization of polyethylene films on migration of low-molecular-mass contaminants

The effect of poling on the kinetics of migration and the total amount of a migrant transferred from polyethylene packaging materials into nonpolar and polar solvents was studied. A decrease in the amount of the migrant from polymer films to nonpolar isooctane and a slight decrease in that to polar ethanol as a result of poling are due to the effect of an induced electric field on the wetting, dissolution, and diffusion processes. Although the formation of oxidized groups on the film surface by corona poling had an effect on the migration process, this effect was not a determining factor. It was noted that the holding of poled materials in ethanol at 40°C resulted in a significant reduction of their electret properties by the sixth day and practically complete charge relaxation by the tenth day. On the basis of the results obtained, it was concluded that the examined polyethylene films hold promise as active food-packaging materials.     

The effect of planar molecular orientation on the mechanical properties of rigid-chain polymide films

The effect of biaxial orientation on the mechanical properties and supramolecular structure of the films based on rigid-chain polyimides and copolyimides was studied. The films were oriented in two different ways: by hot drawing and by cold drawing at the prepolymer stage and the subsequent cyclization according to the specified temperature regime. It was shown that the curing of the precursor films after their preliminary biaxial drawing is accompanied by self-orientation, although its degree is well below that after uniaxial drawing under the same conditions. As compared with homopolyimide films, the films based on rigid-chain copolyimide exhibit a lower tendency toward orientation under biaxial drawing. The reasons for such behavior are discussed.     

Effect of annealing on the ferroelectric behavior of nylon - 11 and nylon - 7

We have discovered recently that melt-quenched and cold-drawn Nylon - 11 films exhibit very clear ferroelectric hysteresis behavior. In the present study, a remanent polarization as high as 86 mC/m² has been found in Nylon - 7 samples; this is significantly higher than that usually observed in poly (vinylidene fluoride) films. The effect of annealing on the electric displacement versus electric field characteristics of both Nylon - 11 and Nylon - 7 films have been studied and show an increased coercive field (62 to 115 MV/m for Nylon - 11 and 79 to 97 MV/m for Nylon - 7) and a decreased remanent polarization (51 to 17.3 mC/m² for Nylon - 11 and 86 to 70.5 mC/m² for Nylon - 7) with increasing annealing temperature from 25 to 145°C.     

The effect of orientation on R-11 bubble frequencies in nucleate pool boiling

R-11 bubble frequencies in nucleate pool boiling have been obtained for a variety of surface orientations at orientation angles ranging from 0° to 90° and cavity radius ranging from 0.3 mm to 0.6 mm. The single-bubble data show the bubble frequency to be a strong function of orientation angle, cavity size and wall superheat. An empirical formula is deduced.     

Effect of molecular orientation on the swelling of nylon 6

The effect of molecular orientation on the linear swelling of nylon 6 caused by absorption of water was studied using two kinds of oriented films, melt drawn and cold drawn. The molecular orientation causes anisotropy in swelling at all humidities such that the swelling is larger in the orientation direction than in the directions perpendicular to it. The large contribution of crystalline orientation to this phenomenon was expected for the melt drawn film which has practically no amorphous orientation. An analysis with a two-phase morphological model reveals that the distance between the crystallites is a prominent factor controlling the degree of linear swelling, and that the anisotropy of swelling arises from the change in the distribution of crystallites due to orientation. By comparing the result for the melt drawn film with that for the cold drawn film, which has considerable amorphous orientation, it was proven that molecular orientation in the amorphous phase where swelling actually occurs does not depend so much on the degree of swelling as on the distribution of crystallites.     

Ferroelectric and piezoelectric properties of nylon 11/poly(vinylidene fluoride) bilaminate films

The ferroelectric and piezoelectric properties of a new class of polymer ferroelectric and piezoelectric materials, nylon 11/polyvinylidene fluoride (PVF₂) bilaminate films, prepared by a co-melt-pressing method, is presented. The bilaminate films exhibit typical ferroelectric D-E hysteresis behavior with a remanent polarization, P_r, of about 75 mC/m², which is higher than the value of 52 mC/m² observed for PVF₂ or nylon 11 films measured under the same conditions. The coercive field, E_c, of the bilaminate films is ～ 78 MV/m, which is higher than that of either PVF₂ or nylon 11 films. Measurements of the temperature dependence of the piezoelectric strain coefficient, d₃₁, and the piezoelectric stress coefficient, e₃₁, were also carried out. The bilaminate films exhibit a piezoelectric strain coefficient, d₃₁, of 41 pC/N at room temperature, which is significantly higher than the PVF₂ films (25 pC/N) and the nylon 11 films (3.1 pC/N). When the temperature is increased to 110°C, d₃₁ of the bilaminate films reaches a maximum value of 63 pC/N, more than five times that of PVF₂ (11 pC/N) and more than four times that of nylon 11 (14 pC/N) at the same temperature. The piezoelectric stress coefficient, e₃₁, of the bilaminate films shows a value of 109 mC/m² at room temperature, almost twice that of the PVF₂ films (59 mC/m²) and about 18 times that of the nylon 11 films (6.2 mC/m²). Measurement of the temperature dependence of the hydrostatic piezoelectric coefficient, d_h, of the bilaminate films also shows an enhancement with respect to the individual components, PVF₂ and nylon 11. ©1995 John Wiley & Sons, Inc.     

Effects of melt processing conditions on photo-oxidation of PP/PPgMA/OMMT composites

This article reports the studies of photo-oxidative behaviour of polypropylene/maleic anhydride-grafted polypropylene/organic modified montmorillonite (PP/PPgMA/OMMT) composites prepared by two different melt processing methods. Samples of pristine polypropylene (PP) and PP/PPgMA/OMMT composites were prepared in an internal mixer and in a twin screw extruder. The samples were exposed to long wavelength radiations (λ > 300 nm) for the photo-oxidation. The samples were examined by FTIR, X-ray diffraction and microscopy. Similar to the pristine (PP), it is found that the photo-oxidation process in the composites depends on the melt processing conditions, which could cause the deterioration of organic modifier of the clay and the polymer matrix. The new radicals formed in addition to the iron impurities in the montmorillonite accelerate the photo-oxidation.     

The effect of processing conditions on the u.v. stability of polyolefins

It is shown that the lifetime of polyolefins in the presence of u.v. light is markedly dependent on the degree of oxidation occurring during the prior processing operation. This is influenced strongly by the presence of pro-oxidants and anti-oxidants, and their effect on subsequent u.v. life can be rationalized on the basis of their functions during processing.     

Self-assembly and orientation of hydrogen-bonded oligothiophene polymorphs at liquid-membrane-liquid interfaces

One of the challenges in organic systems with semiconducting function is the achievement of molecular orientation over large scales. We report here on the use of self-assembly kinetics to control long-range orientation of a quarterthiophene derivative designed to combine intermolecular π-π stacking and hydrogen bonding among amide groups. Assembly of these molecules in the solution phase is prevented by the hydrogen-bond-accepting solvent tetrahydrofuran, whereas formation of H-aggregates is facilitated in toluene. Rapid evaporation of solvent in a solution of the quarterthiophene in a 2:1:1 mixture of 1,4-dioxane/tetrahydrofuran/toluene leads to self-assembly of kinetically trapped mats of bundled fibers. In great contrast, slow drying in a toluene atmosphere leads to the homogeneous nucleation and growth of ordered structures shaped as rhombohedra or hexagonal prisms depending on concentration. Furthermore, exceedingly slow delivery of toluene from a high molecular weight polymer solution into the system through a porous aluminum oxide membrane results in the growth of highly oriented hexagonal prisms perpendicular to the interface. The amide groups of the compound likely adsorb onto the polar aluminum oxide surface and direct the self-assembly pathway toward heterogeneous nucleation and growth to form hexagonal prisms. We propose that the oriented prismatic polymorph results from the synergy of surface interactions rooted in hydrogen bonding on the solid membrane and the slow kinetics of self-assembly. These observations demonstrate how self-assembly conditions can be used to guide the supramolecular energy landscape to generate vastly different structures. These fundamental principles allowed us to grow oriented prismatic assemblies on transparent indium-doped tin oxide electrodes, which are of interest in organic electronics.     

Isolation of glycinin (11S) from lipid-reduced soybean flour: effect of processing conditions on yields and purity

Defatted soybean flour was treated with hexane and ethanol to reduce lipid content and heated to inactivate lipoxygenase (LOX, linoleate:oxygen reductase; EC 1.13.11.12) to obtain lipid-reduced soybean flour (LRSF). The effects of processing conditions such as pH, reducing agent and storage time on yields and purity of glycinin (11S) were evaluated in the fractionation of soybean glycinin isolated from LRSF. Adjusting the pH of protein extract from 6.2 to 6.6, the yield of glycinin decreased by 16.71%, while the purity of the protein increased by 4.60%. Sulfhydryl and disulfide content of proteins increased by degrees with increasing pH. Compared with dithiothreitol (DTT) or β-mercaptoethanol (ME) as reducing agent, the yield of glycinin was the highest when sodium bisulfite (SBS) was added to the protein extract at pH 6.4. The effect of DTT on yields of glycinin was the lowest of the three kinds of reducing agent. The purity of glycinin was similar when the three kinds of reducing agent were used. These results showed that SBS was the best choice for the isolation of 11S-rich fraction. Prolonging storage time in the precipitation stage, 10 h was the best for yields and purity of glycinin in the experiment, while there was no significant difference at P ≥ 0.05 for total sulfhydryl and disulfide content. The decreased free sulfhydryl content of glycinin indicated that the oxidation of free sulfhydryls and the formation of disulfide bonds occurred when the extraction time was prolonged.     

Biphotonic recording effect of polarization gratings based on dye-doped liquid crystal films

This study investigates a holographic recording effect of biphotonic polarization gratings (BPGs) written on dye-doped liquid crystal (DDLC) films. One linearly polarized green light (λ_G = 514.5 nm) and a polarization-modulated interference pattern formed by two mutually coherent orthogonal (±45° with respect to the polarization of the green light) polarized red lights simultaneously excite the DDLC films to generate a BPG. The formation of BPGs depends primarily on the dichroism of the dye molecules and a sequence of mechanisms: photoisomerization, anisotropic adsorption and inhibition of dye adsorption. The cis-isomer absorbance-modulated distribution associated with the red polarization-modulation pattern induces the dye adsorption-modulated pattern, in turn, yielding the permanent BPG which generates a modulated twisted nematic (TN) structure pattern in the sample. It is found that each BPG is verified to be electrically switchable and thermally erasable. The switching time is in the order of milliseconds. Additionally, the recording time to form a BPG decreases with increasing intensity of the green pump beam.